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glnx-lockfile.c 5.77 KiB
/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/

/***
  This file is part of systemd.
  Now copied into libglnx:
    - Use GError

  Copyright 2010 Lennart Poettering
  Copyright 2015 Colin Walters <walters@verbum.org>

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  systemd is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/

#include "config.h"

#include <stdlib.h>
#include <stdbool.h>
#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <limits.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <fcntl.h>

#include "glnx-lockfile.h"
#include "glnx-errors.h"
#include "glnx-fdio.h"
#include "glnx-backport-autocleanups.h"
#include "glnx-local-alloc.h"

#define newa(t, n) ((t*) alloca(sizeof(t)*(n)))

/**
 * glnx_make_lock_file:
 * @dfd: Directory file descriptor (if not `AT_FDCWD`, must have lifetime `>=` @out_lock)
 * @p: Path
 * @operation: one of `LOCK_SH`, `LOCK_EX`, `LOCK_UN`, as passed to flock()
 * @out_lock: (out) (caller allocates): Return location for lock
 * @error: Error
 *
 * Block until a lock file named @p (relative to @dfd) can be created,
 * using the flags in @operation, returning the lock data in the
 * caller-allocated location @out_lock.
 *
 * This API wraps new-style process locking if available, otherwise
 * falls back to BSD locks.
 */
gboolean
glnx_make_lock_file(int dfd, const char *p, int operation, GLnxLockFile *out_lock, GError **error) {
        glnx_autofd int fd = -1;
        g_autofree char *t = NULL;
        int r;

        /*
         * We use UNPOSIX locks if they are available. They have nice
         * semantics, and are mostly compatible with NFS. However,