1 /* Write block to given position in file without changing file pointer.
2 POSIX version.
3 Copyright (C) 1997-2022 Free Software Foundation, Inc.
4 This file is part of the GNU C Library.
5 Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
6
7 The GNU C Library is free software; you can redistribute it and/or
8 modify it under the terms of the GNU Lesser General Public
9 License as published by the Free Software Foundation; either
10 version 2.1 of the License, or (at your option) any later version.
11
12 The GNU C Library is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 Lesser General Public License for more details.
16
17 You should have received a copy of the GNU Lesser General Public
18 License along with the GNU C Library; if not, see
19 <https://www.gnu.org/licenses/>. */
20
21 #include <errno.h>
22 #include <unistd.h>
23
24 /* Note: This implementation of pwrite is not multithread-safe. */
25
26 ssize_t
__libc_pwrite(int fd,const void * buf,size_t nbyte,off_t offset)27 __libc_pwrite (int fd, const void *buf, size_t nbyte, off_t offset)
28 {
29 /* Since we must not change the file pointer preserve the value so that
30 we can restore it later. */
31 int save_errno;
32 ssize_t result;
33 off_t old_offset = __libc_lseek (fd, 0, SEEK_CUR);
34 if (old_offset == (off_t) -1)
35 return -1;
36
37 /* Set to wanted position. */
38 if (__libc_lseek (fd, offset, SEEK_SET) == (off_t) -1)
39 return -1;
40
41 /* Write out the data. */
42 result = __libc_write (fd, buf, nbyte);
43
44 /* Now we have to restore the position. If this fails we have to
45 return this as an error. But if the writing also failed we
46 return this error. */
47 save_errno = errno;
48 if (__libc_lseek (fd, old_offset, SEEK_SET) == (off_t) -1)
49 {
50 if (result == -1)
51 __set_errno (save_errno);
52 return -1;
53 }
54 __set_errno (save_errno);
55
56 return result;
57 }
58
59 #ifndef __libc_pwrite
60 strong_alias (__libc_pwrite, __pwrite)
61 weak_alias (__libc_pwrite, pwrite)
62 #endif
63