grab_excl_lock_file: don't use fio_*

This function checks for concurrent locker by "kill" command, which is
strictly local. There is no way to make it remote reliably.
More over, we have to write pid of remote agent.
So, if for whatever reason we will need to lock backup on remote host,
we'd better call this function from agent.

And, it will be better to use fcntl(F_SETLK) on Unix and
LockFileEx on Windows. But lets leave it for future.

Author: funny-falcon

src/catalog.c

@@ -298,12 +298,17 @@ int
 grab_excl_lock_file(const char *root_dir, const char *backup_id, bool strict)
 {
 	char		lock_file[MAXPGPATH];
-	int			fd = 0;
+	FILE	   *fp = NULL;
 	char		buffer[256];
 	int			ntries = LOCK_TIMEOUT;
 	int			empty_tries = LOCK_STALE_TIMEOUT;
-	int			len;
-	int			encoded_pid;
+	size_t		len;
+	pid_t		encoded_pid;
+	int			save_errno = 0;
+	enum {
+		GELF_FAILED_WRITE = 1,
+		GELF_FAILED_CLOSE = 2,
+	} failed_action = 0;
 
 	join_path_components(lock_file, root_dir, BACKUP_LOCK_FILE);
 
@@ -314,19 +319,17 @@ grab_excl_lock_file(const char *root_dir, const char *backup_id, bool strict)
 	 */
 	do
 	{
-		FILE *fp_out = NULL;
-
 		if (interrupted)
 			elog(ERROR, "Interrupted while locking backup %s", backup_id);
 
 		/*
-		 * Try to create the lock file --- O_EXCL makes this atomic.
+		 * Try to create the lock file --- "wx" makes this atomic.
 		 *
 		 * Think not to make the file protection weaker than 0600.  See
 		 * comments below.
 		 */
-		fd = fio_open(FIO_BACKUP_HOST, lock_file, O_RDWR | O_CREAT | O_EXCL);
-		if (fd >= 0)
+		fp = fopen(lock_file, "wx");
+		if (fp != NULL)
 			break;				/* Success; exit the retry loop */
 
 		/* read-only fs is a special case */
@@ -342,7 +345,6 @@ grab_excl_lock_file(const char *root_dir, const char *backup_id, bool strict)
 		 * If file already exists or we have some permission problem (???),
 		 * then retry;
 		 */
-//		if ((errno != EEXIST && errno != EACCES))
 		if (errno != EEXIST)
 			elog(ERROR, "Could not create lock file \"%s\": %s",
 				 lock_file, strerror(errno));
@@ -352,18 +354,19 @@ grab_excl_lock_file(const char *root_dir, const char *backup_id, bool strict)
 		 * here: file might have been deleted since we tried to create it.
 		 */
 
-		fp_out = fopen(lock_file, "r");
-		if (fp_out == NULL)
+		fp = fopen(lock_file, "r");
+		if (fp == NULL)
 		{
 			if (errno == ENOENT)
 				continue; 	/* race condition; try again */
 			elog(ERROR, "Cannot open lock file \"%s\": %s", lock_file, strerror(errno));
 		}
 
-		len = fread(buffer, 1, sizeof(buffer) - 1, fp_out);
-		if (ferror(fp_out))
+		len = fread(buffer, 1, sizeof(buffer) - 1, fp);
+		if (ferror(fp))
 			elog(ERROR, "Cannot read from lock file: \"%s\"", lock_file);
-		fclose(fp_out);
+		fclose(fp);
+		fp = NULL;
 
 		/*
 		 * There are several possible reasons for lock file
@@ -400,7 +403,7 @@ grab_excl_lock_file(const char *root_dir, const char *backup_id, bool strict)
 			continue;
 		}
 
-		encoded_pid = atoi(buffer);
+		encoded_pid = (pid_t)atoll(buffer);
 
 		if (encoded_pid <= 0)
 		{
@@ -450,7 +453,7 @@ grab_excl_lock_file(const char *root_dir, const char *backup_id, bool strict)
 		 * it.  Need a loop because of possible race condition against other
 		 * would-be creators.
 		 */
-		if (fio_remove(FIO_BACKUP_HOST, lock_file, false) < 0)
+		if (remove(lock_file) < 0)
 		{
 			if (errno == ENOENT)
 				continue; /* race condition, again */
@@ -461,40 +464,32 @@ grab_excl_lock_file(const char *root_dir, const char *backup_id, bool strict)
 	} while (ntries--);
 
 	/* Failed to acquire exclusive lock in time */
-	if (fd <= 0)
+	if (fp == NULL)
 		return LOCK_FAIL_TIMEOUT;
 
 	/*
 	 * Successfully created the file, now fill it.
 	 */
-	snprintf(buffer, sizeof(buffer), "%lld\n", (long long)my_pid);
-
 	errno = 0;
-	if (fio_write(fd, buffer, strlen(buffer)) != strlen(buffer))
-	{
-		int save_errno = errno;
+	fprintf(fp, "%lld\n", (long long)my_pid);
+	fflush(fp);
 
-		fio_close(fd);
-		if (fio_remove(FIO_BACKUP_HOST, lock_file, false) != 0)
-			elog(WARNING, "Cannot remove lock file \"%s\": %s", lock_file, strerror(errno));
-
-		/* In lax mode if we failed to grab lock because of 'out of space error',
-		 * then treat backup as locked.
-		 * Only delete command should be run in lax mode.
-		 */
-		if (!strict && save_errno == ENOSPC)
-			return LOCK_FAIL_ENOSPC;
-		else
-			elog(ERROR, "Could not write lock file \"%s\": %s",
-				 lock_file, strerror(save_errno));
+	if (ferror(fp))
+	{
+		failed_action = GELF_FAILED_WRITE;
+		save_errno = errno;
+		clearerr(fp);
 	}
 
-	if (fio_flush(fd) != 0)
+	if (fclose(fp) && save_errno == 0)
 	{
-		int save_errno = errno;
+		failed_action = GELF_FAILED_CLOSE;
+		save_errno = errno;
+	}
 
-		fio_close(fd);
-		if (fio_remove(FIO_BACKUP_HOST, lock_file, false) != 0)
+	if (save_errno)
+	{
+		if (remove(lock_file) != 0)
 			elog(WARNING, "Cannot remove lock file \"%s\": %s", lock_file, strerror(errno));
 
 		/* In lax mode if we failed to grab lock because of 'out of space error',
@@ -503,21 +498,10 @@ grab_excl_lock_file(const char *root_dir, const char *backup_id, bool strict)
 		 */
 		if (!strict && save_errno == ENOSPC)
 			return LOCK_FAIL_ENOSPC;
-		else
-			elog(ERROR, "Could not flush lock file \"%s\": %s",
-					lock_file, strerror(save_errno));
-	}
-
-	if (fio_close(fd) != 0)
-	{
-		int save_errno = errno;
-
-		if (fio_remove(FIO_BACKUP_HOST, lock_file, false) != 0)
-			elog(WARNING, "Cannot remove lock file \"%s\": %s", lock_file, strerror(errno));
-
-		if (!strict && save_errno == ENOSPC)
-			return LOCK_FAIL_ENOSPC;
-		else
+		else if (failed_action == GELF_FAILED_WRITE)
+			elog(ERROR, "Could not write lock file \"%s\": %s",
+				 lock_file, strerror(save_errno));
+		else if (failed_action == GELF_FAILED_CLOSE)
 			elog(ERROR, "Could not close lock file \"%s\": %s",
 				 lock_file, strerror(save_errno));
 	}