xref: /openbmc/linux/fs/dcache.c (revision a1741e7fcbc19a67520115df480ab17012cc3d0b)
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/syscalls.h>
18 #include <linux/string.h>
19 #include <linux/mm.h>
20 #include <linux/fs.h>
21 #include <linux/fsnotify.h>
22 #include <linux/slab.h>
23 #include <linux/init.h>
24 #include <linux/hash.h>
25 #include <linux/cache.h>
26 #include <linux/module.h>
27 #include <linux/mount.h>
28 #include <linux/file.h>
29 #include <asm/uaccess.h>
30 #include <linux/security.h>
31 #include <linux/seqlock.h>
32 #include <linux/swap.h>
33 #include <linux/bootmem.h>
34 #include <linux/fs_struct.h>
35 #include <linux/hardirq.h>
36 #include <linux/bit_spinlock.h>
37 #include <linux/rculist_bl.h>
38 #include <linux/prefetch.h>
39 #include "internal.h"
40 
41 /*
42  * Usage:
43  * dcache->d_inode->i_lock protects:
44  *   - i_dentry, d_alias, d_inode of aliases
45  * dcache_hash_bucket lock protects:
46  *   - the dcache hash table
47  * s_anon bl list spinlock protects:
48  *   - the s_anon list (see __d_drop)
49  * dcache_lru_lock protects:
50  *   - the dcache lru lists and counters
51  * d_lock protects:
52  *   - d_flags
53  *   - d_name
54  *   - d_lru
55  *   - d_count
56  *   - d_unhashed()
57  *   - d_parent and d_subdirs
58  *   - childrens' d_child and d_parent
59  *   - d_alias, d_inode
60  *
61  * Ordering:
62  * dentry->d_inode->i_lock
63  *   dentry->d_lock
64  *     dcache_lru_lock
65  *     dcache_hash_bucket lock
66  *     s_anon lock
67  *
68  * If there is an ancestor relationship:
69  * dentry->d_parent->...->d_parent->d_lock
70  *   ...
71  *     dentry->d_parent->d_lock
72  *       dentry->d_lock
73  *
74  * If no ancestor relationship:
75  * if (dentry1 < dentry2)
76  *   dentry1->d_lock
77  *     dentry2->d_lock
78  */
79 int sysctl_vfs_cache_pressure __read_mostly = 100;
80 EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
81 
82 static __cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lru_lock);
83 __cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
84 
85 EXPORT_SYMBOL(rename_lock);
86 
87 static struct kmem_cache *dentry_cache __read_mostly;
88 
89 /*
90  * This is the single most critical data structure when it comes
91  * to the dcache: the hashtable for lookups. Somebody should try
92  * to make this good - I've just made it work.
93  *
94  * This hash-function tries to avoid losing too many bits of hash
95  * information, yet avoid using a prime hash-size or similar.
96  */
97 #define D_HASHBITS     d_hash_shift
98 #define D_HASHMASK     d_hash_mask
99 
100 static unsigned int d_hash_mask __read_mostly;
101 static unsigned int d_hash_shift __read_mostly;
102 
103 static struct hlist_bl_head *dentry_hashtable __read_mostly;
104 
105 static inline struct hlist_bl_head *d_hash(struct dentry *parent,
106 					unsigned long hash)
107 {
108 	hash += ((unsigned long) parent ^ GOLDEN_RATIO_PRIME) / L1_CACHE_BYTES;
109 	hash = hash ^ ((hash ^ GOLDEN_RATIO_PRIME) >> D_HASHBITS);
110 	return dentry_hashtable + (hash & D_HASHMASK);
111 }
112 
113 /* Statistics gathering. */
114 struct dentry_stat_t dentry_stat = {
115 	.age_limit = 45,
116 };
117 
118 static DEFINE_PER_CPU(unsigned int, nr_dentry);
119 
120 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
121 static int get_nr_dentry(void)
122 {
123 	int i;
124 	int sum = 0;
125 	for_each_possible_cpu(i)
126 		sum += per_cpu(nr_dentry, i);
127 	return sum < 0 ? 0 : sum;
128 }
129 
130 int proc_nr_dentry(ctl_table *table, int write, void __user *buffer,
131 		   size_t *lenp, loff_t *ppos)
132 {
133 	dentry_stat.nr_dentry = get_nr_dentry();
134 	return proc_dointvec(table, write, buffer, lenp, ppos);
135 }
136 #endif
137 
138 static void __d_free(struct rcu_head *head)
139 {
140 	struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
141 
142 	WARN_ON(!list_empty(&dentry->d_alias));
143 	if (dname_external(dentry))
144 		kfree(dentry->d_name.name);
145 	kmem_cache_free(dentry_cache, dentry);
146 }
147 
148 /*
149  * no locks, please.
150  */
151 static void d_free(struct dentry *dentry)
152 {
153 	BUG_ON(dentry->d_count);
154 	this_cpu_dec(nr_dentry);
155 	if (dentry->d_op && dentry->d_op->d_release)
156 		dentry->d_op->d_release(dentry);
157 
158 	/* if dentry was never visible to RCU, immediate free is OK */
159 	if (!(dentry->d_flags & DCACHE_RCUACCESS))
160 		__d_free(&dentry->d_u.d_rcu);
161 	else
162 		call_rcu(&dentry->d_u.d_rcu, __d_free);
163 }
164 
165 /**
166  * dentry_rcuwalk_barrier - invalidate in-progress rcu-walk lookups
167  * @dentry: the target dentry
168  * After this call, in-progress rcu-walk path lookup will fail. This
169  * should be called after unhashing, and after changing d_inode (if
170  * the dentry has not already been unhashed).
171  */
172 static inline void dentry_rcuwalk_barrier(struct dentry *dentry)
173 {
174 	assert_spin_locked(&dentry->d_lock);
175 	/* Go through a barrier */
176 	write_seqcount_barrier(&dentry->d_seq);
177 }
178 
179 /*
180  * Release the dentry's inode, using the filesystem
181  * d_iput() operation if defined. Dentry has no refcount
182  * and is unhashed.
183  */
184 static void dentry_iput(struct dentry * dentry)
185 	__releases(dentry->d_lock)
186 	__releases(dentry->d_inode->i_lock)
187 {
188 	struct inode *inode = dentry->d_inode;
189 	if (inode) {
190 		dentry->d_inode = NULL;
191 		list_del_init(&dentry->d_alias);
192 		spin_unlock(&dentry->d_lock);
193 		spin_unlock(&inode->i_lock);
194 		if (!inode->i_nlink)
195 			fsnotify_inoderemove(inode);
196 		if (dentry->d_op && dentry->d_op->d_iput)
197 			dentry->d_op->d_iput(dentry, inode);
198 		else
199 			iput(inode);
200 	} else {
201 		spin_unlock(&dentry->d_lock);
202 	}
203 }
204 
205 /*
206  * Release the dentry's inode, using the filesystem
207  * d_iput() operation if defined. dentry remains in-use.
208  */
209 static void dentry_unlink_inode(struct dentry * dentry)
210 	__releases(dentry->d_lock)
211 	__releases(dentry->d_inode->i_lock)
212 {
213 	struct inode *inode = dentry->d_inode;
214 	dentry->d_inode = NULL;
215 	list_del_init(&dentry->d_alias);
216 	dentry_rcuwalk_barrier(dentry);
217 	spin_unlock(&dentry->d_lock);
218 	spin_unlock(&inode->i_lock);
219 	if (!inode->i_nlink)
220 		fsnotify_inoderemove(inode);
221 	if (dentry->d_op && dentry->d_op->d_iput)
222 		dentry->d_op->d_iput(dentry, inode);
223 	else
224 		iput(inode);
225 }
226 
227 /*
228  * dentry_lru_(add|del|move_tail) must be called with d_lock held.
229  */
230 static void dentry_lru_add(struct dentry *dentry)
231 {
232 	if (list_empty(&dentry->d_lru)) {
233 		spin_lock(&dcache_lru_lock);
234 		list_add(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
235 		dentry->d_sb->s_nr_dentry_unused++;
236 		dentry_stat.nr_unused++;
237 		spin_unlock(&dcache_lru_lock);
238 	}
239 }
240 
241 static void __dentry_lru_del(struct dentry *dentry)
242 {
243 	list_del_init(&dentry->d_lru);
244 	dentry->d_sb->s_nr_dentry_unused--;
245 	dentry_stat.nr_unused--;
246 }
247 
248 static void dentry_lru_del(struct dentry *dentry)
249 {
250 	if (!list_empty(&dentry->d_lru)) {
251 		spin_lock(&dcache_lru_lock);
252 		__dentry_lru_del(dentry);
253 		spin_unlock(&dcache_lru_lock);
254 	}
255 }
256 
257 static void dentry_lru_move_tail(struct dentry *dentry)
258 {
259 	spin_lock(&dcache_lru_lock);
260 	if (list_empty(&dentry->d_lru)) {
261 		list_add_tail(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
262 		dentry->d_sb->s_nr_dentry_unused++;
263 		dentry_stat.nr_unused++;
264 	} else {
265 		list_move_tail(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
266 	}
267 	spin_unlock(&dcache_lru_lock);
268 }
269 
270 /**
271  * d_kill - kill dentry and return parent
272  * @dentry: dentry to kill
273  * @parent: parent dentry
274  *
275  * The dentry must already be unhashed and removed from the LRU.
276  *
277  * If this is the root of the dentry tree, return NULL.
278  *
279  * dentry->d_lock and parent->d_lock must be held by caller, and are dropped by
280  * d_kill.
281  */
282 static struct dentry *d_kill(struct dentry *dentry, struct dentry *parent)
283 	__releases(dentry->d_lock)
284 	__releases(parent->d_lock)
285 	__releases(dentry->d_inode->i_lock)
286 {
287 	list_del(&dentry->d_u.d_child);
288 	/*
289 	 * Inform try_to_ascend() that we are no longer attached to the
290 	 * dentry tree
291 	 */
292 	dentry->d_flags |= DCACHE_DISCONNECTED;
293 	if (parent)
294 		spin_unlock(&parent->d_lock);
295 	dentry_iput(dentry);
296 	/*
297 	 * dentry_iput drops the locks, at which point nobody (except
298 	 * transient RCU lookups) can reach this dentry.
299 	 */
300 	d_free(dentry);
301 	return parent;
302 }
303 
304 /*
305  * Unhash a dentry without inserting an RCU walk barrier or checking that
306  * dentry->d_lock is locked.  The caller must take care of that, if
307  * appropriate.
308  */
309 static void __d_shrink(struct dentry *dentry)
310 {
311 	if (!d_unhashed(dentry)) {
312 		struct hlist_bl_head *b;
313 		if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED))
314 			b = &dentry->d_sb->s_anon;
315 		else
316 			b = d_hash(dentry->d_parent, dentry->d_name.hash);
317 
318 		hlist_bl_lock(b);
319 		__hlist_bl_del(&dentry->d_hash);
320 		dentry->d_hash.pprev = NULL;
321 		hlist_bl_unlock(b);
322 	}
323 }
324 
325 /**
326  * d_drop - drop a dentry
327  * @dentry: dentry to drop
328  *
329  * d_drop() unhashes the entry from the parent dentry hashes, so that it won't
330  * be found through a VFS lookup any more. Note that this is different from
331  * deleting the dentry - d_delete will try to mark the dentry negative if
332  * possible, giving a successful _negative_ lookup, while d_drop will
333  * just make the cache lookup fail.
334  *
335  * d_drop() is used mainly for stuff that wants to invalidate a dentry for some
336  * reason (NFS timeouts or autofs deletes).
337  *
338  * __d_drop requires dentry->d_lock.
339  */
340 void __d_drop(struct dentry *dentry)
341 {
342 	if (!d_unhashed(dentry)) {
343 		__d_shrink(dentry);
344 		dentry_rcuwalk_barrier(dentry);
345 	}
346 }
347 EXPORT_SYMBOL(__d_drop);
348 
349 void d_drop(struct dentry *dentry)
350 {
351 	spin_lock(&dentry->d_lock);
352 	__d_drop(dentry);
353 	spin_unlock(&dentry->d_lock);
354 }
355 EXPORT_SYMBOL(d_drop);
356 
357 /*
358  * d_clear_need_lookup - drop a dentry from cache and clear the need lookup flag
359  * @dentry: dentry to drop
360  *
361  * This is called when we do a lookup on a placeholder dentry that needed to be
362  * looked up.  The dentry should have been hashed in order for it to be found by
363  * the lookup code, but now needs to be unhashed while we do the actual lookup
364  * and clear the DCACHE_NEED_LOOKUP flag.
365  */
366 void d_clear_need_lookup(struct dentry *dentry)
367 {
368 	spin_lock(&dentry->d_lock);
369 	__d_drop(dentry);
370 	dentry->d_flags &= ~DCACHE_NEED_LOOKUP;
371 	spin_unlock(&dentry->d_lock);
372 }
373 EXPORT_SYMBOL(d_clear_need_lookup);
374 
375 /*
376  * Finish off a dentry we've decided to kill.
377  * dentry->d_lock must be held, returns with it unlocked.
378  * If ref is non-zero, then decrement the refcount too.
379  * Returns dentry requiring refcount drop, or NULL if we're done.
380  */
381 static inline struct dentry *dentry_kill(struct dentry *dentry, int ref)
382 	__releases(dentry->d_lock)
383 {
384 	struct inode *inode;
385 	struct dentry *parent;
386 
387 	inode = dentry->d_inode;
388 	if (inode && !spin_trylock(&inode->i_lock)) {
389 relock:
390 		spin_unlock(&dentry->d_lock);
391 		cpu_relax();
392 		return dentry; /* try again with same dentry */
393 	}
394 	if (IS_ROOT(dentry))
395 		parent = NULL;
396 	else
397 		parent = dentry->d_parent;
398 	if (parent && !spin_trylock(&parent->d_lock)) {
399 		if (inode)
400 			spin_unlock(&inode->i_lock);
401 		goto relock;
402 	}
403 
404 	if (ref)
405 		dentry->d_count--;
406 	/* if dentry was on the d_lru list delete it from there */
407 	dentry_lru_del(dentry);
408 	/* if it was on the hash then remove it */
409 	__d_drop(dentry);
410 	return d_kill(dentry, parent);
411 }
412 
413 /*
414  * This is dput
415  *
416  * This is complicated by the fact that we do not want to put
417  * dentries that are no longer on any hash chain on the unused
418  * list: we'd much rather just get rid of them immediately.
419  *
420  * However, that implies that we have to traverse the dentry
421  * tree upwards to the parents which might _also_ now be
422  * scheduled for deletion (it may have been only waiting for
423  * its last child to go away).
424  *
425  * This tail recursion is done by hand as we don't want to depend
426  * on the compiler to always get this right (gcc generally doesn't).
427  * Real recursion would eat up our stack space.
428  */
429 
430 /*
431  * dput - release a dentry
432  * @dentry: dentry to release
433  *
434  * Release a dentry. This will drop the usage count and if appropriate
435  * call the dentry unlink method as well as removing it from the queues and
436  * releasing its resources. If the parent dentries were scheduled for release
437  * they too may now get deleted.
438  */
439 void dput(struct dentry *dentry)
440 {
441 	if (!dentry)
442 		return;
443 
444 repeat:
445 	if (dentry->d_count == 1)
446 		might_sleep();
447 	spin_lock(&dentry->d_lock);
448 	BUG_ON(!dentry->d_count);
449 	if (dentry->d_count > 1) {
450 		dentry->d_count--;
451 		spin_unlock(&dentry->d_lock);
452 		return;
453 	}
454 
455 	if (dentry->d_flags & DCACHE_OP_DELETE) {
456 		if (dentry->d_op->d_delete(dentry))
457 			goto kill_it;
458 	}
459 
460 	/* Unreachable? Get rid of it */
461  	if (d_unhashed(dentry))
462 		goto kill_it;
463 
464 	/*
465 	 * If this dentry needs lookup, don't set the referenced flag so that it
466 	 * is more likely to be cleaned up by the dcache shrinker in case of
467 	 * memory pressure.
468 	 */
469 	if (!d_need_lookup(dentry))
470 		dentry->d_flags |= DCACHE_REFERENCED;
471 	dentry_lru_add(dentry);
472 
473 	dentry->d_count--;
474 	spin_unlock(&dentry->d_lock);
475 	return;
476 
477 kill_it:
478 	dentry = dentry_kill(dentry, 1);
479 	if (dentry)
480 		goto repeat;
481 }
482 EXPORT_SYMBOL(dput);
483 
484 /**
485  * d_invalidate - invalidate a dentry
486  * @dentry: dentry to invalidate
487  *
488  * Try to invalidate the dentry if it turns out to be
489  * possible. If there are other dentries that can be
490  * reached through this one we can't delete it and we
491  * return -EBUSY. On success we return 0.
492  *
493  * no dcache lock.
494  */
495 
496 int d_invalidate(struct dentry * dentry)
497 {
498 	/*
499 	 * If it's already been dropped, return OK.
500 	 */
501 	spin_lock(&dentry->d_lock);
502 	if (d_unhashed(dentry)) {
503 		spin_unlock(&dentry->d_lock);
504 		return 0;
505 	}
506 	/*
507 	 * Check whether to do a partial shrink_dcache
508 	 * to get rid of unused child entries.
509 	 */
510 	if (!list_empty(&dentry->d_subdirs)) {
511 		spin_unlock(&dentry->d_lock);
512 		shrink_dcache_parent(dentry);
513 		spin_lock(&dentry->d_lock);
514 	}
515 
516 	/*
517 	 * Somebody else still using it?
518 	 *
519 	 * If it's a directory, we can't drop it
520 	 * for fear of somebody re-populating it
521 	 * with children (even though dropping it
522 	 * would make it unreachable from the root,
523 	 * we might still populate it if it was a
524 	 * working directory or similar).
525 	 */
526 	if (dentry->d_count > 1) {
527 		if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode)) {
528 			spin_unlock(&dentry->d_lock);
529 			return -EBUSY;
530 		}
531 	}
532 
533 	__d_drop(dentry);
534 	spin_unlock(&dentry->d_lock);
535 	return 0;
536 }
537 EXPORT_SYMBOL(d_invalidate);
538 
539 /* This must be called with d_lock held */
540 static inline void __dget_dlock(struct dentry *dentry)
541 {
542 	dentry->d_count++;
543 }
544 
545 static inline void __dget(struct dentry *dentry)
546 {
547 	spin_lock(&dentry->d_lock);
548 	__dget_dlock(dentry);
549 	spin_unlock(&dentry->d_lock);
550 }
551 
552 struct dentry *dget_parent(struct dentry *dentry)
553 {
554 	struct dentry *ret;
555 
556 repeat:
557 	/*
558 	 * Don't need rcu_dereference because we re-check it was correct under
559 	 * the lock.
560 	 */
561 	rcu_read_lock();
562 	ret = dentry->d_parent;
563 	spin_lock(&ret->d_lock);
564 	if (unlikely(ret != dentry->d_parent)) {
565 		spin_unlock(&ret->d_lock);
566 		rcu_read_unlock();
567 		goto repeat;
568 	}
569 	rcu_read_unlock();
570 	BUG_ON(!ret->d_count);
571 	ret->d_count++;
572 	spin_unlock(&ret->d_lock);
573 	return ret;
574 }
575 EXPORT_SYMBOL(dget_parent);
576 
577 /**
578  * d_find_alias - grab a hashed alias of inode
579  * @inode: inode in question
580  * @want_discon:  flag, used by d_splice_alias, to request
581  *          that only a DISCONNECTED alias be returned.
582  *
583  * If inode has a hashed alias, or is a directory and has any alias,
584  * acquire the reference to alias and return it. Otherwise return NULL.
585  * Notice that if inode is a directory there can be only one alias and
586  * it can be unhashed only if it has no children, or if it is the root
587  * of a filesystem.
588  *
589  * If the inode has an IS_ROOT, DCACHE_DISCONNECTED alias, then prefer
590  * any other hashed alias over that one unless @want_discon is set,
591  * in which case only return an IS_ROOT, DCACHE_DISCONNECTED alias.
592  */
593 static struct dentry *__d_find_alias(struct inode *inode, int want_discon)
594 {
595 	struct dentry *alias, *discon_alias;
596 
597 again:
598 	discon_alias = NULL;
599 	list_for_each_entry(alias, &inode->i_dentry, d_alias) {
600 		spin_lock(&alias->d_lock);
601  		if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
602 			if (IS_ROOT(alias) &&
603 			    (alias->d_flags & DCACHE_DISCONNECTED)) {
604 				discon_alias = alias;
605 			} else if (!want_discon) {
606 				__dget_dlock(alias);
607 				spin_unlock(&alias->d_lock);
608 				return alias;
609 			}
610 		}
611 		spin_unlock(&alias->d_lock);
612 	}
613 	if (discon_alias) {
614 		alias = discon_alias;
615 		spin_lock(&alias->d_lock);
616 		if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
617 			if (IS_ROOT(alias) &&
618 			    (alias->d_flags & DCACHE_DISCONNECTED)) {
619 				__dget_dlock(alias);
620 				spin_unlock(&alias->d_lock);
621 				return alias;
622 			}
623 		}
624 		spin_unlock(&alias->d_lock);
625 		goto again;
626 	}
627 	return NULL;
628 }
629 
630 struct dentry *d_find_alias(struct inode *inode)
631 {
632 	struct dentry *de = NULL;
633 
634 	if (!list_empty(&inode->i_dentry)) {
635 		spin_lock(&inode->i_lock);
636 		de = __d_find_alias(inode, 0);
637 		spin_unlock(&inode->i_lock);
638 	}
639 	return de;
640 }
641 EXPORT_SYMBOL(d_find_alias);
642 
643 /*
644  *	Try to kill dentries associated with this inode.
645  * WARNING: you must own a reference to inode.
646  */
647 void d_prune_aliases(struct inode *inode)
648 {
649 	struct dentry *dentry;
650 restart:
651 	spin_lock(&inode->i_lock);
652 	list_for_each_entry(dentry, &inode->i_dentry, d_alias) {
653 		spin_lock(&dentry->d_lock);
654 		if (!dentry->d_count) {
655 			__dget_dlock(dentry);
656 			__d_drop(dentry);
657 			spin_unlock(&dentry->d_lock);
658 			spin_unlock(&inode->i_lock);
659 			dput(dentry);
660 			goto restart;
661 		}
662 		spin_unlock(&dentry->d_lock);
663 	}
664 	spin_unlock(&inode->i_lock);
665 }
666 EXPORT_SYMBOL(d_prune_aliases);
667 
668 /*
669  * Try to throw away a dentry - free the inode, dput the parent.
670  * Requires dentry->d_lock is held, and dentry->d_count == 0.
671  * Releases dentry->d_lock.
672  *
673  * This may fail if locks cannot be acquired no problem, just try again.
674  */
675 static void try_prune_one_dentry(struct dentry *dentry)
676 	__releases(dentry->d_lock)
677 {
678 	struct dentry *parent;
679 
680 	parent = dentry_kill(dentry, 0);
681 	/*
682 	 * If dentry_kill returns NULL, we have nothing more to do.
683 	 * if it returns the same dentry, trylocks failed. In either
684 	 * case, just loop again.
685 	 *
686 	 * Otherwise, we need to prune ancestors too. This is necessary
687 	 * to prevent quadratic behavior of shrink_dcache_parent(), but
688 	 * is also expected to be beneficial in reducing dentry cache
689 	 * fragmentation.
690 	 */
691 	if (!parent)
692 		return;
693 	if (parent == dentry)
694 		return;
695 
696 	/* Prune ancestors. */
697 	dentry = parent;
698 	while (dentry) {
699 		spin_lock(&dentry->d_lock);
700 		if (dentry->d_count > 1) {
701 			dentry->d_count--;
702 			spin_unlock(&dentry->d_lock);
703 			return;
704 		}
705 		dentry = dentry_kill(dentry, 1);
706 	}
707 }
708 
709 static void shrink_dentry_list(struct list_head *list)
710 {
711 	struct dentry *dentry;
712 
713 	rcu_read_lock();
714 	for (;;) {
715 		dentry = list_entry_rcu(list->prev, struct dentry, d_lru);
716 		if (&dentry->d_lru == list)
717 			break; /* empty */
718 		spin_lock(&dentry->d_lock);
719 		if (dentry != list_entry(list->prev, struct dentry, d_lru)) {
720 			spin_unlock(&dentry->d_lock);
721 			continue;
722 		}
723 
724 		/*
725 		 * We found an inuse dentry which was not removed from
726 		 * the LRU because of laziness during lookup.  Do not free
727 		 * it - just keep it off the LRU list.
728 		 */
729 		if (dentry->d_count) {
730 			dentry_lru_del(dentry);
731 			spin_unlock(&dentry->d_lock);
732 			continue;
733 		}
734 
735 		rcu_read_unlock();
736 
737 		try_prune_one_dentry(dentry);
738 
739 		rcu_read_lock();
740 	}
741 	rcu_read_unlock();
742 }
743 
744 /**
745  * __shrink_dcache_sb - shrink the dentry LRU on a given superblock
746  * @sb:		superblock to shrink dentry LRU.
747  * @count:	number of entries to prune
748  * @flags:	flags to control the dentry processing
749  *
750  * If flags contains DCACHE_REFERENCED reference dentries will not be pruned.
751  */
752 static void __shrink_dcache_sb(struct super_block *sb, int count, int flags)
753 {
754 	struct dentry *dentry;
755 	LIST_HEAD(referenced);
756 	LIST_HEAD(tmp);
757 
758 relock:
759 	spin_lock(&dcache_lru_lock);
760 	while (!list_empty(&sb->s_dentry_lru)) {
761 		dentry = list_entry(sb->s_dentry_lru.prev,
762 				struct dentry, d_lru);
763 		BUG_ON(dentry->d_sb != sb);
764 
765 		if (!spin_trylock(&dentry->d_lock)) {
766 			spin_unlock(&dcache_lru_lock);
767 			cpu_relax();
768 			goto relock;
769 		}
770 
771 		/*
772 		 * If we are honouring the DCACHE_REFERENCED flag and the
773 		 * dentry has this flag set, don't free it.  Clear the flag
774 		 * and put it back on the LRU.
775 		 */
776 		if (flags & DCACHE_REFERENCED &&
777 				dentry->d_flags & DCACHE_REFERENCED) {
778 			dentry->d_flags &= ~DCACHE_REFERENCED;
779 			list_move(&dentry->d_lru, &referenced);
780 			spin_unlock(&dentry->d_lock);
781 		} else {
782 			list_move_tail(&dentry->d_lru, &tmp);
783 			spin_unlock(&dentry->d_lock);
784 			if (!--count)
785 				break;
786 		}
787 		cond_resched_lock(&dcache_lru_lock);
788 	}
789 	if (!list_empty(&referenced))
790 		list_splice(&referenced, &sb->s_dentry_lru);
791 	spin_unlock(&dcache_lru_lock);
792 
793 	shrink_dentry_list(&tmp);
794 }
795 
796 /**
797  * prune_dcache_sb - shrink the dcache
798  * @sb: superblock
799  * @nr_to_scan: number of entries to try to free
800  *
801  * Attempt to shrink the superblock dcache LRU by @nr_to_scan entries. This is
802  * done when we need more memory an called from the superblock shrinker
803  * function.
804  *
805  * This function may fail to free any resources if all the dentries are in
806  * use.
807  */
808 void prune_dcache_sb(struct super_block *sb, int nr_to_scan)
809 {
810 	__shrink_dcache_sb(sb, nr_to_scan, DCACHE_REFERENCED);
811 }
812 
813 /**
814  * shrink_dcache_sb - shrink dcache for a superblock
815  * @sb: superblock
816  *
817  * Shrink the dcache for the specified super block. This is used to free
818  * the dcache before unmounting a file system.
819  */
820 void shrink_dcache_sb(struct super_block *sb)
821 {
822 	LIST_HEAD(tmp);
823 
824 	spin_lock(&dcache_lru_lock);
825 	while (!list_empty(&sb->s_dentry_lru)) {
826 		list_splice_init(&sb->s_dentry_lru, &tmp);
827 		spin_unlock(&dcache_lru_lock);
828 		shrink_dentry_list(&tmp);
829 		spin_lock(&dcache_lru_lock);
830 	}
831 	spin_unlock(&dcache_lru_lock);
832 }
833 EXPORT_SYMBOL(shrink_dcache_sb);
834 
835 /*
836  * destroy a single subtree of dentries for unmount
837  * - see the comments on shrink_dcache_for_umount() for a description of the
838  *   locking
839  */
840 static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
841 {
842 	struct dentry *parent;
843 
844 	BUG_ON(!IS_ROOT(dentry));
845 
846 	for (;;) {
847 		/* descend to the first leaf in the current subtree */
848 		while (!list_empty(&dentry->d_subdirs))
849 			dentry = list_entry(dentry->d_subdirs.next,
850 					    struct dentry, d_u.d_child);
851 
852 		/* consume the dentries from this leaf up through its parents
853 		 * until we find one with children or run out altogether */
854 		do {
855 			struct inode *inode;
856 
857 			/* detach from the system */
858 			dentry_lru_del(dentry);
859 			__d_shrink(dentry);
860 
861 			if (dentry->d_count != 0) {
862 				printk(KERN_ERR
863 				       "BUG: Dentry %p{i=%lx,n=%s}"
864 				       " still in use (%d)"
865 				       " [unmount of %s %s]\n",
866 				       dentry,
867 				       dentry->d_inode ?
868 				       dentry->d_inode->i_ino : 0UL,
869 				       dentry->d_name.name,
870 				       dentry->d_count,
871 				       dentry->d_sb->s_type->name,
872 				       dentry->d_sb->s_id);
873 				BUG();
874 			}
875 
876 			if (IS_ROOT(dentry)) {
877 				parent = NULL;
878 				list_del(&dentry->d_u.d_child);
879 			} else {
880 				parent = dentry->d_parent;
881 				parent->d_count--;
882 				list_del(&dentry->d_u.d_child);
883 			}
884 
885 			inode = dentry->d_inode;
886 			if (inode) {
887 				dentry->d_inode = NULL;
888 				list_del_init(&dentry->d_alias);
889 				if (dentry->d_op && dentry->d_op->d_iput)
890 					dentry->d_op->d_iput(dentry, inode);
891 				else
892 					iput(inode);
893 			}
894 
895 			d_free(dentry);
896 
897 			/* finished when we fall off the top of the tree,
898 			 * otherwise we ascend to the parent and move to the
899 			 * next sibling if there is one */
900 			if (!parent)
901 				return;
902 			dentry = parent;
903 		} while (list_empty(&dentry->d_subdirs));
904 
905 		dentry = list_entry(dentry->d_subdirs.next,
906 				    struct dentry, d_u.d_child);
907 	}
908 }
909 
910 /*
911  * destroy the dentries attached to a superblock on unmounting
912  * - we don't need to use dentry->d_lock because:
913  *   - the superblock is detached from all mountings and open files, so the
914  *     dentry trees will not be rearranged by the VFS
915  *   - s_umount is write-locked, so the memory pressure shrinker will ignore
916  *     any dentries belonging to this superblock that it comes across
917  *   - the filesystem itself is no longer permitted to rearrange the dentries
918  *     in this superblock
919  */
920 void shrink_dcache_for_umount(struct super_block *sb)
921 {
922 	struct dentry *dentry;
923 
924 	if (down_read_trylock(&sb->s_umount))
925 		BUG();
926 
927 	dentry = sb->s_root;
928 	sb->s_root = NULL;
929 	dentry->d_count--;
930 	shrink_dcache_for_umount_subtree(dentry);
931 
932 	while (!hlist_bl_empty(&sb->s_anon)) {
933 		dentry = hlist_bl_entry(hlist_bl_first(&sb->s_anon), struct dentry, d_hash);
934 		shrink_dcache_for_umount_subtree(dentry);
935 	}
936 }
937 
938 /*
939  * This tries to ascend one level of parenthood, but
940  * we can race with renaming, so we need to re-check
941  * the parenthood after dropping the lock and check
942  * that the sequence number still matches.
943  */
944 static struct dentry *try_to_ascend(struct dentry *old, int locked, unsigned seq)
945 {
946 	struct dentry *new = old->d_parent;
947 
948 	rcu_read_lock();
949 	spin_unlock(&old->d_lock);
950 	spin_lock(&new->d_lock);
951 
952 	/*
953 	 * might go back up the wrong parent if we have had a rename
954 	 * or deletion
955 	 */
956 	if (new != old->d_parent ||
957 		 (old->d_flags & DCACHE_DISCONNECTED) ||
958 		 (!locked && read_seqretry(&rename_lock, seq))) {
959 		spin_unlock(&new->d_lock);
960 		new = NULL;
961 	}
962 	rcu_read_unlock();
963 	return new;
964 }
965 
966 
967 /*
968  * Search for at least 1 mount point in the dentry's subdirs.
969  * We descend to the next level whenever the d_subdirs
970  * list is non-empty and continue searching.
971  */
972 
973 /**
974  * have_submounts - check for mounts over a dentry
975  * @parent: dentry to check.
976  *
977  * Return true if the parent or its subdirectories contain
978  * a mount point
979  */
980 int have_submounts(struct dentry *parent)
981 {
982 	struct dentry *this_parent;
983 	struct list_head *next;
984 	unsigned seq;
985 	int locked = 0;
986 
987 	seq = read_seqbegin(&rename_lock);
988 again:
989 	this_parent = parent;
990 
991 	if (d_mountpoint(parent))
992 		goto positive;
993 	spin_lock(&this_parent->d_lock);
994 repeat:
995 	next = this_parent->d_subdirs.next;
996 resume:
997 	while (next != &this_parent->d_subdirs) {
998 		struct list_head *tmp = next;
999 		struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
1000 		next = tmp->next;
1001 
1002 		spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
1003 		/* Have we found a mount point ? */
1004 		if (d_mountpoint(dentry)) {
1005 			spin_unlock(&dentry->d_lock);
1006 			spin_unlock(&this_parent->d_lock);
1007 			goto positive;
1008 		}
1009 		if (!list_empty(&dentry->d_subdirs)) {
1010 			spin_unlock(&this_parent->d_lock);
1011 			spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
1012 			this_parent = dentry;
1013 			spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
1014 			goto repeat;
1015 		}
1016 		spin_unlock(&dentry->d_lock);
1017 	}
1018 	/*
1019 	 * All done at this level ... ascend and resume the search.
1020 	 */
1021 	if (this_parent != parent) {
1022 		struct dentry *child = this_parent;
1023 		this_parent = try_to_ascend(this_parent, locked, seq);
1024 		if (!this_parent)
1025 			goto rename_retry;
1026 		next = child->d_u.d_child.next;
1027 		goto resume;
1028 	}
1029 	spin_unlock(&this_parent->d_lock);
1030 	if (!locked && read_seqretry(&rename_lock, seq))
1031 		goto rename_retry;
1032 	if (locked)
1033 		write_sequnlock(&rename_lock);
1034 	return 0; /* No mount points found in tree */
1035 positive:
1036 	if (!locked && read_seqretry(&rename_lock, seq))
1037 		goto rename_retry;
1038 	if (locked)
1039 		write_sequnlock(&rename_lock);
1040 	return 1;
1041 
1042 rename_retry:
1043 	locked = 1;
1044 	write_seqlock(&rename_lock);
1045 	goto again;
1046 }
1047 EXPORT_SYMBOL(have_submounts);
1048 
1049 /*
1050  * Search the dentry child list for the specified parent,
1051  * and move any unused dentries to the end of the unused
1052  * list for prune_dcache(). We descend to the next level
1053  * whenever the d_subdirs list is non-empty and continue
1054  * searching.
1055  *
1056  * It returns zero iff there are no unused children,
1057  * otherwise  it returns the number of children moved to
1058  * the end of the unused list. This may not be the total
1059  * number of unused children, because select_parent can
1060  * drop the lock and return early due to latency
1061  * constraints.
1062  */
1063 static int select_parent(struct dentry * parent)
1064 {
1065 	struct dentry *this_parent;
1066 	struct list_head *next;
1067 	unsigned seq;
1068 	int found = 0;
1069 	int locked = 0;
1070 
1071 	seq = read_seqbegin(&rename_lock);
1072 again:
1073 	this_parent = parent;
1074 	spin_lock(&this_parent->d_lock);
1075 repeat:
1076 	next = this_parent->d_subdirs.next;
1077 resume:
1078 	while (next != &this_parent->d_subdirs) {
1079 		struct list_head *tmp = next;
1080 		struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
1081 		next = tmp->next;
1082 
1083 		spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
1084 
1085 		/*
1086 		 * move only zero ref count dentries to the end
1087 		 * of the unused list for prune_dcache
1088 		 */
1089 		if (!dentry->d_count) {
1090 			dentry_lru_move_tail(dentry);
1091 			found++;
1092 		} else {
1093 			dentry_lru_del(dentry);
1094 		}
1095 
1096 		/*
1097 		 * We can return to the caller if we have found some (this
1098 		 * ensures forward progress). We'll be coming back to find
1099 		 * the rest.
1100 		 */
1101 		if (found && need_resched()) {
1102 			spin_unlock(&dentry->d_lock);
1103 			goto out;
1104 		}
1105 
1106 		/*
1107 		 * Descend a level if the d_subdirs list is non-empty.
1108 		 */
1109 		if (!list_empty(&dentry->d_subdirs)) {
1110 			spin_unlock(&this_parent->d_lock);
1111 			spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
1112 			this_parent = dentry;
1113 			spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
1114 			goto repeat;
1115 		}
1116 
1117 		spin_unlock(&dentry->d_lock);
1118 	}
1119 	/*
1120 	 * All done at this level ... ascend and resume the search.
1121 	 */
1122 	if (this_parent != parent) {
1123 		struct dentry *child = this_parent;
1124 		this_parent = try_to_ascend(this_parent, locked, seq);
1125 		if (!this_parent)
1126 			goto rename_retry;
1127 		next = child->d_u.d_child.next;
1128 		goto resume;
1129 	}
1130 out:
1131 	spin_unlock(&this_parent->d_lock);
1132 	if (!locked && read_seqretry(&rename_lock, seq))
1133 		goto rename_retry;
1134 	if (locked)
1135 		write_sequnlock(&rename_lock);
1136 	return found;
1137 
1138 rename_retry:
1139 	if (found)
1140 		return found;
1141 	locked = 1;
1142 	write_seqlock(&rename_lock);
1143 	goto again;
1144 }
1145 
1146 /**
1147  * shrink_dcache_parent - prune dcache
1148  * @parent: parent of entries to prune
1149  *
1150  * Prune the dcache to remove unused children of the parent dentry.
1151  */
1152 
1153 void shrink_dcache_parent(struct dentry * parent)
1154 {
1155 	struct super_block *sb = parent->d_sb;
1156 	int found;
1157 
1158 	while ((found = select_parent(parent)) != 0)
1159 		__shrink_dcache_sb(sb, found, 0);
1160 }
1161 EXPORT_SYMBOL(shrink_dcache_parent);
1162 
1163 /**
1164  * __d_alloc	-	allocate a dcache entry
1165  * @sb: filesystem it will belong to
1166  * @name: qstr of the name
1167  *
1168  * Allocates a dentry. It returns %NULL if there is insufficient memory
1169  * available. On a success the dentry is returned. The name passed in is
1170  * copied and the copy passed in may be reused after this call.
1171  */
1172 
1173 struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
1174 {
1175 	struct dentry *dentry;
1176 	char *dname;
1177 
1178 	dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
1179 	if (!dentry)
1180 		return NULL;
1181 
1182 	if (name->len > DNAME_INLINE_LEN-1) {
1183 		dname = kmalloc(name->len + 1, GFP_KERNEL);
1184 		if (!dname) {
1185 			kmem_cache_free(dentry_cache, dentry);
1186 			return NULL;
1187 		}
1188 	} else  {
1189 		dname = dentry->d_iname;
1190 	}
1191 	dentry->d_name.name = dname;
1192 
1193 	dentry->d_name.len = name->len;
1194 	dentry->d_name.hash = name->hash;
1195 	memcpy(dname, name->name, name->len);
1196 	dname[name->len] = 0;
1197 
1198 	dentry->d_count = 1;
1199 	dentry->d_flags = 0;
1200 	spin_lock_init(&dentry->d_lock);
1201 	seqcount_init(&dentry->d_seq);
1202 	dentry->d_inode = NULL;
1203 	dentry->d_parent = dentry;
1204 	dentry->d_sb = sb;
1205 	dentry->d_op = NULL;
1206 	dentry->d_fsdata = NULL;
1207 	INIT_HLIST_BL_NODE(&dentry->d_hash);
1208 	INIT_LIST_HEAD(&dentry->d_lru);
1209 	INIT_LIST_HEAD(&dentry->d_subdirs);
1210 	INIT_LIST_HEAD(&dentry->d_alias);
1211 	INIT_LIST_HEAD(&dentry->d_u.d_child);
1212 	d_set_d_op(dentry, dentry->d_sb->s_d_op);
1213 
1214 	this_cpu_inc(nr_dentry);
1215 
1216 	return dentry;
1217 }
1218 
1219 /**
1220  * d_alloc	-	allocate a dcache entry
1221  * @parent: parent of entry to allocate
1222  * @name: qstr of the name
1223  *
1224  * Allocates a dentry. It returns %NULL if there is insufficient memory
1225  * available. On a success the dentry is returned. The name passed in is
1226  * copied and the copy passed in may be reused after this call.
1227  */
1228 struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
1229 {
1230 	struct dentry *dentry = __d_alloc(parent->d_sb, name);
1231 	if (!dentry)
1232 		return NULL;
1233 
1234 	spin_lock(&parent->d_lock);
1235 	/*
1236 	 * don't need child lock because it is not subject
1237 	 * to concurrency here
1238 	 */
1239 	__dget_dlock(parent);
1240 	dentry->d_parent = parent;
1241 	list_add(&dentry->d_u.d_child, &parent->d_subdirs);
1242 	spin_unlock(&parent->d_lock);
1243 
1244 	return dentry;
1245 }
1246 EXPORT_SYMBOL(d_alloc);
1247 
1248 struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
1249 {
1250 	struct dentry *dentry = __d_alloc(sb, name);
1251 	if (dentry)
1252 		dentry->d_flags |= DCACHE_DISCONNECTED;
1253 	return dentry;
1254 }
1255 EXPORT_SYMBOL(d_alloc_pseudo);
1256 
1257 struct dentry *d_alloc_name(struct dentry *parent, const char *name)
1258 {
1259 	struct qstr q;
1260 
1261 	q.name = name;
1262 	q.len = strlen(name);
1263 	q.hash = full_name_hash(q.name, q.len);
1264 	return d_alloc(parent, &q);
1265 }
1266 EXPORT_SYMBOL(d_alloc_name);
1267 
1268 void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
1269 {
1270 	WARN_ON_ONCE(dentry->d_op);
1271 	WARN_ON_ONCE(dentry->d_flags & (DCACHE_OP_HASH	|
1272 				DCACHE_OP_COMPARE	|
1273 				DCACHE_OP_REVALIDATE	|
1274 				DCACHE_OP_DELETE ));
1275 	dentry->d_op = op;
1276 	if (!op)
1277 		return;
1278 	if (op->d_hash)
1279 		dentry->d_flags |= DCACHE_OP_HASH;
1280 	if (op->d_compare)
1281 		dentry->d_flags |= DCACHE_OP_COMPARE;
1282 	if (op->d_revalidate)
1283 		dentry->d_flags |= DCACHE_OP_REVALIDATE;
1284 	if (op->d_delete)
1285 		dentry->d_flags |= DCACHE_OP_DELETE;
1286 
1287 }
1288 EXPORT_SYMBOL(d_set_d_op);
1289 
1290 static void __d_instantiate(struct dentry *dentry, struct inode *inode)
1291 {
1292 	spin_lock(&dentry->d_lock);
1293 	if (inode) {
1294 		if (unlikely(IS_AUTOMOUNT(inode)))
1295 			dentry->d_flags |= DCACHE_NEED_AUTOMOUNT;
1296 		list_add(&dentry->d_alias, &inode->i_dentry);
1297 	}
1298 	dentry->d_inode = inode;
1299 	dentry_rcuwalk_barrier(dentry);
1300 	spin_unlock(&dentry->d_lock);
1301 	fsnotify_d_instantiate(dentry, inode);
1302 }
1303 
1304 /**
1305  * d_instantiate - fill in inode information for a dentry
1306  * @entry: dentry to complete
1307  * @inode: inode to attach to this dentry
1308  *
1309  * Fill in inode information in the entry.
1310  *
1311  * This turns negative dentries into productive full members
1312  * of society.
1313  *
1314  * NOTE! This assumes that the inode count has been incremented
1315  * (or otherwise set) by the caller to indicate that it is now
1316  * in use by the dcache.
1317  */
1318 
1319 void d_instantiate(struct dentry *entry, struct inode * inode)
1320 {
1321 	BUG_ON(!list_empty(&entry->d_alias));
1322 	if (inode)
1323 		spin_lock(&inode->i_lock);
1324 	__d_instantiate(entry, inode);
1325 	if (inode)
1326 		spin_unlock(&inode->i_lock);
1327 	security_d_instantiate(entry, inode);
1328 }
1329 EXPORT_SYMBOL(d_instantiate);
1330 
1331 /**
1332  * d_instantiate_unique - instantiate a non-aliased dentry
1333  * @entry: dentry to instantiate
1334  * @inode: inode to attach to this dentry
1335  *
1336  * Fill in inode information in the entry. On success, it returns NULL.
1337  * If an unhashed alias of "entry" already exists, then we return the
1338  * aliased dentry instead and drop one reference to inode.
1339  *
1340  * Note that in order to avoid conflicts with rename() etc, the caller
1341  * had better be holding the parent directory semaphore.
1342  *
1343  * This also assumes that the inode count has been incremented
1344  * (or otherwise set) by the caller to indicate that it is now
1345  * in use by the dcache.
1346  */
1347 static struct dentry *__d_instantiate_unique(struct dentry *entry,
1348 					     struct inode *inode)
1349 {
1350 	struct dentry *alias;
1351 	int len = entry->d_name.len;
1352 	const char *name = entry->d_name.name;
1353 	unsigned int hash = entry->d_name.hash;
1354 
1355 	if (!inode) {
1356 		__d_instantiate(entry, NULL);
1357 		return NULL;
1358 	}
1359 
1360 	list_for_each_entry(alias, &inode->i_dentry, d_alias) {
1361 		struct qstr *qstr = &alias->d_name;
1362 
1363 		/*
1364 		 * Don't need alias->d_lock here, because aliases with
1365 		 * d_parent == entry->d_parent are not subject to name or
1366 		 * parent changes, because the parent inode i_mutex is held.
1367 		 */
1368 		if (qstr->hash != hash)
1369 			continue;
1370 		if (alias->d_parent != entry->d_parent)
1371 			continue;
1372 		if (dentry_cmp(qstr->name, qstr->len, name, len))
1373 			continue;
1374 		__dget(alias);
1375 		return alias;
1376 	}
1377 
1378 	__d_instantiate(entry, inode);
1379 	return NULL;
1380 }
1381 
1382 struct dentry *d_instantiate_unique(struct dentry *entry, struct inode *inode)
1383 {
1384 	struct dentry *result;
1385 
1386 	BUG_ON(!list_empty(&entry->d_alias));
1387 
1388 	if (inode)
1389 		spin_lock(&inode->i_lock);
1390 	result = __d_instantiate_unique(entry, inode);
1391 	if (inode)
1392 		spin_unlock(&inode->i_lock);
1393 
1394 	if (!result) {
1395 		security_d_instantiate(entry, inode);
1396 		return NULL;
1397 	}
1398 
1399 	BUG_ON(!d_unhashed(result));
1400 	iput(inode);
1401 	return result;
1402 }
1403 
1404 EXPORT_SYMBOL(d_instantiate_unique);
1405 
1406 /**
1407  * d_alloc_root - allocate root dentry
1408  * @root_inode: inode to allocate the root for
1409  *
1410  * Allocate a root ("/") dentry for the inode given. The inode is
1411  * instantiated and returned. %NULL is returned if there is insufficient
1412  * memory or the inode passed is %NULL.
1413  */
1414 
1415 struct dentry * d_alloc_root(struct inode * root_inode)
1416 {
1417 	struct dentry *res = NULL;
1418 
1419 	if (root_inode) {
1420 		static const struct qstr name = { .name = "/", .len = 1 };
1421 
1422 		res = __d_alloc(root_inode->i_sb, &name);
1423 		if (res)
1424 			d_instantiate(res, root_inode);
1425 	}
1426 	return res;
1427 }
1428 EXPORT_SYMBOL(d_alloc_root);
1429 
1430 static struct dentry * __d_find_any_alias(struct inode *inode)
1431 {
1432 	struct dentry *alias;
1433 
1434 	if (list_empty(&inode->i_dentry))
1435 		return NULL;
1436 	alias = list_first_entry(&inode->i_dentry, struct dentry, d_alias);
1437 	__dget(alias);
1438 	return alias;
1439 }
1440 
1441 static struct dentry * d_find_any_alias(struct inode *inode)
1442 {
1443 	struct dentry *de;
1444 
1445 	spin_lock(&inode->i_lock);
1446 	de = __d_find_any_alias(inode);
1447 	spin_unlock(&inode->i_lock);
1448 	return de;
1449 }
1450 
1451 
1452 /**
1453  * d_obtain_alias - find or allocate a dentry for a given inode
1454  * @inode: inode to allocate the dentry for
1455  *
1456  * Obtain a dentry for an inode resulting from NFS filehandle conversion or
1457  * similar open by handle operations.  The returned dentry may be anonymous,
1458  * or may have a full name (if the inode was already in the cache).
1459  *
1460  * When called on a directory inode, we must ensure that the inode only ever
1461  * has one dentry.  If a dentry is found, that is returned instead of
1462  * allocating a new one.
1463  *
1464  * On successful return, the reference to the inode has been transferred
1465  * to the dentry.  In case of an error the reference on the inode is released.
1466  * To make it easier to use in export operations a %NULL or IS_ERR inode may
1467  * be passed in and will be the error will be propagate to the return value,
1468  * with a %NULL @inode replaced by ERR_PTR(-ESTALE).
1469  */
1470 struct dentry *d_obtain_alias(struct inode *inode)
1471 {
1472 	static const struct qstr anonstring = { .name = "" };
1473 	struct dentry *tmp;
1474 	struct dentry *res;
1475 
1476 	if (!inode)
1477 		return ERR_PTR(-ESTALE);
1478 	if (IS_ERR(inode))
1479 		return ERR_CAST(inode);
1480 
1481 	res = d_find_any_alias(inode);
1482 	if (res)
1483 		goto out_iput;
1484 
1485 	tmp = __d_alloc(inode->i_sb, &anonstring);
1486 	if (!tmp) {
1487 		res = ERR_PTR(-ENOMEM);
1488 		goto out_iput;
1489 	}
1490 
1491 	spin_lock(&inode->i_lock);
1492 	res = __d_find_any_alias(inode);
1493 	if (res) {
1494 		spin_unlock(&inode->i_lock);
1495 		dput(tmp);
1496 		goto out_iput;
1497 	}
1498 
1499 	/* attach a disconnected dentry */
1500 	spin_lock(&tmp->d_lock);
1501 	tmp->d_inode = inode;
1502 	tmp->d_flags |= DCACHE_DISCONNECTED;
1503 	list_add(&tmp->d_alias, &inode->i_dentry);
1504 	hlist_bl_lock(&tmp->d_sb->s_anon);
1505 	hlist_bl_add_head(&tmp->d_hash, &tmp->d_sb->s_anon);
1506 	hlist_bl_unlock(&tmp->d_sb->s_anon);
1507 	spin_unlock(&tmp->d_lock);
1508 	spin_unlock(&inode->i_lock);
1509 	security_d_instantiate(tmp, inode);
1510 
1511 	return tmp;
1512 
1513  out_iput:
1514 	if (res && !IS_ERR(res))
1515 		security_d_instantiate(res, inode);
1516 	iput(inode);
1517 	return res;
1518 }
1519 EXPORT_SYMBOL(d_obtain_alias);
1520 
1521 /**
1522  * d_splice_alias - splice a disconnected dentry into the tree if one exists
1523  * @inode:  the inode which may have a disconnected dentry
1524  * @dentry: a negative dentry which we want to point to the inode.
1525  *
1526  * If inode is a directory and has a 'disconnected' dentry (i.e. IS_ROOT and
1527  * DCACHE_DISCONNECTED), then d_move that in place of the given dentry
1528  * and return it, else simply d_add the inode to the dentry and return NULL.
1529  *
1530  * This is needed in the lookup routine of any filesystem that is exportable
1531  * (via knfsd) so that we can build dcache paths to directories effectively.
1532  *
1533  * If a dentry was found and moved, then it is returned.  Otherwise NULL
1534  * is returned.  This matches the expected return value of ->lookup.
1535  *
1536  */
1537 struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
1538 {
1539 	struct dentry *new = NULL;
1540 
1541 	if (IS_ERR(inode))
1542 		return ERR_CAST(inode);
1543 
1544 	if (inode && S_ISDIR(inode->i_mode)) {
1545 		spin_lock(&inode->i_lock);
1546 		new = __d_find_alias(inode, 1);
1547 		if (new) {
1548 			BUG_ON(!(new->d_flags & DCACHE_DISCONNECTED));
1549 			spin_unlock(&inode->i_lock);
1550 			security_d_instantiate(new, inode);
1551 			d_move(new, dentry);
1552 			iput(inode);
1553 		} else {
1554 			/* already taking inode->i_lock, so d_add() by hand */
1555 			__d_instantiate(dentry, inode);
1556 			spin_unlock(&inode->i_lock);
1557 			security_d_instantiate(dentry, inode);
1558 			d_rehash(dentry);
1559 		}
1560 	} else
1561 		d_add(dentry, inode);
1562 	return new;
1563 }
1564 EXPORT_SYMBOL(d_splice_alias);
1565 
1566 /**
1567  * d_add_ci - lookup or allocate new dentry with case-exact name
1568  * @inode:  the inode case-insensitive lookup has found
1569  * @dentry: the negative dentry that was passed to the parent's lookup func
1570  * @name:   the case-exact name to be associated with the returned dentry
1571  *
1572  * This is to avoid filling the dcache with case-insensitive names to the
1573  * same inode, only the actual correct case is stored in the dcache for
1574  * case-insensitive filesystems.
1575  *
1576  * For a case-insensitive lookup match and if the the case-exact dentry
1577  * already exists in in the dcache, use it and return it.
1578  *
1579  * If no entry exists with the exact case name, allocate new dentry with
1580  * the exact case, and return the spliced entry.
1581  */
1582 struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
1583 			struct qstr *name)
1584 {
1585 	int error;
1586 	struct dentry *found;
1587 	struct dentry *new;
1588 
1589 	/*
1590 	 * First check if a dentry matching the name already exists,
1591 	 * if not go ahead and create it now.
1592 	 */
1593 	found = d_hash_and_lookup(dentry->d_parent, name);
1594 	if (!found) {
1595 		new = d_alloc(dentry->d_parent, name);
1596 		if (!new) {
1597 			error = -ENOMEM;
1598 			goto err_out;
1599 		}
1600 
1601 		found = d_splice_alias(inode, new);
1602 		if (found) {
1603 			dput(new);
1604 			return found;
1605 		}
1606 		return new;
1607 	}
1608 
1609 	/*
1610 	 * If a matching dentry exists, and it's not negative use it.
1611 	 *
1612 	 * Decrement the reference count to balance the iget() done
1613 	 * earlier on.
1614 	 */
1615 	if (found->d_inode) {
1616 		if (unlikely(found->d_inode != inode)) {
1617 			/* This can't happen because bad inodes are unhashed. */
1618 			BUG_ON(!is_bad_inode(inode));
1619 			BUG_ON(!is_bad_inode(found->d_inode));
1620 		}
1621 		iput(inode);
1622 		return found;
1623 	}
1624 
1625 	/*
1626 	 * We are going to instantiate this dentry, unhash it and clear the
1627 	 * lookup flag so we can do that.
1628 	 */
1629 	if (unlikely(d_need_lookup(found)))
1630 		d_clear_need_lookup(found);
1631 
1632 	/*
1633 	 * Negative dentry: instantiate it unless the inode is a directory and
1634 	 * already has a dentry.
1635 	 */
1636 	new = d_splice_alias(inode, found);
1637 	if (new) {
1638 		dput(found);
1639 		found = new;
1640 	}
1641 	return found;
1642 
1643 err_out:
1644 	iput(inode);
1645 	return ERR_PTR(error);
1646 }
1647 EXPORT_SYMBOL(d_add_ci);
1648 
1649 /**
1650  * __d_lookup_rcu - search for a dentry (racy, store-free)
1651  * @parent: parent dentry
1652  * @name: qstr of name we wish to find
1653  * @seq: returns d_seq value at the point where the dentry was found
1654  * @inode: returns dentry->d_inode when the inode was found valid.
1655  * Returns: dentry, or NULL
1656  *
1657  * __d_lookup_rcu is the dcache lookup function for rcu-walk name
1658  * resolution (store-free path walking) design described in
1659  * Documentation/filesystems/path-lookup.txt.
1660  *
1661  * This is not to be used outside core vfs.
1662  *
1663  * __d_lookup_rcu must only be used in rcu-walk mode, ie. with vfsmount lock
1664  * held, and rcu_read_lock held. The returned dentry must not be stored into
1665  * without taking d_lock and checking d_seq sequence count against @seq
1666  * returned here.
1667  *
1668  * A refcount may be taken on the found dentry with the __d_rcu_to_refcount
1669  * function.
1670  *
1671  * Alternatively, __d_lookup_rcu may be called again to look up the child of
1672  * the returned dentry, so long as its parent's seqlock is checked after the
1673  * child is looked up. Thus, an interlocking stepping of sequence lock checks
1674  * is formed, giving integrity down the path walk.
1675  */
1676 struct dentry *__d_lookup_rcu(struct dentry *parent, struct qstr *name,
1677 				unsigned *seq, struct inode **inode)
1678 {
1679 	unsigned int len = name->len;
1680 	unsigned int hash = name->hash;
1681 	const unsigned char *str = name->name;
1682 	struct hlist_bl_head *b = d_hash(parent, hash);
1683 	struct hlist_bl_node *node;
1684 	struct dentry *dentry;
1685 
1686 	/*
1687 	 * Note: There is significant duplication with __d_lookup_rcu which is
1688 	 * required to prevent single threaded performance regressions
1689 	 * especially on architectures where smp_rmb (in seqcounts) are costly.
1690 	 * Keep the two functions in sync.
1691 	 */
1692 
1693 	/*
1694 	 * The hash list is protected using RCU.
1695 	 *
1696 	 * Carefully use d_seq when comparing a candidate dentry, to avoid
1697 	 * races with d_move().
1698 	 *
1699 	 * It is possible that concurrent renames can mess up our list
1700 	 * walk here and result in missing our dentry, resulting in the
1701 	 * false-negative result. d_lookup() protects against concurrent
1702 	 * renames using rename_lock seqlock.
1703 	 *
1704 	 * See Documentation/filesystems/path-lookup.txt for more details.
1705 	 */
1706 	hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
1707 		struct inode *i;
1708 		const char *tname;
1709 		int tlen;
1710 
1711 		if (dentry->d_name.hash != hash)
1712 			continue;
1713 
1714 seqretry:
1715 		*seq = read_seqcount_begin(&dentry->d_seq);
1716 		if (dentry->d_parent != parent)
1717 			continue;
1718 		if (d_unhashed(dentry))
1719 			continue;
1720 		tlen = dentry->d_name.len;
1721 		tname = dentry->d_name.name;
1722 		i = dentry->d_inode;
1723 		prefetch(tname);
1724 		/*
1725 		 * This seqcount check is required to ensure name and
1726 		 * len are loaded atomically, so as not to walk off the
1727 		 * edge of memory when walking. If we could load this
1728 		 * atomically some other way, we could drop this check.
1729 		 */
1730 		if (read_seqcount_retry(&dentry->d_seq, *seq))
1731 			goto seqretry;
1732 		if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
1733 			if (parent->d_op->d_compare(parent, *inode,
1734 						dentry, i,
1735 						tlen, tname, name))
1736 				continue;
1737 		} else {
1738 			if (dentry_cmp(tname, tlen, str, len))
1739 				continue;
1740 		}
1741 		/*
1742 		 * No extra seqcount check is required after the name
1743 		 * compare. The caller must perform a seqcount check in
1744 		 * order to do anything useful with the returned dentry
1745 		 * anyway.
1746 		 */
1747 		*inode = i;
1748 		return dentry;
1749 	}
1750 	return NULL;
1751 }
1752 
1753 /**
1754  * d_lookup - search for a dentry
1755  * @parent: parent dentry
1756  * @name: qstr of name we wish to find
1757  * Returns: dentry, or NULL
1758  *
1759  * d_lookup searches the children of the parent dentry for the name in
1760  * question. If the dentry is found its reference count is incremented and the
1761  * dentry is returned. The caller must use dput to free the entry when it has
1762  * finished using it. %NULL is returned if the dentry does not exist.
1763  */
1764 struct dentry *d_lookup(struct dentry *parent, struct qstr *name)
1765 {
1766 	struct dentry *dentry;
1767 	unsigned seq;
1768 
1769         do {
1770                 seq = read_seqbegin(&rename_lock);
1771                 dentry = __d_lookup(parent, name);
1772                 if (dentry)
1773 			break;
1774 	} while (read_seqretry(&rename_lock, seq));
1775 	return dentry;
1776 }
1777 EXPORT_SYMBOL(d_lookup);
1778 
1779 /**
1780  * __d_lookup - search for a dentry (racy)
1781  * @parent: parent dentry
1782  * @name: qstr of name we wish to find
1783  * Returns: dentry, or NULL
1784  *
1785  * __d_lookup is like d_lookup, however it may (rarely) return a
1786  * false-negative result due to unrelated rename activity.
1787  *
1788  * __d_lookup is slightly faster by avoiding rename_lock read seqlock,
1789  * however it must be used carefully, eg. with a following d_lookup in
1790  * the case of failure.
1791  *
1792  * __d_lookup callers must be commented.
1793  */
1794 struct dentry *__d_lookup(struct dentry *parent, struct qstr *name)
1795 {
1796 	unsigned int len = name->len;
1797 	unsigned int hash = name->hash;
1798 	const unsigned char *str = name->name;
1799 	struct hlist_bl_head *b = d_hash(parent, hash);
1800 	struct hlist_bl_node *node;
1801 	struct dentry *found = NULL;
1802 	struct dentry *dentry;
1803 
1804 	/*
1805 	 * Note: There is significant duplication with __d_lookup_rcu which is
1806 	 * required to prevent single threaded performance regressions
1807 	 * especially on architectures where smp_rmb (in seqcounts) are costly.
1808 	 * Keep the two functions in sync.
1809 	 */
1810 
1811 	/*
1812 	 * The hash list is protected using RCU.
1813 	 *
1814 	 * Take d_lock when comparing a candidate dentry, to avoid races
1815 	 * with d_move().
1816 	 *
1817 	 * It is possible that concurrent renames can mess up our list
1818 	 * walk here and result in missing our dentry, resulting in the
1819 	 * false-negative result. d_lookup() protects against concurrent
1820 	 * renames using rename_lock seqlock.
1821 	 *
1822 	 * See Documentation/filesystems/path-lookup.txt for more details.
1823 	 */
1824 	rcu_read_lock();
1825 
1826 	hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
1827 		const char *tname;
1828 		int tlen;
1829 
1830 		if (dentry->d_name.hash != hash)
1831 			continue;
1832 
1833 		spin_lock(&dentry->d_lock);
1834 		if (dentry->d_parent != parent)
1835 			goto next;
1836 		if (d_unhashed(dentry))
1837 			goto next;
1838 
1839 		/*
1840 		 * It is safe to compare names since d_move() cannot
1841 		 * change the qstr (protected by d_lock).
1842 		 */
1843 		tlen = dentry->d_name.len;
1844 		tname = dentry->d_name.name;
1845 		if (parent->d_flags & DCACHE_OP_COMPARE) {
1846 			if (parent->d_op->d_compare(parent, parent->d_inode,
1847 						dentry, dentry->d_inode,
1848 						tlen, tname, name))
1849 				goto next;
1850 		} else {
1851 			if (dentry_cmp(tname, tlen, str, len))
1852 				goto next;
1853 		}
1854 
1855 		dentry->d_count++;
1856 		found = dentry;
1857 		spin_unlock(&dentry->d_lock);
1858 		break;
1859 next:
1860 		spin_unlock(&dentry->d_lock);
1861  	}
1862  	rcu_read_unlock();
1863 
1864  	return found;
1865 }
1866 
1867 /**
1868  * d_hash_and_lookup - hash the qstr then search for a dentry
1869  * @dir: Directory to search in
1870  * @name: qstr of name we wish to find
1871  *
1872  * On hash failure or on lookup failure NULL is returned.
1873  */
1874 struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
1875 {
1876 	struct dentry *dentry = NULL;
1877 
1878 	/*
1879 	 * Check for a fs-specific hash function. Note that we must
1880 	 * calculate the standard hash first, as the d_op->d_hash()
1881 	 * routine may choose to leave the hash value unchanged.
1882 	 */
1883 	name->hash = full_name_hash(name->name, name->len);
1884 	if (dir->d_flags & DCACHE_OP_HASH) {
1885 		if (dir->d_op->d_hash(dir, dir->d_inode, name) < 0)
1886 			goto out;
1887 	}
1888 	dentry = d_lookup(dir, name);
1889 out:
1890 	return dentry;
1891 }
1892 
1893 /**
1894  * d_validate - verify dentry provided from insecure source (deprecated)
1895  * @dentry: The dentry alleged to be valid child of @dparent
1896  * @dparent: The parent dentry (known to be valid)
1897  *
1898  * An insecure source has sent us a dentry, here we verify it and dget() it.
1899  * This is used by ncpfs in its readdir implementation.
1900  * Zero is returned in the dentry is invalid.
1901  *
1902  * This function is slow for big directories, and deprecated, do not use it.
1903  */
1904 int d_validate(struct dentry *dentry, struct dentry *dparent)
1905 {
1906 	struct dentry *child;
1907 
1908 	spin_lock(&dparent->d_lock);
1909 	list_for_each_entry(child, &dparent->d_subdirs, d_u.d_child) {
1910 		if (dentry == child) {
1911 			spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
1912 			__dget_dlock(dentry);
1913 			spin_unlock(&dentry->d_lock);
1914 			spin_unlock(&dparent->d_lock);
1915 			return 1;
1916 		}
1917 	}
1918 	spin_unlock(&dparent->d_lock);
1919 
1920 	return 0;
1921 }
1922 EXPORT_SYMBOL(d_validate);
1923 
1924 /*
1925  * When a file is deleted, we have two options:
1926  * - turn this dentry into a negative dentry
1927  * - unhash this dentry and free it.
1928  *
1929  * Usually, we want to just turn this into
1930  * a negative dentry, but if anybody else is
1931  * currently using the dentry or the inode
1932  * we can't do that and we fall back on removing
1933  * it from the hash queues and waiting for
1934  * it to be deleted later when it has no users
1935  */
1936 
1937 /**
1938  * d_delete - delete a dentry
1939  * @dentry: The dentry to delete
1940  *
1941  * Turn the dentry into a negative dentry if possible, otherwise
1942  * remove it from the hash queues so it can be deleted later
1943  */
1944 
1945 void d_delete(struct dentry * dentry)
1946 {
1947 	struct inode *inode;
1948 	int isdir = 0;
1949 	/*
1950 	 * Are we the only user?
1951 	 */
1952 again:
1953 	spin_lock(&dentry->d_lock);
1954 	inode = dentry->d_inode;
1955 	isdir = S_ISDIR(inode->i_mode);
1956 	if (dentry->d_count == 1) {
1957 		if (inode && !spin_trylock(&inode->i_lock)) {
1958 			spin_unlock(&dentry->d_lock);
1959 			cpu_relax();
1960 			goto again;
1961 		}
1962 		dentry->d_flags &= ~DCACHE_CANT_MOUNT;
1963 		dentry_unlink_inode(dentry);
1964 		fsnotify_nameremove(dentry, isdir);
1965 		return;
1966 	}
1967 
1968 	if (!d_unhashed(dentry))
1969 		__d_drop(dentry);
1970 
1971 	spin_unlock(&dentry->d_lock);
1972 
1973 	fsnotify_nameremove(dentry, isdir);
1974 }
1975 EXPORT_SYMBOL(d_delete);
1976 
1977 static void __d_rehash(struct dentry * entry, struct hlist_bl_head *b)
1978 {
1979 	BUG_ON(!d_unhashed(entry));
1980 	hlist_bl_lock(b);
1981 	entry->d_flags |= DCACHE_RCUACCESS;
1982 	hlist_bl_add_head_rcu(&entry->d_hash, b);
1983 	hlist_bl_unlock(b);
1984 }
1985 
1986 static void _d_rehash(struct dentry * entry)
1987 {
1988 	__d_rehash(entry, d_hash(entry->d_parent, entry->d_name.hash));
1989 }
1990 
1991 /**
1992  * d_rehash	- add an entry back to the hash
1993  * @entry: dentry to add to the hash
1994  *
1995  * Adds a dentry to the hash according to its name.
1996  */
1997 
1998 void d_rehash(struct dentry * entry)
1999 {
2000 	spin_lock(&entry->d_lock);
2001 	_d_rehash(entry);
2002 	spin_unlock(&entry->d_lock);
2003 }
2004 EXPORT_SYMBOL(d_rehash);
2005 
2006 /**
2007  * dentry_update_name_case - update case insensitive dentry with a new name
2008  * @dentry: dentry to be updated
2009  * @name: new name
2010  *
2011  * Update a case insensitive dentry with new case of name.
2012  *
2013  * dentry must have been returned by d_lookup with name @name. Old and new
2014  * name lengths must match (ie. no d_compare which allows mismatched name
2015  * lengths).
2016  *
2017  * Parent inode i_mutex must be held over d_lookup and into this call (to
2018  * keep renames and concurrent inserts, and readdir(2) away).
2019  */
2020 void dentry_update_name_case(struct dentry *dentry, struct qstr *name)
2021 {
2022 	BUG_ON(!mutex_is_locked(&dentry->d_parent->d_inode->i_mutex));
2023 	BUG_ON(dentry->d_name.len != name->len); /* d_lookup gives this */
2024 
2025 	spin_lock(&dentry->d_lock);
2026 	write_seqcount_begin(&dentry->d_seq);
2027 	memcpy((unsigned char *)dentry->d_name.name, name->name, name->len);
2028 	write_seqcount_end(&dentry->d_seq);
2029 	spin_unlock(&dentry->d_lock);
2030 }
2031 EXPORT_SYMBOL(dentry_update_name_case);
2032 
2033 static void switch_names(struct dentry *dentry, struct dentry *target)
2034 {
2035 	if (dname_external(target)) {
2036 		if (dname_external(dentry)) {
2037 			/*
2038 			 * Both external: swap the pointers
2039 			 */
2040 			swap(target->d_name.name, dentry->d_name.name);
2041 		} else {
2042 			/*
2043 			 * dentry:internal, target:external.  Steal target's
2044 			 * storage and make target internal.
2045 			 */
2046 			memcpy(target->d_iname, dentry->d_name.name,
2047 					dentry->d_name.len + 1);
2048 			dentry->d_name.name = target->d_name.name;
2049 			target->d_name.name = target->d_iname;
2050 		}
2051 	} else {
2052 		if (dname_external(dentry)) {
2053 			/*
2054 			 * dentry:external, target:internal.  Give dentry's
2055 			 * storage to target and make dentry internal
2056 			 */
2057 			memcpy(dentry->d_iname, target->d_name.name,
2058 					target->d_name.len + 1);
2059 			target->d_name.name = dentry->d_name.name;
2060 			dentry->d_name.name = dentry->d_iname;
2061 		} else {
2062 			/*
2063 			 * Both are internal.  Just copy target to dentry
2064 			 */
2065 			memcpy(dentry->d_iname, target->d_name.name,
2066 					target->d_name.len + 1);
2067 			dentry->d_name.len = target->d_name.len;
2068 			return;
2069 		}
2070 	}
2071 	swap(dentry->d_name.len, target->d_name.len);
2072 }
2073 
2074 static void dentry_lock_for_move(struct dentry *dentry, struct dentry *target)
2075 {
2076 	/*
2077 	 * XXXX: do we really need to take target->d_lock?
2078 	 */
2079 	if (IS_ROOT(dentry) || dentry->d_parent == target->d_parent)
2080 		spin_lock(&target->d_parent->d_lock);
2081 	else {
2082 		if (d_ancestor(dentry->d_parent, target->d_parent)) {
2083 			spin_lock(&dentry->d_parent->d_lock);
2084 			spin_lock_nested(&target->d_parent->d_lock,
2085 						DENTRY_D_LOCK_NESTED);
2086 		} else {
2087 			spin_lock(&target->d_parent->d_lock);
2088 			spin_lock_nested(&dentry->d_parent->d_lock,
2089 						DENTRY_D_LOCK_NESTED);
2090 		}
2091 	}
2092 	if (target < dentry) {
2093 		spin_lock_nested(&target->d_lock, 2);
2094 		spin_lock_nested(&dentry->d_lock, 3);
2095 	} else {
2096 		spin_lock_nested(&dentry->d_lock, 2);
2097 		spin_lock_nested(&target->d_lock, 3);
2098 	}
2099 }
2100 
2101 static void dentry_unlock_parents_for_move(struct dentry *dentry,
2102 					struct dentry *target)
2103 {
2104 	if (target->d_parent != dentry->d_parent)
2105 		spin_unlock(&dentry->d_parent->d_lock);
2106 	if (target->d_parent != target)
2107 		spin_unlock(&target->d_parent->d_lock);
2108 }
2109 
2110 /*
2111  * When switching names, the actual string doesn't strictly have to
2112  * be preserved in the target - because we're dropping the target
2113  * anyway. As such, we can just do a simple memcpy() to copy over
2114  * the new name before we switch.
2115  *
2116  * Note that we have to be a lot more careful about getting the hash
2117  * switched - we have to switch the hash value properly even if it
2118  * then no longer matches the actual (corrupted) string of the target.
2119  * The hash value has to match the hash queue that the dentry is on..
2120  */
2121 /*
2122  * __d_move - move a dentry
2123  * @dentry: entry to move
2124  * @target: new dentry
2125  *
2126  * Update the dcache to reflect the move of a file name. Negative
2127  * dcache entries should not be moved in this way. Caller must hold
2128  * rename_lock, the i_mutex of the source and target directories,
2129  * and the sb->s_vfs_rename_mutex if they differ. See lock_rename().
2130  */
2131 static void __d_move(struct dentry * dentry, struct dentry * target)
2132 {
2133 	if (!dentry->d_inode)
2134 		printk(KERN_WARNING "VFS: moving negative dcache entry\n");
2135 
2136 	BUG_ON(d_ancestor(dentry, target));
2137 	BUG_ON(d_ancestor(target, dentry));
2138 
2139 	dentry_lock_for_move(dentry, target);
2140 
2141 	write_seqcount_begin(&dentry->d_seq);
2142 	write_seqcount_begin(&target->d_seq);
2143 
2144 	/* __d_drop does write_seqcount_barrier, but they're OK to nest. */
2145 
2146 	/*
2147 	 * Move the dentry to the target hash queue. Don't bother checking
2148 	 * for the same hash queue because of how unlikely it is.
2149 	 */
2150 	__d_drop(dentry);
2151 	__d_rehash(dentry, d_hash(target->d_parent, target->d_name.hash));
2152 
2153 	/* Unhash the target: dput() will then get rid of it */
2154 	__d_drop(target);
2155 
2156 	list_del(&dentry->d_u.d_child);
2157 	list_del(&target->d_u.d_child);
2158 
2159 	/* Switch the names.. */
2160 	switch_names(dentry, target);
2161 	swap(dentry->d_name.hash, target->d_name.hash);
2162 
2163 	/* ... and switch the parents */
2164 	if (IS_ROOT(dentry)) {
2165 		dentry->d_parent = target->d_parent;
2166 		target->d_parent = target;
2167 		INIT_LIST_HEAD(&target->d_u.d_child);
2168 	} else {
2169 		swap(dentry->d_parent, target->d_parent);
2170 
2171 		/* And add them back to the (new) parent lists */
2172 		list_add(&target->d_u.d_child, &target->d_parent->d_subdirs);
2173 	}
2174 
2175 	list_add(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
2176 
2177 	write_seqcount_end(&target->d_seq);
2178 	write_seqcount_end(&dentry->d_seq);
2179 
2180 	dentry_unlock_parents_for_move(dentry, target);
2181 	spin_unlock(&target->d_lock);
2182 	fsnotify_d_move(dentry);
2183 	spin_unlock(&dentry->d_lock);
2184 }
2185 
2186 /*
2187  * d_move - move a dentry
2188  * @dentry: entry to move
2189  * @target: new dentry
2190  *
2191  * Update the dcache to reflect the move of a file name. Negative
2192  * dcache entries should not be moved in this way. See the locking
2193  * requirements for __d_move.
2194  */
2195 void d_move(struct dentry *dentry, struct dentry *target)
2196 {
2197 	write_seqlock(&rename_lock);
2198 	__d_move(dentry, target);
2199 	write_sequnlock(&rename_lock);
2200 }
2201 EXPORT_SYMBOL(d_move);
2202 
2203 /**
2204  * d_ancestor - search for an ancestor
2205  * @p1: ancestor dentry
2206  * @p2: child dentry
2207  *
2208  * Returns the ancestor dentry of p2 which is a child of p1, if p1 is
2209  * an ancestor of p2, else NULL.
2210  */
2211 struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
2212 {
2213 	struct dentry *p;
2214 
2215 	for (p = p2; !IS_ROOT(p); p = p->d_parent) {
2216 		if (p->d_parent == p1)
2217 			return p;
2218 	}
2219 	return NULL;
2220 }
2221 
2222 /*
2223  * This helper attempts to cope with remotely renamed directories
2224  *
2225  * It assumes that the caller is already holding
2226  * dentry->d_parent->d_inode->i_mutex, inode->i_lock and rename_lock
2227  *
2228  * Note: If ever the locking in lock_rename() changes, then please
2229  * remember to update this too...
2230  */
2231 static struct dentry *__d_unalias(struct inode *inode,
2232 		struct dentry *dentry, struct dentry *alias)
2233 {
2234 	struct mutex *m1 = NULL, *m2 = NULL;
2235 	struct dentry *ret;
2236 
2237 	/* If alias and dentry share a parent, then no extra locks required */
2238 	if (alias->d_parent == dentry->d_parent)
2239 		goto out_unalias;
2240 
2241 	/* See lock_rename() */
2242 	ret = ERR_PTR(-EBUSY);
2243 	if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
2244 		goto out_err;
2245 	m1 = &dentry->d_sb->s_vfs_rename_mutex;
2246 	if (!mutex_trylock(&alias->d_parent->d_inode->i_mutex))
2247 		goto out_err;
2248 	m2 = &alias->d_parent->d_inode->i_mutex;
2249 out_unalias:
2250 	__d_move(alias, dentry);
2251 	ret = alias;
2252 out_err:
2253 	spin_unlock(&inode->i_lock);
2254 	if (m2)
2255 		mutex_unlock(m2);
2256 	if (m1)
2257 		mutex_unlock(m1);
2258 	return ret;
2259 }
2260 
2261 /*
2262  * Prepare an anonymous dentry for life in the superblock's dentry tree as a
2263  * named dentry in place of the dentry to be replaced.
2264  * returns with anon->d_lock held!
2265  */
2266 static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
2267 {
2268 	struct dentry *dparent, *aparent;
2269 
2270 	dentry_lock_for_move(anon, dentry);
2271 
2272 	write_seqcount_begin(&dentry->d_seq);
2273 	write_seqcount_begin(&anon->d_seq);
2274 
2275 	dparent = dentry->d_parent;
2276 	aparent = anon->d_parent;
2277 
2278 	switch_names(dentry, anon);
2279 	swap(dentry->d_name.hash, anon->d_name.hash);
2280 
2281 	dentry->d_parent = (aparent == anon) ? dentry : aparent;
2282 	list_del(&dentry->d_u.d_child);
2283 	if (!IS_ROOT(dentry))
2284 		list_add(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
2285 	else
2286 		INIT_LIST_HEAD(&dentry->d_u.d_child);
2287 
2288 	anon->d_parent = (dparent == dentry) ? anon : dparent;
2289 	list_del(&anon->d_u.d_child);
2290 	if (!IS_ROOT(anon))
2291 		list_add(&anon->d_u.d_child, &anon->d_parent->d_subdirs);
2292 	else
2293 		INIT_LIST_HEAD(&anon->d_u.d_child);
2294 
2295 	write_seqcount_end(&dentry->d_seq);
2296 	write_seqcount_end(&anon->d_seq);
2297 
2298 	dentry_unlock_parents_for_move(anon, dentry);
2299 	spin_unlock(&dentry->d_lock);
2300 
2301 	/* anon->d_lock still locked, returns locked */
2302 	anon->d_flags &= ~DCACHE_DISCONNECTED;
2303 }
2304 
2305 /**
2306  * d_materialise_unique - introduce an inode into the tree
2307  * @dentry: candidate dentry
2308  * @inode: inode to bind to the dentry, to which aliases may be attached
2309  *
2310  * Introduces an dentry into the tree, substituting an extant disconnected
2311  * root directory alias in its place if there is one. Caller must hold the
2312  * i_mutex of the parent directory.
2313  */
2314 struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode)
2315 {
2316 	struct dentry *actual;
2317 
2318 	BUG_ON(!d_unhashed(dentry));
2319 
2320 	if (!inode) {
2321 		actual = dentry;
2322 		__d_instantiate(dentry, NULL);
2323 		d_rehash(actual);
2324 		goto out_nolock;
2325 	}
2326 
2327 	spin_lock(&inode->i_lock);
2328 
2329 	if (S_ISDIR(inode->i_mode)) {
2330 		struct dentry *alias;
2331 
2332 		/* Does an aliased dentry already exist? */
2333 		alias = __d_find_alias(inode, 0);
2334 		if (alias) {
2335 			actual = alias;
2336 			write_seqlock(&rename_lock);
2337 
2338 			if (d_ancestor(alias, dentry)) {
2339 				/* Check for loops */
2340 				actual = ERR_PTR(-ELOOP);
2341 			} else if (IS_ROOT(alias)) {
2342 				/* Is this an anonymous mountpoint that we
2343 				 * could splice into our tree? */
2344 				__d_materialise_dentry(dentry, alias);
2345 				write_sequnlock(&rename_lock);
2346 				__d_drop(alias);
2347 				goto found;
2348 			} else {
2349 				/* Nope, but we must(!) avoid directory
2350 				 * aliasing */
2351 				actual = __d_unalias(inode, dentry, alias);
2352 			}
2353 			write_sequnlock(&rename_lock);
2354 			if (IS_ERR(actual))
2355 				dput(alias);
2356 			goto out_nolock;
2357 		}
2358 	}
2359 
2360 	/* Add a unique reference */
2361 	actual = __d_instantiate_unique(dentry, inode);
2362 	if (!actual)
2363 		actual = dentry;
2364 	else
2365 		BUG_ON(!d_unhashed(actual));
2366 
2367 	spin_lock(&actual->d_lock);
2368 found:
2369 	_d_rehash(actual);
2370 	spin_unlock(&actual->d_lock);
2371 	spin_unlock(&inode->i_lock);
2372 out_nolock:
2373 	if (actual == dentry) {
2374 		security_d_instantiate(dentry, inode);
2375 		return NULL;
2376 	}
2377 
2378 	iput(inode);
2379 	return actual;
2380 }
2381 EXPORT_SYMBOL_GPL(d_materialise_unique);
2382 
2383 static int prepend(char **buffer, int *buflen, const char *str, int namelen)
2384 {
2385 	*buflen -= namelen;
2386 	if (*buflen < 0)
2387 		return -ENAMETOOLONG;
2388 	*buffer -= namelen;
2389 	memcpy(*buffer, str, namelen);
2390 	return 0;
2391 }
2392 
2393 static int prepend_name(char **buffer, int *buflen, struct qstr *name)
2394 {
2395 	return prepend(buffer, buflen, name->name, name->len);
2396 }
2397 
2398 /**
2399  * prepend_path - Prepend path string to a buffer
2400  * @path: the dentry/vfsmount to report
2401  * @root: root vfsmnt/dentry (may be modified by this function)
2402  * @buffer: pointer to the end of the buffer
2403  * @buflen: pointer to buffer length
2404  *
2405  * Caller holds the rename_lock.
2406  *
2407  * If path is not reachable from the supplied root, then the value of
2408  * root is changed (without modifying refcounts).
2409  */
2410 static int prepend_path(const struct path *path, struct path *root,
2411 			char **buffer, int *buflen)
2412 {
2413 	struct dentry *dentry = path->dentry;
2414 	struct vfsmount *vfsmnt = path->mnt;
2415 	bool slash = false;
2416 	int error = 0;
2417 
2418 	br_read_lock(vfsmount_lock);
2419 	while (dentry != root->dentry || vfsmnt != root->mnt) {
2420 		struct dentry * parent;
2421 
2422 		if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
2423 			/* Global root? */
2424 			if (vfsmnt->mnt_parent == vfsmnt) {
2425 				goto global_root;
2426 			}
2427 			dentry = vfsmnt->mnt_mountpoint;
2428 			vfsmnt = vfsmnt->mnt_parent;
2429 			continue;
2430 		}
2431 		parent = dentry->d_parent;
2432 		prefetch(parent);
2433 		spin_lock(&dentry->d_lock);
2434 		error = prepend_name(buffer, buflen, &dentry->d_name);
2435 		spin_unlock(&dentry->d_lock);
2436 		if (!error)
2437 			error = prepend(buffer, buflen, "/", 1);
2438 		if (error)
2439 			break;
2440 
2441 		slash = true;
2442 		dentry = parent;
2443 	}
2444 
2445 out:
2446 	if (!error && !slash)
2447 		error = prepend(buffer, buflen, "/", 1);
2448 
2449 	br_read_unlock(vfsmount_lock);
2450 	return error;
2451 
2452 global_root:
2453 	/*
2454 	 * Filesystems needing to implement special "root names"
2455 	 * should do so with ->d_dname()
2456 	 */
2457 	if (IS_ROOT(dentry) &&
2458 	    (dentry->d_name.len != 1 || dentry->d_name.name[0] != '/')) {
2459 		WARN(1, "Root dentry has weird name <%.*s>\n",
2460 		     (int) dentry->d_name.len, dentry->d_name.name);
2461 	}
2462 	root->mnt = vfsmnt;
2463 	root->dentry = dentry;
2464 	goto out;
2465 }
2466 
2467 /**
2468  * __d_path - return the path of a dentry
2469  * @path: the dentry/vfsmount to report
2470  * @root: root vfsmnt/dentry (may be modified by this function)
2471  * @buf: buffer to return value in
2472  * @buflen: buffer length
2473  *
2474  * Convert a dentry into an ASCII path name.
2475  *
2476  * Returns a pointer into the buffer or an error code if the
2477  * path was too long.
2478  *
2479  * "buflen" should be positive.
2480  *
2481  * If path is not reachable from the supplied root, then the value of
2482  * root is changed (without modifying refcounts).
2483  */
2484 char *__d_path(const struct path *path, struct path *root,
2485 	       char *buf, int buflen)
2486 {
2487 	char *res = buf + buflen;
2488 	int error;
2489 
2490 	prepend(&res, &buflen, "\0", 1);
2491 	write_seqlock(&rename_lock);
2492 	error = prepend_path(path, root, &res, &buflen);
2493 	write_sequnlock(&rename_lock);
2494 
2495 	if (error)
2496 		return ERR_PTR(error);
2497 	return res;
2498 }
2499 
2500 /*
2501  * same as __d_path but appends "(deleted)" for unlinked files.
2502  */
2503 static int path_with_deleted(const struct path *path, struct path *root,
2504 				 char **buf, int *buflen)
2505 {
2506 	prepend(buf, buflen, "\0", 1);
2507 	if (d_unlinked(path->dentry)) {
2508 		int error = prepend(buf, buflen, " (deleted)", 10);
2509 		if (error)
2510 			return error;
2511 	}
2512 
2513 	return prepend_path(path, root, buf, buflen);
2514 }
2515 
2516 static int prepend_unreachable(char **buffer, int *buflen)
2517 {
2518 	return prepend(buffer, buflen, "(unreachable)", 13);
2519 }
2520 
2521 /**
2522  * d_path - return the path of a dentry
2523  * @path: path to report
2524  * @buf: buffer to return value in
2525  * @buflen: buffer length
2526  *
2527  * Convert a dentry into an ASCII path name. If the entry has been deleted
2528  * the string " (deleted)" is appended. Note that this is ambiguous.
2529  *
2530  * Returns a pointer into the buffer or an error code if the path was
2531  * too long. Note: Callers should use the returned pointer, not the passed
2532  * in buffer, to use the name! The implementation often starts at an offset
2533  * into the buffer, and may leave 0 bytes at the start.
2534  *
2535  * "buflen" should be positive.
2536  */
2537 char *d_path(const struct path *path, char *buf, int buflen)
2538 {
2539 	char *res = buf + buflen;
2540 	struct path root;
2541 	struct path tmp;
2542 	int error;
2543 
2544 	/*
2545 	 * We have various synthetic filesystems that never get mounted.  On
2546 	 * these filesystems dentries are never used for lookup purposes, and
2547 	 * thus don't need to be hashed.  They also don't need a name until a
2548 	 * user wants to identify the object in /proc/pid/fd/.  The little hack
2549 	 * below allows us to generate a name for these objects on demand:
2550 	 */
2551 	if (path->dentry->d_op && path->dentry->d_op->d_dname)
2552 		return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
2553 
2554 	get_fs_root(current->fs, &root);
2555 	write_seqlock(&rename_lock);
2556 	tmp = root;
2557 	error = path_with_deleted(path, &tmp, &res, &buflen);
2558 	if (error)
2559 		res = ERR_PTR(error);
2560 	write_sequnlock(&rename_lock);
2561 	path_put(&root);
2562 	return res;
2563 }
2564 EXPORT_SYMBOL(d_path);
2565 
2566 /**
2567  * d_path_with_unreachable - return the path of a dentry
2568  * @path: path to report
2569  * @buf: buffer to return value in
2570  * @buflen: buffer length
2571  *
2572  * The difference from d_path() is that this prepends "(unreachable)"
2573  * to paths which are unreachable from the current process' root.
2574  */
2575 char *d_path_with_unreachable(const struct path *path, char *buf, int buflen)
2576 {
2577 	char *res = buf + buflen;
2578 	struct path root;
2579 	struct path tmp;
2580 	int error;
2581 
2582 	if (path->dentry->d_op && path->dentry->d_op->d_dname)
2583 		return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
2584 
2585 	get_fs_root(current->fs, &root);
2586 	write_seqlock(&rename_lock);
2587 	tmp = root;
2588 	error = path_with_deleted(path, &tmp, &res, &buflen);
2589 	if (!error && !path_equal(&tmp, &root))
2590 		error = prepend_unreachable(&res, &buflen);
2591 	write_sequnlock(&rename_lock);
2592 	path_put(&root);
2593 	if (error)
2594 		res =  ERR_PTR(error);
2595 
2596 	return res;
2597 }
2598 
2599 /*
2600  * Helper function for dentry_operations.d_dname() members
2601  */
2602 char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,
2603 			const char *fmt, ...)
2604 {
2605 	va_list args;
2606 	char temp[64];
2607 	int sz;
2608 
2609 	va_start(args, fmt);
2610 	sz = vsnprintf(temp, sizeof(temp), fmt, args) + 1;
2611 	va_end(args);
2612 
2613 	if (sz > sizeof(temp) || sz > buflen)
2614 		return ERR_PTR(-ENAMETOOLONG);
2615 
2616 	buffer += buflen - sz;
2617 	return memcpy(buffer, temp, sz);
2618 }
2619 
2620 /*
2621  * Write full pathname from the root of the filesystem into the buffer.
2622  */
2623 static char *__dentry_path(struct dentry *dentry, char *buf, int buflen)
2624 {
2625 	char *end = buf + buflen;
2626 	char *retval;
2627 
2628 	prepend(&end, &buflen, "\0", 1);
2629 	if (buflen < 1)
2630 		goto Elong;
2631 	/* Get '/' right */
2632 	retval = end-1;
2633 	*retval = '/';
2634 
2635 	while (!IS_ROOT(dentry)) {
2636 		struct dentry *parent = dentry->d_parent;
2637 		int error;
2638 
2639 		prefetch(parent);
2640 		spin_lock(&dentry->d_lock);
2641 		error = prepend_name(&end, &buflen, &dentry->d_name);
2642 		spin_unlock(&dentry->d_lock);
2643 		if (error != 0 || prepend(&end, &buflen, "/", 1) != 0)
2644 			goto Elong;
2645 
2646 		retval = end;
2647 		dentry = parent;
2648 	}
2649 	return retval;
2650 Elong:
2651 	return ERR_PTR(-ENAMETOOLONG);
2652 }
2653 
2654 char *dentry_path_raw(struct dentry *dentry, char *buf, int buflen)
2655 {
2656 	char *retval;
2657 
2658 	write_seqlock(&rename_lock);
2659 	retval = __dentry_path(dentry, buf, buflen);
2660 	write_sequnlock(&rename_lock);
2661 
2662 	return retval;
2663 }
2664 EXPORT_SYMBOL(dentry_path_raw);
2665 
2666 char *dentry_path(struct dentry *dentry, char *buf, int buflen)
2667 {
2668 	char *p = NULL;
2669 	char *retval;
2670 
2671 	write_seqlock(&rename_lock);
2672 	if (d_unlinked(dentry)) {
2673 		p = buf + buflen;
2674 		if (prepend(&p, &buflen, "//deleted", 10) != 0)
2675 			goto Elong;
2676 		buflen++;
2677 	}
2678 	retval = __dentry_path(dentry, buf, buflen);
2679 	write_sequnlock(&rename_lock);
2680 	if (!IS_ERR(retval) && p)
2681 		*p = '/';	/* restore '/' overriden with '\0' */
2682 	return retval;
2683 Elong:
2684 	return ERR_PTR(-ENAMETOOLONG);
2685 }
2686 
2687 /*
2688  * NOTE! The user-level library version returns a
2689  * character pointer. The kernel system call just
2690  * returns the length of the buffer filled (which
2691  * includes the ending '\0' character), or a negative
2692  * error value. So libc would do something like
2693  *
2694  *	char *getcwd(char * buf, size_t size)
2695  *	{
2696  *		int retval;
2697  *
2698  *		retval = sys_getcwd(buf, size);
2699  *		if (retval >= 0)
2700  *			return buf;
2701  *		errno = -retval;
2702  *		return NULL;
2703  *	}
2704  */
2705 SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
2706 {
2707 	int error;
2708 	struct path pwd, root;
2709 	char *page = (char *) __get_free_page(GFP_USER);
2710 
2711 	if (!page)
2712 		return -ENOMEM;
2713 
2714 	get_fs_root_and_pwd(current->fs, &root, &pwd);
2715 
2716 	error = -ENOENT;
2717 	write_seqlock(&rename_lock);
2718 	if (!d_unlinked(pwd.dentry)) {
2719 		unsigned long len;
2720 		struct path tmp = root;
2721 		char *cwd = page + PAGE_SIZE;
2722 		int buflen = PAGE_SIZE;
2723 
2724 		prepend(&cwd, &buflen, "\0", 1);
2725 		error = prepend_path(&pwd, &tmp, &cwd, &buflen);
2726 		write_sequnlock(&rename_lock);
2727 
2728 		if (error)
2729 			goto out;
2730 
2731 		/* Unreachable from current root */
2732 		if (!path_equal(&tmp, &root)) {
2733 			error = prepend_unreachable(&cwd, &buflen);
2734 			if (error)
2735 				goto out;
2736 		}
2737 
2738 		error = -ERANGE;
2739 		len = PAGE_SIZE + page - cwd;
2740 		if (len <= size) {
2741 			error = len;
2742 			if (copy_to_user(buf, cwd, len))
2743 				error = -EFAULT;
2744 		}
2745 	} else {
2746 		write_sequnlock(&rename_lock);
2747 	}
2748 
2749 out:
2750 	path_put(&pwd);
2751 	path_put(&root);
2752 	free_page((unsigned long) page);
2753 	return error;
2754 }
2755 
2756 /*
2757  * Test whether new_dentry is a subdirectory of old_dentry.
2758  *
2759  * Trivially implemented using the dcache structure
2760  */
2761 
2762 /**
2763  * is_subdir - is new dentry a subdirectory of old_dentry
2764  * @new_dentry: new dentry
2765  * @old_dentry: old dentry
2766  *
2767  * Returns 1 if new_dentry is a subdirectory of the parent (at any depth).
2768  * Returns 0 otherwise.
2769  * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
2770  */
2771 
2772 int is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)
2773 {
2774 	int result;
2775 	unsigned seq;
2776 
2777 	if (new_dentry == old_dentry)
2778 		return 1;
2779 
2780 	do {
2781 		/* for restarting inner loop in case of seq retry */
2782 		seq = read_seqbegin(&rename_lock);
2783 		/*
2784 		 * Need rcu_readlock to protect against the d_parent trashing
2785 		 * due to d_move
2786 		 */
2787 		rcu_read_lock();
2788 		if (d_ancestor(old_dentry, new_dentry))
2789 			result = 1;
2790 		else
2791 			result = 0;
2792 		rcu_read_unlock();
2793 	} while (read_seqretry(&rename_lock, seq));
2794 
2795 	return result;
2796 }
2797 
2798 int path_is_under(struct path *path1, struct path *path2)
2799 {
2800 	struct vfsmount *mnt = path1->mnt;
2801 	struct dentry *dentry = path1->dentry;
2802 	int res;
2803 
2804 	br_read_lock(vfsmount_lock);
2805 	if (mnt != path2->mnt) {
2806 		for (;;) {
2807 			if (mnt->mnt_parent == mnt) {
2808 				br_read_unlock(vfsmount_lock);
2809 				return 0;
2810 			}
2811 			if (mnt->mnt_parent == path2->mnt)
2812 				break;
2813 			mnt = mnt->mnt_parent;
2814 		}
2815 		dentry = mnt->mnt_mountpoint;
2816 	}
2817 	res = is_subdir(dentry, path2->dentry);
2818 	br_read_unlock(vfsmount_lock);
2819 	return res;
2820 }
2821 EXPORT_SYMBOL(path_is_under);
2822 
2823 void d_genocide(struct dentry *root)
2824 {
2825 	struct dentry *this_parent;
2826 	struct list_head *next;
2827 	unsigned seq;
2828 	int locked = 0;
2829 
2830 	seq = read_seqbegin(&rename_lock);
2831 again:
2832 	this_parent = root;
2833 	spin_lock(&this_parent->d_lock);
2834 repeat:
2835 	next = this_parent->d_subdirs.next;
2836 resume:
2837 	while (next != &this_parent->d_subdirs) {
2838 		struct list_head *tmp = next;
2839 		struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
2840 		next = tmp->next;
2841 
2842 		spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
2843 		if (d_unhashed(dentry) || !dentry->d_inode) {
2844 			spin_unlock(&dentry->d_lock);
2845 			continue;
2846 		}
2847 		if (!list_empty(&dentry->d_subdirs)) {
2848 			spin_unlock(&this_parent->d_lock);
2849 			spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
2850 			this_parent = dentry;
2851 			spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
2852 			goto repeat;
2853 		}
2854 		if (!(dentry->d_flags & DCACHE_GENOCIDE)) {
2855 			dentry->d_flags |= DCACHE_GENOCIDE;
2856 			dentry->d_count--;
2857 		}
2858 		spin_unlock(&dentry->d_lock);
2859 	}
2860 	if (this_parent != root) {
2861 		struct dentry *child = this_parent;
2862 		if (!(this_parent->d_flags & DCACHE_GENOCIDE)) {
2863 			this_parent->d_flags |= DCACHE_GENOCIDE;
2864 			this_parent->d_count--;
2865 		}
2866 		this_parent = try_to_ascend(this_parent, locked, seq);
2867 		if (!this_parent)
2868 			goto rename_retry;
2869 		next = child->d_u.d_child.next;
2870 		goto resume;
2871 	}
2872 	spin_unlock(&this_parent->d_lock);
2873 	if (!locked && read_seqretry(&rename_lock, seq))
2874 		goto rename_retry;
2875 	if (locked)
2876 		write_sequnlock(&rename_lock);
2877 	return;
2878 
2879 rename_retry:
2880 	locked = 1;
2881 	write_seqlock(&rename_lock);
2882 	goto again;
2883 }
2884 
2885 /**
2886  * find_inode_number - check for dentry with name
2887  * @dir: directory to check
2888  * @name: Name to find.
2889  *
2890  * Check whether a dentry already exists for the given name,
2891  * and return the inode number if it has an inode. Otherwise
2892  * 0 is returned.
2893  *
2894  * This routine is used to post-process directory listings for
2895  * filesystems using synthetic inode numbers, and is necessary
2896  * to keep getcwd() working.
2897  */
2898 
2899 ino_t find_inode_number(struct dentry *dir, struct qstr *name)
2900 {
2901 	struct dentry * dentry;
2902 	ino_t ino = 0;
2903 
2904 	dentry = d_hash_and_lookup(dir, name);
2905 	if (dentry) {
2906 		if (dentry->d_inode)
2907 			ino = dentry->d_inode->i_ino;
2908 		dput(dentry);
2909 	}
2910 	return ino;
2911 }
2912 EXPORT_SYMBOL(find_inode_number);
2913 
2914 static __initdata unsigned long dhash_entries;
2915 static int __init set_dhash_entries(char *str)
2916 {
2917 	if (!str)
2918 		return 0;
2919 	dhash_entries = simple_strtoul(str, &str, 0);
2920 	return 1;
2921 }
2922 __setup("dhash_entries=", set_dhash_entries);
2923 
2924 static void __init dcache_init_early(void)
2925 {
2926 	int loop;
2927 
2928 	/* If hashes are distributed across NUMA nodes, defer
2929 	 * hash allocation until vmalloc space is available.
2930 	 */
2931 	if (hashdist)
2932 		return;
2933 
2934 	dentry_hashtable =
2935 		alloc_large_system_hash("Dentry cache",
2936 					sizeof(struct hlist_bl_head),
2937 					dhash_entries,
2938 					13,
2939 					HASH_EARLY,
2940 					&d_hash_shift,
2941 					&d_hash_mask,
2942 					0);
2943 
2944 	for (loop = 0; loop < (1 << d_hash_shift); loop++)
2945 		INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
2946 }
2947 
2948 static void __init dcache_init(void)
2949 {
2950 	int loop;
2951 
2952 	/*
2953 	 * A constructor could be added for stable state like the lists,
2954 	 * but it is probably not worth it because of the cache nature
2955 	 * of the dcache.
2956 	 */
2957 	dentry_cache = KMEM_CACHE(dentry,
2958 		SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD);
2959 
2960 	/* Hash may have been set up in dcache_init_early */
2961 	if (!hashdist)
2962 		return;
2963 
2964 	dentry_hashtable =
2965 		alloc_large_system_hash("Dentry cache",
2966 					sizeof(struct hlist_bl_head),
2967 					dhash_entries,
2968 					13,
2969 					0,
2970 					&d_hash_shift,
2971 					&d_hash_mask,
2972 					0);
2973 
2974 	for (loop = 0; loop < (1 << d_hash_shift); loop++)
2975 		INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
2976 }
2977 
2978 /* SLAB cache for __getname() consumers */
2979 struct kmem_cache *names_cachep __read_mostly;
2980 EXPORT_SYMBOL(names_cachep);
2981 
2982 EXPORT_SYMBOL(d_genocide);
2983 
2984 void __init vfs_caches_init_early(void)
2985 {
2986 	dcache_init_early();
2987 	inode_init_early();
2988 }
2989 
2990 void __init vfs_caches_init(unsigned long mempages)
2991 {
2992 	unsigned long reserve;
2993 
2994 	/* Base hash sizes on available memory, with a reserve equal to
2995            150% of current kernel size */
2996 
2997 	reserve = min((mempages - nr_free_pages()) * 3/2, mempages - 1);
2998 	mempages -= reserve;
2999 
3000 	names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
3001 			SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
3002 
3003 	dcache_init();
3004 	inode_init();
3005 	files_init(mempages);
3006 	mnt_init();
3007 	bdev_cache_init();
3008 	chrdev_init();
3009 }
3010