Fix single-record reads to use restore_command if available in pg_rewind

readOneRecord() is used now when looking for a checkpoint record to
check if the target server is an ancestor of the source across multiple
timelines, and using a restore_command if available improves the
stability of the operation.  This part was missed in a7e8ece4.

Reported-by: Kyotaro Horiguchi
Discussion: https://postgr.es/m/20200421.150830.1410714948345179794.horikyota.ntt@gmail.com

src/bin/pg_rewind/parsexlog.c

@@ -106,7 +106,8 @@ extractPageMap(const char *datadir, XLogRecPtr startpoint, int tliIndex,
  * doing anything with the record itself.
  */
 XLogRecPtr
-readOneRecord(const char *datadir, XLogRecPtr ptr, int tliIndex)
+readOneRecord(const char *datadir, XLogRecPtr ptr, int tliIndex,
+			  const char *restoreCommand)
 {
 	XLogRecord *record;
 	XLogReaderState *xlogreader;
@@ -115,6 +116,7 @@ readOneRecord(const char *datadir, XLogRecPtr ptr, int tliIndex)
 	XLogRecPtr	endptr;
 
 	private.tliIndex = tliIndex;
+	private.restoreCommand = restoreCommand;
 	xlogreader = XLogReaderAllocate(WalSegSz, datadir, &SimpleXLogPageRead,
 									&private);
 	if (xlogreader == NULL)

src/bin/pg_rewind/pg_rewind.c

@@ -339,7 +339,8 @@ main(int argc, char **argv)
 			/* Read the checkpoint record on the target to see where it ends. */
 			chkptendrec = readOneRecord(datadir_target,
 										ControlFile_target.checkPoint,
-										targetNentries - 1);
+										targetNentries - 1,
+										restore_command);
 
 			/*
 			 * If the histories diverged exactly at the end of the shutdown

src/bin/pg_rewind/pg_rewind.h

@@ -50,7 +50,7 @@ extern void findLastCheckpoint(const char *datadir, XLogRecPtr searchptr,
 							   XLogRecPtr *lastchkptredo,
 							   const char *restoreCommand);
 extern XLogRecPtr readOneRecord(const char *datadir, XLogRecPtr ptr,
-								int tliIndex);
+								int tliIndex, const char *restoreCommand);
 
 /* in pg_rewind.c */
 extern void progress_report(bool force);