lib/opendirat.c

   1 /* Open a directory relative to another directory.
   2
   3    Copyright 2006-2019 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.
  17
  18    Written by Jim Meyering and Paul Eggert.  */
  19
  20 #include <config.h>
  21
  22 #include <opendirat.h>
  23
  24 #include <errno.h>
  25 #include <fcntl--.h>
  26 #include <unistd.h>
  27
  28 /* Relative to DIR_FD, open the directory DIR, passing EXTRA_FLAGS to
  29    the underlying openat call.  On success, store into *PNEW_FD the
  30    underlying file descriptor of the newly opened directory and return
  31    the directory stream.  On failure, return NULL and set errno.
  32
  33    On success, *PNEW_FD is at least 3, so this is a "safer" function.  */
  34
  35 DIR *
  36 opendirat (int dir_fd, char const *dir, int extra_flags, int *pnew_fd)
  37 {
  38   int open_flags = (O_RDONLY | O_CLOEXEC | O_DIRECTORY | O_NOCTTY
  39                     | O_NONBLOCK | extra_flags);
  40   int new_fd = openat (dir_fd, dir, open_flags);
  41
  42   if (new_fd < 0)
  43     return NULL;
  44   DIR *dirp = fdopendir (new_fd);
  45   if (dirp)
  46     *pnew_fd = new_fd;
  47   else
  48     {
  49       int fdopendir_errno = errno;
  50       close (new_fd);
  51       errno = fdopendir_errno;
  52     }
  53   return dirp;
  54 }