1 /* provide a chdir function that tries not to fail due to ENAMETOOLONG
2 Copyright (C) 2004, 2005, 2006 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 2, or (at your option)
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, write to the Free Software Foundation,
16 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
18 /* written by Jim Meyering */
22 #include "chdir-long.h"
36 # error "compile this file only if your system defines PATH_MAX"
45 cdb_init (struct cd_buf *cdb)
51 cdb_fchdir (struct cd_buf const *cdb)
53 return fchdir (cdb->fd);
57 cdb_free (struct cd_buf const *cdb)
61 bool close_fail = close (cdb->fd);
62 assert (! close_fail);
66 /* Given a file descriptor of an open directory (or AT_FDCWD), CDB->fd,
67 try to open the CDB->fd-relative directory, DIR. If the open succeeds,
68 update CDB->fd with the resulting descriptor, close the incoming file
69 descriptor, and return zero. Upon failure, return -1 and set errno. */
71 cdb_advance_fd (struct cd_buf *cdb, char const *dir)
73 int new_fd = openat (cdb->fd, dir,
74 O_RDONLY | O_DIRECTORY | O_NOCTTY | O_NONBLOCK);
84 /* Return a pointer to the first non-slash in S. */
86 find_non_slash (char const *s)
88 size_t n_slash = strspn (s, "/");
89 return (char *) s + n_slash;
92 /* This is a function much like chdir, but without the PATH_MAX limitation
93 on the length of the directory name. A significant difference is that
94 it must be able to modify (albeit only temporarily) the directory
95 name. It handles an arbitrarily long directory name by operating
96 on manageable portions of the name. On systems without the openat
97 syscall, this means changing the working directory to more and more
98 `distant' points along the long directory name and then restoring
99 the working directory. If any of those attempts to save or restore
100 the working directory fails, this function exits nonzero.
102 Note that this function may still fail with errno == ENAMETOOLONG, but
103 only if the specified directory name contains a component that is long
104 enough to provoke such a failure all by itself (e.g. if the component
105 has length PATH_MAX or greater on systems that define PATH_MAX). */
108 chdir_long (char *dir)
111 if (e == 0 || errno != ENAMETOOLONG)
115 size_t len = strlen (dir);
116 char *dir_end = dir + len;
118 size_t n_leading_slash;
122 /* If DIR is the empty string, then the chdir above
123 must have failed and set errno to ENOENT. */
125 assert (PATH_MAX <= len);
127 /* Count leading slashes. */
128 n_leading_slash = strspn (dir, "/");
130 /* Handle any leading slashes as well as any name that matches
131 the regular expression, m!^//hostname[/]*! . Handling this
132 prefix separately usually results in a single additional
133 cdb_advance_fd call, but it's worthwhile, since it makes the
134 code in the following loop cleaner. */
135 if (n_leading_slash == 2)
139 We already know that dir[2] is neither a slash nor '\0'. */
140 char *slash = memchr (dir + 3, '/', dir_end - (dir + 3));
143 errno = ENAMETOOLONG;
147 err = cdb_advance_fd (&cdb, dir);
151 dir = find_non_slash (slash + 1);
153 else if (n_leading_slash)
155 if (cdb_advance_fd (&cdb, "/") != 0)
157 dir += n_leading_slash;
160 assert (*dir != '/');
161 assert (dir <= dir_end);
163 while (PATH_MAX <= dir_end - dir)
166 /* Find a slash that is PATH_MAX or fewer bytes away from dir.
167 I.e. see if there is a slash that will give us a name of
168 length PATH_MAX-1 or less. */
169 char *slash = memrchr (dir, '/', PATH_MAX);
172 errno = ENAMETOOLONG;
177 assert (slash - dir < PATH_MAX);
178 err = cdb_advance_fd (&cdb, dir);
183 dir = find_non_slash (slash + 1);
188 if (cdb_advance_fd (&cdb, dir) != 0)
192 if (cdb_fchdir (&cdb) != 0)
200 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"