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/* Emulate flock on platforms that lack it, primarily Windows and MinGW.
This is derived from sqlite3 sources.
https://www.sqlite.org/src/finfo?name=src/os_win.c
https://www.sqlite.org/copyright.html
Written by Richard W.M. Jones <rjones.at.redhat.com>
Copyright (C) 2008-2025 Free Software Foundation, Inc.
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
#include "libbb.h"
#include <sys/file.h>
/* LockFileEx */
# include <errno.h>
/* _get_osfhandle */
# include <io.h>
/* Determine the current size of a file. Because the other braindead
* APIs we'll call need lower/upper 32 bit pairs, keep the file size
* like that too.
*/
static BOOL
file_size (HANDLE h, DWORD * lower, DWORD * upper)
{
*lower = GetFileSize (h, upper);
return 1;
}
/* LOCKFILE_FAIL_IMMEDIATELY is undefined on some Windows systems. */
# ifndef LOCKFILE_FAIL_IMMEDIATELY
# define LOCKFILE_FAIL_IMMEDIATELY 1
# endif
/* Acquire a lock. */
static BOOL
do_lock (HANDLE h, int non_blocking, int exclusive)
{
BOOL res;
DWORD size_lower, size_upper;
OVERLAPPED ovlp;
int flags = 0;
/* We're going to lock the whole file, so get the file size. */
res = file_size (h, &size_lower, &size_upper);
if (!res)
return 0;
/* Start offset is 0, and also zero the remaining members of this struct. */
memset (&ovlp, 0, sizeof ovlp);
if (non_blocking)
flags |= LOCKFILE_FAIL_IMMEDIATELY;
if (exclusive)
flags |= LOCKFILE_EXCLUSIVE_LOCK;
return LockFileEx (h, flags, 0, size_lower, size_upper, &ovlp);
}
/* Unlock reader or exclusive lock. */
static BOOL
do_unlock (HANDLE h)
{
int res;
DWORD size_lower, size_upper;
res = file_size (h, &size_lower, &size_upper);
if (!res)
return 0;
return UnlockFile (h, 0, 0, size_lower, size_upper);
}
/* Now our BSD-like flock operation. */
int
flock (int fd, int operation)
{
HANDLE h = (HANDLE) _get_osfhandle (fd);
DWORD res;
int non_blocking;
if (h == INVALID_HANDLE_VALUE)
{
errno = EBADF;
return -1;
}
non_blocking = operation & LOCK_NB;
operation &= ~LOCK_NB;
switch (operation)
{
case LOCK_SH:
res = do_lock (h, non_blocking, 0);
break;
case LOCK_EX:
res = do_lock (h, non_blocking, 1);
break;
case LOCK_UN:
res = do_unlock (h);
break;
default:
errno = EINVAL;
return -1;
}
/* Map Windows errors into Unix errnos. As usual MSDN fails to
* document the permissible error codes.
*/
if (!res)
{
errno = err_win_to_posix();
return -1;
}
return 0;
}
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