Refactor more code logic to update the control file

ce6afc6 has begun the refactoring work by plugging pg_rewind into a
central routine to update the control file, and left around two extra
copies, with one in xlog.c for the backend and one in pg_resetwal.c.  By
adding an extra option to the central routine in controldata_utils.c to
control if a flush of the control file needs to be done, it is proving
to be straight-forward to make xlog.c and pg_resetwal.c use the central
code path at the condition of moving the wait event tracking there.
Hence, this allows to have only one central code path to update the
control file, shaving the code from the duplicates.

This refactoring actually fixes a problem in pg_resetwal.  Previously,
the control file was first removed before being recreated.  So if a
crash happened between the moment the file was removed and the moment
the file was created, then it would have been possible to not have a
control file anymore in the database folder.

Author: Fabien Coelho
Reviewed-by: Michael Paquier
Discussion: https://postgr.es/m/alpine.DEB.2.21.1903170935210.2506@lancre

1 files changed, 6 insertions, 42 deletions

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 54d3c558c64..ad12ebc4269 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -40,6 +40,7 @@
 #include "catalog/pg_control.h"
 #include "catalog/pg_database.h"
 #include "commands/tablespace.h"
+#include "common/controldata_utils.h"
 #include "miscadmin.h"
 #include "pgstat.h"
 #include "port/atomics.h"
@@ -4754,51 +4755,14 @@ ReadControlFile(void)
 					PGC_INTERNAL, PGC_S_OVERRIDE);
 }
 
+/*
+ * Utility wrapper to update the control file.  Note that the control
+ * file gets flushed.
+ */
 void
 UpdateControlFile(void)
 {
-	int			fd;
-
-	INIT_CRC32C(ControlFile->crc);
-	COMP_CRC32C(ControlFile->crc,
-				(char *) ControlFile,
-				offsetof(ControlFileData, crc));
-	FIN_CRC32C(ControlFile->crc);
-
-	fd = BasicOpenFile(XLOG_CONTROL_FILE,
-					   O_RDWR | PG_BINARY);
-	if (fd < 0)
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not open file \"%s\": %m", XLOG_CONTROL_FILE)));
-
-	errno = 0;
-	pgstat_report_wait_start(WAIT_EVENT_CONTROL_FILE_WRITE_UPDATE);
-	if (write(fd, ControlFile, sizeof(ControlFileData)) != sizeof(ControlFileData))
-	{
-		/* if write didn't set errno, assume problem is no disk space */
-		if (errno == 0)
-			errno = ENOSPC;
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not write to file \"%s\": %m",
-						XLOG_CONTROL_FILE)));
-	}
-	pgstat_report_wait_end();
-
-	pgstat_report_wait_start(WAIT_EVENT_CONTROL_FILE_SYNC_UPDATE);
-	if (pg_fsync(fd) != 0)
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not fsync file \"%s\": %m",
-						XLOG_CONTROL_FILE)));
-	pgstat_report_wait_end();
-
-	if (close(fd))
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not close file \"%s\": %m",
-						XLOG_CONTROL_FILE)));
+	update_controlfile(DataDir, NULL, ControlFile, true);
 }
 
 /*