/* 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);}