Add OpenTransientFile, with automatic cleanup at end-of-xact.

Files opened with BasicOpenFile or PathNameOpenFile are not automatically
cleaned up on error. That puts unnecessary burden on callers that only want
to keep the file open for a short time. There is AllocateFile, but that
returns a buffered FILE * stream, which in many cases is not the nicest API
to work with. So add function called OpenTransientFile, which returns a
unbuffered fd that's cleaned up like the FILE* returned by AllocateFile().

This plugs a few rare fd leaks in error cases:

1. copy_file() - fixed by by using OpenTransientFile instead of BasicOpenFile
2. XLogFileInit() - fixed by adding close() calls to the error cases. Can't
   use OpenTransientFile here because the fd is supposed to persist over
   transaction boundaries.
3. lo_import/lo_export - fixed by using OpenTransientFile instead of
   PathNameOpenFile.

In addition to plugging those leaks, this replaces many BasicOpenFile() calls
with OpenTransientFile() that were not leaking, because the code meticulously
closed the file on error. That wasn't strictly necessary, but IMHO it's good
for robustness.

The same leaks exist in older versions, but given the rarity of the issues,
I'm not backpatching this. Not yet, anyway - it might be good to backpatch
later, after this mechanism has had some more testing in master branch.

1 files changed, 21 insertions, 10 deletions

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 0d2540c3c23..623704965f4 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -2246,6 +2246,16 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
 
 	unlink(tmppath);
 
+	/*
+	 * Allocate a buffer full of zeros. This is done before opening the file
+	 * so that we don't leak the file descriptor if palloc fails.
+	 *
+	 * Note: palloc zbuffer, instead of just using a local char array, to
+	 * ensure it is reasonably well-aligned; this may save a few cycles
+	 * transferring data to the kernel.
+	 */
+	zbuffer = (char *) palloc0(XLOG_BLCKSZ);
+
 	/* do not use get_sync_bit() here --- want to fsync only at end of fill */
 	fd = BasicOpenFile(tmppath, O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
 					   S_IRUSR | S_IWUSR);
@@ -2262,12 +2272,7 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
 	 * fsync below) that all the indirect blocks are down on disk.	Therefore,
 	 * fdatasync(2) or O_DSYNC will be sufficient to sync future writes to the
 	 * log file.
-	 *
-	 * Note: palloc zbuffer, instead of just using a local char array, to
-	 * ensure it is reasonably well-aligned; this may save a few cycles
-	 * transferring data to the kernel.
 	 */
-	zbuffer = (char *) palloc0(XLOG_BLCKSZ);
 	for (nbytes = 0; nbytes < XLogSegSize; nbytes += XLOG_BLCKSZ)
 	{
 		errno = 0;
@@ -2279,6 +2284,9 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
 			 * If we fail to make the file, delete it to release disk space
 			 */
 			unlink(tmppath);
+
+			close(fd);
+
 			/* if write didn't set errno, assume problem is no disk space */
 			errno = save_errno ? save_errno : ENOSPC;
 
@@ -2290,9 +2298,12 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
 	pfree(zbuffer);
 
 	if (pg_fsync(fd) != 0)
+	{
+		close(fd);
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not fsync file \"%s\": %m", tmppath)));
+	}
 
 	if (close(fd))
 		ereport(ERROR,
@@ -2363,7 +2374,7 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno)
 	 * Open the source file
 	 */
 	XLogFilePath(path, srcTLI, srcsegno);
-	srcfd = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0);
+	srcfd = OpenTransientFile(path, O_RDONLY | PG_BINARY, 0);
 	if (srcfd < 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
@@ -2377,8 +2388,8 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno)
 	unlink(tmppath);
 
 	/* do not use get_sync_bit() here --- want to fsync only at end of fill */
-	fd = BasicOpenFile(tmppath, O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
-					   S_IRUSR | S_IWUSR);
+	fd = OpenTransientFile(tmppath, O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
+						   S_IRUSR | S_IWUSR);
 	if (fd < 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
@@ -2423,12 +2434,12 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno)
 				(errcode_for_file_access(),
 				 errmsg("could not fsync file \"%s\": %m", tmppath)));
 
-	if (close(fd))
+	if (CloseTransientFile(fd))
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not close file \"%s\": %m", tmppath)));
 
-	close(srcfd);
+	CloseTransientFile(srcfd);
 
 	/*
 	 * Now move the segment into place with its final name.