1
2#include <linux/fs.h>
3#include <linux/file.h>
4#include <linux/module.h>
5#include <linux/namei.h>
6
7struct export_operations export_op_default;
8
9#define	CALL(ops,fun) ((ops->fun)?(ops->fun):export_op_default.fun)
10
11#define dprintk(fmt, args...) do{}while(0)
12
13static struct dentry *
14find_acceptable_alias(struct dentry *result,
15		int (*acceptable)(void *context, struct dentry *dentry),
16		void *context)
17{
18	struct dentry *dentry, *toput = NULL;
19
20	spin_lock(&dcache_lock);
21	list_for_each_entry(dentry, &result->d_inode->i_dentry, d_alias) {
22		dget_locked(dentry);
23		spin_unlock(&dcache_lock);
24		if (toput)
25			dput(toput);
26		if (dentry != result && acceptable(context, dentry)) {
27			dput(result);
28			return dentry;
29		}
30		spin_lock(&dcache_lock);
31		toput = dentry;
32	}
33	spin_unlock(&dcache_lock);
34
35	if (toput)
36		dput(toput);
37	return NULL;
38}
39
40/**
41 * find_exported_dentry - helper routine to implement export_operations->decode_fh
42 * @sb:		The &super_block identifying the filesystem
43 * @obj:	An opaque identifier of the object to be found - passed to
44 *		get_inode
45 * @parent:	An optional opqaue identifier of the parent of the object.
46 * @acceptable:	A function used to test possible &dentries to see if they are
47 *		acceptable
48 * @context:	A parameter to @acceptable so that it knows on what basis to
49 *		judge.
50 *
51 * find_exported_dentry is the central helper routine to enable file systems
52 * to provide the decode_fh() export_operation.  It's main task is to take
53 * an &inode, find or create an appropriate &dentry structure, and possibly
54 * splice this into the dcache in the correct place.
55 *
56 * The decode_fh() operation provided by the filesystem should call
57 * find_exported_dentry() with the same parameters that it received except
58 * that instead of the file handle fragment, pointers to opaque identifiers
59 * for the object and optionally its parent are passed.  The default decode_fh
60 * routine passes one pointer to the start of the filehandle fragment, and
61 * one 8 bytes into the fragment.  It is expected that most filesystems will
62 * take this approach, though the offset to the parent identifier may well be
63 * different.
64 *
65 * find_exported_dentry() will call get_dentry to get an dentry pointer from
66 * the file system.  If any &dentry in the d_alias list is acceptable, it will
67 * be returned.  Otherwise find_exported_dentry() will attempt to splice a new
68 * &dentry into the dcache using get_name() and get_parent() to find the
69 * appropriate place.
70 */
71
72struct dentry *
73find_exported_dentry(struct super_block *sb, void *obj, void *parent,
74		     int (*acceptable)(void *context, struct dentry *de),
75		     void *context)
76{
77	struct dentry *result = NULL;
78	struct dentry *target_dir;
79	int err;
80	struct export_operations *nops = sb->s_export_op;
81	struct dentry *alias;
82	int noprogress;
83	char nbuf[NAME_MAX+1];
84
85	/*
86	 * Attempt to find the inode.
87	 */
88	result = CALL(sb->s_export_op,get_dentry)(sb,obj);
89	err = -ESTALE;
90	if (result == NULL)
91		goto err_out;
92	if (IS_ERR(result)) {
93		err = PTR_ERR(result);
94		goto err_out;
95	}
96	if (S_ISDIR(result->d_inode->i_mode) &&
97	    (result->d_flags & DCACHE_DISCONNECTED)) {
98		/* it is an unconnected directory, we must connect it */
99		;
100	} else {
101		if (acceptable(context, result))
102			return result;
103		if (S_ISDIR(result->d_inode->i_mode)) {
104			err = -EACCES;
105			goto err_result;
106		}
107
108		alias = find_acceptable_alias(result, acceptable, context);
109		if (alias)
110			return alias;
111	}
112
113	/* It's a directory, or we are required to confirm the file's
114	 * location in the tree based on the parent information
115 	 */
116	dprintk("find_exported_dentry: need to look harder for %s/%d\n",sb->s_id,*(int*)obj);
117	if (S_ISDIR(result->d_inode->i_mode))
118		target_dir = dget(result);
119	else {
120		if (parent == NULL)
121			goto err_result;
122
123		target_dir = CALL(sb->s_export_op,get_dentry)(sb,parent);
124		if (IS_ERR(target_dir))
125			err = PTR_ERR(target_dir);
126		if (target_dir == NULL || IS_ERR(target_dir))
127			goto err_result;
128	}
129	/*
130	 * Now we need to make sure that target_dir is properly connected.
131	 * It may already be, as the flag isn't always updated when connection
132	 * happens.
133	 * So, we walk up parent links until we find a connected directory,
134	 * or we run out of directories.  Then we find the parent, find
135	 * the name of the child in that parent, and do a lookup.
136	 * This should connect the child into the parent
137	 * We then repeat.
138	 */
139
140	/* it is possible that a confused file system might not let us complete
141	 * the path to the root.  For example, if get_parent returns a directory
142	 * in which we cannot find a name for the child.  While this implies a
143	 * very sick filesystem we don't want it to cause knfsd to spin.  Hence
144	 * the noprogress counter.  If we go through the loop 10 times (2 is
145	 * probably enough) without getting anywhere, we just give up
146	 */
147	noprogress= 0;
148	while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {
149		struct dentry *pd = target_dir;
150
151		dget(pd);
152		spin_lock(&pd->d_lock);
153		while (!IS_ROOT(pd) &&
154				(pd->d_parent->d_flags&DCACHE_DISCONNECTED)) {
155			struct dentry *parent = pd->d_parent;
156
157			dget(parent);
158			spin_unlock(&pd->d_lock);
159			dput(pd);
160			pd = parent;
161			spin_lock(&pd->d_lock);
162		}
163		spin_unlock(&pd->d_lock);
164
165		if (!IS_ROOT(pd)) {
166			/* must have found a connected parent - great */
167			spin_lock(&pd->d_lock);
168			pd->d_flags &= ~DCACHE_DISCONNECTED;
169			spin_unlock(&pd->d_lock);
170			noprogress = 0;
171		} else if (pd == sb->s_root) {
172			printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible\n");
173			spin_lock(&pd->d_lock);
174			pd->d_flags &= ~DCACHE_DISCONNECTED;
175			spin_unlock(&pd->d_lock);
176			noprogress = 0;
177		} else {
178			/* we have hit the top of a disconnected path.  Try
179			 * to find parent and connect
180			 * note: racing with some other process renaming a
181			 * directory isn't much of a problem here.  If someone
182			 * renames the directory, it will end up properly
183			 * connected, which is what we want
184			 */
185			struct dentry *ppd;
186			struct dentry *npd;
187
188			mutex_lock(&pd->d_inode->i_mutex);
189			ppd = CALL(nops,get_parent)(pd);
190			mutex_unlock(&pd->d_inode->i_mutex);
191
192			if (IS_ERR(ppd)) {
193				err = PTR_ERR(ppd);
194				dprintk("find_exported_dentry: get_parent of %ld failed, err %d\n",
195					pd->d_inode->i_ino, err);
196				dput(pd);
197				break;
198			}
199			dprintk("find_exported_dentry: find name of %lu in %lu\n", pd->d_inode->i_ino, ppd->d_inode->i_ino);
200			err = CALL(nops,get_name)(ppd, nbuf, pd);
201			if (err) {
202				dput(ppd);
203				dput(pd);
204				if (err == -ENOENT)
205					/* some race between get_parent and
206					 * get_name?  just try again
207					 */
208					continue;
209				break;
210			}
211			dprintk("find_exported_dentry: found name: %s\n", nbuf);
212			mutex_lock(&ppd->d_inode->i_mutex);
213			npd = lookup_one_len(nbuf, ppd, strlen(nbuf));
214			mutex_unlock(&ppd->d_inode->i_mutex);
215			if (IS_ERR(npd)) {
216				err = PTR_ERR(npd);
217				dprintk("find_exported_dentry: lookup failed: %d\n", err);
218				dput(ppd);
219				dput(pd);
220				break;
221			}
222			/* we didn't really want npd, we really wanted
223			 * a side-effect of the lookup.
224			 * hopefully, npd == pd, though it isn't really
225			 * a problem if it isn't
226			 */
227			if (npd == pd)
228				noprogress = 0;
229			else
230				printk("find_exported_dentry: npd != pd\n");
231			dput(npd);
232			dput(ppd);
233			if (IS_ROOT(pd)) {
234				/* something went wrong, we have to give up */
235				dput(pd);
236				break;
237			}
238		}
239		dput(pd);
240	}
241
242	if (target_dir->d_flags & DCACHE_DISCONNECTED) {
243		/* something went wrong - oh-well */
244		if (!err)
245			err = -ESTALE;
246		goto err_target;
247	}
248	/* if we weren't after a directory, have one more step to go */
249	if (result != target_dir) {
250		struct dentry *nresult;
251		err = CALL(nops,get_name)(target_dir, nbuf, result);
252		if (!err) {
253			mutex_lock(&target_dir->d_inode->i_mutex);
254			nresult = lookup_one_len(nbuf, target_dir, strlen(nbuf));
255			mutex_unlock(&target_dir->d_inode->i_mutex);
256			if (!IS_ERR(nresult)) {
257				if (nresult->d_inode) {
258					dput(result);
259					result = nresult;
260				} else
261					dput(nresult);
262			}
263		}
264	}
265	dput(target_dir);
266	/* now result is properly connected, it is our best bet */
267	if (acceptable(context, result))
268		return result;
269
270	alias = find_acceptable_alias(result, acceptable, context);
271	if (alias)
272		return alias;
273
274	/* drat - I just cannot find anything acceptable */
275	dput(result);
276	/* It might be justifiable to return ESTALE here,
277	 * but the filehandle at-least looks reasonable good
278	 * and it just be a permission problem, so returning
279	 * -EACCESS is safer
280	 */
281	return ERR_PTR(-EACCES);
282
283 err_target:
284	dput(target_dir);
285 err_result:
286	dput(result);
287 err_out:
288	return ERR_PTR(err);
289}
290
291
292
293static struct dentry *get_parent(struct dentry *child)
294{
295	/* get_parent cannot be supported generically, the locking
296	 * is too icky.
297	 * instead, we just return EACCES.  If server reboots or inodes
298	 * get flushed, you lose
299	 */
300	return ERR_PTR(-EACCES);
301}
302
303
304struct getdents_callback {
305	char *name;		/* name that was found. It already points to a
306				   buffer NAME_MAX+1 is size */
307	unsigned long ino;	/* the inum we are looking for */
308	int found;		/* inode matched? */
309	int sequence;		/* sequence counter */
310};
311
312/*
313 * A rather strange filldir function to capture
314 * the name matching the specified inode number.
315 */
316static int filldir_one(void * __buf, const char * name, int len,
317			loff_t pos, u64 ino, unsigned int d_type)
318{
319	struct getdents_callback *buf = __buf;
320	int result = 0;
321
322	buf->sequence++;
323	if (buf->ino == ino) {
324		memcpy(buf->name, name, len);
325		buf->name[len] = '\0';
326		buf->found = 1;
327		result = -1;
328	}
329	return result;
330}
331
332/**
333 * get_name - default export_operations->get_name function
334 * @dentry: the directory in which to find a name
335 * @name:   a pointer to a %NAME_MAX+1 char buffer to store the name
336 * @child:  the dentry for the child directory.
337 *
338 * calls readdir on the parent until it finds an entry with
339 * the same inode number as the child, and returns that.
340 */
341static int get_name(struct dentry *dentry, char *name,
342			struct dentry *child)
343{
344	struct inode *dir = dentry->d_inode;
345	int error;
346	struct file *file;
347	struct getdents_callback buffer;
348
349	error = -ENOTDIR;
350	if (!dir || !S_ISDIR(dir->i_mode))
351		goto out;
352	error = -EINVAL;
353	if (!dir->i_fop)
354		goto out;
355	/*
356	 * Open the directory ...
357	 */
358	file = dentry_open(dget(dentry), NULL, O_RDONLY);
359	error = PTR_ERR(file);
360	if (IS_ERR(file))
361		goto out;
362
363	error = -EINVAL;
364	if (!file->f_op->readdir)
365		goto out_close;
366
367	buffer.name = name;
368	buffer.ino = child->d_inode->i_ino;
369	buffer.found = 0;
370	buffer.sequence = 0;
371	while (1) {
372		int old_seq = buffer.sequence;
373
374		error = vfs_readdir(file, filldir_one, &buffer);
375
376		if (error < 0)
377			break;
378
379		error = 0;
380		if (buffer.found)
381			break;
382		error = -ENOENT;
383		if (old_seq == buffer.sequence)
384			break;
385	}
386
387out_close:
388	fput(file);
389out:
390	return error;
391}
392
393
394static struct dentry *export_iget(struct super_block *sb, unsigned long ino, __u32 generation)
395{
396
397	/* iget isn't really right if the inode is currently unallocated!!
398	 * This should really all be done inside each filesystem
399	 *
400	 * ext2fs' read_inode has been strengthed to return a bad_inode if
401	 * the inode had been deleted.
402	 *
403	 * Currently we don't know the generation for parent directory, so
404	 * a generation of 0 means "accept any"
405	 */
406	struct inode *inode;
407	struct dentry *result;
408	if (ino == 0)
409		return ERR_PTR(-ESTALE);
410	inode = iget(sb, ino);
411	if (inode == NULL)
412		return ERR_PTR(-ENOMEM);
413	if (is_bad_inode(inode)
414	    || (generation && inode->i_generation != generation)
415		) {
416		/* we didn't find the right inode.. */
417		dprintk("fh_verify: Inode %lu, Bad count: %d %d or version  %u %u\n",
418			inode->i_ino,
419			inode->i_nlink, atomic_read(&inode->i_count),
420			inode->i_generation,
421			generation);
422
423		iput(inode);
424		return ERR_PTR(-ESTALE);
425	}
426	/* now to find a dentry.
427	 * If possible, get a well-connected one
428	 */
429	result = d_alloc_anon(inode);
430	if (!result) {
431		iput(inode);
432		return ERR_PTR(-ENOMEM);
433	}
434	return result;
435}
436
437
438static struct dentry *get_object(struct super_block *sb, void *vobjp)
439{
440	__u32 *objp = vobjp;
441	unsigned long ino = objp[0];
442	__u32 generation = objp[1];
443
444	return export_iget(sb, ino, generation);
445}
446
447
448/**
449 * export_encode_fh - default export_operations->encode_fh function
450 * @dentry:  the dentry to encode
451 * @fh:      where to store the file handle fragment
452 * @max_len: maximum length to store there
453 * @connectable: whether to store parent information
454 *
455 * This default encode_fh function assumes that the 32 inode number
456 * is suitable for locating an inode, and that the generation number
457 * can be used to check that it is still valid.  It places them in the
458 * filehandle fragment where export_decode_fh expects to find them.
459 */
460static int export_encode_fh(struct dentry *dentry, __u32 *fh, int *max_len,
461		   int connectable)
462{
463	struct inode * inode = dentry->d_inode;
464	int len = *max_len;
465	int type = 1;
466
467	if (len < 2 || (connectable && len < 4))
468		return 255;
469
470	len = 2;
471	fh[0] = inode->i_ino;
472	fh[1] = inode->i_generation;
473	if (connectable && !S_ISDIR(inode->i_mode)) {
474		struct inode *parent;
475
476		spin_lock(&dentry->d_lock);
477		parent = dentry->d_parent->d_inode;
478		fh[2] = parent->i_ino;
479		fh[3] = parent->i_generation;
480		spin_unlock(&dentry->d_lock);
481		len = 4;
482		type = 2;
483	}
484	*max_len = len;
485	return type;
486}
487
488
489/**
490 * export_decode_fh - default export_operations->decode_fh function
491 * @sb:  The superblock
492 * @fh:  pointer to the file handle fragment
493 * @fh_len: length of file handle fragment
494 * @acceptable: function for testing acceptability of dentrys
495 * @context:   context for @acceptable
496 *
497 * This is the default decode_fh() function.
498 * a fileid_type of 1 indicates that the filehandlefragment
499 * just contains an object identifier understood by  get_dentry.
500 * a fileid_type of 2 says that there is also a directory
501 * identifier 8 bytes in to the filehandlefragement.
502 */
503static struct dentry *export_decode_fh(struct super_block *sb, __u32 *fh, int fh_len,
504			      int fileid_type,
505			 int (*acceptable)(void *context, struct dentry *de),
506			 void *context)
507{
508	__u32 parent[2];
509	parent[0] = parent[1] = 0;
510	if (fh_len < 2 || fileid_type > 2)
511		return NULL;
512	if (fileid_type == 2) {
513		if (fh_len > 2) parent[0] = fh[2];
514		if (fh_len > 3) parent[1] = fh[3];
515	}
516	return find_exported_dentry(sb, fh, parent,
517				   acceptable, context);
518}
519
520struct export_operations export_op_default = {
521	.decode_fh	= export_decode_fh,
522	.encode_fh	= export_encode_fh,
523
524	.get_name	= get_name,
525	.get_parent	= get_parent,
526	.get_dentry	= get_object,
527};
528
529EXPORT_SYMBOL(export_op_default);
530EXPORT_SYMBOL(find_exported_dentry);
531
532MODULE_LICENSE("GPL");
533