249 lines
6.5 KiB
C
249 lines
6.5 KiB
C
/* provide a replacement fdopendir function
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Copyright (C) 2004-2021 Free Software Foundation, Inc.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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/* written by Jim Meyering */
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#include <config.h>
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#include <dirent.h>
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#include <stdlib.h>
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#include <unistd.h>
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#if !HAVE_FDOPENDIR
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# include "openat.h"
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# include "openat-priv.h"
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# include "save-cwd.h"
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# if GNULIB_DIRENT_SAFER
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# include "dirent--.h"
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# endif
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# ifndef REPLACE_FCHDIR
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# define REPLACE_FCHDIR 0
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# endif
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static DIR *fdopendir_with_dup (int, int, struct saved_cwd const *);
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static DIR *fd_clone_opendir (int, struct saved_cwd const *);
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/* Replacement for POSIX fdopendir.
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First, try to simulate it via opendir ("/proc/self/fd/..."). Failing
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that, simulate it by using fchdir metadata, or by doing
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save_cwd/fchdir/opendir(".")/restore_cwd.
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If either the save_cwd or the restore_cwd fails (relatively unlikely),
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then give a diagnostic and exit nonzero.
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If successful, the resulting stream is based on FD in
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implementations where streams are based on file descriptors and in
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applications where no other thread or signal handler allocates or
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frees file descriptors. In other cases, consult dirfd on the result
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to find out whether FD is still being used.
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Otherwise, this function works just like POSIX fdopendir.
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W A R N I N G:
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Unlike other fd-related functions, this one places constraints on FD.
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If this function returns successfully, FD is under control of the
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dirent.h system, and the caller should not close or modify the state of
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FD other than by the dirent.h functions. */
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# ifdef __KLIBC__
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# include <InnoTekLIBC/backend.h>
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DIR *
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fdopendir (int fd)
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{
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char path[_MAX_PATH];
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DIR *dirp;
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/* Get a path from fd */
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if (__libc_Back_ioFHToPath (fd, path, sizeof (path)))
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return NULL;
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dirp = opendir (path);
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if (!dirp)
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return NULL;
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/* Unregister fd registered by opendir() */
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_gl_unregister_dirp_fd (dirfd (dirp));
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/* Register our fd */
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if (_gl_register_dirp_fd (fd, dirp))
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{
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int saved_errno = errno;
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closedir (dirp);
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errno = saved_errno;
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dirp = NULL;
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}
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return dirp;
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}
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# else
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DIR *
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fdopendir (int fd)
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{
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DIR *dir = fdopendir_with_dup (fd, -1, NULL);
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if (! REPLACE_FCHDIR && ! dir)
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{
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int saved_errno = errno;
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if (EXPECTED_ERRNO (saved_errno))
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{
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struct saved_cwd cwd;
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if (save_cwd (&cwd) != 0)
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openat_save_fail (errno);
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dir = fdopendir_with_dup (fd, -1, &cwd);
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saved_errno = errno;
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free_cwd (&cwd);
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errno = saved_errno;
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}
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}
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return dir;
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}
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# endif
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/* Like fdopendir, except that if OLDER_DUPFD is not -1, it is known
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to be a dup of FD which is less than FD - 1 and which will be
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closed by the caller and not otherwise used by the caller. This
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function makes sure that FD is closed and all file descriptors less
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than FD are open, and then calls fd_clone_opendir on a dup of FD.
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That way, barring race conditions, fd_clone_opendir returns a
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stream whose file descriptor is FD.
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If REPLACE_FCHDIR or CWD is null, use opendir ("/proc/self/fd/...",
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falling back on fchdir metadata. Otherwise, CWD is a saved version
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of the working directory; use fchdir/opendir(".")/restore_cwd(CWD). */
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static DIR *
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fdopendir_with_dup (int fd, int older_dupfd, struct saved_cwd const *cwd)
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{
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int dupfd = dup (fd);
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if (dupfd < 0 && errno == EMFILE)
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dupfd = older_dupfd;
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if (dupfd < 0)
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return NULL;
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else
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{
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DIR *dir;
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int saved_errno;
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if (dupfd < fd - 1 && dupfd != older_dupfd)
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{
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dir = fdopendir_with_dup (fd, dupfd, cwd);
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saved_errno = errno;
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}
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else
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{
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close (fd);
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dir = fd_clone_opendir (dupfd, cwd);
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saved_errno = errno;
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if (! dir)
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{
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int fd1 = dup (dupfd);
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if (fd1 != fd)
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openat_save_fail (fd1 < 0 ? errno : EBADF);
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}
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}
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if (dupfd != older_dupfd)
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close (dupfd);
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errno = saved_errno;
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return dir;
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}
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}
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/* Like fdopendir, except the result controls a clone of FD. It is
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the caller's responsibility both to close FD and (if the result is
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not null) to closedir the result. */
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static DIR *
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fd_clone_opendir (int fd, struct saved_cwd const *cwd)
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{
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if (REPLACE_FCHDIR || ! cwd)
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{
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DIR *dir = NULL;
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int saved_errno = EOPNOTSUPP;
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char buf[OPENAT_BUFFER_SIZE];
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char *proc_file = openat_proc_name (buf, fd, ".");
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if (proc_file)
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{
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dir = opendir (proc_file);
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saved_errno = errno;
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if (proc_file != buf)
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free (proc_file);
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}
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# if REPLACE_FCHDIR
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if (! dir && EXPECTED_ERRNO (saved_errno))
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{
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char const *name = _gl_directory_name (fd);
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DIR *dp = name ? opendir (name) : NULL;
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/* The caller has done an elaborate dance to arrange for opendir to
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consume just the right file descriptor. If dirfd returns -1,
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though, we're on a system like mingw where opendir does not
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consume a file descriptor. Consume it via 'dup' instead. */
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if (dp && dirfd (dp) < 0)
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dup (fd);
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return dp;
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}
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# endif
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errno = saved_errno;
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return dir;
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}
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else
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{
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if (fchdir (fd) != 0)
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return NULL;
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else
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{
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DIR *dir = opendir (".");
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int saved_errno = errno;
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if (restore_cwd (cwd) != 0)
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openat_restore_fail (errno);
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errno = saved_errno;
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return dir;
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}
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}
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}
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#else /* HAVE_FDOPENDIR */
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# include <errno.h>
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# include <sys/stat.h>
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# undef fdopendir
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/* Like fdopendir, but work around GNU/Hurd bug by validating FD. */
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DIR *
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rpl_fdopendir (int fd)
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{
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struct stat st;
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if (fstat (fd, &st))
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return NULL;
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if (!S_ISDIR (st.st_mode))
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{
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errno = ENOTDIR;
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return NULL;
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}
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return fdopendir (fd);
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}
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#endif /* HAVE_FDOPENDIR */
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