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(const struct path *path, char *name, struct dentry *child);
25 static int exportfs_get_name(struct vfsmount *mnt, struct dentry *dir,
26 char *name, struct dentry *child)
28 const struct export_operations *nop = dir->d_sb->s_export_op;
29 struct path path = {.mnt = mnt, .dentry = dir};
32 return nop->get_name(dir, name, child);
34 return get_name(&path, 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;
49 if (acceptable(context, result))
52 inode = result->d_inode;
53 spin_lock(&inode->i_lock);
54 hlist_for_each_entry(dentry, p, &inode->i_dentry, d_alias) {
56 spin_unlock(&inode->i_lock);
59 if (dentry != result && acceptable(context, dentry)) {
63 spin_lock(&inode->i_lock);
66 spin_unlock(&inode->i_lock);
74 * Find root of a disconnected subtree and return a reference to it.
76 static struct dentry *
77 find_disconnected_root(struct dentry *dentry)
80 while (!IS_ROOT(dentry)) {
81 struct dentry *parent = dget_parent(dentry);
83 if (!(parent->d_flags & DCACHE_DISCONNECTED)) {
95 * Make sure target_dir is fully connected to the dentry tree.
97 * It may already be, as the flag isn't always updated when connection happens.
100 reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf)
106 * It is possible that a confused file system might not let us complete
107 * the path to the root. For example, if get_parent returns a directory
108 * in which we cannot find a name for the child. While this implies a
109 * very sick filesystem we don't want it to cause knfsd to spin. Hence
110 * the noprogress counter. If we go through the loop 10 times (2 is
111 * probably enough) without getting anywhere, we just give up
113 while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {
114 struct dentry *pd = find_disconnected_root(target_dir);
117 /* must have found a connected parent - great */
118 spin_lock(&pd->d_lock);
119 pd->d_flags &= ~DCACHE_DISCONNECTED;
120 spin_unlock(&pd->d_lock);
122 } else if (pd == mnt->mnt_sb->s_root) {
123 printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible\n");
124 spin_lock(&pd->d_lock);
125 pd->d_flags &= ~DCACHE_DISCONNECTED;
126 spin_unlock(&pd->d_lock);
130 * We have hit the top of a disconnected path, try to
131 * find parent and connect.
133 * Racing with some other process renaming a directory
134 * isn't much of a problem here. If someone renames
135 * the directory, it will end up properly connected,
136 * which is what we want
138 * Getting the parent can't be supported generically,
139 * the locking is too icky.
141 * Instead we just return EACCES. If server reboots
142 * or inodes get flushed, you lose
144 struct dentry *ppd = ERR_PTR(-EACCES);
147 mutex_lock(&pd->d_inode->i_mutex);
148 if (mnt->mnt_sb->s_export_op->get_parent)
149 ppd = mnt->mnt_sb->s_export_op->get_parent(pd);
150 mutex_unlock(&pd->d_inode->i_mutex);
154 dprintk("%s: get_parent of %ld failed, err %d\n",
155 __func__, pd->d_inode->i_ino, err);
160 dprintk("%s: find name of %lu in %lu\n", __func__,
161 pd->d_inode->i_ino, ppd->d_inode->i_ino);
162 err = exportfs_get_name(mnt, ppd, nbuf, pd);
167 /* some race between get_parent and
168 * get_name? just try again
173 dprintk("%s: found name: %s\n", __func__, nbuf);
174 mutex_lock(&ppd->d_inode->i_mutex);
175 npd = lookup_one_len(nbuf, ppd, strlen(nbuf));
176 mutex_unlock(&ppd->d_inode->i_mutex);
179 dprintk("%s: lookup failed: %d\n",
185 /* we didn't really want npd, we really wanted
186 * a side-effect of the lookup.
187 * hopefully, npd == pd, though it isn't really
188 * a problem if it isn't
193 printk("%s: npd != pd\n", __func__);
197 /* something went wrong, we have to give up */
205 if (target_dir->d_flags & DCACHE_DISCONNECTED) {
206 /* something went wrong - oh-well */
215 struct getdents_callback {
216 char *name; /* name that was found. It already points to a
217 buffer NAME_MAX+1 is size */
218 unsigned long ino; /* the inum we are looking for */
219 int found; /* inode matched? */
220 int sequence; /* sequence counter */
224 * A rather strange filldir function to capture
225 * the name matching the specified inode number.
227 static int filldir_one(void * __buf, const char * name, int len,
228 loff_t pos, u64 ino, unsigned int d_type)
230 struct getdents_callback *buf = __buf;
234 if (buf->ino == ino) {
235 memcpy(buf->name, name, len);
236 buf->name[len] = '\0';
244 * get_name - default export_operations->get_name function
245 * @dentry: the directory in which to find a name
246 * @name: a pointer to a %NAME_MAX+1 char buffer to store the name
247 * @child: the dentry for the child directory.
249 * calls readdir on the parent until it finds an entry with
250 * the same inode number as the child, and returns that.
252 static int get_name(const struct path *path, char *name, struct dentry *child)
254 const struct cred *cred = current_cred();
255 struct inode *dir = path->dentry->d_inode;
258 struct getdents_callback buffer;
261 if (!dir || !S_ISDIR(dir->i_mode))
267 * Open the directory ...
269 file = dentry_open(path, O_RDONLY, cred);
270 error = PTR_ERR(file);
275 if (!file->f_op->readdir)
279 buffer.ino = child->d_inode->i_ino;
283 int old_seq = buffer.sequence;
285 error = vfs_readdir(file, filldir_one, &buffer);
295 if (old_seq == buffer.sequence)
306 * export_encode_fh - default export_operations->encode_fh function
307 * @inode: the object to encode
308 * @fh: where to store the file handle fragment
309 * @max_len: maximum length to store there
310 * @parent: parent directory inode, if wanted
312 * This default encode_fh function assumes that the 32 inode number
313 * is suitable for locating an inode, and that the generation number
314 * can be used to check that it is still valid. It places them in the
315 * filehandle fragment where export_decode_fh expects to find them.
317 static int export_encode_fh(struct inode *inode, struct fid *fid,
318 int *max_len, struct inode *parent)
321 int type = FILEID_INO32_GEN;
323 if (parent && (len < 4)) {
325 return FILEID_INVALID;
326 } else if (len < 2) {
328 return FILEID_INVALID;
332 fid->i32.ino = inode->i_ino;
333 fid->i32.gen = inode->i_generation;
335 fid->i32.parent_ino = parent->i_ino;
336 fid->i32.parent_gen = parent->i_generation;
338 type = FILEID_INO32_GEN_PARENT;
344 int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid,
345 int *max_len, struct inode *parent)
347 const struct export_operations *nop = inode->i_sb->s_export_op;
349 if (nop && nop->encode_fh)
350 return nop->encode_fh(inode, fid->raw, max_len, parent);
352 return export_encode_fh(inode, fid, max_len, parent);
354 EXPORT_SYMBOL_GPL(exportfs_encode_inode_fh);
356 int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len,
360 struct dentry *p = NULL;
361 struct inode *inode = dentry->d_inode, *parent = NULL;
363 if (connectable && !S_ISDIR(inode->i_mode)) {
364 p = dget_parent(dentry);
366 * note that while p might've ceased to be our parent already,
367 * it's still pinned by and still positive.
372 error = exportfs_encode_inode_fh(inode, fid, max_len, parent);
377 EXPORT_SYMBOL_GPL(exportfs_encode_fh);
379 struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
380 int fh_len, int fileid_type,
381 int (*acceptable)(void *, struct dentry *), void *context)
383 const struct export_operations *nop = mnt->mnt_sb->s_export_op;
384 struct dentry *result, *alias;
385 char nbuf[NAME_MAX+1];
389 * Try to get any dentry for the given file handle from the filesystem.
391 if (!nop || !nop->fh_to_dentry)
392 return ERR_PTR(-ESTALE);
393 result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type);
395 result = ERR_PTR(-ESTALE);
399 if (S_ISDIR(result->d_inode->i_mode)) {
401 * This request is for a directory.
403 * On the positive side there is only one dentry for each
404 * directory inode. On the negative side this implies that we
405 * to ensure our dentry is connected all the way up to the
408 if (result->d_flags & DCACHE_DISCONNECTED) {
409 err = reconnect_path(mnt, result, nbuf);
414 if (!acceptable(context, result)) {
422 * It's not a directory. Life is a little more complicated.
424 struct dentry *target_dir, *nresult;
427 * See if either the dentry we just got from the filesystem
428 * or any alias for it is acceptable. This is always true
429 * if this filesystem is exported without the subtreecheck
430 * option. If the filesystem is exported with the subtree
431 * check option there's a fair chance we need to look at
432 * the parent directory in the file handle and make sure
433 * it's connected to the filesystem root.
435 alias = find_acceptable_alias(result, acceptable, context);
440 * Try to extract a dentry for the parent directory from the
441 * file handle. If this fails we'll have to give up.
444 if (!nop->fh_to_parent)
447 target_dir = nop->fh_to_parent(mnt->mnt_sb, fid,
448 fh_len, fileid_type);
451 err = PTR_ERR(target_dir);
452 if (IS_ERR(target_dir))
456 * And as usual we need to make sure the parent directory is
457 * connected to the filesystem root. The VFS really doesn't
458 * like disconnected directories..
460 err = reconnect_path(mnt, target_dir, nbuf);
467 * Now that we've got both a well-connected parent and a
468 * dentry for the inode we're after, make sure that our
469 * inode is actually connected to the parent.
471 err = exportfs_get_name(mnt, target_dir, nbuf, result);
473 mutex_lock(&target_dir->d_inode->i_mutex);
474 nresult = lookup_one_len(nbuf, target_dir,
476 mutex_unlock(&target_dir->d_inode->i_mutex);
477 if (!IS_ERR(nresult)) {
478 if (nresult->d_inode) {
487 * At this point we are done with the parent, but it's pinned
488 * by the child dentry anyway.
493 * And finally make sure the dentry is actually acceptable
496 alias = find_acceptable_alias(result, acceptable, context);
509 EXPORT_SYMBOL_GPL(exportfs_decode_fh);
511 MODULE_LICENSE("GPL");