1 /* Invoke open, but return either a desired file descriptor or -1.
2
3 Copyright (C) 2005-2023 Free Software Foundation, Inc.
4
5 This program is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation, either version 3 of the License, or
8 (at your option) any later version.
9
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
14
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <https://www.gnu.org/licenses/>. */
17
18 /* Written by Paul Eggert. */
19
20 #include <config.h>
21
22 #include "fd-reopen.h"
23
24 #include <errno.h>
25 #include <fcntl.h>
26 #include <unistd.h>
27
28 /* Open a file to a particular file descriptor. This is like standard
29 'open', except it always returns DESIRED_FD if successful. */
30
31 int
fd_reopen(int desired_fd,char const * file,int flags,mode_t mode)32 fd_reopen (int desired_fd, char const *file, int flags, mode_t mode)
33 {
34 int fd = open (file, flags, mode);
35
36 if (fd == desired_fd || fd < 0)
37 return fd;
38 else
39 {
40 int fd2 = dup2 (fd, desired_fd);
41 int saved_errno = errno;
42 close (fd);
43 errno = saved_errno;
44 return fd2;
45 }
46 }
47