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Linux/fs/dcache.c

  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/export.h>
 27 #include <linux/mount.h>
 28 #include <linux/file.h>
 29 #include <asm/uaccess.h>
 30 #include <linux/security.h>
 31 #include <linux/seqlock.h>
 32 #include <linux/swap.h>
 33 #include <linux/bootmem.h>
 34 #include <linux/fs_struct.h>
 35 #include <linux/hardirq.h>
 36 #include <linux/bit_spinlock.h>
 37 #include <linux/rculist_bl.h>
 38 #include <linux/prefetch.h>
 39 #include <linux/ratelimit.h>
 40 #include <linux/list_lru.h>
 41 #include <linux/kasan.h>
 42 
 43 #include "internal.h"
 44 #include "mount.h"
 45 
 46 /*
 47  * Usage:
 48  * dcache->d_inode->i_lock protects:
 49  *   - i_dentry, d_u.d_alias, d_inode of aliases
 50  * dcache_hash_bucket lock protects:
 51  *   - the dcache hash table
 52  * s_anon bl list spinlock protects:
 53  *   - the s_anon list (see __d_drop)
 54  * dentry->d_sb->s_dentry_lru_lock protects:
 55  *   - the dcache lru lists and counters
 56  * d_lock protects:
 57  *   - d_flags
 58  *   - d_name
 59  *   - d_lru
 60  *   - d_count
 61  *   - d_unhashed()
 62  *   - d_parent and d_subdirs
 63  *   - childrens' d_child and d_parent
 64  *   - d_u.d_alias, d_inode
 65  *
 66  * Ordering:
 67  * dentry->d_inode->i_lock
 68  *   dentry->d_lock
 69  *     dentry->d_sb->s_dentry_lru_lock
 70  *     dcache_hash_bucket lock
 71  *     s_anon lock
 72  *
 73  * If there is an ancestor relationship:
 74  * dentry->d_parent->...->d_parent->d_lock
 75  *   ...
 76  *     dentry->d_parent->d_lock
 77  *       dentry->d_lock
 78  *
 79  * If no ancestor relationship:
 80  * if (dentry1 < dentry2)
 81  *   dentry1->d_lock
 82  *     dentry2->d_lock
 83  */
 84 int sysctl_vfs_cache_pressure __read_mostly = 100;
 85 EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
 86 
 87 __cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
 88 
 89 EXPORT_SYMBOL(rename_lock);
 90 
 91 static struct kmem_cache *dentry_cache __read_mostly;
 92 
 93 /*
 94  * This is the single most critical data structure when it comes
 95  * to the dcache: the hashtable for lookups. Somebody should try
 96  * to make this good - I've just made it work.
 97  *
 98  * This hash-function tries to avoid losing too many bits of hash
 99  * information, yet avoid using a prime hash-size or similar.
100  */
101 
102 static unsigned int d_hash_mask __read_mostly;
103 static unsigned int d_hash_shift __read_mostly;
104 
105 static struct hlist_bl_head *dentry_hashtable __read_mostly;
106 
107 static inline struct hlist_bl_head *d_hash(const struct dentry *parent,
108                                         unsigned int hash)
109 {
110         hash += (unsigned long) parent / L1_CACHE_BYTES;
111         return dentry_hashtable + hash_32(hash, d_hash_shift);
112 }
113 
114 /* Statistics gathering. */
115 struct dentry_stat_t dentry_stat = {
116         .age_limit = 45,
117 };
118 
119 static DEFINE_PER_CPU(long, nr_dentry);
120 static DEFINE_PER_CPU(long, nr_dentry_unused);
121 
122 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
123 
124 /*
125  * Here we resort to our own counters instead of using generic per-cpu counters
126  * for consistency with what the vfs inode code does. We are expected to harvest
127  * better code and performance by having our own specialized counters.
128  *
129  * Please note that the loop is done over all possible CPUs, not over all online
130  * CPUs. The reason for this is that we don't want to play games with CPUs going
131  * on and off. If one of them goes off, we will just keep their counters.
132  *
133  * glommer: See cffbc8a for details, and if you ever intend to change this,
134  * please update all vfs counters to match.
135  */
136 static long get_nr_dentry(void)
137 {
138         int i;
139         long sum = 0;
140         for_each_possible_cpu(i)
141                 sum += per_cpu(nr_dentry, i);
142         return sum < 0 ? 0 : sum;
143 }
144 
145 static long get_nr_dentry_unused(void)
146 {
147         int i;
148         long sum = 0;
149         for_each_possible_cpu(i)
150                 sum += per_cpu(nr_dentry_unused, i);
151         return sum < 0 ? 0 : sum;
152 }
153 
154 int proc_nr_dentry(struct ctl_table *table, int write, void __user *buffer,
155                    size_t *lenp, loff_t *ppos)
156 {
157         dentry_stat.nr_dentry = get_nr_dentry();
158         dentry_stat.nr_unused = get_nr_dentry_unused();
159         return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
160 }
161 #endif
162 
163 /*
164  * Compare 2 name strings, return 0 if they match, otherwise non-zero.
165  * The strings are both count bytes long, and count is non-zero.
166  */
167 #ifdef CONFIG_DCACHE_WORD_ACCESS
168 
169 #include <asm/word-at-a-time.h>
170 /*
171  * NOTE! 'cs' and 'scount' come from a dentry, so it has a
172  * aligned allocation for this particular component. We don't
173  * strictly need the load_unaligned_zeropad() safety, but it
174  * doesn't hurt either.
175  *
176  * In contrast, 'ct' and 'tcount' can be from a pathname, and do
177  * need the careful unaligned handling.
178  */
179 static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
180 {
181         unsigned long a,b,mask;
182 
183         for (;;) {
184                 a = *(unsigned long *)cs;
185                 b = load_unaligned_zeropad(ct);
186                 if (tcount < sizeof(unsigned long))
187                         break;
188                 if (unlikely(a != b))
189                         return 1;
190                 cs += sizeof(unsigned long);
191                 ct += sizeof(unsigned long);
192                 tcount -= sizeof(unsigned long);
193                 if (!tcount)
194                         return 0;
195         }
196         mask = bytemask_from_count(tcount);
197         return unlikely(!!((a ^ b) & mask));
198 }
199 
200 #else
201 
202 static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
203 {
204         do {
205                 if (*cs != *ct)
206                         return 1;
207                 cs++;
208                 ct++;
209                 tcount--;
210         } while (tcount);
211         return 0;
212 }
213 
214 #endif
215 
216 static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
217 {
218         const unsigned char *cs;
219         /*
220          * Be careful about RCU walk racing with rename:
221          * use ACCESS_ONCE to fetch the name pointer.
222          *
223          * NOTE! Even if a rename will mean that the length
224          * was not loaded atomically, we don't care. The
225          * RCU walk will check the sequence count eventually,
226          * and catch it. And we won't overrun the buffer,
227          * because we're reading the name pointer atomically,
228          * and a dentry name is guaranteed to be properly
229          * terminated with a NUL byte.
230          *
231          * End result: even if 'len' is wrong, we'll exit
232          * early because the data cannot match (there can
233          * be no NUL in the ct/tcount data)
234          */
235         cs = ACCESS_ONCE(dentry->d_name.name);
236         smp_read_barrier_depends();
237         return dentry_string_cmp(cs, ct, tcount);
238 }
239 
240 struct external_name {
241         union {
242                 atomic_t count;
243                 struct rcu_head head;
244         } u;
245         unsigned char name[];
246 };
247 
248 static inline struct external_name *external_name(struct dentry *dentry)
249 {
250         return container_of(dentry->d_name.name, struct external_name, name[0]);
251 }
252 
253 static void __d_free(struct rcu_head *head)
254 {
255         struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
256 
257         kmem_cache_free(dentry_cache, dentry); 
258 }
259 
260 static void __d_free_external(struct rcu_head *head)
261 {
262         struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
263         kfree(external_name(dentry));
264         kmem_cache_free(dentry_cache, dentry); 
265 }
266 
267 static inline int dname_external(const struct dentry *dentry)
268 {
269         return dentry->d_name.name != dentry->d_iname;
270 }
271 
272 /*
273  * Make sure other CPUs see the inode attached before the type is set.
274  */
275 static inline void __d_set_inode_and_type(struct dentry *dentry,
276                                           struct inode *inode,
277                                           unsigned type_flags)
278 {
279         unsigned flags;
280 
281         dentry->d_inode = inode;
282         smp_wmb();
283         flags = READ_ONCE(dentry->d_flags);
284         flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
285         flags |= type_flags;
286         WRITE_ONCE(dentry->d_flags, flags);
287 }
288 
289 /*
290  * Ideally, we want to make sure that other CPUs see the flags cleared before
291  * the inode is detached, but this is really a violation of RCU principles
292  * since the ordering suggests we should always set inode before flags.
293  *
294  * We should instead replace or discard the entire dentry - but that sucks
295  * performancewise on mass deletion/rename.
296  */
297 static inline void __d_clear_type_and_inode(struct dentry *dentry)
298 {
299         unsigned flags = READ_ONCE(dentry->d_flags);
300 
301         flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
302         WRITE_ONCE(dentry->d_flags, flags);
303         smp_wmb();
304         dentry->d_inode = NULL;
305 }
306 
307 static void dentry_free(struct dentry *dentry)
308 {
309         WARN_ON(!hlist_unhashed(&dentry->d_u.d_alias));
310         if (unlikely(dname_external(dentry))) {
311                 struct external_name *p = external_name(dentry);
312                 if (likely(atomic_dec_and_test(&p->u.count))) {
313                         call_rcu(&dentry->d_u.d_rcu, __d_free_external);
314                         return;
315                 }
316         }
317         /* if dentry was never visible to RCU, immediate free is OK */
318         if (!(dentry->d_flags & DCACHE_RCUACCESS))
319                 __d_free(&dentry->d_u.d_rcu);
320         else
321                 call_rcu(&dentry->d_u.d_rcu, __d_free);
322 }
323 
324 /**
325  * dentry_rcuwalk_invalidate - invalidate in-progress rcu-walk lookups
326  * @dentry: the target dentry
327  * After this call, in-progress rcu-walk path lookup will fail. This
328  * should be called after unhashing, and after changing d_inode (if
329  * the dentry has not already been unhashed).
330  */
331 static inline void dentry_rcuwalk_invalidate(struct dentry *dentry)
332 {
333         lockdep_assert_held(&dentry->d_lock);
334         /* Go through am invalidation barrier */
335         write_seqcount_invalidate(&dentry->d_seq);
336 }
337 
338 /*
339  * Release the dentry's inode, using the filesystem
340  * d_iput() operation if defined. Dentry has no refcount
341  * and is unhashed.
342  */
343 static void dentry_iput(struct dentry * dentry)
344         __releases(dentry->d_lock)
345         __releases(dentry->d_inode->i_lock)
346 {
347         struct inode *inode = dentry->d_inode;
348         if (inode) {
349                 __d_clear_type_and_inode(dentry);
350                 hlist_del_init(&dentry->d_u.d_alias);
351                 spin_unlock(&dentry->d_lock);
352                 spin_unlock(&inode->i_lock);
353                 if (!inode->i_nlink)
354                         fsnotify_inoderemove(inode);
355                 if (dentry->d_op && dentry->d_op->d_iput)
356                         dentry->d_op->d_iput(dentry, inode);
357                 else
358                         iput(inode);
359         } else {
360                 spin_unlock(&dentry->d_lock);
361         }
362 }
363 
364 /*
365  * Release the dentry's inode, using the filesystem
366  * d_iput() operation if defined. dentry remains in-use.
367  */
368 static void dentry_unlink_inode(struct dentry * dentry)
369         __releases(dentry->d_lock)
370         __releases(dentry->d_inode->i_lock)
371 {
372         struct inode *inode = dentry->d_inode;
373         __d_clear_type_and_inode(dentry);
374         hlist_del_init(&dentry->d_u.d_alias);
375         dentry_rcuwalk_invalidate(dentry);
376         spin_unlock(&dentry->d_lock);
377         spin_unlock(&inode->i_lock);
378         if (!inode->i_nlink)
379                 fsnotify_inoderemove(inode);
380         if (dentry->d_op && dentry->d_op->d_iput)
381                 dentry->d_op->d_iput(dentry, inode);
382         else
383                 iput(inode);
384 }
385 
386 /*
387  * The DCACHE_LRU_LIST bit is set whenever the 'd_lru' entry
388  * is in use - which includes both the "real" per-superblock
389  * LRU list _and_ the DCACHE_SHRINK_LIST use.
390  *
391  * The DCACHE_SHRINK_LIST bit is set whenever the dentry is
392  * on the shrink list (ie not on the superblock LRU list).
393  *
394  * The per-cpu "nr_dentry_unused" counters are updated with
395  * the DCACHE_LRU_LIST bit.
396  *
397  * These helper functions make sure we always follow the
398  * rules. d_lock must be held by the caller.
399  */
400 #define D_FLAG_VERIFY(dentry,x) WARN_ON_ONCE(((dentry)->d_flags & (DCACHE_LRU_LIST | DCACHE_SHRINK_LIST)) != (x))
401 static void d_lru_add(struct dentry *dentry)
402 {
403         D_FLAG_VERIFY(dentry, 0);
404         dentry->d_flags |= DCACHE_LRU_LIST;
405         this_cpu_inc(nr_dentry_unused);
406         WARN_ON_ONCE(!list_lru_add(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
407 }
408 
409 static void d_lru_del(struct dentry *dentry)
410 {
411         D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
412         dentry->d_flags &= ~DCACHE_LRU_LIST;
413         this_cpu_dec(nr_dentry_unused);
414         WARN_ON_ONCE(!list_lru_del(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
415 }
416 
417 static void d_shrink_del(struct dentry *dentry)
418 {
419         D_FLAG_VERIFY(dentry, DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
420         list_del_init(&dentry->d_lru);
421         dentry->d_flags &= ~(DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
422         this_cpu_dec(nr_dentry_unused);
423 }
424 
425 static void d_shrink_add(struct dentry *dentry, struct list_head *list)
426 {
427         D_FLAG_VERIFY(dentry, 0);
428         list_add(&dentry->d_lru, list);
429         dentry->d_flags |= DCACHE_SHRINK_LIST | DCACHE_LRU_LIST;
430         this_cpu_inc(nr_dentry_unused);
431 }
432 
433 /*
434  * These can only be called under the global LRU lock, ie during the
435  * callback for freeing the LRU list. "isolate" removes it from the
436  * LRU lists entirely, while shrink_move moves it to the indicated
437  * private list.
438  */
439 static void d_lru_isolate(struct list_lru_one *lru, struct dentry *dentry)
440 {
441         D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
442         dentry->d_flags &= ~DCACHE_LRU_LIST;
443         this_cpu_dec(nr_dentry_unused);
444         list_lru_isolate(lru, &dentry->d_lru);
445 }
446 
447 static void d_lru_shrink_move(struct list_lru_one *lru, struct dentry *dentry,
448                               struct list_head *list)
449 {
450         D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
451         dentry->d_flags |= DCACHE_SHRINK_LIST;
452         list_lru_isolate_move(lru, &dentry->d_lru, list);
453 }
454 
455 /*
456  * dentry_lru_(add|del)_list) must be called with d_lock held.
457  */
458 static void dentry_lru_add(struct dentry *dentry)
459 {
460         if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST)))
461                 d_lru_add(dentry);
462 }
463 
464 /**
465  * d_drop - drop a dentry
466  * @dentry: dentry to drop
467  *
468  * d_drop() unhashes the entry from the parent dentry hashes, so that it won't
469  * be found through a VFS lookup any more. Note that this is different from
470  * deleting the dentry - d_delete will try to mark the dentry negative if
471  * possible, giving a successful _negative_ lookup, while d_drop will
472  * just make the cache lookup fail.
473  *
474  * d_drop() is used mainly for stuff that wants to invalidate a dentry for some
475  * reason (NFS timeouts or autofs deletes).
476  *
477  * __d_drop requires dentry->d_lock.
478  */
479 void __d_drop(struct dentry *dentry)
480 {
481         if (!d_unhashed(dentry)) {
482                 struct hlist_bl_head *b;
483                 /*
484                  * Hashed dentries are normally on the dentry hashtable,
485                  * with the exception of those newly allocated by
486                  * d_obtain_alias, which are always IS_ROOT:
487                  */
488                 if (unlikely(IS_ROOT(dentry)))
489                         b = &dentry->d_sb->s_anon;
490                 else
491                         b = d_hash(dentry->d_parent, dentry->d_name.hash);
492 
493                 hlist_bl_lock(b);
494                 __hlist_bl_del(&dentry->d_hash);
495                 dentry->d_hash.pprev = NULL;
496                 hlist_bl_unlock(b);
497                 dentry_rcuwalk_invalidate(dentry);
498         }
499 }
500 EXPORT_SYMBOL(__d_drop);
501 
502 void d_drop(struct dentry *dentry)
503 {
504         spin_lock(&dentry->d_lock);
505         __d_drop(dentry);
506         spin_unlock(&dentry->d_lock);
507 }
508 EXPORT_SYMBOL(d_drop);
509 
510 static void __dentry_kill(struct dentry *dentry)
511 {
512         struct dentry *parent = NULL;
513         bool can_free = true;
514         if (!IS_ROOT(dentry))
515                 parent = dentry->d_parent;
516 
517         /*
518          * The dentry is now unrecoverably dead to the world.
519          */
520         lockref_mark_dead(&dentry->d_lockref);
521 
522         /*
523          * inform the fs via d_prune that this dentry is about to be
524          * unhashed and destroyed.
525          */
526         if (dentry->d_flags & DCACHE_OP_PRUNE)
527                 dentry->d_op->d_prune(dentry);
528 
529         if (dentry->d_flags & DCACHE_LRU_LIST) {
530                 if (!(dentry->d_flags & DCACHE_SHRINK_LIST))
531                         d_lru_del(dentry);
532         }
533         /* if it was on the hash then remove it */
534         __d_drop(dentry);
535         __list_del_entry(&dentry->d_child);
536         /*
537          * Inform d_walk() that we are no longer attached to the
538          * dentry tree
539          */
540         dentry->d_flags |= DCACHE_DENTRY_KILLED;
541         if (parent)
542                 spin_unlock(&parent->d_lock);
543         dentry_iput(dentry);
544         /*
545          * dentry_iput drops the locks, at which point nobody (except
546          * transient RCU lookups) can reach this dentry.
547          */
548         BUG_ON(dentry->d_lockref.count > 0);
549         this_cpu_dec(nr_dentry);
550         if (dentry->d_op && dentry->d_op->d_release)
551                 dentry->d_op->d_release(dentry);
552 
553         spin_lock(&dentry->d_lock);
554         if (dentry->d_flags & DCACHE_SHRINK_LIST) {
555                 dentry->d_flags |= DCACHE_MAY_FREE;
556                 can_free = false;
557         }
558         spin_unlock(&dentry->d_lock);
559         if (likely(can_free))
560                 dentry_free(dentry);
561 }
562 
563 /*
564  * Finish off a dentry we've decided to kill.
565  * dentry->d_lock must be held, returns with it unlocked.
566  * If ref is non-zero, then decrement the refcount too.
567  * Returns dentry requiring refcount drop, or NULL if we're done.
568  */
569 static struct dentry *dentry_kill(struct dentry *dentry)
570         __releases(dentry->d_lock)
571 {
572         struct inode *inode = dentry->d_inode;
573         struct dentry *parent = NULL;
574 
575         if (inode && unlikely(!spin_trylock(&inode->i_lock)))
576                 goto failed;
577 
578         if (!IS_ROOT(dentry)) {
579                 parent = dentry->d_parent;
580                 if (unlikely(!spin_trylock(&parent->d_lock))) {
581                         if (inode)
582                                 spin_unlock(&inode->i_lock);
583                         goto failed;
584                 }
585         }
586 
587         __dentry_kill(dentry);
588         return parent;
589 
590 failed:
591         spin_unlock(&dentry->d_lock);
592         cpu_relax();
593         return dentry; /* try again with same dentry */
594 }
595 
596 static inline struct dentry *lock_parent(struct dentry *dentry)
597 {
598         struct dentry *parent = dentry->d_parent;
599         if (IS_ROOT(dentry))
600                 return NULL;
601         if (unlikely(dentry->d_lockref.count < 0))
602                 return NULL;
603         if (likely(spin_trylock(&parent->d_lock)))
604                 return parent;
605         rcu_read_lock();
606         spin_unlock(&dentry->d_lock);
607 again:
608         parent = ACCESS_ONCE(dentry->d_parent);
609         spin_lock(&parent->d_lock);
610         /*
611          * We can't blindly lock dentry until we are sure
612          * that we won't violate the locking order.
613          * Any changes of dentry->d_parent must have
614          * been done with parent->d_lock held, so
615          * spin_lock() above is enough of a barrier
616          * for checking if it's still our child.
617          */
618         if (unlikely(parent != dentry->d_parent)) {
619                 spin_unlock(&parent->d_lock);
620                 goto again;
621         }
622         rcu_read_unlock();
623         if (parent != dentry)
624                 spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
625         else
626                 parent = NULL;
627         return parent;
628 }
629 
630 /*
631  * Try to do a lockless dput(), and return whether that was successful.
632  *
633  * If unsuccessful, we return false, having already taken the dentry lock.
634  *
635  * The caller needs to hold the RCU read lock, so that the dentry is
636  * guaranteed to stay around even if the refcount goes down to zero!
637  */
638 static inline bool fast_dput(struct dentry *dentry)
639 {
640         int ret;
641         unsigned int d_flags;
642 
643         /*
644          * If we have a d_op->d_delete() operation, we sould not
645          * let the dentry count go to zero, so use "put_or_lock".
646          */
647         if (unlikely(dentry->d_flags & DCACHE_OP_DELETE))
648                 return lockref_put_or_lock(&dentry->d_lockref);
649 
650         /*
651          * .. otherwise, we can try to just decrement the
652          * lockref optimistically.
653          */
654         ret = lockref_put_return(&dentry->d_lockref);
655 
656         /*
657          * If the lockref_put_return() failed due to the lock being held
658          * by somebody else, the fast path has failed. We will need to
659          * get the lock, and then check the count again.
660          */
661         if (unlikely(ret < 0)) {
662                 spin_lock(&dentry->d_lock);
663                 if (dentry->d_lockref.count > 1) {
664                         dentry->d_lockref.count--;
665                         spin_unlock(&dentry->d_lock);
666                         return 1;
667                 }
668                 return 0;
669         }
670 
671         /*
672          * If we weren't the last ref, we're done.
673          */
674         if (ret)
675                 return 1;
676 
677         /*
678          * Careful, careful. The reference count went down
679          * to zero, but we don't hold the dentry lock, so
680          * somebody else could get it again, and do another
681          * dput(), and we need to not race with that.
682          *
683          * However, there is a very special and common case
684          * where we don't care, because there is nothing to
685          * do: the dentry is still hashed, it does not have
686          * a 'delete' op, and it's referenced and already on
687          * the LRU list.
688          *
689          * NOTE! Since we aren't locked, these values are
690          * not "stable". However, it is sufficient that at
691          * some point after we dropped the reference the
692          * dentry was hashed and the flags had the proper
693          * value. Other dentry users may have re-gotten
694          * a reference to the dentry and change that, but
695          * our work is done - we can leave the dentry
696          * around with a zero refcount.
697          */
698         smp_rmb();
699         d_flags = ACCESS_ONCE(dentry->d_flags);
700         d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED;
701 
702         /* Nothing to do? Dropping the reference was all we needed? */
703         if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry))
704                 return 1;
705 
706         /*
707          * Not the fast normal case? Get the lock. We've already decremented
708          * the refcount, but we'll need to re-check the situation after
709          * getting the lock.
710          */
711         spin_lock(&dentry->d_lock);
712 
713         /*
714          * Did somebody else grab a reference to it in the meantime, and
715          * we're no longer the last user after all? Alternatively, somebody
716          * else could have killed it and marked it dead. Either way, we
717          * don't need to do anything else.
718          */
719         if (dentry->d_lockref.count) {
720                 spin_unlock(&dentry->d_lock);
721                 return 1;
722         }
723 
724         /*
725          * Re-get the reference we optimistically dropped. We hold the
726          * lock, and we just tested that it was zero, so we can just
727          * set it to 1.
728          */
729         dentry->d_lockref.count = 1;
730         return 0;
731 }
732 
733 
734 /* 
735  * This is dput
736  *
737  * This is complicated by the fact that we do not want to put
738  * dentries that are no longer on any hash chain on the unused
739  * list: we'd much rather just get rid of them immediately.
740  *
741  * However, that implies that we have to traverse the dentry
742  * tree upwards to the parents which might _also_ now be
743  * scheduled for deletion (it may have been only waiting for
744  * its last child to go away).
745  *
746  * This tail recursion is done by hand as we don't want to depend
747  * on the compiler to always get this right (gcc generally doesn't).
748  * Real recursion would eat up our stack space.
749  */
750 
751 /*
752  * dput - release a dentry
753  * @dentry: dentry to release 
754  *
755  * Release a dentry. This will drop the usage count and if appropriate
756  * call the dentry unlink method as well as removing it from the queues and
757  * releasing its resources. If the parent dentries were scheduled for release
758  * they too may now get deleted.
759  */
760 void dput(struct dentry *dentry)
761 {
762         if (unlikely(!dentry))
763                 return;
764 
765 repeat:
766         rcu_read_lock();
767         if (likely(fast_dput(dentry))) {
768                 rcu_read_unlock();
769                 return;
770         }
771 
772         /* Slow case: now with the dentry lock held */
773         rcu_read_unlock();
774 
775         /* Unreachable? Get rid of it */
776         if (unlikely(d_unhashed(dentry)))
777                 goto kill_it;
778 
779         if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED))
780                 goto kill_it;
781 
782         if (unlikely(dentry->d_flags & DCACHE_OP_DELETE)) {
783                 if (dentry->d_op->d_delete(dentry))
784                         goto kill_it;
785         }
786 
787         if (!(dentry->d_flags & DCACHE_REFERENCED))
788                 dentry->d_flags |= DCACHE_REFERENCED;
789         dentry_lru_add(dentry);
790 
791         dentry->d_lockref.count--;
792         spin_unlock(&dentry->d_lock);
793         return;
794 
795 kill_it:
796         dentry = dentry_kill(dentry);
797         if (dentry)
798                 goto repeat;
799 }
800 EXPORT_SYMBOL(dput);
801 
802 
803 /* This must be called with d_lock held */
804 static inline void __dget_dlock(struct dentry *dentry)
805 {
806         dentry->d_lockref.count++;
807 }
808 
809 static inline void __dget(struct dentry *dentry)
810 {
811         lockref_get(&dentry->d_lockref);
812 }
813 
814 struct dentry *dget_parent(struct dentry *dentry)
815 {
816         int gotref;
817         struct dentry *ret;
818 
819         /*
820          * Do optimistic parent lookup without any
821          * locking.
822          */
823         rcu_read_lock();
824         ret = ACCESS_ONCE(dentry->d_parent);
825         gotref = lockref_get_not_zero(&ret->d_lockref);
826         rcu_read_unlock();
827         if (likely(gotref)) {
828                 if (likely(ret == ACCESS_ONCE(dentry->d_parent)))
829                         return ret;
830                 dput(ret);
831         }
832 
833 repeat:
834         /*
835          * Don't need rcu_dereference because we re-check it was correct under
836          * the lock.
837          */
838         rcu_read_lock();
839         ret = dentry->d_parent;
840         spin_lock(&ret->d_lock);
841         if (unlikely(ret != dentry->d_parent)) {
842                 spin_unlock(&ret->d_lock);
843                 rcu_read_unlock();
844                 goto repeat;
845         }
846         rcu_read_unlock();
847         BUG_ON(!ret->d_lockref.count);
848         ret->d_lockref.count++;
849         spin_unlock(&ret->d_lock);
850         return ret;
851 }
852 EXPORT_SYMBOL(dget_parent);
853 
854 /**
855  * d_find_alias - grab a hashed alias of inode
856  * @inode: inode in question
857  *
858  * If inode has a hashed alias, or is a directory and has any alias,
859  * acquire the reference to alias and return it. Otherwise return NULL.
860  * Notice that if inode is a directory there can be only one alias and
861  * it can be unhashed only if it has no children, or if it is the root
862  * of a filesystem, or if the directory was renamed and d_revalidate
863  * was the first vfs operation to notice.
864  *
865  * If the inode has an IS_ROOT, DCACHE_DISCONNECTED alias, then prefer
866  * any other hashed alias over that one.
867  */
868 static struct dentry *__d_find_alias(struct inode *inode)
869 {
870         struct dentry *alias, *discon_alias;
871 
872 again:
873         discon_alias = NULL;
874         hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
875                 spin_lock(&alias->d_lock);
876                 if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
877                         if (IS_ROOT(alias) &&
878                             (alias->d_flags & DCACHE_DISCONNECTED)) {
879                                 discon_alias = alias;
880                         } else {
881                                 __dget_dlock(alias);
882                                 spin_unlock(&alias->d_lock);
883                                 return alias;
884                         }
885                 }
886                 spin_unlock(&alias->d_lock);
887         }
888         if (discon_alias) {
889                 alias = discon_alias;
890                 spin_lock(&alias->d_lock);
891                 if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
892                         __dget_dlock(alias);
893                         spin_unlock(&alias->d_lock);
894                         return alias;
895                 }
896                 spin_unlock(&alias->d_lock);
897                 goto again;
898         }
899         return NULL;
900 }
901 
902 struct dentry *d_find_alias(struct inode *inode)
903 {
904         struct dentry *de = NULL;
905 
906         if (!hlist_empty(&inode->i_dentry)) {
907                 spin_lock(&inode->i_lock);
908                 de = __d_find_alias(inode);
909                 spin_unlock(&inode->i_lock);
910         }
911         return de;
912 }
913 EXPORT_SYMBOL(d_find_alias);
914 
915 /*
916  *      Try to kill dentries associated with this inode.
917  * WARNING: you must own a reference to inode.
918  */
919 void d_prune_aliases(struct inode *inode)
920 {
921         struct dentry *dentry;
922 restart:
923         spin_lock(&inode->i_lock);
924         hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias) {
925                 spin_lock(&dentry->d_lock);
926                 if (!dentry->d_lockref.count) {
927                         struct dentry *parent = lock_parent(dentry);
928                         if (likely(!dentry->d_lockref.count)) {
929                                 __dentry_kill(dentry);
930                                 dput(parent);
931                                 goto restart;
932                         }
933                         if (parent)
934                                 spin_unlock(&parent->d_lock);
935                 }
936                 spin_unlock(&dentry->d_lock);
937         }
938         spin_unlock(&inode->i_lock);
939 }
940 EXPORT_SYMBOL(d_prune_aliases);
941 
942 static void shrink_dentry_list(struct list_head *list)
943 {
944         struct dentry *dentry, *parent;
945 
946         while (!list_empty(list)) {
947                 struct inode *inode;
948                 dentry = list_entry(list->prev, struct dentry, d_lru);
949                 spin_lock(&dentry->d_lock);
950                 parent = lock_parent(dentry);
951 
952                 /*
953                  * The dispose list is isolated and dentries are not accounted
954                  * to the LRU here, so we can simply remove it from the list
955                  * here regardless of whether it is referenced or not.
956                  */
957                 d_shrink_del(dentry);
958 
959                 /*
960                  * We found an inuse dentry which was not removed from
961                  * the LRU because of laziness during lookup. Do not free it.
962                  */
963                 if (dentry->d_lockref.count > 0) {
964                         spin_unlock(&dentry->d_lock);
965                         if (parent)
966                                 spin_unlock(&parent->d_lock);
967                         continue;
968                 }
969 
970 
971                 if (unlikely(dentry->d_flags & DCACHE_DENTRY_KILLED)) {
972                         bool can_free = dentry->d_flags & DCACHE_MAY_FREE;
973                         spin_unlock(&dentry->d_lock);
974                         if (parent)
975                                 spin_unlock(&parent->d_lock);
976                         if (can_free)
977                                 dentry_free(dentry);
978                         continue;
979                 }
980 
981                 inode = dentry->d_inode;
982                 if (inode && unlikely(!spin_trylock(&inode->i_lock))) {
983                         d_shrink_add(dentry, list);
984                         spin_unlock(&dentry->d_lock);
985                         if (parent)
986                                 spin_unlock(&parent->d_lock);
987                         continue;
988                 }
989 
990                 __dentry_kill(dentry);
991 
992                 /*
993                  * We need to prune ancestors too. This is necessary to prevent
994                  * quadratic behavior of shrink_dcache_parent(), but is also
995                  * expected to be beneficial in reducing dentry cache
996                  * fragmentation.
997                  */
998                 dentry = parent;
999                 while (dentry && !lockref_put_or_lock(&dentry->d_lockref)) {
1000                         parent = lock_parent(dentry);
1001                         if (dentry->d_lockref.count != 1) {
1002                                 dentry->d_lockref.count--;
1003                                 spin_unlock(&dentry->d_lock);
1004                                 if (parent)
1005                                         spin_unlock(&parent->d_lock);
1006                                 break;
1007                         }
1008                         inode = dentry->d_inode;        /* can't be NULL */
1009                         if (unlikely(!spin_trylock(&inode->i_lock))) {
1010                                 spin_unlock(&dentry->d_lock);
1011                                 if (parent)
1012                                         spin_unlock(&parent->d_lock);
1013                                 cpu_relax();
1014                                 continue;
1015                         }
1016                         __dentry_kill(dentry);
1017                         dentry = parent;
1018                 }
1019         }
1020 }
1021 
1022 static enum lru_status dentry_lru_isolate(struct list_head *item,
1023                 struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
1024 {
1025         struct list_head *freeable = arg;
1026         struct dentry   *dentry = container_of(item, struct dentry, d_lru);
1027 
1028 
1029         /*
1030          * we are inverting the lru lock/dentry->d_lock here,
1031          * so use a trylock. If we fail to get the lock, just skip
1032          * it
1033          */
1034         if (!spin_trylock(&dentry->d_lock))
1035                 return LRU_SKIP;
1036 
1037         /*
1038          * Referenced dentries are still in use. If they have active
1039          * counts, just remove them from the LRU. Otherwise give them
1040          * another pass through the LRU.
1041          */
1042         if (dentry->d_lockref.count) {
1043                 d_lru_isolate(lru, dentry);
1044                 spin_unlock(&dentry->d_lock);
1045                 return LRU_REMOVED;
1046         }
1047 
1048         if (dentry->d_flags & DCACHE_REFERENCED) {
1049                 dentry->d_flags &= ~DCACHE_REFERENCED;
1050                 spin_unlock(&dentry->d_lock);
1051 
1052                 /*
1053                  * The list move itself will be made by the common LRU code. At
1054                  * this point, we've dropped the dentry->d_lock but keep the
1055                  * lru lock. This is safe to do, since every list movement is
1056                  * protected by the lru lock even if both locks are held.
1057                  *
1058                  * This is guaranteed by the fact that all LRU management
1059                  * functions are intermediated by the LRU API calls like
1060                  * list_lru_add and list_lru_del. List movement in this file
1061                  * only ever occur through this functions or through callbacks
1062                  * like this one, that are called from the LRU API.
1063                  *
1064                  * The only exceptions to this are functions like
1065                  * shrink_dentry_list, and code that first checks for the
1066                  * DCACHE_SHRINK_LIST flag.  Those are guaranteed to be
1067                  * operating only with stack provided lists after they are
1068                  * properly isolated from the main list.  It is thus, always a
1069                  * local access.
1070                  */
1071                 return LRU_ROTATE;
1072         }
1073 
1074         d_lru_shrink_move(lru, dentry, freeable);
1075         spin_unlock(&dentry->d_lock);
1076 
1077         return LRU_REMOVED;
1078 }
1079 
1080 /**
1081  * prune_dcache_sb - shrink the dcache
1082  * @sb: superblock
1083  * @sc: shrink control, passed to list_lru_shrink_walk()
1084  *
1085  * Attempt to shrink the superblock dcache LRU by @sc->nr_to_scan entries. This
1086  * is done when we need more memory and called from the superblock shrinker
1087  * function.
1088  *
1089  * This function may fail to free any resources if all the dentries are in
1090  * use.
1091  */
1092 long prune_dcache_sb(struct super_block *sb, struct shrink_control *sc)
1093 {
1094         LIST_HEAD(dispose);
1095         long freed;
1096 
1097         freed = list_lru_shrink_walk(&sb->s_dentry_lru, sc,
1098                                      dentry_lru_isolate, &dispose);
1099         shrink_dentry_list(&dispose);
1100         return freed;
1101 }
1102 
1103 static enum lru_status dentry_lru_isolate_shrink(struct list_head *item,
1104                 struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
1105 {
1106         struct list_head *freeable = arg;
1107         struct dentry   *dentry = container_of(item, struct dentry, d_lru);
1108 
1109         /*
1110          * we are inverting the lru lock/dentry->d_lock here,
1111          * so use a trylock. If we fail to get the lock, just skip
1112          * it
1113          */
1114         if (!spin_trylock(&dentry->d_lock))
1115                 return LRU_SKIP;
1116 
1117         d_lru_shrink_move(lru, dentry, freeable);
1118         spin_unlock(&dentry->d_lock);
1119 
1120         return LRU_REMOVED;
1121 }
1122 
1123 
1124 /**
1125  * shrink_dcache_sb - shrink dcache for a superblock
1126  * @sb: superblock
1127  *
1128  * Shrink the dcache for the specified super block. This is used to free
1129  * the dcache before unmounting a file system.
1130  */
1131 void shrink_dcache_sb(struct super_block *sb)
1132 {
1133         long freed;
1134 
1135         do {
1136                 LIST_HEAD(dispose);
1137 
1138                 freed = list_lru_walk(&sb->s_dentry_lru,
1139                         dentry_lru_isolate_shrink, &dispose, UINT_MAX);
1140 
1141                 this_cpu_sub(nr_dentry_unused, freed);
1142                 shrink_dentry_list(&dispose);
1143         } while (freed > 0);
1144 }
1145 EXPORT_SYMBOL(shrink_dcache_sb);
1146 
1147 /**
1148  * enum d_walk_ret - action to talke during tree walk
1149  * @D_WALK_CONTINUE:    contrinue walk
1150  * @D_WALK_QUIT:        quit walk
1151  * @D_WALK_NORETRY:     quit when retry is needed
1152  * @D_WALK_SKIP:        skip this dentry and its children
1153  */
1154 enum d_walk_ret {
1155         D_WALK_CONTINUE,
1156         D_WALK_QUIT,
1157         D_WALK_NORETRY,
1158         D_WALK_SKIP,
1159 };
1160 
1161 /**
1162  * d_walk - walk the dentry tree
1163  * @parent:     start of walk
1164  * @data:       data passed to @enter() and @finish()
1165  * @enter:      callback when first entering the dentry
1166  * @finish:     callback when successfully finished the walk
1167  *
1168  * The @enter() and @finish() callbacks are called with d_lock held.
1169  */
1170 static void d_walk(struct dentry *parent, void *data,
1171                    enum d_walk_ret (*enter)(void *, struct dentry *),
1172                    void (*finish)(void *))
1173 {
1174         struct dentry *this_parent;
1175         struct list_head *next;
1176         unsigned seq = 0;
1177         enum d_walk_ret ret;
1178         bool retry = true;
1179 
1180 again:
1181         read_seqbegin_or_lock(&rename_lock, &seq);
1182         this_parent = parent;
1183         spin_lock(&this_parent->d_lock);
1184 
1185         ret = enter(data, this_parent);
1186         switch (ret) {
1187         case D_WALK_CONTINUE:
1188                 break;
1189         case D_WALK_QUIT:
1190         case D_WALK_SKIP:
1191                 goto out_unlock;
1192         case D_WALK_NORETRY:
1193                 retry = false;
1194                 break;
1195         }
1196 repeat:
1197         next = this_parent->d_subdirs.next;
1198 resume:
1199         while (next != &this_parent->d_subdirs) {
1200                 struct list_head *tmp = next;
1201                 struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
1202                 next = tmp->next;
1203 
1204                 spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
1205 
1206                 ret = enter(data, dentry);
1207                 switch (ret) {
1208                 case D_WALK_CONTINUE:
1209                         break;
1210                 case D_WALK_QUIT:
1211                         spin_unlock(&dentry->d_lock);
1212                         goto out_unlock;
1213                 case D_WALK_NORETRY:
1214                         retry = false;
1215                         break;
1216                 case D_WALK_SKIP:
1217                         spin_unlock(&dentry->d_lock);
1218                         continue;
1219                 }
1220 
1221                 if (!list_empty(&dentry->d_subdirs)) {
1222                         spin_unlock(&this_parent->d_lock);
1223                         spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
1224                         this_parent = dentry;
1225                         spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
1226                         goto repeat;
1227                 }
1228                 spin_unlock(&dentry->d_lock);
1229         }
1230         /*
1231          * All done at this level ... ascend and resume the search.
1232          */
1233         rcu_read_lock();
1234 ascend:
1235         if (this_parent != parent) {
1236                 struct dentry *child = this_parent;
1237                 this_parent = child->d_parent;
1238 
1239                 spin_unlock(&child->d_lock);
1240                 spin_lock(&this_parent->d_lock);
1241 
1242                 /* might go back up the wrong parent if we have had a rename. */
1243                 if (need_seqretry(&rename_lock, seq))
1244                         goto rename_retry;
1245                 /* go into the first sibling still alive */
1246                 do {
1247                         next = child->d_child.next;
1248                         if (next == &this_parent->d_subdirs)
1249                                 goto ascend;
1250                         child = list_entry(next, struct dentry, d_child);
1251                 } while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED));
1252                 rcu_read_unlock();
1253                 goto resume;
1254         }
1255         if (need_seqretry(&rename_lock, seq))
1256                 goto rename_retry;
1257         rcu_read_unlock();
1258         if (finish)
1259                 finish(data);
1260 
1261 out_unlock:
1262         spin_unlock(&this_parent->d_lock);
1263         done_seqretry(&rename_lock, seq);
1264         return;
1265 
1266 rename_retry:
1267         spin_unlock(&this_parent->d_lock);
1268         rcu_read_unlock();
1269         BUG_ON(seq & 1);
1270         if (!retry)
1271                 return;
1272         seq = 1;
1273         goto again;
1274 }
1275 
1276 /*
1277  * Search for at least 1 mount point in the dentry's subdirs.
1278  * We descend to the next level whenever the d_subdirs
1279  * list is non-empty and continue searching.
1280  */
1281 
1282 static enum d_walk_ret check_mount(void *data, struct dentry *dentry)
1283 {
1284         int *ret = data;
1285         if (d_mountpoint(dentry)) {
1286                 *ret = 1;
1287                 return D_WALK_QUIT;
1288         }
1289         return D_WALK_CONTINUE;
1290 }
1291 
1292 /**
1293  * have_submounts - check for mounts over a dentry
1294  * @parent: dentry to check.
1295  *
1296  * Return true if the parent or its subdirectories contain
1297  * a mount point
1298  */
1299 int have_submounts(struct dentry *parent)
1300 {
1301         int ret = 0;
1302 
1303         d_walk(parent, &ret, check_mount, NULL);
1304 
1305         return ret;
1306 }
1307 EXPORT_SYMBOL(have_submounts);
1308 
1309 /*
1310  * Called by mount code to set a mountpoint and check if the mountpoint is
1311  * reachable (e.g. NFS can unhash a directory dentry and then the complete
1312  * subtree can become unreachable).
1313  *
1314  * Only one of d_invalidate() and d_set_mounted() must succeed.  For
1315  * this reason take rename_lock and d_lock on dentry and ancestors.
1316  */
1317 int d_set_mounted(struct dentry *dentry)
1318 {
1319         struct dentry *p;
1320         int ret = -ENOENT;
1321         write_seqlock(&rename_lock);
1322         for (p = dentry->d_parent; !IS_ROOT(p); p = p->d_parent) {
1323                 /* Need exclusion wrt. d_invalidate() */
1324                 spin_lock(&p->d_lock);
1325                 if (unlikely(d_unhashed(p))) {
1326                         spin_unlock(&p->d_lock);
1327                         goto out;
1328                 }
1329                 spin_unlock(&p->d_lock);
1330         }
1331         spin_lock(&dentry->d_lock);
1332         if (!d_unlinked(dentry)) {
1333                 dentry->d_flags |= DCACHE_MOUNTED;
1334                 ret = 0;
1335         }
1336         spin_unlock(&dentry->d_lock);
1337 out:
1338         write_sequnlock(&rename_lock);
1339         return ret;
1340 }
1341 
1342 /*
1343  * Search the dentry child list of the specified parent,
1344  * and move any unused dentries to the end of the unused
1345  * list for prune_dcache(). We descend to the next level
1346  * whenever the d_subdirs list is non-empty and continue
1347  * searching.
1348  *
1349  * It returns zero iff there are no unused children,
1350  * otherwise  it returns the number of children moved to
1351  * the end of the unused list. This may not be the total
1352  * number of unused children, because select_parent can
1353  * drop the lock and return early due to latency
1354  * constraints.
1355  */
1356 
1357 struct select_data {
1358         struct dentry *start;
1359         struct list_head dispose;
1360         int found;
1361 };
1362 
1363 static enum d_walk_ret select_collect(void *_data, struct dentry *dentry)
1364 {
1365         struct select_data *data = _data;
1366         enum d_walk_ret ret = D_WALK_CONTINUE;
1367 
1368         if (data->start == dentry)
1369                 goto out;
1370 
1371         if (dentry->d_flags & DCACHE_SHRINK_LIST) {
1372                 data->found++;
1373         } else {
1374                 if (dentry->d_flags & DCACHE_LRU_LIST)
1375                         d_lru_del(dentry);
1376                 if (!dentry->d_lockref.count) {
1377                         d_shrink_add(dentry, &data->dispose);
1378                         data->found++;
1379                 }
1380         }
1381         /*
1382          * We can return to the caller if we have found some (this
1383          * ensures forward progress). We'll be coming back to find
1384          * the rest.
1385          */
1386         if (!list_empty(&data->dispose))
1387                 ret = need_resched() ? D_WALK_QUIT : D_WALK_NORETRY;
1388 out:
1389         return ret;
1390 }
1391 
1392 /**
1393  * shrink_dcache_parent - prune dcache
1394  * @parent: parent of entries to prune
1395  *
1396  * Prune the dcache to remove unused children of the parent dentry.
1397  */
1398 void shrink_dcache_parent(struct dentry *parent)
1399 {
1400         for (;;) {
1401                 struct select_data data;
1402 
1403                 INIT_LIST_HEAD(&data.dispose);
1404                 data.start = parent;
1405                 data.found = 0;
1406 
1407                 d_walk(parent, &data, select_collect, NULL);
1408                 if (!data.found)
1409                         break;
1410 
1411                 shrink_dentry_list(&data.dispose);
1412                 cond_resched();
1413         }
1414 }
1415 EXPORT_SYMBOL(shrink_dcache_parent);
1416 
1417 static enum d_walk_ret umount_check(void *_data, struct dentry *dentry)
1418 {
1419         /* it has busy descendents; complain about those instead */
1420         if (!list_empty(&dentry->d_subdirs))
1421                 return D_WALK_CONTINUE;
1422 
1423         /* root with refcount 1 is fine */
1424         if (dentry == _data && dentry->d_lockref.count == 1)
1425                 return D_WALK_CONTINUE;
1426 
1427         printk(KERN_ERR "BUG: Dentry %p{i=%lx,n=%pd} "
1428                         " still in use (%d) [unmount of %s %s]\n",
1429                        dentry,
1430                        dentry->d_inode ?
1431                        dentry->d_inode->i_ino : 0UL,
1432                        dentry,
1433                        dentry->d_lockref.count,
1434                        dentry->d_sb->s_type->name,
1435                        dentry->d_sb->s_id);
1436         WARN_ON(1);
1437         return D_WALK_CONTINUE;
1438 }
1439 
1440 static void do_one_tree(struct dentry *dentry)
1441 {
1442         shrink_dcache_parent(dentry);
1443         d_walk(dentry, dentry, umount_check, NULL);
1444         d_drop(dentry);
1445         dput(dentry);
1446 }
1447 
1448 /*
1449  * destroy the dentries attached to a superblock on unmounting
1450  */
1451 void shrink_dcache_for_umount(struct super_block *sb)
1452 {
1453         struct dentry *dentry;
1454 
1455         WARN(down_read_trylock(&sb->s_umount), "s_umount should've been locked");
1456 
1457         dentry = sb->s_root;
1458         sb->s_root = NULL;
1459         do_one_tree(dentry);
1460 
1461         while (!hlist_bl_empty(&sb->s_anon)) {
1462                 dentry = dget(hlist_bl_entry(hlist_bl_first(&sb->s_anon), struct dentry, d_hash));
1463                 do_one_tree(dentry);
1464         }
1465 }
1466 
1467 struct detach_data {
1468         struct select_data select;
1469         struct dentry *mountpoint;
1470 };
1471 static enum d_walk_ret detach_and_collect(void *_data, struct dentry *dentry)
1472 {
1473         struct detach_data *data = _data;
1474 
1475         if (d_mountpoint(dentry)) {
1476                 __dget_dlock(dentry);
1477                 data->mountpoint = dentry;
1478                 return D_WALK_QUIT;
1479         }
1480 
1481         return select_collect(&data->select, dentry);
1482 }
1483 
1484 static void check_and_drop(void *_data)
1485 {
1486         struct detach_data *data = _data;
1487 
1488         if (!data->mountpoint && !data->select.found)
1489                 __d_drop(data->select.start);
1490 }
1491 
1492 /**
1493  * d_invalidate - detach submounts, prune dcache, and drop
1494  * @dentry: dentry to invalidate (aka detach, prune and drop)
1495  *
1496  * no dcache lock.
1497  *
1498  * The final d_drop is done as an atomic operation relative to
1499  * rename_lock ensuring there are no races with d_set_mounted.  This
1500  * ensures there are no unhashed dentries on the path to a mountpoint.
1501  */
1502 void d_invalidate(struct dentry *dentry)
1503 {
1504         /*
1505          * If it's already been dropped, return OK.
1506          */
1507         spin_lock(&dentry->d_lock);
1508         if (d_unhashed(dentry)) {
1509                 spin_unlock(&dentry->d_lock);
1510                 return;
1511         }
1512         spin_unlock(&dentry->d_lock);
1513 
1514         /* Negative dentries can be dropped without further checks */
1515         if (!dentry->d_inode) {
1516                 d_drop(dentry);
1517                 return;
1518         }
1519 
1520         for (;;) {
1521                 struct detach_data data;
1522 
1523                 data.mountpoint = NULL;
1524                 INIT_LIST_HEAD(&data.select.dispose);
1525                 data.select.start = dentry;
1526                 data.select.found = 0;
1527 
1528                 d_walk(dentry, &data, detach_and_collect, check_and_drop);
1529 
1530                 if (data.select.found)
1531                         shrink_dentry_list(&data.select.dispose);
1532 
1533                 if (data.mountpoint) {
1534                         detach_mounts(data.mountpoint);
1535                         dput(data.mountpoint);
1536                 }
1537 
1538                 if (!data.mountpoint && !data.select.found)
1539                         break;
1540 
1541                 cond_resched();
1542         }
1543 }
1544 EXPORT_SYMBOL(d_invalidate);
1545 
1546 /**
1547  * __d_alloc    -       allocate a dcache entry
1548  * @sb: filesystem it will belong to
1549  * @name: qstr of the name
1550  *
1551  * Allocates a dentry. It returns %NULL if there is insufficient memory
1552  * available. On a success the dentry is returned. The name passed in is
1553  * copied and the copy passed in may be reused after this call.
1554  */
1555  
1556 struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
1557 {
1558         struct dentry *dentry;
1559         char *dname;
1560 
1561         dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
1562         if (!dentry)
1563                 return NULL;
1564 
1565         /*
1566          * We guarantee that the inline name is always NUL-terminated.
1567          * This way the memcpy() done by the name switching in rename
1568          * will still always have a NUL at the end, even if we might
1569          * be overwriting an internal NUL character
1570          */
1571         dentry->d_iname[DNAME_INLINE_LEN-1] = 0;
1572         if (name->len > DNAME_INLINE_LEN-1) {
1573                 size_t size = offsetof(struct external_name, name[1]);
1574                 struct external_name *p = kmalloc(size + name->len, GFP_KERNEL);
1575                 if (!p) {
1576                         kmem_cache_free(dentry_cache, dentry); 
1577                         return NULL;
1578                 }
1579                 atomic_set(&p->u.count, 1);
1580                 dname = p->name;
1581                 if (IS_ENABLED(CONFIG_DCACHE_WORD_ACCESS))
1582                         kasan_unpoison_shadow(dname,
1583                                 round_up(name->len + 1, sizeof(unsigned long)));
1584         } else  {
1585                 dname = dentry->d_iname;
1586         }       
1587 
1588         dentry->d_name.len = name->len;
1589         dentry->d_name.hash = name->hash;
1590         memcpy(dname, name->name, name->len);
1591         dname[name->len] = 0;
1592 
1593         /* Make sure we always see the terminating NUL character */
1594         smp_wmb();
1595         dentry->d_name.name = dname;
1596 
1597         dentry->d_lockref.count = 1;
1598         dentry->d_flags = 0;
1599         spin_lock_init(&dentry->d_lock);
1600         seqcount_init(&dentry->d_seq);
1601         dentry->d_inode = NULL;
1602         dentry->d_parent = dentry;
1603         dentry->d_sb = sb;
1604         dentry->d_op = NULL;
1605         dentry->d_fsdata = NULL;
1606         INIT_HLIST_BL_NODE(&dentry->d_hash);
1607         INIT_LIST_HEAD(&dentry->d_lru);
1608         INIT_LIST_HEAD(&dentry->d_subdirs);
1609         INIT_HLIST_NODE(&dentry->d_u.d_alias);
1610         INIT_LIST_HEAD(&dentry->d_child);
1611         d_set_d_op(dentry, dentry->d_sb->s_d_op);
1612 
1613         this_cpu_inc(nr_dentry);
1614 
1615         return dentry;
1616 }
1617 
1618 /**
1619  * d_alloc      -       allocate a dcache entry
1620  * @parent: parent of entry to allocate
1621  * @name: qstr of the name
1622  *
1623  * Allocates a dentry. It returns %NULL if there is insufficient memory
1624  * available. On a success the dentry is returned. The name passed in is
1625  * copied and the copy passed in may be reused after this call.
1626  */
1627 struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
1628 {
1629         struct dentry *dentry = __d_alloc(parent->d_sb, name);
1630         if (!dentry)
1631                 return NULL;
1632 
1633         spin_lock(&parent->d_lock);
1634         /*
1635          * don't need child lock because it is not subject
1636          * to concurrency here
1637          */
1638         __dget_dlock(parent);
1639         dentry->d_parent = parent;
1640         list_add(&dentry->d_child, &parent->d_subdirs);
1641         spin_unlock(&parent->d_lock);
1642 
1643         return dentry;
1644 }
1645 EXPORT_SYMBOL(d_alloc);
1646 
1647 /**
1648  * d_alloc_pseudo - allocate a dentry (for lookup-less filesystems)
1649  * @sb: the superblock
1650  * @name: qstr of the name
1651  *
1652  * For a filesystem that just pins its dentries in memory and never
1653  * performs lookups at all, return an unhashed IS_ROOT dentry.
1654  */
1655 struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
1656 {
1657         return __d_alloc(sb, name);
1658 }
1659 EXPORT_SYMBOL(d_alloc_pseudo);
1660 
1661 struct dentry *d_alloc_name(struct dentry *parent, const char *name)
1662 {
1663         struct qstr q;
1664 
1665         q.name = name;
1666         q.len = strlen(name);
1667         q.hash = full_name_hash(q.name, q.len);
1668         return d_alloc(parent, &q);
1669 }
1670 EXPORT_SYMBOL(d_alloc_name);
1671 
1672 void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
1673 {
1674         WARN_ON_ONCE(dentry->d_op);
1675         WARN_ON_ONCE(dentry->d_flags & (DCACHE_OP_HASH  |
1676                                 DCACHE_OP_COMPARE       |
1677                                 DCACHE_OP_REVALIDATE    |
1678                                 DCACHE_OP_WEAK_REVALIDATE       |
1679                                 DCACHE_OP_DELETE        |
1680                                 DCACHE_OP_SELECT_INODE));
1681         dentry->d_op = op;
1682         if (!op)
1683                 return;
1684         if (op->d_hash)
1685                 dentry->d_flags |= DCACHE_OP_HASH;
1686         if (op->d_compare)
1687                 dentry->d_flags |= DCACHE_OP_COMPARE;
1688         if (op->d_revalidate)
1689                 dentry->d_flags |= DCACHE_OP_REVALIDATE;
1690         if (op->d_weak_revalidate)
1691                 dentry->d_flags |= DCACHE_OP_WEAK_REVALIDATE;
1692         if (op->d_delete)
1693                 dentry->d_flags |= DCACHE_OP_DELETE;
1694         if (op->d_prune)
1695                 dentry->d_flags |= DCACHE_OP_PRUNE;
1696         if (op->d_select_inode)
1697                 dentry->d_flags |= DCACHE_OP_SELECT_INODE;
1698 
1699 }
1700 EXPORT_SYMBOL(d_set_d_op);
1701 
1702 
1703 /*
1704  * d_set_fallthru - Mark a dentry as falling through to a lower layer
1705  * @dentry - The dentry to mark
1706  *
1707  * Mark a dentry as falling through to the lower layer (as set with
1708  * d_pin_lower()).  This flag may be recorded on the medium.
1709  */
1710 void d_set_fallthru(struct dentry *dentry)
1711 {
1712         spin_lock(&dentry->d_lock);
1713         dentry->d_flags |= DCACHE_FALLTHRU;
1714         spin_unlock(&dentry->d_lock);
1715 }
1716 EXPORT_SYMBOL(d_set_fallthru);
1717 
1718 static unsigned d_flags_for_inode(struct inode *inode)
1719 {
1720         unsigned add_flags = DCACHE_REGULAR_TYPE;
1721 
1722         if (!inode)
1723                 return DCACHE_MISS_TYPE;
1724 
1725         if (S_ISDIR(inode->i_mode)) {
1726                 add_flags = DCACHE_DIRECTORY_TYPE;
1727                 if (unlikely(!(inode->i_opflags & IOP_LOOKUP))) {
1728                         if (unlikely(!inode->i_op->lookup))
1729                                 add_flags = DCACHE_AUTODIR_TYPE;
1730                         else
1731                                 inode->i_opflags |= IOP_LOOKUP;
1732                 }
1733                 goto type_determined;
1734         }
1735 
1736         if (unlikely(!(inode->i_opflags & IOP_NOFOLLOW))) {
1737                 if (unlikely(inode->i_op->follow_link)) {
1738                         add_flags = DCACHE_SYMLINK_TYPE;
1739                         goto type_determined;
1740                 }
1741                 inode->i_opflags |= IOP_NOFOLLOW;
1742         }
1743 
1744         if (unlikely(!S_ISREG(inode->i_mode)))
1745                 add_flags = DCACHE_SPECIAL_TYPE;
1746 
1747 type_determined:
1748         if (unlikely(IS_AUTOMOUNT(inode)))
1749                 add_flags |= DCACHE_NEED_AUTOMOUNT;
1750         return add_flags;
1751 }
1752 
1753 static void __d_instantiate(struct dentry *dentry, struct inode *inode)
1754 {
1755         unsigned add_flags = d_flags_for_inode(inode);
1756 
1757         spin_lock(&dentry->d_lock);
1758         if (inode)
1759                 hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
1760         __d_set_inode_and_type(dentry, inode, add_flags);
1761         dentry_rcuwalk_invalidate(dentry);
1762         spin_unlock(&dentry->d_lock);
1763         fsnotify_d_instantiate(dentry, inode);
1764 }
1765 
1766 /**
1767  * d_instantiate - fill in inode information for a dentry
1768  * @entry: dentry to complete
1769  * @inode: inode to attach to this dentry
1770  *
1771  * Fill in inode information in the entry.
1772  *
1773  * This turns negative dentries into productive full members
1774  * of society.
1775  *
1776  * NOTE! This assumes that the inode count has been incremented
1777  * (or otherwise set) by the caller to indicate that it is now
1778  * in use by the dcache.
1779  */
1780  
1781 void d_instantiate(struct dentry *entry, struct inode * inode)
1782 {
1783         BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
1784         if (inode)
1785                 spin_lock(&inode->i_lock);
1786         __d_instantiate(entry, inode);
1787         if (inode)
1788                 spin_unlock(&inode->i_lock);
1789         security_d_instantiate(entry, inode);
1790 }
1791 EXPORT_SYMBOL(d_instantiate);
1792 
1793 /**
1794  * d_instantiate_unique - instantiate a non-aliased dentry
1795  * @entry: dentry to instantiate
1796  * @inode: inode to attach to this dentry
1797  *
1798  * Fill in inode information in the entry. On success, it returns NULL.
1799  * If an unhashed alias of "entry" already exists, then we return the
1800  * aliased dentry instead and drop one reference to inode.
1801  *
1802  * Note that in order to avoid conflicts with rename() etc, the caller
1803  * had better be holding the parent directory semaphore.
1804  *
1805  * This also assumes that the inode count has been incremented
1806  * (or otherwise set) by the caller to indicate that it is now
1807  * in use by the dcache.
1808  */
1809 static struct dentry *__d_instantiate_unique(struct dentry *entry,
1810                                              struct inode *inode)
1811 {
1812         struct dentry *alias;
1813         int len = entry->d_name.len;
1814         const char *name = entry->d_name.name;
1815         unsigned int hash = entry->d_name.hash;
1816 
1817         if (!inode) {
1818                 __d_instantiate(entry, NULL);
1819                 return NULL;
1820         }
1821 
1822         hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
1823                 /*
1824                  * Don't need alias->d_lock here, because aliases with
1825                  * d_parent == entry->d_parent are not subject to name or
1826                  * parent changes, because the parent inode i_mutex is held.
1827                  */
1828                 if (alias->d_name.hash != hash)
1829                         continue;
1830                 if (alias->d_parent != entry->d_parent)
1831                         continue;
1832                 if (alias->d_name.len != len)
1833                         continue;
1834                 if (dentry_cmp(alias, name, len))
1835                         continue;
1836                 __dget(alias);
1837                 return alias;
1838         }
1839 
1840         __d_instantiate(entry, inode);
1841         return NULL;
1842 }
1843 
1844 struct dentry *d_instantiate_unique(struct dentry *entry, struct inode *inode)
1845 {
1846         struct dentry *result;
1847 
1848         BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
1849 
1850         if (inode)
1851                 spin_lock(&inode->i_lock);
1852         result = __d_instantiate_unique(entry, inode);
1853         if (inode)
1854                 spin_unlock(&inode->i_lock);
1855 
1856         if (!result) {
1857                 security_d_instantiate(entry, inode);
1858                 return NULL;
1859         }
1860 
1861         BUG_ON(!d_unhashed(result));
1862         iput(inode);
1863         return result;
1864 }
1865 
1866 EXPORT_SYMBOL(d_instantiate_unique);
1867 
1868 /**
1869  * d_instantiate_no_diralias - instantiate a non-aliased dentry
1870  * @entry: dentry to complete
1871  * @inode: inode to attach to this dentry
1872  *
1873  * Fill in inode information in the entry.  If a directory alias is found, then
1874  * return an error (and drop inode).  Together with d_materialise_unique() this
1875  * guarantees that a directory inode may never have more than one alias.
1876  */
1877 int d_instantiate_no_diralias(struct dentry *entry, struct inode *inode)
1878 {
1879         BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
1880 
1881         spin_lock(&inode->i_lock);
1882         if (S_ISDIR(inode->i_mode) && !hlist_empty(&inode->i_dentry)) {
1883                 spin_unlock(&inode->i_lock);
1884                 iput(inode);
1885                 return -EBUSY;
1886         }
1887         __d_instantiate(entry, inode);
1888         spin_unlock(&inode->i_lock);
1889         security_d_instantiate(entry, inode);
1890 
1891         return 0;
1892 }
1893 EXPORT_SYMBOL(d_instantiate_no_diralias);
1894 
1895 struct dentry *d_make_root(struct inode *root_inode)
1896 {
1897         struct dentry *res = NULL;
1898 
1899         if (root_inode) {
1900                 static const struct qstr name = QSTR_INIT("/", 1);
1901 
1902                 res = __d_alloc(root_inode->i_sb, &name);
1903                 if (res)
1904                         d_instantiate(res, root_inode);
1905                 else
1906                         iput(root_inode);
1907         }
1908         return res;
1909 }
1910 EXPORT_SYMBOL(d_make_root);
1911 
1912 static struct dentry * __d_find_any_alias(struct inode *inode)
1913 {
1914         struct dentry *alias;
1915 
1916         if (hlist_empty(&inode->i_dentry))
1917                 return NULL;
1918         alias = hlist_entry(inode->i_dentry.first, struct dentry, d_u.d_alias);
1919         __dget(alias);
1920         return alias;
1921 }
1922 
1923 /**
1924  * d_find_any_alias - find any alias for a given inode
1925  * @inode: inode to find an alias for
1926  *
1927  * If any aliases exist for the given inode, take and return a
1928  * reference for one of them.  If no aliases exist, return %NULL.
1929  */
1930 struct dentry *d_find_any_alias(struct inode *inode)
1931 {
1932         struct dentry *de;
1933 
1934         spin_lock(&inode->i_lock);
1935         de = __d_find_any_alias(inode);
1936         spin_unlock(&inode->i_lock);
1937         return de;
1938 }
1939 EXPORT_SYMBOL(d_find_any_alias);
1940 
1941 static struct dentry *__d_obtain_alias(struct inode *inode, int disconnected)
1942 {
1943         static const struct qstr anonstring = QSTR_INIT("/", 1);
1944         struct dentry *tmp;
1945         struct dentry *res;
1946         unsigned add_flags;
1947 
1948         if (!inode)
1949                 return ERR_PTR(-ESTALE);
1950         if (IS_ERR(inode))
1951                 return ERR_CAST(inode);
1952 
1953         res = d_find_any_alias(inode);
1954         if (res)
1955                 goto out_iput;
1956 
1957         tmp = __d_alloc(inode->i_sb, &anonstring);
1958         if (!tmp) {
1959                 res = ERR_PTR(-ENOMEM);
1960                 goto out_iput;
1961         }
1962 
1963         spin_lock(&inode->i_lock);
1964         res = __d_find_any_alias(inode);
1965         if (res) {
1966                 spin_unlock(&inode->i_lock);
1967                 dput(tmp);
1968                 goto out_iput;
1969         }
1970 
1971         /* attach a disconnected dentry */
1972         add_flags = d_flags_for_inode(inode);
1973 
1974         if (disconnected)
1975                 add_flags |= DCACHE_DISCONNECTED;
1976 
1977         spin_lock(&tmp->d_lock);
1978         __d_set_inode_and_type(tmp, inode, add_flags);
1979         hlist_add_head(&tmp->d_u.d_alias, &inode->i_dentry);
1980         hlist_bl_lock(&tmp->d_sb->s_anon);
1981         hlist_bl_add_head(&tmp->d_hash, &tmp->d_sb->s_anon);
1982         hlist_bl_unlock(&tmp->d_sb->s_anon);
1983         spin_unlock(&tmp->d_lock);
1984         spin_unlock(&inode->i_lock);
1985         security_d_instantiate(tmp, inode);
1986 
1987         return tmp;
1988 
1989  out_iput:
1990         if (res && !IS_ERR(res))
1991                 security_d_instantiate(res, inode);
1992         iput(inode);
1993         return res;
1994 }
1995 
1996 /**
1997  * d_obtain_alias - find or allocate a DISCONNECTED dentry for a given inode
1998  * @inode: inode to allocate the dentry for
1999  *
2000  * Obtain a dentry for an inode resulting from NFS filehandle conversion or
2001  * similar open by handle operations.  The returned dentry may be anonymous,
2002  * or may have a full name (if the inode was already in the cache).
2003  *
2004  * When called on a directory inode, we must ensure that the inode only ever
2005  * has one dentry.  If a dentry is found, that is returned instead of
2006  * allocating a new one.
2007  *
2008  * On successful return, the reference to the inode has been transferred
2009  * to the dentry.  In case of an error the reference on the inode is released.
2010  * To make it easier to use in export operations a %NULL or IS_ERR inode may
2011  * be passed in and the error will be propagated to the return value,
2012  * with a %NULL @inode replaced by ERR_PTR(-ESTALE).
2013  */
2014 struct dentry *d_obtain_alias(struct inode *inode)
2015 {
2016         return __d_obtain_alias(inode, 1);
2017 }
2018 EXPORT_SYMBOL(d_obtain_alias);
2019 
2020 /**
2021  * d_obtain_root - find or allocate a dentry for a given inode
2022  * @inode: inode to allocate the dentry for
2023  *
2024  * Obtain an IS_ROOT dentry for the root of a filesystem.
2025  *
2026  * We must ensure that directory inodes only ever have one dentry.  If a
2027  * dentry is found, that is returned instead of allocating a new one.
2028  *
2029  * On successful return, the reference to the inode has been transferred
2030  * to the dentry.  In case of an error the reference on the inode is
2031  * released.  A %NULL or IS_ERR inode may be passed in and will be the
2032  * error will be propagate to the return value, with a %NULL @inode
2033  * replaced by ERR_PTR(-ESTALE).
2034  */
2035 struct dentry *d_obtain_root(struct inode *inode)
2036 {
2037         return __d_obtain_alias(inode, 0);
2038 }
2039 EXPORT_SYMBOL(d_obtain_root);
2040 
2041 /**
2042  * d_add_ci - lookup or allocate new dentry with case-exact name
2043  * @inode:  the inode case-insensitive lookup has found
2044  * @dentry: the negative dentry that was passed to the parent's lookup func
2045  * @name:   the case-exact name to be associated with the returned dentry
2046  *
2047  * This is to avoid filling the dcache with case-insensitive names to the
2048  * same inode, only the actual correct case is stored in the dcache for
2049  * case-insensitive filesystems.
2050  *
2051  * For a case-insensitive lookup match and if the the case-exact dentry
2052  * already exists in in the dcache, use it and return it.
2053  *
2054  * If no entry exists with the exact case name, allocate new dentry with
2055  * the exact case, and return the spliced entry.
2056  */
2057 struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
2058                         struct qstr *name)
2059 {
2060         struct dentry *found;
2061         struct dentry *new;
2062 
2063         /*
2064          * First check if a dentry matching the name already exists,
2065          * if not go ahead and create it now.
2066          */
2067         found = d_hash_and_lookup(dentry->d_parent, name);
2068         if (!found) {
2069                 new = d_alloc(dentry->d_parent, name);
2070                 if (!new) {
2071                         found = ERR_PTR(-ENOMEM);
2072                 } else {
2073                         found = d_splice_alias(inode, new);
2074                         if (found) {
2075                                 dput(new);
2076                                 return found;
2077                         }
2078                         return new;
2079                 }
2080         }
2081         iput(inode);
2082         return found;
2083 }
2084 EXPORT_SYMBOL(d_add_ci);
2085 
2086 /*
2087  * Do the slow-case of the dentry name compare.
2088  *
2089  * Unlike the dentry_cmp() function, we need to atomically
2090  * load the name and length information, so that the
2091  * filesystem can rely on them, and can use the 'name' and
2092  * 'len' information without worrying about walking off the
2093  * end of memory etc.
2094  *
2095  * Thus the read_seqcount_retry() and the "duplicate" info
2096  * in arguments (the low-level filesystem should not look
2097  * at the dentry inode or name contents directly, since
2098  * rename can change them while we're in RCU mode).
2099  */
2100 enum slow_d_compare {
2101         D_COMP_OK,
2102         D_COMP_NOMATCH,
2103         D_COMP_SEQRETRY,
2104 };
2105 
2106 static noinline enum slow_d_compare slow_dentry_cmp(
2107                 const struct dentry *parent,
2108                 struct dentry *dentry,
2109                 unsigned int seq,
2110                 const struct qstr *name)
2111 {
2112         int tlen = dentry->d_name.len;
2113         const char *tname = dentry->d_name.name;
2114 
2115         if (read_seqcount_retry(&dentry->d_seq, seq)) {
2116                 cpu_relax();
2117                 return D_COMP_SEQRETRY;
2118         }
2119         if (parent->d_op->d_compare(parent, dentry, tlen, tname, name))
2120                 return D_COMP_NOMATCH;
2121         return D_COMP_OK;
2122 }
2123 
2124 /**
2125  * __d_lookup_rcu - search for a dentry (racy, store-free)
2126  * @parent: parent dentry
2127  * @name: qstr of name we wish to find
2128  * @seqp: returns d_seq value at the point where the dentry was found
2129  * Returns: dentry, or NULL
2130  *
2131  * __d_lookup_rcu is the dcache lookup function for rcu-walk name
2132  * resolution (store-free path walking) design described in
2133  * Documentation/filesystems/path-lookup.txt.
2134  *
2135  * This is not to be used outside core vfs.
2136  *
2137  * __d_lookup_rcu must only be used in rcu-walk mode, ie. with vfsmount lock
2138  * held, and rcu_read_lock held. The returned dentry must not be stored into
2139  * without taking d_lock and checking d_seq sequence count against @seq
2140  * returned here.
2141  *
2142  * A refcount may be taken on the found dentry with the d_rcu_to_refcount
2143  * function.
2144  *
2145  * Alternatively, __d_lookup_rcu may be called again to look up the child of
2146  * the returned dentry, so long as its parent's seqlock is checked after the
2147  * child is looked up. Thus, an interlocking stepping of sequence lock checks
2148  * is formed, giving integrity down the path walk.
2149  *
2150  * NOTE! The caller *has* to check the resulting dentry against the sequence
2151  * number we've returned before using any of the resulting dentry state!
2152  */
2153 struct dentry *__d_lookup_rcu(const struct dentry *parent,
2154                                 const struct qstr *name,
2155                                 unsigned *seqp)
2156 {
2157         u64 hashlen = name->hash_len;
2158         const unsigned char *str = name->name;
2159         struct hlist_bl_head *b = d_hash(parent, hashlen_hash(hashlen));
2160         struct hlist_bl_node *node;
2161         struct dentry *dentry;
2162 
2163         /*
2164          * Note: There is significant duplication with __d_lookup_rcu which is
2165          * required to prevent single threaded performance regressions
2166          * especially on architectures where smp_rmb (in seqcounts) are costly.
2167          * Keep the two functions in sync.
2168          */
2169 
2170         /*
2171          * The hash list is protected using RCU.
2172          *
2173          * Carefully use d_seq when comparing a candidate dentry, to avoid
2174          * races with d_move().
2175          *
2176          * It is possible that concurrent renames can mess up our list
2177          * walk here and result in missing our dentry, resulting in the
2178          * false-negative result. d_lookup() protects against concurrent
2179          * renames using rename_lock seqlock.
2180          *
2181          * See Documentation/filesystems/path-lookup.txt for more details.
2182          */
2183         hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
2184                 unsigned seq;
2185 
2186 seqretry:
2187                 /*
2188                  * The dentry sequence count protects us from concurrent
2189                  * renames, and thus protects parent and name fields.
2190                  *
2191                  * The caller must perform a seqcount check in order
2192                  * to do anything useful with the returned dentry.
2193                  *
2194                  * NOTE! We do a "raw" seqcount_begin here. That means that
2195                  * we don't wait for the sequence count to stabilize if it
2196                  * is in the middle of a sequence change. If we do the slow
2197                  * dentry compare, we will do seqretries until it is stable,
2198                  * and if we end up with a successful lookup, we actually
2199                  * want to exit RCU lookup anyway.
2200                  */
2201                 seq = raw_seqcount_begin(&dentry->d_seq);
2202                 if (dentry->d_parent != parent)
2203                         continue;
2204                 if (d_unhashed(dentry))
2205                         continue;
2206 
2207                 if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
2208                         if (dentry->d_name.hash != hashlen_hash(hashlen))
2209                                 continue;
2210                         *seqp = seq;
2211                         switch (slow_dentry_cmp(parent, dentry, seq, name)) {
2212                         case D_COMP_OK:
2213                                 return dentry;
2214                         case D_COMP_NOMATCH:
2215                                 continue;
2216                         default:
2217                                 goto seqretry;
2218                         }
2219                 }
2220 
2221                 if (dentry->d_name.hash_len != hashlen)
2222                         continue;
2223                 *seqp = seq;
2224                 if (!dentry_cmp(dentry, str, hashlen_len(hashlen)))
2225                         return dentry;
2226         }
2227         return NULL;
2228 }
2229 
2230 /**
2231  * d_lookup - search for a dentry
2232  * @parent: parent dentry
2233  * @name: qstr of name we wish to find
2234  * Returns: dentry, or NULL
2235  *
2236  * d_lookup searches the children of the parent dentry for the name in
2237  * question. If the dentry is found its reference count is incremented and the
2238  * dentry is returned. The caller must use dput to free the entry when it has
2239  * finished using it. %NULL is returned if the dentry does not exist.
2240  */
2241 struct dentry *d_lookup(const struct dentry *parent, const struct qstr *name)
2242 {
2243         struct dentry *dentry;
2244         unsigned seq;
2245 
2246         do {
2247                 seq = read_seqbegin(&rename_lock);
2248                 dentry = __d_lookup(parent, name);
2249                 if (dentry)
2250                         break;
2251         } while (read_seqretry(&rename_lock, seq));
2252         return dentry;
2253 }
2254 EXPORT_SYMBOL(d_lookup);
2255 
2256 /**
2257  * __d_lookup - search for a dentry (racy)
2258  * @parent: parent dentry
2259  * @name: qstr of name we wish to find
2260  * Returns: dentry, or NULL
2261  *
2262  * __d_lookup is like d_lookup, however it may (rarely) return a
2263  * false-negative result due to unrelated rename activity.
2264  *
2265  * __d_lookup is slightly faster by avoiding rename_lock read seqlock,
2266  * however it must be used carefully, eg. with a following d_lookup in
2267  * the case of failure.
2268  *
2269  * __d_lookup callers must be commented.
2270  */
2271 struct dentry *__d_lookup(const struct dentry *parent, const struct qstr *name)
2272 {
2273         unsigned int len = name->len;
2274         unsigned int hash = name->hash;
2275         const unsigned char *str = name->name;
2276         struct hlist_bl_head *b = d_hash(parent, hash);
2277         struct hlist_bl_node *node;
2278         struct dentry *found = NULL;
2279         struct dentry *dentry;
2280 
2281         /*
2282          * Note: There is significant duplication with __d_lookup_rcu which is
2283          * required to prevent single threaded performance regressions
2284          * especially on architectures where smp_rmb (in seqcounts) are costly.
2285          * Keep the two functions in sync.
2286          */
2287 
2288         /*
2289          * The hash list is protected using RCU.
2290          *
2291          * Take d_lock when comparing a candidate dentry, to avoid races
2292          * with d_move().
2293          *
2294          * It is possible that concurrent renames can mess up our list
2295          * walk here and result in missing our dentry, resulting in the
2296          * false-negative result. d_lookup() protects against concurrent
2297          * renames using rename_lock seqlock.
2298          *
2299          * See Documentation/filesystems/path-lookup.txt for more details.
2300          */
2301         rcu_read_lock();
2302         
2303         hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
2304 
2305                 if (dentry->d_name.hash != hash)
2306                         continue;
2307 
2308                 spin_lock(&dentry->d_lock);
2309                 if (dentry->d_parent != parent)
2310                         goto next;
2311                 if (d_unhashed(dentry))
2312                         goto next;
2313 
2314                 /*
2315                  * It is safe to compare names since d_move() cannot
2316                  * change the qstr (protected by d_lock).
2317                  */
2318                 if (parent->d_flags & DCACHE_OP_COMPARE) {
2319                         int tlen = dentry->d_name.len;
2320                         const char *tname = dentry->d_name.name;
2321                         if (parent->d_op->d_compare(parent, dentry, tlen, tname, name))
2322                                 goto next;
2323                 } else {
2324                         if (dentry->d_name.len != len)
2325                                 goto next;
2326                         if (dentry_cmp(dentry, str, len))
2327                                 goto next;
2328                 }
2329 
2330                 dentry->d_lockref.count++;
2331                 found = dentry;
2332                 spin_unlock(&dentry->d_lock);
2333                 break;
2334 next:
2335                 spin_unlock(&dentry->d_lock);
2336         }
2337         rcu_read_unlock();
2338 
2339         return found;
2340 }
2341 
2342 /**
2343  * d_hash_and_lookup - hash the qstr then search for a dentry
2344  * @dir: Directory to search in
2345  * @name: qstr of name we wish to find
2346  *
2347  * On lookup failure NULL is returned; on bad name - ERR_PTR(-error)
2348  */
2349 struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
2350 {
2351         /*
2352          * Check for a fs-specific hash function. Note that we must
2353          * calculate the standard hash first, as the d_op->d_hash()
2354          * routine may choose to leave the hash value unchanged.
2355          */
2356         name->hash = full_name_hash(name->name, name->len);
2357         if (dir->d_flags & DCACHE_OP_HASH) {
2358                 int err = dir->d_op->d_hash(dir, name);
2359                 if (unlikely(err < 0))
2360                         return ERR_PTR(err);
2361         }
2362         return d_lookup(dir, name);
2363 }
2364 EXPORT_SYMBOL(d_hash_and_lookup);
2365 
2366 /*
2367  * When a file is deleted, we have two options:
2368  * - turn this dentry into a negative dentry
2369  * - unhash this dentry and free it.
2370  *
2371  * Usually, we want to just turn this into
2372  * a negative dentry, but if anybody else is
2373  * currently using the dentry or the inode
2374  * we can't do that and we fall back on removing
2375  * it from the hash queues and waiting for
2376  * it to be deleted later when it has no users
2377  */
2378  
2379 /**
2380  * d_delete - delete a dentry
2381  * @dentry: The dentry to delete
2382  *
2383  * Turn the dentry into a negative dentry if possible, otherwise
2384  * remove it from the hash queues so it can be deleted later
2385  */
2386  
2387 void d_delete(struct dentry * dentry)
2388 {
2389         struct inode *inode;
2390         int isdir = 0;
2391         /*
2392          * Are we the only user?
2393          */
2394 again:
2395         spin_lock(&dentry->d_lock);
2396         inode = dentry->d_inode;
2397         isdir = S_ISDIR(inode->i_mode);
2398         if (dentry->d_lockref.count == 1) {
2399                 if (!spin_trylock(&inode->i_lock)) {
2400                         spin_unlock(&dentry->d_lock);
2401                         cpu_relax();
2402                         goto again;
2403                 }
2404                 dentry->d_flags &= ~DCACHE_CANT_MOUNT;
2405                 dentry_unlink_inode(dentry);
2406                 fsnotify_nameremove(dentry, isdir);
2407                 return;
2408         }
2409 
2410         if (!d_unhashed(dentry))
2411                 __d_drop(dentry);
2412 
2413         spin_unlock(&dentry->d_lock);
2414 
2415         fsnotify_nameremove(dentry, isdir);
2416 }
2417 EXPORT_SYMBOL(d_delete);
2418 
2419 static void __d_rehash(struct dentry * entry, struct hlist_bl_head *b)
2420 {
2421         BUG_ON(!d_unhashed(entry));
2422         hlist_bl_lock(b);
2423         entry->d_flags |= DCACHE_RCUACCESS;
2424         hlist_bl_add_head_rcu(&entry->d_hash, b);
2425         hlist_bl_unlock(b);
2426 }
2427 
2428 static void _d_rehash(struct dentry * entry)
2429 {
2430         __d_rehash(entry, d_hash(entry->d_parent, entry->d_name.hash));
2431 }
2432 
2433 /**
2434  * d_rehash     - add an entry back to the hash
2435  * @entry: dentry to add to the hash
2436  *
2437  * Adds a dentry to the hash according to its name.
2438  */
2439  
2440 void d_rehash(struct dentry * entry)
2441 {
2442         spin_lock(&entry->d_lock);
2443         _d_rehash(entry);
2444         spin_unlock(&entry->d_lock);
2445 }
2446 EXPORT_SYMBOL(d_rehash);
2447 
2448 /**
2449  * dentry_update_name_case - update case insensitive dentry with a new name
2450  * @dentry: dentry to be updated
2451  * @name: new name
2452  *
2453  * Update a case insensitive dentry with new case of name.
2454  *
2455  * dentry must have been returned by d_lookup with name @name. Old and new
2456  * name lengths must match (ie. no d_compare which allows mismatched name
2457  * lengths).
2458  *
2459  * Parent inode i_mutex must be held over d_lookup and into this call (to
2460  * keep renames and concurrent inserts, and readdir(2) away).
2461  */
2462 void dentry_update_name_case(struct dentry *dentry, struct qstr *name)
2463 {
2464         BUG_ON(!mutex_is_locked(&dentry->d_parent->d_inode->i_mutex));
2465         BUG_ON(dentry->d_name.len != name->len); /* d_lookup gives this */
2466 
2467         spin_lock(&dentry->d_lock);
2468         write_seqcount_begin(&dentry->d_seq);
2469         memcpy((unsigned char *)dentry->d_name.name, name->name, name->len);
2470         write_seqcount_end(&dentry->d_seq);
2471         spin_unlock(&dentry->d_lock);
2472 }
2473 EXPORT_SYMBOL(dentry_update_name_case);
2474 
2475 static void swap_names(struct dentry *dentry, struct dentry *target)
2476 {
2477         if (unlikely(dname_external(target))) {
2478                 if (unlikely(dname_external(dentry))) {
2479                         /*
2480                          * Both external: swap the pointers
2481                          */
2482                         swap(target->d_name.name, dentry->d_name.name);
2483                 } else {
2484                         /*
2485                          * dentry:internal, target:external.  Steal target's
2486                          * storage and make target internal.
2487                          */
2488                         memcpy(target->d_iname, dentry->d_name.name,
2489                                         dentry->d_name.len + 1);
2490                         dentry->d_name.name = target->d_name.name;
2491                         target->d_name.name = target->d_iname;
2492                 }
2493         } else {
2494                 if (unlikely(dname_external(dentry))) {
2495                         /*
2496                          * dentry:external, target:internal.  Give dentry's
2497                          * storage to target and make dentry internal
2498                          */
2499                         memcpy(dentry->d_iname, target->d_name.name,
2500                                         target->d_name.len + 1);
2501                         target->d_name.name = dentry->d_name.name;
2502                         dentry->d_name.name = dentry->d_iname;
2503                 } else {
2504                         /*
2505                          * Both are internal.
2506                          */
2507                         unsigned int i;
2508                         BUILD_BUG_ON(!IS_ALIGNED(DNAME_INLINE_LEN, sizeof(long)));
2509                         kmemcheck_mark_initialized(dentry->d_iname, DNAME_INLINE_LEN);
2510                         kmemcheck_mark_initialized(target->d_iname, DNAME_INLINE_LEN);
2511                         for (i = 0; i < DNAME_INLINE_LEN / sizeof(long); i++) {
2512                                 swap(((long *) &dentry->d_iname)[i],
2513                                      ((long *) &target->d_iname)[i]);
2514                         }
2515                 }
2516         }
2517         swap(dentry->d_name.hash_len, target->d_name.hash_len);
2518 }
2519 
2520 static void copy_name(struct dentry *dentry, struct dentry *target)
2521 {
2522         struct external_name *old_name = NULL;
2523         if (unlikely(dname_external(dentry)))
2524                 old_name = external_name(dentry);
2525         if (unlikely(dname_external(target))) {
2526                 atomic_inc(&external_name(target)->u.count);
2527                 dentry->d_name = target->d_name;
2528         } else {
2529                 memcpy(dentry->d_iname, target->d_name.name,
2530                                 target->d_name.len + 1);
2531                 dentry->d_name.name = dentry->d_iname;
2532                 dentry->d_name.hash_len = target->d_name.hash_len;
2533         }
2534         if (old_name && likely(atomic_dec_and_test(&old_name->u.count)))
2535                 kfree_rcu(old_name, u.head);
2536 }
2537 
2538 static void dentry_lock_for_move(struct dentry *dentry, struct dentry *target)
2539 {
2540         /*
2541          * XXXX: do we really need to take target->d_lock?
2542          */
2543         if (IS_ROOT(dentry) || dentry->d_parent == target->d_parent)
2544                 spin_lock(&target->d_parent->d_lock);
2545         else {
2546                 if (d_ancestor(dentry->d_parent, target->d_parent)) {
2547                         spin_lock(&dentry->d_parent->d_lock);
2548                         spin_lock_nested(&target->d_parent->d_lock,
2549                                                 DENTRY_D_LOCK_NESTED);
2550                 } else {
2551                         spin_lock(&target->d_parent->d_lock);
2552                         spin_lock_nested(&dentry->d_parent->d_lock,
2553                                                 DENTRY_D_LOCK_NESTED);
2554                 }
2555         }
2556         if (target < dentry) {
2557                 spin_lock_nested(&target->d_lock, 2);
2558                 spin_lock_nested(&dentry->d_lock, 3);
2559         } else {
2560                 spin_lock_nested(&dentry->d_lock, 2);
2561                 spin_lock_nested(&target->d_lock, 3);
2562         }
2563 }
2564 
2565 static void dentry_unlock_for_move(struct dentry *dentry, struct dentry *target)
2566 {
2567         if (target->d_parent != dentry->d_parent)
2568                 spin_unlock(&dentry->d_parent->d_lock);
2569         if (target->d_parent != target)
2570                 spin_unlock(&target->d_parent->d_lock);
2571         spin_unlock(&target->d_lock);
2572         spin_unlock(&dentry->d_lock);
2573 }
2574 
2575 /*
2576  * When switching names, the actual string doesn't strictly have to
2577  * be preserved in the target - because we're dropping the target
2578  * anyway. As such, we can just do a simple memcpy() to copy over
2579  * the new name before we switch, unless we are going to rehash
2580  * it.  Note that if we *do* unhash the target, we are not allowed
2581  * to rehash it without giving it a new name/hash key - whether
2582  * we swap or overwrite the names here, resulting name won't match
2583  * the reality in filesystem; it's only there for d_path() purposes.
2584  * Note that all of this is happening under rename_lock, so the
2585  * any hash lookup seeing it in the middle of manipulations will
2586  * be discarded anyway.  So we do not care what happens to the hash
2587  * key in that case.
2588  */
2589 /*
2590  * __d_move - move a dentry
2591  * @dentry: entry to move
2592  * @target: new dentry
2593  * @exchange: exchange the two dentries
2594  *
2595  * Update the dcache to reflect the move of a file name. Negative
2596  * dcache entries should not be moved in this way. Caller must hold
2597  * rename_lock, the i_mutex of the source and target directories,
2598  * and the sb->s_vfs_rename_mutex if they differ. See lock_rename().
2599  */
2600 static void __d_move(struct dentry *dentry, struct dentry *target,
2601                      bool exchange)
2602 {
2603         if (!dentry->d_inode)
2604                 printk(KERN_WARNING "VFS: moving negative dcache entry\n");
2605 
2606         BUG_ON(d_ancestor(dentry, target));
2607         BUG_ON(d_ancestor(target, dentry));
2608 
2609         dentry_lock_for_move(dentry, target);
2610 
2611         write_seqcount_begin(&dentry->d_seq);
2612         write_seqcount_begin_nested(&target->d_seq, DENTRY_D_LOCK_NESTED);
2613 
2614         /* __d_drop does write_seqcount_barrier, but they're OK to nest. */
2615 
2616         /*
2617          * Move the dentry to the target hash queue. Don't bother checking
2618          * for the same hash queue because of how unlikely it is.
2619          */
2620         __d_drop(dentry);
2621         __d_rehash(dentry, d_hash(target->d_parent, target->d_name.hash));
2622 
2623         /*
2624          * Unhash the target (d_delete() is not usable here).  If exchanging
2625          * the two dentries, then rehash onto the other's hash queue.
2626          */
2627         __d_drop(target);
2628         if (exchange) {
2629                 __d_rehash(target,
2630                            d_hash(dentry->d_parent, dentry->d_name.hash));
2631         }
2632 
2633         /* Switch the names.. */
2634         if (exchange)
2635                 swap_names(dentry, target);
2636         else
2637                 copy_name(dentry, target);
2638 
2639         /* ... and switch them in the tree */
2640         if (IS_ROOT(dentry)) {
2641                 /* splicing a tree */
2642                 dentry->d_parent = target->d_parent;
2643                 target->d_parent = target;
2644                 list_del_init(&target->d_child);
2645                 list_move(&dentry->d_child, &dentry->d_parent->d_subdirs);
2646         } else {
2647                 /* swapping two dentries */
2648                 swap(dentry->d_parent, target->d_parent);
2649                 list_move(&target->d_child, &target->d_parent->d_subdirs);
2650                 list_move(&dentry->d_child, &dentry->d_parent->d_subdirs);
2651                 if (exchange)
2652                         fsnotify_d_move(target);
2653                 fsnotify_d_move(dentry);
2654         }
2655 
2656         write_seqcount_end(&target->d_seq);
2657         write_seqcount_end(&dentry->d_seq);
2658 
2659         dentry_unlock_for_move(dentry, target);
2660 }
2661 
2662 /*
2663  * d_move - move a dentry
2664  * @dentry: entry to move
2665  * @target: new dentry
2666  *
2667  * Update the dcache to reflect the move of a file name. Negative
2668  * dcache entries should not be moved in this way. See the locking
2669  * requirements for __d_move.
2670  */
2671 void d_move(struct dentry *dentry, struct dentry *target)
2672 {
2673         write_seqlock(&rename_lock);
2674         __d_move(dentry, target, false);
2675         write_sequnlock(&rename_lock);
2676 }
2677 EXPORT_SYMBOL(d_move);
2678 
2679 /*
2680  * d_exchange - exchange two dentries
2681  * @dentry1: first dentry
2682  * @dentry2: second dentry
2683  */
2684 void d_exchange(struct dentry *dentry1, struct dentry *dentry2)
2685 {
2686         write_seqlock(&rename_lock);
2687 
2688         WARN_ON(!dentry1->d_inode);
2689         WARN_ON(!dentry2->d_inode);
2690         WARN_ON(IS_ROOT(dentry1));
2691         WARN_ON(IS_ROOT(dentry2));
2692 
2693         __d_move(dentry1, dentry2, true);
2694 
2695         write_sequnlock(&rename_lock);
2696 }
2697 
2698 /**
2699  * d_ancestor - search for an ancestor
2700  * @p1: ancestor dentry
2701  * @p2: child dentry
2702  *
2703  * Returns the ancestor dentry of p2 which is a child of p1, if p1 is
2704  * an ancestor of p2, else NULL.
2705  */
2706 struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
2707 {
2708         struct dentry *p;
2709 
2710         for (p = p2; !IS_ROOT(p); p = p->d_parent) {
2711                 if (p->d_parent == p1)
2712                         return p;
2713         }
2714         return NULL;
2715 }
2716 
2717 /*
2718  * This helper attempts to cope with remotely renamed directories
2719  *
2720  * It assumes that the caller is already holding
2721  * dentry->d_parent->d_inode->i_mutex, and rename_lock
2722  *
2723  * Note: If ever the locking in lock_rename() changes, then please
2724  * remember to update this too...
2725  */
2726 static int __d_unalias(struct inode *inode,
2727                 struct dentry *dentry, struct dentry *alias)
2728 {
2729         struct mutex *m1 = NULL, *m2 = NULL;
2730         int ret = -ESTALE;
2731 
2732         /* If alias and dentry share a parent, then no extra locks required */
2733         if (alias->d_parent == dentry->d_parent)
2734                 goto out_unalias;
2735 
2736         /* See lock_rename() */
2737         if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
2738                 goto out_err;
2739         m1 = &dentry->d_sb->s_vfs_rename_mutex;
2740         if (!mutex_trylock(&alias->d_parent->d_inode->i_mutex))
2741                 goto out_err;
2742         m2 = &alias->d_parent->d_inode->i_mutex;
2743 out_unalias:
2744         __d_move(alias, dentry, false);
2745         ret = 0;
2746 out_err:
2747         if (m2)
2748                 mutex_unlock(m2);
2749         if (m1)
2750                 mutex_unlock(m1);
2751         return ret;
2752 }
2753 
2754 /**
2755  * d_splice_alias - splice a disconnected dentry into the tree if one exists
2756  * @inode:  the inode which may have a disconnected dentry
2757  * @dentry: a negative dentry which we want to point to the inode.
2758  *
2759  * If inode is a directory and has an IS_ROOT alias, then d_move that in
2760  * place of the given dentry and return it, else simply d_add the inode
2761  * to the dentry and return NULL.
2762  *
2763  * If a non-IS_ROOT directory is found, the filesystem is corrupt, and
2764  * we should error out: directories can't have multiple aliases.
2765  *
2766  * This is needed in the lookup routine of any filesystem that is exportable
2767  * (via knfsd) so that we can build dcache paths to directories effectively.
2768  *
2769  * If a dentry was found and moved, then it is returned.  Otherwise NULL
2770  * is returned.  This matches the expected return value of ->lookup.
2771  *
2772  * Cluster filesystems may call this function with a negative, hashed dentry.
2773  * In that case, we know that the inode will be a regular file, and also this
2774  * will only occur during atomic_open. So we need to check for the dentry
2775  * being already hashed only in the final case.
2776  */
2777 struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
2778 {
2779         if (IS_ERR(inode))
2780                 return ERR_CAST(inode);
2781 
2782         BUG_ON(!d_unhashed(dentry));
2783 
2784         if (!inode) {
2785                 __d_instantiate(dentry, NULL);
2786                 goto out;
2787         }
2788         spin_lock(&inode->i_lock);
2789         if (S_ISDIR(inode->i_mode)) {
2790                 struct dentry *new = __d_find_any_alias(inode);
2791                 if (unlikely(new)) {
2792                         /* The reference to new ensures it remains an alias */
2793                         spin_unlock(&inode->i_lock);
2794                         write_seqlock(&rename_lock);
2795                         if (unlikely(d_ancestor(new, dentry))) {
2796                                 write_sequnlock(&rename_lock);
2797                                 dput(new);
2798                                 new = ERR_PTR(-ELOOP);
2799                                 pr_warn_ratelimited(
2800                                         "VFS: Lookup of '%s' in %s %s"
2801                                         " would have caused loop\n",
2802                                         dentry->d_name.name,
2803                                         inode->i_sb->s_type->name,
2804                                         inode->i_sb->s_id);
2805                         } else if (!IS_ROOT(new)) {
2806                                 int err = __d_unalias(inode, dentry, new);
2807                                 write_sequnlock(&rename_lock);
2808                                 if (err) {
2809                                         dput(new);
2810                                         new = ERR_PTR(err);
2811                                 }
2812                         } else {
2813                                 __d_move(new, dentry, false);
2814                                 write_sequnlock(&rename_lock);
2815                                 security_d_instantiate(new, inode);
2816                         }
2817                         iput(inode);
2818                         return new;
2819                 }
2820         }
2821         /* already taking inode->i_lock, so d_add() by hand */
2822         __d_instantiate(dentry, inode);
2823         spin_unlock(&inode->i_lock);
2824 out:
2825         security_d_instantiate(dentry, inode);
2826         d_rehash(dentry);
2827         return NULL;
2828 }
2829 EXPORT_SYMBOL(d_splice_alias);
2830 
2831 static int prepend(char **buffer, int *buflen, const char *str, int namelen)
2832 {
2833         *buflen -= namelen;
2834         if (*buflen < 0)
2835                 return -ENAMETOOLONG;
2836         *buffer -= namelen;
2837         memcpy(*buffer, str, namelen);
2838         return 0;
2839 }
2840 
2841 /**
2842  * prepend_name - prepend a pathname in front of current buffer pointer
2843  * @buffer: buffer pointer
2844  * @buflen: allocated length of the buffer
2845  * @name:   name string and length qstr structure
2846  *
2847  * With RCU path tracing, it may race with d_move(). Use ACCESS_ONCE() to
2848  * make sure that either the old or the new name pointer and length are
2849  * fetched. However, there may be mismatch between length and pointer.
2850  * The length cannot be trusted, we need to copy it byte-by-byte until
2851  * the length is reached or a null byte is found. It also prepends "/" at
2852  * the beginning of the name. The sequence number check at the caller will
2853  * retry it again when a d_move() does happen. So any garbage in the buffer
2854  * due to mismatched pointer and length will be discarded.
2855  *
2856  * Data dependency barrier is needed to make sure that we see that terminating
2857  * NUL.  Alpha strikes again, film at 11...
2858  */
2859 static int prepend_name(char **buffer, int *buflen, struct qstr *name)
2860 {
2861         const char *dname = ACCESS_ONCE(name->name);
2862         u32 dlen = ACCESS_ONCE(name->len);
2863         char *p;
2864 
2865         smp_read_barrier_depends();
2866 
2867         *buflen -= dlen + 1;
2868         if (*buflen < 0)
2869                 return -ENAMETOOLONG;
2870         p = *buffer -= dlen + 1;
2871         *p++ = '/';
2872         while (dlen--) {
2873                 char c = *dname++;
2874                 if (!c)
2875                         break;
2876                 *p++ = c;
2877         }
2878         return 0;
2879 }
2880 
2881 /**
2882  * prepend_path - Prepend path string to a buffer
2883  * @path: the dentry/vfsmount to report
2884  * @root: root vfsmnt/dentry
2885  * @buffer: pointer to the end of the buffer
2886  * @buflen: pointer to buffer length
2887  *
2888  * The function will first try to write out the pathname without taking any
2889  * lock other than the RCU read lock to make sure that dentries won't go away.
2890  * It only checks the sequence number of the global rename_lock as any change
2891  * in the dentry's d_seq will be preceded by changes in the rename_lock
2892  * sequence number. If the sequence number had been changed, it will restart
2893  * the whole pathname back-tracing sequence again by taking the rename_lock.
2894  * In this case, there is no need to take the RCU read lock as the recursive
2895  * parent pointer references will keep the dentry chain alive as long as no
2896  * rename operation is performed.
2897  */
2898 static int prepend_path(const struct path *path,
2899                         const struct path *root,
2900                         char **buffer, int *buflen)
2901 {
2902         struct dentry *dentry;
2903         struct vfsmount *vfsmnt;
2904         struct mount *mnt;
2905         int error = 0;
2906         unsigned seq, m_seq = 0;
2907         char *bptr;
2908         int blen;
2909 
2910         rcu_read_lock();
2911 restart_mnt:
2912         read_seqbegin_or_lock(&mount_lock, &m_seq);
2913         seq = 0;
2914         rcu_read_lock();
2915 restart:
2916         bptr = *buffer;
2917         blen = *buflen;
2918         error = 0;
2919         dentry = path->dentry;
2920         vfsmnt = path->mnt;
2921         mnt = real_mount(vfsmnt);
2922         read_seqbegin_or_lock(&rename_lock, &seq);
2923         while (dentry != root->dentry || vfsmnt != root->mnt) {
2924                 struct dentry * parent;
2925 
2926                 if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
2927                         struct mount *parent = ACCESS_ONCE(mnt->mnt_parent);
2928                         /* Escaped? */
2929                         if (dentry != vfsmnt->mnt_root) {
2930                                 bptr = *buffer;
2931                                 blen = *buflen;
2932                                 error = 3;
2933                                 break;
2934                         }
2935                         /* Global root? */
2936                         if (mnt != parent) {
2937                                 dentry = ACCESS_ONCE(mnt->mnt_mountpoint);
2938                                 mnt = parent;
2939                                 vfsmnt = &mnt->mnt;
2940                                 continue;
2941                         }
2942                         if (!error)
2943                                 error = is_mounted(vfsmnt) ? 1 : 2;
2944                         break;
2945                 }
2946                 parent = dentry->d_parent;
2947                 prefetch(parent);
2948                 error = prepend_name(&bptr, &blen, &dentry->d_name);
2949                 if (error)
2950                         break;
2951 
2952                 dentry = parent;
2953         }
2954         if (!(seq & 1))
2955                 rcu_read_unlock();
2956         if (need_seqretry(&rename_lock, seq)) {
2957                 seq = 1;
2958                 goto restart;
2959         }
2960         done_seqretry(&rename_lock, seq);
2961 
2962         if (!(m_seq & 1))
2963                 rcu_read_unlock();
2964         if (need_seqretry(&mount_lock, m_seq)) {
2965                 m_seq = 1;
2966                 goto restart_mnt;
2967         }
2968         done_seqretry(&mount_lock, m_seq);
2969 
2970         if (error >= 0 && bptr == *buffer) {
2971                 if (--blen < 0)
2972                         error = -ENAMETOOLONG;
2973                 else
2974                         *--bptr = '/';
2975         }
2976         *buffer = bptr;
2977         *buflen = blen;
2978         return error;
2979 }
2980 
2981 /**
2982  * __d_path - return the path of a dentry
2983  * @path: the dentry/vfsmount to report
2984  * @root: root vfsmnt/dentry
2985  * @buf: buffer to return value in
2986  * @buflen: buffer length
2987  *
2988  * Convert a dentry into an ASCII path name.
2989  *
2990  * Returns a pointer into the buffer or an error code if the
2991  * path was too long.
2992  *
2993  * "buflen" should be positive.
2994  *
2995  * If the path is not reachable from the supplied root, return %NULL.
2996  */
2997 char *__d_path(const struct path *path,
2998                const struct path *root,
2999                char *buf, int buflen)
3000 {
3001         char *res = buf + buflen;
3002         int error;
3003 
3004         prepend(&res, &buflen, "\0", 1);
3005         error = prepend_path(path, root, &res, &buflen);
3006 
3007         if (error < 0)
3008                 return ERR_PTR(error);
3009         if (error > 0)
3010                 return NULL;
3011         return res;
3012 }
3013 
3014 char *d_absolute_path(const struct path *path,
3015                char *buf, int buflen)
3016 {
3017         struct path root = {};
3018         char *res = buf + buflen;
3019         int error;
3020 
3021         prepend(&res, &buflen, "\0", 1);
3022         error = prepend_path(path, &root, &res, &buflen);
3023 
3024         if (error > 1)
3025                 error = -EINVAL;
3026         if (error < 0)
3027                 return ERR_PTR(error);
3028         return res;
3029 }
3030 
3031 /*
3032  * same as __d_path but appends "(deleted)" for unlinked files.
3033  */
3034 static int path_with_deleted(const struct path *path,
3035                              const struct path *root,
3036                              char **buf, int *buflen)
3037 {
3038         prepend(buf, buflen, "\0", 1);
3039         if (d_unlinked(path->dentry)) {
3040                 int error = prepend(buf, buflen, " (deleted)", 10);
3041                 if (error)
3042                         return error;
3043         }
3044 
3045         return prepend_path(path, root, buf, buflen);
3046 }
3047 
3048 static int prepend_unreachable(char **buffer, int *buflen)
3049 {
3050         return prepend(buffer, buflen, "(unreachable)", 13);
3051 }
3052 
3053 static void get_fs_root_rcu(struct fs_struct *fs, struct path *root)
3054 {
3055         unsigned seq;
3056 
3057         do {
3058                 seq = read_seqcount_begin(&fs->seq);
3059                 *root = fs->root;
3060         } while (read_seqcount_retry(&fs->seq, seq));
3061 }
3062 
3063 /**
3064  * d_path - return the path of a dentry
3065  * @path: path to report
3066  * @buf: buffer to return value in
3067  * @buflen: buffer length
3068  *
3069  * Convert a dentry into an ASCII path name. If the entry has been deleted
3070  * the string " (deleted)" is appended. Note that this is ambiguous.
3071  *
3072  * Returns a pointer into the buffer or an error code if the path was
3073  * too long. Note: Callers should use the returned pointer, not the passed
3074  * in buffer, to use the name! The implementation often starts at an offset
3075  * into the buffer, and may leave 0 bytes at the start.
3076  *
3077  * "buflen" should be positive.
3078  */
3079 char *d_path(const struct path *path, char *buf, int buflen)
3080 {
3081         char *res = buf + buflen;
3082         struct path root;
3083         int error;
3084 
3085         /*
3086          * We have various synthetic filesystems that never get mounted.  On
3087          * these filesystems dentries are never used for lookup purposes, and
3088          * thus don't need to be hashed.  They also don't need a name until a
3089          * user wants to identify the object in /proc/pid/fd/.  The little hack
3090          * below allows us to generate a name for these objects on demand:
3091          *
3092          * Some pseudo inodes are mountable.  When they are mounted
3093          * path->dentry == path->mnt->mnt_root.  In that case don't call d_dname
3094          * and instead have d_path return the mounted path.
3095          */
3096         if (path->dentry->d_op && path->dentry->d_op->d_dname &&
3097             (!IS_ROOT(path->dentry) || path->dentry != path->mnt->mnt_root))
3098                 return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
3099 
3100         rcu_read_lock();
3101         get_fs_root_rcu(current->fs, &root);
3102         error = path_with_deleted(path, &root, &res, &buflen);
3103         rcu_read_unlock();
3104 
3105         if (error < 0)
3106                 res = ERR_PTR(error);
3107         return res;
3108 }
3109 EXPORT_SYMBOL(d_path);
3110 
3111 /*
3112  * Helper function for dentry_operations.d_dname() members
3113  */
3114 char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,
3115                         const char *fmt, ...)
3116 {
3117         va_list args;
3118         char temp[64];
3119         int sz;
3120 
3121         va_start(args, fmt);
3122         sz = vsnprintf(temp, sizeof(temp), fmt, args) + 1;
3123         va_end(args);
3124 
3125         if (sz > sizeof(temp) || sz > buflen)
3126                 return ERR_PTR(-ENAMETOOLONG);
3127 
3128         buffer += buflen - sz;
3129         return memcpy(buffer, temp, sz);
3130 }
3131 
3132 char *simple_dname(struct dentry *dentry, char *buffer, int buflen)
3133 {
3134         char *end = buffer + buflen;
3135         /* these dentries are never renamed, so d_lock is not needed */
3136         if (prepend(&end, &buflen, " (deleted)", 11) ||
3137             prepend(&end, &buflen, dentry->d_name.name, dentry->d_name.len) ||
3138             prepend(&end, &buflen, "/", 1))  
3139                 end = ERR_PTR(-ENAMETOOLONG);
3140         return end;
3141 }
3142 EXPORT_SYMBOL(simple_dname);
3143 
3144 /*
3145  * Write full pathname from the root of the filesystem into the buffer.
3146  */
3147 static char *__dentry_path(struct dentry *d, char *buf, int buflen)
3148 {
3149         struct dentry *dentry;
3150         char *end, *retval;
3151         int len, seq = 0;
3152         int error = 0;
3153 
3154         if (buflen < 2)
3155                 goto Elong;
3156 
3157         rcu_read_lock();
3158 restart:
3159         dentry = d;
3160         end = buf + buflen;
3161         len = buflen;
3162         prepend(&end, &len, "\0", 1);
3163         /* Get '/' right */
3164         retval = end-1;
3165         *retval = '/';
3166         read_seqbegin_or_lock(&rename_lock, &seq);
3167         while (!IS_ROOT(dentry)) {
3168                 struct dentry *parent = dentry->d_parent;
3169 
3170                 prefetch(parent);
3171                 error = prepend_name(&end, &len, &dentry->d_name);
3172                 if (error)
3173                         break;
3174 
3175                 retval = end;
3176                 dentry = parent;
3177         }
3178         if (!(seq & 1))
3179                 rcu_read_unlock();
3180         if (need_seqretry(&rename_lock, seq)) {
3181                 seq = 1;
3182                 goto restart;
3183         }
3184         done_seqretry(&rename_lock, seq);
3185         if (error)
3186                 goto Elong;
3187         return retval;
3188 Elong:
3189         return ERR_PTR(-ENAMETOOLONG);
3190 }
3191 
3192 char *dentry_path_raw(struct dentry *dentry, char *buf, int buflen)
3193 {
3194         return __dentry_path(dentry, buf, buflen);
3195 }
3196 EXPORT_SYMBOL(dentry_path_raw);
3197 
3198 char *dentry_path(struct dentry *dentry, char *buf, int buflen)
3199 {
3200         char *p = NULL;
3201         char *retval;
3202 
3203         if (d_unlinked(dentry)) {
3204                 p = buf + buflen;
3205                 if (prepend(&p, &buflen, "//deleted", 10) != 0)
3206                         goto Elong;
3207                 buflen++;
3208         }
3209         retval = __dentry_path(dentry, buf, buflen);
3210         if (!IS_ERR(retval) && p)
3211                 *p = '/';       /* restore '/' overriden with '\0' */
3212         return retval;
3213 Elong:
3214         return ERR_PTR(-ENAMETOOLONG);
3215 }
3216 
3217 static void get_fs_root_and_pwd_rcu(struct fs_struct *fs, struct path *root,
3218                                     struct path *pwd)
3219 {
3220         unsigned seq;
3221 
3222         do {
3223                 seq = read_seqcount_begin(&fs->seq);
3224                 *root = fs->root;
3225                 *pwd = fs->pwd;
3226         } while (read_seqcount_retry(&fs->seq, seq));
3227 }
3228 
3229 /*
3230  * NOTE! The user-level library version returns a
3231  * character pointer. The kernel system call just
3232  * returns the length of the buffer filled (which
3233  * includes the ending '\0' character), or a negative
3234  * error value. So libc would do something like
3235  *
3236  *      char *getcwd(char * buf, size_t size)
3237  *      {
3238  *              int retval;
3239  *
3240  *              retval = sys_getcwd(buf, size);
3241  *              if (retval >= 0)
3242  *                      return buf;
3243  *              errno = -retval;
3244  *              return NULL;
3245  *      }
3246  */
3247 SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
3248 {
3249         int error;
3250         struct path pwd, root;
3251         char *page = __getname();
3252 
3253         if (!page)
3254                 return -ENOMEM;
3255 
3256         rcu_read_lock();
3257         get_fs_root_and_pwd_rcu(current->fs, &root, &pwd);
3258 
3259         error = -ENOENT;
3260         if (!d_unlinked(pwd.dentry)) {
3261                 unsigned long len;
3262                 char *cwd = page + PATH_MAX;
3263                 int buflen = PATH_MAX;
3264 
3265                 prepend(&cwd, &buflen, "\0", 1);
3266                 error = prepend_path(&pwd, &root, &cwd, &buflen);
3267                 rcu_read_unlock();
3268 
3269                 if (error < 0)
3270                         goto out;
3271 
3272                 /* Unreachable from current root */
3273                 if (error > 0) {
3274                         error = prepend_unreachable(&cwd, &buflen);
3275                         if (error)
3276                                 goto out;
3277                 }
3278 
3279                 error = -ERANGE;
3280                 len = PATH_MAX + page - cwd;
3281                 if (len <= size) {
3282                         error = len;
3283                         if (copy_to_user(buf, cwd, len))
3284                                 error = -EFAULT;
3285                 }
3286         } else {
3287                 rcu_read_unlock();
3288         }
3289 
3290 out:
3291         __putname(page);
3292         return error;
3293 }
3294 
3295 /*
3296  * Test whether new_dentry is a subdirectory of old_dentry.
3297  *
3298  * Trivially implemented using the dcache structure
3299  */
3300 
3301 /**
3302  * is_subdir - is new dentry a subdirectory of old_dentry
3303  * @new_dentry: new dentry
3304  * @old_dentry: old dentry
3305  *
3306  * Returns 1 if new_dentry is a subdirectory of the parent (at any depth).
3307  * Returns 0 otherwise.
3308  * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
3309  */
3310   
3311 int is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)
3312 {
3313         int result;
3314         unsigned seq;
3315 
3316         if (new_dentry == old_dentry)
3317                 return 1;
3318 
3319         do {
3320                 /* for restarting inner loop in case of seq retry */
3321                 seq = read_seqbegin(&rename_lock);
3322                 /*
3323                  * Need rcu_readlock to protect against the d_parent trashing
3324                  * due to d_move
3325                  */
3326                 rcu_read_lock();
3327                 if (d_ancestor(old_dentry, new_dentry))
3328                         result = 1;
3329                 else
3330                         result = 0;
3331                 rcu_read_unlock();
3332         } while (read_seqretry(&rename_lock, seq));
3333 
3334         return result;
3335 }
3336 
3337 static enum d_walk_ret d_genocide_kill(void *data, struct dentry *dentry)
3338 {
3339         struct dentry *root = data;
3340         if (dentry != root) {
3341                 if (d_unhashed(dentry) || !dentry->d_inode)
3342                         return D_WALK_SKIP;
3343 
3344                 if (!(dentry->d_flags & DCACHE_GENOCIDE)) {
3345                         dentry->d_flags |= DCACHE_GENOCIDE;
3346                         dentry->d_lockref.count--;
3347                 }
3348         }
3349         return D_WALK_CONTINUE;
3350 }
3351 
3352 void d_genocide(struct dentry *parent)
3353 {
3354         d_walk(parent, parent, d_genocide_kill, NULL);
3355 }
3356 
3357 void d_tmpfile(struct dentry *dentry, struct inode *inode)
3358 {
3359         inode_dec_link_count(inode);
3360         BUG_ON(dentry->d_name.name != dentry->d_iname ||
3361                 !hlist_unhashed(&dentry->d_u.d_alias) ||
3362                 !d_unlinked(dentry));
3363         spin_lock(&dentry->d_parent->d_lock);
3364         spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
3365         dentry->d_name.len = sprintf(dentry->d_iname, "#%llu",
3366                                 (unsigned long long)inode->i_ino);
3367         spin_unlock(&dentry->d_lock);
3368         spin_unlock(&dentry->d_parent->d_lock);
3369         d_instantiate(dentry, inode);
3370 }
3371 EXPORT_SYMBOL(d_tmpfile);
3372 
3373 static __initdata unsigned long dhash_entries;
3374 static int __init set_dhash_entries(char *str)
3375 {
3376         if (!str)
3377                 return 0;
3378         dhash_entries = simple_strtoul(str, &str, 0);
3379         return 1;
3380 }
3381 __setup("dhash_entries=", set_dhash_entries);
3382 
3383 static void __init dcache_init_early(void)
3384 {
3385         unsigned int loop;
3386 
3387         /* If hashes are distributed across NUMA nodes, defer
3388          * hash allocation until vmalloc space is available.
3389          */
3390         if (hashdist)
3391                 return;
3392 
3393         dentry_hashtable =
3394                 alloc_large_system_hash("Dentry cache",
3395                                         sizeof(struct hlist_bl_head),
3396                                         dhash_entries,
3397                                         13,
3398                                         HASH_EARLY,
3399                                         &d_hash_shift,
3400                                         &d_hash_mask,
3401                                         0,
3402                                         0);
3403 
3404         for (loop = 0; loop < (1U << d_hash_shift); loop++)
3405                 INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
3406 }
3407 
3408 static void __init dcache_init(void)
3409 {
3410         unsigned int loop;
3411 
3412         /* 
3413          * A constructor could be added for stable state like the lists,
3414          * but it is probably not worth it because of the cache nature
3415          * of the dcache. 
3416          */
3417         dentry_cache = KMEM_CACHE(dentry,
3418                 SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD);
3419 
3420         /* Hash may have been set up in dcache_init_early */
3421         if (!hashdist)
3422                 return;
3423 
3424         dentry_hashtable =
3425                 alloc_large_system_hash("Dentry cache",
3426                                         sizeof(struct hlist_bl_head),
3427                                         dhash_entries,
3428                                         13,
3429                                         0,
3430                                         &d_hash_shift,
3431                                         &d_hash_mask,
3432                                         0,
3433                                         0);
3434 
3435         for (loop = 0; loop < (1U << d_hash_shift); loop++)
3436                 INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
3437 }
3438 
3439 /* SLAB cache for __getname() consumers */
3440 struct kmem_cache *names_cachep __read_mostly;
3441 EXPORT_SYMBOL(names_cachep);
3442 
3443 EXPORT_SYMBOL(d_genocide);
3444 
3445 void __init vfs_caches_init_early(void)
3446 {
3447         dcache_init_early();
3448         inode_init_early();
3449 }
3450 
3451 void __init vfs_caches_init(void)
3452 {
3453         names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
3454                         SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
3455 
3456         dcache_init();
3457         inode_init();
3458         files_init();
3459         files_maxfiles_init();
3460         mnt_init();
3461         bdev_cache_init();
3462         chrdev_init();
3463 }
3464 

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