| 1 | /* provide a replacement fdopendir function
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| 2 | Copyright (C) 2004-2012 Free Software Foundation, Inc.
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| 3 |
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| 4 | This program is free software: you can redistribute it and/or modify
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| 5 | it under the terms of the GNU General Public License as published by
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| 6 | the Free Software Foundation; either version 3 of the License, or
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| 7 | (at your option) any later version.
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| 8 |
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| 9 | This program is distributed in the hope that it will be useful,
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| 10 | but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 12 | GNU General Public License for more details.
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| 13 |
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| 14 | You should have received a copy of the GNU General Public License
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| 15 | along with this program. If not, see <http://www.gnu.org/licenses/>. */
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| 16 |
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| 17 | /* written by Jim Meyering */
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| 18 |
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| 19 | #include <config.h>
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| 20 |
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| 21 | #include <dirent.h>
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| 22 |
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| 23 | #include <stdlib.h>
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| 24 | #include <unistd.h>
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| 25 |
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| 26 | #if !HAVE_FDOPENDIR
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| 27 |
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| 28 | # include "openat.h"
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| 29 | # include "openat-priv.h"
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| 30 | # include "save-cwd.h"
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| 31 |
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| 32 | # if GNULIB_DIRENT_SAFER
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| 33 | # include "dirent--.h"
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| 34 | # endif
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| 35 |
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| 36 | # ifndef REPLACE_FCHDIR
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| 37 | # define REPLACE_FCHDIR 0
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| 38 | # endif
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| 39 |
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| 40 | static DIR *fdopendir_with_dup (int, int, struct saved_cwd const *);
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| 41 | static DIR *fd_clone_opendir (int, struct saved_cwd const *);
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| 42 |
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| 43 | /* Replacement for POSIX fdopendir.
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| 44 |
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| 45 | First, try to simulate it via opendir ("/proc/self/fd/..."). Failing
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| 46 | that, simulate it by using fchdir metadata, or by doing
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| 47 | save_cwd/fchdir/opendir(".")/restore_cwd.
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| 48 | If either the save_cwd or the restore_cwd fails (relatively unlikely),
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| 49 | then give a diagnostic and exit nonzero.
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| 50 |
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| 51 | If successful, the resulting stream is based on FD in
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| 52 | implementations where streams are based on file descriptors and in
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| 53 | applications where no other thread or signal handler allocates or
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| 54 | frees file descriptors. In other cases, consult dirfd on the result
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| 55 | to find out whether FD is still being used.
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| 56 |
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| 57 | Otherwise, this function works just like POSIX fdopendir.
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| 58 |
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| 59 | W A R N I N G:
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| 60 |
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| 61 | Unlike other fd-related functions, this one places constraints on FD.
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| 62 | If this function returns successfully, FD is under control of the
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| 63 | dirent.h system, and the caller should not close or modify the state of
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| 64 | FD other than by the dirent.h functions. */
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| 65 | DIR *
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| 66 | fdopendir (int fd)
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| 67 | {
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| 68 | DIR *dir = fdopendir_with_dup (fd, -1, NULL);
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| 69 |
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| 70 | if (! REPLACE_FCHDIR && ! dir)
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| 71 | {
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| 72 | int saved_errno = errno;
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| 73 | if (EXPECTED_ERRNO (saved_errno))
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| 74 | {
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| 75 | struct saved_cwd cwd;
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| 76 | if (save_cwd (&cwd) != 0)
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| 77 | openat_save_fail (errno);
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| 78 | dir = fdopendir_with_dup (fd, -1, &cwd);
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| 79 | saved_errno = errno;
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| 80 | free_cwd (&cwd);
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| 81 | errno = saved_errno;
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| 82 | }
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| 83 | }
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| 84 |
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| 85 | return dir;
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| 86 | }
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| 87 |
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| 88 | /* Like fdopendir, except that if OLDER_DUPFD is not -1, it is known
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| 89 | to be a dup of FD which is less than FD - 1 and which will be
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| 90 | closed by the caller and not otherwise used by the caller. This
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| 91 | function makes sure that FD is closed and all file descriptors less
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| 92 | than FD are open, and then calls fd_clone_opendir on a dup of FD.
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| 93 | That way, barring race conditions, fd_clone_opendir returns a
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| 94 | stream whose file descriptor is FD.
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| 95 |
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| 96 | If REPLACE_CHDIR or CWD is null, use opendir ("/proc/self/fd/...",
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| 97 | falling back on fchdir metadata. Otherwise, CWD is a saved version
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| 98 | of the working directory; use fchdir/opendir(".")/restore_cwd(CWD). */
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| 99 | static DIR *
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| 100 | fdopendir_with_dup (int fd, int older_dupfd, struct saved_cwd const *cwd)
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| 101 | {
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| 102 | int dupfd = dup (fd);
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| 103 | if (dupfd < 0 && errno == EMFILE)
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| 104 | dupfd = older_dupfd;
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| 105 | if (dupfd < 0)
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| 106 | return NULL;
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| 107 | else
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| 108 | {
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| 109 | DIR *dir;
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| 110 | int saved_errno;
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| 111 | if (dupfd < fd - 1 && dupfd != older_dupfd)
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| 112 | {
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| 113 | dir = fdopendir_with_dup (fd, dupfd, cwd);
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| 114 | saved_errno = errno;
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| 115 | }
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| 116 | else
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| 117 | {
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| 118 | close (fd);
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| 119 | dir = fd_clone_opendir (dupfd, cwd);
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| 120 | saved_errno = errno;
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| 121 | if (! dir)
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| 122 | {
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| 123 | int fd1 = dup (dupfd);
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| 124 | if (fd1 != fd)
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| 125 | openat_save_fail (fd1 < 0 ? errno : EBADF);
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| 126 | }
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| 127 | }
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| 128 |
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| 129 | if (dupfd != older_dupfd)
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| 130 | close (dupfd);
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| 131 | errno = saved_errno;
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| 132 | return dir;
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| 133 | }
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| 134 | }
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| 135 |
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| 136 | /* Like fdopendir, except the result controls a clone of FD. It is
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| 137 | the caller's responsibility both to close FD and (if the result is
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| 138 | not null) to closedir the result. */
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| 139 | static DIR *
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| 140 | fd_clone_opendir (int fd, struct saved_cwd const *cwd)
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| 141 | {
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| 142 | if (REPLACE_FCHDIR || ! cwd)
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| 143 | {
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| 144 | DIR *dir = NULL;
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| 145 | int saved_errno = EOPNOTSUPP;
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| 146 | char buf[OPENAT_BUFFER_SIZE];
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| 147 | char *proc_file = openat_proc_name (buf, fd, ".");
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| 148 | if (proc_file)
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| 149 | {
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| 150 | dir = opendir (proc_file);
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| 151 | saved_errno = errno;
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| 152 | if (proc_file != buf)
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| 153 | free (proc_file);
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| 154 | }
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| 155 | # if REPLACE_FCHDIR
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| 156 | if (! dir && EXPECTED_ERRNO (saved_errno))
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| 157 | {
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| 158 | char const *name = _gl_directory_name (fd);
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| 159 | return (name ? opendir (name) : NULL);
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| 160 | }
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| 161 | # endif
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| 162 | errno = saved_errno;
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| 163 | return dir;
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| 164 | }
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| 165 | else
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| 166 | {
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| 167 | if (fchdir (fd) != 0)
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| 168 | return NULL;
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| 169 | else
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| 170 | {
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| 171 | DIR *dir = opendir (".");
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| 172 | int saved_errno = errno;
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| 173 | if (restore_cwd (cwd) != 0)
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| 174 | openat_restore_fail (errno);
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| 175 | errno = saved_errno;
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| 176 | return dir;
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| 177 | }
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| 178 | }
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| 179 | }
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| 180 |
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| 181 | #else /* HAVE_FDOPENDIR */
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| 182 |
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| 183 | # include <errno.h>
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| 184 | # include <sys/stat.h>
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| 185 |
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| 186 | # undef fdopendir
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| 187 |
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| 188 | /* Like fdopendir, but work around GNU/Hurd bug by validating FD. */
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| 189 |
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| 190 | DIR *
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| 191 | rpl_fdopendir (int fd)
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| 192 | {
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| 193 | struct stat st;
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| 194 | if (fstat (fd, &st))
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| 195 | return NULL;
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| 196 | if (!S_ISDIR (st.st_mode))
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| 197 | {
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| 198 | errno = ENOTDIR;
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| 199 | return NULL;
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| 200 | }
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| 201 | return fdopendir (fd);
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| 202 | }
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| 203 |
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| 204 | #endif /* HAVE_FDOPENDIR */
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