io/lockf.c

   1 /* Copyright (C) 1994-2018 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    <http://www.gnu.org/licenses/>.  */
  17
  18 /* We need to avoid the header declaration of lockf64, because
  19    the types don't match lockf and then the compiler will
  20    complain about the mismatch when we do the alias below.  */
  21 #define lockf64 __renamed_lockf64
  22
  23 #include <fcntl.h>
  24
  25 #undef  lockf64
  26
  27 #include <sys/types.h>
  28 #include <unistd.h>
  29 #include <errno.h>
  30 #include <string.h>
  31
  32 /* lockf is a simplified interface to fcntl's locking facilities.  */
  33
  34 int
  35 lockf (int fd, int cmd, off_t len)
  36 {
  37   struct flock fl;
  38
  39   memset ((char *) &fl, '\0', sizeof (fl));
  40
  41   /* lockf is always relative to the current file position.  */
  42   fl.l_whence = SEEK_CUR;
  43   fl.l_start = 0;
  44   fl.l_len = len;
  45
  46   switch (cmd)
  47     {
  48     case F_TEST:
  49       /* Test the lock: return 0 if FD is unlocked or locked by this process;
  50          return -1, set errno to EACCES, if another process holds the lock.  */
  51       fl.l_type = F_RDLCK;
  52       if (__fcntl (fd, F_GETLK, &fl) < 0)
  53         return -1;
  54       if (fl.l_type == F_UNLCK || fl.l_pid == __getpid ())
  55         return 0;
  56       __set_errno (EACCES);
  57       return -1;
  58
  59     case F_ULOCK:
  60       fl.l_type = F_UNLCK;
  61       cmd = F_SETLK;
  62       break;
  63     case F_LOCK:
  64       fl.l_type = F_WRLCK;
  65       cmd = F_SETLKW;
  66       break;
  67     case F_TLOCK:
  68       fl.l_type = F_WRLCK;
  69       cmd = F_SETLK;
  70       break;
  71
  72     default:
  73       __set_errno (EINVAL);
  74       return -1;
  75     }
  76
  77   /* lockf() is a cancellation point but so is fcntl() if F_SETLKW is
  78      used.  Therefore we don't have to care about cancellation here,
  79      the fcntl() function will take care of it.  */
  80   return __fcntl (fd, cmd, &fl);
  81 }
  82
  83 #ifdef __OFF_T_MATCHES_OFF64_T
  84 weak_alias (lockf, lockf64)
  85 #endif