lib/areadlinkat.c

   1 /* areadlinkat.c -- readlinkat wrapper to return malloc'd link name
   2    Unlike xreadlinkat, only call exit on failure to change directory.
   3
   4    Copyright (C) 2001, 2003-2007, 2009-2024 Free Software Foundation, Inc.
   5
   6    This program is free software: you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation, either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program 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
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  18
  19 /* Written by Jim Meyering <jim@meyering.net>,
  20    and Bruno Haible <bruno@clisp.org>,
  21    and Eric Blake <ebb9@byu.net>.  */
  22
  23 #include <config.h>
  24
  25 /* Specification.  */
  26 #include "areadlink.h"
  27
  28 #include <stdlib.h>
  29
  30 #include "careadlinkat.h"
  31
  32 #if HAVE_READLINKAT
  33
  34 /* Call readlinkat to get the symbolic link value of FILENAME relative to FD.
  35    Return a pointer to that NUL-terminated string in malloc'd storage.
  36    If readlinkat fails, return NULL and set errno (although failure to
  37    change directory will issue a diagnostic and exit).
  38    If allocation fails, or if the link value is longer than SIZE_MAX :-),
  39    return NULL and set errno to ENOMEM.  */
  40
  41 char *
  42 areadlinkat (int fd, char const *filename)
  43 {
  44   return careadlinkat (fd, filename, NULL, 0, NULL, readlinkat);
  45 }
  46
  47 #else /* !HAVE_READLINKAT */
  48
  49 /* It is more efficient to change directories only once and call
  50    areadlink, rather than repeatedly call the replacement
  51    readlinkat.  */
  52
  53 # define AT_FUNC_NAME areadlinkat
  54 # define AT_FUNC_F1 areadlink
  55 # define AT_FUNC_POST_FILE_PARAM_DECLS /* empty */
  56 # define AT_FUNC_POST_FILE_ARGS        /* empty */
  57 # define AT_FUNC_RESULT char *
  58 # define AT_FUNC_FAIL NULL
  59 # include "at-func.c"
  60 # undef AT_FUNC_NAME
  61 # undef AT_FUNC_F1
  62 # undef AT_FUNC_POST_FILE_PARAM_DECLS
  63 # undef AT_FUNC_POST_FILE_ARGS
  64 # undef AT_FUNC_RESULT
  65 # undef AT_FUNC_FAIL
  66
  67 #endif /* !HAVE_READLINKAT */