lib/symlinkat.c

   1 /* Create a symlink relative to an open directory.
   2    Copyright (C) 2009-2021 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 /* Specification.  */
  22 #include <unistd.h>
  23
  24 #include <errno.h>
  25 #include <stdlib.h>
  26
  27 #if HAVE_SYMLINKAT
  28 # undef symlinkat
  29
  30 #include <sys/stat.h>
  31 #include <string.h>
  32
  33 /* Create a symlink, but reject trailing slash.  */
  34 int
  35 rpl_symlinkat (char const *contents, int fd, char const *name)
  36 {
  37   size_t len = strlen (name);
  38   if (len && name[len - 1] == '/')
  39     {
  40       struct stat st;
  41       if (fstatat (fd, name, &st, 0) == 0 || errno == EOVERFLOW)
  42         errno = EEXIST;
  43       return -1;
  44     }
  45   return symlinkat (contents, fd, name);
  46 }
  47
  48 #elif !HAVE_SYMLINK
  49 /* Mingw lacks symlink, and it is more efficient to provide a trivial
  50    wrapper than to go through at-func.c to call rpl_symlink.  */
  51
  52 int
  53 symlinkat (char const *path1 _GL_UNUSED, int fd _GL_UNUSED,
  54            char const *path2 _GL_UNUSED)
  55 {
  56   errno = ENOSYS;
  57   return -1;
  58 }
  59
  60 #else /* HAVE_SYMLINK */
  61
  62 /* Our openat helper functions expect the directory parameter first,
  63    not second.  These shims make life easier.  */
  64
  65 /* Like symlink, but with arguments reversed.  */
  66 static int
  67 symlink_reversed (char const *file, char const *contents)
  68 {
  69   return symlink (contents, file);
  70 }
  71
  72 /* Like symlinkat, but with arguments reversed.  */
  73
  74 static int
  75 symlinkat_reversed (int fd, char const *file, char const *contents);
  76
  77 # define AT_FUNC_NAME symlinkat_reversed
  78 # define AT_FUNC_F1 symlink_reversed
  79 # define AT_FUNC_POST_FILE_PARAM_DECLS , char const *contents
  80 # define AT_FUNC_POST_FILE_ARGS        , contents
  81 # include "at-func.c"
  82 # undef AT_FUNC_NAME
  83 # undef AT_FUNC_F1
  84 # undef AT_FUNC_POST_FILE_PARAM_DECLS
  85 # undef AT_FUNC_POST_FILE_ARGS
  86
  87 /* Create a symlink FILE, in the directory open on descriptor FD,
  88    holding CONTENTS.  If possible, do it without changing the
  89    working directory.  Otherwise, resort to using save_cwd/fchdir,
  90    then symlink/restore_cwd.  If either the save_cwd or the restore_cwd
  91    fails, then give a diagnostic and exit nonzero.  */
  92
  93 int
  94 symlinkat (char const *contents, int fd, char const *file)
  95 {
  96   return symlinkat_reversed (fd, file, contents);
  97 }
  98
  99 #endif /* HAVE_SYMLINK */