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/* $Id: flock.c,v 1.2 1998/12/30 01:31:04 dm Exp $ */
/*
*
* Copyright (C) 1998 David Mazieres (dm@uun.org)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2, or (at
* your option) any later version.
*
* This program 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
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
* USA
*
*/
#include "sysconf.h"
#ifndef HAVE_FLOCK
/* This is a substitute definition for flock in terms of the POSIX
* fcntl file locking. Note that the semantics are not the same. In
* particular, POSIX fcntl locking has very stupid semantics where
* closing any file descriptor for a file relinquishes all locks.
* Thus, unrelated parts of your program can unintentionally nuke your
* locks.
*/
int
flock (int fd, int options)
{
static const char optok[16] = {
0, 1, 1, 0,
0, 1, 1, 0,
1, 0, 0, 0,
0, 0, 0, 0,
};
int ret;
struct flock lf;
if ((u_int) options > 8 || !optok[options]) {
errno = EINVAL;
return -1;
}
bzero (&lf, sizeof (lf));
if (options & LOCK_UN) {
lf.l_type = F_UNLCK;
ret = fcntl (fd, F_SETLK, &lf);
}
else {
int cmd = (options & LOCK_NB) ? F_SETLK : F_SETLKW;
lf.l_type = (options & LOCK_EX) ? F_WRLCK : F_RDLCK;
ret = fcntl (fd, cmd, &lf);
}
return -(ret == -1);
}
#endif /* !HAVE_FLOCK */
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