2 * Copyright (C) Neil Brown 2002
3 * Copyright (C) Christoph Hellwig 2007
5 * This file contains the code mapping from inodes to NFS file handles,
6 * and for mapping back from file handles to dentries.
8 * For details on why we do all the strange and hairy things in here
9 * take a look at Documentation/filesystems/nfs/Exporting.
11 #include <linux/exportfs.h>
13 #include <linux/file.h>
14 #include <linux/module.h>
15 #include <linux/mount.h>
16 #include <linux/namei.h>
17 #include <linux/sched.h>
19 #define dprintk(fmt, args...) do{}while(0)
22 static int get_name(struct vfsmount *mnt, struct dentry *dentry, char *name,
23 struct dentry *child);
26 static int exportfs_get_name(struct vfsmount *mnt, struct dentry *dir,
27 char *name, struct dentry *child)
29 const struct export_operations *nop = dir->d_sb->s_export_op;
32 return nop->get_name(dir, name, child);
34 return get_name(mnt, dir, name, child);
38 * Check if the dentry or any of it's aliases is acceptable.
40 static struct dentry *
41 find_acceptable_alias(struct dentry *result,
42 int (*acceptable)(void *context, struct dentry *dentry),
45 struct dentry *dentry, *toput = NULL;
47 if (acceptable(context, result))
50 spin_lock(&dcache_lock);
51 spin_lock(&dcache_inode_lock);
52 list_for_each_entry(dentry, &result->d_inode->i_dentry, d_alias) {
54 spin_unlock(&dcache_inode_lock);
55 spin_unlock(&dcache_lock);
58 if (dentry != result && acceptable(context, dentry)) {
62 spin_lock(&dcache_lock);
63 spin_lock(&dcache_inode_lock);
66 spin_unlock(&dcache_inode_lock);
67 spin_unlock(&dcache_lock);
75 * Find root of a disconnected subtree and return a reference to it.
77 static struct dentry *
78 find_disconnected_root(struct dentry *dentry)
81 while (!IS_ROOT(dentry)) {
82 struct dentry *parent = dget_parent(dentry);
84 if (!(parent->d_flags & DCACHE_DISCONNECTED)) {
96 * Make sure target_dir is fully connected to the dentry tree.
98 * It may already be, as the flag isn't always updated when connection happens.
101 reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf)
107 * It is possible that a confused file system might not let us complete
108 * the path to the root. For example, if get_parent returns a directory
109 * in which we cannot find a name for the child. While this implies a
110 * very sick filesystem we don't want it to cause knfsd to spin. Hence
111 * the noprogress counter. If we go through the loop 10 times (2 is
112 * probably enough) without getting anywhere, we just give up
114 while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {
115 struct dentry *pd = find_disconnected_root(target_dir);
118 /* must have found a connected parent - great */
119 spin_lock(&pd->d_lock);
120 pd->d_flags &= ~DCACHE_DISCONNECTED;
121 spin_unlock(&pd->d_lock);
123 } else if (pd == mnt->mnt_sb->s_root) {
124 printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible\n");
125 spin_lock(&pd->d_lock);
126 pd->d_flags &= ~DCACHE_DISCONNECTED;
127 spin_unlock(&pd->d_lock);
131 * We have hit the top of a disconnected path, try to
132 * find parent and connect.
134 * Racing with some other process renaming a directory
135 * isn't much of a problem here. If someone renames
136 * the directory, it will end up properly connected,
137 * which is what we want
139 * Getting the parent can't be supported generically,
140 * the locking is too icky.
142 * Instead we just return EACCES. If server reboots
143 * or inodes get flushed, you lose
145 struct dentry *ppd = ERR_PTR(-EACCES);
148 mutex_lock(&pd->d_inode->i_mutex);
149 if (mnt->mnt_sb->s_export_op->get_parent)
150 ppd = mnt->mnt_sb->s_export_op->get_parent(pd);
151 mutex_unlock(&pd->d_inode->i_mutex);
155 dprintk("%s: get_parent of %ld failed, err %d\n",
156 __func__, pd->d_inode->i_ino, err);
161 dprintk("%s: find name of %lu in %lu\n", __func__,
162 pd->d_inode->i_ino, ppd->d_inode->i_ino);
163 err = exportfs_get_name(mnt, ppd, nbuf, pd);
168 /* some race between get_parent and
169 * get_name? just try again
174 dprintk("%s: found name: %s\n", __func__, nbuf);
175 mutex_lock(&ppd->d_inode->i_mutex);
176 npd = lookup_one_len(nbuf, ppd, strlen(nbuf));
177 mutex_unlock(&ppd->d_inode->i_mutex);
180 dprintk("%s: lookup failed: %d\n",
186 /* we didn't really want npd, we really wanted
187 * a side-effect of the lookup.
188 * hopefully, npd == pd, though it isn't really
189 * a problem if it isn't
194 printk("%s: npd != pd\n", __func__);
198 /* something went wrong, we have to give up */
206 if (target_dir->d_flags & DCACHE_DISCONNECTED) {
207 /* something went wrong - oh-well */
216 struct getdents_callback {
217 char *name; /* name that was found. It already points to a
218 buffer NAME_MAX+1 is size */
219 unsigned long ino; /* the inum we are looking for */
220 int found; /* inode matched? */
221 int sequence; /* sequence counter */
225 * A rather strange filldir function to capture
226 * the name matching the specified inode number.
228 static int filldir_one(void * __buf, const char * name, int len,
229 loff_t pos, u64 ino, unsigned int d_type)
231 struct getdents_callback *buf = __buf;
235 if (buf->ino == ino) {
236 memcpy(buf->name, name, len);
237 buf->name[len] = '\0';
245 * get_name - default export_operations->get_name function
246 * @dentry: the directory in which to find a name
247 * @name: a pointer to a %NAME_MAX+1 char buffer to store the name
248 * @child: the dentry for the child directory.
250 * calls readdir on the parent until it finds an entry with
251 * the same inode number as the child, and returns that.
253 static int get_name(struct vfsmount *mnt, struct dentry *dentry,
254 char *name, struct dentry *child)
256 const struct cred *cred = current_cred();
257 struct inode *dir = dentry->d_inode;
260 struct getdents_callback buffer;
263 if (!dir || !S_ISDIR(dir->i_mode))
269 * Open the directory ...
271 file = dentry_open(dget(dentry), mntget(mnt), O_RDONLY, cred);
272 error = PTR_ERR(file);
277 if (!file->f_op->readdir)
281 buffer.ino = child->d_inode->i_ino;
285 int old_seq = buffer.sequence;
287 error = vfs_readdir(file, filldir_one, &buffer);
297 if (old_seq == buffer.sequence)
308 * export_encode_fh - default export_operations->encode_fh function
309 * @dentry: the dentry to encode
310 * @fh: where to store the file handle fragment
311 * @max_len: maximum length to store there
312 * @connectable: whether to store parent information
314 * This default encode_fh function assumes that the 32 inode number
315 * is suitable for locating an inode, and that the generation number
316 * can be used to check that it is still valid. It places them in the
317 * filehandle fragment where export_decode_fh expects to find them.
319 static int export_encode_fh(struct dentry *dentry, struct fid *fid,
320 int *max_len, int connectable)
322 struct inode * inode = dentry->d_inode;
324 int type = FILEID_INO32_GEN;
326 if (len < 2 || (connectable && len < 4))
330 fid->i32.ino = inode->i_ino;
331 fid->i32.gen = inode->i_generation;
332 if (connectable && !S_ISDIR(inode->i_mode)) {
333 struct inode *parent;
335 spin_lock(&dentry->d_lock);
336 parent = dentry->d_parent->d_inode;
337 fid->i32.parent_ino = parent->i_ino;
338 fid->i32.parent_gen = parent->i_generation;
339 spin_unlock(&dentry->d_lock);
341 type = FILEID_INO32_GEN_PARENT;
347 int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len,
350 const struct export_operations *nop = dentry->d_sb->s_export_op;
354 error = nop->encode_fh(dentry, fid->raw, max_len, connectable);
356 error = export_encode_fh(dentry, fid, max_len, connectable);
360 EXPORT_SYMBOL_GPL(exportfs_encode_fh);
362 struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
363 int fh_len, int fileid_type,
364 int (*acceptable)(void *, struct dentry *), void *context)
366 const struct export_operations *nop = mnt->mnt_sb->s_export_op;
367 struct dentry *result, *alias;
368 char nbuf[NAME_MAX+1];
372 * Try to get any dentry for the given file handle from the filesystem.
374 result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type);
376 result = ERR_PTR(-ESTALE);
380 if (S_ISDIR(result->d_inode->i_mode)) {
382 * This request is for a directory.
384 * On the positive side there is only one dentry for each
385 * directory inode. On the negative side this implies that we
386 * to ensure our dentry is connected all the way up to the
389 if (result->d_flags & DCACHE_DISCONNECTED) {
390 err = reconnect_path(mnt, result, nbuf);
395 if (!acceptable(context, result)) {
403 * It's not a directory. Life is a little more complicated.
405 struct dentry *target_dir, *nresult;
408 * See if either the dentry we just got from the filesystem
409 * or any alias for it is acceptable. This is always true
410 * if this filesystem is exported without the subtreecheck
411 * option. If the filesystem is exported with the subtree
412 * check option there's a fair chance we need to look at
413 * the parent directory in the file handle and make sure
414 * it's connected to the filesystem root.
416 alias = find_acceptable_alias(result, acceptable, context);
421 * Try to extract a dentry for the parent directory from the
422 * file handle. If this fails we'll have to give up.
425 if (!nop->fh_to_parent)
428 target_dir = nop->fh_to_parent(mnt->mnt_sb, fid,
429 fh_len, fileid_type);
432 err = PTR_ERR(target_dir);
433 if (IS_ERR(target_dir))
437 * And as usual we need to make sure the parent directory is
438 * connected to the filesystem root. The VFS really doesn't
439 * like disconnected directories..
441 err = reconnect_path(mnt, target_dir, nbuf);
448 * Now that we've got both a well-connected parent and a
449 * dentry for the inode we're after, make sure that our
450 * inode is actually connected to the parent.
452 err = exportfs_get_name(mnt, target_dir, nbuf, result);
454 mutex_lock(&target_dir->d_inode->i_mutex);
455 nresult = lookup_one_len(nbuf, target_dir,
457 mutex_unlock(&target_dir->d_inode->i_mutex);
458 if (!IS_ERR(nresult)) {
459 if (nresult->d_inode) {
468 * At this point we are done with the parent, but it's pinned
469 * by the child dentry anyway.
474 * And finally make sure the dentry is actually acceptable
477 alias = find_acceptable_alias(result, acceptable, context);
490 EXPORT_SYMBOL_GPL(exportfs_decode_fh);
492 MODULE_LICENSE("GPL");