1 /* provide a chdir function that tries not to fail due to ENAMETOOLONG
2 Copyright (C) 2004-2009 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"
33 # error "compile this file only if your system defines PATH_MAX"
42 cdb_init (struct cd_buf *cdb)
48 cdb_fchdir (struct cd_buf const *cdb)
50 return fchdir (cdb->fd);
54 cdb_free (struct cd_buf const *cdb)
58 bool close_fail = close (cdb->fd);
59 assert (! close_fail);
63 /* Given a file descriptor of an open directory (or AT_FDCWD), CDB->fd,
64 try to open the CDB->fd-relative directory, DIR. If the open succeeds,
65 update CDB->fd with the resulting descriptor, close the incoming file
66 descriptor, and return zero. Upon failure, return -1 and set errno. */
68 cdb_advance_fd (struct cd_buf *cdb, char const *dir)
70 int new_fd = openat (cdb->fd, dir,
71 O_RDONLY | O_DIRECTORY | O_NOCTTY | O_NONBLOCK);
81 /* Return a pointer to the first non-slash in S. */
83 find_non_slash (char const *s)
85 size_t n_slash = strspn (s, "/");
86 return (char *) s + n_slash;
89 /* This is a function much like chdir, but without the PATH_MAX limitation
90 on the length of the directory name. A significant difference is that
91 it must be able to modify (albeit only temporarily) the directory
92 name. It handles an arbitrarily long directory name by operating
93 on manageable portions of the name. On systems without the openat
94 syscall, this means changing the working directory to more and more
95 `distant' points along the long directory name and then restoring
96 the working directory. If any of those attempts to save or restore
97 the working directory fails, this function exits nonzero.
99 Note that this function may still fail with errno == ENAMETOOLONG, but
100 only if the specified directory name contains a component that is long
101 enough to provoke such a failure all by itself (e.g. if the component
102 has length PATH_MAX or greater on systems that define PATH_MAX). */
105 chdir_long (char *dir)
108 if (e == 0 || errno != ENAMETOOLONG)
112 size_t len = strlen (dir);
113 char *dir_end = dir + len;
115 size_t n_leading_slash;
119 /* If DIR is the empty string, then the chdir above
120 must have failed and set errno to ENOENT. */
122 assert (PATH_MAX <= len);
124 /* Count leading slashes. */
125 n_leading_slash = strspn (dir, "/");
127 /* Handle any leading slashes as well as any name that matches
128 the regular expression, m!^//hostname[/]*! . Handling this
129 prefix separately usually results in a single additional
130 cdb_advance_fd call, but it's worthwhile, since it makes the
131 code in the following loop cleaner. */
132 if (n_leading_slash == 2)
136 We already know that dir[2] is neither a slash nor '\0'. */
137 char *slash = memchr (dir + 3, '/', dir_end - (dir + 3));
140 errno = ENAMETOOLONG;
144 err = cdb_advance_fd (&cdb, dir);
148 dir = find_non_slash (slash + 1);
150 else if (n_leading_slash)
152 if (cdb_advance_fd (&cdb, "/") != 0)
154 dir += n_leading_slash;
157 assert (*dir != '/');
158 assert (dir <= dir_end);
160 while (PATH_MAX <= dir_end - dir)
163 /* Find a slash that is PATH_MAX or fewer bytes away from dir.
164 I.e. see if there is a slash that will give us a name of
165 length PATH_MAX-1 or less. */
166 char *slash = memrchr (dir, '/', PATH_MAX);
169 errno = ENAMETOOLONG;
174 assert (slash - dir < PATH_MAX);
175 err = cdb_advance_fd (&cdb, dir);
180 dir = find_non_slash (slash + 1);
185 if (cdb_advance_fd (&cdb, dir) != 0)
189 if (cdb_fchdir (&cdb) != 0)
197 int saved_errno = errno;
207 # include "closeout.h"
213 main (int argc, char *argv[])
219 program_name = argv[0];
220 atexit (close_stdout);
222 len = getline (&line, &n, stdin);
225 int saved_errno = errno;
229 error (EXIT_FAILURE, saved_errno,
230 "reading standard input");
235 if (line[len-1] == '\n')
238 if (chdir_long (line) != 0)
239 error (EXIT_FAILURE, errno,
240 "chdir_long failed: %s", line);
244 /* Using `pwd' here makes sense only if it is a robust implementation,
245 like the one in coreutils after the 2004-04-19 changes. */
246 char const *cmd = "pwd";
247 execlp (cmd, (char *) NULL);
248 error (EXIT_FAILURE, errno, "%s", cmd);
260 compile-command: "gcc -DTEST_CHDIR=1 -g -O -W -Wall chdir-long.c libcoreutils.a"