1 /* provide a chdir function that tries not to fail due to ENAMETOOLONG
2 Copyright (C) 2004, 2005, 2006, 2007, 2008 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"
34 # error "compile this file only if your system defines PATH_MAX"
43 cdb_init (struct cd_buf *cdb)
49 cdb_fchdir (struct cd_buf const *cdb)
51 return fchdir (cdb->fd);
55 cdb_free (struct cd_buf const *cdb)
59 bool close_fail = close (cdb->fd);
60 assert (! close_fail);
64 /* Given a file descriptor of an open directory (or AT_FDCWD), CDB->fd,
65 try to open the CDB->fd-relative directory, DIR. If the open succeeds,
66 update CDB->fd with the resulting descriptor, close the incoming file
67 descriptor, and return zero. Upon failure, return -1 and set errno. */
69 cdb_advance_fd (struct cd_buf *cdb, char const *dir)
71 int new_fd = openat (cdb->fd, dir,
72 O_RDONLY | O_DIRECTORY | O_NOCTTY | O_NONBLOCK);
82 /* Return a pointer to the first non-slash in S. */
84 find_non_slash (char const *s)
86 size_t n_slash = strspn (s, "/");
87 return (char *) s + n_slash;
90 /* This is a function much like chdir, but without the PATH_MAX limitation
91 on the length of the directory name. A significant difference is that
92 it must be able to modify (albeit only temporarily) the directory
93 name. It handles an arbitrarily long directory name by operating
94 on manageable portions of the name. On systems without the openat
95 syscall, this means changing the working directory to more and more
96 `distant' points along the long directory name and then restoring
97 the working directory. If any of those attempts to save or restore
98 the working directory fails, this function exits nonzero.
100 Note that this function may still fail with errno == ENAMETOOLONG, but
101 only if the specified directory name contains a component that is long
102 enough to provoke such a failure all by itself (e.g. if the component
103 has length PATH_MAX or greater on systems that define PATH_MAX). */
106 chdir_long (char *dir)
109 if (e == 0 || errno != ENAMETOOLONG)
113 size_t len = strlen (dir);
114 char *dir_end = dir + len;
116 size_t n_leading_slash;
120 /* If DIR is the empty string, then the chdir above
121 must have failed and set errno to ENOENT. */
123 assert (PATH_MAX <= len);
125 /* Count leading slashes. */
126 n_leading_slash = strspn (dir, "/");
128 /* Handle any leading slashes as well as any name that matches
129 the regular expression, m!^//hostname[/]*! . Handling this
130 prefix separately usually results in a single additional
131 cdb_advance_fd call, but it's worthwhile, since it makes the
132 code in the following loop cleaner. */
133 if (n_leading_slash == 2)
137 We already know that dir[2] is neither a slash nor '\0'. */
138 char *slash = memchr (dir + 3, '/', dir_end - (dir + 3));
141 errno = ENAMETOOLONG;
145 err = cdb_advance_fd (&cdb, dir);
149 dir = find_non_slash (slash + 1);
151 else if (n_leading_slash)
153 if (cdb_advance_fd (&cdb, "/") != 0)
155 dir += n_leading_slash;
158 assert (*dir != '/');
159 assert (dir <= dir_end);
161 while (PATH_MAX <= dir_end - dir)
164 /* Find a slash that is PATH_MAX or fewer bytes away from dir.
165 I.e. see if there is a slash that will give us a name of
166 length PATH_MAX-1 or less. */
167 char *slash = memrchr (dir, '/', PATH_MAX);
170 errno = ENAMETOOLONG;
175 assert (slash - dir < PATH_MAX);
176 err = cdb_advance_fd (&cdb, dir);
181 dir = find_non_slash (slash + 1);
186 if (cdb_advance_fd (&cdb, dir) != 0)
190 if (cdb_fchdir (&cdb) != 0)
198 int saved_errno = errno;
208 # include "closeout.h"
214 main (int argc, char *argv[])
220 program_name = argv[0];
221 atexit (close_stdout);
223 len = getline (&line, &n, stdin);
226 int saved_errno = errno;
230 error (EXIT_FAILURE, saved_errno,
231 "reading standard input");
236 if (line[len-1] == '\n')
239 if (chdir_long (line) != 0)
240 error (EXIT_FAILURE, errno,
241 "chdir_long failed: %s", line);
245 /* Using `pwd' here makes sense only if it is a robust implementation,
246 like the one in coreutils after the 2004-04-19 changes. */
247 char const *cmd = "pwd";
248 execlp (cmd, (char *) NULL);
249 error (EXIT_FAILURE, errno, "%s", cmd);
261 compile-command: "gcc -DTEST_CHDIR=1 -g -O -W -Wall chdir-long.c libcoreutils.a"