Make XLogFileCopy() look the same as in 9.4.

XLogFileCopy() was changed heavily in commit de768844. However it was
partially reverted in commit 7abc6859 and most of those changes to
XLogFileCopy() were no longer needed. Then commit 7cbee7c0 removed
those unnecessary code, but XLogFileCopy() looked different in master
and 9.4 though the contents are almost the same.

This patch makes XLogFileCopy() look the same in master and back-branches,
which makes back-patching easier, per discussion on pgsql-hackers.
Back-patch to 9.5.

Discussion: 55760844.7090703@iki.fi

Michael Paquier

src/backend/access/transam/xlog.c

@@ -808,7 +808,7 @@ static bool XLogCheckpointNeeded(XLogSegNo new_segno);
 static void XLogWrite(XLogwrtRqst WriteRqst, bool flexible);
 static bool InstallXLogFileSegment(XLogSegNo *segno, char *tmppath,
 					   bool find_free, XLogSegNo max_segno,
-					   bool use_lock, int elevel);
+					   bool use_lock);
 static int XLogFileRead(XLogSegNo segno, int emode, TimeLineID tli,
 			 int source, bool notexistOk);
 static int	XLogFileReadAnyTLI(XLogSegNo segno, int emode, int source);
@@ -3013,7 +3013,7 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
 	max_segno = logsegno + CheckPointSegments;
 	if (!InstallXLogFileSegment(&installed_segno, tmppath,
 								*use_existent, max_segno,
-								use_lock, LOG))
+								use_lock))
 	{
 		/*
 		 * No need for any more future segments, or InstallXLogFileSegment()
@@ -3040,20 +3040,25 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
 }
 
 /*
- * Copy a WAL segment file in pg_xlog directory.
+ * Create a new XLOG file segment by copying a pre-existing one.
  *
- * srcfname		source filename
- * upto			how much of the source file to copy? (the rest is filled with
- *				zeros)
- * segno		identify segment to install.
+ * destsegno: identify segment to be created.
  *
- * The file is first copied with a temporary filename, and then installed as
- * a newly-created segment.
+ * srcTLI, srclog, srcseg: identify segment to be copied (could be from
+ *		a different timeline)
+ *
+ * upto: how much of the source file to copy (the rest is filled with
+ *		zeros)
+ *
+ * Currently this is only used during recovery, and so there are no locking
+ * considerations.  But we should be just as tense as XLogFileInit to avoid
+ * emplacing a bogus file.
  */
 static void
-XLogFileCopy(char *srcfname, int upto, XLogSegNo segno)
+XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
+			 int upto)
 {
-	char		srcpath[MAXPGPATH];
+	char		path[MAXPGPATH];
 	char		tmppath[MAXPGPATH];
 	char		buffer[XLOG_BLCKSZ];
 	int			srcfd;
@@ -3063,12 +3068,12 @@ XLogFileCopy(char *srcfname, int upto, XLogSegNo segno)
 	/*
 	 * Open the source file
 	 */
-	snprintf(srcpath, MAXPGPATH, XLOGDIR "/%s", srcfname);
-	srcfd = OpenTransientFile(srcpath, O_RDONLY | PG_BINARY, 0);
+	XLogFilePath(path, srcTLI, srcsegno);
+	srcfd = OpenTransientFile(path, O_RDONLY | PG_BINARY, 0);
 	if (srcfd < 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not open file \"%s\": %m", srcpath)));
+				 errmsg("could not open file \"%s\": %m", path)));
 
 	/*
 	 * Copy into a temp file name.
@@ -3112,11 +3117,11 @@ XLogFileCopy(char *srcfname, int upto, XLogSegNo segno)
 					ereport(ERROR,
 							(errcode_for_file_access(),
 							 errmsg("could not read file \"%s\": %m",
-									srcpath)));
+									path)));
 				else
 					ereport(ERROR,
 							(errmsg("not enough data in file \"%s\"",
-									srcpath)));
+									path)));
 			}
 		}
 		errno = 0;
@@ -3149,9 +3154,11 @@ XLogFileCopy(char *srcfname, int upto, XLogSegNo segno)
 
 	CloseTransientFile(srcfd);
 
-	/* install the new file */
-	(void) InstallXLogFileSegment(&segno, tmppath, false,
-								  0, false, ERROR);
+	/*
+	 * Now move the segment into place with its final name.
+	 */
+	if (!InstallXLogFileSegment(&destsegno, tmppath, false, 0, false))
+		elog(ERROR, "InstallXLogFileSegment should not have failed");
 }
 
 /*
@@ -3178,8 +3185,6 @@ XLogFileCopy(char *srcfname, int upto, XLogSegNo segno)
  * place.  This should be TRUE except during bootstrap log creation.  The
  * caller must *not* hold the lock at call.
  *
- * elevel: log level used by this routine.
- *
  * Returns TRUE if the file was installed successfully.  FALSE indicates that
  * max_segno limit was exceeded, or an error occurred while renaming the
  * file into place.
@@ -3187,7 +3192,7 @@ XLogFileCopy(char *srcfname, int upto, XLogSegNo segno)
 static bool
 InstallXLogFileSegment(XLogSegNo *segno, char *tmppath,
 					   bool find_free, XLogSegNo max_segno,
-					   bool use_lock, int elevel)
+					   bool use_lock)
 {
 	char		path[MAXPGPATH];
 	struct stat stat_buf;
@@ -3232,7 +3237,7 @@ InstallXLogFileSegment(XLogSegNo *segno, char *tmppath,
 	{
 		if (use_lock)
 			LWLockRelease(ControlFileLock);
-		ereport(elevel,
+		ereport(LOG,
 				(errcode_for_file_access(),
 				 errmsg("could not link file \"%s\" to \"%s\" (initialization of log file): %m",
 						tmppath, path)));
@@ -3244,7 +3249,7 @@ InstallXLogFileSegment(XLogSegNo *segno, char *tmppath,
 	{
 		if (use_lock)
 			LWLockRelease(ControlFileLock);
-		ereport(elevel,
+		ereport(LOG,
 				(errcode_for_file_access(),
 				 errmsg("could not rename file \"%s\" to \"%s\" (initialization of log file): %m",
 						tmppath, path)));
@@ -3733,7 +3738,7 @@ RemoveXlogFile(const char *segname, XLogRecPtr PriorRedoPtr, XLogRecPtr endptr)
 	if (endlogSegNo <= recycleSegNo &&
 		lstat(path, &statbuf) == 0 && S_ISREG(statbuf.st_mode) &&
 		InstallXLogFileSegment(&endlogSegNo, path,
-							   true, recycleSegNo, true, LOG))
+							   true, recycleSegNo, true))
 	{
 		ereport(DEBUG2,
 				(errmsg("recycled transaction log file \"%s\"",
@@ -5212,8 +5217,6 @@ exitArchiveRecovery(TimeLineID endTLI, XLogRecPtr endOfLog)
 	 */
 	if (endLogSegNo == startLogSegNo)
 	{
-		XLogFileName(xlogfname, endTLI, endLogSegNo);
-
 		/*
 		 * Make a copy of the file on the new timeline.
 		 *
@@ -5221,7 +5224,8 @@ exitArchiveRecovery(TimeLineID endTLI, XLogRecPtr endOfLog)
 		 * considerations. But we should be just as tense as XLogFileInit to
 		 * avoid emplacing a bogus file.
 		 */
-		XLogFileCopy(xlogfname, endOfLog % XLOG_SEG_SIZE, endLogSegNo);
+		XLogFileCopy(endLogSegNo, endTLI, endLogSegNo,
+					 endOfLog % XLOG_SEG_SIZE);
 	}
 	else
 	{