1  /* Write block to given position in file without changing file pointer.
       2     POSIX version.
       3     Copyright (C) 1997-2023 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
      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