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
;
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(struct vfsmount
*mnt
, struct dentry
*dentry
,
253 char *name
, struct dentry
*child
)
255 const struct cred
*cred
= current_cred();
256 struct inode
*dir
= dentry
->d_inode
;
259 struct getdents_callback buffer
;
262 if (!dir
|| !S_ISDIR(dir
->i_mode
))
268 * Open the directory ...
270 file
= dentry_open(dget(dentry
), mntget(mnt
), O_RDONLY
, cred
);
271 error
= PTR_ERR(file
);
276 if (!file
->f_op
->readdir
)
280 buffer
.ino
= child
->d_inode
->i_ino
;
284 int old_seq
= buffer
.sequence
;
286 error
= vfs_readdir(file
, filldir_one
, &buffer
);
296 if (old_seq
== buffer
.sequence
)
307 * export_encode_fh - default export_operations->encode_fh function
308 * @inode: the object to encode
309 * @fh: where to store the file handle fragment
310 * @max_len: maximum length to store there
311 * @parent: parent directory inode, if wanted
313 * This default encode_fh function assumes that the 32 inode number
314 * is suitable for locating an inode, and that the generation number
315 * can be used to check that it is still valid. It places them in the
316 * filehandle fragment where export_decode_fh expects to find them.
318 static int export_encode_fh(struct inode
*inode
, struct fid
*fid
,
319 int *max_len
, struct inode
*parent
)
322 int type
= FILEID_INO32_GEN
;
324 if (parent
&& (len
< 4)) {
327 } else if (len
< 2) {
333 fid
->i32
.ino
= inode
->i_ino
;
334 fid
->i32
.gen
= inode
->i_generation
;
336 fid
->i32
.parent_ino
= parent
->i_ino
;
337 fid
->i32
.parent_gen
= parent
->i_generation
;
339 type
= FILEID_INO32_GEN_PARENT
;
345 int exportfs_encode_fh(struct dentry
*dentry
, struct fid
*fid
, int *max_len
,
348 const struct export_operations
*nop
= dentry
->d_sb
->s_export_op
;
350 struct dentry
*p
= NULL
;
351 struct inode
*inode
= dentry
->d_inode
, *parent
= NULL
;
353 if (connectable
&& !S_ISDIR(inode
->i_mode
)) {
354 p
= dget_parent(dentry
);
356 * note that while p might've ceased to be our parent already,
357 * it's still pinned by and still positive.
362 error
= nop
->encode_fh(inode
, fid
->raw
, max_len
, parent
);
364 error
= export_encode_fh(inode
, fid
, max_len
, parent
);
369 EXPORT_SYMBOL_GPL(exportfs_encode_fh
);
371 struct dentry
*exportfs_decode_fh(struct vfsmount
*mnt
, struct fid
*fid
,
372 int fh_len
, int fileid_type
,
373 int (*acceptable
)(void *, struct dentry
*), void *context
)
375 const struct export_operations
*nop
= mnt
->mnt_sb
->s_export_op
;
376 struct dentry
*result
, *alias
;
377 char nbuf
[NAME_MAX
+1];
381 * Try to get any dentry for the given file handle from the filesystem.
383 if (!nop
|| !nop
->fh_to_dentry
)
384 return ERR_PTR(-ESTALE
);
385 result
= nop
->fh_to_dentry(mnt
->mnt_sb
, fid
, fh_len
, fileid_type
);
387 result
= ERR_PTR(-ESTALE
);
391 if (S_ISDIR(result
->d_inode
->i_mode
)) {
393 * This request is for a directory.
395 * On the positive side there is only one dentry for each
396 * directory inode. On the negative side this implies that we
397 * to ensure our dentry is connected all the way up to the
400 if (result
->d_flags
& DCACHE_DISCONNECTED
) {
401 err
= reconnect_path(mnt
, result
, nbuf
);
406 if (!acceptable(context
, result
)) {
414 * It's not a directory. Life is a little more complicated.
416 struct dentry
*target_dir
, *nresult
;
419 * See if either the dentry we just got from the filesystem
420 * or any alias for it is acceptable. This is always true
421 * if this filesystem is exported without the subtreecheck
422 * option. If the filesystem is exported with the subtree
423 * check option there's a fair chance we need to look at
424 * the parent directory in the file handle and make sure
425 * it's connected to the filesystem root.
427 alias
= find_acceptable_alias(result
, acceptable
, context
);
432 * Try to extract a dentry for the parent directory from the
433 * file handle. If this fails we'll have to give up.
436 if (!nop
->fh_to_parent
)
439 target_dir
= nop
->fh_to_parent(mnt
->mnt_sb
, fid
,
440 fh_len
, fileid_type
);
443 err
= PTR_ERR(target_dir
);
444 if (IS_ERR(target_dir
))
448 * And as usual we need to make sure the parent directory is
449 * connected to the filesystem root. The VFS really doesn't
450 * like disconnected directories..
452 err
= reconnect_path(mnt
, target_dir
, nbuf
);
459 * Now that we've got both a well-connected parent and a
460 * dentry for the inode we're after, make sure that our
461 * inode is actually connected to the parent.
463 err
= exportfs_get_name(mnt
, target_dir
, nbuf
, result
);
465 mutex_lock(&target_dir
->d_inode
->i_mutex
);
466 nresult
= lookup_one_len(nbuf
, target_dir
,
468 mutex_unlock(&target_dir
->d_inode
->i_mutex
);
469 if (!IS_ERR(nresult
)) {
470 if (nresult
->d_inode
) {
479 * At this point we are done with the parent, but it's pinned
480 * by the child dentry anyway.
485 * And finally make sure the dentry is actually acceptable
488 alias
= find_acceptable_alias(result
, acceptable
, context
);
501 EXPORT_SYMBOL_GPL(exportfs_decode_fh
);
503 MODULE_LICENSE("GPL");
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