/* Read a symlink relative to an open directory. Copyright (C) 2009-2015 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 . */ /* written by Eric Blake */ #include #include #include #include #include #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