xref: /openbmc/linux/fs/dcache.c (revision 4800cd83)
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 "internal.h"
39 
40 /*
41  * Usage:
42  * dcache->d_inode->i_lock protects:
43  *   - i_dentry, d_alias, d_inode of aliases
44  * dcache_hash_bucket lock protects:
45  *   - the dcache hash table
46  * s_anon bl list spinlock protects:
47  *   - the s_anon list (see __d_drop)
48  * dcache_lru_lock protects:
49  *   - the dcache lru lists and counters
50  * d_lock protects:
51  *   - d_flags
52  *   - d_name
53  *   - d_lru
54  *   - d_count
55  *   - d_unhashed()
56  *   - d_parent and d_subdirs
57  *   - childrens' d_child and d_parent
58  *   - d_alias, d_inode
59  *
60  * Ordering:
61  * dentry->d_inode->i_lock
62  *   dentry->d_lock
63  *     dcache_lru_lock
64  *     dcache_hash_bucket lock
65  *     s_anon lock
66  *
67  * If there is an ancestor relationship:
68  * dentry->d_parent->...->d_parent->d_lock
69  *   ...
70  *     dentry->d_parent->d_lock
71  *       dentry->d_lock
72  *
73  * If no ancestor relationship:
74  * if (dentry1 < dentry2)
75  *   dentry1->d_lock
76  *     dentry2->d_lock
77  */
78 int sysctl_vfs_cache_pressure __read_mostly = 100;
79 EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
80 
81 static __cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lru_lock);
82 __cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
83 
84 EXPORT_SYMBOL(rename_lock);
85 
86 static struct kmem_cache *dentry_cache __read_mostly;
87 
88 /*
89  * This is the single most critical data structure when it comes
90  * to the dcache: the hashtable for lookups. Somebody should try
91  * to make this good - I've just made it work.
92  *
93  * This hash-function tries to avoid losing too many bits of hash
94  * information, yet avoid using a prime hash-size or similar.
95  */
96 #define D_HASHBITS     d_hash_shift
97 #define D_HASHMASK     d_hash_mask
98 
99 static unsigned int d_hash_mask __read_mostly;
100 static unsigned int d_hash_shift __read_mostly;
101 
102 struct dcache_hash_bucket {
103 	struct hlist_bl_head head;
104 };
105 static struct dcache_hash_bucket *dentry_hashtable __read_mostly;
106 
107 static inline struct dcache_hash_bucket *d_hash(struct dentry *parent,
108 					unsigned long hash)
109 {
110 	hash += ((unsigned long) parent ^ GOLDEN_RATIO_PRIME) / L1_CACHE_BYTES;
111 	hash = hash ^ ((hash ^ GOLDEN_RATIO_PRIME) >> D_HASHBITS);
112 	return dentry_hashtable + (hash & D_HASHMASK);
113 }
114 
115 static inline void spin_lock_bucket(struct dcache_hash_bucket *b)
116 {
117 	bit_spin_lock(0, (unsigned long *)&b->head.first);
118 }
119 
120 static inline void spin_unlock_bucket(struct dcache_hash_bucket *b)
121 {
122 	__bit_spin_unlock(0, (unsigned long *)&b->head.first);
123 }
124 
125 /* Statistics gathering. */
126 struct dentry_stat_t dentry_stat = {
127 	.age_limit = 45,
128 };
129 
130 static DEFINE_PER_CPU(unsigned int, nr_dentry);
131 
132 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
133 static int get_nr_dentry(void)
134 {
135 	int i;
136 	int sum = 0;
137 	for_each_possible_cpu(i)
138 		sum += per_cpu(nr_dentry, i);
139 	return sum < 0 ? 0 : sum;
140 }
141 
142 int proc_nr_dentry(ctl_table *table, int write, void __user *buffer,
143 		   size_t *lenp, loff_t *ppos)
144 {
145 	dentry_stat.nr_dentry = get_nr_dentry();
146 	return proc_dointvec(table, write, buffer, lenp, ppos);
147 }
148 #endif
149 
150 static void __d_free(struct rcu_head *head)
151 {
152 	struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
153 
154 	WARN_ON(!list_empty(&dentry->d_alias));
155 	if (dname_external(dentry))
156 		kfree(dentry->d_name.name);
157 	kmem_cache_free(dentry_cache, dentry);
158 }
159 
160 /*
161  * no locks, please.
162  */
163 static void d_free(struct dentry *dentry)
164 {
165 	BUG_ON(dentry->d_count);
166 	this_cpu_dec(nr_dentry);
167 	if (dentry->d_op && dentry->d_op->d_release)
168 		dentry->d_op->d_release(dentry);
169 
170 	/* if dentry was never inserted into hash, immediate free is OK */
171 	if (hlist_bl_unhashed(&dentry->d_hash))
172 		__d_free(&dentry->d_u.d_rcu);
173 	else
174 		call_rcu(&dentry->d_u.d_rcu, __d_free);
175 }
176 
177 /**
178  * dentry_rcuwalk_barrier - invalidate in-progress rcu-walk lookups
179  * @dentry: the target dentry
180  * After this call, in-progress rcu-walk path lookup will fail. This
181  * should be called after unhashing, and after changing d_inode (if
182  * the dentry has not already been unhashed).
183  */
184 static inline void dentry_rcuwalk_barrier(struct dentry *dentry)
185 {
186 	assert_spin_locked(&dentry->d_lock);
187 	/* Go through a barrier */
188 	write_seqcount_barrier(&dentry->d_seq);
189 }
190 
191 /*
192  * Release the dentry's inode, using the filesystem
193  * d_iput() operation if defined. Dentry has no refcount
194  * and is unhashed.
195  */
196 static void dentry_iput(struct dentry * dentry)
197 	__releases(dentry->d_lock)
198 	__releases(dentry->d_inode->i_lock)
199 {
200 	struct inode *inode = dentry->d_inode;
201 	if (inode) {
202 		dentry->d_inode = NULL;
203 		list_del_init(&dentry->d_alias);
204 		spin_unlock(&dentry->d_lock);
205 		spin_unlock(&inode->i_lock);
206 		if (!inode->i_nlink)
207 			fsnotify_inoderemove(inode);
208 		if (dentry->d_op && dentry->d_op->d_iput)
209 			dentry->d_op->d_iput(dentry, inode);
210 		else
211 			iput(inode);
212 	} else {
213 		spin_unlock(&dentry->d_lock);
214 	}
215 }
216 
217 /*
218  * Release the dentry's inode, using the filesystem
219  * d_iput() operation if defined. dentry remains in-use.
220  */
221 static void dentry_unlink_inode(struct dentry * dentry)
222 	__releases(dentry->d_lock)
223 	__releases(dentry->d_inode->i_lock)
224 {
225 	struct inode *inode = dentry->d_inode;
226 	dentry->d_inode = NULL;
227 	list_del_init(&dentry->d_alias);
228 	dentry_rcuwalk_barrier(dentry);
229 	spin_unlock(&dentry->d_lock);
230 	spin_unlock(&inode->i_lock);
231 	if (!inode->i_nlink)
232 		fsnotify_inoderemove(inode);
233 	if (dentry->d_op && dentry->d_op->d_iput)
234 		dentry->d_op->d_iput(dentry, inode);
235 	else
236 		iput(inode);
237 }
238 
239 /*
240  * dentry_lru_(add|del|move_tail) must be called with d_lock held.
241  */
242 static void dentry_lru_add(struct dentry *dentry)
243 {
244 	if (list_empty(&dentry->d_lru)) {
245 		spin_lock(&dcache_lru_lock);
246 		list_add(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
247 		dentry->d_sb->s_nr_dentry_unused++;
248 		dentry_stat.nr_unused++;
249 		spin_unlock(&dcache_lru_lock);
250 	}
251 }
252 
253 static void __dentry_lru_del(struct dentry *dentry)
254 {
255 	list_del_init(&dentry->d_lru);
256 	dentry->d_sb->s_nr_dentry_unused--;
257 	dentry_stat.nr_unused--;
258 }
259 
260 static void dentry_lru_del(struct dentry *dentry)
261 {
262 	if (!list_empty(&dentry->d_lru)) {
263 		spin_lock(&dcache_lru_lock);
264 		__dentry_lru_del(dentry);
265 		spin_unlock(&dcache_lru_lock);
266 	}
267 }
268 
269 static void dentry_lru_move_tail(struct dentry *dentry)
270 {
271 	spin_lock(&dcache_lru_lock);
272 	if (list_empty(&dentry->d_lru)) {
273 		list_add_tail(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
274 		dentry->d_sb->s_nr_dentry_unused++;
275 		dentry_stat.nr_unused++;
276 	} else {
277 		list_move_tail(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
278 	}
279 	spin_unlock(&dcache_lru_lock);
280 }
281 
282 /**
283  * d_kill - kill dentry and return parent
284  * @dentry: dentry to kill
285  * @parent: parent dentry
286  *
287  * The dentry must already be unhashed and removed from the LRU.
288  *
289  * If this is the root of the dentry tree, return NULL.
290  *
291  * dentry->d_lock and parent->d_lock must be held by caller, and are dropped by
292  * d_kill.
293  */
294 static struct dentry *d_kill(struct dentry *dentry, struct dentry *parent)
295 	__releases(dentry->d_lock)
296 	__releases(parent->d_lock)
297 	__releases(dentry->d_inode->i_lock)
298 {
299 	dentry->d_parent = NULL;
300 	list_del(&dentry->d_u.d_child);
301 	if (parent)
302 		spin_unlock(&parent->d_lock);
303 	dentry_iput(dentry);
304 	/*
305 	 * dentry_iput drops the locks, at which point nobody (except
306 	 * transient RCU lookups) can reach this dentry.
307 	 */
308 	d_free(dentry);
309 	return parent;
310 }
311 
312 /**
313  * d_drop - drop a dentry
314  * @dentry: dentry to drop
315  *
316  * d_drop() unhashes the entry from the parent dentry hashes, so that it won't
317  * be found through a VFS lookup any more. Note that this is different from
318  * deleting the dentry - d_delete will try to mark the dentry negative if
319  * possible, giving a successful _negative_ lookup, while d_drop will
320  * just make the cache lookup fail.
321  *
322  * d_drop() is used mainly for stuff that wants to invalidate a dentry for some
323  * reason (NFS timeouts or autofs deletes).
324  *
325  * __d_drop requires dentry->d_lock.
326  */
327 void __d_drop(struct dentry *dentry)
328 {
329 	if (!(dentry->d_flags & DCACHE_UNHASHED)) {
330 		if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED)) {
331 			bit_spin_lock(0,
332 				(unsigned long *)&dentry->d_sb->s_anon.first);
333 			dentry->d_flags |= DCACHE_UNHASHED;
334 			hlist_bl_del_init(&dentry->d_hash);
335 			__bit_spin_unlock(0,
336 				(unsigned long *)&dentry->d_sb->s_anon.first);
337 		} else {
338 			struct dcache_hash_bucket *b;
339 			b = d_hash(dentry->d_parent, dentry->d_name.hash);
340 			spin_lock_bucket(b);
341 			/*
342 			 * We may not actually need to put DCACHE_UNHASHED
343 			 * manipulations under the hash lock, but follow
344 			 * the principle of least surprise.
345 			 */
346 			dentry->d_flags |= DCACHE_UNHASHED;
347 			hlist_bl_del_rcu(&dentry->d_hash);
348 			spin_unlock_bucket(b);
349 			dentry_rcuwalk_barrier(dentry);
350 		}
351 	}
352 }
353 EXPORT_SYMBOL(__d_drop);
354 
355 void d_drop(struct dentry *dentry)
356 {
357 	spin_lock(&dentry->d_lock);
358 	__d_drop(dentry);
359 	spin_unlock(&dentry->d_lock);
360 }
361 EXPORT_SYMBOL(d_drop);
362 
363 /*
364  * Finish off a dentry we've decided to kill.
365  * dentry->d_lock must be held, returns with it unlocked.
366  * If ref is non-zero, then decrement the refcount too.
367  * Returns dentry requiring refcount drop, or NULL if we're done.
368  */
369 static inline struct dentry *dentry_kill(struct dentry *dentry, int ref)
370 	__releases(dentry->d_lock)
371 {
372 	struct inode *inode;
373 	struct dentry *parent;
374 
375 	inode = dentry->d_inode;
376 	if (inode && !spin_trylock(&inode->i_lock)) {
377 relock:
378 		spin_unlock(&dentry->d_lock);
379 		cpu_relax();
380 		return dentry; /* try again with same dentry */
381 	}
382 	if (IS_ROOT(dentry))
383 		parent = NULL;
384 	else
385 		parent = dentry->d_parent;
386 	if (parent && !spin_trylock(&parent->d_lock)) {
387 		if (inode)
388 			spin_unlock(&inode->i_lock);
389 		goto relock;
390 	}
391 
392 	if (ref)
393 		dentry->d_count--;
394 	/* if dentry was on the d_lru list delete it from there */
395 	dentry_lru_del(dentry);
396 	/* if it was on the hash then remove it */
397 	__d_drop(dentry);
398 	return d_kill(dentry, parent);
399 }
400 
401 /*
402  * This is dput
403  *
404  * This is complicated by the fact that we do not want to put
405  * dentries that are no longer on any hash chain on the unused
406  * list: we'd much rather just get rid of them immediately.
407  *
408  * However, that implies that we have to traverse the dentry
409  * tree upwards to the parents which might _also_ now be
410  * scheduled for deletion (it may have been only waiting for
411  * its last child to go away).
412  *
413  * This tail recursion is done by hand as we don't want to depend
414  * on the compiler to always get this right (gcc generally doesn't).
415  * Real recursion would eat up our stack space.
416  */
417 
418 /*
419  * dput - release a dentry
420  * @dentry: dentry to release
421  *
422  * Release a dentry. This will drop the usage count and if appropriate
423  * call the dentry unlink method as well as removing it from the queues and
424  * releasing its resources. If the parent dentries were scheduled for release
425  * they too may now get deleted.
426  */
427 void dput(struct dentry *dentry)
428 {
429 	if (!dentry)
430 		return;
431 
432 repeat:
433 	if (dentry->d_count == 1)
434 		might_sleep();
435 	spin_lock(&dentry->d_lock);
436 	BUG_ON(!dentry->d_count);
437 	if (dentry->d_count > 1) {
438 		dentry->d_count--;
439 		spin_unlock(&dentry->d_lock);
440 		return;
441 	}
442 
443 	if (dentry->d_flags & DCACHE_OP_DELETE) {
444 		if (dentry->d_op->d_delete(dentry))
445 			goto kill_it;
446 	}
447 
448 	/* Unreachable? Get rid of it */
449  	if (d_unhashed(dentry))
450 		goto kill_it;
451 
452 	/* Otherwise leave it cached and ensure it's on the LRU */
453 	dentry->d_flags |= DCACHE_REFERENCED;
454 	dentry_lru_add(dentry);
455 
456 	dentry->d_count--;
457 	spin_unlock(&dentry->d_lock);
458 	return;
459 
460 kill_it:
461 	dentry = dentry_kill(dentry, 1);
462 	if (dentry)
463 		goto repeat;
464 }
465 EXPORT_SYMBOL(dput);
466 
467 /**
468  * d_invalidate - invalidate a dentry
469  * @dentry: dentry to invalidate
470  *
471  * Try to invalidate the dentry if it turns out to be
472  * possible. If there are other dentries that can be
473  * reached through this one we can't delete it and we
474  * return -EBUSY. On success we return 0.
475  *
476  * no dcache lock.
477  */
478 
479 int d_invalidate(struct dentry * dentry)
480 {
481 	/*
482 	 * If it's already been dropped, return OK.
483 	 */
484 	spin_lock(&dentry->d_lock);
485 	if (d_unhashed(dentry)) {
486 		spin_unlock(&dentry->d_lock);
487 		return 0;
488 	}
489 	/*
490 	 * Check whether to do a partial shrink_dcache
491 	 * to get rid of unused child entries.
492 	 */
493 	if (!list_empty(&dentry->d_subdirs)) {
494 		spin_unlock(&dentry->d_lock);
495 		shrink_dcache_parent(dentry);
496 		spin_lock(&dentry->d_lock);
497 	}
498 
499 	/*
500 	 * Somebody else still using it?
501 	 *
502 	 * If it's a directory, we can't drop it
503 	 * for fear of somebody re-populating it
504 	 * with children (even though dropping it
505 	 * would make it unreachable from the root,
506 	 * we might still populate it if it was a
507 	 * working directory or similar).
508 	 */
509 	if (dentry->d_count > 1) {
510 		if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode)) {
511 			spin_unlock(&dentry->d_lock);
512 			return -EBUSY;
513 		}
514 	}
515 
516 	__d_drop(dentry);
517 	spin_unlock(&dentry->d_lock);
518 	return 0;
519 }
520 EXPORT_SYMBOL(d_invalidate);
521 
522 /* This must be called with d_lock held */
523 static inline void __dget_dlock(struct dentry *dentry)
524 {
525 	dentry->d_count++;
526 }
527 
528 static inline void __dget(struct dentry *dentry)
529 {
530 	spin_lock(&dentry->d_lock);
531 	__dget_dlock(dentry);
532 	spin_unlock(&dentry->d_lock);
533 }
534 
535 struct dentry *dget_parent(struct dentry *dentry)
536 {
537 	struct dentry *ret;
538 
539 repeat:
540 	/*
541 	 * Don't need rcu_dereference because we re-check it was correct under
542 	 * the lock.
543 	 */
544 	rcu_read_lock();
545 	ret = dentry->d_parent;
546 	if (!ret) {
547 		rcu_read_unlock();
548 		goto out;
549 	}
550 	spin_lock(&ret->d_lock);
551 	if (unlikely(ret != dentry->d_parent)) {
552 		spin_unlock(&ret->d_lock);
553 		rcu_read_unlock();
554 		goto repeat;
555 	}
556 	rcu_read_unlock();
557 	BUG_ON(!ret->d_count);
558 	ret->d_count++;
559 	spin_unlock(&ret->d_lock);
560 out:
561 	return ret;
562 }
563 EXPORT_SYMBOL(dget_parent);
564 
565 /**
566  * d_find_alias - grab a hashed alias of inode
567  * @inode: inode in question
568  * @want_discon:  flag, used by d_splice_alias, to request
569  *          that only a DISCONNECTED alias be returned.
570  *
571  * If inode has a hashed alias, or is a directory and has any alias,
572  * acquire the reference to alias and return it. Otherwise return NULL.
573  * Notice that if inode is a directory there can be only one alias and
574  * it can be unhashed only if it has no children, or if it is the root
575  * of a filesystem.
576  *
577  * If the inode has an IS_ROOT, DCACHE_DISCONNECTED alias, then prefer
578  * any other hashed alias over that one unless @want_discon is set,
579  * in which case only return an IS_ROOT, DCACHE_DISCONNECTED alias.
580  */
581 static struct dentry *__d_find_alias(struct inode *inode, int want_discon)
582 {
583 	struct dentry *alias, *discon_alias;
584 
585 again:
586 	discon_alias = NULL;
587 	list_for_each_entry(alias, &inode->i_dentry, d_alias) {
588 		spin_lock(&alias->d_lock);
589  		if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
590 			if (IS_ROOT(alias) &&
591 			    (alias->d_flags & DCACHE_DISCONNECTED)) {
592 				discon_alias = alias;
593 			} else if (!want_discon) {
594 				__dget_dlock(alias);
595 				spin_unlock(&alias->d_lock);
596 				return alias;
597 			}
598 		}
599 		spin_unlock(&alias->d_lock);
600 	}
601 	if (discon_alias) {
602 		alias = discon_alias;
603 		spin_lock(&alias->d_lock);
604 		if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
605 			if (IS_ROOT(alias) &&
606 			    (alias->d_flags & DCACHE_DISCONNECTED)) {
607 				__dget_dlock(alias);
608 				spin_unlock(&alias->d_lock);
609 				return alias;
610 			}
611 		}
612 		spin_unlock(&alias->d_lock);
613 		goto again;
614 	}
615 	return NULL;
616 }
617 
618 struct dentry *d_find_alias(struct inode *inode)
619 {
620 	struct dentry *de = NULL;
621 
622 	if (!list_empty(&inode->i_dentry)) {
623 		spin_lock(&inode->i_lock);
624 		de = __d_find_alias(inode, 0);
625 		spin_unlock(&inode->i_lock);
626 	}
627 	return de;
628 }
629 EXPORT_SYMBOL(d_find_alias);
630 
631 /*
632  *	Try to kill dentries associated with this inode.
633  * WARNING: you must own a reference to inode.
634  */
635 void d_prune_aliases(struct inode *inode)
636 {
637 	struct dentry *dentry;
638 restart:
639 	spin_lock(&inode->i_lock);
640 	list_for_each_entry(dentry, &inode->i_dentry, d_alias) {
641 		spin_lock(&dentry->d_lock);
642 		if (!dentry->d_count) {
643 			__dget_dlock(dentry);
644 			__d_drop(dentry);
645 			spin_unlock(&dentry->d_lock);
646 			spin_unlock(&inode->i_lock);
647 			dput(dentry);
648 			goto restart;
649 		}
650 		spin_unlock(&dentry->d_lock);
651 	}
652 	spin_unlock(&inode->i_lock);
653 }
654 EXPORT_SYMBOL(d_prune_aliases);
655 
656 /*
657  * Try to throw away a dentry - free the inode, dput the parent.
658  * Requires dentry->d_lock is held, and dentry->d_count == 0.
659  * Releases dentry->d_lock.
660  *
661  * This may fail if locks cannot be acquired no problem, just try again.
662  */
663 static void try_prune_one_dentry(struct dentry *dentry)
664 	__releases(dentry->d_lock)
665 {
666 	struct dentry *parent;
667 
668 	parent = dentry_kill(dentry, 0);
669 	/*
670 	 * If dentry_kill returns NULL, we have nothing more to do.
671 	 * if it returns the same dentry, trylocks failed. In either
672 	 * case, just loop again.
673 	 *
674 	 * Otherwise, we need to prune ancestors too. This is necessary
675 	 * to prevent quadratic behavior of shrink_dcache_parent(), but
676 	 * is also expected to be beneficial in reducing dentry cache
677 	 * fragmentation.
678 	 */
679 	if (!parent)
680 		return;
681 	if (parent == dentry)
682 		return;
683 
684 	/* Prune ancestors. */
685 	dentry = parent;
686 	while (dentry) {
687 		spin_lock(&dentry->d_lock);
688 		if (dentry->d_count > 1) {
689 			dentry->d_count--;
690 			spin_unlock(&dentry->d_lock);
691 			return;
692 		}
693 		dentry = dentry_kill(dentry, 1);
694 	}
695 }
696 
697 static void shrink_dentry_list(struct list_head *list)
698 {
699 	struct dentry *dentry;
700 
701 	rcu_read_lock();
702 	for (;;) {
703 		dentry = list_entry_rcu(list->prev, struct dentry, d_lru);
704 		if (&dentry->d_lru == list)
705 			break; /* empty */
706 		spin_lock(&dentry->d_lock);
707 		if (dentry != list_entry(list->prev, struct dentry, d_lru)) {
708 			spin_unlock(&dentry->d_lock);
709 			continue;
710 		}
711 
712 		/*
713 		 * We found an inuse dentry which was not removed from
714 		 * the LRU because of laziness during lookup.  Do not free
715 		 * it - just keep it off the LRU list.
716 		 */
717 		if (dentry->d_count) {
718 			dentry_lru_del(dentry);
719 			spin_unlock(&dentry->d_lock);
720 			continue;
721 		}
722 
723 		rcu_read_unlock();
724 
725 		try_prune_one_dentry(dentry);
726 
727 		rcu_read_lock();
728 	}
729 	rcu_read_unlock();
730 }
731 
732 /**
733  * __shrink_dcache_sb - shrink the dentry LRU on a given superblock
734  * @sb:		superblock to shrink dentry LRU.
735  * @count:	number of entries to prune
736  * @flags:	flags to control the dentry processing
737  *
738  * If flags contains DCACHE_REFERENCED reference dentries will not be pruned.
739  */
740 static void __shrink_dcache_sb(struct super_block *sb, int *count, int flags)
741 {
742 	/* called from prune_dcache() and shrink_dcache_parent() */
743 	struct dentry *dentry;
744 	LIST_HEAD(referenced);
745 	LIST_HEAD(tmp);
746 	int cnt = *count;
747 
748 relock:
749 	spin_lock(&dcache_lru_lock);
750 	while (!list_empty(&sb->s_dentry_lru)) {
751 		dentry = list_entry(sb->s_dentry_lru.prev,
752 				struct dentry, d_lru);
753 		BUG_ON(dentry->d_sb != sb);
754 
755 		if (!spin_trylock(&dentry->d_lock)) {
756 			spin_unlock(&dcache_lru_lock);
757 			cpu_relax();
758 			goto relock;
759 		}
760 
761 		/*
762 		 * If we are honouring the DCACHE_REFERENCED flag and the
763 		 * dentry has this flag set, don't free it.  Clear the flag
764 		 * and put it back on the LRU.
765 		 */
766 		if (flags & DCACHE_REFERENCED &&
767 				dentry->d_flags & DCACHE_REFERENCED) {
768 			dentry->d_flags &= ~DCACHE_REFERENCED;
769 			list_move(&dentry->d_lru, &referenced);
770 			spin_unlock(&dentry->d_lock);
771 		} else {
772 			list_move_tail(&dentry->d_lru, &tmp);
773 			spin_unlock(&dentry->d_lock);
774 			if (!--cnt)
775 				break;
776 		}
777 		cond_resched_lock(&dcache_lru_lock);
778 	}
779 	if (!list_empty(&referenced))
780 		list_splice(&referenced, &sb->s_dentry_lru);
781 	spin_unlock(&dcache_lru_lock);
782 
783 	shrink_dentry_list(&tmp);
784 
785 	*count = cnt;
786 }
787 
788 /**
789  * prune_dcache - shrink the dcache
790  * @count: number of entries to try to free
791  *
792  * Shrink the dcache. This is done when we need more memory, or simply when we
793  * need to unmount something (at which point we need to unuse all dentries).
794  *
795  * This function may fail to free any resources if all the dentries are in use.
796  */
797 static void prune_dcache(int count)
798 {
799 	struct super_block *sb, *p = NULL;
800 	int w_count;
801 	int unused = dentry_stat.nr_unused;
802 	int prune_ratio;
803 	int pruned;
804 
805 	if (unused == 0 || count == 0)
806 		return;
807 	if (count >= unused)
808 		prune_ratio = 1;
809 	else
810 		prune_ratio = unused / count;
811 	spin_lock(&sb_lock);
812 	list_for_each_entry(sb, &super_blocks, s_list) {
813 		if (list_empty(&sb->s_instances))
814 			continue;
815 		if (sb->s_nr_dentry_unused == 0)
816 			continue;
817 		sb->s_count++;
818 		/* Now, we reclaim unused dentrins with fairness.
819 		 * We reclaim them same percentage from each superblock.
820 		 * We calculate number of dentries to scan on this sb
821 		 * as follows, but the implementation is arranged to avoid
822 		 * overflows:
823 		 * number of dentries to scan on this sb =
824 		 * count * (number of dentries on this sb /
825 		 * number of dentries in the machine)
826 		 */
827 		spin_unlock(&sb_lock);
828 		if (prune_ratio != 1)
829 			w_count = (sb->s_nr_dentry_unused / prune_ratio) + 1;
830 		else
831 			w_count = sb->s_nr_dentry_unused;
832 		pruned = w_count;
833 		/*
834 		 * We need to be sure this filesystem isn't being unmounted,
835 		 * otherwise we could race with generic_shutdown_super(), and
836 		 * end up holding a reference to an inode while the filesystem
837 		 * is unmounted.  So we try to get s_umount, and make sure
838 		 * s_root isn't NULL.
839 		 */
840 		if (down_read_trylock(&sb->s_umount)) {
841 			if ((sb->s_root != NULL) &&
842 			    (!list_empty(&sb->s_dentry_lru))) {
843 				__shrink_dcache_sb(sb, &w_count,
844 						DCACHE_REFERENCED);
845 				pruned -= w_count;
846 			}
847 			up_read(&sb->s_umount);
848 		}
849 		spin_lock(&sb_lock);
850 		if (p)
851 			__put_super(p);
852 		count -= pruned;
853 		p = sb;
854 		/* more work left to do? */
855 		if (count <= 0)
856 			break;
857 	}
858 	if (p)
859 		__put_super(p);
860 	spin_unlock(&sb_lock);
861 }
862 
863 /**
864  * shrink_dcache_sb - shrink dcache for a superblock
865  * @sb: superblock
866  *
867  * Shrink the dcache for the specified super block. This is used to free
868  * the dcache before unmounting a file system.
869  */
870 void shrink_dcache_sb(struct super_block *sb)
871 {
872 	LIST_HEAD(tmp);
873 
874 	spin_lock(&dcache_lru_lock);
875 	while (!list_empty(&sb->s_dentry_lru)) {
876 		list_splice_init(&sb->s_dentry_lru, &tmp);
877 		spin_unlock(&dcache_lru_lock);
878 		shrink_dentry_list(&tmp);
879 		spin_lock(&dcache_lru_lock);
880 	}
881 	spin_unlock(&dcache_lru_lock);
882 }
883 EXPORT_SYMBOL(shrink_dcache_sb);
884 
885 /*
886  * destroy a single subtree of dentries for unmount
887  * - see the comments on shrink_dcache_for_umount() for a description of the
888  *   locking
889  */
890 static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
891 {
892 	struct dentry *parent;
893 	unsigned detached = 0;
894 
895 	BUG_ON(!IS_ROOT(dentry));
896 
897 	/* detach this root from the system */
898 	spin_lock(&dentry->d_lock);
899 	dentry_lru_del(dentry);
900 	__d_drop(dentry);
901 	spin_unlock(&dentry->d_lock);
902 
903 	for (;;) {
904 		/* descend to the first leaf in the current subtree */
905 		while (!list_empty(&dentry->d_subdirs)) {
906 			struct dentry *loop;
907 
908 			/* this is a branch with children - detach all of them
909 			 * from the system in one go */
910 			spin_lock(&dentry->d_lock);
911 			list_for_each_entry(loop, &dentry->d_subdirs,
912 					    d_u.d_child) {
913 				spin_lock_nested(&loop->d_lock,
914 						DENTRY_D_LOCK_NESTED);
915 				dentry_lru_del(loop);
916 				__d_drop(loop);
917 				spin_unlock(&loop->d_lock);
918 			}
919 			spin_unlock(&dentry->d_lock);
920 
921 			/* move to the first child */
922 			dentry = list_entry(dentry->d_subdirs.next,
923 					    struct dentry, d_u.d_child);
924 		}
925 
926 		/* consume the dentries from this leaf up through its parents
927 		 * until we find one with children or run out altogether */
928 		do {
929 			struct inode *inode;
930 
931 			if (dentry->d_count != 0) {
932 				printk(KERN_ERR
933 				       "BUG: Dentry %p{i=%lx,n=%s}"
934 				       " still in use (%d)"
935 				       " [unmount of %s %s]\n",
936 				       dentry,
937 				       dentry->d_inode ?
938 				       dentry->d_inode->i_ino : 0UL,
939 				       dentry->d_name.name,
940 				       dentry->d_count,
941 				       dentry->d_sb->s_type->name,
942 				       dentry->d_sb->s_id);
943 				BUG();
944 			}
945 
946 			if (IS_ROOT(dentry)) {
947 				parent = NULL;
948 				list_del(&dentry->d_u.d_child);
949 			} else {
950 				parent = dentry->d_parent;
951 				spin_lock(&parent->d_lock);
952 				parent->d_count--;
953 				list_del(&dentry->d_u.d_child);
954 				spin_unlock(&parent->d_lock);
955 			}
956 
957 			detached++;
958 
959 			inode = dentry->d_inode;
960 			if (inode) {
961 				dentry->d_inode = NULL;
962 				list_del_init(&dentry->d_alias);
963 				if (dentry->d_op && dentry->d_op->d_iput)
964 					dentry->d_op->d_iput(dentry, inode);
965 				else
966 					iput(inode);
967 			}
968 
969 			d_free(dentry);
970 
971 			/* finished when we fall off the top of the tree,
972 			 * otherwise we ascend to the parent and move to the
973 			 * next sibling if there is one */
974 			if (!parent)
975 				return;
976 			dentry = parent;
977 		} while (list_empty(&dentry->d_subdirs));
978 
979 		dentry = list_entry(dentry->d_subdirs.next,
980 				    struct dentry, d_u.d_child);
981 	}
982 }
983 
984 /*
985  * destroy the dentries attached to a superblock on unmounting
986  * - we don't need to use dentry->d_lock because:
987  *   - the superblock is detached from all mountings and open files, so the
988  *     dentry trees will not be rearranged by the VFS
989  *   - s_umount is write-locked, so the memory pressure shrinker will ignore
990  *     any dentries belonging to this superblock that it comes across
991  *   - the filesystem itself is no longer permitted to rearrange the dentries
992  *     in this superblock
993  */
994 void shrink_dcache_for_umount(struct super_block *sb)
995 {
996 	struct dentry *dentry;
997 
998 	if (down_read_trylock(&sb->s_umount))
999 		BUG();
1000 
1001 	dentry = sb->s_root;
1002 	sb->s_root = NULL;
1003 	spin_lock(&dentry->d_lock);
1004 	dentry->d_count--;
1005 	spin_unlock(&dentry->d_lock);
1006 	shrink_dcache_for_umount_subtree(dentry);
1007 
1008 	while (!hlist_bl_empty(&sb->s_anon)) {
1009 		dentry = hlist_bl_entry(hlist_bl_first(&sb->s_anon), struct dentry, d_hash);
1010 		shrink_dcache_for_umount_subtree(dentry);
1011 	}
1012 }
1013 
1014 /*
1015  * Search for at least 1 mount point in the dentry's subdirs.
1016  * We descend to the next level whenever the d_subdirs
1017  * list is non-empty and continue searching.
1018  */
1019 
1020 /**
1021  * have_submounts - check for mounts over a dentry
1022  * @parent: dentry to check.
1023  *
1024  * Return true if the parent or its subdirectories contain
1025  * a mount point
1026  */
1027 int have_submounts(struct dentry *parent)
1028 {
1029 	struct dentry *this_parent;
1030 	struct list_head *next;
1031 	unsigned seq;
1032 	int locked = 0;
1033 
1034 	seq = read_seqbegin(&rename_lock);
1035 again:
1036 	this_parent = parent;
1037 
1038 	if (d_mountpoint(parent))
1039 		goto positive;
1040 	spin_lock(&this_parent->d_lock);
1041 repeat:
1042 	next = this_parent->d_subdirs.next;
1043 resume:
1044 	while (next != &this_parent->d_subdirs) {
1045 		struct list_head *tmp = next;
1046 		struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
1047 		next = tmp->next;
1048 
1049 		spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
1050 		/* Have we found a mount point ? */
1051 		if (d_mountpoint(dentry)) {
1052 			spin_unlock(&dentry->d_lock);
1053 			spin_unlock(&this_parent->d_lock);
1054 			goto positive;
1055 		}
1056 		if (!list_empty(&dentry->d_subdirs)) {
1057 			spin_unlock(&this_parent->d_lock);
1058 			spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
1059 			this_parent = dentry;
1060 			spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
1061 			goto repeat;
1062 		}
1063 		spin_unlock(&dentry->d_lock);
1064 	}
1065 	/*
1066 	 * All done at this level ... ascend and resume the search.
1067 	 */
1068 	if (this_parent != parent) {
1069 		struct dentry *tmp;
1070 		struct dentry *child;
1071 
1072 		tmp = this_parent->d_parent;
1073 		rcu_read_lock();
1074 		spin_unlock(&this_parent->d_lock);
1075 		child = this_parent;
1076 		this_parent = tmp;
1077 		spin_lock(&this_parent->d_lock);
1078 		/* might go back up the wrong parent if we have had a rename
1079 		 * or deletion */
1080 		if (this_parent != child->d_parent ||
1081 			 (!locked && read_seqretry(&rename_lock, seq))) {
1082 			spin_unlock(&this_parent->d_lock);
1083 			rcu_read_unlock();
1084 			goto rename_retry;
1085 		}
1086 		rcu_read_unlock();
1087 		next = child->d_u.d_child.next;
1088 		goto resume;
1089 	}
1090 	spin_unlock(&this_parent->d_lock);
1091 	if (!locked && read_seqretry(&rename_lock, seq))
1092 		goto rename_retry;
1093 	if (locked)
1094 		write_sequnlock(&rename_lock);
1095 	return 0; /* No mount points found in tree */
1096 positive:
1097 	if (!locked && read_seqretry(&rename_lock, seq))
1098 		goto rename_retry;
1099 	if (locked)
1100 		write_sequnlock(&rename_lock);
1101 	return 1;
1102 
1103 rename_retry:
1104 	locked = 1;
1105 	write_seqlock(&rename_lock);
1106 	goto again;
1107 }
1108 EXPORT_SYMBOL(have_submounts);
1109 
1110 /*
1111  * Search the dentry child list for the specified parent,
1112  * and move any unused dentries to the end of the unused
1113  * list for prune_dcache(). We descend to the next level
1114  * whenever the d_subdirs list is non-empty and continue
1115  * searching.
1116  *
1117  * It returns zero iff there are no unused children,
1118  * otherwise  it returns the number of children moved to
1119  * the end of the unused list. This may not be the total
1120  * number of unused children, because select_parent can
1121  * drop the lock and return early due to latency
1122  * constraints.
1123  */
1124 static int select_parent(struct dentry * parent)
1125 {
1126 	struct dentry *this_parent;
1127 	struct list_head *next;
1128 	unsigned seq;
1129 	int found = 0;
1130 	int locked = 0;
1131 
1132 	seq = read_seqbegin(&rename_lock);
1133 again:
1134 	this_parent = parent;
1135 	spin_lock(&this_parent->d_lock);
1136 repeat:
1137 	next = this_parent->d_subdirs.next;
1138 resume:
1139 	while (next != &this_parent->d_subdirs) {
1140 		struct list_head *tmp = next;
1141 		struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
1142 		next = tmp->next;
1143 
1144 		spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
1145 
1146 		/*
1147 		 * move only zero ref count dentries to the end
1148 		 * of the unused list for prune_dcache
1149 		 */
1150 		if (!dentry->d_count) {
1151 			dentry_lru_move_tail(dentry);
1152 			found++;
1153 		} else {
1154 			dentry_lru_del(dentry);
1155 		}
1156 
1157 		/*
1158 		 * We can return to the caller if we have found some (this
1159 		 * ensures forward progress). We'll be coming back to find
1160 		 * the rest.
1161 		 */
1162 		if (found && need_resched()) {
1163 			spin_unlock(&dentry->d_lock);
1164 			goto out;
1165 		}
1166 
1167 		/*
1168 		 * Descend a level if the d_subdirs list is non-empty.
1169 		 */
1170 		if (!list_empty(&dentry->d_subdirs)) {
1171 			spin_unlock(&this_parent->d_lock);
1172 			spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
1173 			this_parent = dentry;
1174 			spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
1175 			goto repeat;
1176 		}
1177 
1178 		spin_unlock(&dentry->d_lock);
1179 	}
1180 	/*
1181 	 * All done at this level ... ascend and resume the search.
1182 	 */
1183 	if (this_parent != parent) {
1184 		struct dentry *tmp;
1185 		struct dentry *child;
1186 
1187 		tmp = this_parent->d_parent;
1188 		rcu_read_lock();
1189 		spin_unlock(&this_parent->d_lock);
1190 		child = this_parent;
1191 		this_parent = tmp;
1192 		spin_lock(&this_parent->d_lock);
1193 		/* might go back up the wrong parent if we have had a rename
1194 		 * or deletion */
1195 		if (this_parent != child->d_parent ||
1196 			(!locked && read_seqretry(&rename_lock, seq))) {
1197 			spin_unlock(&this_parent->d_lock);
1198 			rcu_read_unlock();
1199 			goto rename_retry;
1200 		}
1201 		rcu_read_unlock();
1202 		next = child->d_u.d_child.next;
1203 		goto resume;
1204 	}
1205 out:
1206 	spin_unlock(&this_parent->d_lock);
1207 	if (!locked && read_seqretry(&rename_lock, seq))
1208 		goto rename_retry;
1209 	if (locked)
1210 		write_sequnlock(&rename_lock);
1211 	return found;
1212 
1213 rename_retry:
1214 	if (found)
1215 		return found;
1216 	locked = 1;
1217 	write_seqlock(&rename_lock);
1218 	goto again;
1219 }
1220 
1221 /**
1222  * shrink_dcache_parent - prune dcache
1223  * @parent: parent of entries to prune
1224  *
1225  * Prune the dcache to remove unused children of the parent dentry.
1226  */
1227 
1228 void shrink_dcache_parent(struct dentry * parent)
1229 {
1230 	struct super_block *sb = parent->d_sb;
1231 	int found;
1232 
1233 	while ((found = select_parent(parent)) != 0)
1234 		__shrink_dcache_sb(sb, &found, 0);
1235 }
1236 EXPORT_SYMBOL(shrink_dcache_parent);
1237 
1238 /*
1239  * Scan `nr' dentries and return the number which remain.
1240  *
1241  * We need to avoid reentering the filesystem if the caller is performing a
1242  * GFP_NOFS allocation attempt.  One example deadlock is:
1243  *
1244  * ext2_new_block->getblk->GFP->shrink_dcache_memory->prune_dcache->
1245  * prune_one_dentry->dput->dentry_iput->iput->inode->i_sb->s_op->put_inode->
1246  * ext2_discard_prealloc->ext2_free_blocks->lock_super->DEADLOCK.
1247  *
1248  * In this case we return -1 to tell the caller that we baled.
1249  */
1250 static int shrink_dcache_memory(struct shrinker *shrink, int nr, gfp_t gfp_mask)
1251 {
1252 	if (nr) {
1253 		if (!(gfp_mask & __GFP_FS))
1254 			return -1;
1255 		prune_dcache(nr);
1256 	}
1257 
1258 	return (dentry_stat.nr_unused / 100) * sysctl_vfs_cache_pressure;
1259 }
1260 
1261 static struct shrinker dcache_shrinker = {
1262 	.shrink = shrink_dcache_memory,
1263 	.seeks = DEFAULT_SEEKS,
1264 };
1265 
1266 /**
1267  * d_alloc	-	allocate a dcache entry
1268  * @parent: parent of entry to allocate
1269  * @name: qstr of the name
1270  *
1271  * Allocates a dentry. It returns %NULL if there is insufficient memory
1272  * available. On a success the dentry is returned. The name passed in is
1273  * copied and the copy passed in may be reused after this call.
1274  */
1275 
1276 struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
1277 {
1278 	struct dentry *dentry;
1279 	char *dname;
1280 
1281 	dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
1282 	if (!dentry)
1283 		return NULL;
1284 
1285 	if (name->len > DNAME_INLINE_LEN-1) {
1286 		dname = kmalloc(name->len + 1, GFP_KERNEL);
1287 		if (!dname) {
1288 			kmem_cache_free(dentry_cache, dentry);
1289 			return NULL;
1290 		}
1291 	} else  {
1292 		dname = dentry->d_iname;
1293 	}
1294 	dentry->d_name.name = dname;
1295 
1296 	dentry->d_name.len = name->len;
1297 	dentry->d_name.hash = name->hash;
1298 	memcpy(dname, name->name, name->len);
1299 	dname[name->len] = 0;
1300 
1301 	dentry->d_count = 1;
1302 	dentry->d_flags = DCACHE_UNHASHED;
1303 	spin_lock_init(&dentry->d_lock);
1304 	seqcount_init(&dentry->d_seq);
1305 	dentry->d_inode = NULL;
1306 	dentry->d_parent = NULL;
1307 	dentry->d_sb = NULL;
1308 	dentry->d_op = NULL;
1309 	dentry->d_fsdata = NULL;
1310 	INIT_HLIST_BL_NODE(&dentry->d_hash);
1311 	INIT_LIST_HEAD(&dentry->d_lru);
1312 	INIT_LIST_HEAD(&dentry->d_subdirs);
1313 	INIT_LIST_HEAD(&dentry->d_alias);
1314 	INIT_LIST_HEAD(&dentry->d_u.d_child);
1315 
1316 	if (parent) {
1317 		spin_lock(&parent->d_lock);
1318 		/*
1319 		 * don't need child lock because it is not subject
1320 		 * to concurrency here
1321 		 */
1322 		__dget_dlock(parent);
1323 		dentry->d_parent = parent;
1324 		dentry->d_sb = parent->d_sb;
1325 		d_set_d_op(dentry, dentry->d_sb->s_d_op);
1326 		list_add(&dentry->d_u.d_child, &parent->d_subdirs);
1327 		spin_unlock(&parent->d_lock);
1328 	}
1329 
1330 	this_cpu_inc(nr_dentry);
1331 
1332 	return dentry;
1333 }
1334 EXPORT_SYMBOL(d_alloc);
1335 
1336 struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
1337 {
1338 	struct dentry *dentry = d_alloc(NULL, name);
1339 	if (dentry) {
1340 		dentry->d_sb = sb;
1341 		d_set_d_op(dentry, dentry->d_sb->s_d_op);
1342 		dentry->d_parent = dentry;
1343 		dentry->d_flags |= DCACHE_DISCONNECTED;
1344 	}
1345 	return dentry;
1346 }
1347 EXPORT_SYMBOL(d_alloc_pseudo);
1348 
1349 struct dentry *d_alloc_name(struct dentry *parent, const char *name)
1350 {
1351 	struct qstr q;
1352 
1353 	q.name = name;
1354 	q.len = strlen(name);
1355 	q.hash = full_name_hash(q.name, q.len);
1356 	return d_alloc(parent, &q);
1357 }
1358 EXPORT_SYMBOL(d_alloc_name);
1359 
1360 void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
1361 {
1362 	WARN_ON_ONCE(dentry->d_op);
1363 	WARN_ON_ONCE(dentry->d_flags & (DCACHE_OP_HASH	|
1364 				DCACHE_OP_COMPARE	|
1365 				DCACHE_OP_REVALIDATE	|
1366 				DCACHE_OP_DELETE ));
1367 	dentry->d_op = op;
1368 	if (!op)
1369 		return;
1370 	if (op->d_hash)
1371 		dentry->d_flags |= DCACHE_OP_HASH;
1372 	if (op->d_compare)
1373 		dentry->d_flags |= DCACHE_OP_COMPARE;
1374 	if (op->d_revalidate)
1375 		dentry->d_flags |= DCACHE_OP_REVALIDATE;
1376 	if (op->d_delete)
1377 		dentry->d_flags |= DCACHE_OP_DELETE;
1378 
1379 }
1380 EXPORT_SYMBOL(d_set_d_op);
1381 
1382 static void __d_instantiate(struct dentry *dentry, struct inode *inode)
1383 {
1384 	spin_lock(&dentry->d_lock);
1385 	if (inode) {
1386 		if (unlikely(IS_AUTOMOUNT(inode)))
1387 			dentry->d_flags |= DCACHE_NEED_AUTOMOUNT;
1388 		list_add(&dentry->d_alias, &inode->i_dentry);
1389 	}
1390 	dentry->d_inode = inode;
1391 	dentry_rcuwalk_barrier(dentry);
1392 	spin_unlock(&dentry->d_lock);
1393 	fsnotify_d_instantiate(dentry, inode);
1394 }
1395 
1396 /**
1397  * d_instantiate - fill in inode information for a dentry
1398  * @entry: dentry to complete
1399  * @inode: inode to attach to this dentry
1400  *
1401  * Fill in inode information in the entry.
1402  *
1403  * This turns negative dentries into productive full members
1404  * of society.
1405  *
1406  * NOTE! This assumes that the inode count has been incremented
1407  * (or otherwise set) by the caller to indicate that it is now
1408  * in use by the dcache.
1409  */
1410 
1411 void d_instantiate(struct dentry *entry, struct inode * inode)
1412 {
1413 	BUG_ON(!list_empty(&entry->d_alias));
1414 	if (inode)
1415 		spin_lock(&inode->i_lock);
1416 	__d_instantiate(entry, inode);
1417 	if (inode)
1418 		spin_unlock(&inode->i_lock);
1419 	security_d_instantiate(entry, inode);
1420 }
1421 EXPORT_SYMBOL(d_instantiate);
1422 
1423 /**
1424  * d_instantiate_unique - instantiate a non-aliased dentry
1425  * @entry: dentry to instantiate
1426  * @inode: inode to attach to this dentry
1427  *
1428  * Fill in inode information in the entry. On success, it returns NULL.
1429  * If an unhashed alias of "entry" already exists, then we return the
1430  * aliased dentry instead and drop one reference to inode.
1431  *
1432  * Note that in order to avoid conflicts with rename() etc, the caller
1433  * had better be holding the parent directory semaphore.
1434  *
1435  * This also assumes that the inode count has been incremented
1436  * (or otherwise set) by the caller to indicate that it is now
1437  * in use by the dcache.
1438  */
1439 static struct dentry *__d_instantiate_unique(struct dentry *entry,
1440 					     struct inode *inode)
1441 {
1442 	struct dentry *alias;
1443 	int len = entry->d_name.len;
1444 	const char *name = entry->d_name.name;
1445 	unsigned int hash = entry->d_name.hash;
1446 
1447 	if (!inode) {
1448 		__d_instantiate(entry, NULL);
1449 		return NULL;
1450 	}
1451 
1452 	list_for_each_entry(alias, &inode->i_dentry, d_alias) {
1453 		struct qstr *qstr = &alias->d_name;
1454 
1455 		/*
1456 		 * Don't need alias->d_lock here, because aliases with
1457 		 * d_parent == entry->d_parent are not subject to name or
1458 		 * parent changes, because the parent inode i_mutex is held.
1459 		 */
1460 		if (qstr->hash != hash)
1461 			continue;
1462 		if (alias->d_parent != entry->d_parent)
1463 			continue;
1464 		if (dentry_cmp(qstr->name, qstr->len, name, len))
1465 			continue;
1466 		__dget(alias);
1467 		return alias;
1468 	}
1469 
1470 	__d_instantiate(entry, inode);
1471 	return NULL;
1472 }
1473 
1474 struct dentry *d_instantiate_unique(struct dentry *entry, struct inode *inode)
1475 {
1476 	struct dentry *result;
1477 
1478 	BUG_ON(!list_empty(&entry->d_alias));
1479 
1480 	if (inode)
1481 		spin_lock(&inode->i_lock);
1482 	result = __d_instantiate_unique(entry, inode);
1483 	if (inode)
1484 		spin_unlock(&inode->i_lock);
1485 
1486 	if (!result) {
1487 		security_d_instantiate(entry, inode);
1488 		return NULL;
1489 	}
1490 
1491 	BUG_ON(!d_unhashed(result));
1492 	iput(inode);
1493 	return result;
1494 }
1495 
1496 EXPORT_SYMBOL(d_instantiate_unique);
1497 
1498 /**
1499  * d_alloc_root - allocate root dentry
1500  * @root_inode: inode to allocate the root for
1501  *
1502  * Allocate a root ("/") dentry for the inode given. The inode is
1503  * instantiated and returned. %NULL is returned if there is insufficient
1504  * memory or the inode passed is %NULL.
1505  */
1506 
1507 struct dentry * d_alloc_root(struct inode * root_inode)
1508 {
1509 	struct dentry *res = NULL;
1510 
1511 	if (root_inode) {
1512 		static const struct qstr name = { .name = "/", .len = 1 };
1513 
1514 		res = d_alloc(NULL, &name);
1515 		if (res) {
1516 			res->d_sb = root_inode->i_sb;
1517 			d_set_d_op(res, res->d_sb->s_d_op);
1518 			res->d_parent = res;
1519 			d_instantiate(res, root_inode);
1520 		}
1521 	}
1522 	return res;
1523 }
1524 EXPORT_SYMBOL(d_alloc_root);
1525 
1526 static struct dentry * __d_find_any_alias(struct inode *inode)
1527 {
1528 	struct dentry *alias;
1529 
1530 	if (list_empty(&inode->i_dentry))
1531 		return NULL;
1532 	alias = list_first_entry(&inode->i_dentry, struct dentry, d_alias);
1533 	__dget(alias);
1534 	return alias;
1535 }
1536 
1537 static struct dentry * d_find_any_alias(struct inode *inode)
1538 {
1539 	struct dentry *de;
1540 
1541 	spin_lock(&inode->i_lock);
1542 	de = __d_find_any_alias(inode);
1543 	spin_unlock(&inode->i_lock);
1544 	return de;
1545 }
1546 
1547 
1548 /**
1549  * d_obtain_alias - find or allocate a dentry for a given inode
1550  * @inode: inode to allocate the dentry for
1551  *
1552  * Obtain a dentry for an inode resulting from NFS filehandle conversion or
1553  * similar open by handle operations.  The returned dentry may be anonymous,
1554  * or may have a full name (if the inode was already in the cache).
1555  *
1556  * When called on a directory inode, we must ensure that the inode only ever
1557  * has one dentry.  If a dentry is found, that is returned instead of
1558  * allocating a new one.
1559  *
1560  * On successful return, the reference to the inode has been transferred
1561  * to the dentry.  In case of an error the reference on the inode is released.
1562  * To make it easier to use in export operations a %NULL or IS_ERR inode may
1563  * be passed in and will be the error will be propagate to the return value,
1564  * with a %NULL @inode replaced by ERR_PTR(-ESTALE).
1565  */
1566 struct dentry *d_obtain_alias(struct inode *inode)
1567 {
1568 	static const struct qstr anonstring = { .name = "" };
1569 	struct dentry *tmp;
1570 	struct dentry *res;
1571 
1572 	if (!inode)
1573 		return ERR_PTR(-ESTALE);
1574 	if (IS_ERR(inode))
1575 		return ERR_CAST(inode);
1576 
1577 	res = d_find_any_alias(inode);
1578 	if (res)
1579 		goto out_iput;
1580 
1581 	tmp = d_alloc(NULL, &anonstring);
1582 	if (!tmp) {
1583 		res = ERR_PTR(-ENOMEM);
1584 		goto out_iput;
1585 	}
1586 	tmp->d_parent = tmp; /* make sure dput doesn't croak */
1587 
1588 
1589 	spin_lock(&inode->i_lock);
1590 	res = __d_find_any_alias(inode);
1591 	if (res) {
1592 		spin_unlock(&inode->i_lock);
1593 		dput(tmp);
1594 		goto out_iput;
1595 	}
1596 
1597 	/* attach a disconnected dentry */
1598 	spin_lock(&tmp->d_lock);
1599 	tmp->d_sb = inode->i_sb;
1600 	d_set_d_op(tmp, tmp->d_sb->s_d_op);
1601 	tmp->d_inode = inode;
1602 	tmp->d_flags |= DCACHE_DISCONNECTED;
1603 	list_add(&tmp->d_alias, &inode->i_dentry);
1604 	bit_spin_lock(0, (unsigned long *)&tmp->d_sb->s_anon.first);
1605 	tmp->d_flags &= ~DCACHE_UNHASHED;
1606 	hlist_bl_add_head(&tmp->d_hash, &tmp->d_sb->s_anon);
1607 	__bit_spin_unlock(0, (unsigned long *)&tmp->d_sb->s_anon.first);
1608 	spin_unlock(&tmp->d_lock);
1609 	spin_unlock(&inode->i_lock);
1610 
1611 	return tmp;
1612 
1613  out_iput:
1614 	iput(inode);
1615 	return res;
1616 }
1617 EXPORT_SYMBOL(d_obtain_alias);
1618 
1619 /**
1620  * d_splice_alias - splice a disconnected dentry into the tree if one exists
1621  * @inode:  the inode which may have a disconnected dentry
1622  * @dentry: a negative dentry which we want to point to the inode.
1623  *
1624  * If inode is a directory and has a 'disconnected' dentry (i.e. IS_ROOT and
1625  * DCACHE_DISCONNECTED), then d_move that in place of the given dentry
1626  * and return it, else simply d_add the inode to the dentry and return NULL.
1627  *
1628  * This is needed in the lookup routine of any filesystem that is exportable
1629  * (via knfsd) so that we can build dcache paths to directories effectively.
1630  *
1631  * If a dentry was found and moved, then it is returned.  Otherwise NULL
1632  * is returned.  This matches the expected return value of ->lookup.
1633  *
1634  */
1635 struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
1636 {
1637 	struct dentry *new = NULL;
1638 
1639 	if (inode && S_ISDIR(inode->i_mode)) {
1640 		spin_lock(&inode->i_lock);
1641 		new = __d_find_alias(inode, 1);
1642 		if (new) {
1643 			BUG_ON(!(new->d_flags & DCACHE_DISCONNECTED));
1644 			spin_unlock(&inode->i_lock);
1645 			security_d_instantiate(new, inode);
1646 			d_move(new, dentry);
1647 			iput(inode);
1648 		} else {
1649 			/* already taking inode->i_lock, so d_add() by hand */
1650 			__d_instantiate(dentry, inode);
1651 			spin_unlock(&inode->i_lock);
1652 			security_d_instantiate(dentry, inode);
1653 			d_rehash(dentry);
1654 		}
1655 	} else
1656 		d_add(dentry, inode);
1657 	return new;
1658 }
1659 EXPORT_SYMBOL(d_splice_alias);
1660 
1661 /**
1662  * d_add_ci - lookup or allocate new dentry with case-exact name
1663  * @inode:  the inode case-insensitive lookup has found
1664  * @dentry: the negative dentry that was passed to the parent's lookup func
1665  * @name:   the case-exact name to be associated with the returned dentry
1666  *
1667  * This is to avoid filling the dcache with case-insensitive names to the
1668  * same inode, only the actual correct case is stored in the dcache for
1669  * case-insensitive filesystems.
1670  *
1671  * For a case-insensitive lookup match and if the the case-exact dentry
1672  * already exists in in the dcache, use it and return it.
1673  *
1674  * If no entry exists with the exact case name, allocate new dentry with
1675  * the exact case, and return the spliced entry.
1676  */
1677 struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
1678 			struct qstr *name)
1679 {
1680 	int error;
1681 	struct dentry *found;
1682 	struct dentry *new;
1683 
1684 	/*
1685 	 * First check if a dentry matching the name already exists,
1686 	 * if not go ahead and create it now.
1687 	 */
1688 	found = d_hash_and_lookup(dentry->d_parent, name);
1689 	if (!found) {
1690 		new = d_alloc(dentry->d_parent, name);
1691 		if (!new) {
1692 			error = -ENOMEM;
1693 			goto err_out;
1694 		}
1695 
1696 		found = d_splice_alias(inode, new);
1697 		if (found) {
1698 			dput(new);
1699 			return found;
1700 		}
1701 		return new;
1702 	}
1703 
1704 	/*
1705 	 * If a matching dentry exists, and it's not negative use it.
1706 	 *
1707 	 * Decrement the reference count to balance the iget() done
1708 	 * earlier on.
1709 	 */
1710 	if (found->d_inode) {
1711 		if (unlikely(found->d_inode != inode)) {
1712 			/* This can't happen because bad inodes are unhashed. */
1713 			BUG_ON(!is_bad_inode(inode));
1714 			BUG_ON(!is_bad_inode(found->d_inode));
1715 		}
1716 		iput(inode);
1717 		return found;
1718 	}
1719 
1720 	/*
1721 	 * Negative dentry: instantiate it unless the inode is a directory and
1722 	 * already has a dentry.
1723 	 */
1724 	spin_lock(&inode->i_lock);
1725 	if (!S_ISDIR(inode->i_mode) || list_empty(&inode->i_dentry)) {
1726 		__d_instantiate(found, inode);
1727 		spin_unlock(&inode->i_lock);
1728 		security_d_instantiate(found, inode);
1729 		return found;
1730 	}
1731 
1732 	/*
1733 	 * In case a directory already has a (disconnected) entry grab a
1734 	 * reference to it, move it in place and use it.
1735 	 */
1736 	new = list_entry(inode->i_dentry.next, struct dentry, d_alias);
1737 	__dget(new);
1738 	spin_unlock(&inode->i_lock);
1739 	security_d_instantiate(found, inode);
1740 	d_move(new, found);
1741 	iput(inode);
1742 	dput(found);
1743 	return new;
1744 
1745 err_out:
1746 	iput(inode);
1747 	return ERR_PTR(error);
1748 }
1749 EXPORT_SYMBOL(d_add_ci);
1750 
1751 /**
1752  * __d_lookup_rcu - search for a dentry (racy, store-free)
1753  * @parent: parent dentry
1754  * @name: qstr of name we wish to find
1755  * @seq: returns d_seq value at the point where the dentry was found
1756  * @inode: returns dentry->d_inode when the inode was found valid.
1757  * Returns: dentry, or NULL
1758  *
1759  * __d_lookup_rcu is the dcache lookup function for rcu-walk name
1760  * resolution (store-free path walking) design described in
1761  * Documentation/filesystems/path-lookup.txt.
1762  *
1763  * This is not to be used outside core vfs.
1764  *
1765  * __d_lookup_rcu must only be used in rcu-walk mode, ie. with vfsmount lock
1766  * held, and rcu_read_lock held. The returned dentry must not be stored into
1767  * without taking d_lock and checking d_seq sequence count against @seq
1768  * returned here.
1769  *
1770  * A refcount may be taken on the found dentry with the __d_rcu_to_refcount
1771  * function.
1772  *
1773  * Alternatively, __d_lookup_rcu may be called again to look up the child of
1774  * the returned dentry, so long as its parent's seqlock is checked after the
1775  * child is looked up. Thus, an interlocking stepping of sequence lock checks
1776  * is formed, giving integrity down the path walk.
1777  */
1778 struct dentry *__d_lookup_rcu(struct dentry *parent, struct qstr *name,
1779 				unsigned *seq, struct inode **inode)
1780 {
1781 	unsigned int len = name->len;
1782 	unsigned int hash = name->hash;
1783 	const unsigned char *str = name->name;
1784 	struct dcache_hash_bucket *b = d_hash(parent, hash);
1785 	struct hlist_bl_node *node;
1786 	struct dentry *dentry;
1787 
1788 	/*
1789 	 * Note: There is significant duplication with __d_lookup_rcu which is
1790 	 * required to prevent single threaded performance regressions
1791 	 * especially on architectures where smp_rmb (in seqcounts) are costly.
1792 	 * Keep the two functions in sync.
1793 	 */
1794 
1795 	/*
1796 	 * The hash list is protected using RCU.
1797 	 *
1798 	 * Carefully use d_seq when comparing a candidate dentry, to avoid
1799 	 * races with d_move().
1800 	 *
1801 	 * It is possible that concurrent renames can mess up our list
1802 	 * walk here and result in missing our dentry, resulting in the
1803 	 * false-negative result. d_lookup() protects against concurrent
1804 	 * renames using rename_lock seqlock.
1805 	 *
1806 	 * See Documentation/vfs/dcache-locking.txt for more details.
1807 	 */
1808 	hlist_bl_for_each_entry_rcu(dentry, node, &b->head, d_hash) {
1809 		struct inode *i;
1810 		const char *tname;
1811 		int tlen;
1812 
1813 		if (dentry->d_name.hash != hash)
1814 			continue;
1815 
1816 seqretry:
1817 		*seq = read_seqcount_begin(&dentry->d_seq);
1818 		if (dentry->d_parent != parent)
1819 			continue;
1820 		if (d_unhashed(dentry))
1821 			continue;
1822 		tlen = dentry->d_name.len;
1823 		tname = dentry->d_name.name;
1824 		i = dentry->d_inode;
1825 		prefetch(tname);
1826 		if (i)
1827 			prefetch(i);
1828 		/*
1829 		 * This seqcount check is required to ensure name and
1830 		 * len are loaded atomically, so as not to walk off the
1831 		 * edge of memory when walking. If we could load this
1832 		 * atomically some other way, we could drop this check.
1833 		 */
1834 		if (read_seqcount_retry(&dentry->d_seq, *seq))
1835 			goto seqretry;
1836 		if (parent->d_flags & DCACHE_OP_COMPARE) {
1837 			if (parent->d_op->d_compare(parent, *inode,
1838 						dentry, i,
1839 						tlen, tname, name))
1840 				continue;
1841 		} else {
1842 			if (dentry_cmp(tname, tlen, str, len))
1843 				continue;
1844 		}
1845 		/*
1846 		 * No extra seqcount check is required after the name
1847 		 * compare. The caller must perform a seqcount check in
1848 		 * order to do anything useful with the returned dentry
1849 		 * anyway.
1850 		 */
1851 		*inode = i;
1852 		return dentry;
1853 	}
1854 	return NULL;
1855 }
1856 
1857 /**
1858  * d_lookup - search for a dentry
1859  * @parent: parent dentry
1860  * @name: qstr of name we wish to find
1861  * Returns: dentry, or NULL
1862  *
1863  * d_lookup searches the children of the parent dentry for the name in
1864  * question. If the dentry is found its reference count is incremented and the
1865  * dentry is returned. The caller must use dput to free the entry when it has
1866  * finished using it. %NULL is returned if the dentry does not exist.
1867  */
1868 struct dentry *d_lookup(struct dentry *parent, struct qstr *name)
1869 {
1870 	struct dentry *dentry;
1871 	unsigned seq;
1872 
1873         do {
1874                 seq = read_seqbegin(&rename_lock);
1875                 dentry = __d_lookup(parent, name);
1876                 if (dentry)
1877 			break;
1878 	} while (read_seqretry(&rename_lock, seq));
1879 	return dentry;
1880 }
1881 EXPORT_SYMBOL(d_lookup);
1882 
1883 /**
1884  * __d_lookup - search for a dentry (racy)
1885  * @parent: parent dentry
1886  * @name: qstr of name we wish to find
1887  * Returns: dentry, or NULL
1888  *
1889  * __d_lookup is like d_lookup, however it may (rarely) return a
1890  * false-negative result due to unrelated rename activity.
1891  *
1892  * __d_lookup is slightly faster by avoiding rename_lock read seqlock,
1893  * however it must be used carefully, eg. with a following d_lookup in
1894  * the case of failure.
1895  *
1896  * __d_lookup callers must be commented.
1897  */
1898 struct dentry *__d_lookup(struct dentry *parent, struct qstr *name)
1899 {
1900 	unsigned int len = name->len;
1901 	unsigned int hash = name->hash;
1902 	const unsigned char *str = name->name;
1903 	struct dcache_hash_bucket *b = d_hash(parent, hash);
1904 	struct hlist_bl_node *node;
1905 	struct dentry *found = NULL;
1906 	struct dentry *dentry;
1907 
1908 	/*
1909 	 * Note: There is significant duplication with __d_lookup_rcu which is
1910 	 * required to prevent single threaded performance regressions
1911 	 * especially on architectures where smp_rmb (in seqcounts) are costly.
1912 	 * Keep the two functions in sync.
1913 	 */
1914 
1915 	/*
1916 	 * The hash list is protected using RCU.
1917 	 *
1918 	 * Take d_lock when comparing a candidate dentry, to avoid races
1919 	 * with d_move().
1920 	 *
1921 	 * It is possible that concurrent renames can mess up our list
1922 	 * walk here and result in missing our dentry, resulting in the
1923 	 * false-negative result. d_lookup() protects against concurrent
1924 	 * renames using rename_lock seqlock.
1925 	 *
1926 	 * See Documentation/vfs/dcache-locking.txt for more details.
1927 	 */
1928 	rcu_read_lock();
1929 
1930 	hlist_bl_for_each_entry_rcu(dentry, node, &b->head, d_hash) {
1931 		const char *tname;
1932 		int tlen;
1933 
1934 		if (dentry->d_name.hash != hash)
1935 			continue;
1936 
1937 		spin_lock(&dentry->d_lock);
1938 		if (dentry->d_parent != parent)
1939 			goto next;
1940 		if (d_unhashed(dentry))
1941 			goto next;
1942 
1943 		/*
1944 		 * It is safe to compare names since d_move() cannot
1945 		 * change the qstr (protected by d_lock).
1946 		 */
1947 		tlen = dentry->d_name.len;
1948 		tname = dentry->d_name.name;
1949 		if (parent->d_flags & DCACHE_OP_COMPARE) {
1950 			if (parent->d_op->d_compare(parent, parent->d_inode,
1951 						dentry, dentry->d_inode,
1952 						tlen, tname, name))
1953 				goto next;
1954 		} else {
1955 			if (dentry_cmp(tname, tlen, str, len))
1956 				goto next;
1957 		}
1958 
1959 		dentry->d_count++;
1960 		found = dentry;
1961 		spin_unlock(&dentry->d_lock);
1962 		break;
1963 next:
1964 		spin_unlock(&dentry->d_lock);
1965  	}
1966  	rcu_read_unlock();
1967 
1968  	return found;
1969 }
1970 
1971 /**
1972  * d_hash_and_lookup - hash the qstr then search for a dentry
1973  * @dir: Directory to search in
1974  * @name: qstr of name we wish to find
1975  *
1976  * On hash failure or on lookup failure NULL is returned.
1977  */
1978 struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
1979 {
1980 	struct dentry *dentry = NULL;
1981 
1982 	/*
1983 	 * Check for a fs-specific hash function. Note that we must
1984 	 * calculate the standard hash first, as the d_op->d_hash()
1985 	 * routine may choose to leave the hash value unchanged.
1986 	 */
1987 	name->hash = full_name_hash(name->name, name->len);
1988 	if (dir->d_flags & DCACHE_OP_HASH) {
1989 		if (dir->d_op->d_hash(dir, dir->d_inode, name) < 0)
1990 			goto out;
1991 	}
1992 	dentry = d_lookup(dir, name);
1993 out:
1994 	return dentry;
1995 }
1996 
1997 /**
1998  * d_validate - verify dentry provided from insecure source (deprecated)
1999  * @dentry: The dentry alleged to be valid child of @dparent
2000  * @dparent: The parent dentry (known to be valid)
2001  *
2002  * An insecure source has sent us a dentry, here we verify it and dget() it.
2003  * This is used by ncpfs in its readdir implementation.
2004  * Zero is returned in the dentry is invalid.
2005  *
2006  * This function is slow for big directories, and deprecated, do not use it.
2007  */
2008 int d_validate(struct dentry *dentry, struct dentry *dparent)
2009 {
2010 	struct dentry *child;
2011 
2012 	spin_lock(&dparent->d_lock);
2013 	list_for_each_entry(child, &dparent->d_subdirs, d_u.d_child) {
2014 		if (dentry == child) {
2015 			spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
2016 			__dget_dlock(dentry);
2017 			spin_unlock(&dentry->d_lock);
2018 			spin_unlock(&dparent->d_lock);
2019 			return 1;
2020 		}
2021 	}
2022 	spin_unlock(&dparent->d_lock);
2023 
2024 	return 0;
2025 }
2026 EXPORT_SYMBOL(d_validate);
2027 
2028 /*
2029  * When a file is deleted, we have two options:
2030  * - turn this dentry into a negative dentry
2031  * - unhash this dentry and free it.
2032  *
2033  * Usually, we want to just turn this into
2034  * a negative dentry, but if anybody else is
2035  * currently using the dentry or the inode
2036  * we can't do that and we fall back on removing
2037  * it from the hash queues and waiting for
2038  * it to be deleted later when it has no users
2039  */
2040 
2041 /**
2042  * d_delete - delete a dentry
2043  * @dentry: The dentry to delete
2044  *
2045  * Turn the dentry into a negative dentry if possible, otherwise
2046  * remove it from the hash queues so it can be deleted later
2047  */
2048 
2049 void d_delete(struct dentry * dentry)
2050 {
2051 	struct inode *inode;
2052 	int isdir = 0;
2053 	/*
2054 	 * Are we the only user?
2055 	 */
2056 again:
2057 	spin_lock(&dentry->d_lock);
2058 	inode = dentry->d_inode;
2059 	isdir = S_ISDIR(inode->i_mode);
2060 	if (dentry->d_count == 1) {
2061 		if (inode && !spin_trylock(&inode->i_lock)) {
2062 			spin_unlock(&dentry->d_lock);
2063 			cpu_relax();
2064 			goto again;
2065 		}
2066 		dentry->d_flags &= ~DCACHE_CANT_MOUNT;
2067 		dentry_unlink_inode(dentry);
2068 		fsnotify_nameremove(dentry, isdir);
2069 		return;
2070 	}
2071 
2072 	if (!d_unhashed(dentry))
2073 		__d_drop(dentry);
2074 
2075 	spin_unlock(&dentry->d_lock);
2076 
2077 	fsnotify_nameremove(dentry, isdir);
2078 }
2079 EXPORT_SYMBOL(d_delete);
2080 
2081 static void __d_rehash(struct dentry * entry, struct dcache_hash_bucket *b)
2082 {
2083 	BUG_ON(!d_unhashed(entry));
2084 	spin_lock_bucket(b);
2085  	entry->d_flags &= ~DCACHE_UNHASHED;
2086 	hlist_bl_add_head_rcu(&entry->d_hash, &b->head);
2087 	spin_unlock_bucket(b);
2088 }
2089 
2090 static void _d_rehash(struct dentry * entry)
2091 {
2092 	__d_rehash(entry, d_hash(entry->d_parent, entry->d_name.hash));
2093 }
2094 
2095 /**
2096  * d_rehash	- add an entry back to the hash
2097  * @entry: dentry to add to the hash
2098  *
2099  * Adds a dentry to the hash according to its name.
2100  */
2101 
2102 void d_rehash(struct dentry * entry)
2103 {
2104 	spin_lock(&entry->d_lock);
2105 	_d_rehash(entry);
2106 	spin_unlock(&entry->d_lock);
2107 }
2108 EXPORT_SYMBOL(d_rehash);
2109 
2110 /**
2111  * dentry_update_name_case - update case insensitive dentry with a new name
2112  * @dentry: dentry to be updated
2113  * @name: new name
2114  *
2115  * Update a case insensitive dentry with new case of name.
2116  *
2117  * dentry must have been returned by d_lookup with name @name. Old and new
2118  * name lengths must match (ie. no d_compare which allows mismatched name
2119  * lengths).
2120  *
2121  * Parent inode i_mutex must be held over d_lookup and into this call (to
2122  * keep renames and concurrent inserts, and readdir(2) away).
2123  */
2124 void dentry_update_name_case(struct dentry *dentry, struct qstr *name)
2125 {
2126 	BUG_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
2127 	BUG_ON(dentry->d_name.len != name->len); /* d_lookup gives this */
2128 
2129 	spin_lock(&dentry->d_lock);
2130 	write_seqcount_begin(&dentry->d_seq);
2131 	memcpy((unsigned char *)dentry->d_name.name, name->name, name->len);
2132 	write_seqcount_end(&dentry->d_seq);
2133 	spin_unlock(&dentry->d_lock);
2134 }
2135 EXPORT_SYMBOL(dentry_update_name_case);
2136 
2137 static void switch_names(struct dentry *dentry, struct dentry *target)
2138 {
2139 	if (dname_external(target)) {
2140 		if (dname_external(dentry)) {
2141 			/*
2142 			 * Both external: swap the pointers
2143 			 */
2144 			swap(target->d_name.name, dentry->d_name.name);
2145 		} else {
2146 			/*
2147 			 * dentry:internal, target:external.  Steal target's
2148 			 * storage and make target internal.
2149 			 */
2150 			memcpy(target->d_iname, dentry->d_name.name,
2151 					dentry->d_name.len + 1);
2152 			dentry->d_name.name = target->d_name.name;
2153 			target->d_name.name = target->d_iname;
2154 		}
2155 	} else {
2156 		if (dname_external(dentry)) {
2157 			/*
2158 			 * dentry:external, target:internal.  Give dentry's
2159 			 * storage to target and make dentry internal
2160 			 */
2161 			memcpy(dentry->d_iname, target->d_name.name,
2162 					target->d_name.len + 1);
2163 			target->d_name.name = dentry->d_name.name;
2164 			dentry->d_name.name = dentry->d_iname;
2165 		} else {
2166 			/*
2167 			 * Both are internal.  Just copy target to dentry
2168 			 */
2169 			memcpy(dentry->d_iname, target->d_name.name,
2170 					target->d_name.len + 1);
2171 			dentry->d_name.len = target->d_name.len;
2172 			return;
2173 		}
2174 	}
2175 	swap(dentry->d_name.len, target->d_name.len);
2176 }
2177 
2178 static void dentry_lock_for_move(struct dentry *dentry, struct dentry *target)
2179 {
2180 	/*
2181 	 * XXXX: do we really need to take target->d_lock?
2182 	 */
2183 	if (IS_ROOT(dentry) || dentry->d_parent == target->d_parent)
2184 		spin_lock(&target->d_parent->d_lock);
2185 	else {
2186 		if (d_ancestor(dentry->d_parent, target->d_parent)) {
2187 			spin_lock(&dentry->d_parent->d_lock);
2188 			spin_lock_nested(&target->d_parent->d_lock,
2189 						DENTRY_D_LOCK_NESTED);
2190 		} else {
2191 			spin_lock(&target->d_parent->d_lock);
2192 			spin_lock_nested(&dentry->d_parent->d_lock,
2193 						DENTRY_D_LOCK_NESTED);
2194 		}
2195 	}
2196 	if (target < dentry) {
2197 		spin_lock_nested(&target->d_lock, 2);
2198 		spin_lock_nested(&dentry->d_lock, 3);
2199 	} else {
2200 		spin_lock_nested(&dentry->d_lock, 2);
2201 		spin_lock_nested(&target->d_lock, 3);
2202 	}
2203 }
2204 
2205 static void dentry_unlock_parents_for_move(struct dentry *dentry,
2206 					struct dentry *target)
2207 {
2208 	if (target->d_parent != dentry->d_parent)
2209 		spin_unlock(&dentry->d_parent->d_lock);
2210 	if (target->d_parent != target)
2211 		spin_unlock(&target->d_parent->d_lock);
2212 }
2213 
2214 /*
2215  * When switching names, the actual string doesn't strictly have to
2216  * be preserved in the target - because we're dropping the target
2217  * anyway. As such, we can just do a simple memcpy() to copy over
2218  * the new name before we switch.
2219  *
2220  * Note that we have to be a lot more careful about getting the hash
2221  * switched - we have to switch the hash value properly even if it
2222  * then no longer matches the actual (corrupted) string of the target.
2223  * The hash value has to match the hash queue that the dentry is on..
2224  */
2225 /*
2226  * d_move - move a dentry
2227  * @dentry: entry to move
2228  * @target: new dentry
2229  *
2230  * Update the dcache to reflect the move of a file name. Negative
2231  * dcache entries should not be moved in this way.
2232  */
2233 void d_move(struct dentry * dentry, struct dentry * target)
2234 {
2235 	if (!dentry->d_inode)
2236 		printk(KERN_WARNING "VFS: moving negative dcache entry\n");
2237 
2238 	BUG_ON(d_ancestor(dentry, target));
2239 	BUG_ON(d_ancestor(target, dentry));
2240 
2241 	write_seqlock(&rename_lock);
2242 
2243 	dentry_lock_for_move(dentry, target);
2244 
2245 	write_seqcount_begin(&dentry->d_seq);
2246 	write_seqcount_begin(&target->d_seq);
2247 
2248 	/* __d_drop does write_seqcount_barrier, but they're OK to nest. */
2249 
2250 	/*
2251 	 * Move the dentry to the target hash queue. Don't bother checking
2252 	 * for the same hash queue because of how unlikely it is.
2253 	 */
2254 	__d_drop(dentry);
2255 	__d_rehash(dentry, d_hash(target->d_parent, target->d_name.hash));
2256 
2257 	/* Unhash the target: dput() will then get rid of it */
2258 	__d_drop(target);
2259 
2260 	list_del(&dentry->d_u.d_child);
2261 	list_del(&target->d_u.d_child);
2262 
2263 	/* Switch the names.. */
2264 	switch_names(dentry, target);
2265 	swap(dentry->d_name.hash, target->d_name.hash);
2266 
2267 	/* ... and switch the parents */
2268 	if (IS_ROOT(dentry)) {
2269 		dentry->d_parent = target->d_parent;
2270 		target->d_parent = target;
2271 		INIT_LIST_HEAD(&target->d_u.d_child);
2272 	} else {
2273 		swap(dentry->d_parent, target->d_parent);
2274 
2275 		/* And add them back to the (new) parent lists */
2276 		list_add(&target->d_u.d_child, &target->d_parent->d_subdirs);
2277 	}
2278 
2279 	list_add(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
2280 
2281 	write_seqcount_end(&target->d_seq);
2282 	write_seqcount_end(&dentry->d_seq);
2283 
2284 	dentry_unlock_parents_for_move(dentry, target);
2285 	spin_unlock(&target->d_lock);
2286 	fsnotify_d_move(dentry);
2287 	spin_unlock(&dentry->d_lock);
2288 	write_sequnlock(&rename_lock);
2289 }
2290 EXPORT_SYMBOL(d_move);
2291 
2292 /**
2293  * d_ancestor - search for an ancestor
2294  * @p1: ancestor dentry
2295  * @p2: child dentry
2296  *
2297  * Returns the ancestor dentry of p2 which is a child of p1, if p1 is
2298  * an ancestor of p2, else NULL.
2299  */
2300 struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
2301 {
2302 	struct dentry *p;
2303 
2304 	for (p = p2; !IS_ROOT(p); p = p->d_parent) {
2305 		if (p->d_parent == p1)
2306 			return p;
2307 	}
2308 	return NULL;
2309 }
2310 
2311 /*
2312  * This helper attempts to cope with remotely renamed directories
2313  *
2314  * It assumes that the caller is already holding
2315  * dentry->d_parent->d_inode->i_mutex and the inode->i_lock
2316  *
2317  * Note: If ever the locking in lock_rename() changes, then please
2318  * remember to update this too...
2319  */
2320 static struct dentry *__d_unalias(struct inode *inode,
2321 		struct dentry *dentry, struct dentry *alias)
2322 {
2323 	struct mutex *m1 = NULL, *m2 = NULL;
2324 	struct dentry *ret;
2325 
2326 	/* If alias and dentry share a parent, then no extra locks required */
2327 	if (alias->d_parent == dentry->d_parent)
2328 		goto out_unalias;
2329 
2330 	/* Check for loops */
2331 	ret = ERR_PTR(-ELOOP);
2332 	if (d_ancestor(alias, dentry))
2333 		goto out_err;
2334 
2335 	/* See lock_rename() */
2336 	ret = ERR_PTR(-EBUSY);
2337 	if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
2338 		goto out_err;
2339 	m1 = &dentry->d_sb->s_vfs_rename_mutex;
2340 	if (!mutex_trylock(&alias->d_parent->d_inode->i_mutex))
2341 		goto out_err;
2342 	m2 = &alias->d_parent->d_inode->i_mutex;
2343 out_unalias:
2344 	d_move(alias, dentry);
2345 	ret = alias;
2346 out_err:
2347 	spin_unlock(&inode->i_lock);
2348 	if (m2)
2349 		mutex_unlock(m2);
2350 	if (m1)
2351 		mutex_unlock(m1);
2352 	return ret;
2353 }
2354 
2355 /*
2356  * Prepare an anonymous dentry for life in the superblock's dentry tree as a
2357  * named dentry in place of the dentry to be replaced.
2358  * returns with anon->d_lock held!
2359  */
2360 static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
2361 {
2362 	struct dentry *dparent, *aparent;
2363 
2364 	dentry_lock_for_move(anon, dentry);
2365 
2366 	write_seqcount_begin(&dentry->d_seq);
2367 	write_seqcount_begin(&anon->d_seq);
2368 
2369 	dparent = dentry->d_parent;
2370 	aparent = anon->d_parent;
2371 
2372 	switch_names(dentry, anon);
2373 	swap(dentry->d_name.hash, anon->d_name.hash);
2374 
2375 	dentry->d_parent = (aparent == anon) ? dentry : aparent;
2376 	list_del(&dentry->d_u.d_child);
2377 	if (!IS_ROOT(dentry))
2378 		list_add(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
2379 	else
2380 		INIT_LIST_HEAD(&dentry->d_u.d_child);
2381 
2382 	anon->d_parent = (dparent == dentry) ? anon : dparent;
2383 	list_del(&anon->d_u.d_child);
2384 	if (!IS_ROOT(anon))
2385 		list_add(&anon->d_u.d_child, &anon->d_parent->d_subdirs);
2386 	else
2387 		INIT_LIST_HEAD(&anon->d_u.d_child);
2388 
2389 	write_seqcount_end(&dentry->d_seq);
2390 	write_seqcount_end(&anon->d_seq);
2391 
2392 	dentry_unlock_parents_for_move(anon, dentry);
2393 	spin_unlock(&dentry->d_lock);
2394 
2395 	/* anon->d_lock still locked, returns locked */
2396 	anon->d_flags &= ~DCACHE_DISCONNECTED;
2397 }
2398 
2399 /**
2400  * d_materialise_unique - introduce an inode into the tree
2401  * @dentry: candidate dentry
2402  * @inode: inode to bind to the dentry, to which aliases may be attached
2403  *
2404  * Introduces an dentry into the tree, substituting an extant disconnected
2405  * root directory alias in its place if there is one
2406  */
2407 struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode)
2408 {
2409 	struct dentry *actual;
2410 
2411 	BUG_ON(!d_unhashed(dentry));
2412 
2413 	if (!inode) {
2414 		actual = dentry;
2415 		__d_instantiate(dentry, NULL);
2416 		d_rehash(actual);
2417 		goto out_nolock;
2418 	}
2419 
2420 	spin_lock(&inode->i_lock);
2421 
2422 	if (S_ISDIR(inode->i_mode)) {
2423 		struct dentry *alias;
2424 
2425 		/* Does an aliased dentry already exist? */
2426 		alias = __d_find_alias(inode, 0);
2427 		if (alias) {
2428 			actual = alias;
2429 			/* Is this an anonymous mountpoint that we could splice
2430 			 * into our tree? */
2431 			if (IS_ROOT(alias)) {
2432 				__d_materialise_dentry(dentry, alias);
2433 				__d_drop(alias);
2434 				goto found;
2435 			}
2436 			/* Nope, but we must(!) avoid directory aliasing */
2437 			actual = __d_unalias(inode, dentry, alias);
2438 			if (IS_ERR(actual))
2439 				dput(alias);
2440 			goto out_nolock;
2441 		}
2442 	}
2443 
2444 	/* Add a unique reference */
2445 	actual = __d_instantiate_unique(dentry, inode);
2446 	if (!actual)
2447 		actual = dentry;
2448 	else
2449 		BUG_ON(!d_unhashed(actual));
2450 
2451 	spin_lock(&actual->d_lock);
2452 found:
2453 	_d_rehash(actual);
2454 	spin_unlock(&actual->d_lock);
2455 	spin_unlock(&inode->i_lock);
2456 out_nolock:
2457 	if (actual == dentry) {
2458 		security_d_instantiate(dentry, inode);
2459 		return NULL;
2460 	}
2461 
2462 	iput(inode);
2463 	return actual;
2464 }
2465 EXPORT_SYMBOL_GPL(d_materialise_unique);
2466 
2467 static int prepend(char **buffer, int *buflen, const char *str, int namelen)
2468 {
2469 	*buflen -= namelen;
2470 	if (*buflen < 0)
2471 		return -ENAMETOOLONG;
2472 	*buffer -= namelen;
2473 	memcpy(*buffer, str, namelen);
2474 	return 0;
2475 }
2476 
2477 static int prepend_name(char **buffer, int *buflen, struct qstr *name)
2478 {
2479 	return prepend(buffer, buflen, name->name, name->len);
2480 }
2481 
2482 /**
2483  * prepend_path - Prepend path string to a buffer
2484  * @path: the dentry/vfsmount to report
2485  * @root: root vfsmnt/dentry (may be modified by this function)
2486  * @buffer: pointer to the end of the buffer
2487  * @buflen: pointer to buffer length
2488  *
2489  * Caller holds the rename_lock.
2490  *
2491  * If path is not reachable from the supplied root, then the value of
2492  * root is changed (without modifying refcounts).
2493  */
2494 static int prepend_path(const struct path *path, struct path *root,
2495 			char **buffer, int *buflen)
2496 {
2497 	struct dentry *dentry = path->dentry;
2498 	struct vfsmount *vfsmnt = path->mnt;
2499 	bool slash = false;
2500 	int error = 0;
2501 
2502 	br_read_lock(vfsmount_lock);
2503 	while (dentry != root->dentry || vfsmnt != root->mnt) {
2504 		struct dentry * parent;
2505 
2506 		if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
2507 			/* Global root? */
2508 			if (vfsmnt->mnt_parent == vfsmnt) {
2509 				goto global_root;
2510 			}
2511 			dentry = vfsmnt->mnt_mountpoint;
2512 			vfsmnt = vfsmnt->mnt_parent;
2513 			continue;
2514 		}
2515 		parent = dentry->d_parent;
2516 		prefetch(parent);
2517 		spin_lock(&dentry->d_lock);
2518 		error = prepend_name(buffer, buflen, &dentry->d_name);
2519 		spin_unlock(&dentry->d_lock);
2520 		if (!error)
2521 			error = prepend(buffer, buflen, "/", 1);
2522 		if (error)
2523 			break;
2524 
2525 		slash = true;
2526 		dentry = parent;
2527 	}
2528 
2529 out:
2530 	if (!error && !slash)
2531 		error = prepend(buffer, buflen, "/", 1);
2532 
2533 	br_read_unlock(vfsmount_lock);
2534 	return error;
2535 
2536 global_root:
2537 	/*
2538 	 * Filesystems needing to implement special "root names"
2539 	 * should do so with ->d_dname()
2540 	 */
2541 	if (IS_ROOT(dentry) &&
2542 	    (dentry->d_name.len != 1 || dentry->d_name.name[0] != '/')) {
2543 		WARN(1, "Root dentry has weird name <%.*s>\n",
2544 		     (int) dentry->d_name.len, dentry->d_name.name);
2545 	}
2546 	root->mnt = vfsmnt;
2547 	root->dentry = dentry;
2548 	goto out;
2549 }
2550 
2551 /**
2552  * __d_path - return the path of a dentry
2553  * @path: the dentry/vfsmount to report
2554  * @root: root vfsmnt/dentry (may be modified by this function)
2555  * @buf: buffer to return value in
2556  * @buflen: buffer length
2557  *
2558  * Convert a dentry into an ASCII path name.
2559  *
2560  * Returns a pointer into the buffer or an error code if the
2561  * path was too long.
2562  *
2563  * "buflen" should be positive.
2564  *
2565  * If path is not reachable from the supplied root, then the value of
2566  * root is changed (without modifying refcounts).
2567  */
2568 char *__d_path(const struct path *path, struct path *root,
2569 	       char *buf, int buflen)
2570 {
2571 	char *res = buf + buflen;
2572 	int error;
2573 
2574 	prepend(&res, &buflen, "\0", 1);
2575 	write_seqlock(&rename_lock);
2576 	error = prepend_path(path, root, &res, &buflen);
2577 	write_sequnlock(&rename_lock);
2578 
2579 	if (error)
2580 		return ERR_PTR(error);
2581 	return res;
2582 }
2583 
2584 /*
2585  * same as __d_path but appends "(deleted)" for unlinked files.
2586  */
2587 static int path_with_deleted(const struct path *path, struct path *root,
2588 				 char **buf, int *buflen)
2589 {
2590 	prepend(buf, buflen, "\0", 1);
2591 	if (d_unlinked(path->dentry)) {
2592 		int error = prepend(buf, buflen, " (deleted)", 10);
2593 		if (error)
2594 			return error;
2595 	}
2596 
2597 	return prepend_path(path, root, buf, buflen);
2598 }
2599 
2600 static int prepend_unreachable(char **buffer, int *buflen)
2601 {
2602 	return prepend(buffer, buflen, "(unreachable)", 13);
2603 }
2604 
2605 /**
2606  * d_path - return the path of a dentry
2607  * @path: path to report
2608  * @buf: buffer to return value in
2609  * @buflen: buffer length
2610  *
2611  * Convert a dentry into an ASCII path name. If the entry has been deleted
2612  * the string " (deleted)" is appended. Note that this is ambiguous.
2613  *
2614  * Returns a pointer into the buffer or an error code if the path was
2615  * too long. Note: Callers should use the returned pointer, not the passed
2616  * in buffer, to use the name! The implementation often starts at an offset
2617  * into the buffer, and may leave 0 bytes at the start.
2618  *
2619  * "buflen" should be positive.
2620  */
2621 char *d_path(const struct path *path, char *buf, int buflen)
2622 {
2623 	char *res = buf + buflen;
2624 	struct path root;
2625 	struct path tmp;
2626 	int error;
2627 
2628 	/*
2629 	 * We have various synthetic filesystems that never get mounted.  On
2630 	 * these filesystems dentries are never used for lookup purposes, and
2631 	 * thus don't need to be hashed.  They also don't need a name until a
2632 	 * user wants to identify the object in /proc/pid/fd/.  The little hack
2633 	 * below allows us to generate a name for these objects on demand:
2634 	 */
2635 	if (path->dentry->d_op && path->dentry->d_op->d_dname)
2636 		return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
2637 
2638 	get_fs_root(current->fs, &root);
2639 	write_seqlock(&rename_lock);
2640 	tmp = root;
2641 	error = path_with_deleted(path, &tmp, &res, &buflen);
2642 	if (error)
2643 		res = ERR_PTR(error);
2644 	write_sequnlock(&rename_lock);
2645 	path_put(&root);
2646 	return res;
2647 }
2648 EXPORT_SYMBOL(d_path);
2649 
2650 /**
2651  * d_path_with_unreachable - return the path of a dentry
2652  * @path: path to report
2653  * @buf: buffer to return value in
2654  * @buflen: buffer length
2655  *
2656  * The difference from d_path() is that this prepends "(unreachable)"
2657  * to paths which are unreachable from the current process' root.
2658  */
2659 char *d_path_with_unreachable(const struct path *path, char *buf, int buflen)
2660 {
2661 	char *res = buf + buflen;
2662 	struct path root;
2663 	struct path tmp;
2664 	int error;
2665 
2666 	if (path->dentry->d_op && path->dentry->d_op->d_dname)
2667 		return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
2668 
2669 	get_fs_root(current->fs, &root);
2670 	write_seqlock(&rename_lock);
2671 	tmp = root;
2672 	error = path_with_deleted(path, &tmp, &res, &buflen);
2673 	if (!error && !path_equal(&tmp, &root))
2674 		error = prepend_unreachable(&res, &buflen);
2675 	write_sequnlock(&rename_lock);
2676 	path_put(&root);
2677 	if (error)
2678 		res =  ERR_PTR(error);
2679 
2680 	return res;
2681 }
2682 
2683 /*
2684  * Helper function for dentry_operations.d_dname() members
2685  */
2686 char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,
2687 			const char *fmt, ...)
2688 {
2689 	va_list args;
2690 	char temp[64];
2691 	int sz;
2692 
2693 	va_start(args, fmt);
2694 	sz = vsnprintf(temp, sizeof(temp), fmt, args) + 1;
2695 	va_end(args);
2696 
2697 	if (sz > sizeof(temp) || sz > buflen)
2698 		return ERR_PTR(-ENAMETOOLONG);
2699 
2700 	buffer += buflen - sz;
2701 	return memcpy(buffer, temp, sz);
2702 }
2703 
2704 /*
2705  * Write full pathname from the root of the filesystem into the buffer.
2706  */
2707 static char *__dentry_path(struct dentry *dentry, char *buf, int buflen)
2708 {
2709 	char *end = buf + buflen;
2710 	char *retval;
2711 
2712 	prepend(&end, &buflen, "\0", 1);
2713 	if (buflen < 1)
2714 		goto Elong;
2715 	/* Get '/' right */
2716 	retval = end-1;
2717 	*retval = '/';
2718 
2719 	while (!IS_ROOT(dentry)) {
2720 		struct dentry *parent = dentry->d_parent;
2721 		int error;
2722 
2723 		prefetch(parent);
2724 		spin_lock(&dentry->d_lock);
2725 		error = prepend_name(&end, &buflen, &dentry->d_name);
2726 		spin_unlock(&dentry->d_lock);
2727 		if (error != 0 || prepend(&end, &buflen, "/", 1) != 0)
2728 			goto Elong;
2729 
2730 		retval = end;
2731 		dentry = parent;
2732 	}
2733 	return retval;
2734 Elong:
2735 	return ERR_PTR(-ENAMETOOLONG);
2736 }
2737 
2738 char *dentry_path_raw(struct dentry *dentry, char *buf, int buflen)
2739 {
2740 	char *retval;
2741 
2742 	write_seqlock(&rename_lock);
2743 	retval = __dentry_path(dentry, buf, buflen);
2744 	write_sequnlock(&rename_lock);
2745 
2746 	return retval;
2747 }
2748 EXPORT_SYMBOL(dentry_path_raw);
2749 
2750 char *dentry_path(struct dentry *dentry, char *buf, int buflen)
2751 {
2752 	char *p = NULL;
2753 	char *retval;
2754 
2755 	write_seqlock(&rename_lock);
2756 	if (d_unlinked(dentry)) {
2757 		p = buf + buflen;
2758 		if (prepend(&p, &buflen, "//deleted", 10) != 0)
2759 			goto Elong;
2760 		buflen++;
2761 	}
2762 	retval = __dentry_path(dentry, buf, buflen);
2763 	write_sequnlock(&rename_lock);
2764 	if (!IS_ERR(retval) && p)
2765 		*p = '/';	/* restore '/' overriden with '\0' */
2766 	return retval;
2767 Elong:
2768 	return ERR_PTR(-ENAMETOOLONG);
2769 }
2770 
2771 /*
2772  * NOTE! The user-level library version returns a
2773  * character pointer. The kernel system call just
2774  * returns the length of the buffer filled (which
2775  * includes the ending '\0' character), or a negative
2776  * error value. So libc would do something like
2777  *
2778  *	char *getcwd(char * buf, size_t size)
2779  *	{
2780  *		int retval;
2781  *
2782  *		retval = sys_getcwd(buf, size);
2783  *		if (retval >= 0)
2784  *			return buf;
2785  *		errno = -retval;
2786  *		return NULL;
2787  *	}
2788  */
2789 SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
2790 {
2791 	int error;
2792 	struct path pwd, root;
2793 	char *page = (char *) __get_free_page(GFP_USER);
2794 
2795 	if (!page)
2796 		return -ENOMEM;
2797 
2798 	get_fs_root_and_pwd(current->fs, &root, &pwd);
2799 
2800 	error = -ENOENT;
2801 	write_seqlock(&rename_lock);
2802 	if (!d_unlinked(pwd.dentry)) {
2803 		unsigned long len;
2804 		struct path tmp = root;
2805 		char *cwd = page + PAGE_SIZE;
2806 		int buflen = PAGE_SIZE;
2807 
2808 		prepend(&cwd, &buflen, "\0", 1);
2809 		error = prepend_path(&pwd, &tmp, &cwd, &buflen);
2810 		write_sequnlock(&rename_lock);
2811 
2812 		if (error)
2813 			goto out;
2814 
2815 		/* Unreachable from current root */
2816 		if (!path_equal(&tmp, &root)) {
2817 			error = prepend_unreachable(&cwd, &buflen);
2818 			if (error)
2819 				goto out;
2820 		}
2821 
2822 		error = -ERANGE;
2823 		len = PAGE_SIZE + page - cwd;
2824 		if (len <= size) {
2825 			error = len;
2826 			if (copy_to_user(buf, cwd, len))
2827 				error = -EFAULT;
2828 		}
2829 	} else {
2830 		write_sequnlock(&rename_lock);
2831 	}
2832 
2833 out:
2834 	path_put(&pwd);
2835 	path_put(&root);
2836 	free_page((unsigned long) page);
2837 	return error;
2838 }
2839 
2840 /*
2841  * Test whether new_dentry is a subdirectory of old_dentry.
2842  *
2843  * Trivially implemented using the dcache structure
2844  */
2845 
2846 /**
2847  * is_subdir - is new dentry a subdirectory of old_dentry
2848  * @new_dentry: new dentry
2849  * @old_dentry: old dentry
2850  *
2851  * Returns 1 if new_dentry is a subdirectory of the parent (at any depth).
2852  * Returns 0 otherwise.
2853  * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
2854  */
2855 
2856 int is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)
2857 {
2858 	int result;
2859 	unsigned seq;
2860 
2861 	if (new_dentry == old_dentry)
2862 		return 1;
2863 
2864 	do {
2865 		/* for restarting inner loop in case of seq retry */
2866 		seq = read_seqbegin(&rename_lock);
2867 		/*
2868 		 * Need rcu_readlock to protect against the d_parent trashing
2869 		 * due to d_move
2870 		 */
2871 		rcu_read_lock();
2872 		if (d_ancestor(old_dentry, new_dentry))
2873 			result = 1;
2874 		else
2875 			result = 0;
2876 		rcu_read_unlock();
2877 	} while (read_seqretry(&rename_lock, seq));
2878 
2879 	return result;
2880 }
2881 
2882 int path_is_under(struct path *path1, struct path *path2)
2883 {
2884 	struct vfsmount *mnt = path1->mnt;
2885 	struct dentry *dentry = path1->dentry;
2886 	int res;
2887 
2888 	br_read_lock(vfsmount_lock);
2889 	if (mnt != path2->mnt) {
2890 		for (;;) {
2891 			if (mnt->mnt_parent == mnt) {
2892 				br_read_unlock(vfsmount_lock);
2893 				return 0;
2894 			}
2895 			if (mnt->mnt_parent == path2->mnt)
2896 				break;
2897 			mnt = mnt->mnt_parent;
2898 		}
2899 		dentry = mnt->mnt_mountpoint;
2900 	}
2901 	res = is_subdir(dentry, path2->dentry);
2902 	br_read_unlock(vfsmount_lock);
2903 	return res;
2904 }
2905 EXPORT_SYMBOL(path_is_under);
2906 
2907 void d_genocide(struct dentry *root)
2908 {
2909 	struct dentry *this_parent;
2910 	struct list_head *next;
2911 	unsigned seq;
2912 	int locked = 0;
2913 
2914 	seq = read_seqbegin(&rename_lock);
2915 again:
2916 	this_parent = root;
2917 	spin_lock(&this_parent->d_lock);
2918 repeat:
2919 	next = this_parent->d_subdirs.next;
2920 resume:
2921 	while (next != &this_parent->d_subdirs) {
2922 		struct list_head *tmp = next;
2923 		struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
2924 		next = tmp->next;
2925 
2926 		spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
2927 		if (d_unhashed(dentry) || !dentry->d_inode) {
2928 			spin_unlock(&dentry->d_lock);
2929 			continue;
2930 		}
2931 		if (!list_empty(&dentry->d_subdirs)) {
2932 			spin_unlock(&this_parent->d_lock);
2933 			spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
2934 			this_parent = dentry;
2935 			spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
2936 			goto repeat;
2937 		}
2938 		if (!(dentry->d_flags & DCACHE_GENOCIDE)) {
2939 			dentry->d_flags |= DCACHE_GENOCIDE;
2940 			dentry->d_count--;
2941 		}
2942 		spin_unlock(&dentry->d_lock);
2943 	}
2944 	if (this_parent != root) {
2945 		struct dentry *tmp;
2946 		struct dentry *child;
2947 
2948 		tmp = this_parent->d_parent;
2949 		if (!(this_parent->d_flags & DCACHE_GENOCIDE)) {
2950 			this_parent->d_flags |= DCACHE_GENOCIDE;
2951 			this_parent->d_count--;
2952 		}
2953 		rcu_read_lock();
2954 		spin_unlock(&this_parent->d_lock);
2955 		child = this_parent;
2956 		this_parent = tmp;
2957 		spin_lock(&this_parent->d_lock);
2958 		/* might go back up the wrong parent if we have had a rename
2959 		 * or deletion */
2960 		if (this_parent != child->d_parent ||
2961 			 (!locked && read_seqretry(&rename_lock, seq))) {
2962 			spin_unlock(&this_parent->d_lock);
2963 			rcu_read_unlock();
2964 			goto rename_retry;
2965 		}
2966 		rcu_read_unlock();
2967 		next = child->d_u.d_child.next;
2968 		goto resume;
2969 	}
2970 	spin_unlock(&this_parent->d_lock);
2971 	if (!locked && read_seqretry(&rename_lock, seq))
2972 		goto rename_retry;
2973 	if (locked)
2974 		write_sequnlock(&rename_lock);
2975 	return;
2976 
2977 rename_retry:
2978 	locked = 1;
2979 	write_seqlock(&rename_lock);
2980 	goto again;
2981 }
2982 
2983 /**
2984  * find_inode_number - check for dentry with name
2985  * @dir: directory to check
2986  * @name: Name to find.
2987  *
2988  * Check whether a dentry already exists for the given name,
2989  * and return the inode number if it has an inode. Otherwise
2990  * 0 is returned.
2991  *
2992  * This routine is used to post-process directory listings for
2993  * filesystems using synthetic inode numbers, and is necessary
2994  * to keep getcwd() working.
2995  */
2996 
2997 ino_t find_inode_number(struct dentry *dir, struct qstr *name)
2998 {
2999 	struct dentry * dentry;
3000 	ino_t ino = 0;
3001 
3002 	dentry = d_hash_and_lookup(dir, name);
3003 	if (dentry) {
3004 		if (dentry->d_inode)
3005 			ino = dentry->d_inode->i_ino;
3006 		dput(dentry);
3007 	}
3008 	return ino;
3009 }
3010 EXPORT_SYMBOL(find_inode_number);
3011 
3012 static __initdata unsigned long dhash_entries;
3013 static int __init set_dhash_entries(char *str)
3014 {
3015 	if (!str)
3016 		return 0;
3017 	dhash_entries = simple_strtoul(str, &str, 0);
3018 	return 1;
3019 }
3020 __setup("dhash_entries=", set_dhash_entries);
3021 
3022 static void __init dcache_init_early(void)
3023 {
3024 	int loop;
3025 
3026 	/* If hashes are distributed across NUMA nodes, defer
3027 	 * hash allocation until vmalloc space is available.
3028 	 */
3029 	if (hashdist)
3030 		return;
3031 
3032 	dentry_hashtable =
3033 		alloc_large_system_hash("Dentry cache",
3034 					sizeof(struct dcache_hash_bucket),
3035 					dhash_entries,
3036 					13,
3037 					HASH_EARLY,
3038 					&d_hash_shift,
3039 					&d_hash_mask,
3040 					0);
3041 
3042 	for (loop = 0; loop < (1 << d_hash_shift); loop++)
3043 		INIT_HLIST_BL_HEAD(&dentry_hashtable[loop].head);
3044 }
3045 
3046 static void __init dcache_init(void)
3047 {
3048 	int loop;
3049 
3050 	/*
3051 	 * A constructor could be added for stable state like the lists,
3052 	 * but it is probably not worth it because of the cache nature
3053 	 * of the dcache.
3054 	 */
3055 	dentry_cache = KMEM_CACHE(dentry,
3056 		SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD);
3057 
3058 	register_shrinker(&dcache_shrinker);
3059 
3060 	/* Hash may have been set up in dcache_init_early */
3061 	if (!hashdist)
3062 		return;
3063 
3064 	dentry_hashtable =
3065 		alloc_large_system_hash("Dentry cache",
3066 					sizeof(struct dcache_hash_bucket),
3067 					dhash_entries,
3068 					13,
3069 					0,
3070 					&d_hash_shift,
3071 					&d_hash_mask,
3072 					0);
3073 
3074 	for (loop = 0; loop < (1 << d_hash_shift); loop++)
3075 		INIT_HLIST_BL_HEAD(&dentry_hashtable[loop].head);
3076 }
3077 
3078 /* SLAB cache for __getname() consumers */
3079 struct kmem_cache *names_cachep __read_mostly;
3080 EXPORT_SYMBOL(names_cachep);
3081 
3082 EXPORT_SYMBOL(d_genocide);
3083 
3084 void __init vfs_caches_init_early(void)
3085 {
3086 	dcache_init_early();
3087 	inode_init_early();
3088 }
3089 
3090 void __init vfs_caches_init(unsigned long mempages)
3091 {
3092 	unsigned long reserve;
3093 
3094 	/* Base hash sizes on available memory, with a reserve equal to
3095            150% of current kernel size */
3096 
3097 	reserve = min((mempages - nr_free_pages()) * 3/2, mempages - 1);
3098 	mempages -= reserve;
3099 
3100 	names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
3101 			SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
3102 
3103 	dcache_init();
3104 	inode_init();
3105 	files_init(mempages);
3106 	mnt_init();
3107 	bdev_cache_init();
3108 	chrdev_init();
3109 }
3110