| /* Write block to given position in file without changing file pointer. |
| POSIX version. |
| Copyright (C) 1997-1999, 2002, 2011-2020 Free Software Foundation, Inc. |
| This file is part of the GNU C Library. |
| Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997. |
| |
| This program is free software: you can redistribute it and/or modify |
| it under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 3 of the License, or |
| (at your option) any later version. |
| |
| This program 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 General Public License for more details. |
| |
| You should have received a copy of the GNU General Public License |
| along with this program. If not, see <https://www.gnu.org/licenses/>. */ |
| |
| #include <config.h> |
| |
| /* Specification. */ |
| #include <unistd.h> |
| |
| #include <errno.h> |
| |
| #define __libc_lseek(f,o,w) lseek (f, o, w) |
| #define __set_errno(Val) errno = (Val) |
| #define __libc_write(f,b,n) write (f, b, n) |
| |
| /* Note: This implementation of pwrite is not multithread-safe. */ |
| |
| ssize_t |
| pwrite (int fd, const 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_write (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; |
| } |