usr/src/cmd/sendmail/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 #pragma ident   "%Z%%M% %I%     %E% SMI"
  15
  16 #include <sendmail.h>
  17
  18 SM_RCSID("@(#)$Id: lockfile.c,v 8.21 2003/11/10 22:57:38 ca Exp $")
  19
  20
  21 /*
  22 **  LOCKFILE -- lock a file using flock or (shudder) fcntl locking
  23 **
  24 **      Parameters:
  25 **              fd -- the file descriptor of the file.
  26 **              filename -- the file name (for error messages). [unused]
  27 **              ext -- the filename extension. [unused]
  28 **              type -- type of the lock.  Bits can be:
  29 **                      LOCK_EX -- exclusive lock.
  30 **                      LOCK_NB -- non-blocking.
  31 **                      LOCK_UN -- unlock.
  32 **
  33 **      Returns:
  34 **              true if the lock was acquired.
  35 **              false otherwise.
  36 */
  37
  38 bool
  39 lockfile(fd, filename, ext, type)
  40         int fd;
  41         char *filename;
  42         char *ext;
  43         int type;
  44 {
  45 #if !HASFLOCK
  46         int action;
  47         struct flock lfd;
  48
  49         memset(&lfd, '\0', sizeof lfd);
  50         if (bitset(LOCK_UN, type))
  51                 lfd.l_type = F_UNLCK;
  52         else if (bitset(LOCK_EX, type))
  53                 lfd.l_type = F_WRLCK;
  54         else
  55                 lfd.l_type = F_RDLCK;
  56         if (bitset(LOCK_NB, type))
  57                 action = F_SETLK;
  58         else
  59                 action = F_SETLKW;
  60
  61         if (fcntl(fd, action, &lfd) >= 0)
  62                 return true;
  63
  64         /*
  65         **  On SunOS, if you are testing using -oQ/tmp/mqueue or
  66         **  -oA/tmp/aliases or anything like that, and /tmp is mounted
  67         **  as type "tmp" (that is, served from swap space), the
  68         **  previous fcntl will fail with "Invalid argument" errors.
  69         **  Since this is fairly common during testing, we will assume
  70         **  that this indicates that the lock is successfully grabbed.
  71         */
  72
  73         if (errno == EINVAL)
  74                 return true;
  75
  76 #else /* !HASFLOCK */
  77
  78         if (flock(fd, type) >= 0)
  79                 return true;
  80
  81 #endif /* !HASFLOCK */
  82
  83         return false;
  84 }