lib/symlinkat.c

   1 /* Create a symlink relative to an open directory.
   2    Copyright (C) 2009-2019 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 <https://www.gnu.org/licenses/>.  */
  16
  17 /* written by Eric Blake */
  18
  19 #include <config.h>
  20
  21 #include <unistd.h>
  22 #include <errno.h>
  23
  24 #if HAVE_SYMLINKAT
  25 # undef symlinkat
  26
  27 #include <sys/stat.h>
  28 #include <string.h>
  29
  30 /* Create a symlink, but reject trailing slash.  */
  31 int
  32 rpl_symlinkat (char const *contents, int fd, char const *name)
  33 {
  34   size_t len = strlen (name);
  35   if (len && name[len - 1] == '/')
  36     {
  37       struct stat st;
  38       if (fstatat (fd, name, &st, 0) == 0)
  39         errno = EEXIST;
  40       return -1;
  41     }
  42   return symlinkat (contents, fd, name);
  43 }
  44
  45 #elif !HAVE_SYMLINK
  46 /* Mingw lacks symlink, and it is more efficient to provide a trivial
  47    wrapper than to go through at-func.c to call rpl_symlink.  */
  48
  49 int
  50 symlinkat (char const *path1 _GL_UNUSED, int fd _GL_UNUSED,
  51            char const *path2 _GL_UNUSED)
  52 {
  53   errno = ENOSYS;
  54   return -1;
  55 }
  56
  57 #else /* HAVE_SYMLINK */
  58
  59 /* Our openat helper functions expect the directory parameter first,
  60    not second.  These shims make life easier.  */
  61
  62 /* Like symlink, but with arguments reversed.  */
  63 static int
  64 symlink_reversed (char const *file, char const *contents)
  65 {
  66   return symlink (contents, file);
  67 }
  68
  69 /* Like symlinkat, but with arguments reversed.  */
  70
  71 static int
  72 symlinkat_reversed (int fd, char const *file, char const *contents);
  73
  74 # define AT_FUNC_NAME symlinkat_reversed
  75 # define AT_FUNC_F1 symlink_reversed
  76 # define AT_FUNC_POST_FILE_PARAM_DECLS , char const *contents
  77 # define AT_FUNC_POST_FILE_ARGS        , contents
  78 # include "at-func.c"
  79 # undef AT_FUNC_NAME
  80 # undef AT_FUNC_F1
  81 # undef AT_FUNC_POST_FILE_PARAM_DECLS
  82 # undef AT_FUNC_POST_FILE_ARGS
  83
  84 /* Create a symlink FILE, in the directory open on descriptor FD,
  85    holding CONTENTS.  If possible, do it without changing the
  86    working directory.  Otherwise, resort to using save_cwd/fchdir,
  87    then symlink/restore_cwd.  If either the save_cwd or the restore_cwd
  88    fails, then give a diagnostic and exit nonzero.  */
  89
  90 int
  91 symlinkat (char const *contents, int fd, char const *file)
  92 {
  93   return symlinkat_reversed (fd, file, contents);
  94 }
  95
  96 #endif /* HAVE_SYMLINK */