1 /* provide a chdir function that tries not to fail due to ENAMETOOLONG
2 Copyright (C) 2004-2011 Free Software Foundation, Inc.
4 This program is free software: you can redistribute it and/or modify
5 it under the terms of the GNU General Public License as published by
6 the Free Software Foundation; either version 3 of the License, or
7 (at your option) any later version.
9 This program is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 GNU General Public License for more details.
14 You should have received a copy of the GNU General Public License
15 along with this program. If not, see <http://www.gnu.org/licenses/>. */
17 /* written by Jim Meyering */
21 #include "chdir-long.h"
32 # error "compile this file only if your system defines PATH_MAX"
35 /* The results of openat() in this file are not leaked to any
36 single-threaded code that could use stdio.
37 FIXME - if the kernel ever adds support for multi-thread safety for
38 avoiding standard fds, then we should use openat_safer. */
46 cdb_init (struct cd_buf *cdb)
52 cdb_fchdir (struct cd_buf const *cdb)
54 return fchdir (cdb->fd);
58 cdb_free (struct cd_buf const *cdb)
62 bool close_fail = close (cdb->fd);
63 assert (! close_fail);
67 /* Given a file descriptor of an open directory (or AT_FDCWD), CDB->fd,
68 try to open the CDB->fd-relative directory, DIR. If the open succeeds,
69 update CDB->fd with the resulting descriptor, close the incoming file
70 descriptor, and return zero. Upon failure, return -1 and set errno. */
72 cdb_advance_fd (struct cd_buf *cdb, char const *dir)
74 int new_fd = openat (cdb->fd, dir,
75 O_SEARCH | O_DIRECTORY | O_NOCTTY | O_NONBLOCK);
85 /* Return a pointer to the first non-slash in S. */
87 find_non_slash (char const *s)
89 size_t n_slash = strspn (s, "/");
90 return (char *) s + n_slash;
93 /* This is a function much like chdir, but without the PATH_MAX limitation
94 on the length of the directory name. A significant difference is that
95 it must be able to modify (albeit only temporarily) the directory
96 name. It handles an arbitrarily long directory name by operating
97 on manageable portions of the name. On systems without the openat
98 syscall, this means changing the working directory to more and more
99 `distant' points along the long directory name and then restoring
100 the working directory. If any of those attempts to save or restore
101 the working directory fails, this function exits nonzero.
103 Note that this function may still fail with errno == ENAMETOOLONG, but
104 only if the specified directory name contains a component that is long
105 enough to provoke such a failure all by itself (e.g. if the component
106 has length PATH_MAX or greater on systems that define PATH_MAX). */
109 chdir_long (char *dir)
112 if (e == 0 || errno != ENAMETOOLONG)
116 size_t len = strlen (dir);
117 char *dir_end = dir + len;
119 size_t n_leading_slash;
123 /* If DIR is the empty string, then the chdir above
124 must have failed and set errno to ENOENT. */
126 assert (PATH_MAX <= len);
128 /* Count leading slashes. */
129 n_leading_slash = strspn (dir, "/");
131 /* Handle any leading slashes as well as any name that matches
132 the regular expression, m!^//hostname[/]*! . Handling this
133 prefix separately usually results in a single additional
134 cdb_advance_fd call, but it's worthwhile, since it makes the
135 code in the following loop cleaner. */
136 if (n_leading_slash == 2)
140 We already know that dir[2] is neither a slash nor '\0'. */
141 char *slash = memchr (dir + 3, '/', dir_end - (dir + 3));
144 errno = ENAMETOOLONG;
148 err = cdb_advance_fd (&cdb, dir);
152 dir = find_non_slash (slash + 1);
154 else if (n_leading_slash)
156 if (cdb_advance_fd (&cdb, "/") != 0)
158 dir += n_leading_slash;
161 assert (*dir != '/');
162 assert (dir <= dir_end);
164 while (PATH_MAX <= dir_end - dir)
167 /* Find a slash that is PATH_MAX or fewer bytes away from dir.
168 I.e. see if there is a slash that will give us a name of
169 length PATH_MAX-1 or less. */
170 char *slash = memrchr (dir, '/', PATH_MAX);
173 errno = ENAMETOOLONG;
178 assert (slash - dir < PATH_MAX);
179 err = cdb_advance_fd (&cdb, dir);
184 dir = find_non_slash (slash + 1);
189 if (cdb_advance_fd (&cdb, dir) != 0)
193 if (cdb_fchdir (&cdb) != 0)
201 int saved_errno = errno;
211 # include "closeout.h"
217 main (int argc, char *argv[])
223 program_name = argv[0];
224 atexit (close_stdout);
226 len = getline (&line, &n, stdin);
229 int saved_errno = errno;
233 error (EXIT_FAILURE, saved_errno,
234 "reading standard input");
239 if (line[len-1] == '\n')
242 if (chdir_long (line) != 0)
243 error (EXIT_FAILURE, errno,
244 "chdir_long failed: %s", line);
248 /* Using `pwd' here makes sense only if it is a robust implementation,
249 like the one in coreutils after the 2004-04-19 changes. */
250 char const *cmd = "pwd";
251 execlp (cmd, (char *) NULL);
252 error (EXIT_FAILURE, errno, "%s", cmd);
264 compile-command: "gcc -DTEST_CHDIR=1 -g -O -W -Wall chdir-long.c libcoreutils.a"