mirror of
https://git.savannah.gnu.org/git/emacs.git
synced 2024-11-23 07:19:15 +00:00
114 lines
3.6 KiB
C
114 lines
3.6 KiB
C
/* Read a symlink relative to an open directory.
|
|
Copyright (C) 2009-2023 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 fstatat
|
|
# undef readlinkat
|
|
|
|
ssize_t
|
|
rpl_readlinkat (int fd, char const *file, char *buf, size_t bufsize)
|
|
{
|
|
# 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 fstatat(..., 0) to distinguish between EINVAL and
|
|
ENOTDIR/ENOENT, avoiding extra overhead of rpl_fstatat(). */
|
|
struct stat st;
|
|
if (fstatat (fd, file, &st, 0) == 0 || errno == EOVERFLOW)
|
|
errno = EINVAL;
|
|
return -1;
|
|
}
|
|
# endif /* READLINK_TRAILING_SLASH_BUG */
|
|
|
|
ssize_t r = readlinkat (fd, file, buf, bufsize);
|
|
|
|
# if READLINK_TRUNCATE_BUG
|
|
if (r < 0 && errno == ERANGE)
|
|
{
|
|
/* Try again with a bigger buffer. This is just for test cases;
|
|
real code invariably discards short reads. */
|
|
char stackbuf[4032];
|
|
r = readlinkat (fd, file, stackbuf, sizeof stackbuf);
|
|
if (r < 0)
|
|
{
|
|
if (errno == ERANGE)
|
|
{
|
|
/* Clear the buffer, which is good enough for real code.
|
|
Thankfully, no test cases try short reads of enormous
|
|
symlinks and what would be the point anyway? */
|
|
r = bufsize;
|
|
memset (buf, 0, r);
|
|
}
|
|
}
|
|
else
|
|
{
|
|
if (bufsize < r)
|
|
r = bufsize;
|
|
memcpy (buf, stackbuf, r);
|
|
}
|
|
}
|
|
# endif
|
|
|
|
return r;
|
|
}
|
|
|
|
#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 BUFSIZE, 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 bufsize
|
|
# define AT_FUNC_POST_FILE_ARGS , buf, bufsize
|
|
# 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
|