xref: /openbmc/linux/fs/exportfs/expfs.c (revision 87c2ce3b)
1 
2 #include <linux/fs.h>
3 #include <linux/file.h>
4 #include <linux/module.h>
5 #include <linux/smp_lock.h>
6 #include <linux/namei.h>
7 
8 struct export_operations export_op_default;
9 
10 #define	CALL(ops,fun) ((ops->fun)?(ops->fun):export_op_default.fun)
11 
12 #define dprintk(fmt, args...) do{}while(0)
13 
14 /**
15  * find_exported_dentry - helper routine to implement export_operations->decode_fh
16  * @sb:		The &super_block identifying the filesystem
17  * @obj:	An opaque identifier of the object to be found - passed to
18  *		get_inode
19  * @parent:	An optional opqaue identifier of the parent of the object.
20  * @acceptable:	A function used to test possible &dentries to see if they are
21  *		acceptable
22  * @context:	A parameter to @acceptable so that it knows on what basis to
23  *		judge.
24  *
25  * find_exported_dentry is the central helper routine to enable file systems
26  * to provide the decode_fh() export_operation.  It's main task is to take
27  * an &inode, find or create an appropriate &dentry structure, and possibly
28  * splice this into the dcache in the correct place.
29  *
30  * The decode_fh() operation provided by the filesystem should call
31  * find_exported_dentry() with the same parameters that it received except
32  * that instead of the file handle fragment, pointers to opaque identifiers
33  * for the object and optionally its parent are passed.  The default decode_fh
34  * routine passes one pointer to the start of the filehandle fragment, and
35  * one 8 bytes into the fragment.  It is expected that most filesystems will
36  * take this approach, though the offset to the parent identifier may well be
37  * different.
38  *
39  * find_exported_dentry() will call get_dentry to get an dentry pointer from
40  * the file system.  If any &dentry in the d_alias list is acceptable, it will
41  * be returned.  Otherwise find_exported_dentry() will attempt to splice a new
42  * &dentry into the dcache using get_name() and get_parent() to find the
43  * appropriate place.
44  */
45 
46 struct dentry *
47 find_exported_dentry(struct super_block *sb, void *obj, void *parent,
48 		     int (*acceptable)(void *context, struct dentry *de),
49 		     void *context)
50 {
51 	struct dentry *result = NULL;
52 	struct dentry *target_dir;
53 	int err;
54 	struct export_operations *nops = sb->s_export_op;
55 	struct list_head *le, *head;
56 	struct dentry *toput = NULL;
57 	int noprogress;
58 	char nbuf[NAME_MAX+1];
59 
60 	/*
61 	 * Attempt to find the inode.
62 	 */
63 	result = CALL(sb->s_export_op,get_dentry)(sb,obj);
64 	err = -ESTALE;
65 	if (result == NULL)
66 		goto err_out;
67 	if (IS_ERR(result)) {
68 		err = PTR_ERR(result);
69 		goto err_out;
70 	}
71 	if (S_ISDIR(result->d_inode->i_mode) &&
72 	    (result->d_flags & DCACHE_DISCONNECTED)) {
73 		/* it is an unconnected directory, we must connect it */
74 		;
75 	} else {
76 		if (acceptable(context, result))
77 			return result;
78 		if (S_ISDIR(result->d_inode->i_mode)) {
79 			/* there is no other dentry, so fail */
80 			goto err_result;
81 		}
82 		/* try any other aliases */
83 		spin_lock(&dcache_lock);
84 		head = &result->d_inode->i_dentry;
85 		list_for_each(le, head) {
86 			struct dentry *dentry = list_entry(le, struct dentry, d_alias);
87 			dget_locked(dentry);
88 			spin_unlock(&dcache_lock);
89 			if (toput)
90 				dput(toput);
91 			toput = NULL;
92 			if (dentry != result &&
93 			    acceptable(context, dentry)) {
94 				dput(result);
95 				return dentry;
96 			}
97 			spin_lock(&dcache_lock);
98 			toput = dentry;
99 		}
100 		spin_unlock(&dcache_lock);
101 		if (toput)
102 			dput(toput);
103 	}
104 
105 	/* It's a directory, or we are required to confirm the file's
106 	 * location in the tree based on the parent information
107  	 */
108 	dprintk("find_exported_dentry: need to look harder for %s/%d\n",sb->s_id,*(int*)obj);
109 	if (S_ISDIR(result->d_inode->i_mode))
110 		target_dir = dget(result);
111 	else {
112 		if (parent == NULL)
113 			goto err_result;
114 
115 		target_dir = CALL(sb->s_export_op,get_dentry)(sb,parent);
116 		if (IS_ERR(target_dir))
117 			err = PTR_ERR(target_dir);
118 		if (target_dir == NULL || IS_ERR(target_dir))
119 			goto err_result;
120 	}
121 	/*
122 	 * Now we need to make sure that target_dir is properly connected.
123 	 * It may already be, as the flag isn't always updated when connection
124 	 * happens.
125 	 * So, we walk up parent links until we find a connected directory,
126 	 * or we run out of directories.  Then we find the parent, find
127 	 * the name of the child in that parent, and do a lookup.
128 	 * This should connect the child into the parent
129 	 * We then repeat.
130 	 */
131 
132 	/* it is possible that a confused file system might not let us complete
133 	 * the path to the root.  For example, if get_parent returns a directory
134 	 * in which we cannot find a name for the child.  While this implies a
135 	 * very sick filesystem we don't want it to cause knfsd to spin.  Hence
136 	 * the noprogress counter.  If we go through the loop 10 times (2 is
137 	 * probably enough) without getting anywhere, we just give up
138 	 */
139 	noprogress= 0;
140 	while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {
141 		struct dentry *pd = target_dir;
142 
143 		dget(pd);
144 		spin_lock(&pd->d_lock);
145 		while (!IS_ROOT(pd) &&
146 				(pd->d_parent->d_flags&DCACHE_DISCONNECTED)) {
147 			struct dentry *parent = pd->d_parent;
148 
149 			dget(parent);
150 			spin_unlock(&pd->d_lock);
151 			dput(pd);
152 			pd = parent;
153 			spin_lock(&pd->d_lock);
154 		}
155 		spin_unlock(&pd->d_lock);
156 
157 		if (!IS_ROOT(pd)) {
158 			/* must have found a connected parent - great */
159 			spin_lock(&pd->d_lock);
160 			pd->d_flags &= ~DCACHE_DISCONNECTED;
161 			spin_unlock(&pd->d_lock);
162 			noprogress = 0;
163 		} else if (pd == sb->s_root) {
164 			printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible\n");
165 			spin_lock(&pd->d_lock);
166 			pd->d_flags &= ~DCACHE_DISCONNECTED;
167 			spin_unlock(&pd->d_lock);
168 			noprogress = 0;
169 		} else {
170 			/* we have hit the top of a disconnected path.  Try
171 			 * to find parent and connect
172 			 * note: racing with some other process renaming a
173 			 * directory isn't much of a problem here.  If someone
174 			 * renames the directory, it will end up properly
175 			 * connected, which is what we want
176 			 */
177 			struct dentry *ppd;
178 			struct dentry *npd;
179 
180 			mutex_lock(&pd->d_inode->i_mutex);
181 			ppd = CALL(nops,get_parent)(pd);
182 			mutex_unlock(&pd->d_inode->i_mutex);
183 
184 			if (IS_ERR(ppd)) {
185 				err = PTR_ERR(ppd);
186 				dprintk("find_exported_dentry: get_parent of %ld failed, err %d\n",
187 					pd->d_inode->i_ino, err);
188 				dput(pd);
189 				break;
190 			}
191 			dprintk("find_exported_dentry: find name of %lu in %lu\n", pd->d_inode->i_ino, ppd->d_inode->i_ino);
192 			err = CALL(nops,get_name)(ppd, nbuf, pd);
193 			if (err) {
194 				dput(ppd);
195 				dput(pd);
196 				if (err == -ENOENT)
197 					/* some race between get_parent and
198 					 * get_name?  just try again
199 					 */
200 					continue;
201 				break;
202 			}
203 			dprintk("find_exported_dentry: found name: %s\n", nbuf);
204 			mutex_lock(&ppd->d_inode->i_mutex);
205 			npd = lookup_one_len(nbuf, ppd, strlen(nbuf));
206 			mutex_unlock(&ppd->d_inode->i_mutex);
207 			if (IS_ERR(npd)) {
208 				err = PTR_ERR(npd);
209 				dprintk("find_exported_dentry: lookup failed: %d\n", err);
210 				dput(ppd);
211 				dput(pd);
212 				break;
213 			}
214 			/* we didn't really want npd, we really wanted
215 			 * a side-effect of the lookup.
216 			 * hopefully, npd == pd, though it isn't really
217 			 * a problem if it isn't
218 			 */
219 			if (npd == pd)
220 				noprogress = 0;
221 			else
222 				printk("find_exported_dentry: npd != pd\n");
223 			dput(npd);
224 			dput(ppd);
225 			if (IS_ROOT(pd)) {
226 				/* something went wrong, we have to give up */
227 				dput(pd);
228 				break;
229 			}
230 		}
231 		dput(pd);
232 	}
233 
234 	if (target_dir->d_flags & DCACHE_DISCONNECTED) {
235 		/* something went wrong - oh-well */
236 		if (!err)
237 			err = -ESTALE;
238 		goto err_target;
239 	}
240 	/* if we weren't after a directory, have one more step to go */
241 	if (result != target_dir) {
242 		struct dentry *nresult;
243 		err = CALL(nops,get_name)(target_dir, nbuf, result);
244 		if (!err) {
245 			mutex_lock(&target_dir->d_inode->i_mutex);
246 			nresult = lookup_one_len(nbuf, target_dir, strlen(nbuf));
247 			mutex_unlock(&target_dir->d_inode->i_mutex);
248 			if (!IS_ERR(nresult)) {
249 				if (nresult->d_inode) {
250 					dput(result);
251 					result = nresult;
252 				} else
253 					dput(nresult);
254 			}
255 		}
256 	}
257 	dput(target_dir);
258 	/* now result is properly connected, it is our best bet */
259 	if (acceptable(context, result))
260 		return result;
261 	/* one last try of the aliases.. */
262 	spin_lock(&dcache_lock);
263 	toput = NULL;
264 	head = &result->d_inode->i_dentry;
265 	list_for_each(le, head) {
266 		struct dentry *dentry = list_entry(le, struct dentry, d_alias);
267 		dget_locked(dentry);
268 		spin_unlock(&dcache_lock);
269 		if (toput) dput(toput);
270 		if (dentry != result &&
271 		    acceptable(context, dentry)) {
272 			dput(result);
273 			return dentry;
274 		}
275 		spin_lock(&dcache_lock);
276 		toput = dentry;
277 	}
278 	spin_unlock(&dcache_lock);
279 	if (toput)
280 		dput(toput);
281 
282 	/* drat - I just cannot find anything acceptable */
283 	dput(result);
284 	/* It might be justifiable to return ESTALE here,
285 	 * but the filehandle at-least looks reasonable good
286 	 * and it just be a permission problem, so returning
287 	 * -EACCESS is safer
288 	 */
289 	return ERR_PTR(-EACCES);
290 
291  err_target:
292 	dput(target_dir);
293  err_result:
294 	dput(result);
295  err_out:
296 	return ERR_PTR(err);
297 }
298 
299 
300 
301 static struct dentry *get_parent(struct dentry *child)
302 {
303 	/* get_parent cannot be supported generically, the locking
304 	 * is too icky.
305 	 * instead, we just return EACCES.  If server reboots or inodes
306 	 * get flushed, you lose
307 	 */
308 	return ERR_PTR(-EACCES);
309 }
310 
311 
312 struct getdents_callback {
313 	char *name;		/* name that was found. It already points to a
314 				   buffer NAME_MAX+1 is size */
315 	unsigned long ino;	/* the inum we are looking for */
316 	int found;		/* inode matched? */
317 	int sequence;		/* sequence counter */
318 };
319 
320 /*
321  * A rather strange filldir function to capture
322  * the name matching the specified inode number.
323  */
324 static int filldir_one(void * __buf, const char * name, int len,
325 			loff_t pos, ino_t ino, unsigned int d_type)
326 {
327 	struct getdents_callback *buf = __buf;
328 	int result = 0;
329 
330 	buf->sequence++;
331 	if (buf->ino == ino) {
332 		memcpy(buf->name, name, len);
333 		buf->name[len] = '\0';
334 		buf->found = 1;
335 		result = -1;
336 	}
337 	return result;
338 }
339 
340 /**
341  * get_name - default export_operations->get_name function
342  * @dentry: the directory in which to find a name
343  * @name:   a pointer to a %NAME_MAX+1 char buffer to store the name
344  * @child:  the dentry for the child directory.
345  *
346  * calls readdir on the parent until it finds an entry with
347  * the same inode number as the child, and returns that.
348  */
349 static int get_name(struct dentry *dentry, char *name,
350 			struct dentry *child)
351 {
352 	struct inode *dir = dentry->d_inode;
353 	int error;
354 	struct file *file;
355 	struct getdents_callback buffer;
356 
357 	error = -ENOTDIR;
358 	if (!dir || !S_ISDIR(dir->i_mode))
359 		goto out;
360 	error = -EINVAL;
361 	if (!dir->i_fop)
362 		goto out;
363 	/*
364 	 * Open the directory ...
365 	 */
366 	file = dentry_open(dget(dentry), NULL, O_RDONLY);
367 	error = PTR_ERR(file);
368 	if (IS_ERR(file))
369 		goto out;
370 
371 	error = -EINVAL;
372 	if (!file->f_op->readdir)
373 		goto out_close;
374 
375 	buffer.name = name;
376 	buffer.ino = child->d_inode->i_ino;
377 	buffer.found = 0;
378 	buffer.sequence = 0;
379 	while (1) {
380 		int old_seq = buffer.sequence;
381 
382 		error = vfs_readdir(file, filldir_one, &buffer);
383 
384 		if (error < 0)
385 			break;
386 
387 		error = 0;
388 		if (buffer.found)
389 			break;
390 		error = -ENOENT;
391 		if (old_seq == buffer.sequence)
392 			break;
393 	}
394 
395 out_close:
396 	fput(file);
397 out:
398 	return error;
399 }
400 
401 
402 static struct dentry *export_iget(struct super_block *sb, unsigned long ino, __u32 generation)
403 {
404 
405 	/* iget isn't really right if the inode is currently unallocated!!
406 	 * This should really all be done inside each filesystem
407 	 *
408 	 * ext2fs' read_inode has been strengthed to return a bad_inode if
409 	 * the inode had been deleted.
410 	 *
411 	 * Currently we don't know the generation for parent directory, so
412 	 * a generation of 0 means "accept any"
413 	 */
414 	struct inode *inode;
415 	struct dentry *result;
416 	if (ino == 0)
417 		return ERR_PTR(-ESTALE);
418 	inode = iget(sb, ino);
419 	if (inode == NULL)
420 		return ERR_PTR(-ENOMEM);
421 	if (is_bad_inode(inode)
422 	    || (generation && inode->i_generation != generation)
423 		) {
424 		/* we didn't find the right inode.. */
425 		dprintk("fh_verify: Inode %lu, Bad count: %d %d or version  %u %u\n",
426 			inode->i_ino,
427 			inode->i_nlink, atomic_read(&inode->i_count),
428 			inode->i_generation,
429 			generation);
430 
431 		iput(inode);
432 		return ERR_PTR(-ESTALE);
433 	}
434 	/* now to find a dentry.
435 	 * If possible, get a well-connected one
436 	 */
437 	result = d_alloc_anon(inode);
438 	if (!result) {
439 		iput(inode);
440 		return ERR_PTR(-ENOMEM);
441 	}
442 	return result;
443 }
444 
445 
446 static struct dentry *get_object(struct super_block *sb, void *vobjp)
447 {
448 	__u32 *objp = vobjp;
449 	unsigned long ino = objp[0];
450 	__u32 generation = objp[1];
451 
452 	return export_iget(sb, ino, generation);
453 }
454 
455 
456 /**
457  * export_encode_fh - default export_operations->encode_fh function
458  * @dentry:  the dentry to encode
459  * @fh:      where to store the file handle fragment
460  * @max_len: maximum length to store there
461  * @connectable: whether to store parent information
462  *
463  * This default encode_fh function assumes that the 32 inode number
464  * is suitable for locating an inode, and that the generation number
465  * can be used to check that it is still valid.  It places them in the
466  * filehandle fragment where export_decode_fh expects to find them.
467  */
468 static int export_encode_fh(struct dentry *dentry, __u32 *fh, int *max_len,
469 		   int connectable)
470 {
471 	struct inode * inode = dentry->d_inode;
472 	int len = *max_len;
473 	int type = 1;
474 
475 	if (len < 2 || (connectable && len < 4))
476 		return 255;
477 
478 	len = 2;
479 	fh[0] = inode->i_ino;
480 	fh[1] = inode->i_generation;
481 	if (connectable && !S_ISDIR(inode->i_mode)) {
482 		struct inode *parent;
483 
484 		spin_lock(&dentry->d_lock);
485 		parent = dentry->d_parent->d_inode;
486 		fh[2] = parent->i_ino;
487 		fh[3] = parent->i_generation;
488 		spin_unlock(&dentry->d_lock);
489 		len = 4;
490 		type = 2;
491 	}
492 	*max_len = len;
493 	return type;
494 }
495 
496 
497 /**
498  * export_decode_fh - default export_operations->decode_fh function
499  * @sb:  The superblock
500  * @fh:  pointer to the file handle fragment
501  * @fh_len: length of file handle fragment
502  * @acceptable: function for testing acceptability of dentrys
503  * @context:   context for @acceptable
504  *
505  * This is the default decode_fh() function.
506  * a fileid_type of 1 indicates that the filehandlefragment
507  * just contains an object identifier understood by  get_dentry.
508  * a fileid_type of 2 says that there is also a directory
509  * identifier 8 bytes in to the filehandlefragement.
510  */
511 static struct dentry *export_decode_fh(struct super_block *sb, __u32 *fh, int fh_len,
512 			      int fileid_type,
513 			 int (*acceptable)(void *context, struct dentry *de),
514 			 void *context)
515 {
516 	__u32 parent[2];
517 	parent[0] = parent[1] = 0;
518 	if (fh_len < 2 || fileid_type > 2)
519 		return NULL;
520 	if (fileid_type == 2) {
521 		if (fh_len > 2) parent[0] = fh[2];
522 		if (fh_len > 3) parent[1] = fh[3];
523 	}
524 	return find_exported_dentry(sb, fh, parent,
525 				   acceptable, context);
526 }
527 
528 struct export_operations export_op_default = {
529 	.decode_fh	= export_decode_fh,
530 	.encode_fh	= export_encode_fh,
531 
532 	.get_name	= get_name,
533 	.get_parent	= get_parent,
534 	.get_dentry	= get_object,
535 };
536 
537 EXPORT_SYMBOL(export_op_default);
538 EXPORT_SYMBOL(find_exported_dentry);
539 
540 MODULE_LICENSE("GPL");
541