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 attribute __pure__ was added in gcc 2.96. */
36 #undef _GL_ATTRIBUTE_PURE
37 #if __GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 96)
38 # define _GL_ATTRIBUTE_PURE __attribute__ ((__pure__))
40 # define _GL_ATTRIBUTE_PURE /* empty */
43 /* The results of openat() in this file are not leaked to any
44 single-threaded code that could use stdio.
45 FIXME - if the kernel ever adds support for multi-thread safety for
46 avoiding standard fds, then we should use openat_safer. */
54 cdb_init (struct cd_buf *cdb)
60 cdb_fchdir (struct cd_buf const *cdb)
62 return fchdir (cdb->fd);
66 cdb_free (struct cd_buf const *cdb)
70 bool close_fail = close (cdb->fd);
71 assert (! close_fail);
75 /* Given a file descriptor of an open directory (or AT_FDCWD), CDB->fd,
76 try to open the CDB->fd-relative directory, DIR. If the open succeeds,
77 update CDB->fd with the resulting descriptor, close the incoming file
78 descriptor, and return zero. Upon failure, return -1 and set errno. */
80 cdb_advance_fd (struct cd_buf *cdb, char const *dir)
82 int new_fd = openat (cdb->fd, dir,
83 O_SEARCH | O_DIRECTORY | O_NOCTTY | O_NONBLOCK);
93 /* Return a pointer to the first non-slash in S. */
94 static inline char * _GL_ATTRIBUTE_PURE
95 find_non_slash (char const *s)
97 size_t n_slash = strspn (s, "/");
98 return (char *) s + n_slash;
101 /* This is a function much like chdir, but without the PATH_MAX limitation
102 on the length of the directory name. A significant difference is that
103 it must be able to modify (albeit only temporarily) the directory
104 name. It handles an arbitrarily long directory name by operating
105 on manageable portions of the name. On systems without the openat
106 syscall, this means changing the working directory to more and more
107 `distant' points along the long directory name and then restoring
108 the working directory. If any of those attempts to save or restore
109 the working directory fails, this function exits nonzero.
111 Note that this function may still fail with errno == ENAMETOOLONG, but
112 only if the specified directory name contains a component that is long
113 enough to provoke such a failure all by itself (e.g. if the component
114 has length PATH_MAX or greater on systems that define PATH_MAX). */
117 chdir_long (char *dir)
120 if (e == 0 || errno != ENAMETOOLONG)
124 size_t len = strlen (dir);
125 char *dir_end = dir + len;
127 size_t n_leading_slash;
131 /* If DIR is the empty string, then the chdir above
132 must have failed and set errno to ENOENT. */
134 assert (PATH_MAX <= len);
136 /* Count leading slashes. */
137 n_leading_slash = strspn (dir, "/");
139 /* Handle any leading slashes as well as any name that matches
140 the regular expression, m!^//hostname[/]*! . Handling this
141 prefix separately usually results in a single additional
142 cdb_advance_fd call, but it's worthwhile, since it makes the
143 code in the following loop cleaner. */
144 if (n_leading_slash == 2)
148 We already know that dir[2] is neither a slash nor '\0'. */
149 char *slash = memchr (dir + 3, '/', dir_end - (dir + 3));
152 errno = ENAMETOOLONG;
156 err = cdb_advance_fd (&cdb, dir);
160 dir = find_non_slash (slash + 1);
162 else if (n_leading_slash)
164 if (cdb_advance_fd (&cdb, "/") != 0)
166 dir += n_leading_slash;
169 assert (*dir != '/');
170 assert (dir <= dir_end);
172 while (PATH_MAX <= dir_end - dir)
175 /* Find a slash that is PATH_MAX or fewer bytes away from dir.
176 I.e. see if there is a slash that will give us a name of
177 length PATH_MAX-1 or less. */
178 char *slash = memrchr (dir, '/', PATH_MAX);
181 errno = ENAMETOOLONG;
186 assert (slash - dir < PATH_MAX);
187 err = cdb_advance_fd (&cdb, dir);
192 dir = find_non_slash (slash + 1);
197 if (cdb_advance_fd (&cdb, dir) != 0)
201 if (cdb_fchdir (&cdb) != 0)
209 int saved_errno = errno;
219 # include "closeout.h"
225 main (int argc, char *argv[])
231 program_name = argv[0];
232 atexit (close_stdout);
234 len = getline (&line, &n, stdin);
237 int saved_errno = errno;
241 error (EXIT_FAILURE, saved_errno,
242 "reading standard input");
247 if (line[len-1] == '\n')
250 if (chdir_long (line) != 0)
251 error (EXIT_FAILURE, errno,
252 "chdir_long failed: %s", line);
256 /* Using `pwd' here makes sense only if it is a robust implementation,
257 like the one in coreutils after the 2004-04-19 changes. */
258 char const *cmd = "pwd";
259 execlp (cmd, (char *) NULL);
260 error (EXIT_FAILURE, errno, "%s", cmd);
272 compile-command: "gcc -DTEST_CHDIR=1 -g -O -W -Wall chdir-long.c libcoreutils.a"