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  
       6     The GNU C Library is free software; you can redistribute it and/or
       7     modify it under the terms of the GNU Lesser General Public
       8     License as published by the Free Software Foundation; either
       9     version 2.1 of the License, or (at your option) any later version.
      10  
      11     The GNU C Library is distributed in the hope that it will be useful,
      12     but WITHOUT ANY WARRANTY; without even the implied warranty of
      13     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      14     Lesser General Public License for more details.
      15  
      16     You should have received a copy of the GNU Lesser General Public
      17     License along with the GNU C Library; if not, see
      18     <https://www.gnu.org/licenses/>.  */
      19  
      20  #include <errno.h>
      21  #include <unistd.h>
      22  
      23  /* Note: This implementation of pwrite64 is not multithread-safe.  */
      24  
      25  ssize_t
      26  __libc_pwrite64 (int fd, const void *buf, size_t nbyte, off64_t offset)
      27  {
      28    /* Since we must not change the file pointer preserve the value so that
      29       we can restore it later.  */
      30    int save_errno;
      31    ssize_t result;
      32    off64_t old_offset = __libc_lseek64 (fd, 0, SEEK_CUR);
      33    if (old_offset == (off64_t) -1)
      34      return -1;
      35  
      36    /* Set to wanted position.  */
      37    if (__libc_lseek64 (fd, offset, SEEK_SET) == (off64_t) -1)
      38      return -1;
      39  
      40    /* Write out the data.  */
      41    result = __libc_write (fd, buf, nbyte);
      42  
      43    /* Now we have to restore the position.  If this fails we have to
      44       return this as an error.  But if the writing also failed we
      45       return this error.  */
      46    save_errno = errno;
      47    if (__libc_lseek64 (fd, old_offset, SEEK_SET) == (off64_t) -1)
      48      {
      49        if (result == -1)
      50  	__set_errno (save_errno);
      51        return -1;
      52      }
      53    __set_errno (save_errno);
      54  
      55    return result;
      56  }
      57  #ifndef __libc_pwrite64
      58  weak_alias (__libc_pwrite64, __pwrite64)
      59  libc_hidden_weak (__pwrite64)
      60  weak_alias (__libc_pwrite64, pwrite64)
      61  #endif