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/* Read block from given position in file without changing file pointer.
POSIX version.
Copyright (C) 1997-2021 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 pread64 is not multithread-safe. */
ssize_t
__libc_pread64 (int fd, void *buf, size_t nbyte, off64_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;
off64_t old_offset = __libc_lseek64 (fd, 0, SEEK_CUR);
if (old_offset == (off64_t) -1)
return -1;
/* Set to wanted position. */
if (__libc_lseek64 (fd, offset, SEEK_SET) == (off64_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_lseek64 (fd, old_offset, SEEK_SET) == (off64_t) -1)
{
if (result == -1)
__set_errno (save_errno);
return -1;
}
__set_errno (save_errno);
return result;
}
#ifndef __libc_pread64
weak_alias (__libc_pread64, __pread64)
libc_hidden_weak (__pread64)
weak_alias (__libc_pread64, pread64)
#endif
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