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/* Copyright (C) 1994, 1996, 1997, 1998, 2000 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or

   modify it under the terms of the GNU Library General Public License as

   published by the Free Software Foundation; either version 2 of the

   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public

   License along with the GNU C Library; see the file COPYING.LIB.  If not,

   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,

   Boston, MA 02111-1307, USA.  */

#include <sys/types.h>

#include <unistd.h>

#include <fcntl.h>

#include <errno.h>

#include <string.h>

/* lockf is a simplified interface to fcntl's locking facilities.  */

int lockf (int fd, int cmd, off_t len)

{

    struct flock fl;

    memset ((char *) &fl, '\0', sizeof (fl));

    /* lockf is always relative to the current file position.  */

    fl.l_whence = SEEK_CUR;

    fl.l_start = 0;

    fl.l_len = len;

    switch (cmd)

    {

        case F_TEST:

            /* Test the lock: return 0 if FD is unlocked or locked by this process;

               return -1, set errno to EACCES, if another process holds the lock.  */

            fl.l_type = F_RDLCK;

            if (fcntl (fd, F_GETLK, &fl) < 0)

                return -1;

            if (fl.l_type == F_UNLCK || fl.l_pid == getpid ())

                return 0;

            __set_errno(EACCES);

            return -1;

        case F_ULOCK:

            fl.l_type = F_UNLCK;

            cmd = F_SETLK;

            break;

        case F_LOCK:

            fl.l_type = F_WRLCK;

            cmd = F_SETLKW;

            break;

        case F_TLOCK:

            fl.l_type = F_WRLCK;

            cmd = F_SETLK;

            break;

        default:

            __set_errno(EINVAL);

            return -1;

    }

    return fcntl(fd, cmd, &fl);

}