Refactor more code logic to update the control file

ce6afc68 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

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);
 }
 
 /*

src/bin/pg_resetwal/pg_resetwal.c

@@ -49,8 +49,7 @@
 #include "access/multixact.h"
 #include "access/xlog.h"
 #include "access/xlog_internal.h"
-#include "catalog/catversion.h"
-#include "catalog/pg_control.h"
+#include "common/controldata_utils.h"
 #include "common/fe_memutils.h"
 #include "common/file_perm.h"
 #include "common/restricted_token.h"
@@ -918,18 +917,6 @@ PrintNewControlValues(void)
 static void
 RewriteControlFile(void)
 {
-	int			fd;
-	char		buffer[PG_CONTROL_FILE_SIZE];	/* need not be aligned */
-
-	/*
-	 * For good luck, apply the same static assertions as in backend's
-	 * WriteControlFile().
-	 */
-	StaticAssertStmt(sizeof(ControlFileData) <= PG_CONTROL_MAX_SAFE_SIZE,
-					 "pg_control is too large for atomic disk writes");
-	StaticAssertStmt(sizeof(ControlFileData) <= PG_CONTROL_FILE_SIZE,
-					 "sizeof(ControlFileData) exceeds PG_CONTROL_FILE_SIZE");
-
 	/*
 	 * Adjust fields as needed to force an empty XLOG starting at
 	 * newXlogSegNo.
@@ -961,53 +948,8 @@ RewriteControlFile(void)
 	ControlFile.max_prepared_xacts = 0;
 	ControlFile.max_locks_per_xact = 64;
 
-	/* Contents are protected with a CRC */
-	INIT_CRC32C(ControlFile.crc);
-	COMP_CRC32C(ControlFile.crc,
-				(char *) &ControlFile,
-				offsetof(ControlFileData, crc));
-	FIN_CRC32C(ControlFile.crc);
-
-	/*
-	 * We write out PG_CONTROL_FILE_SIZE bytes into pg_control, zero-padding
-	 * the excess over sizeof(ControlFileData).  This reduces the odds of
-	 * premature-EOF errors when reading pg_control.  We'll still fail when we
-	 * check the contents of the file, but hopefully with a more specific
-	 * error than "couldn't read pg_control".
-	 */
-	memset(buffer, 0, PG_CONTROL_FILE_SIZE);
-	memcpy(buffer, &ControlFile, sizeof(ControlFileData));
-
-	unlink(XLOG_CONTROL_FILE);
-
-	fd = open(XLOG_CONTROL_FILE,
-			  O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
-			  pg_file_create_mode);
-	if (fd < 0)
-	{
-		fprintf(stderr, _("%s: could not create pg_control file: %s\n"),
-				progname, strerror(errno));
-		exit(1);
-	}
-
-	errno = 0;
-	if (write(fd, buffer, PG_CONTROL_FILE_SIZE) != PG_CONTROL_FILE_SIZE)
-	{
-		/* if write didn't set errno, assume problem is no disk space */
-		if (errno == 0)
-			errno = ENOSPC;
-		fprintf(stderr, _("%s: could not write pg_control file: %s\n"),
-				progname, strerror(errno));
-		exit(1);
-	}
-
-	if (fsync(fd) != 0)
-	{
-		fprintf(stderr, _("%s: fsync error: %s\n"), progname, strerror(errno));
-		exit(1);
-	}
-
-	close(fd);
+	/* The control file gets flushed here. */
+	update_controlfile(".", progname, &ControlFile, true);
 }
 
 

src/bin/pg_rewind/pg_rewind.c

@@ -377,7 +377,7 @@ main(int argc, char **argv)
 	ControlFile_new.minRecoveryPoint = endrec;
 	ControlFile_new.minRecoveryPointTLI = endtli;
 	ControlFile_new.state = DB_IN_ARCHIVE_RECOVERY;
-	update_controlfile(datadir_target, progname, &ControlFile_new);
+	update_controlfile(datadir_target, progname, &ControlFile_new, do_sync);
 
 	pg_log(PG_PROGRESS, "syncing target data directory\n");
 	syncTargetDirectory();

src/common/controldata_utils.c

@@ -29,7 +29,9 @@
 #include "common/controldata_utils.h"
 #include "common/file_perm.h"
 #include "port/pg_crc32c.h"
+
 #ifndef FRONTEND
+#include "pgstat.h"
 #include "storage/fd.h"
 #endif
 
@@ -144,13 +146,14 @@ get_controlfile(const char *DataDir, const char *progname, bool *crc_ok_p)
  * update_controlfile()
  *
  * Update controlfile values with the contents given by caller.  The
- * contents to write are included in "ControlFile".  Note that it is up
- * to the caller to fsync the updated file, and to properly lock
- * ControlFileLock when calling this routine in the backend.
+ * contents to write are included in "ControlFile". "do_sync" can be
+ * optionally used to flush the updated control file.  Note that it is up
+ * to the caller to properly lock ControlFileLock when calling this
+ * routine in the backend.
  */
 void
 update_controlfile(const char *DataDir, const char *progname,
-				   ControlFileData *ControlFile)
+				   ControlFileData *ControlFile, bool do_sync)
 {
 	int			fd;
 	char		buffer[PG_CONTROL_FILE_SIZE];
@@ -182,7 +185,12 @@ update_controlfile(const char *DataDir, const char *progname,
 	snprintf(ControlFilePath, sizeof(ControlFilePath), "%s/%s", DataDir, XLOG_CONTROL_FILE);
 
 #ifndef FRONTEND
-	if ((fd = OpenTransientFile(ControlFilePath, O_WRONLY | PG_BINARY)) == -1)
+
+	/*
+	 * All errors issue a PANIC, so no need to use OpenTransientFile() and to
+	 * worry about file descriptor leaks.
+	 */
+	if ((fd = BasicOpenFile(ControlFilePath, O_RDWR | PG_BINARY)) < 0)
 		ereport(PANIC,
 				(errcode_for_file_access(),
 				 errmsg("could not open file \"%s\": %m",
@@ -198,6 +206,9 @@ update_controlfile(const char *DataDir, const char *progname,
 #endif
 
 	errno = 0;
+#ifndef FRONTEND
+	pgstat_report_wait_start(WAIT_EVENT_CONTROL_FILE_WRITE_UPDATE);
+#endif
 	if (write(fd, buffer, PG_CONTROL_FILE_SIZE) != PG_CONTROL_FILE_SIZE)
 	{
 		/* if write didn't set errno, assume problem is no disk space */
@@ -215,19 +226,41 @@ update_controlfile(const char *DataDir, const char *progname,
 		exit(EXIT_FAILURE);
 #endif
 	}
+#ifndef FRONTEND
+	pgstat_report_wait_end();
+#endif
 
+	if (do_sync)
+	{
 #ifndef FRONTEND
-	if (CloseTransientFile(fd))
+		pgstat_report_wait_start(WAIT_EVENT_CONTROL_FILE_SYNC_UPDATE);
+		if (pg_fsync(fd) != 0)
 			ereport(PANIC,
 					(errcode_for_file_access(),
-				 errmsg("could not close file \"%s\": %m",
+					 errmsg("could not fsync file \"%s\": %m",
 							ControlFilePath)));
+		pgstat_report_wait_end();
 #else
+		if (fsync(fd) != 0)
+		{
+			fprintf(stderr, _("%s: could not fsync file \"%s\": %s\n"),
+					progname, ControlFilePath, strerror(errno));
+			exit(EXIT_FAILURE);
+		}
+#endif
+	}
+
 	if (close(fd) < 0)
 	{
+#ifndef FRONTEND
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not close file \"%s\": %m",
+						ControlFilePath)));
+#else
 		fprintf(stderr, _("%s: could not close file \"%s\": %s\n"),
 				progname, ControlFilePath, strerror(errno));
 		exit(EXIT_FAILURE);
-	}
 #endif
+	}
 }

src/include/common/controldata_utils.h

@@ -16,6 +16,6 @@ extern ControlFileData *get_controlfile(const char *DataDir,
 				const char *progname,
 				bool *crc_ok_p);
 extern void update_controlfile(const char *DataDir, const char *progname,
-							   ControlFileData *ControlFile);
+				   ControlFileData *ControlFile, bool do_sync);
 
 #endif							/* COMMON_CONTROLDATA_UTILS_H */