From 04063a995759c9f32bd87b0155c68a2c5fb346ed Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Wed, 26 Feb 2025 11:44:36 -0600
Subject: [PATCH v3 3/4] Add new frontend functions for durable file
 operations.

This commit exports the existing pre_sync_fname() function and adds
durable_mkdir_p() and durable_rename_dir() for use in frontend
programs.  A follow-up commit will use this to help optimize
pg_upgrade's file transfer step.

Discussion: https://postgr.es/m/Zyvop-LxLXBLrZil%40nathan
---
 src/common/file_utils.c         | 55 +++++++++++++++++++++++++++------
 src/include/common/file_utils.h |  3 ++
 2 files changed, 49 insertions(+), 9 deletions(-)

diff --git a/src/common/file_utils.c b/src/common/file_utils.c
index 78e272916f5..a5a03abd7ca 100644
--- a/src/common/file_utils.c
+++ b/src/common/file_utils.c
@@ -26,6 +26,7 @@
 
 #include "common/file_utils.h"
 #ifdef FRONTEND
+#include "common/file_perm.h"
 #include "common/logging.h"
 #endif
 #include "common/relpath.h"
@@ -45,9 +46,6 @@
  */
 #define MINIMUM_VERSION_FOR_PG_WAL	100000
 
-#ifdef PG_FLUSH_DATA_WORKS
-static int	pre_sync_fname(const char *fname, bool isdir);
-#endif
 static void walkdir(const char *path,
 					int (*action) (const char *fname, bool isdir),
 					bool process_symlinks,
@@ -352,16 +350,16 @@ walkdir(const char *path,
 }
 
 /*
- * Hint to the OS that it should get ready to fsync() this file.
+ * Hint to the OS that it should get ready to fsync() this file, if supported
+ * by the platform.
  *
  * Ignores errors trying to open unreadable files, and reports other errors
  * non-fatally.
  */
-#ifdef PG_FLUSH_DATA_WORKS
-
-static int
+int
 pre_sync_fname(const char *fname, bool isdir)
 {
+#ifdef PG_FLUSH_DATA_WORKS
 	int			fd;
 
 	fd = open(fname, O_RDONLY | PG_BINARY, 0);
@@ -388,11 +386,10 @@ pre_sync_fname(const char *fname, bool isdir)
 #endif
 
 	(void) close(fd);
+#endif							/* PG_FLUSH_DATA_WORKS */
 	return 0;
 }
 
-#endif							/* PG_FLUSH_DATA_WORKS */
-
 /*
  * fsync_fname -- Try to fsync a file or directory
  *
@@ -539,6 +536,46 @@ durable_rename(const char *oldfile, const char *newfile)
 	return 0;
 }
 
+/*
+ * durable_rename_dir: rename(2) wrapper for directories, issuing fsyncs
+ * required for durability.
+ */
+int
+durable_rename_dir(const char *olddir, const char *newdir)
+{
+	if (fsync_fname(olddir, true) != 0 ||
+		fsync_parent_path(olddir) != 0 ||
+		fsync_parent_path(newdir) != 0)
+		return -1;
+
+	if (rename(olddir, newdir) != 0)
+		return -1;
+
+	if (fsync_fname(newdir, true) != 0 ||
+		fsync_parent_path(olddir) != 0 ||
+		fsync_parent_path(newdir) != 0)
+		return -1;
+
+	return 0;
+}
+
+/*
+ * durable_mkdir_p: pg_mkdir_p() wrapper, issuing fsyncs required for
+ * durability.
+ */
+int
+durable_mkdir_p(char *newdir)
+{
+	if (pg_mkdir_p(newdir, pg_dir_create_mode) && errno != EEXIST)
+		return -1;
+
+	if (fsync_fname(newdir, true) != 0 ||
+		fsync_parent_path(newdir) != 0)
+		return -1;
+
+	return 0;
+}
+
 #endif							/* FRONTEND */
 
 /*
diff --git a/src/include/common/file_utils.h b/src/include/common/file_utils.h
index 8274bc877ab..7d253a4cb51 100644
--- a/src/include/common/file_utils.h
+++ b/src/include/common/file_utils.h
@@ -33,11 +33,14 @@ typedef enum DataDirSyncMethod
 struct iovec;					/* avoid including port/pg_iovec.h here */
 
 #ifdef FRONTEND
+extern int	pre_sync_fname(const char *fname, bool isdir);
 extern int	fsync_fname(const char *fname, bool isdir);
 extern void sync_pgdata(const char *pg_data, int serverVersion,
 						DataDirSyncMethod sync_method, bool sync_data_files);
 extern void sync_dir_recurse(const char *dir, DataDirSyncMethod sync_method);
 extern int	durable_rename(const char *oldfile, const char *newfile);
+extern int	durable_rename_dir(const char *olddir, const char *newdir);
+extern int	durable_mkdir_p(char *newdir);
 extern int	fsync_parent_path(const char *fname);
 #endif
 
-- 
2.39.5 (Apple Git-154)