1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
|
/* Read block from given position in file without changing file pointer.
POSIX version.
Copyright (C) 1997-2022 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 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.
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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <errno.h>
#include <unistd.h>
/* Note: This implementation of pread is not multithread-safe. */
ssize_t
__libc_pread (int fd, void *buf, size_t nbyte, off_t offset)
{
/* Since we must not change the file pointer preserve the value so that
we can restore it later. */
int save_errno;
ssize_t result;
off_t old_offset = __libc_lseek (fd, 0, SEEK_CUR);
if (old_offset == (off_t) -1)
return -1;
/* Set to wanted position. */
if (__libc_lseek (fd, offset, SEEK_SET) == (off_t) -1)
return -1;
/* Write out the data. */
result = __libc_read (fd, buf, nbyte);
/* Now we have to restore the position. If this fails we have to
return this as an error. But if the writing also failed we
return this error. */
save_errno = errno;
if (__libc_lseek (fd, old_offset, SEEK_SET) == (off_t) -1)
{
if (result == -1)
__set_errno (save_errno);
return -1;
}
__set_errno (save_errno);
return result;
}
#ifndef __libc_pread
strong_alias (__libc_pread, __pread)
weak_alias (__libc_pread, pread)
#endif
|
