Re: forgotten initalization of a variable

[Michael Paquier]

On Tue, Apr 21, 2020 at 03:08:30PM +0900, Kyotaro Horiguchi wrote:
> The commit a7e8ece41c adds a new member restoreCommand to
> XLogPageReadPrivate. readOneRecord doesn't make use of it but forgets
> to set NULL. That can lead to illegal pointer access.

That's an oversight of the original commit.  Now, instead of failing
even if there is a restore command, wouldn't it be better to pass down
the restore_command to readOneRecord() so as we can optionally
improve the stability of a single record lookup?  This only applies to
a checkpoint record now, but this routine could be called elsewhere in
the future.  Please see the attached.
--
Michael

diff --git a/src/bin/pg_rewind/parsexlog.c b/src/bin/pg_rewind/parsexlog.c
index 14a5db5433..c51b5db315 100644
--- a/src/bin/pg_rewind/parsexlog.c
+++ b/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)
diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c
index 101f0911be..633955f7be 100644
--- a/src/bin/pg_rewind/pg_rewind.c
+++ b/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
diff --git a/src/bin/pg_rewind/pg_rewind.h b/src/bin/pg_rewind/pg_rewind.h
index b122ae43e5..5cf5f17bb5 100644
--- a/src/bin/pg_rewind/pg_rewind.h
+++ b/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);

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