sysdeps/posix/flock.c

   1 /* Copyright (C) 1992-2024 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 Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the 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    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 /* This file implements the `flock' function in terms of the POSIX.1 `fcntl'
  19    locking mechanism.  In 4BSD, these are two incompatible locking mechanisms,
  20    perhaps with different semantics?  */
  21
  22 #include <errno.h>
  23 #include <unistd.h>
  24 #include <fcntl.h>
  25 #include <sys/file.h>
  26
  27 /* Apply or remove an advisory lock, according to OPERATION,
  28    on the file FD refers to.  */
  29 int
  30 __flock (int fd, int operation)
  31 {
  32   struct flock lbuf;
  33
  34   switch (operation & ~LOCK_NB)
  35     {
  36     case LOCK_SH:
  37       lbuf.l_type = F_RDLCK;
  38       break;
  39     case LOCK_EX:
  40       lbuf.l_type = F_WRLCK;
  41       break;
  42     case LOCK_UN:
  43       lbuf.l_type = F_UNLCK;
  44       break;
  45     default:
  46       __set_errno (EINVAL);
  47       return -1;
  48     }
  49
  50   lbuf.l_whence = SEEK_SET;
  51   lbuf.l_start = lbuf.l_len = 0L; /* Lock the whole file.  */
  52
  53   return __fcntl (fd, (operation & LOCK_NB) ? F_SETLK : F_SETLKW, &lbuf);
  54 }
  55
  56 weak_alias (__flock, flock)