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;
48 if (acceptable(context, result))
51 inode = result->d_inode;
52 spin_lock(&inode->i_lock);
53 hlist_for_each_entry(dentry, &inode->i_dentry, d_alias) {
55 spin_unlock(&inode->i_lock);
58 if (dentry != result && acceptable(context, dentry)) {
62 spin_lock(&inode->i_lock);
65 spin_unlock(&inode->i_lock);
73 * Find root of a disconnected subtree and return a reference to it.
75 static struct dentry *
76 find_disconnected_root(struct dentry *dentry)
79 while (!IS_ROOT(dentry)) {
80 struct dentry *parent = dget_parent(dentry);
82 if (!(parent->d_flags & DCACHE_DISCONNECTED)) {
94 * Make sure target_dir is fully connected to the dentry tree.
96 * It may already be, as the flag isn't always updated when connection happens.
99 reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf)
105 * It is possible that a confused file system might not let us complete
106 * the path to the root. For example, if get_parent returns a directory
107 * in which we cannot find a name for the child. While this implies a
108 * very sick filesystem we don't want it to cause knfsd to spin. Hence
109 * the noprogress counter. If we go through the loop 10 times (2 is
110 * probably enough) without getting anywhere, we just give up
112 while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {
113 struct dentry *pd = find_disconnected_root(target_dir);
116 /* must have found a connected parent - great */
117 spin_lock(&pd->d_lock);
118 pd->d_flags &= ~DCACHE_DISCONNECTED;
119 spin_unlock(&pd->d_lock);
121 } else if (pd == mnt->mnt_sb->s_root) {
122 printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible\n");
123 spin_lock(&pd->d_lock);
124 pd->d_flags &= ~DCACHE_DISCONNECTED;
125 spin_unlock(&pd->d_lock);
129 * We have hit the top of a disconnected path, try to
130 * find parent and connect.
132 * Racing with some other process renaming a directory
133 * isn't much of a problem here. If someone renames
134 * the directory, it will end up properly connected,
135 * which is what we want
137 * Getting the parent can't be supported generically,
138 * the locking is too icky.
140 * Instead we just return EACCES. If server reboots
141 * or inodes get flushed, you lose
143 struct dentry *ppd = ERR_PTR(-EACCES);
146 mutex_lock(&pd->d_inode->i_mutex);
147 if (mnt->mnt_sb->s_export_op->get_parent)
148 ppd = mnt->mnt_sb->s_export_op->get_parent(pd);
149 mutex_unlock(&pd->d_inode->i_mutex);
153 dprintk("%s: get_parent of %ld failed, err %d\n",
154 __func__, pd->d_inode->i_ino, err);
159 dprintk("%s: find name of %lu in %lu\n", __func__,
160 pd->d_inode->i_ino, ppd->d_inode->i_ino);
161 err = exportfs_get_name(mnt, ppd, nbuf, pd);
166 /* some race between get_parent and
167 * get_name? just try again
172 dprintk("%s: found name: %s\n", __func__, nbuf);
173 mutex_lock(&ppd->d_inode->i_mutex);
174 npd = lookup_one_len(nbuf, ppd, strlen(nbuf));
175 mutex_unlock(&ppd->d_inode->i_mutex);
178 dprintk("%s: lookup failed: %d\n",
184 /* we didn't really want npd, we really wanted
185 * a side-effect of the lookup.
186 * hopefully, npd == pd, though it isn't really
187 * a problem if it isn't
192 printk("%s: npd != pd\n", __func__);
196 /* something went wrong, we have to give up */
204 if (target_dir->d_flags & DCACHE_DISCONNECTED) {
205 /* something went wrong - oh-well */
214 struct getdents_callback {
215 char *name; /* name that was found. It already points to a
216 buffer NAME_MAX+1 is size */
217 unsigned long ino; /* the inum we are looking for */
218 int found; /* inode matched? */
219 int sequence; /* sequence counter */
223 * A rather strange filldir function to capture
224 * the name matching the specified inode number.
226 static int filldir_one(void * __buf, const char * name, int len,
227 loff_t pos, u64 ino, unsigned int d_type)
229 struct getdents_callback *buf = __buf;
233 if (buf->ino == ino) {
234 memcpy(buf->name, name, len);
235 buf->name[len] = '\0';
243 * get_name - default export_operations->get_name function
244 * @dentry: the directory in which to find a name
245 * @name: a pointer to a %NAME_MAX+1 char buffer to store the name
246 * @child: the dentry for the child directory.
248 * calls readdir on the parent until it finds an entry with
249 * the same inode number as the child, and returns that.
251 static int get_name(const struct path *path, char *name, struct dentry *child)
253 const struct cred *cred = current_cred();
254 struct inode *dir = path->dentry->d_inode;
257 struct getdents_callback buffer;
260 if (!dir || !S_ISDIR(dir->i_mode))
266 * Open the directory ...
268 file = dentry_open(path, O_RDONLY, cred);
269 error = PTR_ERR(file);
274 if (!file->f_op->readdir)
278 buffer.ino = child->d_inode->i_ino;
282 int old_seq = buffer.sequence;
284 error = vfs_readdir(file, filldir_one, &buffer);
294 if (old_seq == buffer.sequence)
305 * export_encode_fh - default export_operations->encode_fh function
306 * @inode: the object to encode
307 * @fh: where to store the file handle fragment
308 * @max_len: maximum length to store there
309 * @parent: parent directory inode, if wanted
311 * This default encode_fh function assumes that the 32 inode number
312 * is suitable for locating an inode, and that the generation number
313 * can be used to check that it is still valid. It places them in the
314 * filehandle fragment where export_decode_fh expects to find them.
316 static int export_encode_fh(struct inode *inode, struct fid *fid,
317 int *max_len, struct inode *parent)
320 int type = FILEID_INO32_GEN;
322 if (parent && (len < 4)) {
324 return FILEID_INVALID;
325 } else if (len < 2) {
327 return FILEID_INVALID;
331 fid->i32.ino = inode->i_ino;
332 fid->i32.gen = inode->i_generation;
334 fid->i32.parent_ino = parent->i_ino;
335 fid->i32.parent_gen = parent->i_generation;
337 type = FILEID_INO32_GEN_PARENT;
343 int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid,
344 int *max_len, struct inode *parent)
346 const struct export_operations *nop = inode->i_sb->s_export_op;
348 if (nop && nop->encode_fh)
349 return nop->encode_fh(inode, fid->raw, max_len, parent);
351 return export_encode_fh(inode, fid, max_len, parent);
353 EXPORT_SYMBOL_GPL(exportfs_encode_inode_fh);
355 int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len,
359 struct dentry *p = NULL;
360 struct inode *inode = dentry->d_inode, *parent = NULL;
362 if (connectable && !S_ISDIR(inode->i_mode)) {
363 p = dget_parent(dentry);
365 * note that while p might've ceased to be our parent already,
366 * it's still pinned by and still positive.
371 error = exportfs_encode_inode_fh(inode, fid, max_len, parent);
376 EXPORT_SYMBOL_GPL(exportfs_encode_fh);
378 struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
379 int fh_len, int fileid_type,
380 int (*acceptable)(void *, struct dentry *), void *context)
382 const struct export_operations *nop = mnt->mnt_sb->s_export_op;
383 struct dentry *result, *alias;
384 char nbuf[NAME_MAX+1];
388 * Try to get any dentry for the given file handle from the filesystem.
390 if (!nop || !nop->fh_to_dentry)
391 return ERR_PTR(-ESTALE);
392 result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type);
394 result = ERR_PTR(-ESTALE);
398 if (S_ISDIR(result->d_inode->i_mode)) {
400 * This request is for a directory.
402 * On the positive side there is only one dentry for each
403 * directory inode. On the negative side this implies that we
404 * to ensure our dentry is connected all the way up to the
407 if (result->d_flags & DCACHE_DISCONNECTED) {
408 err = reconnect_path(mnt, result, nbuf);
413 if (!acceptable(context, result)) {
421 * It's not a directory. Life is a little more complicated.
423 struct dentry *target_dir, *nresult;
426 * See if either the dentry we just got from the filesystem
427 * or any alias for it is acceptable. This is always true
428 * if this filesystem is exported without the subtreecheck
429 * option. If the filesystem is exported with the subtree
430 * check option there's a fair chance we need to look at
431 * the parent directory in the file handle and make sure
432 * it's connected to the filesystem root.
434 alias = find_acceptable_alias(result, acceptable, context);
439 * Try to extract a dentry for the parent directory from the
440 * file handle. If this fails we'll have to give up.
443 if (!nop->fh_to_parent)
446 target_dir = nop->fh_to_parent(mnt->mnt_sb, fid,
447 fh_len, fileid_type);
450 err = PTR_ERR(target_dir);
451 if (IS_ERR(target_dir))
455 * And as usual we need to make sure the parent directory is
456 * connected to the filesystem root. The VFS really doesn't
457 * like disconnected directories..
459 err = reconnect_path(mnt, target_dir, nbuf);
466 * Now that we've got both a well-connected parent and a
467 * dentry for the inode we're after, make sure that our
468 * inode is actually connected to the parent.
470 err = exportfs_get_name(mnt, target_dir, nbuf, result);
472 mutex_lock(&target_dir->d_inode->i_mutex);
473 nresult = lookup_one_len(nbuf, target_dir,
475 mutex_unlock(&target_dir->d_inode->i_mutex);
476 if (!IS_ERR(nresult)) {
477 if (nresult->d_inode) {
486 * At this point we are done with the parent, but it's pinned
487 * by the child dentry anyway.
492 * And finally make sure the dentry is actually acceptable
495 alias = find_acceptable_alias(result, acceptable, context);
508 EXPORT_SYMBOL_GPL(exportfs_decode_fh);
510 MODULE_LICENSE("GPL");