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/* provide a replacement fdopendir function
Copyright (C) 2004-2024 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 Jim Meyering */
#include <config.h>
#include <dirent.h>
#include <stdlib.h>
#include <unistd.h>
#if !HAVE_FDOPENDIR
# if GNULIB_defined_DIR
/* We are in control of the file descriptor of a DIR. */
# include "dirent-private.h"
# if !REPLACE_FCHDIR
# error "unexpected configuration: GNULIB_defined_DIR but fchdir not replaced"
# endif
DIR *
fdopendir (int fd)
{
char const *name = _gl_directory_name (fd);
DIR *dirp = name ? opendir (name) : NULL;
if (dirp != NULL)
dirp->fd_to_close = fd;
return dirp;
}
# else
/* We are not in control of the file descriptor of a DIR, and therefore have to
play tricks with file descriptors before and after a call to opendir(). */
# include "openat.h"
# include "openat-priv.h"
# include "save-cwd.h"
# if GNULIB_DIRENT_SAFER
# include "dirent--.h"
# endif
# ifndef REPLACE_FCHDIR
# define REPLACE_FCHDIR 0
# endif
static DIR *fdopendir_with_dup (int, int, struct saved_cwd const *);
static DIR *fd_clone_opendir (int, struct saved_cwd const *);
/* Replacement for POSIX fdopendir.
First, try to simulate it via opendir ("/proc/self/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)
{
DIR *dir = fdopendir_with_dup (fd, -1, NULL);
if (! REPLACE_FCHDIR && ! dir)
{
int saved_errno = errno;
if (EXPECTED_ERRNO (saved_errno))
{
struct saved_cwd cwd;
if (save_cwd (&cwd) != 0)
openat_save_fail (errno);
dir = fdopendir_with_dup (fd, -1, &cwd);
saved_errno = errno;
free_cwd (&cwd);
errno = saved_errno;
}
}
return dir;
}
/* 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.
If REPLACE_FCHDIR or CWD is null, use opendir ("/proc/self/fd/...",
falling back on fchdir metadata. Otherwise, CWD is a saved version
of the working directory; use fchdir/opendir(".")/restore_cwd(CWD). */
static DIR *
fdopendir_with_dup (int fd, int older_dupfd, struct saved_cwd const *cwd)
{
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, cwd);
saved_errno = errno;
}
else
{
close (fd);
dir = fd_clone_opendir (dupfd, cwd);
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, struct saved_cwd const *cwd)
{
if (REPLACE_FCHDIR || ! cwd)
{
DIR *dir = NULL;
int saved_errno = EOPNOTSUPP;
char buf[OPENAT_BUFFER_SIZE];
char *proc_file = openat_proc_name (buf, fd, ".");
if (proc_file)
{
dir = opendir (proc_file);
saved_errno = errno;
if (proc_file != buf)
free (proc_file);
}
# if REPLACE_FCHDIR
if (! dir && EXPECTED_ERRNO (saved_errno))
{
char const *name = _gl_directory_name (fd);
DIR *dp = name ? opendir (name) : NULL;
/* The caller has done an elaborate dance to arrange for opendir to
consume just the right file descriptor. If dirfd returns -1,
though, we're on a system like mingw where opendir does not
consume a file descriptor. Consume it via 'dup' instead. */
if (dp && dirfd (dp) < 0)
dup (fd);
return dp;
}
# endif
errno = saved_errno;
return dir;
}
else
{
if (fchdir (fd) != 0)
return NULL;
else
{
DIR *dir = opendir (".");
int saved_errno = errno;
if (restore_cwd (cwd) != 0)
openat_restore_fail (errno);
errno = saved_errno;
return dir;
}
}
}
# endif
#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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