0001-Revert-Remove-HAVE_WORKING_LINK.patch

From 961f9a03d4c27220c33e88402d5ef274424a0ab2 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Wed, 17 Mar 2021 07:12:35 +0900
Subject: [PATCH] Revert "Remove HAVE_WORKING_LINK"

This reverts commit aaa3aeddee51dd0058d38469907865052706a590.
---
 src/include/pg_config_manual.h        |  7 +++++++
 src/include/storage/fd.h              |  2 +-
 src/backend/access/transam/timeline.c |  4 ++--
 src/backend/access/transam/xlog.c     |  4 ++--
 src/backend/storage/file/fd.c         | 21 ++++++++++++++++-----
 5 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/src/include/pg_config_manual.h b/src/include/pg_config_manual.h
index 8f3ec6bde1..966da99742 100644
--- a/src/include/pg_config_manual.h
+++ b/src/include/pg_config_manual.h
@@ -135,6 +135,13 @@
 #define EXEC_BACKEND
 #endif
 
+/*
+ * Define this if your operating system supports link()
+ */
+#if !defined(WIN32) && !defined(__CYGWIN__)
+#define HAVE_WORKING_LINK 1
+#endif
+
 /*
  * USE_POSIX_FADVISE controls whether Postgres will attempt to use the
  * posix_fadvise() kernel call.  Usually the automatic configure tests are
diff --git a/src/include/storage/fd.h b/src/include/storage/fd.h
index 8cd125d7df..2085c62b41 100644
--- a/src/include/storage/fd.h
+++ b/src/include/storage/fd.h
@@ -157,7 +157,7 @@ extern void fsync_fname(const char *fname, bool isdir);
 extern int	fsync_fname_ext(const char *fname, bool isdir, bool ignore_perm, int elevel);
 extern int	durable_rename(const char *oldfile, const char *newfile, int loglevel);
 extern int	durable_unlink(const char *fname, int loglevel);
-extern int	durable_rename_excl(const char *oldfile, const char *newfile, int loglevel);
+extern int	durable_link_or_rename(const char *oldfile, const char *newfile, int loglevel);
 extern void SyncDataDirectory(void);
 extern int	data_sync_elevel(int elevel);
 
diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c
index e6a29d9a9b..27d70ff869 100644
--- a/src/backend/access/transam/timeline.c
+++ b/src/backend/access/transam/timeline.c
@@ -446,7 +446,7 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI,
 	 * Perform the rename using link if available, paranoidly trying to avoid
 	 * overwriting an existing file (there shouldn't be one).
 	 */
-	durable_rename_excl(tmppath, path, ERROR);
+	durable_link_or_rename(tmppath, path, ERROR);
 
 	/* The history file can be archived immediately. */
 	if (XLogArchivingActive())
@@ -524,7 +524,7 @@ writeTimeLineHistoryFile(TimeLineID tli, char *content, int size)
 	 * Perform the rename using link if available, paranoidly trying to avoid
 	 * overwriting an existing file (there shouldn't be one).
 	 */
-	durable_rename_excl(tmppath, path, ERROR);
+	durable_link_or_rename(tmppath, path, ERROR);
 }
 
 /*
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 7daa7c43ad..82e070e431 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -3624,11 +3624,11 @@ InstallXLogFileSegment(XLogSegNo *segno, char *tmppath,
 	 * Perform the rename using link if available, paranoidly trying to avoid
 	 * overwriting an existing file (there shouldn't be one).
 	 */
-	if (durable_rename_excl(tmppath, path, LOG) != 0)
+	if (durable_link_or_rename(tmppath, path, LOG) != 0)
 	{
 		if (use_lock)
 			LWLockRelease(ControlFileLock);
-		/* durable_rename_excl already emitted log message */
+		/* durable_link_or_rename already emitted log message */
 		return false;
 	}
 
diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index e5950b0726..ba92ceaf65 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -767,11 +767,10 @@ durable_unlink(const char *fname, int elevel)
 }
 
 /*
- * durable_rename_excl -- rename a file in a durable manner, without
- * overwriting an existing target file
+ * durable_link_or_rename -- rename a file in a durable manner.
  *
- * Similar to durable_rename(), except that this routine will fail if the
- * target file already exists.
+ * Similar to durable_rename(), except that this routine tries (but does not
+ * guarantee) not to overwrite the target file.
  *
  * Note that a crash in an unfortunate moment can leave you with two links to
  * the target file.
@@ -782,7 +781,7 @@ durable_unlink(const char *fname, int elevel)
  * valid upon return.
  */
 int
-durable_rename_excl(const char *oldfile, const char *newfile, int elevel)
+durable_link_or_rename(const char *oldfile, const char *newfile, int elevel)
 {
 	/*
 	 * Ensure that, if we crash directly after the rename/link, a file with
@@ -791,6 +790,7 @@ durable_rename_excl(const char *oldfile, const char *newfile, int elevel)
 	if (fsync_fname_ext(oldfile, false, false, elevel) != 0)
 		return -1;
 
+#ifdef HAVE_WORKING_LINK
 	if (link(oldfile, newfile) < 0)
 	{
 		ereport(elevel,
@@ -800,6 +800,17 @@ durable_rename_excl(const char *oldfile, const char *newfile, int elevel)
 		return -1;
 	}
 	unlink(oldfile);
+#else
+	/* XXX: Add racy file existence check? */
+	if (rename(oldfile, newfile) < 0)
+	{
+		ereport(elevel,
+				(errcode_for_file_access(),
+				 errmsg("could not rename file \"%s\" to \"%s\": %m",
+						oldfile, newfile)));
+		return -1;
+	}
+#endif
 
 	/*
 	 * Make change persistent in case of an OS crash, both the new entry and
-- 
2.30.2