Simplify logic to sync target directory at the end of pg_rewind

The previous sync logic relied on looking for and then launching
externally initdb -S, which is a simple wrapper on top of fsync_pgdata.
There is nothing preventing pg_rewind to directly call this routine, so
remove the dependency to initdb and just call it directly.

Author: Michael Paquier
Reviewed-by: Heikki Linnakangas
Discussion: https://postgr.es/m/20180325122607.GB3707@paquier.xyz

Author: michaelpq

src/bin/pg_rewind/pg_rewind.c

@@ -25,6 +25,7 @@
 #include "catalog/catversion.h"
 #include "catalog/pg_control.h"
 #include "common/file_perm.h"
+#include "common/file_utils.h"
 #include "common/restricted_token.h"
 #include "getopt_long.h"
 #include "storage/bufpage.h"
@@ -701,50 +702,15 @@ updateControlFile(ControlFileData *ControlFile)
  *
  * We do this once, for the whole data directory, for performance reasons.  At
  * the end of pg_rewind's run, the kernel is likely to already have flushed
- * most dirty buffers to disk. Additionally initdb -S uses a two-pass approach
- * (only initiating writeback in the first pass), which often reduces the
- * overall amount of IO noticeably.
+ * most dirty buffers to disk.  Additionally fsync_pgdata uses a two-pass
+ * approach (only initiating writeback in the first pass), which often reduces
+ * the overall amount of IO noticeably.
  */
 static void
 syncTargetDirectory(const char *argv0)
 {
-	int			ret;
-#define MAXCMDLEN (2 * MAXPGPATH)
-	char		exec_path[MAXPGPATH];
-	char		cmd[MAXCMDLEN];
-
-	/* locate initdb binary */
-	if ((ret = find_other_exec(argv0, "initdb",
-							   "initdb (PostgreSQL) " PG_VERSION "\n",
-							   exec_path)) < 0)
-	{
-		char		full_path[MAXPGPATH];
-
-		if (find_my_exec(argv0, full_path) < 0)
-			strlcpy(full_path, progname, sizeof(full_path));
-
-		if (ret == -1)
-			pg_fatal("The program \"initdb\" is needed by %s but was\n"
-					 "not found in the same directory as \"%s\".\n"
-					 "Check your installation.\n", progname, full_path);
-		else
-			pg_fatal("The program \"initdb\" was found by \"%s\"\n"
-					 "but was not the same version as %s.\n"
-					 "Check your installation.\n", full_path, progname);
-	}
-
-	/* only skip processing after ensuring presence of initdb */
 	if (dry_run)
 		return;
 
-	/* finally run initdb -S */
-	if (debug)
-		snprintf(cmd, MAXCMDLEN, "\"%s\" -D \"%s\" -S",
-				 exec_path, datadir_target);
-	else
-		snprintf(cmd, MAXCMDLEN, "\"%s\" -D \"%s\" -S > \"%s\"",
-				 exec_path, datadir_target, DEVNULL);
-
-	if (system(cmd) != 0)
-		pg_fatal("sync of target directory failed\n");
+	fsync_pgdata(datadir_target, progname, PG_VERSION_NUM);
 }