| /* Read a symlink relative to an open directory. |
| Copyright (C) 2009-2020 Free Software Foundation, Inc. |
| |
| This program is free software: you can redistribute it and/or modify |
| it under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 3 of the License, or |
| (at your option) any later version. |
| |
| This program is distributed in the hope that it will be useful, |
| but WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| GNU General Public License for more details. |
| |
| You should have received a copy of the GNU General Public License |
| along with this program. If not, see <https://www.gnu.org/licenses/>. */ |
| |
| /* written by Eric Blake */ |
| |
| #include <config.h> |
| |
| /* Specification. */ |
| #include <unistd.h> |
| |
| #include <errno.h> |
| #include <stdlib.h> |
| #include <string.h> |
| #include <sys/stat.h> |
| |
| #if HAVE_READLINKAT |
| |
| # undef readlinkat |
| |
| ssize_t |
| rpl_readlinkat (int fd, char const *file, char *buf, size_t len) |
| { |
| # if READLINK_TRAILING_SLASH_BUG |
| size_t file_len = strlen (file); |
| if (file_len && file[file_len - 1] == '/') |
| { |
| /* Even if FILE without the slash is a symlink to a directory, |
| both lstat() and stat() must resolve the trailing slash to |
| the directory rather than the symlink. We can therefore |
| safely use stat() to distinguish between EINVAL and |
| ENOTDIR/ENOENT, avoiding extra overhead of rpl_lstat(). */ |
| struct stat st; |
| if (stat (file, &st) == 0) |
| errno = EINVAL; |
| return -1; |
| } |
| # endif /* READLINK_TRAILING_SLASH_BUG */ |
| return readlinkat (fd, file, buf, len); |
| } |
| |
| #else |
| |
| /* Gnulib provides a readlink stub for mingw; use it for distinction |
| between EINVAL and ENOENT, rather than always failing with ENOSYS. */ |
| |
| /* POSIX 2008 says that unlike readlink, readlinkat returns 0 for |
| success instead of the buffer length. But this would render |
| readlinkat worthless since readlink does not guarantee a |
| NUL-terminated buffer. Assume this was a bug in POSIX. */ |
| |
| /* Read the contents of symlink FILE into buffer BUF of size LEN, in the |
| directory open on descriptor FD. If possible, do it without changing |
| the working directory. Otherwise, resort to using save_cwd/fchdir, |
| then readlink/restore_cwd. If either the save_cwd or the restore_cwd |
| fails, then give a diagnostic and exit nonzero. */ |
| |
| # define AT_FUNC_NAME readlinkat |
| # define AT_FUNC_F1 readlink |
| # define AT_FUNC_POST_FILE_PARAM_DECLS , char *buf, size_t len |
| # define AT_FUNC_POST_FILE_ARGS , buf, len |
| # define AT_FUNC_RESULT ssize_t |
| # include "at-func.c" |
| # undef AT_FUNC_NAME |
| # undef AT_FUNC_F1 |
| # undef AT_FUNC_POST_FILE_PARAM_DECLS |
| # undef AT_FUNC_POST_FILE_ARGS |
| # undef AT_FUNC_RESULT |
| |
| #endif |