Remove HAVE_WORKING_LINK

Previously, hard links were not used on Windows and Cygwin, but they
support them just fine in currently supported OS versions, so we can
use them there as well.

Since all supported platforms now support hard links, we can remove
the alternative code paths.

Rename durable_link_or_rename() to durable_rename_excl() to make the
purpose more clear without referencing the implementation details.

Discussion: https://www.postgresql.org/message-id/flat/72fff73f-dc9c-4ef4-83e8-d2e60c98df48%402ndquadrant.com

src/backend/access/transam/timeline.c

@@ -429,7 +429,7 @@ 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_link_or_rename(tmppath, path, ERROR);
+	durable_rename_excl(tmppath, path, ERROR);
 
 	/* The history file can be archived immediately. */
 	if (XLogArchivingActive())
@@ -507,7 +507,7 @@ 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_link_or_rename(tmppath, path, ERROR);
+	durable_rename_excl(tmppath, path, ERROR);
 }
 
 /*

src/backend/access/transam/xlog.c

@@ -3591,11 +3591,11 @@ 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_link_or_rename(tmppath, path, LOG) != 0)
+	if (durable_rename_excl(tmppath, path, LOG) != 0)
 	{
 		if (use_lock)
 			LWLockRelease(ControlFileLock);
-		/* durable_link_or_rename already emitted log message */
+		/* durable_rename_excl already emitted log message */
 		return false;
 	}
 

src/backend/storage/file/fd.c

@@ -765,10 +765,11 @@ durable_unlink(const char *fname, int elevel)
 }
 
 /*
- * durable_link_or_rename -- rename a file in a durable manner.
+ * durable_rename_excl -- rename a file in a durable manner, without
+ * overwriting an existing target file
  *
- * Similar to durable_rename(), except that this routine tries (but does not
- * guarantee) not to overwrite the target file.
+ * Similar to durable_rename(), except that this routine will fail if the
+ * target file already exists.
  *
  * Note that a crash in an unfortunate moment can leave you with two links to
  * the target file.
@@ -779,7 +780,7 @@ durable_unlink(const char *fname, int elevel)
  * valid upon return.
  */
 int
-durable_link_or_rename(const char *oldfile, const char *newfile, int elevel)
+durable_rename_excl(const char *oldfile, const char *newfile, int elevel)
 {
 	/*
 	 * Ensure that, if we crash directly after the rename/link, a file with
@@ -788,7 +789,6 @@ durable_link_or_rename(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,
@@ -798,17 +798,6 @@ durable_link_or_rename(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

src/include/pg_config_manual.h

@@ -129,13 +129,6 @@
 #undef HAVE_UNIX_SOCKETS
 #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

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_link_or_rename(const char *oldfile, const char *newfile, int loglevel);
+extern int	durable_rename_excl(const char *oldfile, const char *newfile, int loglevel);
 extern void SyncDataDirectory(void);
 extern int	data_sync_elevel(int elevel);