xref: /openbmc/linux/fs/dcache.c (revision d5cb9783536a41df9f9cba5b0a1d78047ed787f7)
1 /*
2  * fs/dcache.c
3  *
4  * Complete reimplementation
5  * (C) 1997 Thomas Schoebel-Theuer,
6  * with heavy changes by Linus Torvalds
7  */
8 
9 /*
10  * Notes on the allocation strategy:
11  *
12  * The dcache is a master of the icache - whenever a dcache entry
13  * exists, the inode will always exist. "iput()" is done either when
14  * the dcache entry is deleted or garbage collected.
15  */
16 
17 #include <linux/config.h>
18 #include <linux/syscalls.h>
19 #include <linux/string.h>
20 #include <linux/mm.h>
21 #include <linux/fs.h>
22 #include <linux/fsnotify.h>
23 #include <linux/slab.h>
24 #include <linux/init.h>
25 #include <linux/smp_lock.h>
26 #include <linux/hash.h>
27 #include <linux/cache.h>
28 #include <linux/module.h>
29 #include <linux/mount.h>
30 #include <linux/file.h>
31 #include <asm/uaccess.h>
32 #include <linux/security.h>
33 #include <linux/seqlock.h>
34 #include <linux/swap.h>
35 #include <linux/bootmem.h>
36 
37 /* #define DCACHE_DEBUG 1 */
38 
39 int sysctl_vfs_cache_pressure = 100;
40 EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
41 
42  __cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lock);
43 static seqlock_t rename_lock __cacheline_aligned_in_smp = SEQLOCK_UNLOCKED;
44 
45 EXPORT_SYMBOL(dcache_lock);
46 
47 static kmem_cache_t *dentry_cache;
48 
49 #define DNAME_INLINE_LEN (sizeof(struct dentry)-offsetof(struct dentry,d_iname))
50 
51 /*
52  * This is the single most critical data structure when it comes
53  * to the dcache: the hashtable for lookups. Somebody should try
54  * to make this good - I've just made it work.
55  *
56  * This hash-function tries to avoid losing too many bits of hash
57  * information, yet avoid using a prime hash-size or similar.
58  */
59 #define D_HASHBITS     d_hash_shift
60 #define D_HASHMASK     d_hash_mask
61 
62 static unsigned int d_hash_mask;
63 static unsigned int d_hash_shift;
64 static struct hlist_head *dentry_hashtable;
65 static LIST_HEAD(dentry_unused);
66 
67 /* Statistics gathering. */
68 struct dentry_stat_t dentry_stat = {
69 	.age_limit = 45,
70 };
71 
72 static void d_callback(struct rcu_head *head)
73 {
74 	struct dentry * dentry = container_of(head, struct dentry, d_rcu);
75 
76 	if (dname_external(dentry))
77 		kfree(dentry->d_name.name);
78 	kmem_cache_free(dentry_cache, dentry);
79 }
80 
81 /*
82  * no dcache_lock, please.  The caller must decrement dentry_stat.nr_dentry
83  * inside dcache_lock.
84  */
85 static void d_free(struct dentry *dentry)
86 {
87 	if (dentry->d_op && dentry->d_op->d_release)
88 		dentry->d_op->d_release(dentry);
89  	call_rcu(&dentry->d_rcu, d_callback);
90 }
91 
92 /*
93  * Release the dentry's inode, using the filesystem
94  * d_iput() operation if defined.
95  * Called with dcache_lock and per dentry lock held, drops both.
96  */
97 static inline void dentry_iput(struct dentry * dentry)
98 {
99 	struct inode *inode = dentry->d_inode;
100 	if (inode) {
101 		dentry->d_inode = NULL;
102 		list_del_init(&dentry->d_alias);
103 		spin_unlock(&dentry->d_lock);
104 		spin_unlock(&dcache_lock);
105 		if (!inode->i_nlink)
106 			fsnotify_inoderemove(inode);
107 		if (dentry->d_op && dentry->d_op->d_iput)
108 			dentry->d_op->d_iput(dentry, inode);
109 		else
110 			iput(inode);
111 	} else {
112 		spin_unlock(&dentry->d_lock);
113 		spin_unlock(&dcache_lock);
114 	}
115 }
116 
117 /*
118  * This is dput
119  *
120  * This is complicated by the fact that we do not want to put
121  * dentries that are no longer on any hash chain on the unused
122  * list: we'd much rather just get rid of them immediately.
123  *
124  * However, that implies that we have to traverse the dentry
125  * tree upwards to the parents which might _also_ now be
126  * scheduled for deletion (it may have been only waiting for
127  * its last child to go away).
128  *
129  * This tail recursion is done by hand as we don't want to depend
130  * on the compiler to always get this right (gcc generally doesn't).
131  * Real recursion would eat up our stack space.
132  */
133 
134 /*
135  * dput - release a dentry
136  * @dentry: dentry to release
137  *
138  * Release a dentry. This will drop the usage count and if appropriate
139  * call the dentry unlink method as well as removing it from the queues and
140  * releasing its resources. If the parent dentries were scheduled for release
141  * they too may now get deleted.
142  *
143  * no dcache lock, please.
144  */
145 
146 void dput(struct dentry *dentry)
147 {
148 	if (!dentry)
149 		return;
150 
151 repeat:
152 	if (atomic_read(&dentry->d_count) == 1)
153 		might_sleep();
154 	if (!atomic_dec_and_lock(&dentry->d_count, &dcache_lock))
155 		return;
156 
157 	spin_lock(&dentry->d_lock);
158 	if (atomic_read(&dentry->d_count)) {
159 		spin_unlock(&dentry->d_lock);
160 		spin_unlock(&dcache_lock);
161 		return;
162 	}
163 
164 	/*
165 	 * AV: ->d_delete() is _NOT_ allowed to block now.
166 	 */
167 	if (dentry->d_op && dentry->d_op->d_delete) {
168 		if (dentry->d_op->d_delete(dentry))
169 			goto unhash_it;
170 	}
171 	/* Unreachable? Get rid of it */
172  	if (d_unhashed(dentry))
173 		goto kill_it;
174   	if (list_empty(&dentry->d_lru)) {
175   		dentry->d_flags |= DCACHE_REFERENCED;
176   		list_add(&dentry->d_lru, &dentry_unused);
177   		dentry_stat.nr_unused++;
178   	}
179  	spin_unlock(&dentry->d_lock);
180 	spin_unlock(&dcache_lock);
181 	return;
182 
183 unhash_it:
184 	__d_drop(dentry);
185 
186 kill_it: {
187 		struct dentry *parent;
188 
189 		/* If dentry was on d_lru list
190 		 * delete it from there
191 		 */
192   		if (!list_empty(&dentry->d_lru)) {
193   			list_del(&dentry->d_lru);
194   			dentry_stat.nr_unused--;
195   		}
196   		list_del(&dentry->d_child);
197 		dentry_stat.nr_dentry--;	/* For d_free, below */
198 		/*drops the locks, at that point nobody can reach this dentry */
199 		dentry_iput(dentry);
200 		parent = dentry->d_parent;
201 		d_free(dentry);
202 		if (dentry == parent)
203 			return;
204 		dentry = parent;
205 		goto repeat;
206 	}
207 }
208 
209 /**
210  * d_invalidate - invalidate a dentry
211  * @dentry: dentry to invalidate
212  *
213  * Try to invalidate the dentry if it turns out to be
214  * possible. If there are other dentries that can be
215  * reached through this one we can't delete it and we
216  * return -EBUSY. On success we return 0.
217  *
218  * no dcache lock.
219  */
220 
221 int d_invalidate(struct dentry * dentry)
222 {
223 	/*
224 	 * If it's already been dropped, return OK.
225 	 */
226 	spin_lock(&dcache_lock);
227 	if (d_unhashed(dentry)) {
228 		spin_unlock(&dcache_lock);
229 		return 0;
230 	}
231 	/*
232 	 * Check whether to do a partial shrink_dcache
233 	 * to get rid of unused child entries.
234 	 */
235 	if (!list_empty(&dentry->d_subdirs)) {
236 		spin_unlock(&dcache_lock);
237 		shrink_dcache_parent(dentry);
238 		spin_lock(&dcache_lock);
239 	}
240 
241 	/*
242 	 * Somebody else still using it?
243 	 *
244 	 * If it's a directory, we can't drop it
245 	 * for fear of somebody re-populating it
246 	 * with children (even though dropping it
247 	 * would make it unreachable from the root,
248 	 * we might still populate it if it was a
249 	 * working directory or similar).
250 	 */
251 	spin_lock(&dentry->d_lock);
252 	if (atomic_read(&dentry->d_count) > 1) {
253 		if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode)) {
254 			spin_unlock(&dentry->d_lock);
255 			spin_unlock(&dcache_lock);
256 			return -EBUSY;
257 		}
258 	}
259 
260 	__d_drop(dentry);
261 	spin_unlock(&dentry->d_lock);
262 	spin_unlock(&dcache_lock);
263 	return 0;
264 }
265 
266 /* This should be called _only_ with dcache_lock held */
267 
268 static inline struct dentry * __dget_locked(struct dentry *dentry)
269 {
270 	atomic_inc(&dentry->d_count);
271 	if (!list_empty(&dentry->d_lru)) {
272 		dentry_stat.nr_unused--;
273 		list_del_init(&dentry->d_lru);
274 	}
275 	return dentry;
276 }
277 
278 struct dentry * dget_locked(struct dentry *dentry)
279 {
280 	return __dget_locked(dentry);
281 }
282 
283 /**
284  * d_find_alias - grab a hashed alias of inode
285  * @inode: inode in question
286  * @want_discon:  flag, used by d_splice_alias, to request
287  *          that only a DISCONNECTED alias be returned.
288  *
289  * If inode has a hashed alias, or is a directory and has any alias,
290  * acquire the reference to alias and return it. Otherwise return NULL.
291  * Notice that if inode is a directory there can be only one alias and
292  * it can be unhashed only if it has no children, or if it is the root
293  * of a filesystem.
294  *
295  * If the inode has a DCACHE_DISCONNECTED alias, then prefer
296  * any other hashed alias over that one unless @want_discon is set,
297  * in which case only return a DCACHE_DISCONNECTED alias.
298  */
299 
300 static struct dentry * __d_find_alias(struct inode *inode, int want_discon)
301 {
302 	struct list_head *head, *next, *tmp;
303 	struct dentry *alias, *discon_alias=NULL;
304 
305 	head = &inode->i_dentry;
306 	next = inode->i_dentry.next;
307 	while (next != head) {
308 		tmp = next;
309 		next = tmp->next;
310 		prefetch(next);
311 		alias = list_entry(tmp, struct dentry, d_alias);
312  		if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
313 			if (alias->d_flags & DCACHE_DISCONNECTED)
314 				discon_alias = alias;
315 			else if (!want_discon) {
316 				__dget_locked(alias);
317 				return alias;
318 			}
319 		}
320 	}
321 	if (discon_alias)
322 		__dget_locked(discon_alias);
323 	return discon_alias;
324 }
325 
326 struct dentry * d_find_alias(struct inode *inode)
327 {
328 	struct dentry *de;
329 	spin_lock(&dcache_lock);
330 	de = __d_find_alias(inode, 0);
331 	spin_unlock(&dcache_lock);
332 	return de;
333 }
334 
335 /*
336  *	Try to kill dentries associated with this inode.
337  * WARNING: you must own a reference to inode.
338  */
339 void d_prune_aliases(struct inode *inode)
340 {
341 	struct dentry *dentry;
342 restart:
343 	spin_lock(&dcache_lock);
344 	list_for_each_entry(dentry, &inode->i_dentry, d_alias) {
345 		spin_lock(&dentry->d_lock);
346 		if (!atomic_read(&dentry->d_count)) {
347 			__dget_locked(dentry);
348 			__d_drop(dentry);
349 			spin_unlock(&dentry->d_lock);
350 			spin_unlock(&dcache_lock);
351 			dput(dentry);
352 			goto restart;
353 		}
354 		spin_unlock(&dentry->d_lock);
355 	}
356 	spin_unlock(&dcache_lock);
357 }
358 
359 /*
360  * Throw away a dentry - free the inode, dput the parent.
361  * This requires that the LRU list has already been
362  * removed.
363  * Called with dcache_lock, drops it and then regains.
364  */
365 static inline void prune_one_dentry(struct dentry * dentry)
366 {
367 	struct dentry * parent;
368 
369 	__d_drop(dentry);
370 	list_del(&dentry->d_child);
371 	dentry_stat.nr_dentry--;	/* For d_free, below */
372 	dentry_iput(dentry);
373 	parent = dentry->d_parent;
374 	d_free(dentry);
375 	if (parent != dentry)
376 		dput(parent);
377 	spin_lock(&dcache_lock);
378 }
379 
380 /**
381  * prune_dcache - shrink the dcache
382  * @count: number of entries to try and free
383  *
384  * Shrink the dcache. This is done when we need
385  * more memory, or simply when we need to unmount
386  * something (at which point we need to unuse
387  * all dentries).
388  *
389  * This function may fail to free any resources if
390  * all the dentries are in use.
391  */
392 
393 static void prune_dcache(int count)
394 {
395 	spin_lock(&dcache_lock);
396 	for (; count ; count--) {
397 		struct dentry *dentry;
398 		struct list_head *tmp;
399 
400 		cond_resched_lock(&dcache_lock);
401 
402 		tmp = dentry_unused.prev;
403 		if (tmp == &dentry_unused)
404 			break;
405 		list_del_init(tmp);
406 		prefetch(dentry_unused.prev);
407  		dentry_stat.nr_unused--;
408 		dentry = list_entry(tmp, struct dentry, d_lru);
409 
410  		spin_lock(&dentry->d_lock);
411 		/*
412 		 * We found an inuse dentry which was not removed from
413 		 * dentry_unused because of laziness during lookup.  Do not free
414 		 * it - just keep it off the dentry_unused list.
415 		 */
416  		if (atomic_read(&dentry->d_count)) {
417  			spin_unlock(&dentry->d_lock);
418 			continue;
419 		}
420 		/* If the dentry was recently referenced, don't free it. */
421 		if (dentry->d_flags & DCACHE_REFERENCED) {
422 			dentry->d_flags &= ~DCACHE_REFERENCED;
423  			list_add(&dentry->d_lru, &dentry_unused);
424  			dentry_stat.nr_unused++;
425  			spin_unlock(&dentry->d_lock);
426 			continue;
427 		}
428 		prune_one_dentry(dentry);
429 	}
430 	spin_unlock(&dcache_lock);
431 }
432 
433 /*
434  * Shrink the dcache for the specified super block.
435  * This allows us to unmount a device without disturbing
436  * the dcache for the other devices.
437  *
438  * This implementation makes just two traversals of the
439  * unused list.  On the first pass we move the selected
440  * dentries to the most recent end, and on the second
441  * pass we free them.  The second pass must restart after
442  * each dput(), but since the target dentries are all at
443  * the end, it's really just a single traversal.
444  */
445 
446 /**
447  * shrink_dcache_sb - shrink dcache for a superblock
448  * @sb: superblock
449  *
450  * Shrink the dcache for the specified super block. This
451  * is used to free the dcache before unmounting a file
452  * system
453  */
454 
455 void shrink_dcache_sb(struct super_block * sb)
456 {
457 	struct list_head *tmp, *next;
458 	struct dentry *dentry;
459 
460 	/*
461 	 * Pass one ... move the dentries for the specified
462 	 * superblock to the most recent end of the unused list.
463 	 */
464 	spin_lock(&dcache_lock);
465 	list_for_each_safe(tmp, next, &dentry_unused) {
466 		dentry = list_entry(tmp, struct dentry, d_lru);
467 		if (dentry->d_sb != sb)
468 			continue;
469 		list_del(tmp);
470 		list_add(tmp, &dentry_unused);
471 	}
472 
473 	/*
474 	 * Pass two ... free the dentries for this superblock.
475 	 */
476 repeat:
477 	list_for_each_safe(tmp, next, &dentry_unused) {
478 		dentry = list_entry(tmp, struct dentry, d_lru);
479 		if (dentry->d_sb != sb)
480 			continue;
481 		dentry_stat.nr_unused--;
482 		list_del_init(tmp);
483 		spin_lock(&dentry->d_lock);
484 		if (atomic_read(&dentry->d_count)) {
485 			spin_unlock(&dentry->d_lock);
486 			continue;
487 		}
488 		prune_one_dentry(dentry);
489 		goto repeat;
490 	}
491 	spin_unlock(&dcache_lock);
492 }
493 
494 /*
495  * Search for at least 1 mount point in the dentry's subdirs.
496  * We descend to the next level whenever the d_subdirs
497  * list is non-empty and continue searching.
498  */
499 
500 /**
501  * have_submounts - check for mounts over a dentry
502  * @parent: dentry to check.
503  *
504  * Return true if the parent or its subdirectories contain
505  * a mount point
506  */
507 
508 int have_submounts(struct dentry *parent)
509 {
510 	struct dentry *this_parent = parent;
511 	struct list_head *next;
512 
513 	spin_lock(&dcache_lock);
514 	if (d_mountpoint(parent))
515 		goto positive;
516 repeat:
517 	next = this_parent->d_subdirs.next;
518 resume:
519 	while (next != &this_parent->d_subdirs) {
520 		struct list_head *tmp = next;
521 		struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
522 		next = tmp->next;
523 		/* Have we found a mount point ? */
524 		if (d_mountpoint(dentry))
525 			goto positive;
526 		if (!list_empty(&dentry->d_subdirs)) {
527 			this_parent = dentry;
528 			goto repeat;
529 		}
530 	}
531 	/*
532 	 * All done at this level ... ascend and resume the search.
533 	 */
534 	if (this_parent != parent) {
535 		next = this_parent->d_child.next;
536 		this_parent = this_parent->d_parent;
537 		goto resume;
538 	}
539 	spin_unlock(&dcache_lock);
540 	return 0; /* No mount points found in tree */
541 positive:
542 	spin_unlock(&dcache_lock);
543 	return 1;
544 }
545 
546 /*
547  * Search the dentry child list for the specified parent,
548  * and move any unused dentries to the end of the unused
549  * list for prune_dcache(). We descend to the next level
550  * whenever the d_subdirs list is non-empty and continue
551  * searching.
552  *
553  * It returns zero iff there are no unused children,
554  * otherwise  it returns the number of children moved to
555  * the end of the unused list. This may not be the total
556  * number of unused children, because select_parent can
557  * drop the lock and return early due to latency
558  * constraints.
559  */
560 static int select_parent(struct dentry * parent)
561 {
562 	struct dentry *this_parent = parent;
563 	struct list_head *next;
564 	int found = 0;
565 
566 	spin_lock(&dcache_lock);
567 repeat:
568 	next = this_parent->d_subdirs.next;
569 resume:
570 	while (next != &this_parent->d_subdirs) {
571 		struct list_head *tmp = next;
572 		struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
573 		next = tmp->next;
574 
575 		if (!list_empty(&dentry->d_lru)) {
576 			dentry_stat.nr_unused--;
577 			list_del_init(&dentry->d_lru);
578 		}
579 		/*
580 		 * move only zero ref count dentries to the end
581 		 * of the unused list for prune_dcache
582 		 */
583 		if (!atomic_read(&dentry->d_count)) {
584 			list_add(&dentry->d_lru, dentry_unused.prev);
585 			dentry_stat.nr_unused++;
586 			found++;
587 		}
588 
589 		/*
590 		 * We can return to the caller if we have found some (this
591 		 * ensures forward progress). We'll be coming back to find
592 		 * the rest.
593 		 */
594 		if (found && need_resched())
595 			goto out;
596 
597 		/*
598 		 * Descend a level if the d_subdirs list is non-empty.
599 		 */
600 		if (!list_empty(&dentry->d_subdirs)) {
601 			this_parent = dentry;
602 #ifdef DCACHE_DEBUG
603 printk(KERN_DEBUG "select_parent: descending to %s/%s, found=%d\n",
604 dentry->d_parent->d_name.name, dentry->d_name.name, found);
605 #endif
606 			goto repeat;
607 		}
608 	}
609 	/*
610 	 * All done at this level ... ascend and resume the search.
611 	 */
612 	if (this_parent != parent) {
613 		next = this_parent->d_child.next;
614 		this_parent = this_parent->d_parent;
615 #ifdef DCACHE_DEBUG
616 printk(KERN_DEBUG "select_parent: ascending to %s/%s, found=%d\n",
617 this_parent->d_parent->d_name.name, this_parent->d_name.name, found);
618 #endif
619 		goto resume;
620 	}
621 out:
622 	spin_unlock(&dcache_lock);
623 	return found;
624 }
625 
626 /**
627  * shrink_dcache_parent - prune dcache
628  * @parent: parent of entries to prune
629  *
630  * Prune the dcache to remove unused children of the parent dentry.
631  */
632 
633 void shrink_dcache_parent(struct dentry * parent)
634 {
635 	int found;
636 
637 	while ((found = select_parent(parent)) != 0)
638 		prune_dcache(found);
639 }
640 
641 /**
642  * shrink_dcache_anon - further prune the cache
643  * @head: head of d_hash list of dentries to prune
644  *
645  * Prune the dentries that are anonymous
646  *
647  * parsing d_hash list does not hlist_for_each_rcu() as it
648  * done under dcache_lock.
649  *
650  */
651 void shrink_dcache_anon(struct hlist_head *head)
652 {
653 	struct hlist_node *lp;
654 	int found;
655 	do {
656 		found = 0;
657 		spin_lock(&dcache_lock);
658 		hlist_for_each(lp, head) {
659 			struct dentry *this = hlist_entry(lp, struct dentry, d_hash);
660 			if (!list_empty(&this->d_lru)) {
661 				dentry_stat.nr_unused--;
662 				list_del_init(&this->d_lru);
663 			}
664 
665 			/*
666 			 * move only zero ref count dentries to the end
667 			 * of the unused list for prune_dcache
668 			 */
669 			if (!atomic_read(&this->d_count)) {
670 				list_add_tail(&this->d_lru, &dentry_unused);
671 				dentry_stat.nr_unused++;
672 				found++;
673 			}
674 		}
675 		spin_unlock(&dcache_lock);
676 		prune_dcache(found);
677 	} while(found);
678 }
679 
680 /*
681  * Scan `nr' dentries and return the number which remain.
682  *
683  * We need to avoid reentering the filesystem if the caller is performing a
684  * GFP_NOFS allocation attempt.  One example deadlock is:
685  *
686  * ext2_new_block->getblk->GFP->shrink_dcache_memory->prune_dcache->
687  * prune_one_dentry->dput->dentry_iput->iput->inode->i_sb->s_op->put_inode->
688  * ext2_discard_prealloc->ext2_free_blocks->lock_super->DEADLOCK.
689  *
690  * In this case we return -1 to tell the caller that we baled.
691  */
692 static int shrink_dcache_memory(int nr, gfp_t gfp_mask)
693 {
694 	if (nr) {
695 		if (!(gfp_mask & __GFP_FS))
696 			return -1;
697 		prune_dcache(nr);
698 	}
699 	return (dentry_stat.nr_unused / 100) * sysctl_vfs_cache_pressure;
700 }
701 
702 /**
703  * d_alloc	-	allocate a dcache entry
704  * @parent: parent of entry to allocate
705  * @name: qstr of the name
706  *
707  * Allocates a dentry. It returns %NULL if there is insufficient memory
708  * available. On a success the dentry is returned. The name passed in is
709  * copied and the copy passed in may be reused after this call.
710  */
711 
712 struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
713 {
714 	struct dentry *dentry;
715 	char *dname;
716 
717 	dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
718 	if (!dentry)
719 		return NULL;
720 
721 	if (name->len > DNAME_INLINE_LEN-1) {
722 		dname = kmalloc(name->len + 1, GFP_KERNEL);
723 		if (!dname) {
724 			kmem_cache_free(dentry_cache, dentry);
725 			return NULL;
726 		}
727 	} else  {
728 		dname = dentry->d_iname;
729 	}
730 	dentry->d_name.name = dname;
731 
732 	dentry->d_name.len = name->len;
733 	dentry->d_name.hash = name->hash;
734 	memcpy(dname, name->name, name->len);
735 	dname[name->len] = 0;
736 
737 	atomic_set(&dentry->d_count, 1);
738 	dentry->d_flags = DCACHE_UNHASHED;
739 	spin_lock_init(&dentry->d_lock);
740 	dentry->d_inode = NULL;
741 	dentry->d_parent = NULL;
742 	dentry->d_sb = NULL;
743 	dentry->d_op = NULL;
744 	dentry->d_fsdata = NULL;
745 	dentry->d_mounted = 0;
746 	dentry->d_cookie = NULL;
747 	INIT_HLIST_NODE(&dentry->d_hash);
748 	INIT_LIST_HEAD(&dentry->d_lru);
749 	INIT_LIST_HEAD(&dentry->d_subdirs);
750 	INIT_LIST_HEAD(&dentry->d_alias);
751 
752 	if (parent) {
753 		dentry->d_parent = dget(parent);
754 		dentry->d_sb = parent->d_sb;
755 	} else {
756 		INIT_LIST_HEAD(&dentry->d_child);
757 	}
758 
759 	spin_lock(&dcache_lock);
760 	if (parent)
761 		list_add(&dentry->d_child, &parent->d_subdirs);
762 	dentry_stat.nr_dentry++;
763 	spin_unlock(&dcache_lock);
764 
765 	return dentry;
766 }
767 
768 struct dentry *d_alloc_name(struct dentry *parent, const char *name)
769 {
770 	struct qstr q;
771 
772 	q.name = name;
773 	q.len = strlen(name);
774 	q.hash = full_name_hash(q.name, q.len);
775 	return d_alloc(parent, &q);
776 }
777 
778 /**
779  * d_instantiate - fill in inode information for a dentry
780  * @entry: dentry to complete
781  * @inode: inode to attach to this dentry
782  *
783  * Fill in inode information in the entry.
784  *
785  * This turns negative dentries into productive full members
786  * of society.
787  *
788  * NOTE! This assumes that the inode count has been incremented
789  * (or otherwise set) by the caller to indicate that it is now
790  * in use by the dcache.
791  */
792 
793 void d_instantiate(struct dentry *entry, struct inode * inode)
794 {
795 	if (!list_empty(&entry->d_alias)) BUG();
796 	spin_lock(&dcache_lock);
797 	if (inode)
798 		list_add(&entry->d_alias, &inode->i_dentry);
799 	entry->d_inode = inode;
800 	spin_unlock(&dcache_lock);
801 	security_d_instantiate(entry, inode);
802 }
803 
804 /**
805  * d_instantiate_unique - instantiate a non-aliased dentry
806  * @entry: dentry to instantiate
807  * @inode: inode to attach to this dentry
808  *
809  * Fill in inode information in the entry. On success, it returns NULL.
810  * If an unhashed alias of "entry" already exists, then we return the
811  * aliased dentry instead.
812  *
813  * Note that in order to avoid conflicts with rename() etc, the caller
814  * had better be holding the parent directory semaphore.
815  */
816 struct dentry *d_instantiate_unique(struct dentry *entry, struct inode *inode)
817 {
818 	struct dentry *alias;
819 	int len = entry->d_name.len;
820 	const char *name = entry->d_name.name;
821 	unsigned int hash = entry->d_name.hash;
822 
823 	BUG_ON(!list_empty(&entry->d_alias));
824 	spin_lock(&dcache_lock);
825 	if (!inode)
826 		goto do_negative;
827 	list_for_each_entry(alias, &inode->i_dentry, d_alias) {
828 		struct qstr *qstr = &alias->d_name;
829 
830 		if (qstr->hash != hash)
831 			continue;
832 		if (alias->d_parent != entry->d_parent)
833 			continue;
834 		if (qstr->len != len)
835 			continue;
836 		if (memcmp(qstr->name, name, len))
837 			continue;
838 		dget_locked(alias);
839 		spin_unlock(&dcache_lock);
840 		BUG_ON(!d_unhashed(alias));
841 		return alias;
842 	}
843 	list_add(&entry->d_alias, &inode->i_dentry);
844 do_negative:
845 	entry->d_inode = inode;
846 	spin_unlock(&dcache_lock);
847 	security_d_instantiate(entry, inode);
848 	return NULL;
849 }
850 EXPORT_SYMBOL(d_instantiate_unique);
851 
852 /**
853  * d_alloc_root - allocate root dentry
854  * @root_inode: inode to allocate the root for
855  *
856  * Allocate a root ("/") dentry for the inode given. The inode is
857  * instantiated and returned. %NULL is returned if there is insufficient
858  * memory or the inode passed is %NULL.
859  */
860 
861 struct dentry * d_alloc_root(struct inode * root_inode)
862 {
863 	struct dentry *res = NULL;
864 
865 	if (root_inode) {
866 		static const struct qstr name = { .name = "/", .len = 1 };
867 
868 		res = d_alloc(NULL, &name);
869 		if (res) {
870 			res->d_sb = root_inode->i_sb;
871 			res->d_parent = res;
872 			d_instantiate(res, root_inode);
873 		}
874 	}
875 	return res;
876 }
877 
878 static inline struct hlist_head *d_hash(struct dentry *parent,
879 					unsigned long hash)
880 {
881 	hash += ((unsigned long) parent ^ GOLDEN_RATIO_PRIME) / L1_CACHE_BYTES;
882 	hash = hash ^ ((hash ^ GOLDEN_RATIO_PRIME) >> D_HASHBITS);
883 	return dentry_hashtable + (hash & D_HASHMASK);
884 }
885 
886 /**
887  * d_alloc_anon - allocate an anonymous dentry
888  * @inode: inode to allocate the dentry for
889  *
890  * This is similar to d_alloc_root.  It is used by filesystems when
891  * creating a dentry for a given inode, often in the process of
892  * mapping a filehandle to a dentry.  The returned dentry may be
893  * anonymous, or may have a full name (if the inode was already
894  * in the cache).  The file system may need to make further
895  * efforts to connect this dentry into the dcache properly.
896  *
897  * When called on a directory inode, we must ensure that
898  * the inode only ever has one dentry.  If a dentry is
899  * found, that is returned instead of allocating a new one.
900  *
901  * On successful return, the reference to the inode has been transferred
902  * to the dentry.  If %NULL is returned (indicating kmalloc failure),
903  * the reference on the inode has not been released.
904  */
905 
906 struct dentry * d_alloc_anon(struct inode *inode)
907 {
908 	static const struct qstr anonstring = { .name = "" };
909 	struct dentry *tmp;
910 	struct dentry *res;
911 
912 	if ((res = d_find_alias(inode))) {
913 		iput(inode);
914 		return res;
915 	}
916 
917 	tmp = d_alloc(NULL, &anonstring);
918 	if (!tmp)
919 		return NULL;
920 
921 	tmp->d_parent = tmp; /* make sure dput doesn't croak */
922 
923 	spin_lock(&dcache_lock);
924 	res = __d_find_alias(inode, 0);
925 	if (!res) {
926 		/* attach a disconnected dentry */
927 		res = tmp;
928 		tmp = NULL;
929 		spin_lock(&res->d_lock);
930 		res->d_sb = inode->i_sb;
931 		res->d_parent = res;
932 		res->d_inode = inode;
933 		res->d_flags |= DCACHE_DISCONNECTED;
934 		res->d_flags &= ~DCACHE_UNHASHED;
935 		list_add(&res->d_alias, &inode->i_dentry);
936 		hlist_add_head(&res->d_hash, &inode->i_sb->s_anon);
937 		spin_unlock(&res->d_lock);
938 
939 		inode = NULL; /* don't drop reference */
940 	}
941 	spin_unlock(&dcache_lock);
942 
943 	if (inode)
944 		iput(inode);
945 	if (tmp)
946 		dput(tmp);
947 	return res;
948 }
949 
950 
951 /**
952  * d_splice_alias - splice a disconnected dentry into the tree if one exists
953  * @inode:  the inode which may have a disconnected dentry
954  * @dentry: a negative dentry which we want to point to the inode.
955  *
956  * If inode is a directory and has a 'disconnected' dentry (i.e. IS_ROOT and
957  * DCACHE_DISCONNECTED), then d_move that in place of the given dentry
958  * and return it, else simply d_add the inode to the dentry and return NULL.
959  *
960  * This is needed in the lookup routine of any filesystem that is exportable
961  * (via knfsd) so that we can build dcache paths to directories effectively.
962  *
963  * If a dentry was found and moved, then it is returned.  Otherwise NULL
964  * is returned.  This matches the expected return value of ->lookup.
965  *
966  */
967 struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
968 {
969 	struct dentry *new = NULL;
970 
971 	if (inode) {
972 		spin_lock(&dcache_lock);
973 		new = __d_find_alias(inode, 1);
974 		if (new) {
975 			BUG_ON(!(new->d_flags & DCACHE_DISCONNECTED));
976 			spin_unlock(&dcache_lock);
977 			security_d_instantiate(new, inode);
978 			d_rehash(dentry);
979 			d_move(new, dentry);
980 			iput(inode);
981 		} else {
982 			/* d_instantiate takes dcache_lock, so we do it by hand */
983 			list_add(&dentry->d_alias, &inode->i_dentry);
984 			dentry->d_inode = inode;
985 			spin_unlock(&dcache_lock);
986 			security_d_instantiate(dentry, inode);
987 			d_rehash(dentry);
988 		}
989 	} else
990 		d_add(dentry, inode);
991 	return new;
992 }
993 
994 
995 /**
996  * d_lookup - search for a dentry
997  * @parent: parent dentry
998  * @name: qstr of name we wish to find
999  *
1000  * Searches the children of the parent dentry for the name in question. If
1001  * the dentry is found its reference count is incremented and the dentry
1002  * is returned. The caller must use d_put to free the entry when it has
1003  * finished using it. %NULL is returned on failure.
1004  *
1005  * __d_lookup is dcache_lock free. The hash list is protected using RCU.
1006  * Memory barriers are used while updating and doing lockless traversal.
1007  * To avoid races with d_move while rename is happening, d_lock is used.
1008  *
1009  * Overflows in memcmp(), while d_move, are avoided by keeping the length
1010  * and name pointer in one structure pointed by d_qstr.
1011  *
1012  * rcu_read_lock() and rcu_read_unlock() are used to disable preemption while
1013  * lookup is going on.
1014  *
1015  * dentry_unused list is not updated even if lookup finds the required dentry
1016  * in there. It is updated in places such as prune_dcache, shrink_dcache_sb,
1017  * select_parent and __dget_locked. This laziness saves lookup from dcache_lock
1018  * acquisition.
1019  *
1020  * d_lookup() is protected against the concurrent renames in some unrelated
1021  * directory using the seqlockt_t rename_lock.
1022  */
1023 
1024 struct dentry * d_lookup(struct dentry * parent, struct qstr * name)
1025 {
1026 	struct dentry * dentry = NULL;
1027 	unsigned long seq;
1028 
1029         do {
1030                 seq = read_seqbegin(&rename_lock);
1031                 dentry = __d_lookup(parent, name);
1032                 if (dentry)
1033 			break;
1034 	} while (read_seqretry(&rename_lock, seq));
1035 	return dentry;
1036 }
1037 
1038 struct dentry * __d_lookup(struct dentry * parent, struct qstr * name)
1039 {
1040 	unsigned int len = name->len;
1041 	unsigned int hash = name->hash;
1042 	const unsigned char *str = name->name;
1043 	struct hlist_head *head = d_hash(parent,hash);
1044 	struct dentry *found = NULL;
1045 	struct hlist_node *node;
1046 
1047 	rcu_read_lock();
1048 
1049 	hlist_for_each_rcu(node, head) {
1050 		struct dentry *dentry;
1051 		struct qstr *qstr;
1052 
1053 		dentry = hlist_entry(node, struct dentry, d_hash);
1054 
1055 		if (dentry->d_name.hash != hash)
1056 			continue;
1057 		if (dentry->d_parent != parent)
1058 			continue;
1059 
1060 		spin_lock(&dentry->d_lock);
1061 
1062 		/*
1063 		 * Recheck the dentry after taking the lock - d_move may have
1064 		 * changed things.  Don't bother checking the hash because we're
1065 		 * about to compare the whole name anyway.
1066 		 */
1067 		if (dentry->d_parent != parent)
1068 			goto next;
1069 
1070 		/*
1071 		 * It is safe to compare names since d_move() cannot
1072 		 * change the qstr (protected by d_lock).
1073 		 */
1074 		qstr = &dentry->d_name;
1075 		if (parent->d_op && parent->d_op->d_compare) {
1076 			if (parent->d_op->d_compare(parent, qstr, name))
1077 				goto next;
1078 		} else {
1079 			if (qstr->len != len)
1080 				goto next;
1081 			if (memcmp(qstr->name, str, len))
1082 				goto next;
1083 		}
1084 
1085 		if (!d_unhashed(dentry)) {
1086 			atomic_inc(&dentry->d_count);
1087 			found = dentry;
1088 		}
1089 		spin_unlock(&dentry->d_lock);
1090 		break;
1091 next:
1092 		spin_unlock(&dentry->d_lock);
1093  	}
1094  	rcu_read_unlock();
1095 
1096  	return found;
1097 }
1098 
1099 /**
1100  * d_validate - verify dentry provided from insecure source
1101  * @dentry: The dentry alleged to be valid child of @dparent
1102  * @dparent: The parent dentry (known to be valid)
1103  * @hash: Hash of the dentry
1104  * @len: Length of the name
1105  *
1106  * An insecure source has sent us a dentry, here we verify it and dget() it.
1107  * This is used by ncpfs in its readdir implementation.
1108  * Zero is returned in the dentry is invalid.
1109  */
1110 
1111 int d_validate(struct dentry *dentry, struct dentry *dparent)
1112 {
1113 	struct hlist_head *base;
1114 	struct hlist_node *lhp;
1115 
1116 	/* Check whether the ptr might be valid at all.. */
1117 	if (!kmem_ptr_validate(dentry_cache, dentry))
1118 		goto out;
1119 
1120 	if (dentry->d_parent != dparent)
1121 		goto out;
1122 
1123 	spin_lock(&dcache_lock);
1124 	base = d_hash(dparent, dentry->d_name.hash);
1125 	hlist_for_each(lhp,base) {
1126 		/* hlist_for_each_rcu() not required for d_hash list
1127 		 * as it is parsed under dcache_lock
1128 		 */
1129 		if (dentry == hlist_entry(lhp, struct dentry, d_hash)) {
1130 			__dget_locked(dentry);
1131 			spin_unlock(&dcache_lock);
1132 			return 1;
1133 		}
1134 	}
1135 	spin_unlock(&dcache_lock);
1136 out:
1137 	return 0;
1138 }
1139 
1140 /*
1141  * When a file is deleted, we have two options:
1142  * - turn this dentry into a negative dentry
1143  * - unhash this dentry and free it.
1144  *
1145  * Usually, we want to just turn this into
1146  * a negative dentry, but if anybody else is
1147  * currently using the dentry or the inode
1148  * we can't do that and we fall back on removing
1149  * it from the hash queues and waiting for
1150  * it to be deleted later when it has no users
1151  */
1152 
1153 /**
1154  * d_delete - delete a dentry
1155  * @dentry: The dentry to delete
1156  *
1157  * Turn the dentry into a negative dentry if possible, otherwise
1158  * remove it from the hash queues so it can be deleted later
1159  */
1160 
1161 void d_delete(struct dentry * dentry)
1162 {
1163 	int isdir = 0;
1164 	/*
1165 	 * Are we the only user?
1166 	 */
1167 	spin_lock(&dcache_lock);
1168 	spin_lock(&dentry->d_lock);
1169 	isdir = S_ISDIR(dentry->d_inode->i_mode);
1170 	if (atomic_read(&dentry->d_count) == 1) {
1171 		dentry_iput(dentry);
1172 		fsnotify_nameremove(dentry, isdir);
1173 		return;
1174 	}
1175 
1176 	if (!d_unhashed(dentry))
1177 		__d_drop(dentry);
1178 
1179 	spin_unlock(&dentry->d_lock);
1180 	spin_unlock(&dcache_lock);
1181 
1182 	fsnotify_nameremove(dentry, isdir);
1183 }
1184 
1185 static void __d_rehash(struct dentry * entry, struct hlist_head *list)
1186 {
1187 
1188  	entry->d_flags &= ~DCACHE_UNHASHED;
1189  	hlist_add_head_rcu(&entry->d_hash, list);
1190 }
1191 
1192 /**
1193  * d_rehash	- add an entry back to the hash
1194  * @entry: dentry to add to the hash
1195  *
1196  * Adds a dentry to the hash according to its name.
1197  */
1198 
1199 void d_rehash(struct dentry * entry)
1200 {
1201 	struct hlist_head *list = d_hash(entry->d_parent, entry->d_name.hash);
1202 
1203 	spin_lock(&dcache_lock);
1204 	spin_lock(&entry->d_lock);
1205 	__d_rehash(entry, list);
1206 	spin_unlock(&entry->d_lock);
1207 	spin_unlock(&dcache_lock);
1208 }
1209 
1210 #define do_switch(x,y) do { \
1211 	__typeof__ (x) __tmp = x; \
1212 	x = y; y = __tmp; } while (0)
1213 
1214 /*
1215  * When switching names, the actual string doesn't strictly have to
1216  * be preserved in the target - because we're dropping the target
1217  * anyway. As such, we can just do a simple memcpy() to copy over
1218  * the new name before we switch.
1219  *
1220  * Note that we have to be a lot more careful about getting the hash
1221  * switched - we have to switch the hash value properly even if it
1222  * then no longer matches the actual (corrupted) string of the target.
1223  * The hash value has to match the hash queue that the dentry is on..
1224  */
1225 static void switch_names(struct dentry *dentry, struct dentry *target)
1226 {
1227 	if (dname_external(target)) {
1228 		if (dname_external(dentry)) {
1229 			/*
1230 			 * Both external: swap the pointers
1231 			 */
1232 			do_switch(target->d_name.name, dentry->d_name.name);
1233 		} else {
1234 			/*
1235 			 * dentry:internal, target:external.  Steal target's
1236 			 * storage and make target internal.
1237 			 */
1238 			dentry->d_name.name = target->d_name.name;
1239 			target->d_name.name = target->d_iname;
1240 		}
1241 	} else {
1242 		if (dname_external(dentry)) {
1243 			/*
1244 			 * dentry:external, target:internal.  Give dentry's
1245 			 * storage to target and make dentry internal
1246 			 */
1247 			memcpy(dentry->d_iname, target->d_name.name,
1248 					target->d_name.len + 1);
1249 			target->d_name.name = dentry->d_name.name;
1250 			dentry->d_name.name = dentry->d_iname;
1251 		} else {
1252 			/*
1253 			 * Both are internal.  Just copy target to dentry
1254 			 */
1255 			memcpy(dentry->d_iname, target->d_name.name,
1256 					target->d_name.len + 1);
1257 		}
1258 	}
1259 }
1260 
1261 /*
1262  * We cannibalize "target" when moving dentry on top of it,
1263  * because it's going to be thrown away anyway. We could be more
1264  * polite about it, though.
1265  *
1266  * This forceful removal will result in ugly /proc output if
1267  * somebody holds a file open that got deleted due to a rename.
1268  * We could be nicer about the deleted file, and let it show
1269  * up under the name it got deleted rather than the name that
1270  * deleted it.
1271  */
1272 
1273 /**
1274  * d_move - move a dentry
1275  * @dentry: entry to move
1276  * @target: new dentry
1277  *
1278  * Update the dcache to reflect the move of a file name. Negative
1279  * dcache entries should not be moved in this way.
1280  */
1281 
1282 void d_move(struct dentry * dentry, struct dentry * target)
1283 {
1284 	struct hlist_head *list;
1285 
1286 	if (!dentry->d_inode)
1287 		printk(KERN_WARNING "VFS: moving negative dcache entry\n");
1288 
1289 	spin_lock(&dcache_lock);
1290 	write_seqlock(&rename_lock);
1291 	/*
1292 	 * XXXX: do we really need to take target->d_lock?
1293 	 */
1294 	if (target < dentry) {
1295 		spin_lock(&target->d_lock);
1296 		spin_lock(&dentry->d_lock);
1297 	} else {
1298 		spin_lock(&dentry->d_lock);
1299 		spin_lock(&target->d_lock);
1300 	}
1301 
1302 	/* Move the dentry to the target hash queue, if on different bucket */
1303 	if (dentry->d_flags & DCACHE_UNHASHED)
1304 		goto already_unhashed;
1305 
1306 	hlist_del_rcu(&dentry->d_hash);
1307 
1308 already_unhashed:
1309 	list = d_hash(target->d_parent, target->d_name.hash);
1310 	__d_rehash(dentry, list);
1311 
1312 	/* Unhash the target: dput() will then get rid of it */
1313 	__d_drop(target);
1314 
1315 	list_del(&dentry->d_child);
1316 	list_del(&target->d_child);
1317 
1318 	/* Switch the names.. */
1319 	switch_names(dentry, target);
1320 	do_switch(dentry->d_name.len, target->d_name.len);
1321 	do_switch(dentry->d_name.hash, target->d_name.hash);
1322 
1323 	/* ... and switch the parents */
1324 	if (IS_ROOT(dentry)) {
1325 		dentry->d_parent = target->d_parent;
1326 		target->d_parent = target;
1327 		INIT_LIST_HEAD(&target->d_child);
1328 	} else {
1329 		do_switch(dentry->d_parent, target->d_parent);
1330 
1331 		/* And add them back to the (new) parent lists */
1332 		list_add(&target->d_child, &target->d_parent->d_subdirs);
1333 	}
1334 
1335 	list_add(&dentry->d_child, &dentry->d_parent->d_subdirs);
1336 	spin_unlock(&target->d_lock);
1337 	spin_unlock(&dentry->d_lock);
1338 	write_sequnlock(&rename_lock);
1339 	spin_unlock(&dcache_lock);
1340 }
1341 
1342 /**
1343  * d_path - return the path of a dentry
1344  * @dentry: dentry to report
1345  * @vfsmnt: vfsmnt to which the dentry belongs
1346  * @root: root dentry
1347  * @rootmnt: vfsmnt to which the root dentry belongs
1348  * @buffer: buffer to return value in
1349  * @buflen: buffer length
1350  *
1351  * Convert a dentry into an ASCII path name. If the entry has been deleted
1352  * the string " (deleted)" is appended. Note that this is ambiguous.
1353  *
1354  * Returns the buffer or an error code if the path was too long.
1355  *
1356  * "buflen" should be positive. Caller holds the dcache_lock.
1357  */
1358 static char * __d_path( struct dentry *dentry, struct vfsmount *vfsmnt,
1359 			struct dentry *root, struct vfsmount *rootmnt,
1360 			char *buffer, int buflen)
1361 {
1362 	char * end = buffer+buflen;
1363 	char * retval;
1364 	int namelen;
1365 
1366 	*--end = '\0';
1367 	buflen--;
1368 	if (!IS_ROOT(dentry) && d_unhashed(dentry)) {
1369 		buflen -= 10;
1370 		end -= 10;
1371 		if (buflen < 0)
1372 			goto Elong;
1373 		memcpy(end, " (deleted)", 10);
1374 	}
1375 
1376 	if (buflen < 1)
1377 		goto Elong;
1378 	/* Get '/' right */
1379 	retval = end-1;
1380 	*retval = '/';
1381 
1382 	for (;;) {
1383 		struct dentry * parent;
1384 
1385 		if (dentry == root && vfsmnt == rootmnt)
1386 			break;
1387 		if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
1388 			/* Global root? */
1389 			spin_lock(&vfsmount_lock);
1390 			if (vfsmnt->mnt_parent == vfsmnt) {
1391 				spin_unlock(&vfsmount_lock);
1392 				goto global_root;
1393 			}
1394 			dentry = vfsmnt->mnt_mountpoint;
1395 			vfsmnt = vfsmnt->mnt_parent;
1396 			spin_unlock(&vfsmount_lock);
1397 			continue;
1398 		}
1399 		parent = dentry->d_parent;
1400 		prefetch(parent);
1401 		namelen = dentry->d_name.len;
1402 		buflen -= namelen + 1;
1403 		if (buflen < 0)
1404 			goto Elong;
1405 		end -= namelen;
1406 		memcpy(end, dentry->d_name.name, namelen);
1407 		*--end = '/';
1408 		retval = end;
1409 		dentry = parent;
1410 	}
1411 
1412 	return retval;
1413 
1414 global_root:
1415 	namelen = dentry->d_name.len;
1416 	buflen -= namelen;
1417 	if (buflen < 0)
1418 		goto Elong;
1419 	retval -= namelen-1;	/* hit the slash */
1420 	memcpy(retval, dentry->d_name.name, namelen);
1421 	return retval;
1422 Elong:
1423 	return ERR_PTR(-ENAMETOOLONG);
1424 }
1425 
1426 /* write full pathname into buffer and return start of pathname */
1427 char * d_path(struct dentry *dentry, struct vfsmount *vfsmnt,
1428 				char *buf, int buflen)
1429 {
1430 	char *res;
1431 	struct vfsmount *rootmnt;
1432 	struct dentry *root;
1433 
1434 	read_lock(&current->fs->lock);
1435 	rootmnt = mntget(current->fs->rootmnt);
1436 	root = dget(current->fs->root);
1437 	read_unlock(&current->fs->lock);
1438 	spin_lock(&dcache_lock);
1439 	res = __d_path(dentry, vfsmnt, root, rootmnt, buf, buflen);
1440 	spin_unlock(&dcache_lock);
1441 	dput(root);
1442 	mntput(rootmnt);
1443 	return res;
1444 }
1445 
1446 /*
1447  * NOTE! The user-level library version returns a
1448  * character pointer. The kernel system call just
1449  * returns the length of the buffer filled (which
1450  * includes the ending '\0' character), or a negative
1451  * error value. So libc would do something like
1452  *
1453  *	char *getcwd(char * buf, size_t size)
1454  *	{
1455  *		int retval;
1456  *
1457  *		retval = sys_getcwd(buf, size);
1458  *		if (retval >= 0)
1459  *			return buf;
1460  *		errno = -retval;
1461  *		return NULL;
1462  *	}
1463  */
1464 asmlinkage long sys_getcwd(char __user *buf, unsigned long size)
1465 {
1466 	int error;
1467 	struct vfsmount *pwdmnt, *rootmnt;
1468 	struct dentry *pwd, *root;
1469 	char *page = (char *) __get_free_page(GFP_USER);
1470 
1471 	if (!page)
1472 		return -ENOMEM;
1473 
1474 	read_lock(&current->fs->lock);
1475 	pwdmnt = mntget(current->fs->pwdmnt);
1476 	pwd = dget(current->fs->pwd);
1477 	rootmnt = mntget(current->fs->rootmnt);
1478 	root = dget(current->fs->root);
1479 	read_unlock(&current->fs->lock);
1480 
1481 	error = -ENOENT;
1482 	/* Has the current directory has been unlinked? */
1483 	spin_lock(&dcache_lock);
1484 	if (pwd->d_parent == pwd || !d_unhashed(pwd)) {
1485 		unsigned long len;
1486 		char * cwd;
1487 
1488 		cwd = __d_path(pwd, pwdmnt, root, rootmnt, page, PAGE_SIZE);
1489 		spin_unlock(&dcache_lock);
1490 
1491 		error = PTR_ERR(cwd);
1492 		if (IS_ERR(cwd))
1493 			goto out;
1494 
1495 		error = -ERANGE;
1496 		len = PAGE_SIZE + page - cwd;
1497 		if (len <= size) {
1498 			error = len;
1499 			if (copy_to_user(buf, cwd, len))
1500 				error = -EFAULT;
1501 		}
1502 	} else
1503 		spin_unlock(&dcache_lock);
1504 
1505 out:
1506 	dput(pwd);
1507 	mntput(pwdmnt);
1508 	dput(root);
1509 	mntput(rootmnt);
1510 	free_page((unsigned long) page);
1511 	return error;
1512 }
1513 
1514 /*
1515  * Test whether new_dentry is a subdirectory of old_dentry.
1516  *
1517  * Trivially implemented using the dcache structure
1518  */
1519 
1520 /**
1521  * is_subdir - is new dentry a subdirectory of old_dentry
1522  * @new_dentry: new dentry
1523  * @old_dentry: old dentry
1524  *
1525  * Returns 1 if new_dentry is a subdirectory of the parent (at any depth).
1526  * Returns 0 otherwise.
1527  * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
1528  */
1529 
1530 int is_subdir(struct dentry * new_dentry, struct dentry * old_dentry)
1531 {
1532 	int result;
1533 	struct dentry * saved = new_dentry;
1534 	unsigned long seq;
1535 
1536 	/* need rcu_readlock to protect against the d_parent trashing due to
1537 	 * d_move
1538 	 */
1539 	rcu_read_lock();
1540         do {
1541 		/* for restarting inner loop in case of seq retry */
1542 		new_dentry = saved;
1543 		result = 0;
1544 		seq = read_seqbegin(&rename_lock);
1545 		for (;;) {
1546 			if (new_dentry != old_dentry) {
1547 				struct dentry * parent = new_dentry->d_parent;
1548 				if (parent == new_dentry)
1549 					break;
1550 				new_dentry = parent;
1551 				continue;
1552 			}
1553 			result = 1;
1554 			break;
1555 		}
1556 	} while (read_seqretry(&rename_lock, seq));
1557 	rcu_read_unlock();
1558 
1559 	return result;
1560 }
1561 
1562 void d_genocide(struct dentry *root)
1563 {
1564 	struct dentry *this_parent = root;
1565 	struct list_head *next;
1566 
1567 	spin_lock(&dcache_lock);
1568 repeat:
1569 	next = this_parent->d_subdirs.next;
1570 resume:
1571 	while (next != &this_parent->d_subdirs) {
1572 		struct list_head *tmp = next;
1573 		struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
1574 		next = tmp->next;
1575 		if (d_unhashed(dentry)||!dentry->d_inode)
1576 			continue;
1577 		if (!list_empty(&dentry->d_subdirs)) {
1578 			this_parent = dentry;
1579 			goto repeat;
1580 		}
1581 		atomic_dec(&dentry->d_count);
1582 	}
1583 	if (this_parent != root) {
1584 		next = this_parent->d_child.next;
1585 		atomic_dec(&this_parent->d_count);
1586 		this_parent = this_parent->d_parent;
1587 		goto resume;
1588 	}
1589 	spin_unlock(&dcache_lock);
1590 }
1591 
1592 /**
1593  * find_inode_number - check for dentry with name
1594  * @dir: directory to check
1595  * @name: Name to find.
1596  *
1597  * Check whether a dentry already exists for the given name,
1598  * and return the inode number if it has an inode. Otherwise
1599  * 0 is returned.
1600  *
1601  * This routine is used to post-process directory listings for
1602  * filesystems using synthetic inode numbers, and is necessary
1603  * to keep getcwd() working.
1604  */
1605 
1606 ino_t find_inode_number(struct dentry *dir, struct qstr *name)
1607 {
1608 	struct dentry * dentry;
1609 	ino_t ino = 0;
1610 
1611 	/*
1612 	 * Check for a fs-specific hash function. Note that we must
1613 	 * calculate the standard hash first, as the d_op->d_hash()
1614 	 * routine may choose to leave the hash value unchanged.
1615 	 */
1616 	name->hash = full_name_hash(name->name, name->len);
1617 	if (dir->d_op && dir->d_op->d_hash)
1618 	{
1619 		if (dir->d_op->d_hash(dir, name) != 0)
1620 			goto out;
1621 	}
1622 
1623 	dentry = d_lookup(dir, name);
1624 	if (dentry)
1625 	{
1626 		if (dentry->d_inode)
1627 			ino = dentry->d_inode->i_ino;
1628 		dput(dentry);
1629 	}
1630 out:
1631 	return ino;
1632 }
1633 
1634 static __initdata unsigned long dhash_entries;
1635 static int __init set_dhash_entries(char *str)
1636 {
1637 	if (!str)
1638 		return 0;
1639 	dhash_entries = simple_strtoul(str, &str, 0);
1640 	return 1;
1641 }
1642 __setup("dhash_entries=", set_dhash_entries);
1643 
1644 static void __init dcache_init_early(void)
1645 {
1646 	int loop;
1647 
1648 	/* If hashes are distributed across NUMA nodes, defer
1649 	 * hash allocation until vmalloc space is available.
1650 	 */
1651 	if (hashdist)
1652 		return;
1653 
1654 	dentry_hashtable =
1655 		alloc_large_system_hash("Dentry cache",
1656 					sizeof(struct hlist_head),
1657 					dhash_entries,
1658 					13,
1659 					HASH_EARLY,
1660 					&d_hash_shift,
1661 					&d_hash_mask,
1662 					0);
1663 
1664 	for (loop = 0; loop < (1 << d_hash_shift); loop++)
1665 		INIT_HLIST_HEAD(&dentry_hashtable[loop]);
1666 }
1667 
1668 static void __init dcache_init(unsigned long mempages)
1669 {
1670 	int loop;
1671 
1672 	/*
1673 	 * A constructor could be added for stable state like the lists,
1674 	 * but it is probably not worth it because of the cache nature
1675 	 * of the dcache.
1676 	 */
1677 	dentry_cache = kmem_cache_create("dentry_cache",
1678 					 sizeof(struct dentry),
1679 					 0,
1680 					 SLAB_RECLAIM_ACCOUNT|SLAB_PANIC,
1681 					 NULL, NULL);
1682 
1683 	set_shrinker(DEFAULT_SEEKS, shrink_dcache_memory);
1684 
1685 	/* Hash may have been set up in dcache_init_early */
1686 	if (!hashdist)
1687 		return;
1688 
1689 	dentry_hashtable =
1690 		alloc_large_system_hash("Dentry cache",
1691 					sizeof(struct hlist_head),
1692 					dhash_entries,
1693 					13,
1694 					0,
1695 					&d_hash_shift,
1696 					&d_hash_mask,
1697 					0);
1698 
1699 	for (loop = 0; loop < (1 << d_hash_shift); loop++)
1700 		INIT_HLIST_HEAD(&dentry_hashtable[loop]);
1701 }
1702 
1703 /* SLAB cache for __getname() consumers */
1704 kmem_cache_t *names_cachep;
1705 
1706 /* SLAB cache for file structures */
1707 kmem_cache_t *filp_cachep;
1708 
1709 EXPORT_SYMBOL(d_genocide);
1710 
1711 extern void bdev_cache_init(void);
1712 extern void chrdev_init(void);
1713 
1714 void __init vfs_caches_init_early(void)
1715 {
1716 	dcache_init_early();
1717 	inode_init_early();
1718 }
1719 
1720 void __init vfs_caches_init(unsigned long mempages)
1721 {
1722 	unsigned long reserve;
1723 
1724 	/* Base hash sizes on available memory, with a reserve equal to
1725            150% of current kernel size */
1726 
1727 	reserve = min((mempages - nr_free_pages()) * 3/2, mempages - 1);
1728 	mempages -= reserve;
1729 
1730 	names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
1731 			SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
1732 
1733 	filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
1734 			SLAB_HWCACHE_ALIGN|SLAB_PANIC, filp_ctor, filp_dtor);
1735 
1736 	dcache_init(mempages);
1737 	inode_init(mempages);
1738 	files_init(mempages);
1739 	mnt_init(mempages);
1740 	bdev_cache_init();
1741 	chrdev_init();
1742 }
1743 
1744 EXPORT_SYMBOL(d_alloc);
1745 EXPORT_SYMBOL(d_alloc_anon);
1746 EXPORT_SYMBOL(d_alloc_root);
1747 EXPORT_SYMBOL(d_delete);
1748 EXPORT_SYMBOL(d_find_alias);
1749 EXPORT_SYMBOL(d_instantiate);
1750 EXPORT_SYMBOL(d_invalidate);
1751 EXPORT_SYMBOL(d_lookup);
1752 EXPORT_SYMBOL(d_move);
1753 EXPORT_SYMBOL(d_path);
1754 EXPORT_SYMBOL(d_prune_aliases);
1755 EXPORT_SYMBOL(d_rehash);
1756 EXPORT_SYMBOL(d_splice_alias);
1757 EXPORT_SYMBOL(d_validate);
1758 EXPORT_SYMBOL(dget_locked);
1759 EXPORT_SYMBOL(dput);
1760 EXPORT_SYMBOL(find_inode_number);
1761 EXPORT_SYMBOL(have_submounts);
1762 EXPORT_SYMBOL(names_cachep);
1763 EXPORT_SYMBOL(shrink_dcache_parent);
1764 EXPORT_SYMBOL(shrink_dcache_sb);
1765