sendmail/libsmutil/lockfile.c

/*
 * Copyright (c) 1998-2001 Sendmail, Inc. and its suppliers.
 *  All rights reserved.
 * Copyright (c) 1983, 1995-1997 Eric P. Allman.  All rights reserved.
 * Copyright (c) 1988, 1993
 *  The Regents of the University of California.  All rights reserved.
 *
 * By using this file, you agree to the terms and conditions set
 * forth in the LICENSE file which can be found at the top level of
 * the sendmail distribution.
 *
 */

#pragma ident   "%Z%%M% %I% %E% SMI"

#include <sendmail.h>

SM_RCSID("@(#)$Id: lockfile.c,v 8.21 2003/11/10 22:57:38 ca Exp $")


/*
**  LOCKFILE -- lock a file using flock or (shudder) fcntl locking
**
**  Parameters:
**      fd -- the file descriptor of the file.
**      filename -- the file name (for error messages). [unused]
**      ext -- the filename extension. [unused]
**      type -- type of the lock.  Bits can be:
**          LOCK_EX -- exclusive lock.
**          LOCK_NB -- non-blocking.
**          LOCK_UN -- unlock.
**
**  Returns:
**      true if the lock was acquired.
**      false otherwise.
*/

bool
lockfile(fd, filename, ext, type)
    int fd;
    char *filename;
    char *ext;
    int type;
{
#if !HASFLOCK
    int action;
    struct flock lfd;

    memset(&lfd, '\0', sizeof lfd);
    if (bitset(LOCK_UN, type))
        lfd.l_type = F_UNLCK;
    else if (bitset(LOCK_EX, type))
        lfd.l_type = F_WRLCK;
    else
        lfd.l_type = F_RDLCK;
    if (bitset(LOCK_NB, type))
        action = F_SETLK;
    else
        action = F_SETLKW;

    if (fcntl(fd, action, &lfd) >= 0)
        return true;

    /*
    **  On SunOS, if you are testing using -oQ/tmp/mqueue or
    **  -oA/tmp/aliases or anything like that, and /tmp is mounted
    **  as type "tmp" (that is, served from swap space), the
    **  previous fcntl will fail with "Invalid argument" errors.
    **  Since this is fairly common during testing, we will assume
    **  that this indicates that the lock is successfully grabbed.
    */

    if (errno == EINVAL)
        return true;

#else /* !HASFLOCK */

    if (flock(fd, type) >= 0)
        return true;

#endif /* !HASFLOCK */

    return false;
}