[BZ #6771]
[glibc.git] / sysdeps / posix / pread.c
blob3b226a0dc018697b8895cf45c6c011df7287d249
1 /* Read block from given position in file without changing file pointer.
2 POSIX version.
3 Copyright (C) 1997, 1998, 1999, 2002 Free Software Foundation, Inc.
4 This file is part of the GNU C Library.
5 Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
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.
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.
17 You should have received a copy of the GNU Lesser General Public
18 License along with the GNU C Library; if not, write to the Free
19 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
20 02111-1307 USA. */
22 #include <errno.h>
23 #include <unistd.h>
25 /* Note: This implementation of pread is not multithread-safe. */
27 ssize_t
28 __libc_pread (int fd, void *buf, size_t nbyte, off_t offset)
30 /* Since we must not change the file pointer preserve the value so that
31 we can restore it later. */
32 int save_errno;
33 ssize_t result;
34 off_t old_offset = __libc_lseek (fd, 0, SEEK_CUR);
35 if (old_offset == (off_t) -1)
36 return -1;
38 /* Set to wanted position. */
39 if (__libc_lseek (fd, offset, SEEK_SET) == (off_t) -1)
40 return -1;
42 /* Write out the data. */
43 result = __libc_read (fd, buf, nbyte);
45 /* Now we have to restore the position. If this fails we have to
46 return this as an error. But if the writing also failed we
47 return this error. */
48 save_errno = errno;
49 if (__libc_lseek (fd, old_offset, SEEK_SET) == (off_t) -1)
51 if (result == -1)
52 __set_errno (save_errno);
53 return -1;
55 __set_errno (save_errno);
57 return result;
60 #ifndef __libc_pread
61 strong_alias (__libc_pread, __pread)
62 weak_alias (__libc_pread, pread)
63 #endif