contrib/sendmail-8.14/libsmutil/lockfile.c

   1 /*
   2  * Copyright (c) 1998-2001 Sendmail, Inc. and its suppliers.
   3  *      All rights reserved.
   4  * Copyright (c) 1983, 1995-1997 Eric P. Allman.  All rights reserved.
   5  * Copyright (c) 1988, 1993
   6  *      The Regents of the University of California.  All rights reserved.
   7  *
   8  * By using this file, you agree to the terms and conditions set
   9  * forth in the LICENSE file which can be found at the top level of
  10  * the sendmail distribution.
  11  *
  12  */
  13
  14 #include <sendmail.h>
  15
  16 SM_RCSID("@(#)$Id: lockfile.c,v 8.21 2003/11/10 22:57:38 ca Exp $")
  17
  18
  19 /*
  20 **  LOCKFILE -- lock a file using flock or (shudder) fcntl locking
  21 **
  22 **      Parameters:
  23 **              fd -- the file descriptor of the file.
  24 **              filename -- the file name (for error messages). [unused]
  25 **              ext -- the filename extension. [unused]
  26 **              type -- type of the lock.  Bits can be:
  27 **                      LOCK_EX -- exclusive lock.
  28 **                      LOCK_NB -- non-blocking.
  29 **                      LOCK_UN -- unlock.
  30 **
  31 **      Returns:
  32 **              true if the lock was acquired.
  33 **              false otherwise.
  34 */
  35
  36 bool
  37 lockfile(fd, filename, ext, type)
  38         int fd;
  39         char *filename;
  40         char *ext;
  41         int type;
  42 {
  43 #if !HASFLOCK
  44         int action;
  45         struct flock lfd;
  46
  47         memset(&lfd, '\0', sizeof lfd);
  48         if (bitset(LOCK_UN, type))
  49                 lfd.l_type = F_UNLCK;
  50         else if (bitset(LOCK_EX, type))
  51                 lfd.l_type = F_WRLCK;
  52         else
  53                 lfd.l_type = F_RDLCK;
  54         if (bitset(LOCK_NB, type))
  55                 action = F_SETLK;
  56         else
  57                 action = F_SETLKW;
  58
  59         if (fcntl(fd, action, &lfd) >= 0)
  60                 return true;
  61
  62         /*
  63         **  On SunOS, if you are testing using -oQ/tmp/mqueue or
  64         **  -oA/tmp/aliases or anything like that, and /tmp is mounted
  65         **  as type "tmp" (that is, served from swap space), the
  66         **  previous fcntl will fail with "Invalid argument" errors.
  67         **  Since this is fairly common during testing, we will assume
  68         **  that this indicates that the lock is successfully grabbed.
  69         */
  70
  71         if (errno == EINVAL)
  72                 return true;
  73
  74 #else /* !HASFLOCK */
  75
  76         if (flock(fd, type) >= 0)
  77                 return true;
  78
  79 #endif /* !HASFLOCK */
  80
  81         return false;
  82 }