1 /* provide a chdir function that tries not to fail due to ENAMETOOLONG
2 Copyright (C) 2004, 2005 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"
37 # define O_DIRECTORY 0
41 # error "compile this file only if your system defines PATH_MAX"
50 cdb_init (struct cd_buf *cdb)
56 cdb_fchdir (struct cd_buf const *cdb)
58 return fchdir (cdb->fd);
62 cdb_free (struct cd_buf const *cdb)
66 bool close_fail = close (cdb->fd);
67 assert (! close_fail);
71 /* Given a file descriptor of an open directory (or AT_FDCWD), CDB->fd,
72 try to open the CDB->fd-relative directory, DIR. If the open succeeds,
73 update CDB->fd with the resulting descriptor, close the incoming file
74 descriptor, and return zero. Upon failure, return -1 and set errno. */
76 cdb_advance_fd (struct cd_buf *cdb, char const *dir)
78 int new_fd = openat (cdb->fd, dir, O_RDONLY | O_DIRECTORY);
81 new_fd = openat (cdb->fd, dir, O_WRONLY | O_DIRECTORY);
92 /* Return a pointer to the first non-slash in S. */
94 find_non_slash (char const *s)
96 size_t n_slash = strspn (s, "/");
97 return (char *) s + n_slash;
100 /* This is a function much like chdir, but without the PATH_MAX limitation
101 on the length of the directory name. A significant difference is that
102 it must be able to modify (albeit only temporarily) the directory
103 name. It handles an arbitrarily long directory name by operating
104 on manageable portions of the name. On systems without the openat
105 syscall, this means changing the working directory to more and more
106 `distant' points along the long directory name and then restoring
107 the working directory. If any of those attempts to save or restore
108 the working directory fails, this function exits nonzero.
110 Note that this function may still fail with errno == ENAMETOOLONG, but
111 only if the specified directory name contains a component that is long
112 enough to provoke such a failure all by itself (e.g. if the component
113 has length PATH_MAX or greater on systems that define PATH_MAX). */
116 chdir_long (char *dir)
119 if (e == 0 || errno != ENAMETOOLONG)
123 size_t len = strlen (dir);
124 char *dir_end = dir + len;
126 size_t n_leading_slash;
130 /* If DIR is the empty string, then the chdir above
131 must have failed and set errno to ENOENT. */
133 assert (PATH_MAX <= len);
135 /* Count leading slashes. */
136 n_leading_slash = strspn (dir, "/");
138 /* Handle any leading slashes as well as any name that matches
139 the regular expression, m!^//hostname[/]*! . Handling this
140 prefix separately usually results in a single additional
141 cdb_advance_fd call, but it's worthwhile, since it makes the
142 code in the following loop cleaner. */
143 if (n_leading_slash == 2)
147 We already know that dir[2] is neither a slash nor '\0'. */
148 char *slash = memchr (dir + 3, '/', dir_end - (dir + 3));
151 errno = ENAMETOOLONG;
155 err = cdb_advance_fd (&cdb, dir);
159 dir = find_non_slash (slash + 1);
161 else if (n_leading_slash)
163 if (cdb_advance_fd (&cdb, "/") != 0)
165 dir += n_leading_slash;
168 assert (*dir != '/');
169 assert (dir <= dir_end);
171 while (PATH_MAX <= dir_end - dir)
174 /* Find a slash that is PATH_MAX or fewer bytes away from dir.
175 I.e. see if there is a slash that will give us a name of
176 length PATH_MAX-1 or less. */
177 char *slash = memrchr (dir, '/', PATH_MAX);
180 errno = ENAMETOOLONG;
185 assert (slash - dir < PATH_MAX);
186 err = cdb_advance_fd (&cdb, dir);
191 dir = find_non_slash (slash + 1);
196 if (cdb_advance_fd (&cdb, dir) != 0)
200 if (cdb_fchdir (&cdb) != 0)
208 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 -DHAVE_CONFIG_H -I.. -g -O -W -Wall chdir-long.c libcoreutils.a"