1 /* Create a hard link relative to open directories.
2 Copyright (C) 2009-2011 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 Eric Blake */
30 #include "areadlink.h"
32 #include "filenamecat.h"
33 #include "openat-priv.h"
36 # include <sys/param.h>
40 # define MAXSYMLINKS SYMLOOP_MAX
42 # define MAXSYMLINKS 20
48 /* Create a link. If FILE1 is a symlink, either create a hardlink to
49 that symlink, or fake it by creating an identical symlink. */
50 # if LINK_FOLLOWS_SYMLINKS == 0
51 # define link_immediate link
54 link_immediate (char const *file1, char const *file2)
56 char *target = areadlink (file1);
59 /* A symlink cannot be modified in-place. Therefore, creating
60 an identical symlink behaves like a hard link to a symlink,
61 except for incorrect st_ino and st_nlink. However, we must
62 be careful of EXDEV. */
65 char *dir = mdir_name (file2);
72 if (lstat (file1, &st1) == 0 && stat (dir, &st2) == 0)
74 if (st1.st_dev == st2.st_dev)
76 int result = symlink (target, file2);
77 int saved_errno = errno;
93 return link (file1, file2);
95 # endif /* LINK_FOLLOWS_SYMLINKS == 0 */
97 /* Create a link. If FILE1 is a symlink, create a hardlink to the
98 canonicalized file. */
99 # if 0 < LINK_FOLLOWS_SYMLINKS
100 # define link_follow link
103 link_follow (char const *file1, char const *file2)
105 char *name = (char *) file1;
110 /* Using realpath or canonicalize_file_name is too heavy-handed: we
111 don't need an absolute name, and we don't need to resolve
112 intermediate symlinks, just the basename of each iteration. */
113 while (i-- && (target = areadlink (name)))
115 if (IS_ABSOLUTE_FILE_NAME (target))
123 char *dir = mdir_name (name);
132 name = mfile_name_concat (dir, target, NULL);
147 if (!target && errno != EINVAL)
151 int saved_errno = errno;
157 result = link (name, file2);
160 int saved_errno = errno;
166 # endif /* 0 < LINK_FOLLOWS_SYMLINKS */
168 /* On Solaris, link() doesn't follow symlinks by default, but does so as soon
169 as a library or executable takes part in the program that has been compiled
170 with "c99" or "cc -xc99=all" or "cc ... /usr/lib/values-xpg4.o ...". */
171 # if LINK_FOLLOWS_SYMLINKS == -1
173 /* Reduce the penalty of link_immediate and link_follow by incorporating the
174 knowledge that link()'s behaviour depends on the __xpg4 variable. */
178 solaris_optimized_link_immediate (char const *file1, char const *file2)
181 return link (file1, file2);
182 return link_immediate (file1, file2);
186 solaris_optimized_link_follow (char const *file1, char const *file2)
189 return link (file1, file2);
190 return link_follow (file1, file2);
193 # define link_immediate solaris_optimized_link_immediate
194 # define link_follow solaris_optimized_link_follow
198 /* Create a link to FILE1, in the directory open on descriptor FD1, to FILE2,
199 in the directory open on descriptor FD2. If FILE1 is a symlink, FLAG
200 controls whether to dereference FILE1 first. If possible, do it without
201 changing the working directory. Otherwise, resort to using
202 save_cwd/fchdir, then rename/restore_cwd. If either the save_cwd or
203 the restore_cwd fails, then give a diagnostic and exit nonzero. */
206 linkat (int fd1, char const *file1, int fd2, char const *file2, int flag)
208 if (flag & ~AT_SYMLINK_FOLLOW)
213 return at_func2 (fd1, file1, fd2, file2,
214 flag ? link_follow : link_immediate);
217 #else /* HAVE_LINKAT */
221 /* Create a link. If FILE1 is a symlink, create a hardlink to the
222 canonicalized file. */
225 linkat_follow (int fd1, char const *file1, int fd2, char const *file2)
227 char *name = (char *) file1;
232 /* There is no realpathat. */
233 while (i-- && (target = areadlinkat (fd1, name)))
235 if (IS_ABSOLUTE_FILE_NAME (target))
243 char *dir = mdir_name (name);
252 name = mfile_name_concat (dir, target, NULL);
267 if (!target && errno != EINVAL)
271 int saved_errno = errno;
277 result = linkat (fd1, name, fd2, file2, 0);
280 int saved_errno = errno;
288 /* Like linkat, but guarantee that AT_SYMLINK_FOLLOW works even on
289 older Linux kernels. */
292 rpl_linkat (int fd1, char const *file1, int fd2, char const *file2, int flag)
294 if (flag & ~AT_SYMLINK_FOLLOW)
300 # if LINKAT_TRAILING_SLASH_BUG
301 /* Reject trailing slashes on non-directories. */
303 size_t len1 = strlen (file1);
304 size_t len2 = strlen (file2);
305 if ((len1 && file1[len1 - 1] == '/')
306 || (len2 && file2[len2 - 1] == '/'))
308 /* Let linkat() decide whether hard-linking directories is legal.
309 If fstatat() fails, then linkat() should fail for the same reason;
310 if fstatat() succeeds, require a directory. */
312 if (fstatat (fd1, file1, &st, flag ? 0 : AT_SYMLINK_NOFOLLOW))
314 if (!S_ISDIR (st.st_mode))
324 return linkat (fd1, file1, fd2, file2, flag);
326 /* Cache the information on whether the system call really works. */
328 static int have_follow_really; /* 0 = unknown, 1 = yes, -1 = no */
329 if (0 <= have_follow_really)
331 int result = linkat (fd1, file1, fd2, file2, flag);
332 if (!(result == -1 && errno == EINVAL))
334 have_follow_really = 1;
337 have_follow_really = -1;
340 return linkat_follow (fd1, file1, fd2, file2);
343 #endif /* HAVE_LINKAT */