Properly handle unlink failure for RemoveOldXlogFiles

Originally, the return code was ignored. Now, if unlink failed for any
reason, the error message will be logged, and also adjust the
CheckpointStats properly.

Now MirroredFlatFile_Drop() returned the same return code as unlink(),
and also the errno is preserved, so the correct error message can be
logged by the caller.
Signed-off-by: NXin Zhang <xzhang@pivotal.io>

src/backend/access/transam/xlog.c

@@ -3197,7 +3197,7 @@ RemoveOldXlogFiles(uint32 log, uint32 seg, XLogRecPtr endptr)
 				else
 				{
 					/* No need for any more future segments... */
-					//int rc;
+					int rc = 0;
 
 					ereport(DEBUG2,
 							(errmsg("removing transaction log file \"%s\"",
@@ -3227,22 +3227,19 @@ RemoveOldXlogFiles(uint32 log, uint32 seg, XLogRecPtr endptr)
 						continue;
 					}
 					snprintf(newfilename, MAXPGPATH, "%s.deleted", xlde->d_name);
-					MirroredFlatFile_Drop(
+					rc = MirroredFlatFile_Drop(
 										  XLOGDIR,
 										  newfilename,
 										  /* suppressError */ true,
 										  /*isMirrorRecovery */ false);
 #else
-					MirroredFlatFile_Drop(
+					rc = MirroredFlatFile_Drop(
 										  XLOGDIR,
 										  xlde->d_name,
 										  /* suppressError */ true,
 										  /*isMirrorRecovery */ false);
 #endif
 
-					/* GPDB_83_MERGE_FIXME: MirroredFlatFile_Drop doesn't return a return
-					 * code */
-#if 0
 					if (rc != 0)
 					{
 						ereport(LOG,
@@ -3251,7 +3248,7 @@ RemoveOldXlogFiles(uint32 log, uint32 seg, XLogRecPtr endptr)
 										path)));
 						continue;
 					}
-#endif
+
 					CheckpointStats.ckpt_segs_removed++;
 				}
 

src/backend/cdb/cdbmirroredflatfile.c

@@ -851,6 +851,7 @@ int MirroredFlatFile_Drop(
 	char *path;
 	bool mirrorDrop = TRUE;
 	int	 save_errno = 0;
+	int	return_value = 0;
 	char *dir = NULL, *mirrorDir = NULL;
 	
 	if (isTxnDir(subDirectory))
@@ -884,10 +885,12 @@ int MirroredFlatFile_Drop(
 	
 	if (! isMirrorRecovery) {
 		errno = 0;
-		if (unlink(path) < 0 && !suppressError)
+		return_value = unlink(path);
+		if (return_value < 0 && !suppressError){
 			ereport(ERROR,
 					(errcode_for_file_access(),
 					 errmsg("could not unlink file \"%s\": %m", path)));
+		}
 		save_errno = errno;
 	}
 	
@@ -905,7 +908,8 @@ int MirroredFlatFile_Drop(
 	pfree(dir);
 	pfree(mirrorDir);
 
-	return save_errno;
+	errno = save_errno;
+	return return_value;
 }