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 list_for_each_entry(dentry, &result->d_inode->i_dentry, d_alias) {
53 spin_unlock(&dcache_lock);
56 if (dentry != result && acceptable(context, dentry)) {
60 spin_lock(&dcache_lock);
63 spin_unlock(&dcache_lock);
71 * Find root of a disconnected subtree and return a reference to it.
73 static struct dentry *
74 find_disconnected_root(struct dentry *dentry)
77 while (!IS_ROOT(dentry)) {
78 struct dentry *parent = dget_parent(dentry);
80 if (!(parent->d_flags & DCACHE_DISCONNECTED)) {
92 * Make sure target_dir is fully connected to the dentry tree.
94 * It may already be, as the flag isn't always updated when connection happens.
97 reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf)
103 * It is possible that a confused file system might not let us complete
104 * the path to the root. For example, if get_parent returns a directory
105 * in which we cannot find a name for the child. While this implies a
106 * very sick filesystem we don't want it to cause knfsd to spin. Hence
107 * the noprogress counter. If we go through the loop 10 times (2 is
108 * probably enough) without getting anywhere, we just give up
110 while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {
111 struct dentry *pd = find_disconnected_root(target_dir);
114 /* must have found a connected parent - great */
115 spin_lock(&pd->d_lock);
116 pd->d_flags &= ~DCACHE_DISCONNECTED;
117 spin_unlock(&pd->d_lock);
119 } else if (pd == mnt->mnt_sb->s_root) {
120 printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible\n");
121 spin_lock(&pd->d_lock);
122 pd->d_flags &= ~DCACHE_DISCONNECTED;
123 spin_unlock(&pd->d_lock);
127 * We have hit the top of a disconnected path, try to
128 * find parent and connect.
130 * Racing with some other process renaming a directory
131 * isn't much of a problem here. If someone renames
132 * the directory, it will end up properly connected,
133 * which is what we want
135 * Getting the parent can't be supported generically,
136 * the locking is too icky.
138 * Instead we just return EACCES. If server reboots
139 * or inodes get flushed, you lose
141 struct dentry *ppd = ERR_PTR(-EACCES);
144 mutex_lock(&pd->d_inode->i_mutex);
145 if (mnt->mnt_sb->s_export_op->get_parent)
146 ppd = mnt->mnt_sb->s_export_op->get_parent(pd);
147 mutex_unlock(&pd->d_inode->i_mutex);
151 dprintk("%s: get_parent of %ld failed, err %d\n",
152 __func__, pd->d_inode->i_ino, err);
157 dprintk("%s: find name of %lu in %lu\n", __func__,
158 pd->d_inode->i_ino, ppd->d_inode->i_ino);
159 err = exportfs_get_name(mnt, ppd, nbuf, pd);
164 /* some race between get_parent and
165 * get_name? just try again
170 dprintk("%s: found name: %s\n", __func__, nbuf);
171 mutex_lock(&ppd->d_inode->i_mutex);
172 npd = lookup_one_len(nbuf, ppd, strlen(nbuf));
173 mutex_unlock(&ppd->d_inode->i_mutex);
176 dprintk("%s: lookup failed: %d\n",
182 /* we didn't really want npd, we really wanted
183 * a side-effect of the lookup.
184 * hopefully, npd == pd, though it isn't really
185 * a problem if it isn't
190 printk("%s: npd != pd\n", __func__);
194 /* something went wrong, we have to give up */
202 if (target_dir->d_flags & DCACHE_DISCONNECTED) {
203 /* something went wrong - oh-well */
212 struct getdents_callback {
213 char *name; /* name that was found. It already points to a
214 buffer NAME_MAX+1 is size */
215 unsigned long ino; /* the inum we are looking for */
216 int found; /* inode matched? */
217 int sequence; /* sequence counter */
221 * A rather strange filldir function to capture
222 * the name matching the specified inode number.
224 static int filldir_one(void * __buf, const char * name, int len,
225 loff_t pos, u64 ino, unsigned int d_type)
227 struct getdents_callback *buf = __buf;
231 if (buf->ino == ino) {
232 memcpy(buf->name, name, len);
233 buf->name[len] = '\0';
241 * get_name - default export_operations->get_name function
242 * @dentry: the directory in which to find a name
243 * @name: a pointer to a %NAME_MAX+1 char buffer to store the name
244 * @child: the dentry for the child directory.
246 * calls readdir on the parent until it finds an entry with
247 * the same inode number as the child, and returns that.
249 static int get_name(struct vfsmount *mnt, struct dentry *dentry,
250 char *name, struct dentry *child)
252 const struct cred *cred = current_cred();
253 struct inode *dir = dentry->d_inode;
256 struct getdents_callback buffer;
259 if (!dir || !S_ISDIR(dir->i_mode))
265 * Open the directory ...
267 file = dentry_open(dget(dentry), mntget(mnt), O_RDONLY, cred);
268 error = PTR_ERR(file);
273 if (!file->f_op->readdir)
277 buffer.ino = child->d_inode->i_ino;
281 int old_seq = buffer.sequence;
283 error = vfs_readdir(file, filldir_one, &buffer);
293 if (old_seq == buffer.sequence)
304 * export_encode_fh - default export_operations->encode_fh function
305 * @dentry: the dentry to encode
306 * @fh: where to store the file handle fragment
307 * @max_len: maximum length to store there
308 * @connectable: whether to store parent information
310 * This default encode_fh function assumes that the 32 inode number
311 * is suitable for locating an inode, and that the generation number
312 * can be used to check that it is still valid. It places them in the
313 * filehandle fragment where export_decode_fh expects to find them.
315 static int export_encode_fh(struct dentry *dentry, struct fid *fid,
316 int *max_len, int connectable)
318 struct inode * inode = dentry->d_inode;
320 int type = FILEID_INO32_GEN;
322 if (len < 2 || (connectable && len < 4))
326 fid->i32.ino = inode->i_ino;
327 fid->i32.gen = inode->i_generation;
328 if (connectable && !S_ISDIR(inode->i_mode)) {
329 struct inode *parent;
331 spin_lock(&dentry->d_lock);
332 parent = dentry->d_parent->d_inode;
333 fid->i32.parent_ino = parent->i_ino;
334 fid->i32.parent_gen = parent->i_generation;
335 spin_unlock(&dentry->d_lock);
337 type = FILEID_INO32_GEN_PARENT;
343 int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len,
346 const struct export_operations *nop = dentry->d_sb->s_export_op;
350 error = nop->encode_fh(dentry, fid->raw, max_len, connectable);
352 error = export_encode_fh(dentry, fid, max_len, connectable);
356 EXPORT_SYMBOL_GPL(exportfs_encode_fh);
358 struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
359 int fh_len, int fileid_type,
360 int (*acceptable)(void *, struct dentry *), void *context)
362 const struct export_operations *nop = mnt->mnt_sb->s_export_op;
363 struct dentry *result, *alias;
364 char nbuf[NAME_MAX+1];
368 * Try to get any dentry for the given file handle from the filesystem.
370 result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type);
372 result = ERR_PTR(-ESTALE);
376 if (S_ISDIR(result->d_inode->i_mode)) {
378 * This request is for a directory.
380 * On the positive side there is only one dentry for each
381 * directory inode. On the negative side this implies that we
382 * to ensure our dentry is connected all the way up to the
385 if (result->d_flags & DCACHE_DISCONNECTED) {
386 err = reconnect_path(mnt, result, nbuf);
391 if (!acceptable(context, result)) {
399 * It's not a directory. Life is a little more complicated.
401 struct dentry *target_dir, *nresult;
404 * See if either the dentry we just got from the filesystem
405 * or any alias for it is acceptable. This is always true
406 * if this filesystem is exported without the subtreecheck
407 * option. If the filesystem is exported with the subtree
408 * check option there's a fair chance we need to look at
409 * the parent directory in the file handle and make sure
410 * it's connected to the filesystem root.
412 alias = find_acceptable_alias(result, acceptable, context);
417 * Try to extract a dentry for the parent directory from the
418 * file handle. If this fails we'll have to give up.
421 if (!nop->fh_to_parent)
424 target_dir = nop->fh_to_parent(mnt->mnt_sb, fid,
425 fh_len, fileid_type);
428 err = PTR_ERR(target_dir);
429 if (IS_ERR(target_dir))
433 * And as usual we need to make sure the parent directory is
434 * connected to the filesystem root. The VFS really doesn't
435 * like disconnected directories..
437 err = reconnect_path(mnt, target_dir, nbuf);
444 * Now that we've got both a well-connected parent and a
445 * dentry for the inode we're after, make sure that our
446 * inode is actually connected to the parent.
448 err = exportfs_get_name(mnt, target_dir, nbuf, result);
450 mutex_lock(&target_dir->d_inode->i_mutex);
451 nresult = lookup_one_len(nbuf, target_dir,
453 mutex_unlock(&target_dir->d_inode->i_mutex);
454 if (!IS_ERR(nresult)) {
455 if (nresult->d_inode) {
464 * At this point we are done with the parent, but it's pinned
465 * by the child dentry anyway.
470 * And finally make sure the dentry is actually acceptable
473 alias = find_acceptable_alias(result, acceptable, context);
486 EXPORT_SYMBOL_GPL(exportfs_decode_fh);
488 MODULE_LICENSE("GPL");