Fix some error handling for read() and errno

diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c
index 87942b4cca..d487347cc6 100644
--- a/src/backend/access/transam/slru.c
+++ b/src/backend/access/transam/slru.c
@@ -683,6 +683,11 @@ SlruPhysicalReadPage(SlruCtl ctl, int pageno, int slotno)
 	pgstat_report_wait_start(WAIT_EVENT_SLRU_READ);
 	if (read(fd, shared->page_buffer[slotno], BLCKSZ) != BLCKSZ)
 	{
+		/*
+		 * XXX: Note that this may actually report sucess if the number
+		 * of bytes read is positive, but lacking data so that errno is
+		 * not set.
+		 */
 		pgstat_report_wait_end();
 		slru_errcause = SLRU_READ_FAILED;
 		slru_errno = errno;
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 65194db70e..52f634e706 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -1219,6 +1219,7 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	uint32		crc_offset;
 	pg_crc32c	calc_crc,
 				file_crc;
+	int			r;
 
 	TwoPhaseFilePath(path, xid);
 
@@ -1272,15 +1273,28 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	buf = (char *) palloc(stat.st_size);
 
 	pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_READ);
-	if (read(fd, buf, stat.st_size) != stat.st_size)
+	r = read(fd, buf, stat.st_size);
+	if (r != stat.st_size)
 	{
+		int		save_errno = errno;
+
 		pgstat_report_wait_end();
 		CloseTransientFile(fd);
 		if (give_warnings)
-			ereport(WARNING,
-					(errcode_for_file_access(),
-					 errmsg("could not read two-phase state file \"%s\": %m",
-							path)));
+		{
+			if (r < 0)
+			{
+				errno = save_errno;
+				ereport(WARNING,
+						(errcode_for_file_access(),
+						 errmsg("could not read two-phase state file \"%s\": %m",
+								path)));
+			}
+			else
+				ereport(WARNING,
+						(errmsg("could not read two-phase state file \"%s\": %d read, expected %zu",
+								path, r, stat.st_size)));
+		}
 		pfree(buf);
 		return NULL;
 	}
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index adbd6a2126..2f2102eb71 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -3395,21 +3395,24 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
 
 		if (nread > 0)
 		{
+			int		r;
+
 			if (nread > sizeof(buffer))
 				nread = sizeof(buffer);
 			errno = 0;
 			pgstat_report_wait_start(WAIT_EVENT_WAL_COPY_READ);
-			if (read(srcfd, buffer, nread) != nread)
+			r = read(srcfd, buffer, nread);
+			if (r != nread)
 			{
-				if (errno != 0)
+				if (r < 0)
 					ereport(ERROR,
 							(errcode_for_file_access(),
 							 errmsg("could not read file \"%s\": %m",
 									path)));
 				else
 					ereport(ERROR,
-							(errmsg("not enough data in file \"%s\"",
-									path)));
+							(errmsg("not enough data in file \"%s\": read %d, expected %d",
+									path, r, nread)));
 			}
 			pgstat_report_wait_end();
 		}
@@ -11594,6 +11597,7 @@ XLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr, int reqLen,
 	int			emode = private->emode;
 	uint32		targetPageOff;
 	XLogSegNo	targetSegNo PG_USED_FOR_ASSERTS_ONLY;
+	int			r;
 
 	XLByteToSeg(targetPagePtr, targetSegNo, wal_segment_size);
 	targetPageOff = XLogSegmentOffset(targetPagePtr, wal_segment_size);
@@ -11675,8 +11679,10 @@ retry:
 	if (lseek(readFile, (off_t) readOff, SEEK_SET) < 0)
 	{
 		char		fname[MAXFNAMELEN];
+		int			save_errno = errno;
 
 		XLogFileName(fname, curFileTLI, readSegNo, wal_segment_size);
+		errno = save_errno;
 		ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
 				(errcode_for_file_access(),
 				 errmsg("could not seek in log segment %s to offset %u: %m",
@@ -11685,16 +11691,28 @@ retry:
 	}
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
-	if (read(readFile, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+	r = read(readFile, readBuf, XLOG_BLCKSZ);
+	if (r != XLOG_BLCKSZ)
 	{
 		char		fname[MAXFNAMELEN];
+		int			save_errno = errno;
 
 		pgstat_report_wait_end();
 		XLogFileName(fname, curFileTLI, readSegNo, wal_segment_size);
-		ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
-				(errcode_for_file_access(),
-				 errmsg("could not read from log segment %s, offset %u: %m",
-						fname, readOff)));
+
+		if (r < 0)
+		{
+			errno = save_errno;
+			ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
+					(errcode_for_file_access(),
+					 errmsg("could not read from log segment %s, offset %u: %m",
+							fname, readOff)));
+		}
+		else
+			ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
+					(errmsg("could not read from log segment %s, offset %u: read %d, expected %d",
+							fname, readOff, r, XLOG_BLCKSZ)));
+
 		goto next_record_is_invalid;
 	}
 	pgstat_report_wait_end();
diff --git a/src/backend/replication/logical/origin.c b/src/backend/replication/logical/origin.c
index 963878a5d8..c39d023d22 100644
--- a/src/backend/replication/logical/origin.c
+++ b/src/backend/replication/logical/origin.c
@@ -697,9 +697,16 @@ StartupReplicationOrigin(void)
 	/* verify magic, that is written even if nothing was active */
 	readBytes = read(fd, &magic, sizeof(magic));
 	if (readBytes != sizeof(magic))
-		ereport(PANIC,
-				(errmsg("could not read file \"%s\": %m",
-						path)));
+	{
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": %m",
+							path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": %d read of %zu",
+							path, readBytes, sizeof(magic))));
+	}
 	COMP_CRC32C(crc, &magic, sizeof(magic));
 
 	if (magic != REPLICATION_STATE_MAGIC)
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 4123cdebcf..f99a885c5d 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1708,11 +1708,20 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	pgstat_report_wait_end();
 	if (readBytes != SnapBuildOnDiskConstantSize)
 	{
+		int		save_errno = errno;
 		CloseTransientFile(fd);
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) SnapBuildOnDiskConstantSize)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, SnapBuildOnDiskConstantSize)));
 	}
 
 	if (ondisk.magic != SNAPBUILD_MAGIC)
@@ -1736,11 +1745,20 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	pgstat_report_wait_end();
 	if (readBytes != sizeof(SnapBuild))
 	{
+		int		save_errno = errno;
 		CloseTransientFile(fd);
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sizeof(SnapBuild))));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sizeof(SnapBuild))));
 	}
 	COMP_CRC32C(checksum, &ondisk.builder, sizeof(SnapBuild));
 
@@ -1753,11 +1771,20 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	pgstat_report_wait_end();
 	if (readBytes != sz)
 	{
+		int		save_errno = errno;
 		CloseTransientFile(fd);
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sz)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sz)));
 	}
 	COMP_CRC32C(checksum, ondisk.builder.was_running.was_xip, sz);
 
@@ -1769,11 +1796,20 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	pgstat_report_wait_end();
 	if (readBytes != sz)
 	{
+		int		save_errno = errno;
 		CloseTransientFile(fd);
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sz)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sz)));
 	}
 	COMP_CRC32C(checksum, ondisk.builder.committed.xip, sz);
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 056628fe8e..cc64ff22ac 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1394,11 +1394,15 @@ RestoreSlotFromDisk(const char *name)
 
 		CloseTransientFile(fd);
 		errno = saved_errno;
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %u: %m",
-						path, readBytes,
-						(uint32) ReplicationSlotOnDiskConstantSize)));
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d of %u",
+							path, readBytes,
+							(uint32) ReplicationSlotOnDiskConstantSize)));
 	}
 
 	/* verify magic */
@@ -1434,10 +1438,14 @@ RestoreSlotFromDisk(const char *name)
 
 		CloseTransientFile(fd);
 		errno = saved_errno;
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %u: %m",
-						path, readBytes, cp.length)));
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d of %u",
+							path, readBytes, cp.length)));
 	}
 
 	CloseTransientFile(fd);
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index e47ddca6bc..727c3acbcb 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -501,11 +501,16 @@ SendTimeLineHistory(TimeLineHistoryCmd *cmd)
 		pgstat_report_wait_start(WAIT_EVENT_WALSENDER_TIMELINE_HISTORY_READ);
 		nread = read(fd, rbuf, sizeof(rbuf));
 		pgstat_report_wait_end();
-		if (nread <= 0)
+		if (nread < 0)
 			ereport(ERROR,
 					(errcode_for_file_access(),
 					 errmsg("could not read file \"%s\": %m",
 							path)));
+		else if (nread == 0)
+			ereport(ERROR,
+					(errmsg("could not read empty file \"%s\"",
+							path)));
+
 		pq_sendbytes(&buf, rbuf, nread);
 		bytesleft -= nread;
 	}
@@ -2425,7 +2430,7 @@ retry:
 		pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 		readbytes = read(sendFile, p, segbytes);
 		pgstat_report_wait_end();
-		if (readbytes <= 0)
+		if (readbytes < 0)
 		{
 			ereport(ERROR,
 					(errcode_for_file_access(),
@@ -2433,6 +2438,13 @@ retry:
 							XLogFileNameP(curFileTimeLine, sendSegNo),
 							sendOff, (unsigned long) segbytes)));
 		}
+		else if (readbytes == 0)
+		{
+			ereport(ERROR,
+					(errmsg("could not read any data from log segment %s, offset %u, length %lu",
+							XLogFileNameP(curFileTimeLine, sendSegNo),
+							sendOff, (unsigned long) segbytes)));
+		}
 
 		/* Update state for read */
 		recptr += readbytes;
diff --git a/src/backend/utils/cache/relmapper.c b/src/backend/utils/cache/relmapper.c
index 99d095f2df..c4839b11f6 100644
--- a/src/backend/utils/cache/relmapper.c
+++ b/src/backend/utils/cache/relmapper.c
@@ -629,6 +629,7 @@ load_relmap_file(bool shared)
 	char		mapfilename[MAXPGPATH];
 	pg_crc32c	crc;
 	int			fd;
+	int			r;
 
 	if (shared)
 	{
@@ -659,11 +660,19 @@ load_relmap_file(bool shared)
 	 * are able to access any relation that's affected by the change.
 	 */
 	pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_READ);
-	if (read(fd, map, sizeof(RelMapFile)) != sizeof(RelMapFile))
-		ereport(FATAL,
-				(errcode_for_file_access(),
-				 errmsg("could not read relation mapping file \"%s\": %m",
-						mapfilename)));
+	r = read(fd, map, sizeof(RelMapFile));
+	if (r != sizeof(RelMapFile))
+	{
+		if (r < 0)
+			ereport(FATAL,
+					(errcode_for_file_access(),
+					 errmsg("could not read relation mapping file \"%s\": %m",
+							mapfilename)));
+		else
+			ereport(FATAL,
+					(errmsg("could not read relation mapping file \"%s\": %d read, expected %zu",
+							mapfilename, r, sizeof(RelMapFile))));
+	}
 	pgstat_report_wait_end();
 
 	CloseTransientFile(fd);
diff --git a/src/bin/pg_basebackup/pg_receivewal.c b/src/bin/pg_basebackup/pg_receivewal.c
index 071b32d19d..ddc3e90e79 100644
--- a/src/bin/pg_basebackup/pg_receivewal.c
+++ b/src/bin/pg_basebackup/pg_receivewal.c
@@ -284,6 +284,7 @@ FindStreamingStart(uint32 *tli)
 			char		buf[4];
 			int			bytes_out;
 			char		fullpath[MAXPGPATH * 2];
+			int			r;
 
 			snprintf(fullpath, sizeof(fullpath), "%s/%s", basedir, dirent->d_name);
 
@@ -300,10 +301,16 @@ FindStreamingStart(uint32 *tli)
 						progname, fullpath, strerror(errno));
 				disconnect_and_exit(1);
 			}
-			if (read(fd, (char *) buf, sizeof(buf)) != sizeof(buf))
+			r = read(fd, (char *) buf, sizeof(buf));
+			if (r != sizeof(buf))
 			{
-				fprintf(stderr, _("%s: could not read compressed file \"%s\": %s\n"),
-						progname, fullpath, strerror(errno));
+				if (r < 0)
+					fprintf(stderr, _("%s: could not read compressed file \"%s\": %s\n"),
+							progname, fullpath, strerror(errno));
+				else
+					fprintf(stderr,
+							_("%s: could not read compressed file \"%s\": read %d out of %zu\n"),
+							progname, fullpath, r, sizeof(buf));
 				disconnect_and_exit(1);
 			}
 
diff --git a/src/bin/pg_rewind/file_ops.c b/src/bin/pg_rewind/file_ops.c
index 94bcc13ae8..174ca7216d 100644
--- a/src/bin/pg_rewind/file_ops.c
+++ b/src/bin/pg_rewind/file_ops.c
@@ -289,6 +289,7 @@ slurpFile(const char *datadir, const char *path, size_t *filesize)
 	struct stat statbuf;
 	char		fullpath[MAXPGPATH];
 	int			len;
+	int			r;
 
 	snprintf(fullpath, sizeof(fullpath), "%s/%s", datadir, path);
 
@@ -304,9 +305,17 @@ slurpFile(const char *datadir, const char *path, size_t *filesize)
 
 	buffer = pg_malloc(len + 1);
 
-	if (read(fd, buffer, len) != len)
-		pg_fatal("could not read file \"%s\": %s\n",
-				 fullpath, strerror(errno));
+	r = read(fd, buffer, len);
+	if (r != len)
+	{
+		if (r < 0)
+			pg_fatal("could not read file \"%s\": %s\n",
+					 fullpath, strerror(errno));
+		else
+			pg_fatal("could not read file \"%s\": read %d, expected %d\n",
+					 fullpath, r, len);
+
+	}
 	close(fd);
 
 	/* Zero-terminate the buffer. */
diff --git a/src/bin/pg_rewind/parsexlog.c b/src/bin/pg_rewind/parsexlog.c
index b4c1f827a6..4f27cfe42b 100644
--- a/src/bin/pg_rewind/parsexlog.c
+++ b/src/bin/pg_rewind/parsexlog.c
@@ -246,6 +246,7 @@ SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
 	uint32		targetPageOff;
 	XLogRecPtr	targetSegEnd;
 	XLogSegNo	targetSegNo;
+	int			r;
 
 	XLByteToSeg(targetPagePtr, targetSegNo, WalSegSz);
 	XLogSegNoOffsetToRecPtr(targetSegNo + 1, 0, targetSegEnd, WalSegSz);
@@ -309,10 +310,17 @@ SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
 		return -1;
 	}
 
-	if (read(xlogreadfd, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+
+	r = read(xlogreadfd, readBuf, XLOG_BLCKSZ);
+	if (r != XLOG_BLCKSZ)
 	{
-		printf(_("could not read from file \"%s\": %s\n"), xlogfpath,
-			   strerror(errno));
+		if (r < 0)
+			printf(_("could not read from file \"%s\": %s\n"), xlogfpath,
+				   strerror(errno));
+		else
+			printf(_("could not read from file \"%s\": read %d, expected %d\n"),
+				   xlogfpath, r, XLOG_BLCKSZ);
+
 		return -1;
 	}
 
diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index 5c4f38e597..61464d44c5 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -210,8 +210,10 @@ search_directory(const char *directory, const char *fname)
 	if (fd >= 0)
 	{
 		char		buf[XLOG_BLCKSZ];
+		int			r;
 
-		if (read(fd, buf, XLOG_BLCKSZ) == XLOG_BLCKSZ)
+		r = read(fd, buf, XLOG_BLCKSZ);
+		if (r == XLOG_BLCKSZ)
 		{
 			XLogLongPageHeader longhdr = (XLogLongPageHeader) buf;
 
@@ -229,7 +231,8 @@ search_directory(const char *directory, const char *fname)
 				fatal_error("could not read file \"%s\": %s",
 							fname, strerror(errno));
 			else
-				fatal_error("not enough data in file \"%s\"", fname);
+				fatal_error("not enough data in file \"%s\": %d read, %d expected",
+							fname, r, XLOG_BLCKSZ);
 		}
 		close(fd);
 		return true;
@@ -411,11 +414,17 @@ XLogDumpXLogRead(const char *directory, TimeLineID timeline_id,
 		{
 			int			err = errno;
 			char		fname[MAXPGPATH];
+			int			save_errno = errno;
 
 			XLogFileName(fname, timeline_id, sendSegNo, WalSegSz);
+			errno = save_errno;
 
-			fatal_error("could not read from log file %s, offset %u, length %d: %s",
-						fname, sendOff, segbytes, strerror(err));
+			if (readbytes < 0)
+				fatal_error("could not read from log file %s, offset %u, length %d: %s",
+							fname, sendOff, segbytes, strerror(err));
+			else if (readbytes == 0)
+				fatal_error("could not read any data from log file %s, offset %u, length %d",
+							fname, sendOff, segbytes);
 		}
 
 		/* Update state for read */

diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c
index 87942b4cca..d487347cc6 100644
--- a/src/backend/access/transam/slru.c
+++ b/src/backend/access/transam/slru.c
@@ -683,6 +683,11 @@ SlruPhysicalReadPage(SlruCtl ctl, int pageno, int slotno)
 	pgstat_report_wait_start(WAIT_EVENT_SLRU_READ);
 	if (read(fd, shared->page_buffer[slotno], BLCKSZ) != BLCKSZ)
 	{
+		/*
+		 * XXX: Note that this may actually report sucess if the number
+		 * of bytes read is positive, but lacking data so that errno is
+		 * not set.
+		 */
 		pgstat_report_wait_end();
 		slru_errcause = SLRU_READ_FAILED;
 		slru_errno = errno;
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 65194db70e..52f634e706 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -1219,6 +1219,7 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	uint32		crc_offset;
 	pg_crc32c	calc_crc,
 				file_crc;
+	int			r;
 
 	TwoPhaseFilePath(path, xid);
 
@@ -1272,15 +1273,28 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	buf = (char *) palloc(stat.st_size);
 
 	pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_READ);
-	if (read(fd, buf, stat.st_size) != stat.st_size)
+	r = read(fd, buf, stat.st_size);
+	if (r != stat.st_size)
 	{
+		int		save_errno = errno;
+
 		pgstat_report_wait_end();
 		CloseTransientFile(fd);
 		if (give_warnings)
-			ereport(WARNING,
-					(errcode_for_file_access(),
-					 errmsg("could not read two-phase state file \"%s\": %m",
-							path)));
+		{
+			if (r < 0)
+			{
+				errno = save_errno;
+				ereport(WARNING,
+						(errcode_for_file_access(),
+						 errmsg("could not read two-phase state file \"%s\": %m",
+								path)));
+			}
+			else
+				ereport(WARNING,
+						(errmsg("could not read two-phase state file \"%s\": %d read, expected %zu",
+								path, r, stat.st_size)));
+		}
 		pfree(buf);
 		return NULL;
 	}
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index adbd6a2126..2f2102eb71 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -3395,21 +3395,24 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
 
 		if (nread > 0)
 		{
+			int		r;
+
 			if (nread > sizeof(buffer))
 				nread = sizeof(buffer);
 			errno = 0;
 			pgstat_report_wait_start(WAIT_EVENT_WAL_COPY_READ);
-			if (read(srcfd, buffer, nread) != nread)
+			r = read(srcfd, buffer, nread);
+			if (r != nread)
 			{
-				if (errno != 0)
+				if (r < 0)
 					ereport(ERROR,
 							(errcode_for_file_access(),
 							 errmsg("could not read file \"%s\": %m",
 									path)));
 				else
 					ereport(ERROR,
-							(errmsg("not enough data in file \"%s\"",
-									path)));
+							(errmsg("not enough data in file \"%s\": read %d, expected %d",
+									path, r, nread)));
 			}
 			pgstat_report_wait_end();
 		}
@@ -11594,6 +11597,7 @@ XLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr, int reqLen,
 	int			emode = private->emode;
 	uint32		targetPageOff;
 	XLogSegNo	targetSegNo PG_USED_FOR_ASSERTS_ONLY;
+	int			r;
 
 	XLByteToSeg(targetPagePtr, targetSegNo, wal_segment_size);
 	targetPageOff = XLogSegmentOffset(targetPagePtr, wal_segment_size);
@@ -11675,8 +11679,10 @@ retry:
 	if (lseek(readFile, (off_t) readOff, SEEK_SET) < 0)
 	{
 		char		fname[MAXFNAMELEN];
+		int			save_errno = errno;
 
 		XLogFileName(fname, curFileTLI, readSegNo, wal_segment_size);
+		errno = save_errno;
 		ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
 				(errcode_for_file_access(),
 				 errmsg("could not seek in log segment %s to offset %u: %m",
@@ -11685,16 +11691,28 @@ retry:
 	}
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
-	if (read(readFile, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+	r = read(readFile, readBuf, XLOG_BLCKSZ);
+	if (r != XLOG_BLCKSZ)
 	{
 		char		fname[MAXFNAMELEN];
+		int			save_errno = errno;
 
 		pgstat_report_wait_end();
 		XLogFileName(fname, curFileTLI, readSegNo, wal_segment_size);
-		ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
-				(errcode_for_file_access(),
-				 errmsg("could not read from log segment %s, offset %u: %m",
-						fname, readOff)));
+
+		if (r < 0)
+		{
+			errno = save_errno;
+			ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
+					(errcode_for_file_access(),
+					 errmsg("could not read from log segment %s, offset %u: %m",
+							fname, readOff)));
+		}
+		else
+			ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
+					(errmsg("could not read from log segment %s, offset %u: read %d, expected %d",
+							fname, readOff, r, XLOG_BLCKSZ)));
+
 		goto next_record_is_invalid;
 	}
 	pgstat_report_wait_end();
diff --git a/src/backend/replication/logical/origin.c b/src/backend/replication/logical/origin.c
index 963878a5d8..c39d023d22 100644
--- a/src/backend/replication/logical/origin.c
+++ b/src/backend/replication/logical/origin.c
@@ -697,9 +697,16 @@ StartupReplicationOrigin(void)
 	/* verify magic, that is written even if nothing was active */
 	readBytes = read(fd, &magic, sizeof(magic));
 	if (readBytes != sizeof(magic))
-		ereport(PANIC,
-				(errmsg("could not read file \"%s\": %m",
-						path)));
+	{
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": %m",
+							path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": %d read of %zu",
+							path, readBytes, sizeof(magic))));
+	}
 	COMP_CRC32C(crc, &magic, sizeof(magic));
 
 	if (magic != REPLICATION_STATE_MAGIC)
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 4123cdebcf..f99a885c5d 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1708,11 +1708,20 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	pgstat_report_wait_end();
 	if (readBytes != SnapBuildOnDiskConstantSize)
 	{
+		int		save_errno = errno;
 		CloseTransientFile(fd);
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) SnapBuildOnDiskConstantSize)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, SnapBuildOnDiskConstantSize)));
 	}
 
 	if (ondisk.magic != SNAPBUILD_MAGIC)
@@ -1736,11 +1745,20 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	pgstat_report_wait_end();
 	if (readBytes != sizeof(SnapBuild))
 	{
+		int		save_errno = errno;
 		CloseTransientFile(fd);
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sizeof(SnapBuild))));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sizeof(SnapBuild))));
 	}
 	COMP_CRC32C(checksum, &ondisk.builder, sizeof(SnapBuild));
 
@@ -1753,11 +1771,20 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	pgstat_report_wait_end();
 	if (readBytes != sz)
 	{
+		int		save_errno = errno;
 		CloseTransientFile(fd);
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sz)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sz)));
 	}
 	COMP_CRC32C(checksum, ondisk.builder.was_running.was_xip, sz);
 
@@ -1769,11 +1796,20 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	pgstat_report_wait_end();
 	if (readBytes != sz)
 	{
+		int		save_errno = errno;
 		CloseTransientFile(fd);
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sz)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sz)));
 	}
 	COMP_CRC32C(checksum, ondisk.builder.committed.xip, sz);
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 056628fe8e..cc64ff22ac 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1394,11 +1394,15 @@ RestoreSlotFromDisk(const char *name)
 
 		CloseTransientFile(fd);
 		errno = saved_errno;
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %u: %m",
-						path, readBytes,
-						(uint32) ReplicationSlotOnDiskConstantSize)));
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d of %u",
+							path, readBytes,
+							(uint32) ReplicationSlotOnDiskConstantSize)));
 	}
 
 	/* verify magic */
@@ -1434,10 +1438,14 @@ RestoreSlotFromDisk(const char *name)
 
 		CloseTransientFile(fd);
 		errno = saved_errno;
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %u: %m",
-						path, readBytes, cp.length)));
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d of %u",
+							path, readBytes, cp.length)));
 	}
 
 	CloseTransientFile(fd);
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index e47ddca6bc..5003860673 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -501,11 +501,16 @@ SendTimeLineHistory(TimeLineHistoryCmd *cmd)
 		pgstat_report_wait_start(WAIT_EVENT_WALSENDER_TIMELINE_HISTORY_READ);
 		nread = read(fd, rbuf, sizeof(rbuf));
 		pgstat_report_wait_end();
-		if (nread <= 0)
+		if (nread < 0)
 			ereport(ERROR,
 					(errcode_for_file_access(),
 					 errmsg("could not read file \"%s\": %m",
 							path)));
+		else if (nread == 0)
+			ereport(ERROR,
+					(errmsg("no data read from file \"%s\": expected %zu more bytes",
+							path, bytesleft)));
+
 		pq_sendbytes(&buf, rbuf, nread);
 		bytesleft -= nread;
 	}
@@ -2425,7 +2430,7 @@ retry:
 		pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 		readbytes = read(sendFile, p, segbytes);
 		pgstat_report_wait_end();
-		if (readbytes <= 0)
+		if (readbytes < 0)
 		{
 			ereport(ERROR,
 					(errcode_for_file_access(),
@@ -2433,6 +2438,13 @@ retry:
 							XLogFileNameP(curFileTimeLine, sendSegNo),
 							sendOff, (unsigned long) segbytes)));
 		}
+		else if (readbytes == 0)
+		{
+			ereport(ERROR,
+					(errmsg("could not read any data from log segment %s, offset %u, length %lu",
+							XLogFileNameP(curFileTimeLine, sendSegNo),
+							sendOff, (unsigned long) segbytes)));
+		}
 
 		/* Update state for read */
 		recptr += readbytes;
diff --git a/src/backend/utils/cache/relmapper.c b/src/backend/utils/cache/relmapper.c
index 99d095f2df..c4839b11f6 100644
--- a/src/backend/utils/cache/relmapper.c
+++ b/src/backend/utils/cache/relmapper.c
@@ -629,6 +629,7 @@ load_relmap_file(bool shared)
 	char		mapfilename[MAXPGPATH];
 	pg_crc32c	crc;
 	int			fd;
+	int			r;
 
 	if (shared)
 	{
@@ -659,11 +660,19 @@ load_relmap_file(bool shared)
 	 * are able to access any relation that's affected by the change.
 	 */
 	pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_READ);
-	if (read(fd, map, sizeof(RelMapFile)) != sizeof(RelMapFile))
-		ereport(FATAL,
-				(errcode_for_file_access(),
-				 errmsg("could not read relation mapping file \"%s\": %m",
-						mapfilename)));
+	r = read(fd, map, sizeof(RelMapFile));
+	if (r != sizeof(RelMapFile))
+	{
+		if (r < 0)
+			ereport(FATAL,
+					(errcode_for_file_access(),
+					 errmsg("could not read relation mapping file \"%s\": %m",
+							mapfilename)));
+		else
+			ereport(FATAL,
+					(errmsg("could not read relation mapping file \"%s\": %d read, expected %zu",
+							mapfilename, r, sizeof(RelMapFile))));
+	}
 	pgstat_report_wait_end();
 
 	CloseTransientFile(fd);
diff --git a/src/bin/pg_basebackup/pg_receivewal.c b/src/bin/pg_basebackup/pg_receivewal.c
index 071b32d19d..ddc3e90e79 100644
--- a/src/bin/pg_basebackup/pg_receivewal.c
+++ b/src/bin/pg_basebackup/pg_receivewal.c
@@ -284,6 +284,7 @@ FindStreamingStart(uint32 *tli)
 			char		buf[4];
 			int			bytes_out;
 			char		fullpath[MAXPGPATH * 2];
+			int			r;
 
 			snprintf(fullpath, sizeof(fullpath), "%s/%s", basedir, dirent->d_name);
 
@@ -300,10 +301,16 @@ FindStreamingStart(uint32 *tli)
 						progname, fullpath, strerror(errno));
 				disconnect_and_exit(1);
 			}
-			if (read(fd, (char *) buf, sizeof(buf)) != sizeof(buf))
+			r = read(fd, (char *) buf, sizeof(buf));
+			if (r != sizeof(buf))
 			{
-				fprintf(stderr, _("%s: could not read compressed file \"%s\": %s\n"),
-						progname, fullpath, strerror(errno));
+				if (r < 0)
+					fprintf(stderr, _("%s: could not read compressed file \"%s\": %s\n"),
+							progname, fullpath, strerror(errno));
+				else
+					fprintf(stderr,
+							_("%s: could not read compressed file \"%s\": read %d out of %zu\n"),
+							progname, fullpath, r, sizeof(buf));
 				disconnect_and_exit(1);
 			}
 
diff --git a/src/bin/pg_rewind/file_ops.c b/src/bin/pg_rewind/file_ops.c
index 94bcc13ae8..174ca7216d 100644
--- a/src/bin/pg_rewind/file_ops.c
+++ b/src/bin/pg_rewind/file_ops.c
@@ -289,6 +289,7 @@ slurpFile(const char *datadir, const char *path, size_t *filesize)
 	struct stat statbuf;
 	char		fullpath[MAXPGPATH];
 	int			len;
+	int			r;
 
 	snprintf(fullpath, sizeof(fullpath), "%s/%s", datadir, path);
 
@@ -304,9 +305,17 @@ slurpFile(const char *datadir, const char *path, size_t *filesize)
 
 	buffer = pg_malloc(len + 1);
 
-	if (read(fd, buffer, len) != len)
-		pg_fatal("could not read file \"%s\": %s\n",
-				 fullpath, strerror(errno));
+	r = read(fd, buffer, len);
+	if (r != len)
+	{
+		if (r < 0)
+			pg_fatal("could not read file \"%s\": %s\n",
+					 fullpath, strerror(errno));
+		else
+			pg_fatal("could not read file \"%s\": read %d, expected %d\n",
+					 fullpath, r, len);
+
+	}
 	close(fd);
 
 	/* Zero-terminate the buffer. */
diff --git a/src/bin/pg_rewind/parsexlog.c b/src/bin/pg_rewind/parsexlog.c
index b4c1f827a6..4f27cfe42b 100644
--- a/src/bin/pg_rewind/parsexlog.c
+++ b/src/bin/pg_rewind/parsexlog.c
@@ -246,6 +246,7 @@ SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
 	uint32		targetPageOff;
 	XLogRecPtr	targetSegEnd;
 	XLogSegNo	targetSegNo;
+	int			r;
 
 	XLByteToSeg(targetPagePtr, targetSegNo, WalSegSz);
 	XLogSegNoOffsetToRecPtr(targetSegNo + 1, 0, targetSegEnd, WalSegSz);
@@ -309,10 +310,17 @@ SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
 		return -1;
 	}
 
-	if (read(xlogreadfd, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+
+	r = read(xlogreadfd, readBuf, XLOG_BLCKSZ);
+	if (r != XLOG_BLCKSZ)
 	{
-		printf(_("could not read from file \"%s\": %s\n"), xlogfpath,
-			   strerror(errno));
+		if (r < 0)
+			printf(_("could not read from file \"%s\": %s\n"), xlogfpath,
+				   strerror(errno));
+		else
+			printf(_("could not read from file \"%s\": read %d, expected %d\n"),
+				   xlogfpath, r, XLOG_BLCKSZ);
+
 		return -1;
 	}
 
diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index 5c4f38e597..61464d44c5 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -210,8 +210,10 @@ search_directory(const char *directory, const char *fname)
 	if (fd >= 0)
 	{
 		char		buf[XLOG_BLCKSZ];
+		int			r;
 
-		if (read(fd, buf, XLOG_BLCKSZ) == XLOG_BLCKSZ)
+		r = read(fd, buf, XLOG_BLCKSZ);
+		if (r == XLOG_BLCKSZ)
 		{
 			XLogLongPageHeader longhdr = (XLogLongPageHeader) buf;
 
@@ -229,7 +231,8 @@ search_directory(const char *directory, const char *fname)
 				fatal_error("could not read file \"%s\": %s",
 							fname, strerror(errno));
 			else
-				fatal_error("not enough data in file \"%s\"", fname);
+				fatal_error("not enough data in file \"%s\": %d read, %d expected",
+							fname, r, XLOG_BLCKSZ);
 		}
 		close(fd);
 		return true;
@@ -411,11 +414,17 @@ XLogDumpXLogRead(const char *directory, TimeLineID timeline_id,
 		{
 			int			err = errno;
 			char		fname[MAXPGPATH];
+			int			save_errno = errno;
 
 			XLogFileName(fname, timeline_id, sendSegNo, WalSegSz);
+			errno = save_errno;
 
-			fatal_error("could not read from log file %s, offset %u, length %d: %s",
-						fname, sendOff, segbytes, strerror(err));
+			if (readbytes < 0)
+				fatal_error("could not read from log file %s, offset %u, length %d: %s",
+							fname, sendOff, segbytes, strerror(err));
+			else if (readbytes == 0)
+				fatal_error("could not read any data from log file %s, offset %u, length %d",
+							fname, sendOff, segbytes);
 		}
 
 		/* Update state for read */

diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c
index 1132eef038..805aa521cf 100644
--- a/src/backend/access/transam/slru.c
+++ b/src/backend/access/transam/slru.c
@@ -684,6 +684,14 @@ SlruPhysicalReadPage(SlruCtl ctl, int pageno, int slotno)
 	if (read(fd, shared->page_buffer[slotno], BLCKSZ) != BLCKSZ)
 	{
 		pgstat_report_wait_end();
+
+		/*
+		 * Note that this would report success if the number of bytes read is
+		 * positive, but lacking data so that errno is not set, which would be
+		 * confusing, so set errno to EIO in this case.
+		 */
+		if (errno == 0)
+			errno = EIO;
 		slru_errcause = SLRU_READ_FAILED;
 		slru_errno = errno;
 		CloseTransientFile(fd);
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 65194db70e..95ab03628f 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -1219,6 +1219,7 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	uint32		crc_offset;
 	pg_crc32c	calc_crc,
 				file_crc;
+	int			r;
 
 	TwoPhaseFilePath(path, xid);
 
@@ -1272,15 +1273,28 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	buf = (char *) palloc(stat.st_size);
 
 	pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_READ);
-	if (read(fd, buf, stat.st_size) != stat.st_size)
+	r = read(fd, buf, stat.st_size);
+	if (r != stat.st_size)
 	{
+		int			save_errno = errno;
+
 		pgstat_report_wait_end();
 		CloseTransientFile(fd);
 		if (give_warnings)
-			ereport(WARNING,
-					(errcode_for_file_access(),
-					 errmsg("could not read two-phase state file \"%s\": %m",
-							path)));
+		{
+			if (r < 0)
+			{
+				errno = save_errno;
+				ereport(WARNING,
+						(errcode_for_file_access(),
+						 errmsg("could not read two-phase state file \"%s\": %m",
+								path)));
+			}
+			else
+				ereport(WARNING,
+						(errmsg("could not read two-phase state file \"%s\": read %d bytes, expected %zu",
+								path, r, stat.st_size)));
+		}
 		pfree(buf);
 		return NULL;
 	}
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index adbd6a2126..471ef87842 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -3395,21 +3395,24 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
 
 		if (nread > 0)
 		{
+			int			r;
+
 			if (nread > sizeof(buffer))
 				nread = sizeof(buffer);
 			errno = 0;
 			pgstat_report_wait_start(WAIT_EVENT_WAL_COPY_READ);
-			if (read(srcfd, buffer, nread) != nread)
+			r = read(srcfd, buffer, nread);
+			if (r != nread)
 			{
-				if (errno != 0)
+				if (r < 0)
 					ereport(ERROR,
 							(errcode_for_file_access(),
 							 errmsg("could not read file \"%s\": %m",
 									path)));
 				else
 					ereport(ERROR,
-							(errmsg("not enough data in file \"%s\"",
-									path)));
+							(errmsg("could not read file \"%s\": read %d bytes, expected %d",
+									path, r, nread)));
 			}
 			pgstat_report_wait_end();
 		}
@@ -4509,7 +4512,8 @@ ReadControlFile(void)
 					 errmsg("could not read from control file: %m")));
 		else
 			ereport(PANIC,
-					 (errmsg("could not read from control file: read %d bytes, expected %d", r, (int) sizeof(ControlFileData))));
+					(errmsg("could not read from control file: read %d bytes, expected %zu",
+							r, sizeof(ControlFileData))));
 	}
 	pgstat_report_wait_end();
 
@@ -11594,6 +11598,7 @@ XLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr, int reqLen,
 	int			emode = private->emode;
 	uint32		targetPageOff;
 	XLogSegNo	targetSegNo PG_USED_FOR_ASSERTS_ONLY;
+	int			r;
 
 	XLByteToSeg(targetPagePtr, targetSegNo, wal_segment_size);
 	targetPageOff = XLogSegmentOffset(targetPagePtr, wal_segment_size);
@@ -11675,8 +11680,10 @@ retry:
 	if (lseek(readFile, (off_t) readOff, SEEK_SET) < 0)
 	{
 		char		fname[MAXFNAMELEN];
+		int			save_errno = errno;
 
 		XLogFileName(fname, curFileTLI, readSegNo, wal_segment_size);
+		errno = save_errno;
 		ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
 				(errcode_for_file_access(),
 				 errmsg("could not seek in log segment %s to offset %u: %m",
@@ -11685,16 +11692,28 @@ retry:
 	}
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
-	if (read(readFile, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+	r = read(readFile, readBuf, XLOG_BLCKSZ);
+	if (r != XLOG_BLCKSZ)
 	{
 		char		fname[MAXFNAMELEN];
+		int			save_errno = errno;
 
 		pgstat_report_wait_end();
 		XLogFileName(fname, curFileTLI, readSegNo, wal_segment_size);
-		ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
-				(errcode_for_file_access(),
-				 errmsg("could not read from log segment %s, offset %u: %m",
-						fname, readOff)));
+
+		if (r < 0)
+		{
+			errno = save_errno;
+			ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
+					(errcode_for_file_access(),
+					 errmsg("could not read from log segment %s, offset %u: %m",
+							fname, readOff)));
+		}
+		else
+			ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
+					(errmsg("could not read from log segment %s, offset %u: read %d bytes, expected %d",
+							fname, readOff, r, XLOG_BLCKSZ)));
+
 		goto next_record_is_invalid;
 	}
 	pgstat_report_wait_end();
diff --git a/src/backend/replication/logical/origin.c b/src/backend/replication/logical/origin.c
index 963878a5d8..053c13c43e 100644
--- a/src/backend/replication/logical/origin.c
+++ b/src/backend/replication/logical/origin.c
@@ -697,9 +697,16 @@ StartupReplicationOrigin(void)
 	/* verify magic, that is written even if nothing was active */
 	readBytes = read(fd, &magic, sizeof(magic));
 	if (readBytes != sizeof(magic))
-		ereport(PANIC,
-				(errmsg("could not read file \"%s\": %m",
-						path)));
+	{
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": %m",
+							path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d bytes, expected %zu",
+							path, readBytes, sizeof(magic))));
+	}
 	COMP_CRC32C(crc, &magic, sizeof(magic));
 
 	if (magic != REPLICATION_STATE_MAGIC)
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 4123cdebcf..448f6a87c5 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1708,11 +1708,21 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	pgstat_report_wait_end();
 	if (readBytes != SnapBuildOnDiskConstantSize)
 	{
+		int			save_errno = errno;
+
 		CloseTransientFile(fd);
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) SnapBuildOnDiskConstantSize)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d bytes, expected %zu",
+							path, readBytes, SnapBuildOnDiskConstantSize)));
 	}
 
 	if (ondisk.magic != SNAPBUILD_MAGIC)
@@ -1736,11 +1746,21 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	pgstat_report_wait_end();
 	if (readBytes != sizeof(SnapBuild))
 	{
+		int			save_errno = errno;
+
 		CloseTransientFile(fd);
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sizeof(SnapBuild))));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d bytes, expected %zu",
+							path, readBytes, sizeof(SnapBuild))));
 	}
 	COMP_CRC32C(checksum, &ondisk.builder, sizeof(SnapBuild));
 
@@ -1753,11 +1773,21 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	pgstat_report_wait_end();
 	if (readBytes != sz)
 	{
+		int			save_errno = errno;
+
 		CloseTransientFile(fd);
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sz)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d bytes, expected %zu",
+							path, readBytes, sz)));
 	}
 	COMP_CRC32C(checksum, ondisk.builder.was_running.was_xip, sz);
 
@@ -1769,11 +1799,21 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	pgstat_report_wait_end();
 	if (readBytes != sz)
 	{
+		int			save_errno = errno;
+
 		CloseTransientFile(fd);
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sz)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d bytes, expected %zu",
+							path, readBytes, sz)));
 	}
 	COMP_CRC32C(checksum, ondisk.builder.committed.xip, sz);
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index e8b76b2f20..54e02f9963 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1401,11 +1401,15 @@ RestoreSlotFromDisk(const char *name)
 
 		CloseTransientFile(fd);
 		errno = saved_errno;
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %u: %m",
-						path, readBytes,
-						(uint32) ReplicationSlotOnDiskConstantSize)));
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d bytes, expected %u",
+							path, readBytes,
+							(uint32) ReplicationSlotOnDiskConstantSize)));
 	}
 
 	/* verify magic */
@@ -1441,10 +1445,14 @@ RestoreSlotFromDisk(const char *name)
 
 		CloseTransientFile(fd);
 		errno = saved_errno;
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %u: %m",
-						path, readBytes, cp.length)));
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d bytes, expected %u",
+							path, readBytes, cp.length)));
 	}
 
 	CloseTransientFile(fd);
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index e47ddca6bc..15508ae633 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -501,11 +501,16 @@ SendTimeLineHistory(TimeLineHistoryCmd *cmd)
 		pgstat_report_wait_start(WAIT_EVENT_WALSENDER_TIMELINE_HISTORY_READ);
 		nread = read(fd, rbuf, sizeof(rbuf));
 		pgstat_report_wait_end();
-		if (nread <= 0)
+		if (nread < 0)
 			ereport(ERROR,
 					(errcode_for_file_access(),
 					 errmsg("could not read file \"%s\": %m",
 							path)));
+		else if (nread == 0)
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d bytes, expected %zu",
+							path, nread, bytesleft)));
+
 		pq_sendbytes(&buf, rbuf, nread);
 		bytesleft -= nread;
 	}
@@ -2425,7 +2430,7 @@ retry:
 		pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 		readbytes = read(sendFile, p, segbytes);
 		pgstat_report_wait_end();
-		if (readbytes <= 0)
+		if (readbytes < 0)
 		{
 			ereport(ERROR,
 					(errcode_for_file_access(),
@@ -2433,6 +2438,13 @@ retry:
 							XLogFileNameP(curFileTimeLine, sendSegNo),
 							sendOff, (unsigned long) segbytes)));
 		}
+		else if (readbytes == 0)
+		{
+			ereport(ERROR,
+					(errmsg("could not read from log segment %s, offset %u: read %d bytes, expected %lu",
+							XLogFileNameP(curFileTimeLine, sendSegNo),
+							sendOff, readbytes, (unsigned long) segbytes)));
+		}
 
 		/* Update state for read */
 		recptr += readbytes;
diff --git a/src/backend/utils/cache/relmapper.c b/src/backend/utils/cache/relmapper.c
index 99d095f2df..f4fd0f1819 100644
--- a/src/backend/utils/cache/relmapper.c
+++ b/src/backend/utils/cache/relmapper.c
@@ -629,6 +629,7 @@ load_relmap_file(bool shared)
 	char		mapfilename[MAXPGPATH];
 	pg_crc32c	crc;
 	int			fd;
+	int			r;
 
 	if (shared)
 	{
@@ -659,11 +660,19 @@ load_relmap_file(bool shared)
 	 * are able to access any relation that's affected by the change.
 	 */
 	pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_READ);
-	if (read(fd, map, sizeof(RelMapFile)) != sizeof(RelMapFile))
-		ereport(FATAL,
-				(errcode_for_file_access(),
-				 errmsg("could not read relation mapping file \"%s\": %m",
-						mapfilename)));
+	r = read(fd, map, sizeof(RelMapFile));
+	if (r != sizeof(RelMapFile))
+	{
+		if (r < 0)
+			ereport(FATAL,
+					(errcode_for_file_access(),
+					 errmsg("could not read relation mapping file \"%s\": %m",
+							mapfilename)));
+		else
+			ereport(FATAL,
+					(errmsg("could not read relation mapping file \"%s\": read %d bytes, expected %zu",
+							mapfilename, r, sizeof(RelMapFile))));
+	}
 	pgstat_report_wait_end();
 
 	CloseTransientFile(fd);
diff --git a/src/bin/pg_basebackup/pg_receivewal.c b/src/bin/pg_basebackup/pg_receivewal.c
index 071b32d19d..fc4e2d0492 100644
--- a/src/bin/pg_basebackup/pg_receivewal.c
+++ b/src/bin/pg_basebackup/pg_receivewal.c
@@ -284,6 +284,7 @@ FindStreamingStart(uint32 *tli)
 			char		buf[4];
 			int			bytes_out;
 			char		fullpath[MAXPGPATH * 2];
+			int			r;
 
 			snprintf(fullpath, sizeof(fullpath), "%s/%s", basedir, dirent->d_name);
 
@@ -300,10 +301,15 @@ FindStreamingStart(uint32 *tli)
 						progname, fullpath, strerror(errno));
 				disconnect_and_exit(1);
 			}
-			if (read(fd, (char *) buf, sizeof(buf)) != sizeof(buf))
+			r = read(fd, (char *) buf, sizeof(buf));
+			if (r != sizeof(buf))
 			{
-				fprintf(stderr, _("%s: could not read compressed file \"%s\": %s\n"),
-						progname, fullpath, strerror(errno));
+				if (r < 0)
+					fprintf(stderr, _("%s: could not read compressed file \"%s\": %s\n"),
+							progname, fullpath, strerror(errno));
+				else
+					fprintf(stderr, _("%s: could not read compressed file \"%s\": read %d bytes, expected %zu\n"),
+							progname, fullpath, r, sizeof(buf));
 				disconnect_and_exit(1);
 			}
 
diff --git a/src/bin/pg_rewind/file_ops.c b/src/bin/pg_rewind/file_ops.c
index 94bcc13ae8..895eb50cc0 100644
--- a/src/bin/pg_rewind/file_ops.c
+++ b/src/bin/pg_rewind/file_ops.c
@@ -289,6 +289,7 @@ slurpFile(const char *datadir, const char *path, size_t *filesize)
 	struct stat statbuf;
 	char		fullpath[MAXPGPATH];
 	int			len;
+	int			r;
 
 	snprintf(fullpath, sizeof(fullpath), "%s/%s", datadir, path);
 
@@ -304,9 +305,16 @@ slurpFile(const char *datadir, const char *path, size_t *filesize)
 
 	buffer = pg_malloc(len + 1);
 
-	if (read(fd, buffer, len) != len)
-		pg_fatal("could not read file \"%s\": %s\n",
-				 fullpath, strerror(errno));
+	r = read(fd, buffer, len);
+	if (r != len)
+	{
+		if (r < 0)
+			pg_fatal("could not read file \"%s\": %s\n",
+					 fullpath, strerror(errno));
+		else
+			pg_fatal("not enough data in file \"%s\": read %d bytes, expected %d\n",
+					 fullpath, r, len);
+	}
 	close(fd);
 
 	/* Zero-terminate the buffer. */
diff --git a/src/bin/pg_rewind/parsexlog.c b/src/bin/pg_rewind/parsexlog.c
index b4c1f827a6..de3112a1bd 100644
--- a/src/bin/pg_rewind/parsexlog.c
+++ b/src/bin/pg_rewind/parsexlog.c
@@ -246,6 +246,7 @@ SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
 	uint32		targetPageOff;
 	XLogRecPtr	targetSegEnd;
 	XLogSegNo	targetSegNo;
+	int			r;
 
 	XLByteToSeg(targetPagePtr, targetSegNo, WalSegSz);
 	XLogSegNoOffsetToRecPtr(targetSegNo + 1, 0, targetSegEnd, WalSegSz);
@@ -309,10 +310,17 @@ SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
 		return -1;
 	}
 
-	if (read(xlogreadfd, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+
+	r = read(xlogreadfd, readBuf, XLOG_BLCKSZ);
+	if (r != XLOG_BLCKSZ)
 	{
-		printf(_("could not read from file \"%s\": %s\n"), xlogfpath,
-			   strerror(errno));
+		if (r < 0)
+			printf(_("could not read from file \"%s\": %s\n"), xlogfpath,
+				   strerror(errno));
+		else
+			printf(_("could not read from file \"%s\": read %d bytes, expected %d\n"),
+				   xlogfpath, r, XLOG_BLCKSZ);
+
 		return -1;
 	}
 
diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index 5c4f38e597..ef142e8095 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -210,8 +210,10 @@ search_directory(const char *directory, const char *fname)
 	if (fd >= 0)
 	{
 		char		buf[XLOG_BLCKSZ];
+		int			r;
 
-		if (read(fd, buf, XLOG_BLCKSZ) == XLOG_BLCKSZ)
+		r = read(fd, buf, XLOG_BLCKSZ);
+		if (r == XLOG_BLCKSZ)
 		{
 			XLogLongPageHeader longhdr = (XLogLongPageHeader) buf;
 
@@ -229,7 +231,8 @@ search_directory(const char *directory, const char *fname)
 				fatal_error("could not read file \"%s\": %s",
 							fname, strerror(errno));
 			else
-				fatal_error("not enough data in file \"%s\"", fname);
+				fatal_error("could not read file \"%s\": read %d bytes, %d expected",
+							fname, r, XLOG_BLCKSZ);
 		}
 		close(fd);
 		return true;
@@ -411,11 +414,17 @@ XLogDumpXLogRead(const char *directory, TimeLineID timeline_id,
 		{
 			int			err = errno;
 			char		fname[MAXPGPATH];
+			int			save_errno = errno;
 
 			XLogFileName(fname, timeline_id, sendSegNo, WalSegSz);
+			errno = save_errno;
 
-			fatal_error("could not read from log file %s, offset %u, length %d: %s",
-						fname, sendOff, segbytes, strerror(err));
+			if (readbytes < 0)
+				fatal_error("could not read from log file %s, offset %u, length %d: %s",
+							fname, sendOff, segbytes, strerror(err));
+			else if (readbytes == 0)
+				fatal_error("could not read from log file %s, offset %u: read %d bytes, expected %d",
+							fname, sendOff, readbytes, segbytes);
 		}
 
 		/* Update state for read */

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 65194db70e..f72c149d46 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -1219,6 +1219,7 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	uint32		crc_offset;
 	pg_crc32c	calc_crc,
 				file_crc;
+	int			r;
 
 	TwoPhaseFilePath(path, xid);
 
@@ -1228,8 +1229,7 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 		if (give_warnings)
 			ereport(WARNING,
 					(errcode_for_file_access(),
-					 errmsg("could not open two-phase state file \"%s\": %m",
-							path)));
+					 errmsg("could not open file \"%s\": %m", path)));
 		return NULL;
 	}
 
@@ -1245,8 +1245,7 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 		if (give_warnings)
 			ereport(WARNING,
 					(errcode_for_file_access(),
-					 errmsg("could not stat two-phase state file \"%s\": %m",
-							path)));
+					 errmsg("could not stat file \"%s\": %m", path)));
 		return NULL;
 	}
 
@@ -1272,15 +1271,27 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	buf = (char *) palloc(stat.st_size);
 
 	pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_READ);
-	if (read(fd, buf, stat.st_size) != stat.st_size)
+	r = read(fd, buf, stat.st_size);
+	if (r != stat.st_size)
 	{
+		int			save_errno = errno;
+
 		pgstat_report_wait_end();
 		CloseTransientFile(fd);
 		if (give_warnings)
-			ereport(WARNING,
-					(errcode_for_file_access(),
-					 errmsg("could not read two-phase state file \"%s\": %m",
-							path)));
+		{
+			if (r < 0)
+			{
+				errno = save_errno;
+				ereport(WARNING,
+						(errcode_for_file_access(),
+						 errmsg("could not read file \"%s\": %m", path)));
+			}
+			else
+				ereport(WARNING,
+						(errmsg("could not read file \"%s\": read %d bytes, expected %zu",
+								path, r, stat.st_size)));
+		}
 		pfree(buf);
 		return NULL;
 	}
@@ -1627,8 +1638,7 @@ RemoveTwoPhaseFile(TransactionId xid, bool giveWarning)
 		if (errno != ENOENT || giveWarning)
 			ereport(WARNING,
 					(errcode_for_file_access(),
-					 errmsg("could not remove two-phase state file \"%s\": %m",
-							path)));
+					 errmsg("could not remove file \"%s\": %m", path)));
 }
 
 /*
@@ -1656,26 +1666,31 @@ RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
 	if (fd < 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not recreate two-phase state file \"%s\": %m",
-						path)));
+				 errmsg("could not recreate file \"%s\": %m", path)));
 
 	/* Write content and CRC */
 	pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_WRITE);
 	if (write(fd, content, len) != len)
 	{
+		int			save_errno = errno;
+
 		pgstat_report_wait_end();
 		CloseTransientFile(fd);
+		errno = save_errno;
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not write two-phase state file: %m")));
+				 errmsg("could not write file \"%s\": %m", path)));
 	}
 	if (write(fd, &statefile_crc, sizeof(pg_crc32c)) != sizeof(pg_crc32c))
 	{
+		int			save_errno = errno;
+
 		pgstat_report_wait_end();
 		CloseTransientFile(fd);
+		errno = save_errno;
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not write two-phase state file: %m")));
+				 errmsg("could not write file \"%s\": %m", path)));
 	}
 	pgstat_report_wait_end();
 
@@ -1686,17 +1701,20 @@ RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
 	pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_SYNC);
 	if (pg_fsync(fd) != 0)
 	{
+		int			save_errno = errno;
+
 		CloseTransientFile(fd);
+		errno = save_errno;
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not fsync two-phase state file: %m")));
+				 errmsg("could not fsync file \"%s\": %m", path)));
 	}
 	pgstat_report_wait_end();
 
 	if (CloseTransientFile(fd) != 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not close two-phase state file: %m")));
+				 errmsg("could not close file \"%s\": %m", path)));
 }
 
 /*
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index adbd6a2126..0123f93705 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -3395,21 +3395,24 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
 
 		if (nread > 0)
 		{
+			int			r;
+
 			if (nread > sizeof(buffer))
 				nread = sizeof(buffer);
 			errno = 0;
 			pgstat_report_wait_start(WAIT_EVENT_WAL_COPY_READ);
-			if (read(srcfd, buffer, nread) != nread)
+			r = read(srcfd, buffer, nread);
+			if (r != nread)
 			{
-				if (errno != 0)
+				if (r < 0)
 					ereport(ERROR,
 							(errcode_for_file_access(),
 							 errmsg("could not read file \"%s\": %m",
 									path)));
 				else
 					ereport(ERROR,
-							(errmsg("not enough data in file \"%s\"",
-									path)));
+							(errmsg("could not read file \"%s\": read %d bytes, expected %d",
+									path, r, nread)));
 			}
 			pgstat_report_wait_end();
 		}
@@ -4496,7 +4499,7 @@ ReadControlFile(void)
 	if (fd < 0)
 		ereport(PANIC,
 				(errcode_for_file_access(),
-				 errmsg("could not open control file \"%s\": %m",
+				 errmsg("could not open file \"%s\": %m",
 						XLOG_CONTROL_FILE)));
 
 	pgstat_report_wait_start(WAIT_EVENT_CONTROL_FILE_READ);
@@ -4506,10 +4509,12 @@ ReadControlFile(void)
 		if (r < 0)
 			ereport(PANIC,
 					(errcode_for_file_access(),
-					 errmsg("could not read from control file: %m")));
+					 errmsg("could not read file \"%s\": %m",
+							XLOG_CONTROL_FILE)));
 		else
 			ereport(PANIC,
-					 (errmsg("could not read from control file: read %d bytes, expected %d", r, (int) sizeof(ControlFileData))));
+					(errmsg("could not read file \"%s\": read %d bytes, expected %zu",
+							XLOG_CONTROL_FILE, r, sizeof(ControlFileData))));
 	}
 	pgstat_report_wait_end();
 
@@ -11594,6 +11599,7 @@ XLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr, int reqLen,
 	int			emode = private->emode;
 	uint32		targetPageOff;
 	XLogSegNo	targetSegNo PG_USED_FOR_ASSERTS_ONLY;
+	int			r;
 
 	XLByteToSeg(targetPagePtr, targetSegNo, wal_segment_size);
 	targetPageOff = XLogSegmentOffset(targetPagePtr, wal_segment_size);
@@ -11675,8 +11681,10 @@ retry:
 	if (lseek(readFile, (off_t) readOff, SEEK_SET) < 0)
 	{
 		char		fname[MAXFNAMELEN];
+		int			save_errno = errno;
 
 		XLogFileName(fname, curFileTLI, readSegNo, wal_segment_size);
+		errno = save_errno;
 		ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
 				(errcode_for_file_access(),
 				 errmsg("could not seek in log segment %s to offset %u: %m",
@@ -11685,16 +11693,28 @@ retry:
 	}
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
-	if (read(readFile, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+	r = read(readFile, readBuf, XLOG_BLCKSZ);
+	if (r != XLOG_BLCKSZ)
 	{
 		char		fname[MAXFNAMELEN];
+		int			save_errno = errno;
 
 		pgstat_report_wait_end();
 		XLogFileName(fname, curFileTLI, readSegNo, wal_segment_size);
-		ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
-				(errcode_for_file_access(),
-				 errmsg("could not read from log segment %s, offset %u: %m",
-						fname, readOff)));
+
+		if (r < 0)
+		{
+			errno = save_errno;
+			ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
+					(errcode_for_file_access(),
+					 errmsg("could not read from log segment %s, offset %u: %m",
+							fname, readOff)));
+		}
+		else
+			ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
+					(errmsg("could not read from log segment %s, offset %u: read %d bytes, expected %d",
+							fname, readOff, r, XLOG_BLCKSZ)));
+
 		goto next_record_is_invalid;
 	}
 	pgstat_report_wait_end();
diff --git a/src/backend/replication/logical/origin.c b/src/backend/replication/logical/origin.c
index 963878a5d8..053c13c43e 100644
--- a/src/backend/replication/logical/origin.c
+++ b/src/backend/replication/logical/origin.c
@@ -697,9 +697,16 @@ StartupReplicationOrigin(void)
 	/* verify magic, that is written even if nothing was active */
 	readBytes = read(fd, &magic, sizeof(magic));
 	if (readBytes != sizeof(magic))
-		ereport(PANIC,
-				(errmsg("could not read file \"%s\": %m",
-						path)));
+	{
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": %m",
+							path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d bytes, expected %zu",
+							path, readBytes, sizeof(magic))));
+	}
 	COMP_CRC32C(crc, &magic, sizeof(magic));
 
 	if (magic != REPLICATION_STATE_MAGIC)
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 4123cdebcf..448f6a87c5 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1708,11 +1708,21 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	pgstat_report_wait_end();
 	if (readBytes != SnapBuildOnDiskConstantSize)
 	{
+		int			save_errno = errno;
+
 		CloseTransientFile(fd);
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) SnapBuildOnDiskConstantSize)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d bytes, expected %zu",
+							path, readBytes, SnapBuildOnDiskConstantSize)));
 	}
 
 	if (ondisk.magic != SNAPBUILD_MAGIC)
@@ -1736,11 +1746,21 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	pgstat_report_wait_end();
 	if (readBytes != sizeof(SnapBuild))
 	{
+		int			save_errno = errno;
+
 		CloseTransientFile(fd);
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sizeof(SnapBuild))));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d bytes, expected %zu",
+							path, readBytes, sizeof(SnapBuild))));
 	}
 	COMP_CRC32C(checksum, &ondisk.builder, sizeof(SnapBuild));
 
@@ -1753,11 +1773,21 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	pgstat_report_wait_end();
 	if (readBytes != sz)
 	{
+		int			save_errno = errno;
+
 		CloseTransientFile(fd);
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sz)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d bytes, expected %zu",
+							path, readBytes, sz)));
 	}
 	COMP_CRC32C(checksum, ondisk.builder.was_running.was_xip, sz);
 
@@ -1769,11 +1799,21 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	pgstat_report_wait_end();
 	if (readBytes != sz)
 	{
+		int			save_errno = errno;
+
 		CloseTransientFile(fd);
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sz)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d bytes, expected %zu",
+							path, readBytes, sz)));
 	}
 	COMP_CRC32C(checksum, ondisk.builder.committed.xip, sz);
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index e8b76b2f20..54e02f9963 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1401,11 +1401,15 @@ RestoreSlotFromDisk(const char *name)
 
 		CloseTransientFile(fd);
 		errno = saved_errno;
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %u: %m",
-						path, readBytes,
-						(uint32) ReplicationSlotOnDiskConstantSize)));
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d bytes, expected %u",
+							path, readBytes,
+							(uint32) ReplicationSlotOnDiskConstantSize)));
 	}
 
 	/* verify magic */
@@ -1441,10 +1445,14 @@ RestoreSlotFromDisk(const char *name)
 
 		CloseTransientFile(fd);
 		errno = saved_errno;
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %u: %m",
-						path, readBytes, cp.length)));
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d bytes, expected %u",
+							path, readBytes, cp.length)));
 	}
 
 	CloseTransientFile(fd);
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index e47ddca6bc..15508ae633 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -501,11 +501,16 @@ SendTimeLineHistory(TimeLineHistoryCmd *cmd)
 		pgstat_report_wait_start(WAIT_EVENT_WALSENDER_TIMELINE_HISTORY_READ);
 		nread = read(fd, rbuf, sizeof(rbuf));
 		pgstat_report_wait_end();
-		if (nread <= 0)
+		if (nread < 0)
 			ereport(ERROR,
 					(errcode_for_file_access(),
 					 errmsg("could not read file \"%s\": %m",
 							path)));
+		else if (nread == 0)
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d bytes, expected %zu",
+							path, nread, bytesleft)));
+
 		pq_sendbytes(&buf, rbuf, nread);
 		bytesleft -= nread;
 	}
@@ -2425,7 +2430,7 @@ retry:
 		pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 		readbytes = read(sendFile, p, segbytes);
 		pgstat_report_wait_end();
-		if (readbytes <= 0)
+		if (readbytes < 0)
 		{
 			ereport(ERROR,
 					(errcode_for_file_access(),
@@ -2433,6 +2438,13 @@ retry:
 							XLogFileNameP(curFileTimeLine, sendSegNo),
 							sendOff, (unsigned long) segbytes)));
 		}
+		else if (readbytes == 0)
+		{
+			ereport(ERROR,
+					(errmsg("could not read from log segment %s, offset %u: read %d bytes, expected %lu",
+							XLogFileNameP(curFileTimeLine, sendSegNo),
+							sendOff, readbytes, (unsigned long) segbytes)));
+		}
 
 		/* Update state for read */
 		recptr += readbytes;
diff --git a/src/backend/utils/cache/relmapper.c b/src/backend/utils/cache/relmapper.c
index 99d095f2df..3f97c8d597 100644
--- a/src/backend/utils/cache/relmapper.c
+++ b/src/backend/utils/cache/relmapper.c
@@ -629,6 +629,7 @@ load_relmap_file(bool shared)
 	char		mapfilename[MAXPGPATH];
 	pg_crc32c	crc;
 	int			fd;
+	int			r;
 
 	if (shared)
 	{
@@ -648,7 +649,7 @@ load_relmap_file(bool shared)
 	if (fd < 0)
 		ereport(FATAL,
 				(errcode_for_file_access(),
-				 errmsg("could not open relation mapping file \"%s\": %m",
+				 errmsg("could not open file \"%s\": %m",
 						mapfilename)));
 
 	/*
@@ -659,11 +660,18 @@ load_relmap_file(bool shared)
 	 * are able to access any relation that's affected by the change.
 	 */
 	pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_READ);
-	if (read(fd, map, sizeof(RelMapFile)) != sizeof(RelMapFile))
-		ereport(FATAL,
-				(errcode_for_file_access(),
-				 errmsg("could not read relation mapping file \"%s\": %m",
-						mapfilename)));
+	r = read(fd, map, sizeof(RelMapFile));
+	if (r != sizeof(RelMapFile))
+	{
+		if (r < 0)
+			ereport(FATAL,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", mapfilename)));
+		else
+			ereport(FATAL,
+					(errmsg("could not read file \"%s\": read %d bytes, expected %zu",
+							mapfilename, r, sizeof(RelMapFile))));
+	}
 	pgstat_report_wait_end();
 
 	CloseTransientFile(fd);
@@ -748,7 +756,7 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 	if (fd < 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not open relation mapping file \"%s\": %m",
+				 errmsg("could not open file \"%s\": %m",
 						mapfilename)));
 
 	if (write_wal)
@@ -782,7 +790,7 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 			errno = ENOSPC;
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not write to relation mapping file \"%s\": %m",
+				 errmsg("could not write file \"%s\": %m",
 						mapfilename)));
 	}
 	pgstat_report_wait_end();
@@ -797,14 +805,14 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 	if (pg_fsync(fd) != 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not fsync relation mapping file \"%s\": %m",
+				 errmsg("could not fsync file \"%s\": %m",
 						mapfilename)));
 	pgstat_report_wait_end();
 
 	if (CloseTransientFile(fd))
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not close relation mapping file \"%s\": %m",
+				 errmsg("could not close file \"%s\": %m",
 						mapfilename)));
 
 	/*
diff --git a/src/bin/pg_basebackup/pg_receivewal.c b/src/bin/pg_basebackup/pg_receivewal.c
index 071b32d19d..fc4e2d0492 100644
--- a/src/bin/pg_basebackup/pg_receivewal.c
+++ b/src/bin/pg_basebackup/pg_receivewal.c
@@ -284,6 +284,7 @@ FindStreamingStart(uint32 *tli)
 			char		buf[4];
 			int			bytes_out;
 			char		fullpath[MAXPGPATH * 2];
+			int			r;
 
 			snprintf(fullpath, sizeof(fullpath), "%s/%s", basedir, dirent->d_name);
 
@@ -300,10 +301,15 @@ FindStreamingStart(uint32 *tli)
 						progname, fullpath, strerror(errno));
 				disconnect_and_exit(1);
 			}
-			if (read(fd, (char *) buf, sizeof(buf)) != sizeof(buf))
+			r = read(fd, (char *) buf, sizeof(buf));
+			if (r != sizeof(buf))
 			{
-				fprintf(stderr, _("%s: could not read compressed file \"%s\": %s\n"),
-						progname, fullpath, strerror(errno));
+				if (r < 0)
+					fprintf(stderr, _("%s: could not read compressed file \"%s\": %s\n"),
+							progname, fullpath, strerror(errno));
+				else
+					fprintf(stderr, _("%s: could not read compressed file \"%s\": read %d bytes, expected %zu\n"),
+							progname, fullpath, r, sizeof(buf));
 				disconnect_and_exit(1);
 			}
 
diff --git a/src/bin/pg_rewind/file_ops.c b/src/bin/pg_rewind/file_ops.c
index 94bcc13ae8..20bbf32705 100644
--- a/src/bin/pg_rewind/file_ops.c
+++ b/src/bin/pg_rewind/file_ops.c
@@ -289,6 +289,7 @@ slurpFile(const char *datadir, const char *path, size_t *filesize)
 	struct stat statbuf;
 	char		fullpath[MAXPGPATH];
 	int			len;
+	int			r;
 
 	snprintf(fullpath, sizeof(fullpath), "%s/%s", datadir, path);
 
@@ -304,9 +305,16 @@ slurpFile(const char *datadir, const char *path, size_t *filesize)
 
 	buffer = pg_malloc(len + 1);
 
-	if (read(fd, buffer, len) != len)
-		pg_fatal("could not read file \"%s\": %s\n",
-				 fullpath, strerror(errno));
+	r = read(fd, buffer, len);
+	if (r != len)
+	{
+		if (r < 0)
+			pg_fatal("could not read file \"%s\": %s\n",
+					 fullpath, strerror(errno));
+		else
+			pg_fatal("could not read file \"%s\": read %d bytes, expected %d\n",
+					 fullpath, r, len);
+	}
 	close(fd);
 
 	/* Zero-terminate the buffer. */
diff --git a/src/bin/pg_rewind/parsexlog.c b/src/bin/pg_rewind/parsexlog.c
index b4c1f827a6..de3112a1bd 100644
--- a/src/bin/pg_rewind/parsexlog.c
+++ b/src/bin/pg_rewind/parsexlog.c
@@ -246,6 +246,7 @@ SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
 	uint32		targetPageOff;
 	XLogRecPtr	targetSegEnd;
 	XLogSegNo	targetSegNo;
+	int			r;
 
 	XLByteToSeg(targetPagePtr, targetSegNo, WalSegSz);
 	XLogSegNoOffsetToRecPtr(targetSegNo + 1, 0, targetSegEnd, WalSegSz);
@@ -309,10 +310,17 @@ SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
 		return -1;
 	}
 
-	if (read(xlogreadfd, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+
+	r = read(xlogreadfd, readBuf, XLOG_BLCKSZ);
+	if (r != XLOG_BLCKSZ)
 	{
-		printf(_("could not read from file \"%s\": %s\n"), xlogfpath,
-			   strerror(errno));
+		if (r < 0)
+			printf(_("could not read from file \"%s\": %s\n"), xlogfpath,
+				   strerror(errno));
+		else
+			printf(_("could not read from file \"%s\": read %d bytes, expected %d\n"),
+				   xlogfpath, r, XLOG_BLCKSZ);
+
 		return -1;
 	}
 
diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index 5c4f38e597..ef142e8095 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -210,8 +210,10 @@ search_directory(const char *directory, const char *fname)
 	if (fd >= 0)
 	{
 		char		buf[XLOG_BLCKSZ];
+		int			r;
 
-		if (read(fd, buf, XLOG_BLCKSZ) == XLOG_BLCKSZ)
+		r = read(fd, buf, XLOG_BLCKSZ);
+		if (r == XLOG_BLCKSZ)
 		{
 			XLogLongPageHeader longhdr = (XLogLongPageHeader) buf;
 
@@ -229,7 +231,8 @@ search_directory(const char *directory, const char *fname)
 				fatal_error("could not read file \"%s\": %s",
 							fname, strerror(errno));
 			else
-				fatal_error("not enough data in file \"%s\"", fname);
+				fatal_error("could not read file \"%s\": read %d bytes, %d expected",
+							fname, r, XLOG_BLCKSZ);
 		}
 		close(fd);
 		return true;
@@ -411,11 +414,17 @@ XLogDumpXLogRead(const char *directory, TimeLineID timeline_id,
 		{
 			int			err = errno;
 			char		fname[MAXPGPATH];
+			int			save_errno = errno;
 
 			XLogFileName(fname, timeline_id, sendSegNo, WalSegSz);
+			errno = save_errno;
 
-			fatal_error("could not read from log file %s, offset %u, length %d: %s",
-						fname, sendOff, segbytes, strerror(err));
+			if (readbytes < 0)
+				fatal_error("could not read from log file %s, offset %u, length %d: %s",
+							fname, sendOff, segbytes, strerror(err));
+			else if (readbytes == 0)
+				fatal_error("could not read from log file %s, offset %u: read %d bytes, expected %d",
+							fname, sendOff, readbytes, segbytes);
 		}
 
 		/* Update state for read */

From 041068b821dd555e437f77a99e95795eceff3189 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Mon, 25 Jun 2018 14:37:18 +0900
Subject: [PATCH 1/2] Rework error messages around file handling

Some error messages related to file handling are using the code path
context to define their state.  For example, 2PC-related errors are
referring to "two-phase status files", or "relation mapping file" is
used for catalog-to-filenode mapping, however those prove to be
difficult to translate, and are not more helpful than just referring to
the path of the file being manipulated.  So simplify all those error
messages by just referring to files with their path used.  In some
cases, like the manipulation of WAL segments, the context is helpful so
those are kept.

Calls to the system function read() have also been rather inconsistent
with their error handling sometimes not reporting the number of bytes
read, and some other code paths trying to use an errno which has not
been set.  The in-core functions are using a more consistent pattern
with this patch, which checks for both errno if set or if an
inconsistent read is happening.

So as to care about pluralization when reading an unexpected number of
bytes, "could not read: read %d of %d" is used as error message.

Author: Michael Paquier
Discussion: https://postgr.es/m/20180622234803.GA1134@paquier.xyz
---
 src/backend/access/transam/twophase.c       | 40 ++++++------
 src/backend/access/transam/xlog.c           | 40 ++++++++----
 src/backend/replication/logical/origin.c    | 13 +++-
 src/backend/replication/logical/snapbuild.c | 68 +++++++++++++++------
 src/backend/replication/slot.c              | 26 +++++---
 src/backend/replication/walsender.c         | 16 ++++-
 src/backend/utils/cache/relmapper.c         | 28 ++++++---
 src/bin/pg_basebackup/pg_receivewal.c       | 12 +++-
 src/bin/pg_rewind/file_ops.c                | 14 ++++-
 src/bin/pg_rewind/parsexlog.c               | 14 ++++-
 src/bin/pg_waldump/pg_waldump.c             | 17 ++++--
 11 files changed, 200 insertions(+), 88 deletions(-)

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index a9ef1b3d73..10c1e31c0f 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -1219,6 +1219,7 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	uint32		crc_offset;
 	pg_crc32c	calc_crc,
 				file_crc;
+	int			r;
 
 	TwoPhaseFilePath(path, xid);
 
@@ -1228,8 +1229,7 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 		if (give_warnings)
 			ereport(WARNING,
 					(errcode_for_file_access(),
-					 errmsg("could not open two-phase state file \"%s\": %m",
-							path)));
+					 errmsg("could not open file \"%s\": %m", path)));
 		return NULL;
 	}
 
@@ -1249,8 +1249,7 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 			errno = save_errno;
 			ereport(WARNING,
 					(errcode_for_file_access(),
-					 errmsg("could not stat two-phase state file \"%s\": %m",
-							path)));
+					 errmsg("could not stat file \"%s\": %m", path)));
 		}
 		return NULL;
 	}
@@ -1277,7 +1276,8 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	buf = (char *) palloc(stat.st_size);
 
 	pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_READ);
-	if (read(fd, buf, stat.st_size) != stat.st_size)
+	r = read(fd, buf, stat.st_size);
+	if (r != stat.st_size)
 	{
 		int			save_errno = errno;
 
@@ -1285,11 +1285,17 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 		CloseTransientFile(fd);
 		if (give_warnings)
 		{
-			errno = save_errno;
-			ereport(WARNING,
-					(errcode_for_file_access(),
-					 errmsg("could not read two-phase state file \"%s\": %m",
-							path)));
+			if (r < 0)
+			{
+				errno = save_errno;
+				ereport(WARNING,
+						(errcode_for_file_access(),
+						 errmsg("could not read file \"%s\": %m", path)));
+			}
+			else
+				ereport(WARNING,
+						(errmsg("could not read file \"%s\": read %d of %zu",
+								path, r, stat.st_size)));
 		}
 		pfree(buf);
 		return NULL;
@@ -1637,8 +1643,7 @@ RemoveTwoPhaseFile(TransactionId xid, bool giveWarning)
 		if (errno != ENOENT || giveWarning)
 			ereport(WARNING,
 					(errcode_for_file_access(),
-					 errmsg("could not remove two-phase state file \"%s\": %m",
-							path)));
+					 errmsg("could not remove file \"%s\": %m", path)));
 }
 
 /*
@@ -1666,8 +1671,7 @@ RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
 	if (fd < 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not recreate two-phase state file \"%s\": %m",
-						path)));
+				 errmsg("could not recreate file \"%s\": %m", path)));
 
 	/* Write content and CRC */
 	pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_WRITE);
@@ -1682,7 +1686,7 @@ RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
 		errno = save_errno ? save_errno : ENOSPC;
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not write two-phase state file: %m")));
+				 errmsg("could not write file \"%s\": %m", path)));
 	}
 	if (write(fd, &statefile_crc, sizeof(pg_crc32c)) != sizeof(pg_crc32c))
 	{
@@ -1695,7 +1699,7 @@ RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
 		errno = save_errno ? save_errno : ENOSPC;
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not write two-phase state file: %m")));
+				 errmsg("could not write file \"%s\": %m", path)));
 	}
 	pgstat_report_wait_end();
 
@@ -1712,14 +1716,14 @@ RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
 		errno = save_errno;
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not fsync two-phase state file: %m")));
+				 errmsg("could not fsync file \"%s\": %m", path)));
 	}
 	pgstat_report_wait_end();
 
 	if (CloseTransientFile(fd) != 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not close two-phase state file: %m")));
+				 errmsg("could not close file \"%s\": %m", path)));
 }
 
 /*
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 1a419aa49b..5bb19cef31 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -3398,21 +3398,24 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
 
 		if (nread > 0)
 		{
+			int			r;
+
 			if (nread > sizeof(buffer))
 				nread = sizeof(buffer);
 			errno = 0;
 			pgstat_report_wait_start(WAIT_EVENT_WAL_COPY_READ);
-			if (read(srcfd, buffer, nread) != nread)
+			r = read(srcfd, buffer, nread);
+			if (r != nread)
 			{
-				if (errno != 0)
+				if (r < 0)
 					ereport(ERROR,
 							(errcode_for_file_access(),
 							 errmsg("could not read file \"%s\": %m",
 									path)));
 				else
 					ereport(ERROR,
-							(errmsg("not enough data in file \"%s\"",
-									path)));
+							(errmsg("could not read file \"%s\": read %d of %d",
+									path, r, nread)));
 			}
 			pgstat_report_wait_end();
 		}
@@ -4499,7 +4502,7 @@ ReadControlFile(void)
 	if (fd < 0)
 		ereport(PANIC,
 				(errcode_for_file_access(),
-				 errmsg("could not open control file \"%s\": %m",
+				 errmsg("could not open file \"%s\": %m",
 						XLOG_CONTROL_FILE)));
 
 	pgstat_report_wait_start(WAIT_EVENT_CONTROL_FILE_READ);
@@ -4509,10 +4512,12 @@ ReadControlFile(void)
 		if (r < 0)
 			ereport(PANIC,
 					(errcode_for_file_access(),
-					 errmsg("could not read from control file: %m")));
+					 errmsg("could not read file \"%s\": %m",
+							XLOG_CONTROL_FILE)));
 		else
 			ereport(PANIC,
-					 (errmsg("could not read from control file: read %d bytes, expected %d", r, (int) sizeof(ControlFileData))));
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							XLOG_CONTROL_FILE, r, sizeof(ControlFileData))));
 	}
 	pgstat_report_wait_end();
 
@@ -11597,6 +11602,7 @@ XLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr, int reqLen,
 	int			emode = private->emode;
 	uint32		targetPageOff;
 	XLogSegNo	targetSegNo PG_USED_FOR_ASSERTS_ONLY;
+	int			r;
 
 	XLByteToSeg(targetPagePtr, targetSegNo, wal_segment_size);
 	targetPageOff = XLogSegmentOffset(targetPagePtr, wal_segment_size);
@@ -11690,18 +11696,26 @@ retry:
 	}
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
-	if (read(readFile, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+	r = read(readFile, readBuf, XLOG_BLCKSZ);
+	if (r != XLOG_BLCKSZ)
 	{
 		char		fname[MAXFNAMELEN];
 		int			save_errno = errno;
 
 		pgstat_report_wait_end();
 		XLogFileName(fname, curFileTLI, readSegNo, wal_segment_size);
-		errno = save_errno;
-		ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
-				(errcode_for_file_access(),
-				 errmsg("could not read from log segment %s, offset %u: %m",
-						fname, readOff)));
+		if (r < 0)
+		{
+			errno = save_errno;
+			ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
+					(errcode_for_file_access(),
+					 errmsg("could not read from log segment %s, offset %u: %m",
+							fname, readOff)));
+		}
+		else
+			ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
+					(errmsg("could not read from log segment %s, offset %u: read %d of %d",
+							fname, readOff, r, XLOG_BLCKSZ)));
 		goto next_record_is_invalid;
 	}
 	pgstat_report_wait_end();
diff --git a/src/backend/replication/logical/origin.c b/src/backend/replication/logical/origin.c
index 3d3f6dff1b..841e24c03d 100644
--- a/src/backend/replication/logical/origin.c
+++ b/src/backend/replication/logical/origin.c
@@ -712,9 +712,16 @@ StartupReplicationOrigin(void)
 	/* verify magic, that is written even if nothing was active */
 	readBytes = read(fd, &magic, sizeof(magic));
 	if (readBytes != sizeof(magic))
-		ereport(PANIC,
-				(errmsg("could not read file \"%s\": %m",
-						path)));
+	{
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": %m",
+							path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sizeof(magic))));
+	}
 	COMP_CRC32C(crc, &magic, sizeof(magic));
 
 	if (magic != REPLICATION_STATE_MAGIC)
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 2c4a1bab4b..da97efc305 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1719,11 +1719,18 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 		int			save_errno = errno;
 
 		CloseTransientFile(fd);
-		errno = save_errno;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) SnapBuildOnDiskConstantSize)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, SnapBuildOnDiskConstantSize)));
 	}
 
 	if (ondisk.magic != SNAPBUILD_MAGIC)
@@ -1750,11 +1757,18 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 		int			save_errno = errno;
 
 		CloseTransientFile(fd);
-		errno = save_errno;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sizeof(SnapBuild))));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sizeof(SnapBuild))));
 	}
 	COMP_CRC32C(checksum, &ondisk.builder, sizeof(SnapBuild));
 
@@ -1770,11 +1784,18 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 		int			save_errno = errno;
 
 		CloseTransientFile(fd);
-		errno = save_errno;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sz)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sz)));
 	}
 	COMP_CRC32C(checksum, ondisk.builder.was_running.was_xip, sz);
 
@@ -1789,11 +1810,18 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 		int			save_errno = errno;
 
 		CloseTransientFile(fd);
-		errno = save_errno;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sz)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sz)));
 	}
 	COMP_CRC32C(checksum, ondisk.builder.committed.xip, sz);
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index f5927b4d1d..ddd91ef886 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1406,11 +1406,15 @@ RestoreSlotFromDisk(const char *name)
 
 		CloseTransientFile(fd);
 		errno = saved_errno;
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %u: %m",
-						path, readBytes,
-						(uint32) ReplicationSlotOnDiskConstantSize)));
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d of %u",
+							path, readBytes,
+							(uint32) ReplicationSlotOnDiskConstantSize)));
 	}
 
 	/* verify magic */
@@ -1446,10 +1450,14 @@ RestoreSlotFromDisk(const char *name)
 
 		CloseTransientFile(fd);
 		errno = saved_errno;
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %u: %m",
-						path, readBytes, cp.length)));
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d of %u",
+							path, readBytes, cp.length)));
 	}
 
 	CloseTransientFile(fd);
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index e47ddca6bc..9b87c7ca41 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -501,11 +501,16 @@ SendTimeLineHistory(TimeLineHistoryCmd *cmd)
 		pgstat_report_wait_start(WAIT_EVENT_WALSENDER_TIMELINE_HISTORY_READ);
 		nread = read(fd, rbuf, sizeof(rbuf));
 		pgstat_report_wait_end();
-		if (nread <= 0)
+		if (nread < 0)
 			ereport(ERROR,
 					(errcode_for_file_access(),
 					 errmsg("could not read file \"%s\": %m",
 							path)));
+		else if (nread == 0)
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, nread, bytesleft)));
+
 		pq_sendbytes(&buf, rbuf, nread);
 		bytesleft -= nread;
 	}
@@ -2425,7 +2430,7 @@ retry:
 		pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 		readbytes = read(sendFile, p, segbytes);
 		pgstat_report_wait_end();
-		if (readbytes <= 0)
+		if (readbytes < 0)
 		{
 			ereport(ERROR,
 					(errcode_for_file_access(),
@@ -2433,6 +2438,13 @@ retry:
 							XLogFileNameP(curFileTimeLine, sendSegNo),
 							sendOff, (unsigned long) segbytes)));
 		}
+		else if (readbytes == 0)
+		{
+			ereport(ERROR,
+					(errmsg("could not read from log segment %s, offset %u: read %d of %lu",
+							XLogFileNameP(curFileTimeLine, sendSegNo),
+							sendOff, readbytes, (unsigned long) segbytes)));
+		}
 
 		/* Update state for read */
 		recptr += readbytes;
diff --git a/src/backend/utils/cache/relmapper.c b/src/backend/utils/cache/relmapper.c
index 99d095f2df..2d31f9f912 100644
--- a/src/backend/utils/cache/relmapper.c
+++ b/src/backend/utils/cache/relmapper.c
@@ -629,6 +629,7 @@ load_relmap_file(bool shared)
 	char		mapfilename[MAXPGPATH];
 	pg_crc32c	crc;
 	int			fd;
+	int			r;
 
 	if (shared)
 	{
@@ -648,7 +649,7 @@ load_relmap_file(bool shared)
 	if (fd < 0)
 		ereport(FATAL,
 				(errcode_for_file_access(),
-				 errmsg("could not open relation mapping file \"%s\": %m",
+				 errmsg("could not open file \"%s\": %m",
 						mapfilename)));
 
 	/*
@@ -659,11 +660,18 @@ load_relmap_file(bool shared)
 	 * are able to access any relation that's affected by the change.
 	 */
 	pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_READ);
-	if (read(fd, map, sizeof(RelMapFile)) != sizeof(RelMapFile))
-		ereport(FATAL,
-				(errcode_for_file_access(),
-				 errmsg("could not read relation mapping file \"%s\": %m",
-						mapfilename)));
+	r = read(fd, map, sizeof(RelMapFile));
+	if (r != sizeof(RelMapFile))
+	{
+		if (r < 0)
+			ereport(FATAL,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", mapfilename)));
+		else
+			ereport(FATAL,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							mapfilename, r, sizeof(RelMapFile))));
+	}
 	pgstat_report_wait_end();
 
 	CloseTransientFile(fd);
@@ -748,7 +756,7 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 	if (fd < 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not open relation mapping file \"%s\": %m",
+				 errmsg("could not open file \"%s\": %m",
 						mapfilename)));
 
 	if (write_wal)
@@ -782,7 +790,7 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 			errno = ENOSPC;
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not write to relation mapping file \"%s\": %m",
+				 errmsg("could not write file \"%s\": %m",
 						mapfilename)));
 	}
 	pgstat_report_wait_end();
@@ -797,14 +805,14 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 	if (pg_fsync(fd) != 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not fsync relation mapping file \"%s\": %m",
+				 errmsg("could not fsync file \"%s\": %m",
 						mapfilename)));
 	pgstat_report_wait_end();
 
 	if (CloseTransientFile(fd))
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not close relation mapping file \"%s\": %m",
+				 errmsg("could not close file \"%s\": %m",
 						mapfilename)));
 
 	/*
diff --git a/src/bin/pg_basebackup/pg_receivewal.c b/src/bin/pg_basebackup/pg_receivewal.c
index 071b32d19d..bdea9a85ff 100644
--- a/src/bin/pg_basebackup/pg_receivewal.c
+++ b/src/bin/pg_basebackup/pg_receivewal.c
@@ -284,6 +284,7 @@ FindStreamingStart(uint32 *tli)
 			char		buf[4];
 			int			bytes_out;
 			char		fullpath[MAXPGPATH * 2];
+			int			r;
 
 			snprintf(fullpath, sizeof(fullpath), "%s/%s", basedir, dirent->d_name);
 
@@ -300,10 +301,15 @@ FindStreamingStart(uint32 *tli)
 						progname, fullpath, strerror(errno));
 				disconnect_and_exit(1);
 			}
-			if (read(fd, (char *) buf, sizeof(buf)) != sizeof(buf))
+			r = read(fd, (char *) buf, sizeof(buf));
+			if (r != sizeof(buf))
 			{
-				fprintf(stderr, _("%s: could not read compressed file \"%s\": %s\n"),
-						progname, fullpath, strerror(errno));
+				if (r < 0)
+					fprintf(stderr, _("%s: could not read compressed file \"%s\": %s\n"),
+							progname, fullpath, strerror(errno));
+				else
+					fprintf(stderr, _("%s: could not read compressed file \"%s\": read %d of %zu\n"),
+							progname, fullpath, r, sizeof(buf));
 				disconnect_and_exit(1);
 			}
 
diff --git a/src/bin/pg_rewind/file_ops.c b/src/bin/pg_rewind/file_ops.c
index 94bcc13ae8..da2bf449e4 100644
--- a/src/bin/pg_rewind/file_ops.c
+++ b/src/bin/pg_rewind/file_ops.c
@@ -289,6 +289,7 @@ slurpFile(const char *datadir, const char *path, size_t *filesize)
 	struct stat statbuf;
 	char		fullpath[MAXPGPATH];
 	int			len;
+	int			r;
 
 	snprintf(fullpath, sizeof(fullpath), "%s/%s", datadir, path);
 
@@ -304,9 +305,16 @@ slurpFile(const char *datadir, const char *path, size_t *filesize)
 
 	buffer = pg_malloc(len + 1);
 
-	if (read(fd, buffer, len) != len)
-		pg_fatal("could not read file \"%s\": %s\n",
-				 fullpath, strerror(errno));
+	r = read(fd, buffer, len);
+	if (r != len)
+	{
+		if (r < 0)
+			pg_fatal("could not read file \"%s\": %s\n",
+					 fullpath, strerror(errno));
+		else
+			pg_fatal("could not read file \"%s\": read %d of %d\n",
+					 fullpath, r, len);
+	}
 	close(fd);
 
 	/* Zero-terminate the buffer. */
diff --git a/src/bin/pg_rewind/parsexlog.c b/src/bin/pg_rewind/parsexlog.c
index b4c1f827a6..6b3a337509 100644
--- a/src/bin/pg_rewind/parsexlog.c
+++ b/src/bin/pg_rewind/parsexlog.c
@@ -246,6 +246,7 @@ SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
 	uint32		targetPageOff;
 	XLogRecPtr	targetSegEnd;
 	XLogSegNo	targetSegNo;
+	int			r;
 
 	XLByteToSeg(targetPagePtr, targetSegNo, WalSegSz);
 	XLogSegNoOffsetToRecPtr(targetSegNo + 1, 0, targetSegEnd, WalSegSz);
@@ -309,10 +310,17 @@ SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
 		return -1;
 	}
 
-	if (read(xlogreadfd, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+
+	r = read(xlogreadfd, readBuf, XLOG_BLCKSZ);
+	if (r != XLOG_BLCKSZ)
 	{
-		printf(_("could not read from file \"%s\": %s\n"), xlogfpath,
-			   strerror(errno));
+		if (r < 0)
+			printf(_("could not read from file \"%s\": %s\n"), xlogfpath,
+				   strerror(errno));
+		else
+			printf(_("could not read from file \"%s\": read %d of %d\n"),
+				   xlogfpath, r, XLOG_BLCKSZ);
+
 		return -1;
 	}
 
diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index 5c4f38e597..147929f52b 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -210,8 +210,10 @@ search_directory(const char *directory, const char *fname)
 	if (fd >= 0)
 	{
 		char		buf[XLOG_BLCKSZ];
+		int			r;
 
-		if (read(fd, buf, XLOG_BLCKSZ) == XLOG_BLCKSZ)
+		r = read(fd, buf, XLOG_BLCKSZ);
+		if (r == XLOG_BLCKSZ)
 		{
 			XLogLongPageHeader longhdr = (XLogLongPageHeader) buf;
 
@@ -229,7 +231,8 @@ search_directory(const char *directory, const char *fname)
 				fatal_error("could not read file \"%s\": %s",
 							fname, strerror(errno));
 			else
-				fatal_error("not enough data in file \"%s\"", fname);
+				fatal_error("could not read file \"%s\": read %d of %d",
+							fname, r, XLOG_BLCKSZ);
 		}
 		close(fd);
 		return true;
@@ -411,11 +414,17 @@ XLogDumpXLogRead(const char *directory, TimeLineID timeline_id,
 		{
 			int			err = errno;
 			char		fname[MAXPGPATH];
+			int			save_errno = errno;
 
 			XLogFileName(fname, timeline_id, sendSegNo, WalSegSz);
+			errno = save_errno;
 
-			fatal_error("could not read from log file %s, offset %u, length %d: %s",
-						fname, sendOff, segbytes, strerror(err));
+			if (readbytes < 0)
+				fatal_error("could not read from log file %s, offset %u, length %d: %s",
+							fname, sendOff, segbytes, strerror(err));
+			else if (readbytes == 0)
+				fatal_error("could not read from log file %s, offset %u: read %d of %d",
+							fname, sendOff, readbytes, segbytes);
 		}
 
 		/* Update state for read */
-- 
2.18.0

From 057d3ec6b42c1c5a5b332b82af89e532ac2893f3 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Mon, 25 Jun 2018 16:15:03 +0900
Subject: [PATCH 2/2] Add interface to read/write/fsync with transient files

The following set of routines gets added for the manipulation of
transient files:
void WriteTransientFile(int fd, char *buf, Size count, int elevel,
    const char *filename, uint32 wait_event_info);
bool ReadTransientFile(int fd, char *buf, Size count, int elevel,
    const char *filename, uint32 wait_event_info);
void SyncTransientFile(int fd, int elevel, const char *filename,
    uint32 wait_event_info);

This simplifies code related to replication slots, 2PC files, relation
mapper files and snapshot builds:
- Centralize errno handling for transient files with ENOSPC for write(2)
and read count for read(2)
- Wait events have to be defined, so those would unlikely get forgotten
in the future.
- Error handling for CloseTransientFile in code paths is centralized.
---
 src/backend/access/transam/twophase.c       |  25 +----
 src/backend/replication/logical/snapbuild.c | 110 ++------------------
 src/backend/replication/slot.c              |  46 +-------
 src/backend/storage/file/fd.c               |  97 ++++++++++++++++-
 src/backend/utils/cache/relmapper.c         |  40 ++-----
 src/include/storage/fd.h                    |  10 +-
 6 files changed, 128 insertions(+), 200 deletions(-)

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 10c1e31c0f..61b3780119 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -1219,7 +1219,6 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	uint32		crc_offset;
 	pg_crc32c	calc_crc,
 				file_crc;
-	int			r;
 
 	TwoPhaseFilePath(path, xid);
 
@@ -1275,28 +1274,10 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	 */
 	buf = (char *) palloc(stat.st_size);
 
-	pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_READ);
-	r = read(fd, buf, stat.st_size);
-	if (r != stat.st_size)
+	if (!ReadTransientFile(fd, buf, stat.st_size,
+						   give_warnings ? WARNING : DEBUG3, path,
+						   WAIT_EVENT_TWOPHASE_FILE_READ))
 	{
-		int			save_errno = errno;
-
-		pgstat_report_wait_end();
-		CloseTransientFile(fd);
-		if (give_warnings)
-		{
-			if (r < 0)
-			{
-				errno = save_errno;
-				ereport(WARNING,
-						(errcode_for_file_access(),
-						 errmsg("could not read file \"%s\": %m", path)));
-			}
-			else
-				ereport(WARNING,
-						(errmsg("could not read file \"%s\": read %d of %zu",
-								path, r, stat.st_size)));
-		}
 		pfree(buf);
 		return NULL;
 	}
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index da97efc305..4ea8be6c34 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1602,20 +1602,8 @@ SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn)
 		ereport(ERROR,
 				(errmsg("could not open file \"%s\": %m", path)));
 
-	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_WRITE);
-	if ((write(fd, ondisk, needed_length)) != needed_length)
-	{
-		int			save_errno = errno;
-
-		CloseTransientFile(fd);
-
-		/* if write didn't set errno, assume problem is no disk space */
-		errno = save_errno ? save_errno : ENOSPC;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not write to file \"%s\": %m", tmppath)));
-	}
-	pgstat_report_wait_end();
+	WriteTransientFile(fd, (char *) ondisk, needed_length, ERROR, tmppath,
+					   WAIT_EVENT_SNAPBUILD_WRITE);
 
 	/*
 	 * fsync the file before renaming so that even if we crash after this we
@@ -1679,7 +1667,6 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	int			fd;
 	char		path[MAXPGPATH];
 	Size		sz;
-	int			readBytes;
 	pg_crc32c	checksum;
 
 	/* no point in loading a snapshot if we're already there */
@@ -1709,29 +1696,9 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	fsync_fname(path, false);
 	fsync_fname("pg_logical/snapshots", true);
 
-
 	/* read statically sized portion of snapshot */
-	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
-	readBytes = read(fd, &ondisk, SnapBuildOnDiskConstantSize);
-	pgstat_report_wait_end();
-	if (readBytes != SnapBuildOnDiskConstantSize)
-	{
-		int			save_errno = errno;
-
-		CloseTransientFile(fd);
-
-		if (readBytes < 0)
-		{
-			errno = save_errno;
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		}
-		else
-			ereport(ERROR,
-					(errmsg("could not read file \"%s\": read %d of %zu",
-							path, readBytes, SnapBuildOnDiskConstantSize)));
-	}
+	(void) ReadTransientFile(fd, (char *) &ondisk, SnapBuildOnDiskConstantSize,
+					  ERROR, path, WAIT_EVENT_SNAPBUILD_READ);
 
 	if (ondisk.magic != SNAPBUILD_MAGIC)
 		ereport(ERROR,
@@ -1749,80 +1716,23 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 				SnapBuildOnDiskConstantSize - SnapBuildOnDiskNotChecksummedSize);
 
 	/* read SnapBuild */
-	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
-	readBytes = read(fd, &ondisk.builder, sizeof(SnapBuild));
-	pgstat_report_wait_end();
-	if (readBytes != sizeof(SnapBuild))
-	{
-		int			save_errno = errno;
-
-		CloseTransientFile(fd);
-
-		if (readBytes < 0)
-		{
-			errno = save_errno;
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		}
-		else
-			ereport(ERROR,
-					(errmsg("could not read file \"%s\": read %d of %zu",
-							path, readBytes, sizeof(SnapBuild))));
-	}
+	(void) ReadTransientFile(fd, (char *) &ondisk.builder, sizeof(SnapBuild),
+					  ERROR, path, WAIT_EVENT_SNAPBUILD_READ);
 	COMP_CRC32C(checksum, &ondisk.builder, sizeof(SnapBuild));
 
 	/* restore running xacts (dead, but kept for backward compat) */
 	sz = sizeof(TransactionId) * ondisk.builder.was_running.was_xcnt_space;
 	ondisk.builder.was_running.was_xip =
 		MemoryContextAllocZero(builder->context, sz);
-	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
-	readBytes = read(fd, ondisk.builder.was_running.was_xip, sz);
-	pgstat_report_wait_end();
-	if (readBytes != sz)
-	{
-		int			save_errno = errno;
-
-		CloseTransientFile(fd);
-
-		if (readBytes < 0)
-		{
-			errno = save_errno;
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		}
-		else
-			ereport(ERROR,
-					(errmsg("could not read file \"%s\": read %d of %zu",
-							path, readBytes, sz)));
-	}
+	(void) ReadTransientFile(fd, (char *) ondisk.builder.was_running.was_xip, sz,
+					  ERROR, path, WAIT_EVENT_SNAPBUILD_READ);
 	COMP_CRC32C(checksum, ondisk.builder.was_running.was_xip, sz);
 
 	/* restore committed xacts information */
 	sz = sizeof(TransactionId) * ondisk.builder.committed.xcnt;
 	ondisk.builder.committed.xip = MemoryContextAllocZero(builder->context, sz);
-	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
-	readBytes = read(fd, ondisk.builder.committed.xip, sz);
-	pgstat_report_wait_end();
-	if (readBytes != sz)
-	{
-		int			save_errno = errno;
-
-		CloseTransientFile(fd);
-
-		if (readBytes < 0)
-		{
-			errno = save_errno;
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		}
-		else
-			ereport(ERROR,
-					(errmsg("could not read file \"%s\": read %d of %zu",
-							path, readBytes, sz)));
-	}
+	(void) ReadTransientFile(fd, (char *) ondisk.builder.committed.xip, sz,
+					  ERROR, path, WAIT_EVENT_SNAPBUILD_READ);
 	COMP_CRC32C(checksum, ondisk.builder.committed.xip, sz);
 
 	CloseTransientFile(fd);
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index ddd91ef886..3f06aac2cd 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1346,7 +1346,6 @@ RestoreSlotFromDisk(const char *name)
 	char		path[MAXPGPATH + 22];
 	int			fd;
 	bool		restored = false;
-	int			readBytes;
 	pg_crc32c	checksum;
 
 	/* no need to lock here, no concurrent access allowed yet */
@@ -1397,25 +1396,8 @@ RestoreSlotFromDisk(const char *name)
 	END_CRIT_SECTION();
 
 	/* read part of statefile that's guaranteed to be version independent */
-	pgstat_report_wait_start(WAIT_EVENT_REPLICATION_SLOT_READ);
-	readBytes = read(fd, &cp, ReplicationSlotOnDiskConstantSize);
-	pgstat_report_wait_end();
-	if (readBytes != ReplicationSlotOnDiskConstantSize)
-	{
-		int			saved_errno = errno;
-
-		CloseTransientFile(fd);
-		errno = saved_errno;
-		if (readBytes < 0)
-			ereport(PANIC,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		else
-			ereport(PANIC,
-					(errmsg("could not read file \"%s\": read %d of %u",
-							path, readBytes,
-							(uint32) ReplicationSlotOnDiskConstantSize)));
-	}
+	(void) ReadTransientFile(fd, (char *) &cp, ReplicationSlotOnDiskConstantSize,
+							 PANIC, path, WAIT_EVENT_REPLICATION_SLOT_READ);
 
 	/* verify magic */
 	if (cp.magic != SLOT_MAGIC)
@@ -1439,27 +1421,9 @@ RestoreSlotFromDisk(const char *name)
 						path, cp.length)));
 
 	/* Now that we know the size, read the entire file */
-	pgstat_report_wait_start(WAIT_EVENT_REPLICATION_SLOT_READ);
-	readBytes = read(fd,
-					 (char *) &cp + ReplicationSlotOnDiskConstantSize,
-					 cp.length);
-	pgstat_report_wait_end();
-	if (readBytes != cp.length)
-	{
-		int			saved_errno = errno;
-
-		CloseTransientFile(fd);
-		errno = saved_errno;
-		if (readBytes < 0)
-			ereport(PANIC,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		else
-			ereport(PANIC,
-					(errmsg("could not read file \"%s\": read %d of %u",
-							path, readBytes, cp.length)));
-	}
-
+	(void) ReadTransientFile(fd, (char *) &cp + ReplicationSlotOnDiskConstantSize,
+							 cp.length, PANIC, path,
+							 WAIT_EVENT_REPLICATION_SLOT_READ);
 	CloseTransientFile(fd);
 
 	/* now verify the CRC */
diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index 8dd51f1767..fba7774ddc 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -47,8 +47,9 @@
  * ownership mechanism that provides automatic cleanup for shared files when
  * the last of a group of backends detaches.
  *
- * AllocateFile, AllocateDir, OpenPipeStream and OpenTransientFile are
- * wrappers around fopen(3), opendir(3), popen(3) and open(2), respectively.
+ * AllocateFile, AllocateDir, OpenPipeStream, OpenTransientFile,
+ * WriteTransientFile and ReadTransientFile are wrappers around fopen(3),
+ * opendir(3), popen(3), open(2), write(2) and read(2) respectively.
  * They behave like the corresponding native functions, except that the handle
  * is registered with the current subtransaction, and will be automatically
  * closed at abort. These are intended mainly for short operations like
@@ -2480,6 +2481,98 @@ TryAgain:
 	return NULL;
 }
 
+/*
+ * Write to a file which has been opened using OpenTransientFile or
+ * OpenTransientFilePerm.  Equivalent to write(2).
+ */
+void
+WriteTransientFile(int fd, char *buf, Size count, int elevel,
+				   const char *filename, uint32 wait_event_info)
+{
+	int			r;
+
+	pgstat_report_wait_start(wait_event_info);
+	r = write(fd, buf, count);
+	pgstat_report_wait_end();
+
+	if (r != count)
+	{
+		int         save_errno = errno;
+
+		(void) CloseTransientFile(fd);
+
+		/* if write didn't set errno, assume problem is no disk space */
+		errno = save_errno ? save_errno : ENOSPC;
+		ereport(elevel,
+				(errcode_for_file_access(),
+				 errmsg("could not write to file \"%s\": %m", filename)));
+	}
+}
+
+/*
+ * Read from a file which has been opened using OpenTransientFile or
+ * OpenTransientFilePerm.  Equivalent to read(2).  Returns true on
+ * success and false on failure.
+ */
+bool
+ReadTransientFile(int fd, char *buf, Size count, int elevel,
+				  const char *filename, uint32 wait_event_info)
+{
+	int			r;
+
+	pgstat_report_wait_start(wait_event_info);
+	r = read(fd, buf, count);
+	pgstat_report_wait_end();
+
+	if (r != count)
+	{
+		int         save_errno = errno;
+
+		CloseTransientFile(fd);
+
+		if (r < 0)
+		{
+			errno = save_errno;
+			ereport(elevel,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", filename)));
+		}
+		else
+			ereport(elevel,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							filename, r, count)));
+		return false;
+	}
+
+	return true;
+}
+
+/*
+ * Write to a file which has been opened using OpenTransientFile or
+ * OpenTransientFilePerm.  Equivalent to fsync(2).
+ */
+void
+SyncTransientFile(int fd, int elevel, const char *filename,
+				  uint32 wait_event_info)
+{
+	int			status;
+
+	pgstat_report_wait_start(wait_event_info);
+	status = pg_fsync(fd);
+	pgstat_report_wait_end();
+
+	if (status != 0)
+	{
+		int         save_errno = errno;
+
+		(void) CloseTransientFile(fd);
+		errno = save_errno;
+		ereport(elevel,
+				(errcode_for_file_access(),
+				 errmsg("could not fsync file \"%s\": %m", filename)));
+	}
+}
+
 /*
  * Free an AllocateDesc of any type.
  *
diff --git a/src/backend/utils/cache/relmapper.c b/src/backend/utils/cache/relmapper.c
index 2d31f9f912..e6eff58d40 100644
--- a/src/backend/utils/cache/relmapper.c
+++ b/src/backend/utils/cache/relmapper.c
@@ -629,7 +629,6 @@ load_relmap_file(bool shared)
 	char		mapfilename[MAXPGPATH];
 	pg_crc32c	crc;
 	int			fd;
-	int			r;
 
 	if (shared)
 	{
@@ -659,20 +658,8 @@ load_relmap_file(bool shared)
 	 * look, the sinval signaling mechanism will make us re-read it before we
 	 * are able to access any relation that's affected by the change.
 	 */
-	pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_READ);
-	r = read(fd, map, sizeof(RelMapFile));
-	if (r != sizeof(RelMapFile))
-	{
-		if (r < 0)
-			ereport(FATAL,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", mapfilename)));
-		else
-			ereport(FATAL,
-					(errmsg("could not read file \"%s\": read %d of %zu",
-							mapfilename, r, sizeof(RelMapFile))));
-	}
-	pgstat_report_wait_end();
+	(void) ReadTransientFile(fd, (char *) map, sizeof(RelMapFile), FATAL,
+							 mapfilename, WAIT_EVENT_RELATION_MAP_READ);
 
 	CloseTransientFile(fd);
 
@@ -782,18 +769,9 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 	}
 
 	errno = 0;
-	pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_WRITE);
-	if (write(fd, newmap, sizeof(RelMapFile)) != sizeof(RelMapFile))
-	{
-		/* if write didn't set errno, assume problem is no disk space */
-		if (errno == 0)
-			errno = ENOSPC;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not write file \"%s\": %m",
-						mapfilename)));
-	}
-	pgstat_report_wait_end();
+
+	WriteTransientFile(fd, (char *) newmap, sizeof(RelMapFile), ERROR,
+					   mapfilename, WAIT_EVENT_RELATION_MAP_WRITE);
 
 	/*
 	 * We choose to fsync the data to disk before considering the task done.
@@ -801,13 +779,7 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 	 * issue, but it would complicate checkpointing --- see notes for
 	 * CheckPointRelationMap.
 	 */
-	pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_SYNC);
-	if (pg_fsync(fd) != 0)
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not fsync file \"%s\": %m",
-						mapfilename)));
-	pgstat_report_wait_end();
+	SyncTransientFile(fd, ERROR, mapfilename, WAIT_EVENT_RELATION_MAP_SYNC);
 
 	if (CloseTransientFile(fd))
 		ereport(ERROR,
diff --git a/src/include/storage/fd.h b/src/include/storage/fd.h
index 8e7c9728f4..4309d9da95 100644
--- a/src/include/storage/fd.h
+++ b/src/include/storage/fd.h
@@ -34,7 +34,9 @@
  *
  * Likewise, use AllocateDir/FreeDir, not opendir/closedir, to allocate
  * open directories (DIR*), and OpenTransientFile/CloseTransient File for an
- * unbuffered file descriptor.
+ * unbuffered file descriptor.  WriteTransientFile should be used instead
+ * of write(2), ReadTransientFile instead of read(2), and SyncTransientFile
+ * instead of fsync(2).
  */
 #ifndef FD_H
 #define FD_H
@@ -105,6 +107,12 @@ extern int	FreeDir(DIR *dir);
 /* Operations to allow use of a plain kernel FD, with automatic cleanup */
 extern int	OpenTransientFile(const char *fileName, int fileFlags);
 extern int	OpenTransientFilePerm(const char *fileName, int fileFlags, mode_t fileMode);
+extern void WriteTransientFile(int fd, char *buf, Size count, int elevel,
+							   const char *filename, uint32 wait_event_info);
+extern bool ReadTransientFile(int fd, char *buf, Size count, int elevel,
+							  const char *filename, uint32 wait_event_info);
+extern void SyncTransientFile(int fd, int elevel,  const char *filename,
+							  uint32 wait_event_info);
 extern int	CloseTransientFile(int fd);
 
 /* If you've really really gotta have a plain kernel FD, use this */
-- 
2.18.0

From c1bf79e30eae60ae3d57f28b8ba28361c5447468 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Mon, 25 Jun 2018 14:37:18 +0900
Subject: [PATCH 1/2] Rework error messages around file handling

Some error messages related to file handling are using the code path
context to define their state.  For example, 2PC-related errors are
referring to "two-phase status files", or "relation mapping file" is
used for catalog-to-filenode mapping, however those prove to be
difficult to translate, and are not more helpful than just referring to
the path of the file being manipulated.  So simplify all those error
messages by just referring to files with their path used.  In some
cases, like the manipulation of WAL segments, the context is helpful so
those are kept.

Calls to the system function read() have also been rather inconsistent
with their error handling sometimes not reporting the number of bytes
read, and some other code paths trying to use an errno which has not
been set.  The in-core functions are using a more consistent pattern
with this patch, which checks for both errno if set or if an
inconsistent read is happening.

So as to care about pluralization when reading an unexpected number of
bytes, "could not read: read %d of %d" is used as error message.

Author: Michael Paquier
Discussion: https://postgr.es/m/20180622234803.GA1134@paquier.xyz
---
 src/backend/access/transam/twophase.c       | 40 ++++++------
 src/backend/access/transam/xlog.c           | 40 ++++++++----
 src/backend/replication/logical/origin.c    | 13 +++-
 src/backend/replication/logical/snapbuild.c | 68 +++++++++++++++------
 src/backend/replication/slot.c              | 26 +++++---
 src/backend/replication/walsender.c         | 16 ++++-
 src/backend/utils/cache/relmapper.c         | 28 ++++++---
 src/bin/pg_basebackup/pg_receivewal.c       | 12 +++-
 src/bin/pg_rewind/file_ops.c                | 14 ++++-
 src/bin/pg_rewind/parsexlog.c               | 14 ++++-
 src/bin/pg_waldump/pg_waldump.c             | 17 ++++--
 11 files changed, 200 insertions(+), 88 deletions(-)

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index e8d4e37fe3..0c99b33664 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -1219,6 +1219,7 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	uint32		crc_offset;
 	pg_crc32c	calc_crc,
 				file_crc;
+	int			r;
 
 	TwoPhaseFilePath(path, xid);
 
@@ -1228,8 +1229,7 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 		if (give_warnings)
 			ereport(WARNING,
 					(errcode_for_file_access(),
-					 errmsg("could not open two-phase state file \"%s\": %m",
-							path)));
+					 errmsg("could not open file \"%s\": %m", path)));
 		return NULL;
 	}
 
@@ -1249,8 +1249,7 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 			errno = save_errno;
 			ereport(WARNING,
 					(errcode_for_file_access(),
-					 errmsg("could not stat two-phase state file \"%s\": %m",
-							path)));
+					 errmsg("could not stat file \"%s\": %m", path)));
 		}
 		return NULL;
 	}
@@ -1277,7 +1276,8 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	buf = (char *) palloc(stat.st_size);
 
 	pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_READ);
-	if (read(fd, buf, stat.st_size) != stat.st_size)
+	r = read(fd, buf, stat.st_size);
+	if (r != stat.st_size)
 	{
 		int			save_errno = errno;
 
@@ -1285,11 +1285,17 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 		CloseTransientFile(fd);
 		if (give_warnings)
 		{
-			errno = save_errno;
-			ereport(WARNING,
-					(errcode_for_file_access(),
-					 errmsg("could not read two-phase state file \"%s\": %m",
-							path)));
+			if (r < 0)
+			{
+				errno = save_errno;
+				ereport(WARNING,
+						(errcode_for_file_access(),
+						 errmsg("could not read file \"%s\": %m", path)));
+			}
+			else
+				ereport(WARNING,
+						(errmsg("could not read file \"%s\": read %d of %zu",
+								path, r, stat.st_size)));
 		}
 		pfree(buf);
 		return NULL;
@@ -1632,8 +1638,7 @@ RemoveTwoPhaseFile(TransactionId xid, bool giveWarning)
 		if (errno != ENOENT || giveWarning)
 			ereport(WARNING,
 					(errcode_for_file_access(),
-					 errmsg("could not remove two-phase state file \"%s\": %m",
-							path)));
+					 errmsg("could not remove file \"%s\": %m", path)));
 }
 
 /*
@@ -1661,8 +1666,7 @@ RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
 	if (fd < 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not recreate two-phase state file \"%s\": %m",
-						path)));
+				 errmsg("could not recreate file \"%s\": %m", path)));
 
 	/* Write content and CRC */
 	pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_WRITE);
@@ -1677,7 +1681,7 @@ RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
 		errno = save_errno ? save_errno : ENOSPC;
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not write two-phase state file: %m")));
+				 errmsg("could not write file \"%s\": %m", path)));
 	}
 	if (write(fd, &statefile_crc, sizeof(pg_crc32c)) != sizeof(pg_crc32c))
 	{
@@ -1690,7 +1694,7 @@ RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
 		errno = save_errno ? save_errno : ENOSPC;
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not write two-phase state file: %m")));
+				 errmsg("could not write file \"%s\": %m", path)));
 	}
 	pgstat_report_wait_end();
 
@@ -1707,14 +1711,14 @@ RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
 		errno = save_errno;
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not fsync two-phase state file: %m")));
+				 errmsg("could not fsync file \"%s\": %m", path)));
 	}
 	pgstat_report_wait_end();
 
 	if (CloseTransientFile(fd) != 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not close two-phase state file: %m")));
+				 errmsg("could not close file \"%s\": %m", path)));
 }
 
 /*
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 4049deb968..1e8919df06 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -3408,21 +3408,24 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
 
 		if (nread > 0)
 		{
+			int			r;
+
 			if (nread > sizeof(buffer))
 				nread = sizeof(buffer);
 			errno = 0;
 			pgstat_report_wait_start(WAIT_EVENT_WAL_COPY_READ);
-			if (read(srcfd, buffer, nread) != nread)
+			r = read(srcfd, buffer, nread);
+			if (r != nread)
 			{
-				if (errno != 0)
+				if (r < 0)
 					ereport(ERROR,
 							(errcode_for_file_access(),
 							 errmsg("could not read file \"%s\": %m",
 									path)));
 				else
 					ereport(ERROR,
-							(errmsg("not enough data in file \"%s\"",
-									path)));
+							(errmsg("could not read file \"%s\": read %d of %d",
+									path, r, nread)));
 			}
 			pgstat_report_wait_end();
 		}
@@ -4544,7 +4547,7 @@ ReadControlFile(void)
 	if (fd < 0)
 		ereport(PANIC,
 				(errcode_for_file_access(),
-				 errmsg("could not open control file \"%s\": %m",
+				 errmsg("could not open file \"%s\": %m",
 						XLOG_CONTROL_FILE)));
 
 	pgstat_report_wait_start(WAIT_EVENT_CONTROL_FILE_READ);
@@ -4554,10 +4557,12 @@ ReadControlFile(void)
 		if (r < 0)
 			ereport(PANIC,
 					(errcode_for_file_access(),
-					 errmsg("could not read from control file: %m")));
+					 errmsg("could not read file \"%s\": %m",
+							XLOG_CONTROL_FILE)));
 		else
 			ereport(PANIC,
-					(errmsg("could not read from control file: read %d bytes, expected %d", r, (int) sizeof(ControlFileData))));
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							XLOG_CONTROL_FILE, r, sizeof(ControlFileData))));
 	}
 	pgstat_report_wait_end();
 
@@ -11689,6 +11694,7 @@ XLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr, int reqLen,
 	int			emode = private->emode;
 	uint32		targetPageOff;
 	XLogSegNo	targetSegNo PG_USED_FOR_ASSERTS_ONLY;
+	int			r;
 
 	XLByteToSeg(targetPagePtr, targetSegNo, wal_segment_size);
 	targetPageOff = XLogSegmentOffset(targetPagePtr, wal_segment_size);
@@ -11782,18 +11788,26 @@ retry:
 	}
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
-	if (read(readFile, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+	r = read(readFile, readBuf, XLOG_BLCKSZ);
+	if (r != XLOG_BLCKSZ)
 	{
 		char		fname[MAXFNAMELEN];
 		int			save_errno = errno;
 
 		pgstat_report_wait_end();
 		XLogFileName(fname, curFileTLI, readSegNo, wal_segment_size);
-		errno = save_errno;
-		ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
-				(errcode_for_file_access(),
-				 errmsg("could not read from log segment %s, offset %u: %m",
-						fname, readOff)));
+		if (r < 0)
+		{
+			errno = save_errno;
+			ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
+					(errcode_for_file_access(),
+					 errmsg("could not read from log segment %s, offset %u: %m",
+							fname, readOff)));
+		}
+		else
+			ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
+					(errmsg("could not read from log segment %s, offset %u: read %d of %d",
+							fname, readOff, r, XLOG_BLCKSZ)));
 		goto next_record_is_invalid;
 	}
 	pgstat_report_wait_end();
diff --git a/src/backend/replication/logical/origin.c b/src/backend/replication/logical/origin.c
index 3d3f6dff1b..841e24c03d 100644
--- a/src/backend/replication/logical/origin.c
+++ b/src/backend/replication/logical/origin.c
@@ -712,9 +712,16 @@ StartupReplicationOrigin(void)
 	/* verify magic, that is written even if nothing was active */
 	readBytes = read(fd, &magic, sizeof(magic));
 	if (readBytes != sizeof(magic))
-		ereport(PANIC,
-				(errmsg("could not read file \"%s\": %m",
-						path)));
+	{
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": %m",
+							path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sizeof(magic))));
+	}
 	COMP_CRC32C(crc, &magic, sizeof(magic));
 
 	if (magic != REPLICATION_STATE_MAGIC)
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index e975faeb8c..61bc9e8f14 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1726,11 +1726,18 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 		int			save_errno = errno;
 
 		CloseTransientFile(fd);
-		errno = save_errno;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) SnapBuildOnDiskConstantSize)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, SnapBuildOnDiskConstantSize)));
 	}
 
 	if (ondisk.magic != SNAPBUILD_MAGIC)
@@ -1757,11 +1764,18 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 		int			save_errno = errno;
 
 		CloseTransientFile(fd);
-		errno = save_errno;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sizeof(SnapBuild))));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sizeof(SnapBuild))));
 	}
 	COMP_CRC32C(checksum, &ondisk.builder, sizeof(SnapBuild));
 
@@ -1777,11 +1791,18 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 		int			save_errno = errno;
 
 		CloseTransientFile(fd);
-		errno = save_errno;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sz)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sz)));
 	}
 	COMP_CRC32C(checksum, ondisk.builder.was_running.was_xip, sz);
 
@@ -1796,11 +1817,18 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 		int			save_errno = errno;
 
 		CloseTransientFile(fd);
-		errno = save_errno;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sz)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sz)));
 	}
 	COMP_CRC32C(checksum, ondisk.builder.committed.xip, sz);
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index fb95b44ed8..e0c61c9199 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1414,11 +1414,15 @@ RestoreSlotFromDisk(const char *name)
 
 		CloseTransientFile(fd);
 		errno = saved_errno;
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %u: %m",
-						path, readBytes,
-						(uint32) ReplicationSlotOnDiskConstantSize)));
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d of %u",
+							path, readBytes,
+							(uint32) ReplicationSlotOnDiskConstantSize)));
 	}
 
 	/* verify magic */
@@ -1454,10 +1458,14 @@ RestoreSlotFromDisk(const char *name)
 
 		CloseTransientFile(fd);
 		errno = saved_errno;
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %u: %m",
-						path, readBytes, cp.length)));
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d of %u",
+							path, readBytes, cp.length)));
 	}
 
 	CloseTransientFile(fd);
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 3a0106bc93..d4ac319258 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -501,11 +501,16 @@ SendTimeLineHistory(TimeLineHistoryCmd *cmd)
 		pgstat_report_wait_start(WAIT_EVENT_WALSENDER_TIMELINE_HISTORY_READ);
 		nread = read(fd, rbuf, sizeof(rbuf));
 		pgstat_report_wait_end();
-		if (nread <= 0)
+		if (nread < 0)
 			ereport(ERROR,
 					(errcode_for_file_access(),
 					 errmsg("could not read file \"%s\": %m",
 							path)));
+		else if (nread == 0)
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, nread, bytesleft)));
+
 		pq_sendbytes(&buf, rbuf, nread);
 		bytesleft -= nread;
 	}
@@ -2425,7 +2430,7 @@ retry:
 		pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 		readbytes = read(sendFile, p, segbytes);
 		pgstat_report_wait_end();
-		if (readbytes <= 0)
+		if (readbytes < 0)
 		{
 			ereport(ERROR,
 					(errcode_for_file_access(),
@@ -2433,6 +2438,13 @@ retry:
 							XLogFileNameP(curFileTimeLine, sendSegNo),
 							sendOff, (unsigned long) segbytes)));
 		}
+		else if (readbytes == 0)
+		{
+			ereport(ERROR,
+					(errmsg("could not read from log segment %s, offset %u: read %d of %lu",
+							XLogFileNameP(curFileTimeLine, sendSegNo),
+							sendOff, readbytes, (unsigned long) segbytes)));
+		}
 
 		/* Update state for read */
 		recptr += readbytes;
diff --git a/src/backend/utils/cache/relmapper.c b/src/backend/utils/cache/relmapper.c
index 99d095f2df..2d31f9f912 100644
--- a/src/backend/utils/cache/relmapper.c
+++ b/src/backend/utils/cache/relmapper.c
@@ -629,6 +629,7 @@ load_relmap_file(bool shared)
 	char		mapfilename[MAXPGPATH];
 	pg_crc32c	crc;
 	int			fd;
+	int			r;
 
 	if (shared)
 	{
@@ -648,7 +649,7 @@ load_relmap_file(bool shared)
 	if (fd < 0)
 		ereport(FATAL,
 				(errcode_for_file_access(),
-				 errmsg("could not open relation mapping file \"%s\": %m",
+				 errmsg("could not open file \"%s\": %m",
 						mapfilename)));
 
 	/*
@@ -659,11 +660,18 @@ load_relmap_file(bool shared)
 	 * are able to access any relation that's affected by the change.
 	 */
 	pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_READ);
-	if (read(fd, map, sizeof(RelMapFile)) != sizeof(RelMapFile))
-		ereport(FATAL,
-				(errcode_for_file_access(),
-				 errmsg("could not read relation mapping file \"%s\": %m",
-						mapfilename)));
+	r = read(fd, map, sizeof(RelMapFile));
+	if (r != sizeof(RelMapFile))
+	{
+		if (r < 0)
+			ereport(FATAL,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", mapfilename)));
+		else
+			ereport(FATAL,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							mapfilename, r, sizeof(RelMapFile))));
+	}
 	pgstat_report_wait_end();
 
 	CloseTransientFile(fd);
@@ -748,7 +756,7 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 	if (fd < 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not open relation mapping file \"%s\": %m",
+				 errmsg("could not open file \"%s\": %m",
 						mapfilename)));
 
 	if (write_wal)
@@ -782,7 +790,7 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 			errno = ENOSPC;
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not write to relation mapping file \"%s\": %m",
+				 errmsg("could not write file \"%s\": %m",
 						mapfilename)));
 	}
 	pgstat_report_wait_end();
@@ -797,14 +805,14 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 	if (pg_fsync(fd) != 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not fsync relation mapping file \"%s\": %m",
+				 errmsg("could not fsync file \"%s\": %m",
 						mapfilename)));
 	pgstat_report_wait_end();
 
 	if (CloseTransientFile(fd))
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not close relation mapping file \"%s\": %m",
+				 errmsg("could not close file \"%s\": %m",
 						mapfilename)));
 
 	/*
diff --git a/src/bin/pg_basebackup/pg_receivewal.c b/src/bin/pg_basebackup/pg_receivewal.c
index ed9d7f6378..8be8d48a8a 100644
--- a/src/bin/pg_basebackup/pg_receivewal.c
+++ b/src/bin/pg_basebackup/pg_receivewal.c
@@ -284,6 +284,7 @@ FindStreamingStart(uint32 *tli)
 			char		buf[4];
 			int			bytes_out;
 			char		fullpath[MAXPGPATH * 2];
+			int			r;
 
 			snprintf(fullpath, sizeof(fullpath), "%s/%s", basedir, dirent->d_name);
 
@@ -300,10 +301,15 @@ FindStreamingStart(uint32 *tli)
 						progname, fullpath, strerror(errno));
 				disconnect_and_exit(1);
 			}
-			if (read(fd, (char *) buf, sizeof(buf)) != sizeof(buf))
+			r = read(fd, (char *) buf, sizeof(buf));
+			if (r != sizeof(buf))
 			{
-				fprintf(stderr, _("%s: could not read compressed file \"%s\": %s\n"),
-						progname, fullpath, strerror(errno));
+				if (r < 0)
+					fprintf(stderr, _("%s: could not read compressed file \"%s\": %s\n"),
+							progname, fullpath, strerror(errno));
+				else
+					fprintf(stderr, _("%s: could not read compressed file \"%s\": read %d of %zu\n"),
+							progname, fullpath, r, sizeof(buf));
 				disconnect_and_exit(1);
 			}
 
diff --git a/src/bin/pg_rewind/file_ops.c b/src/bin/pg_rewind/file_ops.c
index 94bcc13ae8..da2bf449e4 100644
--- a/src/bin/pg_rewind/file_ops.c
+++ b/src/bin/pg_rewind/file_ops.c
@@ -289,6 +289,7 @@ slurpFile(const char *datadir, const char *path, size_t *filesize)
 	struct stat statbuf;
 	char		fullpath[MAXPGPATH];
 	int			len;
+	int			r;
 
 	snprintf(fullpath, sizeof(fullpath), "%s/%s", datadir, path);
 
@@ -304,9 +305,16 @@ slurpFile(const char *datadir, const char *path, size_t *filesize)
 
 	buffer = pg_malloc(len + 1);
 
-	if (read(fd, buffer, len) != len)
-		pg_fatal("could not read file \"%s\": %s\n",
-				 fullpath, strerror(errno));
+	r = read(fd, buffer, len);
+	if (r != len)
+	{
+		if (r < 0)
+			pg_fatal("could not read file \"%s\": %s\n",
+					 fullpath, strerror(errno));
+		else
+			pg_fatal("could not read file \"%s\": read %d of %d\n",
+					 fullpath, r, len);
+	}
 	close(fd);
 
 	/* Zero-terminate the buffer. */
diff --git a/src/bin/pg_rewind/parsexlog.c b/src/bin/pg_rewind/parsexlog.c
index 1689279767..f698659b3a 100644
--- a/src/bin/pg_rewind/parsexlog.c
+++ b/src/bin/pg_rewind/parsexlog.c
@@ -246,6 +246,7 @@ SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
 	uint32		targetPageOff;
 	XLogRecPtr	targetSegEnd;
 	XLogSegNo	targetSegNo;
+	int			r;
 
 	XLByteToSeg(targetPagePtr, targetSegNo, WalSegSz);
 	XLogSegNoOffsetToRecPtr(targetSegNo + 1, 0, WalSegSz, targetSegEnd);
@@ -309,10 +310,17 @@ SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
 		return -1;
 	}
 
-	if (read(xlogreadfd, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+
+	r = read(xlogreadfd, readBuf, XLOG_BLCKSZ);
+	if (r != XLOG_BLCKSZ)
 	{
-		printf(_("could not read from file \"%s\": %s\n"), xlogfpath,
-			   strerror(errno));
+		if (r < 0)
+			printf(_("could not read from file \"%s\": %s\n"), xlogfpath,
+				   strerror(errno));
+		else
+			printf(_("could not read from file \"%s\": read %d of %d\n"),
+				   xlogfpath, r, XLOG_BLCKSZ);
+
 		return -1;
 	}
 
diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index d41b831b18..744b1f52a3 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -210,8 +210,10 @@ search_directory(const char *directory, const char *fname)
 	if (fd >= 0)
 	{
 		char		buf[XLOG_BLCKSZ];
+		int			r;
 
-		if (read(fd, buf, XLOG_BLCKSZ) == XLOG_BLCKSZ)
+		r = read(fd, buf, XLOG_BLCKSZ);
+		if (r == XLOG_BLCKSZ)
 		{
 			XLogLongPageHeader longhdr = (XLogLongPageHeader) buf;
 
@@ -229,7 +231,8 @@ search_directory(const char *directory, const char *fname)
 				fatal_error("could not read file \"%s\": %s",
 							fname, strerror(errno));
 			else
-				fatal_error("not enough data in file \"%s\"", fname);
+				fatal_error("could not read file \"%s\": read %d of %d",
+							fname, r, XLOG_BLCKSZ);
 		}
 		close(fd);
 		return true;
@@ -411,11 +414,17 @@ XLogDumpXLogRead(const char *directory, TimeLineID timeline_id,
 		{
 			int			err = errno;
 			char		fname[MAXPGPATH];
+			int			save_errno = errno;
 
 			XLogFileName(fname, timeline_id, sendSegNo, WalSegSz);
+			errno = save_errno;
 
-			fatal_error("could not read from log file %s, offset %u, length %d: %s",
-						fname, sendOff, segbytes, strerror(err));
+			if (readbytes < 0)
+				fatal_error("could not read from log file %s, offset %u, length %d: %s",
+							fname, sendOff, segbytes, strerror(err));
+			else if (readbytes == 0)
+				fatal_error("could not read from log file %s, offset %u: read %d of %d",
+							fname, sendOff, readbytes, segbytes);
 		}
 
 		/* Update state for read */
-- 
2.18.0

From cca233d62fd875ed0bdd76726742342ea9bc37c3 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Mon, 25 Jun 2018 16:15:03 +0900
Subject: [PATCH 2/2] Add interface to read/write/fsync with transient files

The following set of routines gets added for the manipulation of
transient files:
void WriteTransientFile(int fd, char *buf, Size count, int elevel,
    const char *filename, uint32 wait_event_info);
bool ReadTransientFile(int fd, char *buf, Size count, int elevel,
    const char *filename, uint32 wait_event_info);
void SyncTransientFile(int fd, int elevel, const char *filename,
    uint32 wait_event_info);

This simplifies code related to replication slots, 2PC files, relation
mapper files and snapshot builds:
- Centralize errno handling for transient files with ENOSPC for write(2)
and read count for read(2)
- Wait events have to be defined, so those would unlikely get forgotten
in the future.
- Error handling for CloseTransientFile in code paths is centralized.
---
 src/backend/access/transam/twophase.c       |  25 +----
 src/backend/replication/logical/snapbuild.c | 110 ++------------------
 src/backend/replication/slot.c              |  46 +-------
 src/backend/storage/file/fd.c               |  97 ++++++++++++++++-
 src/backend/utils/cache/relmapper.c         |  40 ++-----
 src/include/storage/fd.h                    |  10 +-
 6 files changed, 128 insertions(+), 200 deletions(-)

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 0c99b33664..557261fc31 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -1219,7 +1219,6 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	uint32		crc_offset;
 	pg_crc32c	calc_crc,
 				file_crc;
-	int			r;
 
 	TwoPhaseFilePath(path, xid);
 
@@ -1275,28 +1274,10 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	 */
 	buf = (char *) palloc(stat.st_size);
 
-	pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_READ);
-	r = read(fd, buf, stat.st_size);
-	if (r != stat.st_size)
+	if (!ReadTransientFile(fd, buf, stat.st_size,
+						   give_warnings ? WARNING : DEBUG3, path,
+						   WAIT_EVENT_TWOPHASE_FILE_READ))
 	{
-		int			save_errno = errno;
-
-		pgstat_report_wait_end();
-		CloseTransientFile(fd);
-		if (give_warnings)
-		{
-			if (r < 0)
-			{
-				errno = save_errno;
-				ereport(WARNING,
-						(errcode_for_file_access(),
-						 errmsg("could not read file \"%s\": %m", path)));
-			}
-			else
-				ereport(WARNING,
-						(errmsg("could not read file \"%s\": read %d of %zu",
-								path, r, stat.st_size)));
-		}
 		pfree(buf);
 		return NULL;
 	}
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 61bc9e8f14..05b74a61a3 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1609,20 +1609,8 @@ SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn)
 		ereport(ERROR,
 				(errmsg("could not open file \"%s\": %m", path)));
 
-	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_WRITE);
-	if ((write(fd, ondisk, needed_length)) != needed_length)
-	{
-		int			save_errno = errno;
-
-		CloseTransientFile(fd);
-
-		/* if write didn't set errno, assume problem is no disk space */
-		errno = save_errno ? save_errno : ENOSPC;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not write to file \"%s\": %m", tmppath)));
-	}
-	pgstat_report_wait_end();
+	WriteTransientFile(fd, (char *) ondisk, needed_length, ERROR, tmppath,
+					   WAIT_EVENT_SNAPBUILD_WRITE);
 
 	/*
 	 * fsync the file before renaming so that even if we crash after this we
@@ -1686,7 +1674,6 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	int			fd;
 	char		path[MAXPGPATH];
 	Size		sz;
-	int			readBytes;
 	pg_crc32c	checksum;
 
 	/* no point in loading a snapshot if we're already there */
@@ -1716,29 +1703,9 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	fsync_fname(path, false);
 	fsync_fname("pg_logical/snapshots", true);
 
-
 	/* read statically sized portion of snapshot */
-	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
-	readBytes = read(fd, &ondisk, SnapBuildOnDiskConstantSize);
-	pgstat_report_wait_end();
-	if (readBytes != SnapBuildOnDiskConstantSize)
-	{
-		int			save_errno = errno;
-
-		CloseTransientFile(fd);
-
-		if (readBytes < 0)
-		{
-			errno = save_errno;
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		}
-		else
-			ereport(ERROR,
-					(errmsg("could not read file \"%s\": read %d of %zu",
-							path, readBytes, SnapBuildOnDiskConstantSize)));
-	}
+	(void) ReadTransientFile(fd, (char *) &ondisk, SnapBuildOnDiskConstantSize,
+					  ERROR, path, WAIT_EVENT_SNAPBUILD_READ);
 
 	if (ondisk.magic != SNAPBUILD_MAGIC)
 		ereport(ERROR,
@@ -1756,80 +1723,23 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 				SnapBuildOnDiskConstantSize - SnapBuildOnDiskNotChecksummedSize);
 
 	/* read SnapBuild */
-	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
-	readBytes = read(fd, &ondisk.builder, sizeof(SnapBuild));
-	pgstat_report_wait_end();
-	if (readBytes != sizeof(SnapBuild))
-	{
-		int			save_errno = errno;
-
-		CloseTransientFile(fd);
-
-		if (readBytes < 0)
-		{
-			errno = save_errno;
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		}
-		else
-			ereport(ERROR,
-					(errmsg("could not read file \"%s\": read %d of %zu",
-							path, readBytes, sizeof(SnapBuild))));
-	}
+	(void) ReadTransientFile(fd, (char *) &ondisk.builder, sizeof(SnapBuild),
+					  ERROR, path, WAIT_EVENT_SNAPBUILD_READ);
 	COMP_CRC32C(checksum, &ondisk.builder, sizeof(SnapBuild));
 
 	/* restore running xacts (dead, but kept for backward compat) */
 	sz = sizeof(TransactionId) * ondisk.builder.was_running.was_xcnt_space;
 	ondisk.builder.was_running.was_xip =
 		MemoryContextAllocZero(builder->context, sz);
-	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
-	readBytes = read(fd, ondisk.builder.was_running.was_xip, sz);
-	pgstat_report_wait_end();
-	if (readBytes != sz)
-	{
-		int			save_errno = errno;
-
-		CloseTransientFile(fd);
-
-		if (readBytes < 0)
-		{
-			errno = save_errno;
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		}
-		else
-			ereport(ERROR,
-					(errmsg("could not read file \"%s\": read %d of %zu",
-							path, readBytes, sz)));
-	}
+	(void) ReadTransientFile(fd, (char *) ondisk.builder.was_running.was_xip, sz,
+					  ERROR, path, WAIT_EVENT_SNAPBUILD_READ);
 	COMP_CRC32C(checksum, ondisk.builder.was_running.was_xip, sz);
 
 	/* restore committed xacts information */
 	sz = sizeof(TransactionId) * ondisk.builder.committed.xcnt;
 	ondisk.builder.committed.xip = MemoryContextAllocZero(builder->context, sz);
-	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
-	readBytes = read(fd, ondisk.builder.committed.xip, sz);
-	pgstat_report_wait_end();
-	if (readBytes != sz)
-	{
-		int			save_errno = errno;
-
-		CloseTransientFile(fd);
-
-		if (readBytes < 0)
-		{
-			errno = save_errno;
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		}
-		else
-			ereport(ERROR,
-					(errmsg("could not read file \"%s\": read %d of %zu",
-							path, readBytes, sz)));
-	}
+	(void) ReadTransientFile(fd, (char *) ondisk.builder.committed.xip, sz,
+					  ERROR, path, WAIT_EVENT_SNAPBUILD_READ);
 	COMP_CRC32C(checksum, ondisk.builder.committed.xip, sz);
 
 	CloseTransientFile(fd);
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index e0c61c9199..818b13e973 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1354,7 +1354,6 @@ RestoreSlotFromDisk(const char *name)
 	char		path[MAXPGPATH + 22];
 	int			fd;
 	bool		restored = false;
-	int			readBytes;
 	pg_crc32c	checksum;
 
 	/* no need to lock here, no concurrent access allowed yet */
@@ -1405,25 +1404,8 @@ RestoreSlotFromDisk(const char *name)
 	END_CRIT_SECTION();
 
 	/* read part of statefile that's guaranteed to be version independent */
-	pgstat_report_wait_start(WAIT_EVENT_REPLICATION_SLOT_READ);
-	readBytes = read(fd, &cp, ReplicationSlotOnDiskConstantSize);
-	pgstat_report_wait_end();
-	if (readBytes != ReplicationSlotOnDiskConstantSize)
-	{
-		int			saved_errno = errno;
-
-		CloseTransientFile(fd);
-		errno = saved_errno;
-		if (readBytes < 0)
-			ereport(PANIC,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		else
-			ereport(PANIC,
-					(errmsg("could not read file \"%s\": read %d of %u",
-							path, readBytes,
-							(uint32) ReplicationSlotOnDiskConstantSize)));
-	}
+	(void) ReadTransientFile(fd, (char *) &cp, ReplicationSlotOnDiskConstantSize,
+							 PANIC, path, WAIT_EVENT_REPLICATION_SLOT_READ);
 
 	/* verify magic */
 	if (cp.magic != SLOT_MAGIC)
@@ -1447,27 +1429,9 @@ RestoreSlotFromDisk(const char *name)
 						path, cp.length)));
 
 	/* Now that we know the size, read the entire file */
-	pgstat_report_wait_start(WAIT_EVENT_REPLICATION_SLOT_READ);
-	readBytes = read(fd,
-					 (char *) &cp + ReplicationSlotOnDiskConstantSize,
-					 cp.length);
-	pgstat_report_wait_end();
-	if (readBytes != cp.length)
-	{
-		int			saved_errno = errno;
-
-		CloseTransientFile(fd);
-		errno = saved_errno;
-		if (readBytes < 0)
-			ereport(PANIC,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		else
-			ereport(PANIC,
-					(errmsg("could not read file \"%s\": read %d of %u",
-							path, readBytes, cp.length)));
-	}
-
+	(void) ReadTransientFile(fd, (char *) &cp + ReplicationSlotOnDiskConstantSize,
+							 cp.length, PANIC, path,
+							 WAIT_EVENT_REPLICATION_SLOT_READ);
 	CloseTransientFile(fd);
 
 	/* now verify the CRC */
diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index 8dd51f1767..fba7774ddc 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -47,8 +47,9 @@
  * ownership mechanism that provides automatic cleanup for shared files when
  * the last of a group of backends detaches.
  *
- * AllocateFile, AllocateDir, OpenPipeStream and OpenTransientFile are
- * wrappers around fopen(3), opendir(3), popen(3) and open(2), respectively.
+ * AllocateFile, AllocateDir, OpenPipeStream, OpenTransientFile,
+ * WriteTransientFile and ReadTransientFile are wrappers around fopen(3),
+ * opendir(3), popen(3), open(2), write(2) and read(2) respectively.
  * They behave like the corresponding native functions, except that the handle
  * is registered with the current subtransaction, and will be automatically
  * closed at abort. These are intended mainly for short operations like
@@ -2480,6 +2481,98 @@ TryAgain:
 	return NULL;
 }
 
+/*
+ * Write to a file which has been opened using OpenTransientFile or
+ * OpenTransientFilePerm.  Equivalent to write(2).
+ */
+void
+WriteTransientFile(int fd, char *buf, Size count, int elevel,
+				   const char *filename, uint32 wait_event_info)
+{
+	int			r;
+
+	pgstat_report_wait_start(wait_event_info);
+	r = write(fd, buf, count);
+	pgstat_report_wait_end();
+
+	if (r != count)
+	{
+		int         save_errno = errno;
+
+		(void) CloseTransientFile(fd);
+
+		/* if write didn't set errno, assume problem is no disk space */
+		errno = save_errno ? save_errno : ENOSPC;
+		ereport(elevel,
+				(errcode_for_file_access(),
+				 errmsg("could not write to file \"%s\": %m", filename)));
+	}
+}
+
+/*
+ * Read from a file which has been opened using OpenTransientFile or
+ * OpenTransientFilePerm.  Equivalent to read(2).  Returns true on
+ * success and false on failure.
+ */
+bool
+ReadTransientFile(int fd, char *buf, Size count, int elevel,
+				  const char *filename, uint32 wait_event_info)
+{
+	int			r;
+
+	pgstat_report_wait_start(wait_event_info);
+	r = read(fd, buf, count);
+	pgstat_report_wait_end();
+
+	if (r != count)
+	{
+		int         save_errno = errno;
+
+		CloseTransientFile(fd);
+
+		if (r < 0)
+		{
+			errno = save_errno;
+			ereport(elevel,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", filename)));
+		}
+		else
+			ereport(elevel,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							filename, r, count)));
+		return false;
+	}
+
+	return true;
+}
+
+/*
+ * Write to a file which has been opened using OpenTransientFile or
+ * OpenTransientFilePerm.  Equivalent to fsync(2).
+ */
+void
+SyncTransientFile(int fd, int elevel, const char *filename,
+				  uint32 wait_event_info)
+{
+	int			status;
+
+	pgstat_report_wait_start(wait_event_info);
+	status = pg_fsync(fd);
+	pgstat_report_wait_end();
+
+	if (status != 0)
+	{
+		int         save_errno = errno;
+
+		(void) CloseTransientFile(fd);
+		errno = save_errno;
+		ereport(elevel,
+				(errcode_for_file_access(),
+				 errmsg("could not fsync file \"%s\": %m", filename)));
+	}
+}
+
 /*
  * Free an AllocateDesc of any type.
  *
diff --git a/src/backend/utils/cache/relmapper.c b/src/backend/utils/cache/relmapper.c
index 2d31f9f912..e6eff58d40 100644
--- a/src/backend/utils/cache/relmapper.c
+++ b/src/backend/utils/cache/relmapper.c
@@ -629,7 +629,6 @@ load_relmap_file(bool shared)
 	char		mapfilename[MAXPGPATH];
 	pg_crc32c	crc;
 	int			fd;
-	int			r;
 
 	if (shared)
 	{
@@ -659,20 +658,8 @@ load_relmap_file(bool shared)
 	 * look, the sinval signaling mechanism will make us re-read it before we
 	 * are able to access any relation that's affected by the change.
 	 */
-	pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_READ);
-	r = read(fd, map, sizeof(RelMapFile));
-	if (r != sizeof(RelMapFile))
-	{
-		if (r < 0)
-			ereport(FATAL,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", mapfilename)));
-		else
-			ereport(FATAL,
-					(errmsg("could not read file \"%s\": read %d of %zu",
-							mapfilename, r, sizeof(RelMapFile))));
-	}
-	pgstat_report_wait_end();
+	(void) ReadTransientFile(fd, (char *) map, sizeof(RelMapFile), FATAL,
+							 mapfilename, WAIT_EVENT_RELATION_MAP_READ);
 
 	CloseTransientFile(fd);
 
@@ -782,18 +769,9 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 	}
 
 	errno = 0;
-	pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_WRITE);
-	if (write(fd, newmap, sizeof(RelMapFile)) != sizeof(RelMapFile))
-	{
-		/* if write didn't set errno, assume problem is no disk space */
-		if (errno == 0)
-			errno = ENOSPC;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not write file \"%s\": %m",
-						mapfilename)));
-	}
-	pgstat_report_wait_end();
+
+	WriteTransientFile(fd, (char *) newmap, sizeof(RelMapFile), ERROR,
+					   mapfilename, WAIT_EVENT_RELATION_MAP_WRITE);
 
 	/*
 	 * We choose to fsync the data to disk before considering the task done.
@@ -801,13 +779,7 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 	 * issue, but it would complicate checkpointing --- see notes for
 	 * CheckPointRelationMap.
 	 */
-	pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_SYNC);
-	if (pg_fsync(fd) != 0)
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not fsync file \"%s\": %m",
-						mapfilename)));
-	pgstat_report_wait_end();
+	SyncTransientFile(fd, ERROR, mapfilename, WAIT_EVENT_RELATION_MAP_SYNC);
 
 	if (CloseTransientFile(fd))
 		ereport(ERROR,
diff --git a/src/include/storage/fd.h b/src/include/storage/fd.h
index 8e7c9728f4..4309d9da95 100644
--- a/src/include/storage/fd.h
+++ b/src/include/storage/fd.h
@@ -34,7 +34,9 @@
  *
  * Likewise, use AllocateDir/FreeDir, not opendir/closedir, to allocate
  * open directories (DIR*), and OpenTransientFile/CloseTransient File for an
- * unbuffered file descriptor.
+ * unbuffered file descriptor.  WriteTransientFile should be used instead
+ * of write(2), ReadTransientFile instead of read(2), and SyncTransientFile
+ * instead of fsync(2).
  */
 #ifndef FD_H
 #define FD_H
@@ -105,6 +107,12 @@ extern int	FreeDir(DIR *dir);
 /* Operations to allow use of a plain kernel FD, with automatic cleanup */
 extern int	OpenTransientFile(const char *fileName, int fileFlags);
 extern int	OpenTransientFilePerm(const char *fileName, int fileFlags, mode_t fileMode);
+extern void WriteTransientFile(int fd, char *buf, Size count, int elevel,
+							   const char *filename, uint32 wait_event_info);
+extern bool ReadTransientFile(int fd, char *buf, Size count, int elevel,
+							  const char *filename, uint32 wait_event_info);
+extern void SyncTransientFile(int fd, int elevel,  const char *filename,
+							  uint32 wait_event_info);
 extern int	CloseTransientFile(int fd);
 
 /* If you've really really gotta have a plain kernel FD, use this */
-- 
2.18.0

From 434481d861575ffab6294d871089897762a6b911 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Sat, 14 Jul 2018 15:30:55 +0900
Subject: [PATCH 1/2] Rework error messages around file handling

Some error messages related to file handling are using the code path
context to define their state.  For example, 2PC-related errors are
referring to "two-phase status files", or "relation mapping file" is
used for catalog-to-filenode mapping, however those prove to be
difficult to translate, and are not more helpful than just referring to
the path of the file being manipulated.  So simplify all those error
messages by just referring to files with their path used.  In some
cases, like the manipulation of WAL segments, the context is helpful so
those are kept.

Calls to the system function read() have also been rather inconsistent
with their error handling sometimes not reporting the number of bytes
read, and some other code paths trying to use an errno which has not
been set.  The in-core functions are using a more consistent pattern
with this patch, which checks for both errno if set or if an
inconsistent read is happening.

So as to care about pluralization when reading an unexpected number of
bytes, "could not read: read %d of %zu" is used as error message.

Author: Michael Paquier
Discussion: https://postgr.es/m/20180622234803.GA1134@paquier.xyz
---
 src/backend/access/transam/twophase.c       | 40 ++++++------
 src/backend/access/transam/xlog.c           | 40 ++++++++----
 src/backend/replication/logical/origin.c    | 13 +++-
 src/backend/replication/logical/snapbuild.c | 68 +++++++++++++++------
 src/backend/replication/slot.c              | 26 +++++---
 src/backend/replication/walsender.c         | 20 ++++--
 src/backend/utils/cache/relmapper.c         | 28 ++++++---
 src/bin/pg_basebackup/pg_receivewal.c       | 12 +++-
 src/bin/pg_rewind/file_ops.c                | 14 ++++-
 src/bin/pg_rewind/parsexlog.c               | 14 ++++-
 src/bin/pg_waldump/pg_waldump.c             | 17 ++++--
 src/common/controldata_utils.c              |  8 +--
 12 files changed, 206 insertions(+), 94 deletions(-)

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index e8d4e37fe3..0c99b33664 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -1219,6 +1219,7 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	uint32		crc_offset;
 	pg_crc32c	calc_crc,
 				file_crc;
+	int			r;
 
 	TwoPhaseFilePath(path, xid);
 
@@ -1228,8 +1229,7 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 		if (give_warnings)
 			ereport(WARNING,
 					(errcode_for_file_access(),
-					 errmsg("could not open two-phase state file \"%s\": %m",
-							path)));
+					 errmsg("could not open file \"%s\": %m", path)));
 		return NULL;
 	}
 
@@ -1249,8 +1249,7 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 			errno = save_errno;
 			ereport(WARNING,
 					(errcode_for_file_access(),
-					 errmsg("could not stat two-phase state file \"%s\": %m",
-							path)));
+					 errmsg("could not stat file \"%s\": %m", path)));
 		}
 		return NULL;
 	}
@@ -1277,7 +1276,8 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	buf = (char *) palloc(stat.st_size);
 
 	pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_READ);
-	if (read(fd, buf, stat.st_size) != stat.st_size)
+	r = read(fd, buf, stat.st_size);
+	if (r != stat.st_size)
 	{
 		int			save_errno = errno;
 
@@ -1285,11 +1285,17 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 		CloseTransientFile(fd);
 		if (give_warnings)
 		{
-			errno = save_errno;
-			ereport(WARNING,
-					(errcode_for_file_access(),
-					 errmsg("could not read two-phase state file \"%s\": %m",
-							path)));
+			if (r < 0)
+			{
+				errno = save_errno;
+				ereport(WARNING,
+						(errcode_for_file_access(),
+						 errmsg("could not read file \"%s\": %m", path)));
+			}
+			else
+				ereport(WARNING,
+						(errmsg("could not read file \"%s\": read %d of %zu",
+								path, r, stat.st_size)));
 		}
 		pfree(buf);
 		return NULL;
@@ -1632,8 +1638,7 @@ RemoveTwoPhaseFile(TransactionId xid, bool giveWarning)
 		if (errno != ENOENT || giveWarning)
 			ereport(WARNING,
 					(errcode_for_file_access(),
-					 errmsg("could not remove two-phase state file \"%s\": %m",
-							path)));
+					 errmsg("could not remove file \"%s\": %m", path)));
 }
 
 /*
@@ -1661,8 +1666,7 @@ RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
 	if (fd < 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not recreate two-phase state file \"%s\": %m",
-						path)));
+				 errmsg("could not recreate file \"%s\": %m", path)));
 
 	/* Write content and CRC */
 	pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_WRITE);
@@ -1677,7 +1681,7 @@ RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
 		errno = save_errno ? save_errno : ENOSPC;
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not write two-phase state file: %m")));
+				 errmsg("could not write file \"%s\": %m", path)));
 	}
 	if (write(fd, &statefile_crc, sizeof(pg_crc32c)) != sizeof(pg_crc32c))
 	{
@@ -1690,7 +1694,7 @@ RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
 		errno = save_errno ? save_errno : ENOSPC;
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not write two-phase state file: %m")));
+				 errmsg("could not write file \"%s\": %m", path)));
 	}
 	pgstat_report_wait_end();
 
@@ -1707,14 +1711,14 @@ RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
 		errno = save_errno;
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not fsync two-phase state file: %m")));
+				 errmsg("could not fsync file \"%s\": %m", path)));
 	}
 	pgstat_report_wait_end();
 
 	if (CloseTransientFile(fd) != 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not close two-phase state file: %m")));
+				 errmsg("could not close file \"%s\": %m", path)));
 }
 
 /*
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 4049deb968..bebe6405de 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -3408,21 +3408,24 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
 
 		if (nread > 0)
 		{
+			int			r;
+
 			if (nread > sizeof(buffer))
 				nread = sizeof(buffer);
 			errno = 0;
 			pgstat_report_wait_start(WAIT_EVENT_WAL_COPY_READ);
-			if (read(srcfd, buffer, nread) != nread)
+			r = read(srcfd, buffer, nread);
+			if (r != nread)
 			{
-				if (errno != 0)
+				if (r < 0)
 					ereport(ERROR,
 							(errcode_for_file_access(),
 							 errmsg("could not read file \"%s\": %m",
 									path)));
 				else
 					ereport(ERROR,
-							(errmsg("not enough data in file \"%s\"",
-									path)));
+							(errmsg("could not read file \"%s\": read %d of %zu",
+									path, r, (Size) nread)));
 			}
 			pgstat_report_wait_end();
 		}
@@ -4544,7 +4547,7 @@ ReadControlFile(void)
 	if (fd < 0)
 		ereport(PANIC,
 				(errcode_for_file_access(),
-				 errmsg("could not open control file \"%s\": %m",
+				 errmsg("could not open file \"%s\": %m",
 						XLOG_CONTROL_FILE)));
 
 	pgstat_report_wait_start(WAIT_EVENT_CONTROL_FILE_READ);
@@ -4554,10 +4557,12 @@ ReadControlFile(void)
 		if (r < 0)
 			ereport(PANIC,
 					(errcode_for_file_access(),
-					 errmsg("could not read from control file: %m")));
+					 errmsg("could not read file \"%s\": %m",
+							XLOG_CONTROL_FILE)));
 		else
 			ereport(PANIC,
-					(errmsg("could not read from control file: read %d bytes, expected %d", r, (int) sizeof(ControlFileData))));
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							XLOG_CONTROL_FILE, r, sizeof(ControlFileData))));
 	}
 	pgstat_report_wait_end();
 
@@ -11689,6 +11694,7 @@ XLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr, int reqLen,
 	int			emode = private->emode;
 	uint32		targetPageOff;
 	XLogSegNo	targetSegNo PG_USED_FOR_ASSERTS_ONLY;
+	int			r;
 
 	XLByteToSeg(targetPagePtr, targetSegNo, wal_segment_size);
 	targetPageOff = XLogSegmentOffset(targetPagePtr, wal_segment_size);
@@ -11782,18 +11788,26 @@ retry:
 	}
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
-	if (read(readFile, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+	r = read(readFile, readBuf, XLOG_BLCKSZ);
+	if (r != XLOG_BLCKSZ)
 	{
 		char		fname[MAXFNAMELEN];
 		int			save_errno = errno;
 
 		pgstat_report_wait_end();
 		XLogFileName(fname, curFileTLI, readSegNo, wal_segment_size);
-		errno = save_errno;
-		ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
-				(errcode_for_file_access(),
-				 errmsg("could not read from log segment %s, offset %u: %m",
-						fname, readOff)));
+		if (r < 0)
+		{
+			errno = save_errno;
+			ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
+					(errcode_for_file_access(),
+					 errmsg("could not read from log segment %s, offset %u: %m",
+							fname, readOff)));
+		}
+		else
+			ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
+					(errmsg("could not read from log segment %s, offset %u: read %d of %zu",
+							fname, readOff, r, (Size) XLOG_BLCKSZ)));
 		goto next_record_is_invalid;
 	}
 	pgstat_report_wait_end();
diff --git a/src/backend/replication/logical/origin.c b/src/backend/replication/logical/origin.c
index 3d3f6dff1b..841e24c03d 100644
--- a/src/backend/replication/logical/origin.c
+++ b/src/backend/replication/logical/origin.c
@@ -712,9 +712,16 @@ StartupReplicationOrigin(void)
 	/* verify magic, that is written even if nothing was active */
 	readBytes = read(fd, &magic, sizeof(magic));
 	if (readBytes != sizeof(magic))
-		ereport(PANIC,
-				(errmsg("could not read file \"%s\": %m",
-						path)));
+	{
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": %m",
+							path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sizeof(magic))));
+	}
 	COMP_CRC32C(crc, &magic, sizeof(magic));
 
 	if (magic != REPLICATION_STATE_MAGIC)
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index e975faeb8c..61bc9e8f14 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1726,11 +1726,18 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 		int			save_errno = errno;
 
 		CloseTransientFile(fd);
-		errno = save_errno;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) SnapBuildOnDiskConstantSize)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, SnapBuildOnDiskConstantSize)));
 	}
 
 	if (ondisk.magic != SNAPBUILD_MAGIC)
@@ -1757,11 +1764,18 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 		int			save_errno = errno;
 
 		CloseTransientFile(fd);
-		errno = save_errno;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sizeof(SnapBuild))));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sizeof(SnapBuild))));
 	}
 	COMP_CRC32C(checksum, &ondisk.builder, sizeof(SnapBuild));
 
@@ -1777,11 +1791,18 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 		int			save_errno = errno;
 
 		CloseTransientFile(fd);
-		errno = save_errno;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sz)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sz)));
 	}
 	COMP_CRC32C(checksum, ondisk.builder.was_running.was_xip, sz);
 
@@ -1796,11 +1817,18 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 		int			save_errno = errno;
 
 		CloseTransientFile(fd);
-		errno = save_errno;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %d: %m",
-						path, readBytes, (int) sz)));
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sz)));
 	}
 	COMP_CRC32C(checksum, ondisk.builder.committed.xip, sz);
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index fb95b44ed8..afbaf8c80d 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1414,11 +1414,15 @@ RestoreSlotFromDisk(const char *name)
 
 		CloseTransientFile(fd);
 		errno = saved_errno;
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %u: %m",
-						path, readBytes,
-						(uint32) ReplicationSlotOnDiskConstantSize)));
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes,
+							ReplicationSlotOnDiskConstantSize)));
 	}
 
 	/* verify magic */
@@ -1454,10 +1458,14 @@ RestoreSlotFromDisk(const char *name)
 
 		CloseTransientFile(fd);
 		errno = saved_errno;
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\", read %d of %u: %m",
-						path, readBytes, cp.length)));
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		else
+			ereport(PANIC,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, (Size) cp.length)));
 	}
 
 	CloseTransientFile(fd);
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 3a0106bc93..e3df5495c3 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -501,11 +501,16 @@ SendTimeLineHistory(TimeLineHistoryCmd *cmd)
 		pgstat_report_wait_start(WAIT_EVENT_WALSENDER_TIMELINE_HISTORY_READ);
 		nread = read(fd, rbuf, sizeof(rbuf));
 		pgstat_report_wait_end();
-		if (nread <= 0)
+		if (nread < 0)
 			ereport(ERROR,
 					(errcode_for_file_access(),
 					 errmsg("could not read file \"%s\": %m",
 							path)));
+		else if (nread == 0)
+			ereport(ERROR,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							path, nread, bytesleft)));
+
 		pq_sendbytes(&buf, rbuf, nread);
 		bytesleft -= nread;
 	}
@@ -2425,13 +2430,20 @@ retry:
 		pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 		readbytes = read(sendFile, p, segbytes);
 		pgstat_report_wait_end();
-		if (readbytes <= 0)
+		if (readbytes < 0)
 		{
 			ereport(ERROR,
 					(errcode_for_file_access(),
-					 errmsg("could not read from log segment %s, offset %u, length %lu: %m",
+					 errmsg("could not read from log segment %s, offset %u, length %zu: %m",
 							XLogFileNameP(curFileTimeLine, sendSegNo),
-							sendOff, (unsigned long) segbytes)));
+							sendOff, (Size) segbytes)));
+		}
+		else if (readbytes == 0)
+		{
+			ereport(ERROR,
+					(errmsg("could not read from log segment %s, offset %u: read %d of %zu",
+							XLogFileNameP(curFileTimeLine, sendSegNo),
+							sendOff, readbytes, (Size) segbytes)));
 		}
 
 		/* Update state for read */
diff --git a/src/backend/utils/cache/relmapper.c b/src/backend/utils/cache/relmapper.c
index 99d095f2df..2d31f9f912 100644
--- a/src/backend/utils/cache/relmapper.c
+++ b/src/backend/utils/cache/relmapper.c
@@ -629,6 +629,7 @@ load_relmap_file(bool shared)
 	char		mapfilename[MAXPGPATH];
 	pg_crc32c	crc;
 	int			fd;
+	int			r;
 
 	if (shared)
 	{
@@ -648,7 +649,7 @@ load_relmap_file(bool shared)
 	if (fd < 0)
 		ereport(FATAL,
 				(errcode_for_file_access(),
-				 errmsg("could not open relation mapping file \"%s\": %m",
+				 errmsg("could not open file \"%s\": %m",
 						mapfilename)));
 
 	/*
@@ -659,11 +660,18 @@ load_relmap_file(bool shared)
 	 * are able to access any relation that's affected by the change.
 	 */
 	pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_READ);
-	if (read(fd, map, sizeof(RelMapFile)) != sizeof(RelMapFile))
-		ereport(FATAL,
-				(errcode_for_file_access(),
-				 errmsg("could not read relation mapping file \"%s\": %m",
-						mapfilename)));
+	r = read(fd, map, sizeof(RelMapFile));
+	if (r != sizeof(RelMapFile))
+	{
+		if (r < 0)
+			ereport(FATAL,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", mapfilename)));
+		else
+			ereport(FATAL,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							mapfilename, r, sizeof(RelMapFile))));
+	}
 	pgstat_report_wait_end();
 
 	CloseTransientFile(fd);
@@ -748,7 +756,7 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 	if (fd < 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not open relation mapping file \"%s\": %m",
+				 errmsg("could not open file \"%s\": %m",
 						mapfilename)));
 
 	if (write_wal)
@@ -782,7 +790,7 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 			errno = ENOSPC;
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not write to relation mapping file \"%s\": %m",
+				 errmsg("could not write file \"%s\": %m",
 						mapfilename)));
 	}
 	pgstat_report_wait_end();
@@ -797,14 +805,14 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 	if (pg_fsync(fd) != 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not fsync relation mapping file \"%s\": %m",
+				 errmsg("could not fsync file \"%s\": %m",
 						mapfilename)));
 	pgstat_report_wait_end();
 
 	if (CloseTransientFile(fd))
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not close relation mapping file \"%s\": %m",
+				 errmsg("could not close file \"%s\": %m",
 						mapfilename)));
 
 	/*
diff --git a/src/bin/pg_basebackup/pg_receivewal.c b/src/bin/pg_basebackup/pg_receivewal.c
index ed9d7f6378..8be8d48a8a 100644
--- a/src/bin/pg_basebackup/pg_receivewal.c
+++ b/src/bin/pg_basebackup/pg_receivewal.c
@@ -284,6 +284,7 @@ FindStreamingStart(uint32 *tli)
 			char		buf[4];
 			int			bytes_out;
 			char		fullpath[MAXPGPATH * 2];
+			int			r;
 
 			snprintf(fullpath, sizeof(fullpath), "%s/%s", basedir, dirent->d_name);
 
@@ -300,10 +301,15 @@ FindStreamingStart(uint32 *tli)
 						progname, fullpath, strerror(errno));
 				disconnect_and_exit(1);
 			}
-			if (read(fd, (char *) buf, sizeof(buf)) != sizeof(buf))
+			r = read(fd, (char *) buf, sizeof(buf));
+			if (r != sizeof(buf))
 			{
-				fprintf(stderr, _("%s: could not read compressed file \"%s\": %s\n"),
-						progname, fullpath, strerror(errno));
+				if (r < 0)
+					fprintf(stderr, _("%s: could not read compressed file \"%s\": %s\n"),
+							progname, fullpath, strerror(errno));
+				else
+					fprintf(stderr, _("%s: could not read compressed file \"%s\": read %d of %zu\n"),
+							progname, fullpath, r, sizeof(buf));
 				disconnect_and_exit(1);
 			}
 
diff --git a/src/bin/pg_rewind/file_ops.c b/src/bin/pg_rewind/file_ops.c
index 94bcc13ae8..0bd110f9b0 100644
--- a/src/bin/pg_rewind/file_ops.c
+++ b/src/bin/pg_rewind/file_ops.c
@@ -289,6 +289,7 @@ slurpFile(const char *datadir, const char *path, size_t *filesize)
 	struct stat statbuf;
 	char		fullpath[MAXPGPATH];
 	int			len;
+	int			r;
 
 	snprintf(fullpath, sizeof(fullpath), "%s/%s", datadir, path);
 
@@ -304,9 +305,16 @@ slurpFile(const char *datadir, const char *path, size_t *filesize)
 
 	buffer = pg_malloc(len + 1);
 
-	if (read(fd, buffer, len) != len)
-		pg_fatal("could not read file \"%s\": %s\n",
-				 fullpath, strerror(errno));
+	r = read(fd, buffer, len);
+	if (r != len)
+	{
+		if (r < 0)
+			pg_fatal("could not read file \"%s\": %s\n",
+					 fullpath, strerror(errno));
+		else
+			pg_fatal("could not read file \"%s\": read %d of %zu\n",
+					 fullpath, r, (Size) len);
+	}
 	close(fd);
 
 	/* Zero-terminate the buffer. */
diff --git a/src/bin/pg_rewind/parsexlog.c b/src/bin/pg_rewind/parsexlog.c
index 1689279767..40028471bf 100644
--- a/src/bin/pg_rewind/parsexlog.c
+++ b/src/bin/pg_rewind/parsexlog.c
@@ -246,6 +246,7 @@ SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
 	uint32		targetPageOff;
 	XLogRecPtr	targetSegEnd;
 	XLogSegNo	targetSegNo;
+	int			r;
 
 	XLByteToSeg(targetPagePtr, targetSegNo, WalSegSz);
 	XLogSegNoOffsetToRecPtr(targetSegNo + 1, 0, WalSegSz, targetSegEnd);
@@ -309,10 +310,17 @@ SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
 		return -1;
 	}
 
-	if (read(xlogreadfd, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+
+	r = read(xlogreadfd, readBuf, XLOG_BLCKSZ);
+	if (r != XLOG_BLCKSZ)
 	{
-		printf(_("could not read from file \"%s\": %s\n"), xlogfpath,
-			   strerror(errno));
+		if (r < 0)
+			printf(_("could not read file \"%s\": %s\n"), xlogfpath,
+				   strerror(errno));
+		else
+			printf(_("could not read file \"%s\": read %d of %zu\n"),
+				   xlogfpath, r, (Size) XLOG_BLCKSZ);
+
 		return -1;
 	}
 
diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index d41b831b18..2a557b37e5 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -210,8 +210,10 @@ search_directory(const char *directory, const char *fname)
 	if (fd >= 0)
 	{
 		char		buf[XLOG_BLCKSZ];
+		int			r;
 
-		if (read(fd, buf, XLOG_BLCKSZ) == XLOG_BLCKSZ)
+		r = read(fd, buf, XLOG_BLCKSZ);
+		if (r == XLOG_BLCKSZ)
 		{
 			XLogLongPageHeader longhdr = (XLogLongPageHeader) buf;
 
@@ -229,7 +231,8 @@ search_directory(const char *directory, const char *fname)
 				fatal_error("could not read file \"%s\": %s",
 							fname, strerror(errno));
 			else
-				fatal_error("not enough data in file \"%s\"", fname);
+				fatal_error("could not read file \"%s\": read %d of %zu",
+							fname, r, (Size) XLOG_BLCKSZ);
 		}
 		close(fd);
 		return true;
@@ -411,11 +414,17 @@ XLogDumpXLogRead(const char *directory, TimeLineID timeline_id,
 		{
 			int			err = errno;
 			char		fname[MAXPGPATH];
+			int			save_errno = errno;
 
 			XLogFileName(fname, timeline_id, sendSegNo, WalSegSz);
+			errno = save_errno;
 
-			fatal_error("could not read from log file %s, offset %u, length %d: %s",
-						fname, sendOff, segbytes, strerror(err));
+			if (readbytes < 0)
+				fatal_error("could not read from log file %s, offset %u, length %d: %s",
+							fname, sendOff, segbytes, strerror(err));
+			else if (readbytes == 0)
+				fatal_error("could not read from log file %s, offset %u: read %d of %zu",
+							fname, sendOff, readbytes, (Size) segbytes);
 		}
 
 		/* Update state for read */
diff --git a/src/common/controldata_utils.c b/src/common/controldata_utils.c
index e83d60d438..60197b2440 100644
--- a/src/common/controldata_utils.c
+++ b/src/common/controldata_utils.c
@@ -83,12 +83,12 @@ get_controlfile(const char *DataDir, const char *progname, bool *crc_ok_p)
 		else
 #ifndef FRONTEND
 			ereport(ERROR,
-					(errmsg("could not read file \"%s\": read %d of %d",
-							ControlFilePath, r, (int) sizeof(ControlFileData))));
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							ControlFilePath, r, sizeof(ControlFileData))));
 #else
 		{
-			fprintf(stderr, _("%s: could not read file \"%s\": read %d of %d\n"),
-					progname, ControlFilePath, r, (int) sizeof(ControlFileData));
+			fprintf(stderr, _("%s: could not read file \"%s\": read %d of %zu\n"),
+					progname, ControlFilePath, r, sizeof(ControlFileData));
 			exit(EXIT_FAILURE);
 		}
 #endif
-- 
2.18.0

From bfabee80635269c0950864d6cd2cf59d613f2d21 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Mon, 25 Jun 2018 16:15:03 +0900
Subject: [PATCH 2/2] Add interface to read/write/fsync with transient files

The following set of routines gets added for the manipulation of
transient files:
void WriteTransientFile(int fd, char *buf, Size count, int elevel,
    const char *filename, uint32 wait_event_info);
bool ReadTransientFile(int fd, char *buf, Size count, int elevel,
    const char *filename, uint32 wait_event_info);
void SyncTransientFile(int fd, int elevel, const char *filename,
    uint32 wait_event_info);

This simplifies code related to replication slots, 2PC files, relation
mapper files and snapshot builds:
- Centralize errno handling for transient files with ENOSPC for write(2)
and read count for read(2)
- Wait events have to be defined, so those would unlikely get forgotten
in the future.
- Error handling for CloseTransientFile in code paths is centralized.
---
 src/backend/access/transam/twophase.c       |  25 +----
 src/backend/replication/logical/snapbuild.c | 110 ++------------------
 src/backend/replication/slot.c              |  46 +-------
 src/backend/storage/file/fd.c               |  97 ++++++++++++++++-
 src/backend/utils/cache/relmapper.c         |  40 ++-----
 src/include/storage/fd.h                    |  10 +-
 6 files changed, 128 insertions(+), 200 deletions(-)

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 0c99b33664..557261fc31 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -1219,7 +1219,6 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	uint32		crc_offset;
 	pg_crc32c	calc_crc,
 				file_crc;
-	int			r;
 
 	TwoPhaseFilePath(path, xid);
 
@@ -1275,28 +1274,10 @@ ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
 	 */
 	buf = (char *) palloc(stat.st_size);
 
-	pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_READ);
-	r = read(fd, buf, stat.st_size);
-	if (r != stat.st_size)
+	if (!ReadTransientFile(fd, buf, stat.st_size,
+						   give_warnings ? WARNING : DEBUG3, path,
+						   WAIT_EVENT_TWOPHASE_FILE_READ))
 	{
-		int			save_errno = errno;
-
-		pgstat_report_wait_end();
-		CloseTransientFile(fd);
-		if (give_warnings)
-		{
-			if (r < 0)
-			{
-				errno = save_errno;
-				ereport(WARNING,
-						(errcode_for_file_access(),
-						 errmsg("could not read file \"%s\": %m", path)));
-			}
-			else
-				ereport(WARNING,
-						(errmsg("could not read file \"%s\": read %d of %zu",
-								path, r, stat.st_size)));
-		}
 		pfree(buf);
 		return NULL;
 	}
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 61bc9e8f14..05b74a61a3 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1609,20 +1609,8 @@ SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn)
 		ereport(ERROR,
 				(errmsg("could not open file \"%s\": %m", path)));
 
-	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_WRITE);
-	if ((write(fd, ondisk, needed_length)) != needed_length)
-	{
-		int			save_errno = errno;
-
-		CloseTransientFile(fd);
-
-		/* if write didn't set errno, assume problem is no disk space */
-		errno = save_errno ? save_errno : ENOSPC;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not write to file \"%s\": %m", tmppath)));
-	}
-	pgstat_report_wait_end();
+	WriteTransientFile(fd, (char *) ondisk, needed_length, ERROR, tmppath,
+					   WAIT_EVENT_SNAPBUILD_WRITE);
 
 	/*
 	 * fsync the file before renaming so that even if we crash after this we
@@ -1686,7 +1674,6 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	int			fd;
 	char		path[MAXPGPATH];
 	Size		sz;
-	int			readBytes;
 	pg_crc32c	checksum;
 
 	/* no point in loading a snapshot if we're already there */
@@ -1716,29 +1703,9 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	fsync_fname(path, false);
 	fsync_fname("pg_logical/snapshots", true);
 
-
 	/* read statically sized portion of snapshot */
-	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
-	readBytes = read(fd, &ondisk, SnapBuildOnDiskConstantSize);
-	pgstat_report_wait_end();
-	if (readBytes != SnapBuildOnDiskConstantSize)
-	{
-		int			save_errno = errno;
-
-		CloseTransientFile(fd);
-
-		if (readBytes < 0)
-		{
-			errno = save_errno;
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		}
-		else
-			ereport(ERROR,
-					(errmsg("could not read file \"%s\": read %d of %zu",
-							path, readBytes, SnapBuildOnDiskConstantSize)));
-	}
+	(void) ReadTransientFile(fd, (char *) &ondisk, SnapBuildOnDiskConstantSize,
+					  ERROR, path, WAIT_EVENT_SNAPBUILD_READ);
 
 	if (ondisk.magic != SNAPBUILD_MAGIC)
 		ereport(ERROR,
@@ -1756,80 +1723,23 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 				SnapBuildOnDiskConstantSize - SnapBuildOnDiskNotChecksummedSize);
 
 	/* read SnapBuild */
-	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
-	readBytes = read(fd, &ondisk.builder, sizeof(SnapBuild));
-	pgstat_report_wait_end();
-	if (readBytes != sizeof(SnapBuild))
-	{
-		int			save_errno = errno;
-
-		CloseTransientFile(fd);
-
-		if (readBytes < 0)
-		{
-			errno = save_errno;
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		}
-		else
-			ereport(ERROR,
-					(errmsg("could not read file \"%s\": read %d of %zu",
-							path, readBytes, sizeof(SnapBuild))));
-	}
+	(void) ReadTransientFile(fd, (char *) &ondisk.builder, sizeof(SnapBuild),
+					  ERROR, path, WAIT_EVENT_SNAPBUILD_READ);
 	COMP_CRC32C(checksum, &ondisk.builder, sizeof(SnapBuild));
 
 	/* restore running xacts (dead, but kept for backward compat) */
 	sz = sizeof(TransactionId) * ondisk.builder.was_running.was_xcnt_space;
 	ondisk.builder.was_running.was_xip =
 		MemoryContextAllocZero(builder->context, sz);
-	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
-	readBytes = read(fd, ondisk.builder.was_running.was_xip, sz);
-	pgstat_report_wait_end();
-	if (readBytes != sz)
-	{
-		int			save_errno = errno;
-
-		CloseTransientFile(fd);
-
-		if (readBytes < 0)
-		{
-			errno = save_errno;
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		}
-		else
-			ereport(ERROR,
-					(errmsg("could not read file \"%s\": read %d of %zu",
-							path, readBytes, sz)));
-	}
+	(void) ReadTransientFile(fd, (char *) ondisk.builder.was_running.was_xip, sz,
+					  ERROR, path, WAIT_EVENT_SNAPBUILD_READ);
 	COMP_CRC32C(checksum, ondisk.builder.was_running.was_xip, sz);
 
 	/* restore committed xacts information */
 	sz = sizeof(TransactionId) * ondisk.builder.committed.xcnt;
 	ondisk.builder.committed.xip = MemoryContextAllocZero(builder->context, sz);
-	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
-	readBytes = read(fd, ondisk.builder.committed.xip, sz);
-	pgstat_report_wait_end();
-	if (readBytes != sz)
-	{
-		int			save_errno = errno;
-
-		CloseTransientFile(fd);
-
-		if (readBytes < 0)
-		{
-			errno = save_errno;
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		}
-		else
-			ereport(ERROR,
-					(errmsg("could not read file \"%s\": read %d of %zu",
-							path, readBytes, sz)));
-	}
+	(void) ReadTransientFile(fd, (char *) ondisk.builder.committed.xip, sz,
+					  ERROR, path, WAIT_EVENT_SNAPBUILD_READ);
 	COMP_CRC32C(checksum, ondisk.builder.committed.xip, sz);
 
 	CloseTransientFile(fd);
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index afbaf8c80d..818b13e973 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1354,7 +1354,6 @@ RestoreSlotFromDisk(const char *name)
 	char		path[MAXPGPATH + 22];
 	int			fd;
 	bool		restored = false;
-	int			readBytes;
 	pg_crc32c	checksum;
 
 	/* no need to lock here, no concurrent access allowed yet */
@@ -1405,25 +1404,8 @@ RestoreSlotFromDisk(const char *name)
 	END_CRIT_SECTION();
 
 	/* read part of statefile that's guaranteed to be version independent */
-	pgstat_report_wait_start(WAIT_EVENT_REPLICATION_SLOT_READ);
-	readBytes = read(fd, &cp, ReplicationSlotOnDiskConstantSize);
-	pgstat_report_wait_end();
-	if (readBytes != ReplicationSlotOnDiskConstantSize)
-	{
-		int			saved_errno = errno;
-
-		CloseTransientFile(fd);
-		errno = saved_errno;
-		if (readBytes < 0)
-			ereport(PANIC,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		else
-			ereport(PANIC,
-					(errmsg("could not read file \"%s\": read %d of %zu",
-							path, readBytes,
-							ReplicationSlotOnDiskConstantSize)));
-	}
+	(void) ReadTransientFile(fd, (char *) &cp, ReplicationSlotOnDiskConstantSize,
+							 PANIC, path, WAIT_EVENT_REPLICATION_SLOT_READ);
 
 	/* verify magic */
 	if (cp.magic != SLOT_MAGIC)
@@ -1447,27 +1429,9 @@ RestoreSlotFromDisk(const char *name)
 						path, cp.length)));
 
 	/* Now that we know the size, read the entire file */
-	pgstat_report_wait_start(WAIT_EVENT_REPLICATION_SLOT_READ);
-	readBytes = read(fd,
-					 (char *) &cp + ReplicationSlotOnDiskConstantSize,
-					 cp.length);
-	pgstat_report_wait_end();
-	if (readBytes != cp.length)
-	{
-		int			saved_errno = errno;
-
-		CloseTransientFile(fd);
-		errno = saved_errno;
-		if (readBytes < 0)
-			ereport(PANIC,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", path)));
-		else
-			ereport(PANIC,
-					(errmsg("could not read file \"%s\": read %d of %zu",
-							path, readBytes, (Size) cp.length)));
-	}
-
+	(void) ReadTransientFile(fd, (char *) &cp + ReplicationSlotOnDiskConstantSize,
+							 cp.length, PANIC, path,
+							 WAIT_EVENT_REPLICATION_SLOT_READ);
 	CloseTransientFile(fd);
 
 	/* now verify the CRC */
diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index 8dd51f1767..fba7774ddc 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -47,8 +47,9 @@
  * ownership mechanism that provides automatic cleanup for shared files when
  * the last of a group of backends detaches.
  *
- * AllocateFile, AllocateDir, OpenPipeStream and OpenTransientFile are
- * wrappers around fopen(3), opendir(3), popen(3) and open(2), respectively.
+ * AllocateFile, AllocateDir, OpenPipeStream, OpenTransientFile,
+ * WriteTransientFile and ReadTransientFile are wrappers around fopen(3),
+ * opendir(3), popen(3), open(2), write(2) and read(2) respectively.
  * They behave like the corresponding native functions, except that the handle
  * is registered with the current subtransaction, and will be automatically
  * closed at abort. These are intended mainly for short operations like
@@ -2480,6 +2481,98 @@ TryAgain:
 	return NULL;
 }
 
+/*
+ * Write to a file which has been opened using OpenTransientFile or
+ * OpenTransientFilePerm.  Equivalent to write(2).
+ */
+void
+WriteTransientFile(int fd, char *buf, Size count, int elevel,
+				   const char *filename, uint32 wait_event_info)
+{
+	int			r;
+
+	pgstat_report_wait_start(wait_event_info);
+	r = write(fd, buf, count);
+	pgstat_report_wait_end();
+
+	if (r != count)
+	{
+		int         save_errno = errno;
+
+		(void) CloseTransientFile(fd);
+
+		/* if write didn't set errno, assume problem is no disk space */
+		errno = save_errno ? save_errno : ENOSPC;
+		ereport(elevel,
+				(errcode_for_file_access(),
+				 errmsg("could not write to file \"%s\": %m", filename)));
+	}
+}
+
+/*
+ * Read from a file which has been opened using OpenTransientFile or
+ * OpenTransientFilePerm.  Equivalent to read(2).  Returns true on
+ * success and false on failure.
+ */
+bool
+ReadTransientFile(int fd, char *buf, Size count, int elevel,
+				  const char *filename, uint32 wait_event_info)
+{
+	int			r;
+
+	pgstat_report_wait_start(wait_event_info);
+	r = read(fd, buf, count);
+	pgstat_report_wait_end();
+
+	if (r != count)
+	{
+		int         save_errno = errno;
+
+		CloseTransientFile(fd);
+
+		if (r < 0)
+		{
+			errno = save_errno;
+			ereport(elevel,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", filename)));
+		}
+		else
+			ereport(elevel,
+					(errmsg("could not read file \"%s\": read %d of %zu",
+							filename, r, count)));
+		return false;
+	}
+
+	return true;
+}
+
+/*
+ * Write to a file which has been opened using OpenTransientFile or
+ * OpenTransientFilePerm.  Equivalent to fsync(2).
+ */
+void
+SyncTransientFile(int fd, int elevel, const char *filename,
+				  uint32 wait_event_info)
+{
+	int			status;
+
+	pgstat_report_wait_start(wait_event_info);
+	status = pg_fsync(fd);
+	pgstat_report_wait_end();
+
+	if (status != 0)
+	{
+		int         save_errno = errno;
+
+		(void) CloseTransientFile(fd);
+		errno = save_errno;
+		ereport(elevel,
+				(errcode_for_file_access(),
+				 errmsg("could not fsync file \"%s\": %m", filename)));
+	}
+}
+
 /*
  * Free an AllocateDesc of any type.
  *
diff --git a/src/backend/utils/cache/relmapper.c b/src/backend/utils/cache/relmapper.c
index 2d31f9f912..e6eff58d40 100644
--- a/src/backend/utils/cache/relmapper.c
+++ b/src/backend/utils/cache/relmapper.c
@@ -629,7 +629,6 @@ load_relmap_file(bool shared)
 	char		mapfilename[MAXPGPATH];
 	pg_crc32c	crc;
 	int			fd;
-	int			r;
 
 	if (shared)
 	{
@@ -659,20 +658,8 @@ load_relmap_file(bool shared)
 	 * look, the sinval signaling mechanism will make us re-read it before we
 	 * are able to access any relation that's affected by the change.
 	 */
-	pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_READ);
-	r = read(fd, map, sizeof(RelMapFile));
-	if (r != sizeof(RelMapFile))
-	{
-		if (r < 0)
-			ereport(FATAL,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m", mapfilename)));
-		else
-			ereport(FATAL,
-					(errmsg("could not read file \"%s\": read %d of %zu",
-							mapfilename, r, sizeof(RelMapFile))));
-	}
-	pgstat_report_wait_end();
+	(void) ReadTransientFile(fd, (char *) map, sizeof(RelMapFile), FATAL,
+							 mapfilename, WAIT_EVENT_RELATION_MAP_READ);
 
 	CloseTransientFile(fd);
 
@@ -782,18 +769,9 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 	}
 
 	errno = 0;
-	pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_WRITE);
-	if (write(fd, newmap, sizeof(RelMapFile)) != sizeof(RelMapFile))
-	{
-		/* if write didn't set errno, assume problem is no disk space */
-		if (errno == 0)
-			errno = ENOSPC;
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not write file \"%s\": %m",
-						mapfilename)));
-	}
-	pgstat_report_wait_end();
+
+	WriteTransientFile(fd, (char *) newmap, sizeof(RelMapFile), ERROR,
+					   mapfilename, WAIT_EVENT_RELATION_MAP_WRITE);
 
 	/*
 	 * We choose to fsync the data to disk before considering the task done.
@@ -801,13 +779,7 @@ write_relmap_file(bool shared, RelMapFile *newmap,
 	 * issue, but it would complicate checkpointing --- see notes for
 	 * CheckPointRelationMap.
 	 */
-	pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_SYNC);
-	if (pg_fsync(fd) != 0)
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not fsync file \"%s\": %m",
-						mapfilename)));
-	pgstat_report_wait_end();
+	SyncTransientFile(fd, ERROR, mapfilename, WAIT_EVENT_RELATION_MAP_SYNC);
 
 	if (CloseTransientFile(fd))
 		ereport(ERROR,
diff --git a/src/include/storage/fd.h b/src/include/storage/fd.h
index 8e7c9728f4..4309d9da95 100644
--- a/src/include/storage/fd.h
+++ b/src/include/storage/fd.h
@@ -34,7 +34,9 @@
  *
  * Likewise, use AllocateDir/FreeDir, not opendir/closedir, to allocate
  * open directories (DIR*), and OpenTransientFile/CloseTransient File for an
- * unbuffered file descriptor.
+ * unbuffered file descriptor.  WriteTransientFile should be used instead
+ * of write(2), ReadTransientFile instead of read(2), and SyncTransientFile
+ * instead of fsync(2).
  */
 #ifndef FD_H
 #define FD_H
@@ -105,6 +107,12 @@ extern int	FreeDir(DIR *dir);
 /* Operations to allow use of a plain kernel FD, with automatic cleanup */
 extern int	OpenTransientFile(const char *fileName, int fileFlags);
 extern int	OpenTransientFilePerm(const char *fileName, int fileFlags, mode_t fileMode);
+extern void WriteTransientFile(int fd, char *buf, Size count, int elevel,
+							   const char *filename, uint32 wait_event_info);
+extern bool ReadTransientFile(int fd, char *buf, Size count, int elevel,
+							  const char *filename, uint32 wait_event_info);
+extern void SyncTransientFile(int fd, int elevel,  const char *filename,
+							  uint32 wait_event_info);
 extern int	CloseTransientFile(int fd);
 
 /* If you've really really gotta have a plain kernel FD, use this */
-- 
2.18.0