sysdeps/posix/flock.c

   1 /* Copyright (C) 1992, 1995, 1996 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3
   4 The GNU C Library is free software; you can redistribute it and/or
   5 modify it under the terms of the GNU Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 License, or (at your option) any later version.
   8
   9 The GNU C Library is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 /* This file implements the `flock' function in terms of the POSIX.1 `fcntl'
  20    locking mechanism.  In 4BSD, these are two incompatible locking mechanisms,
  21    perhaps with different semantics?  */
  22
  23 #include <errno.h>
  24 #include <unistd.h>
  25 #include <fcntl.h>
  26 #include <sys/file.h>
  27
  28 /* Apply or remove an advisory lock, according to OPERATION,
  29    on the file FD refers to.  */
  30 int
  31 __flock (fd, operation)
  32      int fd;
  33      int operation;
  34 {
  35   struct flock lbuf;
  36
  37   switch (operation & ~LOCK_NB)
  38     {
  39     case LOCK_SH:
  40       lbuf.l_type = F_RDLCK;
  41       break;
  42     case LOCK_EX:
  43       lbuf.l_type = F_WRLCK;
  44       break;
  45     case LOCK_UN:
  46       lbuf.l_type = F_UNLCK;
  47       break;
  48     default:
  49       __set_errno (EINVAL);
  50       return -1;
  51     }
  52
  53   lbuf.l_whence = SEEK_SET;
  54   lbuf.l_start = lbuf.l_len = 0L; /* Lock the whole file.  */
  55
  56   return __fcntl (fd, (operation & LOCK_NB) ? F_SETLK : F_SETLKW, &lbuf);
  57 }
  58
  59 weak_alias (__flock, flock)