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glibc  2.9
flock.c
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00001 /* Copyright (C) 1992, 1995, 1996, 1997 Free Software Foundation, Inc.
00002    This file is part of the GNU C Library.
00003 
00004    The GNU C Library is free software; you can redistribute it and/or
00005    modify it under the terms of the GNU Lesser General Public
00006    License as published by the Free Software Foundation; either
00007    version 2.1 of the License, or (at your option) any later version.
00008 
00009    The GNU C Library is distributed in the hope that it will be useful,
00010    but WITHOUT ANY WARRANTY; without even the implied warranty of
00011    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00012    Lesser General Public License for more details.
00013 
00014    You should have received a copy of the GNU Lesser General Public
00015    License along with the GNU C Library; if not, write to the Free
00016    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00017    02111-1307 USA.  */
00018 
00019 /* This file implements the `flock' function in terms of the POSIX.1 `fcntl'
00020    locking mechanism.  In 4BSD, these are two incompatible locking mechanisms,
00021    perhaps with different semantics?  */
00022 
00023 #include <errno.h>
00024 #include <unistd.h>
00025 #include <fcntl.h>
00026 #include <sys/file.h>
00027 
00028 /* Apply or remove an advisory lock, according to OPERATION,
00029    on the file FD refers to.  */
00030 int
00031 __flock (fd, operation)
00032      int fd;
00033      int operation;
00034 {
00035   struct flock lbuf;
00036 
00037   switch (operation & ~LOCK_NB)
00038     {
00039     case LOCK_SH:
00040       lbuf.l_type = F_RDLCK;
00041       break;
00042     case LOCK_EX:
00043       lbuf.l_type = F_WRLCK;
00044       break;
00045     case LOCK_UN:
00046       lbuf.l_type = F_UNLCK;
00047       break;
00048     default:
00049       __set_errno (EINVAL);
00050       return -1;
00051     }
00052 
00053   lbuf.l_whence = SEEK_SET;
00054   lbuf.l_start = lbuf.l_len = 0L; /* Lock the whole file.  */
00055 
00056   return __fcntl (fd, (operation & LOCK_NB) ? F_SETLK : F_SETLKW, &lbuf);
00057 }
00058 
00059 weak_alias (__flock, flock)