From 6c6760e6553ac86c334e7c35d2ddbac8fdc1cb9b Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Fri, 19 Jan 2024 15:38:34 -0600
Subject: [PATCH v1 2/2] Add hash/compare functions for dshash tables with
 string keys.

---
 src/backend/lib/dshash.c               | 23 +++++++++++++++++++++++
 src/backend/storage/ipc/dsm_registry.c |  8 +++-----
 src/include/lib/dshash.h               |  4 ++++
 3 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index b0bc0abda0..e497238e8f 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -583,6 +583,29 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * A compare function that forwards to strcmp.
+ */
+int
+dshash_strcmp(const void *a, const void *b, size_t size, void *arg)
+{
+	Assert(strlen((const char *) a) < size);
+	Assert(strlen((const char *) b) < size);
+
+	return strcmp((const char *) a, (const char *) b);
+}
+
+/*
+ * A hash function that forwards to string_hash.
+ */
+dshash_hash
+dshash_strhash(const void *v, size_t size, void *arg)
+{
+	Assert(strlen((const char *) v) < size);
+
+	return string_hash((const char *) v, size);
+}
+
 /*
  * Sequentially scan through dshash table and return all the elements one by
  * one, return NULL when all elements have been returned.
diff --git a/src/backend/storage/ipc/dsm_registry.c b/src/backend/storage/ipc/dsm_registry.c
index ac11f51375..9dce41e8ab 100644
--- a/src/backend/storage/ipc/dsm_registry.c
+++ b/src/backend/storage/ipc/dsm_registry.c
@@ -50,8 +50,8 @@ typedef struct DSMRegistryEntry
 static const dshash_parameters dsh_params = {
 	offsetof(DSMRegistryEntry, handle),
 	sizeof(DSMRegistryEntry),
-	dshash_memcmp,
-	dshash_memhash,
+	dshash_strcmp,
+	dshash_strhash,
 	LWTRANCHE_DSM_REGISTRY_HASH
 };
 
@@ -132,7 +132,6 @@ GetNamedDSMSegment(const char *name, size_t size,
 {
 	DSMRegistryEntry *entry;
 	MemoryContext oldcontext;
-	char		name_padded[offsetof(DSMRegistryEntry, handle)] = {0};
 	void	   *ret;
 
 	Assert(found);
@@ -155,8 +154,7 @@ GetNamedDSMSegment(const char *name, size_t size,
 	/* Connect to the registry. */
 	init_dsm_registry();
 
-	strcpy(name_padded, name);
-	entry = dshash_find_or_insert(dsm_registry_table, name_padded, found);
+	entry = dshash_find_or_insert(dsm_registry_table, name, found);
 	if (!(*found))
 	{
 		/* Initialize the segment. */
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index 91f70ac2b5..1861e5a8b1 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -109,6 +109,10 @@ extern void dshash_delete_current(dshash_seq_status *status);
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
 
+/* Convenience hash and compare functions wrapping strcmp and string_hash. */
+extern int	dshash_strcmp(const void *a, const void *b, size_t size, void *arg);
+extern dshash_hash dshash_strhash(const void *v, size_t size, void *arg);
+
 /* Debugging support. */
 extern void dshash_dump(dshash_table *hash_table);
 
-- 
2.25.1