Function maybe_create_new_scb

plugins/chanbackup.c:189–246

checks if the SCB file exists, creates a new one in case it doesn't. */

/* checks if the SCB file exists, creates a new one in case it doesn't. */
static void maybe_create_new_scb(struct plugin *p,
				 struct modern_scb_chan **channels)
{

	/* Note that this is opened for write-only, even though the permissions
	 * are set to read-only.  That's perfectly valid! */
	int fd = open(FILENAME, O_CREAT|O_EXCL|O_WRONLY, 0400);
	if (fd < 0) {
		/* Don't do anything if the file already exists. */
		if (errno == EEXIST)
			return;
		plugin_err(p, "creating: %s", strerror(errno));
	}

	/* Comes here only if the file haven't existed before */
	unlink_noerr(FILENAME);

	/* This couldn't give EEXIST because we call unlink_noerr("scb.tmp")
	 * in INIT */
	fd = open("scb.tmp", O_CREAT|O_EXCL|O_WRONLY, 0400);
	if (fd < 0)
		plugin_err(p, "Opening: %s", strerror(errno));

	plugin_log(p, LOG_INFORM, "Creating Emergency Recovery");

	write_scb(p, fd, channels);

	/* fsync (mostly!) ensures that the file has reached the disk. */
	if (fsync(fd) != 0) {
		unlink_noerr("scb.tmp");
		plugin_err(p, "fsync : %s", strerror(errno));
	}

	/* This should never fail if fsync succeeded.  But paranoia good, and
	 * bugs exist. */
	if (close(fd) != 0) {
		unlink_noerr("scb.tmp");
		plugin_err(p, "closing: %s", strerror(errno));
	}

	/* We actually need to sync the *directory itself* to make sure the
	 * file exists!  You're only allowed to open directories read-only in
	 * modern Unix though. */
	fd = open(".", O_RDONLY);
	if (fd < 0)
		plugin_err(p, "Opening: %s", strerror(errno));

	if (fsync(fd) != 0) {
		unlink_noerr("scb.tmp");
		plugin_err(p, "closing: %s", strerror(errno));
	}

	/* This will never fail, if fsync worked! */
	close(fd);

	/* This will update the scb file */
	rename("scb.tmp", FILENAME);
}