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/* provide a replacement fdopendir function
Copyright (C) 2004-2010 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 <http://www.gnu.org/licenses/>. */
/* written by Jim Meyering */
#include <config.h>
#include <dirent.h>
#include <stdlib.h>
#include <unistd.h>
#if !HAVE_FDOPENDIR
# include "openat.h"
# include "openat-priv.h"
# include "save-cwd.h"
# if GNULIB_DIRENT_SAFER
# include "dirent--.h"
# endif
static DIR *fdopendir_with_dup (int, int);
static DIR *fd_clone_opendir (int);
/* Replacement for POSIX fdopendir.
First, try to simulate it via opendir ("/proc/self/fd/FD"). Failing
that, simulate it by using fchdir metadata, or by doing
save_cwd/fchdir/opendir(".")/restore_cwd.
If either the save_cwd or the restore_cwd fails (relatively unlikely),
then give a diagnostic and exit nonzero.
If successful, the resulting stream is based on FD in
implementations where streams are based on file descriptors and in
applications where no other thread or signal handler allocates or
frees file descriptors. In other cases, consult dirfd on the result
to find out whether FD is still being used.
Otherwise, this function works just like POSIX fdopendir.
W A R N I N G:
Unlike other fd-related functions, this one places constraints on FD.
If this function returns successfully, FD is under control of the
dirent.h system, and the caller should not close or modify the state of
FD other than by the dirent.h functions. */
DIR *
fdopendir (int fd)
{
return fdopendir_with_dup (fd, -1);
}
/* Like fdopendir, except that if OLDER_DUPFD is not -1, it is known
to be a dup of FD which is less than FD - 1 and which will be
closed by the caller and not otherwise used by the caller. This
function makes sure that FD is closed and all file descriptors less
than FD are open, and then calls fd_clone_opendir on a dup of FD.
That way, barring race conditions, fd_clone_opendir returns a
stream whose file descriptor is FD. */
static DIR *
fdopendir_with_dup (int fd, int older_dupfd)
{
int dupfd = dup (fd);
if (dupfd < 0 && errno == EMFILE)
dupfd = older_dupfd;
if (dupfd < 0)
return NULL;
else
{
DIR *dir;
int saved_errno;
if (dupfd < fd - 1 && dupfd != older_dupfd)
{
dir = fdopendir_with_dup (fd, dupfd);
saved_errno = errno;
}
else
{
close (fd);
dir = fd_clone_opendir (dupfd);
saved_errno = errno;
if (! dir)
{
int fd1 = dup (dupfd);
if (fd1 != fd)
openat_save_fail (fd1 < 0 ? errno : EBADF);
}
}
if (dupfd != older_dupfd)
close (dupfd);
errno = saved_errno;
return dir;
}
}
/* Like fdopendir, except the result controls a clone of FD. It is
the caller's responsibility both to close FD and (if the result is
not null) to closedir the result. */
static DIR *
fd_clone_opendir (int fd)
{
int saved_errno;
DIR *dir;
char buf[OPENAT_BUFFER_SIZE];
char *proc_file = openat_proc_name (buf, fd, ".");
if (proc_file)
{
dir = opendir (proc_file);
saved_errno = errno;
}
else
{
dir = NULL;
saved_errno = EOPNOTSUPP;
}
/* If the syscall fails with an expected errno value, resort to
save_cwd/restore_cwd. */
if (! dir && EXPECTED_ERRNO (saved_errno))
{
# if REPLACE_FCHDIR
const char *name = _gl_directory_name (fd);
if (name)
dir = opendir (name);
saved_errno = errno;
# else /* !REPLACE_FCHDIR */
struct saved_cwd saved_cwd;
if (save_cwd (&saved_cwd) != 0)
openat_save_fail (errno);
if (fchdir (fd) != 0)
{
dir = NULL;
saved_errno = errno;
}
else
{
dir = opendir (".");
saved_errno = errno;
if (restore_cwd (&saved_cwd) != 0)
openat_restore_fail (errno);
}
free_cwd (&saved_cwd);
# endif /* !REPLACE_FCHDIR */
}
if (proc_file != buf)
free (proc_file);
errno = saved_errno;
return dir;
}
#else /* HAVE_FDOPENDIR */
# include <errno.h>
# include <sys/stat.h>
# undef fdopendir
/* Like fdopendir, but work around GNU/Hurd bug by validating FD. */
DIR *
rpl_fdopendir (int fd)
{
struct stat st;
if (fstat (fd, &st))
return NULL;
if (!S_ISDIR (st.st_mode))
{
errno = ENOTDIR;
return NULL;
}
return fdopendir (fd);
}
#endif /* HAVE_FDOPENDIR */
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