lib/readlinkat.c

   1 /* Read a symlink relative to an open directory.
   2    Copyright (C) 2009-2013 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  16
  17 /* written by Eric Blake */
  18
  19 #include <config.h>
  20
  21 #include <unistd.h>
  22
  23 /* Gnulib provides a readlink stub for mingw; use it for distinction
  24    between EINVAL and ENOENT, rather than always failing with ENOSYS.  */
  25
  26 /* POSIX 2008 says that unlike readlink, readlinkat returns 0 for
  27    success instead of the buffer length.  But this would render
  28    readlinkat worthless since readlink does not guarantee a
  29    NUL-terminated buffer.  Assume this was a bug in POSIX.  */
  30
  31 /* Read the contents of symlink FILE into buffer BUF of size LEN, in the
  32    directory open on descriptor FD.  If possible, do it without changing
  33    the working directory.  Otherwise, resort to using save_cwd/fchdir,
  34    then readlink/restore_cwd.  If either the save_cwd or the restore_cwd
  35    fails, then give a diagnostic and exit nonzero.  */
  36
  37 #define AT_FUNC_NAME readlinkat
  38 #define AT_FUNC_F1 readlink
  39 #define AT_FUNC_POST_FILE_PARAM_DECLS , char *buf, size_t len
  40 #define AT_FUNC_POST_FILE_ARGS        , buf, len
  41 #define AT_FUNC_RESULT ssize_t
  42 #include "at-func.c"
  43 #undef AT_FUNC_NAME
  44 #undef AT_FUNC_F1
  45 #undef AT_FUNC_POST_FILE_PARAM_DECLS
  46 #undef AT_FUNC_POST_FILE_ARGS
  47 #undef AT_FUNC_RESULT