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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_barrier - 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_barrier(struct dentry *dentry)
332 {
333         assert_spin_locked(&dentry->d_lock);
334         /* Go through a barrier */
335         write_seqcount_barrier(&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_barrier(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_barrier(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;
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_OP_DELETE)) {
780                 if (dentry->d_op->d_delete(dentry))
781                         goto kill_it;
782         }
783 
784         if (!(dentry->d_flags & DCACHE_REFERENCED))
785                 dentry->d_flags |= DCACHE_REFERENCED;
786         dentry_lru_add(dentry);
787 
788         dentry->d_lockref.count--;
789         spin_unlock(&dentry->d_lock);
790         return;
791 
792 kill_it:
793         dentry = dentry_kill(dentry);
794         if (dentry)
795                 goto repeat;
796 }
797 EXPORT_SYMBOL(dput);
798 
799 
800 /* This must be called with d_lock held */
801 static inline void __dget_dlock(struct dentry *dentry)
802 {
803         dentry->d_lockref.count++;
804 }
805 
806 static inline void __dget(struct dentry *dentry)
807 {
808         lockref_get(&dentry->d_lockref);
809 }
810 
811 struct dentry *dget_parent(struct dentry *dentry)
812 {
813         int gotref;
814         struct dentry *ret;
815 
816         /*
817          * Do optimistic parent lookup without any
818          * locking.
819          */
820         rcu_read_lock();
821         ret = ACCESS_ONCE(dentry->d_parent);
822         gotref = lockref_get_not_zero(&ret->d_lockref);
823         rcu_read_unlock();
824         if (likely(gotref)) {
825                 if (likely(ret == ACCESS_ONCE(dentry->d_parent)))
826                         return ret;
827                 dput(ret);
828         }
829 
830 repeat:
831         /*
832          * Don't need rcu_dereference because we re-check it was correct under
833          * the lock.
834          */
835         rcu_read_lock();
836         ret = dentry->d_parent;
837         spin_lock(&ret->d_lock);
838         if (unlikely(ret != dentry->d_parent)) {
839                 spin_unlock(&ret->d_lock);
840                 rcu_read_unlock();
841                 goto repeat;
842         }
843         rcu_read_unlock();
844         BUG_ON(!ret->d_lockref.count);
845         ret->d_lockref.count++;
846         spin_unlock(&ret->d_lock);
847         return ret;
848 }
849 EXPORT_SYMBOL(dget_parent);
850 
851 /**
852  * d_find_alias - grab a hashed alias of inode
853  * @inode: inode in question
854  *
855  * If inode has a hashed alias, or is a directory and has any alias,
856  * acquire the reference to alias and return it. Otherwise return NULL.
857  * Notice that if inode is a directory there can be only one alias and
858  * it can be unhashed only if it has no children, or if it is the root
859  * of a filesystem, or if the directory was renamed and d_revalidate
860  * was the first vfs operation to notice.
861  *
862  * If the inode has an IS_ROOT, DCACHE_DISCONNECTED alias, then prefer
863  * any other hashed alias over that one.
864  */
865 static struct dentry *__d_find_alias(struct inode *inode)
866 {
867         struct dentry *alias, *discon_alias;
868 
869 again:
870         discon_alias = NULL;
871         hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
872                 spin_lock(&alias->d_lock);
873                 if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
874                         if (IS_ROOT(alias) &&
875                             (alias->d_flags & DCACHE_DISCONNECTED)) {
876                                 discon_alias = alias;
877                         } else {
878                                 __dget_dlock(alias);
879                                 spin_unlock(&alias->d_lock);
880                                 return alias;
881                         }
882                 }
883                 spin_unlock(&alias->d_lock);
884         }
885         if (discon_alias) {
886                 alias = discon_alias;
887                 spin_lock(&alias->d_lock);
888                 if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
889                         __dget_dlock(alias);
890                         spin_unlock(&alias->d_lock);
891                         return alias;
892                 }
893                 spin_unlock(&alias->d_lock);
894                 goto again;
895         }
896         return NULL;
897 }
898 
899 struct dentry *d_find_alias(struct inode *inode)
900 {
901         struct dentry *de = NULL;
902 
903         if (!hlist_empty(&inode->i_dentry)) {
904                 spin_lock(&inode->i_lock);
905                 de = __d_find_alias(inode);
906                 spin_unlock(&inode->i_lock);
907         }
908         return de;
909 }
910 EXPORT_SYMBOL(d_find_alias);
911 
912 /*
913  *      Try to kill dentries associated with this inode.
914  * WARNING: you must own a reference to inode.
915  */
916 void d_prune_aliases(struct inode *inode)
917 {
918         struct dentry *dentry;
919 restart:
920         spin_lock(&inode->i_lock);
921         hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias) {
922                 spin_lock(&dentry->d_lock);
923                 if (!dentry->d_lockref.count) {
924                         struct dentry *parent = lock_parent(dentry);
925                         if (likely(!dentry->d_lockref.count)) {
926                                 __dentry_kill(dentry);
927                                 dput(parent);
928                                 goto restart;
929                         }
930                         if (parent)
931                                 spin_unlock(&parent->d_lock);
932                 }
933                 spin_unlock(&dentry->d_lock);
934         }
935         spin_unlock(&inode->i_lock);
936 }
937 EXPORT_SYMBOL(d_prune_aliases);
938 
939 static void shrink_dentry_list(struct list_head *list)
940 {
941         struct dentry *dentry, *parent;
942 
943         while (!list_empty(list)) {
944                 struct inode *inode;
945                 dentry = list_entry(list->prev, struct dentry, d_lru);
946                 spin_lock(&dentry->d_lock);
947                 parent = lock_parent(dentry);
948 
949                 /*
950                  * The dispose list is isolated and dentries are not accounted
951                  * to the LRU here, so we can simply remove it from the list
952                  * here regardless of whether it is referenced or not.
953                  */
954                 d_shrink_del(dentry);
955 
956                 /*
957                  * We found an inuse dentry which was not removed from
958                  * the LRU because of laziness during lookup. Do not free it.
959                  */
960                 if (dentry->d_lockref.count > 0) {
961                         spin_unlock(&dentry->d_lock);
962                         if (parent)
963                                 spin_unlock(&parent->d_lock);
964                         continue;
965                 }
966 
967 
968                 if (unlikely(dentry->d_flags & DCACHE_DENTRY_KILLED)) {
969                         bool can_free = dentry->d_flags & DCACHE_MAY_FREE;
970                         spin_unlock(&dentry->d_lock);
971                         if (parent)
972                                 spin_unlock(&parent->d_lock);
973                         if (can_free)
974                                 dentry_free(dentry);
975                         continue;
976                 }
977 
978                 inode = dentry->d_inode;
979                 if (inode && unlikely(!spin_trylock(&inode->i_lock))) {
980                         d_shrink_add(dentry, list);
981                         spin_unlock(&dentry->d_lock);
982                         if (parent)
983                                 spin_unlock(&parent->d_lock);
984                         continue;
985                 }
986 
987                 __dentry_kill(dentry);
988 
989                 /*
990                  * We need to prune ancestors too. This is necessary to prevent
991                  * quadratic behavior of shrink_dcache_parent(), but is also
992                  * expected to be beneficial in reducing dentry cache
993                  * fragmentation.
994                  */
995                 dentry = parent;
996                 while (dentry && !lockref_put_or_lock(&dentry->d_lockref)) {
997                         parent = lock_parent(dentry);
998                         if (dentry->d_lockref.count != 1) {
999                                 dentry->d_lockref.count--;
1000                                 spin_unlock(&dentry->d_lock);
1001                                 if (parent)
1002                                         spin_unlock(&parent->d_lock);
1003                                 break;
1004                         }
1005                         inode = dentry->d_inode;        /* can't be NULL */
1006                         if (unlikely(!spin_trylock(&inode->i_lock))) {
1007                                 spin_unlock(&dentry->d_lock);
1008                                 if (parent)
1009                                         spin_unlock(&parent->d_lock);
1010                                 cpu_relax();
1011                                 continue;
1012                         }
1013                         __dentry_kill(dentry);
1014                         dentry = parent;
1015                 }
1016         }
1017 }
1018 
1019 static enum lru_status dentry_lru_isolate(struct list_head *item,
1020                 struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
1021 {
1022         struct list_head *freeable = arg;
1023         struct dentry   *dentry = container_of(item, struct dentry, d_lru);
1024 
1025 
1026         /*
1027          * we are inverting the lru lock/dentry->d_lock here,
1028          * so use a trylock. If we fail to get the lock, just skip
1029          * it
1030          */
1031         if (!spin_trylock(&dentry->d_lock))
1032                 return LRU_SKIP;
1033 
1034         /*
1035          * Referenced dentries are still in use. If they have active
1036          * counts, just remove them from the LRU. Otherwise give them
1037          * another pass through the LRU.
1038          */
1039         if (dentry->d_lockref.count) {
1040                 d_lru_isolate(lru, dentry);
1041                 spin_unlock(&dentry->d_lock);
1042                 return LRU_REMOVED;
1043         }
1044 
1045         if (dentry->d_flags & DCACHE_REFERENCED) {
1046                 dentry->d_flags &= ~DCACHE_REFERENCED;
1047                 spin_unlock(&dentry->d_lock);
1048 
1049                 /*
1050                  * The list move itself will be made by the common LRU code. At
1051                  * this point, we've dropped the dentry->d_lock but keep the
1052                  * lru lock. This is safe to do, since every list movement is
1053                  * protected by the lru lock even if both locks are held.
1054                  *
1055                  * This is guaranteed by the fact that all LRU management
1056                  * functions are intermediated by the LRU API calls like
1057                  * list_lru_add and list_lru_del. List movement in this file
1058                  * only ever occur through this functions or through callbacks
1059                  * like this one, that are called from the LRU API.
1060                  *
1061                  * The only exceptions to this are functions like
1062                  * shrink_dentry_list, and code that first checks for the
1063                  * DCACHE_SHRINK_LIST flag.  Those are guaranteed to be
1064                  * operating only with stack provided lists after they are
1065                  * properly isolated from the main list.  It is thus, always a
1066                  * local access.
1067                  */
1068                 return LRU_ROTATE;
1069         }
1070 
1071         d_lru_shrink_move(lru, dentry, freeable);
1072         spin_unlock(&dentry->d_lock);
1073 
1074         return LRU_REMOVED;
1075 }
1076 
1077 /**
1078  * prune_dcache_sb - shrink the dcache
1079  * @sb: superblock
1080  * @sc: shrink control, passed to list_lru_shrink_walk()
1081  *
1082  * Attempt to shrink the superblock dcache LRU by @sc->nr_to_scan entries. This
1083  * is done when we need more memory and called from the superblock shrinker
1084  * function.
1085  *
1086  * This function may fail to free any resources if all the dentries are in
1087  * use.
1088  */
1089 long prune_dcache_sb(struct super_block *sb, struct shrink_control *sc)
1090 {
1091         LIST_HEAD(dispose);
1092         long freed;
1093 
1094         freed = list_lru_shrink_walk(&sb->s_dentry_lru, sc,
1095                                      dentry_lru_isolate, &dispose);
1096         shrink_dentry_list(&dispose);
1097         return freed;
1098 }
1099 
1100 static enum lru_status dentry_lru_isolate_shrink(struct list_head *item,
1101                 struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
1102 {
1103         struct list_head *freeable = arg;
1104         struct dentry   *dentry = container_of(item, struct dentry, d_lru);
1105 
1106         /*
1107          * we are inverting the lru lock/dentry->d_lock here,
1108          * so use a trylock. If we fail to get the lock, just skip
1109          * it
1110          */
1111         if (!spin_trylock(&dentry->d_lock))
1112                 return LRU_SKIP;
1113 
1114         d_lru_shrink_move(lru, dentry, freeable);
1115         spin_unlock(&dentry->d_lock);
1116 
1117         return LRU_REMOVED;
1118 }
1119 
1120 
1121 /**
1122  * shrink_dcache_sb - shrink dcache for a superblock
1123  * @sb: superblock
1124  *
1125  * Shrink the dcache for the specified super block. This is used to free
1126  * the dcache before unmounting a file system.
1127  */
1128 void shrink_dcache_sb(struct super_block *sb)
1129 {
1130         long freed;
1131 
1132         do {
1133                 LIST_HEAD(dispose);
1134 
1135                 freed = list_lru_walk(&sb->s_dentry_lru,
1136                         dentry_lru_isolate_shrink, &dispose, UINT_MAX);
1137 
1138                 this_cpu_sub(nr_dentry_unused, freed);
1139                 shrink_dentry_list(&dispose);
1140         } while (freed > 0);
1141 }
1142 EXPORT_SYMBOL(shrink_dcache_sb);
1143 
1144 /**
1145  * enum d_walk_ret - action to talke during tree walk
1146  * @D_WALK_CONTINUE:    contrinue walk
1147  * @D_WALK_QUIT:        quit walk
1148  * @D_WALK_NORETRY:     quit when retry is needed
1149  * @D_WALK_SKIP:        skip this dentry and its children
1150  */
1151 enum d_walk_ret {
1152         D_WALK_CONTINUE,
1153         D_WALK_QUIT,
1154         D_WALK_NORETRY,
1155         D_WALK_SKIP,
1156 };
1157 
1158 /**
1159  * d_walk - walk the dentry tree
1160  * @parent:     start of walk
1161  * @data:       data passed to @enter() and @finish()
1162  * @enter:      callback when first entering the dentry
1163  * @finish:     callback when successfully finished the walk
1164  *
1165  * The @enter() and @finish() callbacks are called with d_lock held.
1166  */
1167 static void d_walk(struct dentry *parent, void *data,
1168                    enum d_walk_ret (*enter)(void *, struct dentry *),
1169                    void (*finish)(void *))
1170 {
1171         struct dentry *this_parent;
1172         struct list_head *next;
1173         unsigned seq = 0;
1174         enum d_walk_ret ret;
1175         bool retry = true;
1176 
1177 again:
1178         read_seqbegin_or_lock(&rename_lock, &seq);
1179         this_parent = parent;
1180         spin_lock(&this_parent->d_lock);
1181 
1182         ret = enter(data, this_parent);
1183         switch (ret) {
1184         case D_WALK_CONTINUE:
1185                 break;
1186         case D_WALK_QUIT:
1187         case D_WALK_SKIP:
1188                 goto out_unlock;
1189         case D_WALK_NORETRY:
1190                 retry = false;
1191                 break;
1192         }
1193 repeat:
1194         next = this_parent->d_subdirs.next;
1195 resume:
1196         while (next != &this_parent->d_subdirs) {
1197                 struct list_head *tmp = next;
1198                 struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
1199                 next = tmp->next;
1200 
1201                 spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
1202 
1203                 ret = enter(data, dentry);
1204                 switch (ret) {
1205                 case D_WALK_CONTINUE:
1206                         break;
1207                 case D_WALK_QUIT:
1208                         spin_unlock(&dentry->d_lock);
1209                         goto out_unlock;
1210                 case D_WALK_NORETRY:
1211                         retry = false;
1212                         break;
1213                 case D_WALK_SKIP:
1214                         spin_unlock(&dentry->d_lock);
1215                         continue;
1216                 }
1217 
1218                 if (!list_empty(&dentry->d_subdirs)) {
1219                         spin_unlock(&this_parent->d_lock);
1220                         spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
1221                         this_parent = dentry;
1222                         spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
1223                         goto repeat;
1224                 }
1225                 spin_unlock(&dentry->d_lock);
1226         }
1227         /*
1228          * All done at this level ... ascend and resume the search.
1229          */
1230         rcu_read_lock();
1231 ascend:
1232         if (this_parent != parent) {
1233                 struct dentry *child = this_parent;
1234                 this_parent = child->d_parent;
1235 
1236                 spin_unlock(&child->d_lock);
1237                 spin_lock(&this_parent->d_lock);
1238 
1239                 /* might go back up the wrong parent if we have had a rename. */
1240                 if (need_seqretry(&rename_lock, seq))
1241                         goto rename_retry;
1242                 /* go into the first sibling still alive */
1243                 do {
1244                         next = child->d_child.next;
1245                         if (next == &this_parent->d_subdirs)
1246                                 goto ascend;
1247                         child = list_entry(next, struct dentry, d_child);
1248                 } while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED));
1249                 rcu_read_unlock();
1250                 goto resume;
1251         }
1252         if (need_seqretry(&rename_lock, seq))
1253                 goto rename_retry;
1254         rcu_read_unlock();
1255         if (finish)
1256                 finish(data);
1257 
1258 out_unlock:
1259         spin_unlock(&this_parent->d_lock);
1260         done_seqretry(&rename_lock, seq);
1261         return;
1262 
1263 rename_retry:
1264         spin_unlock(&this_parent->d_lock);
1265         rcu_read_unlock();
1266         BUG_ON(seq & 1);
1267         if (!retry)
1268                 return;
1269         seq = 1;
1270         goto again;
1271 }
1272 
1273 /*
1274  * Search for at least 1 mount point in the dentry's subdirs.
1275  * We descend to the next level whenever the d_subdirs
1276  * list is non-empty and continue searching.
1277  */
1278 
1279 static enum d_walk_ret check_mount(void *data, struct dentry *dentry)
1280 {
1281         int *ret = data;
1282         if (d_mountpoint(dentry)) {
1283                 *ret = 1;
1284                 return D_WALK_QUIT;
1285         }
1286         return D_WALK_CONTINUE;
1287 }
1288 
1289 /**
1290  * have_submounts - check for mounts over a dentry
1291  * @parent: dentry to check.
1292  *
1293  * Return true if the parent or its subdirectories contain
1294  * a mount point
1295  */
1296 int have_submounts(struct dentry *parent)
1297 {
1298         int ret = 0;
1299 
1300         d_walk(parent, &ret, check_mount, NULL);
1301 
1302         return ret;
1303 }
1304 EXPORT_SYMBOL(have_submounts);
1305 
1306 /*
1307  * Called by mount code to set a mountpoint and check if the mountpoint is
1308  * reachable (e.g. NFS can unhash a directory dentry and then the complete
1309  * subtree can become unreachable).
1310  *
1311  * Only one of d_invalidate() and d_set_mounted() must succeed.  For
1312  * this reason take rename_lock and d_lock on dentry and ancestors.
1313  */
1314 int d_set_mounted(struct dentry *dentry)
1315 {
1316         struct dentry *p;
1317         int ret = -ENOENT;
1318         write_seqlock(&rename_lock);
1319         for (p = dentry->d_parent; !IS_ROOT(p); p = p->d_parent) {
1320                 /* Need exclusion wrt. d_invalidate() */
1321                 spin_lock(&p->d_lock);
1322                 if (unlikely(d_unhashed(p))) {
1323                         spin_unlock(&p->d_lock);
1324                         goto out;
1325                 }
1326                 spin_unlock(&p->d_lock);
1327         }
1328         spin_lock(&dentry->d_lock);
1329         if (!d_unlinked(dentry)) {
1330                 dentry->d_flags |= DCACHE_MOUNTED;
1331                 ret = 0;
1332         }
1333         spin_unlock(&dentry->d_lock);
1334 out:
1335         write_sequnlock(&rename_lock);
1336         return ret;
1337 }
1338 
1339 /*
1340  * Search the dentry child list of the specified parent,
1341  * and move any unused dentries to the end of the unused
1342  * list for prune_dcache(). We descend to the next level
1343  * whenever the d_subdirs list is non-empty and continue
1344  * searching.
1345  *
1346  * It returns zero iff there are no unused children,
1347  * otherwise  it returns the number of children moved to
1348  * the end of the unused list. This may not be the total
1349  * number of unused children, because select_parent can
1350  * drop the lock and return early due to latency
1351  * constraints.
1352  */
1353 
1354 struct select_data {
1355         struct dentry *start;
1356         struct list_head dispose;
1357         int found;
1358 };
1359 
1360 static enum d_walk_ret select_collect(void *_data, struct dentry *dentry)
1361 {
1362         struct select_data *data = _data;
1363         enum d_walk_ret ret = D_WALK_CONTINUE;
1364 
1365         if (data->start == dentry)
1366                 goto out;
1367 
1368         if (dentry->d_flags & DCACHE_SHRINK_LIST) {
1369                 data->found++;
1370         } else {
1371                 if (dentry->d_flags & DCACHE_LRU_LIST)
1372                         d_lru_del(dentry);
1373                 if (!dentry->d_lockref.count) {
1374                         d_shrink_add(dentry, &data->dispose);
1375                         data->found++;
1376                 }
1377         }
1378         /*
1379          * We can return to the caller if we have found some (this
1380          * ensures forward progress). We'll be coming back to find
1381          * the rest.
1382          */
1383         if (!list_empty(&data->dispose))
1384                 ret = need_resched() ? D_WALK_QUIT : D_WALK_NORETRY;
1385 out:
1386         return ret;
1387 }
1388 
1389 /**
1390  * shrink_dcache_parent - prune dcache
1391  * @parent: parent of entries to prune
1392  *
1393  * Prune the dcache to remove unused children of the parent dentry.
1394  */
1395 void shrink_dcache_parent(struct dentry *parent)
1396 {
1397         for (;;) {
1398                 struct select_data data;
1399 
1400                 INIT_LIST_HEAD(&data.dispose);
1401                 data.start = parent;
1402                 data.found = 0;
1403 
1404                 d_walk(parent, &data, select_collect, NULL);
1405                 if (!data.found)
1406                         break;
1407 
1408                 shrink_dentry_list(&data.dispose);
1409                 cond_resched();
1410         }
1411 }
1412 EXPORT_SYMBOL(shrink_dcache_parent);
1413 
1414 static enum d_walk_ret umount_check(void *_data, struct dentry *dentry)
1415 {
1416         /* it has busy descendents; complain about those instead */
1417         if (!list_empty(&dentry->d_subdirs))
1418                 return D_WALK_CONTINUE;
1419 
1420         /* root with refcount 1 is fine */
1421         if (dentry == _data && dentry->d_lockref.count == 1)
1422                 return D_WALK_CONTINUE;
1423 
1424         printk(KERN_ERR "BUG: Dentry %p{i=%lx,n=%pd} "
1425                         " still in use (%d) [unmount of %s %s]\n",
1426                        dentry,
1427                        dentry->d_inode ?
1428                        dentry->d_inode->i_ino : 0UL,
1429                        dentry,
1430                        dentry->d_lockref.count,
1431                        dentry->d_sb->s_type->name,
1432                        dentry->d_sb->s_id);
1433         WARN_ON(1);
1434         return D_WALK_CONTINUE;
1435 }
1436 
1437 static void do_one_tree(struct dentry *dentry)
1438 {
1439         shrink_dcache_parent(dentry);
1440         d_walk(dentry, dentry, umount_check, NULL);
1441         d_drop(dentry);
1442         dput(dentry);
1443 }
1444 
1445 /*
1446  * destroy the dentries attached to a superblock on unmounting
1447  */
1448 void shrink_dcache_for_umount(struct super_block *sb)
1449 {
1450         struct dentry *dentry;
1451 
1452         WARN(down_read_trylock(&sb->s_umount), "s_umount should've been locked");
1453 
1454         dentry = sb->s_root;
1455         sb->s_root = NULL;
1456         do_one_tree(dentry);
1457 
1458         while (!hlist_bl_empty(&sb->s_anon)) {
1459                 dentry = dget(hlist_bl_entry(hlist_bl_first(&sb->s_anon), struct dentry, d_hash));
1460                 do_one_tree(dentry);
1461         }
1462 }
1463 
1464 struct detach_data {
1465         struct select_data select;
1466         struct dentry *mountpoint;
1467 };
1468 static enum d_walk_ret detach_and_collect(void *_data, struct dentry *dentry)
1469 {
1470         struct detach_data *data = _data;
1471 
1472         if (d_mountpoint(dentry)) {
1473                 __dget_dlock(dentry);
1474                 data->mountpoint = dentry;
1475                 return D_WALK_QUIT;
1476         }
1477 
1478         return select_collect(&data->select, dentry);
1479 }
1480 
1481 static void check_and_drop(void *_data)
1482 {
1483         struct detach_data *data = _data;
1484 
1485         if (!data->mountpoint && !data->select.found)
1486                 __d_drop(data->select.start);
1487 }
1488 
1489 /**
1490  * d_invalidate - detach submounts, prune dcache, and drop
1491  * @dentry: dentry to invalidate (aka detach, prune and drop)
1492  *
1493  * no dcache lock.
1494  *
1495  * The final d_drop is done as an atomic operation relative to
1496  * rename_lock ensuring there are no races with d_set_mounted.  This
1497  * ensures there are no unhashed dentries on the path to a mountpoint.
1498  */
1499 void d_invalidate(struct dentry *dentry)
1500 {
1501         /*
1502          * If it's already been dropped, return OK.
1503          */
1504         spin_lock(&dentry->d_lock);
1505         if (d_unhashed(dentry)) {
1506                 spin_unlock(&dentry->d_lock);
1507                 return;
1508         }
1509         spin_unlock(&dentry->d_lock);
1510 
1511         /* Negative dentries can be dropped without further checks */
1512         if (!dentry->d_inode) {
1513                 d_drop(dentry);
1514                 return;
1515         }
1516 
1517         for (;;) {
1518                 struct detach_data data;
1519 
1520                 data.mountpoint = NULL;
1521                 INIT_LIST_HEAD(&data.select.dispose);
1522                 data.select.start = dentry;
1523                 data.select.found = 0;
1524 
1525                 d_walk(dentry, &data, detach_and_collect, check_and_drop);
1526 
1527                 if (data.select.found)
1528                         shrink_dentry_list(&data.select.dispose);
1529 
1530                 if (data.mountpoint) {
1531                         detach_mounts(data.mountpoint);
1532                         dput(data.mountpoint);
1533                 }
1534 
1535                 if (!data.mountpoint && !data.select.found)
1536                         break;
1537 
1538                 cond_resched();
1539         }
1540 }
1541 EXPORT_SYMBOL(d_invalidate);
1542 
1543 /**
1544  * __d_alloc    -       allocate a dcache entry
1545  * @sb: filesystem it will belong to
1546  * @name: qstr of the name
1547  *
1548  * Allocates a dentry. It returns %NULL if there is insufficient memory
1549  * available. On a success the dentry is returned. The name passed in is
1550  * copied and the copy passed in may be reused after this call.
1551  */
1552  
1553 struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
1554 {
1555         struct dentry *dentry;
1556         char *dname;
1557 
1558         dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
1559         if (!dentry)
1560                 return NULL;
1561 
1562         /*
1563          * We guarantee that the inline name is always NUL-terminated.
1564          * This way the memcpy() done by the name switching in rename
1565          * will still always have a NUL at the end, even if we might
1566          * be overwriting an internal NUL character
1567          */
1568         dentry->d_iname[DNAME_INLINE_LEN-1] = 0;
1569         if (name->len > DNAME_INLINE_LEN-1) {
1570                 size_t size = offsetof(struct external_name, name[1]);
1571                 struct external_name *p = kmalloc(size + name->len, GFP_KERNEL);
1572                 if (!p) {
1573                         kmem_cache_free(dentry_cache, dentry); 
1574                         return NULL;
1575                 }
1576                 atomic_set(&p->u.count, 1);
1577                 dname = p->name;
1578                 if (IS_ENABLED(CONFIG_DCACHE_WORD_ACCESS))
1579                         kasan_unpoison_shadow(dname,
1580                                 round_up(name->len + 1, sizeof(unsigned long)));
1581         } else  {
1582                 dname = dentry->d_iname;
1583         }       
1584 
1585         dentry->d_name.len = name->len;
1586         dentry->d_name.hash = name->hash;
1587         memcpy(dname, name->name, name->len);
1588         dname[name->len] = 0;
1589 
1590         /* Make sure we always see the terminating NUL character */
1591         smp_wmb();
1592         dentry->d_name.name = dname;
1593 
1594         dentry->d_lockref.count = 1;
1595         dentry->d_flags = 0;
1596         spin_lock_init(&dentry->d_lock);
1597         seqcount_init(&dentry->d_seq);
1598         dentry->d_inode = NULL;
1599         dentry->d_parent = dentry;
1600         dentry->d_sb = sb;
1601         dentry->d_op = NULL;
1602         dentry->d_fsdata = NULL;
1603         INIT_HLIST_BL_NODE(&dentry->d_hash);
1604         INIT_LIST_HEAD(&dentry->d_lru);
1605         INIT_LIST_HEAD(&dentry->d_subdirs);
1606         INIT_HLIST_NODE(&dentry->d_u.d_alias);
1607         INIT_LIST_HEAD(&dentry->d_child);
1608         d_set_d_op(dentry, dentry->d_sb->s_d_op);
1609 
1610         this_cpu_inc(nr_dentry);
1611 
1612         return dentry;
1613 }
1614 
1615 /**
1616  * d_alloc      -       allocate a dcache entry
1617  * @parent: parent of entry to allocate
1618  * @name: qstr of the name
1619  *
1620  * Allocates a dentry. It returns %NULL if there is insufficient memory
1621  * available. On a success the dentry is returned. The name passed in is
1622  * copied and the copy passed in may be reused after this call.
1623  */
1624 struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
1625 {
1626         struct dentry *dentry = __d_alloc(parent->d_sb, name);
1627         if (!dentry)
1628                 return NULL;
1629 
1630         spin_lock(&parent->d_lock);
1631         /*
1632          * don't need child lock because it is not subject
1633          * to concurrency here
1634          */
1635         __dget_dlock(parent);
1636         dentry->d_parent = parent;
1637         list_add(&dentry->d_child, &parent->d_subdirs);
1638         spin_unlock(&parent->d_lock);
1639 
1640         return dentry;
1641 }
1642 EXPORT_SYMBOL(d_alloc);
1643 
1644 /**
1645  * d_alloc_pseudo - allocate a dentry (for lookup-less filesystems)
1646  * @sb: the superblock
1647  * @name: qstr of the name
1648  *
1649  * For a filesystem that just pins its dentries in memory and never
1650  * performs lookups at all, return an unhashed IS_ROOT dentry.
1651  */
1652 struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
1653 {
1654         return __d_alloc(sb, name);
1655 }
1656 EXPORT_SYMBOL(d_alloc_pseudo);
1657 
1658 struct dentry *d_alloc_name(struct dentry *parent, const char *name)
1659 {
1660         struct qstr q;
1661 
1662         q.name = name;
1663         q.len = strlen(name);
1664         q.hash = full_name_hash(q.name, q.len);
1665         return d_alloc(parent, &q);
1666 }
1667 EXPORT_SYMBOL(d_alloc_name);
1668 
1669 void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
1670 {
1671         WARN_ON_ONCE(dentry->d_op);
1672         WARN_ON_ONCE(dentry->d_flags & (DCACHE_OP_HASH  |
1673                                 DCACHE_OP_COMPARE       |
1674                                 DCACHE_OP_REVALIDATE    |
1675                                 DCACHE_OP_WEAK_REVALIDATE       |
1676                                 DCACHE_OP_DELETE ));
1677         dentry->d_op = op;
1678         if (!op)
1679                 return;
1680         if (op->d_hash)
1681                 dentry->d_flags |= DCACHE_OP_HASH;
1682         if (op->d_compare)
1683                 dentry->d_flags |= DCACHE_OP_COMPARE;
1684         if (op->d_revalidate)
1685                 dentry->d_flags |= DCACHE_OP_REVALIDATE;
1686         if (op->d_weak_revalidate)
1687                 dentry->d_flags |= DCACHE_OP_WEAK_REVALIDATE;
1688         if (op->d_delete)
1689                 dentry->d_flags |= DCACHE_OP_DELETE;
1690         if (op->d_prune)
1691                 dentry->d_flags |= DCACHE_OP_PRUNE;
1692 
1693 }
1694 EXPORT_SYMBOL(d_set_d_op);
1695 
1696 
1697 /*
1698  * d_set_fallthru - Mark a dentry as falling through to a lower layer
1699  * @dentry - The dentry to mark
1700  *
1701  * Mark a dentry as falling through to the lower layer (as set with
1702  * d_pin_lower()).  This flag may be recorded on the medium.
1703  */
1704 void d_set_fallthru(struct dentry *dentry)
1705 {
1706         spin_lock(&dentry->d_lock);
1707         dentry->d_flags |= DCACHE_FALLTHRU;
1708         spin_unlock(&dentry->d_lock);
1709 }
1710 EXPORT_SYMBOL(d_set_fallthru);
1711 
1712 static unsigned d_flags_for_inode(struct inode *inode)
1713 {
1714         unsigned add_flags = DCACHE_REGULAR_TYPE;
1715 
1716         if (!inode)
1717                 return DCACHE_MISS_TYPE;
1718 
1719         if (S_ISDIR(inode->i_mode)) {
1720                 add_flags = DCACHE_DIRECTORY_TYPE;
1721                 if (unlikely(!(inode->i_opflags & IOP_LOOKUP))) {
1722                         if (unlikely(!inode->i_op->lookup))
1723                                 add_flags = DCACHE_AUTODIR_TYPE;
1724                         else
1725                                 inode->i_opflags |= IOP_LOOKUP;
1726                 }
1727                 goto type_determined;
1728         }
1729 
1730         if (unlikely(!(inode->i_opflags & IOP_NOFOLLOW))) {
1731                 if (unlikely(inode->i_op->follow_link)) {
1732                         add_flags = DCACHE_SYMLINK_TYPE;
1733                         goto type_determined;
1734                 }
1735                 inode->i_opflags |= IOP_NOFOLLOW;
1736         }
1737 
1738         if (unlikely(!S_ISREG(inode->i_mode)))
1739                 add_flags = DCACHE_SPECIAL_TYPE;
1740 
1741 type_determined:
1742         if (unlikely(IS_AUTOMOUNT(inode)))
1743                 add_flags |= DCACHE_NEED_AUTOMOUNT;
1744         return add_flags;
1745 }
1746 
1747 static void __d_instantiate(struct dentry *dentry, struct inode *inode)
1748 {
1749         unsigned add_flags = d_flags_for_inode(inode);
1750 
1751         spin_lock(&dentry->d_lock);
1752         if (inode)
1753                 hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
1754         __d_set_inode_and_type(dentry, inode, add_flags);
1755         dentry_rcuwalk_barrier(dentry);
1756         spin_unlock(&dentry->d_lock);
1757         fsnotify_d_instantiate(dentry, inode);
1758 }
1759 
1760 /**
1761  * d_instantiate - fill in inode information for a dentry
1762  * @entry: dentry to complete
1763  * @inode: inode to attach to this dentry
1764  *
1765  * Fill in inode information in the entry.
1766  *
1767  * This turns negative dentries into productive full members
1768  * of society.
1769  *
1770  * NOTE! This assumes that the inode count has been incremented
1771  * (or otherwise set) by the caller to indicate that it is now
1772  * in use by the dcache.
1773  */
1774  
1775 void d_instantiate(struct dentry *entry, struct inode * inode)
1776 {
1777         BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
1778         if (inode)
1779                 spin_lock(&inode->i_lock);
1780         __d_instantiate(entry, inode);
1781         if (inode)
1782                 spin_unlock(&inode->i_lock);
1783         security_d_instantiate(entry, inode);
1784 }
1785 EXPORT_SYMBOL(d_instantiate);
1786 
1787 /**
1788  * d_instantiate_unique - instantiate a non-aliased dentry
1789  * @entry: dentry to instantiate
1790  * @inode: inode to attach to this dentry
1791  *
1792  * Fill in inode information in the entry. On success, it returns NULL.
1793  * If an unhashed alias of "entry" already exists, then we return the
1794  * aliased dentry instead and drop one reference to inode.
1795  *
1796  * Note that in order to avoid conflicts with rename() etc, the caller
1797  * had better be holding the parent directory semaphore.
1798  *
1799  * This also assumes that the inode count has been incremented
1800  * (or otherwise set) by the caller to indicate that it is now
1801  * in use by the dcache.
1802  */
1803 static struct dentry *__d_instantiate_unique(struct dentry *entry,
1804                                              struct inode *inode)
1805 {
1806         struct dentry *alias;
1807         int len = entry->d_name.len;
1808         const char *name = entry->d_name.name;
1809         unsigned int hash = entry->d_name.hash;
1810 
1811         if (!inode) {
1812                 __d_instantiate(entry, NULL);
1813                 return NULL;
1814         }
1815 
1816         hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
1817                 /*
1818                  * Don't need alias->d_lock here, because aliases with
1819                  * d_parent == entry->d_parent are not subject to name or
1820                  * parent changes, because the parent inode i_mutex is held.
1821                  */
1822                 if (alias->d_name.hash != hash)
1823                         continue;
1824                 if (alias->d_parent != entry->d_parent)
1825                         continue;
1826                 if (alias->d_name.len != len)
1827                         continue;
1828                 if (dentry_cmp(alias, name, len))
1829                         continue;
1830                 __dget(alias);
1831                 return alias;
1832         }
1833 
1834         __d_instantiate(entry, inode);
1835         return NULL;
1836 }
1837 
1838 struct dentry *d_instantiate_unique(struct dentry *entry, struct inode *inode)
1839 {
1840         struct dentry *result;
1841 
1842         BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
1843 
1844         if (inode)
1845                 spin_lock(&inode->i_lock);
1846         result = __d_instantiate_unique(entry, inode);
1847         if (inode)
1848                 spin_unlock(&inode->i_lock);
1849 
1850         if (!result) {
1851                 security_d_instantiate(entry, inode);
1852                 return NULL;
1853         }
1854 
1855         BUG_ON(!d_unhashed(result));
1856         iput(inode);
1857         return result;
1858 }
1859 
1860 EXPORT_SYMBOL(d_instantiate_unique);
1861 
1862 /**
1863  * d_instantiate_no_diralias - instantiate a non-aliased dentry
1864  * @entry: dentry to complete
1865  * @inode: inode to attach to this dentry
1866  *
1867  * Fill in inode information in the entry.  If a directory alias is found, then
1868  * return an error (and drop inode).  Together with d_materialise_unique() this
1869  * guarantees that a directory inode may never have more than one alias.
1870  */
1871 int d_instantiate_no_diralias(struct dentry *entry, struct inode *inode)
1872 {
1873         BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
1874 
1875         spin_lock(&inode->i_lock);
1876         if (S_ISDIR(inode->i_mode) && !hlist_empty(&inode->i_dentry)) {
1877                 spin_unlock(&inode->i_lock);
1878                 iput(inode);
1879                 return -EBUSY;
1880         }
1881         __d_instantiate(entry, inode);
1882         spin_unlock(&inode->i_lock);
1883         security_d_instantiate(entry, inode);
1884 
1885         return 0;
1886 }
1887 EXPORT_SYMBOL(d_instantiate_no_diralias);
1888 
1889 struct dentry *d_make_root(struct inode *root_inode)
1890 {
1891         struct dentry *res = NULL;
1892 
1893         if (root_inode) {
1894                 static const struct qstr name = QSTR_INIT("/", 1);
1895 
1896                 res = __d_alloc(root_inode->i_sb, &name);
1897                 if (res)
1898                         d_instantiate(res, root_inode);
1899                 else
1900                         iput(root_inode);
1901         }
1902         return res;
1903 }
1904 EXPORT_SYMBOL(d_make_root);
1905 
1906 static struct dentry * __d_find_any_alias(struct inode *inode)
1907 {
1908         struct dentry *alias;
1909 
1910         if (hlist_empty(&inode->i_dentry))
1911                 return NULL;
1912         alias = hlist_entry(inode->i_dentry.first, struct dentry, d_u.d_alias);
1913         __dget(alias);
1914         return alias;
1915 }
1916 
1917 /**
1918  * d_find_any_alias - find any alias for a given inode
1919  * @inode: inode to find an alias for
1920  *
1921  * If any aliases exist for the given inode, take and return a
1922  * reference for one of them.  If no aliases exist, return %NULL.
1923  */
1924 struct dentry *d_find_any_alias(struct inode *inode)
1925 {
1926         struct dentry *de;
1927 
1928         spin_lock(&inode->i_lock);
1929         de = __d_find_any_alias(inode);
1930         spin_unlock(&inode->i_lock);
1931         return de;
1932 }
1933 EXPORT_SYMBOL(d_find_any_alias);
1934 
1935 static struct dentry *__d_obtain_alias(struct inode *inode, int disconnected)
1936 {
1937         static const struct qstr anonstring = QSTR_INIT("/", 1);
1938         struct dentry *tmp;
1939         struct dentry *res;
1940         unsigned add_flags;
1941 
1942         if (!inode)
1943                 return ERR_PTR(-ESTALE);
1944         if (IS_ERR(inode))
1945                 return ERR_CAST(inode);
1946 
1947         res = d_find_any_alias(inode);
1948         if (res)
1949                 goto out_iput;
1950 
1951         tmp = __d_alloc(inode->i_sb, &anonstring);
1952         if (!tmp) {
1953                 res = ERR_PTR(-ENOMEM);
1954                 goto out_iput;
1955         }
1956 
1957         spin_lock(&inode->i_lock);
1958         res = __d_find_any_alias(inode);
1959         if (res) {
1960                 spin_unlock(&inode->i_lock);
1961                 dput(tmp);
1962                 goto out_iput;
1963         }
1964 
1965         /* attach a disconnected dentry */
1966         add_flags = d_flags_for_inode(inode);
1967 
1968         if (disconnected)
1969                 add_flags |= DCACHE_DISCONNECTED;
1970 
1971         spin_lock(&tmp->d_lock);
1972         __d_set_inode_and_type(tmp, inode, add_flags);
1973         hlist_add_head(&tmp->d_u.d_alias, &inode->i_dentry);
1974         hlist_bl_lock(&tmp->d_sb->s_anon);
1975         hlist_bl_add_head(&tmp->d_hash, &tmp->d_sb->s_anon);
1976         hlist_bl_unlock(&tmp->d_sb->s_anon);
1977         spin_unlock(&tmp->d_lock);
1978         spin_unlock(&inode->i_lock);
1979         security_d_instantiate(tmp, inode);
1980 
1981         return tmp;
1982 
1983  out_iput:
1984         if (res && !IS_ERR(res))
1985                 security_d_instantiate(res, inode);
1986         iput(inode);
1987         return res;
1988 }
1989 
1990 /**
1991  * d_obtain_alias - find or allocate a DISCONNECTED dentry for a given inode
1992  * @inode: inode to allocate the dentry for
1993  *
1994  * Obtain a dentry for an inode resulting from NFS filehandle conversion or
1995  * similar open by handle operations.  The returned dentry may be anonymous,
1996  * or may have a full name (if the inode was already in the cache).
1997  *
1998  * When called on a directory inode, we must ensure that the inode only ever
1999  * has one dentry.  If a dentry is found, that is returned instead of
2000  * allocating a new one.
2001  *
2002  * On successful return, the reference to the inode has been transferred
2003  * to the dentry.  In case of an error the reference on the inode is released.
2004  * To make it easier to use in export operations a %NULL or IS_ERR inode may
2005  * be passed in and the error will be propagated to the return value,
2006  * with a %NULL @inode replaced by ERR_PTR(-ESTALE).
2007  */
2008 struct dentry *d_obtain_alias(struct inode *inode)
2009 {
2010         return __d_obtain_alias(inode, 1);
2011 }
2012 EXPORT_SYMBOL(d_obtain_alias);
2013 
2014 /**
2015  * d_obtain_root - find or allocate a dentry for a given inode
2016  * @inode: inode to allocate the dentry for
2017  *
2018  * Obtain an IS_ROOT dentry for the root of a filesystem.
2019  *
2020  * We must ensure that directory inodes only ever have one dentry.  If a
2021  * dentry is found, that is returned instead of allocating a new one.
2022  *
2023  * On successful return, the reference to the inode has been transferred
2024  * to the dentry.  In case of an error the reference on the inode is
2025  * released.  A %NULL or IS_ERR inode may be passed in and will be the
2026  * error will be propagate to the return value, with a %NULL @inode
2027  * replaced by ERR_PTR(-ESTALE).
2028  */
2029 struct dentry *d_obtain_root(struct inode *inode)
2030 {
2031         return __d_obtain_alias(inode, 0);
2032 }
2033 EXPORT_SYMBOL(d_obtain_root);
2034 
2035 /**
2036  * d_add_ci - lookup or allocate new dentry with case-exact name
2037  * @inode:  the inode case-insensitive lookup has found
2038  * @dentry: the negative dentry that was passed to the parent's lookup func
2039  * @name:   the case-exact name to be associated with the returned dentry
2040  *
2041  * This is to avoid filling the dcache with case-insensitive names to the
2042  * same inode, only the actual correct case is stored in the dcache for
2043  * case-insensitive filesystems.
2044  *
2045  * For a case-insensitive lookup match and if the the case-exact dentry
2046  * already exists in in the dcache, use it and return it.
2047  *
2048  * If no entry exists with the exact case name, allocate new dentry with
2049  * the exact case, and return the spliced entry.
2050  */
2051 struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
2052                         struct qstr *name)
2053 {
2054         struct dentry *found;
2055         struct dentry *new;
2056 
2057         /*
2058          * First check if a dentry matching the name already exists,
2059          * if not go ahead and create it now.
2060          */
2061         found = d_hash_and_lookup(dentry->d_parent, name);
2062         if (!found) {
2063                 new = d_alloc(dentry->d_parent, name);
2064                 if (!new) {
2065                         found = ERR_PTR(-ENOMEM);
2066                 } else {
2067                         found = d_splice_alias(inode, new);
2068                         if (found) {
2069                                 dput(new);
2070                                 return found;
2071                         }
2072                         return new;
2073                 }
2074         }
2075         iput(inode);
2076         return found;
2077 }
2078 EXPORT_SYMBOL(d_add_ci);
2079 
2080 /*
2081  * Do the slow-case of the dentry name compare.
2082  *
2083  * Unlike the dentry_cmp() function, we need to atomically
2084  * load the name and length information, so that the
2085  * filesystem can rely on them, and can use the 'name' and
2086  * 'len' information without worrying about walking off the
2087  * end of memory etc.
2088  *
2089  * Thus the read_seqcount_retry() and the "duplicate" info
2090  * in arguments (the low-level filesystem should not look
2091  * at the dentry inode or name contents directly, since
2092  * rename can change them while we're in RCU mode).
2093  */
2094 enum slow_d_compare {
2095         D_COMP_OK,
2096         D_COMP_NOMATCH,
2097         D_COMP_SEQRETRY,
2098 };
2099 
2100 static noinline enum slow_d_compare slow_dentry_cmp(
2101                 const struct dentry *parent,
2102                 struct dentry *dentry,
2103                 unsigned int seq,
2104                 const struct qstr *name)
2105 {
2106         int tlen = dentry->d_name.len;
2107         const char *tname = dentry->d_name.name;
2108 
2109         if (read_seqcount_retry(&dentry->d_seq, seq)) {
2110                 cpu_relax();
2111                 return D_COMP_SEQRETRY;
2112         }
2113         if (parent->d_op->d_compare(parent, dentry, tlen, tname, name))
2114                 return D_COMP_NOMATCH;
2115         return D_COMP_OK;
2116 }
2117 
2118 /**
2119  * __d_lookup_rcu - search for a dentry (racy, store-free)
2120  * @parent: parent dentry
2121  * @name: qstr of name we wish to find
2122  * @seqp: returns d_seq value at the point where the dentry was found
2123  * Returns: dentry, or NULL
2124  *
2125  * __d_lookup_rcu is the dcache lookup function for rcu-walk name
2126  * resolution (store-free path walking) design described in
2127  * Documentation/filesystems/path-lookup.txt.
2128  *
2129  * This is not to be used outside core vfs.
2130  *
2131  * __d_lookup_rcu must only be used in rcu-walk mode, ie. with vfsmount lock
2132  * held, and rcu_read_lock held. The returned dentry must not be stored into
2133  * without taking d_lock and checking d_seq sequence count against @seq
2134  * returned here.
2135  *
2136  * A refcount may be taken on the found dentry with the d_rcu_to_refcount
2137  * function.
2138  *
2139  * Alternatively, __d_lookup_rcu may be called again to look up the child of
2140  * the returned dentry, so long as its parent's seqlock is checked after the
2141  * child is looked up. Thus, an interlocking stepping of sequence lock checks
2142  * is formed, giving integrity down the path walk.
2143  *
2144  * NOTE! The caller *has* to check the resulting dentry against the sequence
2145  * number we've returned before using any of the resulting dentry state!
2146  */
2147 struct dentry *__d_lookup_rcu(const struct dentry *parent,
2148                                 const struct qstr *name,
2149                                 unsigned *seqp)
2150 {
2151         u64 hashlen = name->hash_len;
2152         const unsigned char *str = name->name;
2153         struct hlist_bl_head *b = d_hash(parent, hashlen_hash(hashlen));
2154         struct hlist_bl_node *node;
2155         struct dentry *dentry;
2156 
2157         /*
2158          * Note: There is significant duplication with __d_lookup_rcu which is
2159          * required to prevent single threaded performance regressions
2160          * especially on architectures where smp_rmb (in seqcounts) are costly.
2161          * Keep the two functions in sync.
2162          */
2163 
2164         /*
2165          * The hash list is protected using RCU.
2166          *
2167          * Carefully use d_seq when comparing a candidate dentry, to avoid
2168          * races with d_move().
2169          *
2170          * It is possible that concurrent renames can mess up our list
2171          * walk here and result in missing our dentry, resulting in the
2172          * false-negative result. d_lookup() protects against concurrent
2173          * renames using rename_lock seqlock.
2174          *
2175          * See Documentation/filesystems/path-lookup.txt for more details.
2176          */
2177         hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
2178                 unsigned seq;
2179 
2180 seqretry:
2181                 /*
2182                  * The dentry sequence count protects us from concurrent
2183                  * renames, and thus protects parent and name fields.
2184                  *
2185                  * The caller must perform a seqcount check in order
2186                  * to do anything useful with the returned dentry.
2187                  *
2188                  * NOTE! We do a "raw" seqcount_begin here. That means that
2189                  * we don't wait for the sequence count to stabilize if it
2190                  * is in the middle of a sequence change. If we do the slow
2191                  * dentry compare, we will do seqretries until it is stable,
2192                  * and if we end up with a successful lookup, we actually
2193                  * want to exit RCU lookup anyway.
2194                  */
2195                 seq = raw_seqcount_begin(&dentry->d_seq);
2196                 if (dentry->d_parent != parent)
2197                         continue;
2198                 if (d_unhashed(dentry))
2199                         continue;
2200 
2201                 if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
2202                         if (dentry->d_name.hash != hashlen_hash(hashlen))
2203                                 continue;
2204                         *seqp = seq;
2205                         switch (slow_dentry_cmp(parent, dentry, seq, name)) {
2206                         case D_COMP_OK:
2207                                 return dentry;
2208                         case D_COMP_NOMATCH:
2209                                 continue;
2210                         default:
2211                                 goto seqretry;
2212                         }
2213                 }
2214 
2215                 if (dentry->d_name.hash_len != hashlen)
2216                         continue;
2217                 *seqp = seq;
2218                 if (!dentry_cmp(dentry, str, hashlen_len(hashlen)))
2219                         return dentry;
2220         }
2221         return NULL;
2222 }
2223 
2224 /**
2225  * d_lookup - search for a dentry
2226  * @parent: parent dentry
2227  * @name: qstr of name we wish to find
2228  * Returns: dentry, or NULL
2229  *
2230  * d_lookup searches the children of the parent dentry for the name in
2231  * question. If the dentry is found its reference count is incremented and the
2232  * dentry is returned. The caller must use dput to free the entry when it has
2233  * finished using it. %NULL is returned if the dentry does not exist.
2234  */
2235 struct dentry *d_lookup(const struct dentry *parent, const struct qstr *name)
2236 {
2237         struct dentry *dentry;
2238         unsigned seq;
2239 
2240         do {
2241                 seq = read_seqbegin(&rename_lock);
2242                 dentry = __d_lookup(parent, name);
2243                 if (dentry)
2244                         break;
2245         } while (read_seqretry(&rename_lock, seq));
2246         return dentry;
2247 }
2248 EXPORT_SYMBOL(d_lookup);
2249 
2250 /**
2251  * __d_lookup - search for a dentry (racy)
2252  * @parent: parent dentry
2253  * @name: qstr of name we wish to find
2254  * Returns: dentry, or NULL
2255  *
2256  * __d_lookup is like d_lookup, however it may (rarely) return a
2257  * false-negative result due to unrelated rename activity.
2258  *
2259  * __d_lookup is slightly faster by avoiding rename_lock read seqlock,
2260  * however it must be used carefully, eg. with a following d_lookup in
2261  * the case of failure.
2262  *
2263  * __d_lookup callers must be commented.
2264  */
2265 struct dentry *__d_lookup(const struct dentry *parent, const struct qstr *name)
2266 {
2267         unsigned int len = name->len;
2268         unsigned int hash = name->hash;
2269         const unsigned char *str = name->name;
2270         struct hlist_bl_head *b = d_hash(parent, hash);
2271         struct hlist_bl_node *node;
2272         struct dentry *found = NULL;
2273         struct dentry *dentry;
2274 
2275         /*
2276          * Note: There is significant duplication with __d_lookup_rcu which is
2277          * required to prevent single threaded performance regressions
2278          * especially on architectures where smp_rmb (in seqcounts) are costly.
2279          * Keep the two functions in sync.
2280          */
2281 
2282         /*
2283          * The hash list is protected using RCU.
2284          *
2285          * Take d_lock when comparing a candidate dentry, to avoid races
2286          * with d_move().
2287          *
2288          * It is possible that concurrent renames can mess up our list
2289          * walk here and result in missing our dentry, resulting in the
2290          * false-negative result. d_lookup() protects against concurrent
2291          * renames using rename_lock seqlock.
2292          *
2293          * See Documentation/filesystems/path-lookup.txt for more details.
2294          */
2295         rcu_read_lock();
2296         
2297         hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
2298 
2299                 if (dentry->d_name.hash != hash)
2300                         continue;
2301 
2302                 spin_lock(&dentry->d_lock);
2303                 if (dentry->d_parent != parent)
2304                         goto next;
2305                 if (d_unhashed(dentry))
2306                         goto next;
2307 
2308                 /*
2309                  * It is safe to compare names since d_move() cannot
2310                  * change the qstr (protected by d_lock).
2311                  */
2312                 if (parent->d_flags & DCACHE_OP_COMPARE) {
2313                         int tlen = dentry->d_name.len;
2314                         const char *tname = dentry->d_name.name;
2315                         if (parent->d_op->d_compare(parent, dentry, tlen, tname, name))
2316                                 goto next;
2317                 } else {
2318                         if (dentry->d_name.len != len)
2319                                 goto next;
2320                         if (dentry_cmp(dentry, str, len))
2321                                 goto next;
2322                 }
2323 
2324                 dentry->d_lockref.count++;
2325                 found = dentry;
2326                 spin_unlock(&dentry->d_lock);
2327                 break;
2328 next:
2329                 spin_unlock(&dentry->d_lock);
2330         }
2331         rcu_read_unlock();
2332 
2333         return found;
2334 }
2335 
2336 /**
2337  * d_hash_and_lookup - hash the qstr then search for a dentry
2338  * @dir: Directory to search in
2339  * @name: qstr of name we wish to find
2340  *
2341  * On lookup failure NULL is returned; on bad name - ERR_PTR(-error)
2342  */
2343 struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
2344 {
2345         /*
2346          * Check for a fs-specific hash function. Note that we must
2347          * calculate the standard hash first, as the d_op->d_hash()
2348          * routine may choose to leave the hash value unchanged.
2349          */
2350         name->hash = full_name_hash(name->name, name->len);
2351         if (dir->d_flags & DCACHE_OP_HASH) {
2352                 int err = dir->d_op->d_hash(dir, name);
2353                 if (unlikely(err < 0))
2354                         return ERR_PTR(err);
2355         }
2356         return d_lookup(dir, name);
2357 }
2358 EXPORT_SYMBOL(d_hash_and_lookup);
2359 
2360 /*
2361  * When a file is deleted, we have two options:
2362  * - turn this dentry into a negative dentry
2363  * - unhash this dentry and free it.
2364  *
2365  * Usually, we want to just turn this into
2366  * a negative dentry, but if anybody else is
2367  * currently using the dentry or the inode
2368  * we can't do that and we fall back on removing
2369  * it from the hash queues and waiting for
2370  * it to be deleted later when it has no users
2371  */
2372  
2373 /**
2374  * d_delete - delete a dentry
2375  * @dentry: The dentry to delete
2376  *
2377  * Turn the dentry into a negative dentry if possible, otherwise
2378  * remove it from the hash queues so it can be deleted later
2379  */
2380  
2381 void d_delete(struct dentry * dentry)
2382 {
2383         struct inode *inode;
2384         int isdir = 0;
2385         /*
2386          * Are we the only user?
2387          */
2388 again:
2389         spin_lock(&dentry->d_lock);
2390         inode = dentry->d_inode;
2391         isdir = S_ISDIR(inode->i_mode);
2392         if (dentry->d_lockref.count == 1) {
2393                 if (!spin_trylock(&inode->i_lock)) {
2394                         spin_unlock(&dentry->d_lock);
2395                         cpu_relax();
2396                         goto again;
2397                 }
2398                 dentry->d_flags &= ~DCACHE_CANT_MOUNT;
2399                 dentry_unlink_inode(dentry);
2400                 fsnotify_nameremove(dentry, isdir);
2401                 return;
2402         }
2403 
2404         if (!d_unhashed(dentry))
2405                 __d_drop(dentry);
2406 
2407         spin_unlock(&dentry->d_lock);
2408 
2409         fsnotify_nameremove(dentry, isdir);
2410 }
2411 EXPORT_SYMBOL(d_delete);
2412 
2413 static void __d_rehash(struct dentry * entry, struct hlist_bl_head *b)
2414 {
2415         BUG_ON(!d_unhashed(entry));
2416         hlist_bl_lock(b);
2417         entry->d_flags |= DCACHE_RCUACCESS;
2418         hlist_bl_add_head_rcu(&entry->d_hash, b);
2419         hlist_bl_unlock(b);
2420 }
2421 
2422 static void _d_rehash(struct dentry * entry)
2423 {
2424         __d_rehash(entry, d_hash(entry->d_parent, entry->d_name.hash));
2425 }
2426 
2427 /**
2428  * d_rehash     - add an entry back to the hash
2429  * @entry: dentry to add to the hash
2430  *
2431  * Adds a dentry to the hash according to its name.
2432  */
2433  
2434 void d_rehash(struct dentry * entry)
2435 {
2436         spin_lock(&entry->d_lock);
2437         _d_rehash(entry);
2438         spin_unlock(&entry->d_lock);
2439 }
2440 EXPORT_SYMBOL(d_rehash);
2441 
2442 /**
2443  * dentry_update_name_case - update case insensitive dentry with a new name
2444  * @dentry: dentry to be updated
2445  * @name: new name
2446  *
2447  * Update a case insensitive dentry with new case of name.
2448  *
2449  * dentry must have been returned by d_lookup with name @name. Old and new
2450  * name lengths must match (ie. no d_compare which allows mismatched name
2451  * lengths).
2452  *
2453  * Parent inode i_mutex must be held over d_lookup and into this call (to
2454  * keep renames and concurrent inserts, and readdir(2) away).
2455  */
2456 void dentry_update_name_case(struct dentry *dentry, struct qstr *name)
2457 {
2458         BUG_ON(!mutex_is_locked(&dentry->d_parent->d_inode->i_mutex));
2459         BUG_ON(dentry->d_name.len != name->len); /* d_lookup gives this */
2460 
2461         spin_lock(&dentry->d_lock);
2462         write_seqcount_begin(&dentry->d_seq);
2463         memcpy((unsigned char *)dentry->d_name.name, name->name, name->len);
2464         write_seqcount_end(&dentry->d_seq);
2465         spin_unlock(&dentry->d_lock);
2466 }
2467 EXPORT_SYMBOL(dentry_update_name_case);
2468 
2469 static void swap_names(struct dentry *dentry, struct dentry *target)
2470 {
2471         if (unlikely(dname_external(target))) {
2472                 if (unlikely(dname_external(dentry))) {
2473                         /*
2474                          * Both external: swap the pointers
2475                          */
2476                         swap(target->d_name.name, dentry->d_name.name);
2477                 } else {
2478                         /*
2479                          * dentry:internal, target:external.  Steal target's
2480                          * storage and make target internal.
2481                          */
2482                         memcpy(target->d_iname, dentry->d_name.name,
2483                                         dentry->d_name.len + 1);
2484                         dentry->d_name.name = target->d_name.name;
2485                         target->d_name.name = target->d_iname;
2486                 }
2487         } else {
2488                 if (unlikely(dname_external(dentry))) {
2489                         /*
2490                          * dentry:external, target:internal.  Give dentry's
2491                          * storage to target and make dentry internal
2492                          */
2493                         memcpy(dentry->d_iname, target->d_name.name,
2494                                         target->d_name.len + 1);
2495                         target->d_name.name = dentry->d_name.name;
2496                         dentry->d_name.name = dentry->d_iname;
2497                 } else {
2498                         /*
2499                          * Both are internal.
2500                          */
2501                         unsigned int i;
2502                         BUILD_BUG_ON(!IS_ALIGNED(DNAME_INLINE_LEN, sizeof(long)));
2503                         kmemcheck_mark_initialized(dentry->d_iname, DNAME_INLINE_LEN);
2504                         kmemcheck_mark_initialized(target->d_iname, DNAME_INLINE_LEN);
2505                         for (i = 0; i < DNAME_INLINE_LEN / sizeof(long); i++) {
2506                                 swap(((long *) &dentry->d_iname)[i],
2507                                      ((long *) &target->d_iname)[i]);
2508                         }
2509                 }
2510         }
2511         swap(dentry->d_name.hash_len, target->d_name.hash_len);
2512 }
2513 
2514 static void copy_name(struct dentry *dentry, struct dentry *target)
2515 {
2516         struct external_name *old_name = NULL;
2517         if (unlikely(dname_external(dentry)))
2518                 old_name = external_name(dentry);
2519         if (unlikely(dname_external(target))) {
2520                 atomic_inc(&external_name(target)->u.count);
2521                 dentry->d_name = target->d_name;
2522         } else {
2523                 memcpy(dentry->d_iname, target->d_name.name,
2524                                 target->d_name.len + 1);
2525                 dentry->d_name.name = dentry->d_iname;
2526                 dentry->d_name.hash_len = target->d_name.hash_len;
2527         }
2528         if (old_name && likely(atomic_dec_and_test(&old_name->u.count)))
2529                 kfree_rcu(old_name, u.head);
2530 }
2531 
2532 static void dentry_lock_for_move(struct dentry *dentry, struct dentry *target)
2533 {
2534         /*
2535          * XXXX: do we really need to take target->d_lock?
2536          */
2537         if (IS_ROOT(dentry) || dentry->d_parent == target->d_parent)
2538                 spin_lock(&target->d_parent->d_lock);
2539         else {
2540                 if (d_ancestor(dentry->d_parent, target->d_parent)) {
2541                         spin_lock(&dentry->d_parent->d_lock);
2542                         spin_lock_nested(&target->d_parent->d_lock,
2543                                                 DENTRY_D_LOCK_NESTED);
2544                 } else {
2545                         spin_lock(&target->d_parent->d_lock);
2546                         spin_lock_nested(&dentry->d_parent->d_lock,
2547                                                 DENTRY_D_LOCK_NESTED);
2548                 }
2549         }
2550         if (target < dentry) {
2551                 spin_lock_nested(&target->d_lock, 2);
2552                 spin_lock_nested(&dentry->d_lock, 3);
2553         } else {
2554                 spin_lock_nested(&dentry->d_lock, 2);
2555                 spin_lock_nested(&target->d_lock, 3);
2556         }
2557 }
2558 
2559 static void dentry_unlock_for_move(struct dentry *dentry, struct dentry *target)
2560 {
2561         if (target->d_parent != dentry->d_parent)
2562                 spin_unlock(&dentry->d_parent->d_lock);
2563         if (target->d_parent != target)
2564                 spin_unlock(&target->d_parent->d_lock);
2565         spin_unlock(&target->d_lock);
2566         spin_unlock(&dentry->d_lock);
2567 }
2568 
2569 /*
2570  * When switching names, the actual string doesn't strictly have to
2571  * be preserved in the target - because we're dropping the target
2572  * anyway. As such, we can just do a simple memcpy() to copy over
2573  * the new name before we switch, unless we are going to rehash
2574  * it.  Note that if we *do* unhash the target, we are not allowed
2575  * to rehash it without giving it a new name/hash key - whether
2576  * we swap or overwrite the names here, resulting name won't match
2577  * the reality in filesystem; it's only there for d_path() purposes.
2578  * Note that all of this is happening under rename_lock, so the
2579  * any hash lookup seeing it in the middle of manipulations will
2580  * be discarded anyway.  So we do not care what happens to the hash
2581  * key in that case.
2582  */
2583 /*
2584  * __d_move - move a dentry
2585  * @dentry: entry to move
2586  * @target: new dentry
2587  * @exchange: exchange the two dentries
2588  *
2589  * Update the dcache to reflect the move of a file name. Negative
2590  * dcache entries should not be moved in this way. Caller must hold
2591  * rename_lock, the i_mutex of the source and target directories,
2592  * and the sb->s_vfs_rename_mutex if they differ. See lock_rename().
2593  */
2594 static void __d_move(struct dentry *dentry, struct dentry *target,
2595                      bool exchange)
2596 {
2597         if (!dentry->d_inode)
2598                 printk(KERN_WARNING "VFS: moving negative dcache entry\n");
2599 
2600         BUG_ON(d_ancestor(dentry, target));
2601         BUG_ON(d_ancestor(target, dentry));
2602 
2603         dentry_lock_for_move(dentry, target);
2604 
2605         write_seqcount_begin(&dentry->d_seq);
2606         write_seqcount_begin_nested(&target->d_seq, DENTRY_D_LOCK_NESTED);
2607 
2608         /* __d_drop does write_seqcount_barrier, but they're OK to nest. */
2609 
2610         /*
2611          * Move the dentry to the target hash queue. Don't bother checking
2612          * for the same hash queue because of how unlikely it is.
2613          */
2614         __d_drop(dentry);
2615         __d_rehash(dentry, d_hash(target->d_parent, target->d_name.hash));
2616 
2617         /*
2618          * Unhash the target (d_delete() is not usable here).  If exchanging
2619          * the two dentries, then rehash onto the other's hash queue.
2620          */
2621         __d_drop(target);
2622         if (exchange) {
2623                 __d_rehash(target,
2624                            d_hash(dentry->d_parent, dentry->d_name.hash));
2625         }
2626 
2627         /* Switch the names.. */
2628         if (exchange)
2629                 swap_names(dentry, target);
2630         else
2631                 copy_name(dentry, target);
2632 
2633         /* ... and switch them in the tree */
2634         if (IS_ROOT(dentry)) {
2635                 /* splicing a tree */
2636                 dentry->d_parent = target->d_parent;
2637                 target->d_parent = target;
2638                 list_del_init(&target->d_child);
2639                 list_move(&dentry->d_child, &dentry->d_parent->d_subdirs);
2640         } else {
2641                 /* swapping two dentries */
2642                 swap(dentry->d_parent, target->d_parent);
2643                 list_move(&target->d_child, &target->d_parent->d_subdirs);
2644                 list_move(&dentry->d_child, &dentry->d_parent->d_subdirs);
2645                 if (exchange)
2646                         fsnotify_d_move(target);
2647                 fsnotify_d_move(dentry);
2648         }
2649 
2650         write_seqcount_end(&target->d_seq);
2651         write_seqcount_end(&dentry->d_seq);
2652 
2653         dentry_unlock_for_move(dentry, target);
2654 }
2655 
2656 /*
2657  * d_move - move a dentry
2658  * @dentry: entry to move
2659  * @target: new dentry
2660  *
2661  * Update the dcache to reflect the move of a file name. Negative
2662  * dcache entries should not be moved in this way. See the locking
2663  * requirements for __d_move.
2664  */
2665 void d_move(struct dentry *dentry, struct dentry *target)
2666 {
2667         write_seqlock(&rename_lock);
2668         __d_move(dentry, target, false);
2669         write_sequnlock(&rename_lock);
2670 }
2671 EXPORT_SYMBOL(d_move);
2672 
2673 /*
2674  * d_exchange - exchange two dentries
2675  * @dentry1: first dentry
2676  * @dentry2: second dentry
2677  */
2678 void d_exchange(struct dentry *dentry1, struct dentry *dentry2)
2679 {
2680         write_seqlock(&rename_lock);
2681 
2682         WARN_ON(!dentry1->d_inode);
2683         WARN_ON(!dentry2->d_inode);
2684         WARN_ON(IS_ROOT(dentry1));
2685         WARN_ON(IS_ROOT(dentry2));
2686 
2687         __d_move(dentry1, dentry2, true);
2688 
2689         write_sequnlock(&rename_lock);
2690 }
2691 
2692 /**
2693  * d_ancestor - search for an ancestor
2694  * @p1: ancestor dentry
2695  * @p2: child dentry
2696  *
2697  * Returns the ancestor dentry of p2 which is a child of p1, if p1 is
2698  * an ancestor of p2, else NULL.
2699  */
2700 struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
2701 {
2702         struct dentry *p;
2703 
2704         for (p = p2; !IS_ROOT(p); p = p->d_parent) {
2705                 if (p->d_parent == p1)
2706                         return p;
2707         }
2708         return NULL;
2709 }
2710 
2711 /*
2712  * This helper attempts to cope with remotely renamed directories
2713  *
2714  * It assumes that the caller is already holding
2715  * dentry->d_parent->d_inode->i_mutex, inode->i_lock and rename_lock
2716  *
2717  * Note: If ever the locking in lock_rename() changes, then please
2718  * remember to update this too...
2719  */
2720 static int __d_unalias(struct inode *inode,
2721                 struct dentry *dentry, struct dentry *alias)
2722 {
2723         struct mutex *m1 = NULL, *m2 = NULL;
2724         int ret = -ESTALE;
2725 
2726         /* If alias and dentry share a parent, then no extra locks required */
2727         if (alias->d_parent == dentry->d_parent)
2728                 goto out_unalias;
2729 
2730         /* See lock_rename() */
2731         if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
2732                 goto out_err;
2733         m1 = &dentry->d_sb->s_vfs_rename_mutex;
2734         if (!mutex_trylock(&alias->d_parent->d_inode->i_mutex))
2735                 goto out_err;
2736         m2 = &alias->d_parent->d_inode->i_mutex;
2737 out_unalias:
2738         __d_move(alias, dentry, false);
2739         ret = 0;
2740 out_err:
2741         spin_unlock(&inode->i_lock);
2742         if (m2)
2743                 mutex_unlock(m2);
2744         if (m1)
2745                 mutex_unlock(m1);
2746         return ret;
2747 }
2748 
2749 /**
2750  * d_splice_alias - splice a disconnected dentry into the tree if one exists
2751  * @inode:  the inode which may have a disconnected dentry
2752  * @dentry: a negative dentry which we want to point to the inode.
2753  *
2754  * If inode is a directory and has an IS_ROOT alias, then d_move that in
2755  * place of the given dentry and return it, else simply d_add the inode
2756  * to the dentry and return NULL.
2757  *
2758  * If a non-IS_ROOT directory is found, the filesystem is corrupt, and
2759  * we should error out: directories can't have multiple aliases.
2760  *
2761  * This is needed in the lookup routine of any filesystem that is exportable
2762  * (via knfsd) so that we can build dcache paths to directories effectively.
2763  *
2764  * If a dentry was found and moved, then it is returned.  Otherwise NULL
2765  * is returned.  This matches the expected return value of ->lookup.
2766  *
2767  * Cluster filesystems may call this function with a negative, hashed dentry.
2768  * In that case, we know that the inode will be a regular file, and also this
2769  * will only occur during atomic_open. So we need to check for the dentry
2770  * being already hashed only in the final case.
2771  */
2772 struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
2773 {
2774         if (IS_ERR(inode))
2775                 return ERR_CAST(inode);
2776 
2777         BUG_ON(!d_unhashed(dentry));
2778 
2779         if (!inode) {
2780                 __d_instantiate(dentry, NULL);
2781                 goto out;
2782         }
2783         spin_lock(&inode->i_lock);
2784         if (S_ISDIR(inode->i_mode)) {
2785                 struct dentry *new = __d_find_any_alias(inode);
2786                 if (unlikely(new)) {
2787                         write_seqlock(&rename_lock);
2788                         if (unlikely(d_ancestor(new, dentry))) {
2789                                 write_sequnlock(&rename_lock);
2790                                 spin_unlock(&inode->i_lock);
2791                                 dput(new);
2792                                 new = ERR_PTR(-ELOOP);
2793                                 pr_warn_ratelimited(
2794                                         "VFS: Lookup of '%s' in %s %s"
2795                                         " would have caused loop\n",
2796                                         dentry->d_name.name,
2797                                         inode->i_sb->s_type->name,
2798                                         inode->i_sb->s_id);
2799                         } else if (!IS_ROOT(new)) {
2800                                 int err = __d_unalias(inode, dentry, new);
2801                                 write_sequnlock(&rename_lock);
2802                                 if (err) {
2803                                         dput(new);
2804                                         new = ERR_PTR(err);
2805                                 }
2806                         } else {
2807                                 __d_move(new, dentry, false);
2808                                 write_sequnlock(&rename_lock);
2809                                 spin_unlock(&inode->i_lock);
2810                                 security_d_instantiate(new, inode);
2811                         }
2812                         iput(inode);
2813                         return new;
2814                 }
2815         }
2816         /* already taking inode->i_lock, so d_add() by hand */
2817         __d_instantiate(dentry, inode);
2818         spin_unlock(&inode->i_lock);
2819 out:
2820         security_d_instantiate(dentry, inode);
2821         d_rehash(dentry);
2822         return NULL;
2823 }
2824 EXPORT_SYMBOL(d_splice_alias);
2825 
2826 static int prepend(char **buffer, int *buflen, const char *str, int namelen)
2827 {
2828         *buflen -= namelen;
2829         if (*buflen < 0)
2830                 return -ENAMETOOLONG;
2831         *buffer -= namelen;
2832         memcpy(*buffer, str, namelen);
2833         return 0;
2834 }
2835 
2836 /**
2837  * prepend_name - prepend a pathname in front of current buffer pointer
2838  * @buffer: buffer pointer
2839  * @buflen: allocated length of the buffer
2840  * @name:   name string and length qstr structure
2841  *
2842  * With RCU path tracing, it may race with d_move(). Use ACCESS_ONCE() to
2843  * make sure that either the old or the new name pointer and length are
2844  * fetched. However, there may be mismatch between length and pointer.
2845  * The length cannot be trusted, we need to copy it byte-by-byte until
2846  * the length is reached or a null byte is found. It also prepends "/" at
2847  * the beginning of the name. The sequence number check at the caller will
2848  * retry it again when a d_move() does happen. So any garbage in the buffer
2849  * due to mismatched pointer and length will be discarded.
2850  *
2851  * Data dependency barrier is needed to make sure that we see that terminating
2852  * NUL.  Alpha strikes again, film at 11...
2853  */
2854 static int prepend_name(char **buffer, int *buflen, struct qstr *name)
2855 {
2856         const char *dname = ACCESS_ONCE(name->name);
2857         u32 dlen = ACCESS_ONCE(name->len);
2858         char *p;
2859 
2860         smp_read_barrier_depends();
2861 
2862         *buflen -= dlen + 1;
2863         if (*buflen < 0)
2864                 return -ENAMETOOLONG;
2865         p = *buffer -= dlen + 1;
2866         *p++ = '/';
2867         while (dlen--) {
2868                 char c = *dname++;
2869                 if (!c)
2870                         break;
2871                 *p++ = c;
2872         }
2873         return 0;
2874 }
2875 
2876 /**
2877  * prepend_path - Prepend path string to a buffer
2878  * @path: the dentry/vfsmount to report
2879  * @root: root vfsmnt/dentry
2880  * @buffer: pointer to the end of the buffer
2881  * @buflen: pointer to buffer length
2882  *
2883  * The function will first try to write out the pathname without taking any
2884  * lock other than the RCU read lock to make sure that dentries won't go away.
2885  * It only checks the sequence number of the global rename_lock as any change
2886  * in the dentry's d_seq will be preceded by changes in the rename_lock
2887  * sequence number. If the sequence number had been changed, it will restart
2888  * the whole pathname back-tracing sequence again by taking the rename_lock.
2889  * In this case, there is no need to take the RCU read lock as the recursive
2890  * parent pointer references will keep the dentry chain alive as long as no
2891  * rename operation is performed.
2892  */
2893 static int prepend_path(const struct path *path,
2894                         const struct path *root,
2895                         char **buffer, int *buflen)
2896 {
2897         struct dentry *dentry;
2898         struct vfsmount *vfsmnt;
2899         struct mount *mnt;
2900         int error = 0;
2901         unsigned seq, m_seq = 0;
2902         char *bptr;
2903         int blen;
2904 
2905         rcu_read_lock();
2906 restart_mnt:
2907         read_seqbegin_or_lock(&mount_lock, &m_seq);
2908         seq = 0;
2909         rcu_read_lock();
2910 restart:
2911         bptr = *buffer;
2912         blen = *buflen;
2913         error = 0;
2914         dentry = path->dentry;
2915         vfsmnt = path->mnt;
2916         mnt = real_mount(vfsmnt);
2917         read_seqbegin_or_lock(&rename_lock, &seq);
2918         while (dentry != root->dentry || vfsmnt != root->mnt) {
2919                 struct dentry * parent;
2920 
2921                 if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
2922                         struct mount *parent = ACCESS_ONCE(mnt->mnt_parent);
2923                         /* Global root? */
2924                         if (mnt != parent) {
2925                                 dentry = ACCESS_ONCE(mnt->mnt_mountpoint);
2926                                 mnt = parent;
2927                                 vfsmnt = &mnt->mnt;
2928                                 continue;
2929                         }
2930                         /*
2931                          * Filesystems needing to implement special "root names"
2932                          * should do so with ->d_dname()
2933                          */
2934                         if (IS_ROOT(dentry) &&
2935                            (dentry->d_name.len != 1 ||
2936                             dentry->d_name.name[0] != '/')) {
2937                                 WARN(1, "Root dentry has weird name <%.*s>\n",
2938                                      (int) dentry->d_name.len,
2939                                      dentry->d_name.name);
2940                         }
2941                         if (!error)
2942                                 error = is_mounted(vfsmnt) ? 1 : 2;
2943                         break;
2944                 }
2945                 parent = dentry->d_parent;
2946                 prefetch(parent);
2947                 error = prepend_name(&bptr, &blen, &dentry->d_name);
2948                 if (error)
2949                         break;
2950 
2951                 dentry = parent;
2952         }
2953         if (!(seq & 1))
2954                 rcu_read_unlock();
2955         if (need_seqretry(&rename_lock, seq)) {
2956                 seq = 1;
2957                 goto restart;
2958         }
2959         done_seqretry(&rename_lock, seq);
2960 
2961         if (!(m_seq & 1))
2962                 rcu_read_unlock();
2963         if (need_seqretry(&mount_lock, m_seq)) {
2964                 m_seq = 1;
2965                 goto restart_mnt;
2966         }
2967         done_seqretry(&mount_lock, m_seq);
2968 
2969         if (error >= 0 && bptr == *buffer) {
2970                 if (--blen < 0)
2971                         error = -ENAMETOOLONG;
2972                 else
2973                         *--bptr = '/';
2974         }
2975         *buffer = bptr;
2976         *buflen = blen;
2977         return error;
2978 }
2979 
2980 /**
2981  * __d_path - return the path of a dentry
2982  * @path: the dentry/vfsmount to report
2983  * @root: root vfsmnt/dentry
2984  * @buf: buffer to return value in
2985  * @buflen: buffer length
2986  *
2987  * Convert a dentry into an ASCII path name.
2988  *
2989  * Returns a pointer into the buffer or an error code if the
2990  * path was too long.
2991  *
2992  * "buflen" should be positive.
2993  *
2994  * If the path is not reachable from the supplied root, return %NULL.
2995  */
2996 char *__d_path(const struct path *path,
2997                const struct path *root,
2998                char *buf, int buflen)
2999 {
3000         char *res = buf + buflen;
3001         int error;
3002 
3003         prepend(&res, &buflen, "\0", 1);
3004         error = prepend_path(path, root, &res, &buflen);
3005 
3006         if (error < 0)
3007                 return ERR_PTR(error);
3008         if (error > 0)
3009                 return NULL;
3010         return res;
3011 }
3012 
3013 char *d_absolute_path(const struct path *path,
3014                char *buf, int buflen)
3015 {
3016         struct path root = {};
3017         char *res = buf + buflen;
3018         int error;
3019 
3020         prepend(&res, &buflen, "\0", 1);
3021         error = prepend_path(path, &root, &res, &buflen);
3022 
3023         if (error > 1)
3024                 error = -EINVAL;
3025         if (error < 0)
3026                 return ERR_PTR(error);
3027         return res;
3028 }
3029 
3030 /*
3031  * same as __d_path but appends "(deleted)" for unlinked files.
3032  */
3033 static int path_with_deleted(const struct path *path,
3034                              const struct path *root,
3035                              char **buf, int *buflen)
3036 {
3037         prepend(buf, buflen, "\0", 1);
3038         if (d_unlinked(path->dentry)) {
3039                 int error = prepend(buf, buflen, " (deleted)", 10);
3040                 if (error)
3041                         return error;
3042         }
3043 
3044         return prepend_path(path, root, buf, buflen);
3045 }
3046 
3047 static int prepend_unreachable(char **buffer, int *buflen)
3048 {
3049         return prepend(buffer, buflen, "(unreachable)", 13);
3050 }
3051 
3052 static void get_fs_root_rcu(struct fs_struct *fs, struct path *root)
3053 {
3054         unsigned seq;
3055 
3056         do {
3057                 seq = read_seqcount_begin(&fs->seq);
3058                 *root = fs->root;
3059         } while (read_seqcount_retry(&fs->seq, seq));
3060 }
3061 
3062 /**
3063  * d_path - return the path of a dentry
3064  * @path: path to report
3065  * @buf: buffer to return value in
3066  * @buflen: buffer length
3067  *
3068  * Convert a dentry into an ASCII path name. If the entry has been deleted
3069  * the string " (deleted)" is appended. Note that this is ambiguous.
3070  *
3071  * Returns a pointer into the buffer or an error code if the path was
3072  * too long. Note: Callers should use the returned pointer, not the passed
3073  * in buffer, to use the name! The implementation often starts at an offset
3074  * into the buffer, and may leave 0 bytes at the start.
3075  *
3076  * "buflen" should be positive.
3077  */
3078 char *d_path(const struct path *path, char *buf, int buflen)
3079 {
3080         char *res = buf + buflen;
3081         struct path root;
3082         int error;
3083 
3084         /*
3085          * We have various synthetic filesystems that never get mounted.  On
3086          * these filesystems dentries are never used for lookup purposes, and
3087          * thus don't need to be hashed.  They also don't need a name until a
3088          * user wants to identify the object in /proc/pid/fd/.  The little hack
3089          * below allows us to generate a name for these objects on demand:
3090          *
3091          * Some pseudo inodes are mountable.  When they are mounted
3092          * path->dentry == path->mnt->mnt_root.  In that case don't call d_dname
3093          * and instead have d_path return the mounted path.
3094          */
3095         if (path->dentry->d_op && path->dentry->d_op->d_dname &&
3096             (!IS_ROOT(path->dentry) || path->dentry != path->mnt->mnt_root))
3097                 return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
3098 
3099         rcu_read_lock();
3100         get_fs_root_rcu(current->fs, &root);
3101         error = path_with_deleted(path, &root, &res, &buflen);
3102         rcu_read_unlock();
3103 
3104         if (error < 0)
3105                 res = ERR_PTR(error);
3106         return res;
3107 }
3108 EXPORT_SYMBOL(d_path);
3109 
3110 /*
3111  * Helper function for dentry_operations.d_dname() members
3112  */
3113 char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,
3114                         const char *fmt, ...)
3115 {
3116         va_list args;
3117         char temp[64];
3118         int sz;
3119 
3120         va_start(args, fmt);
3121         sz = vsnprintf(temp, sizeof(temp), fmt, args) + 1;
3122         va_end(args);
3123 
3124         if (sz > sizeof(temp) || sz > buflen)
3125                 return ERR_PTR(-ENAMETOOLONG);
3126 
3127         buffer += buflen - sz;
3128         return memcpy(buffer, temp, sz);
3129 }
3130 
3131 char *simple_dname(struct dentry *dentry, char *buffer, int buflen)
3132 {
3133         char *end = buffer + buflen;
3134         /* these dentries are never renamed, so d_lock is not needed */
3135         if (prepend(&end, &buflen, " (deleted)", 11) ||
3136             prepend(&end, &buflen, dentry->d_name.name, dentry->d_name.len) ||
3137             prepend(&end, &buflen, "/", 1))  
3138                 end = ERR_PTR(-ENAMETOOLONG);
3139         return end;
3140 }
3141 EXPORT_SYMBOL(simple_dname);
3142 
3143 /*
3144  * Write full pathname from the root of the filesystem into the buffer.
3145  */
3146 static char *__dentry_path(struct dentry *d, char *buf, int buflen)
3147 {
3148         struct dentry *dentry;
3149         char *end, *retval;
3150         int len, seq = 0;
3151         int error = 0;
3152 
3153         if (buflen < 2)
3154                 goto Elong;
3155 
3156         rcu_read_lock();
3157 restart:
3158         dentry = d;
3159         end = buf + buflen;
3160         len = buflen;
3161         prepend(&end, &len, "\0", 1);
3162         /* Get '/' right */
3163         retval = end-1;
3164         *retval = '/';
3165         read_seqbegin_or_lock(&rename_lock, &seq);
3166         while (!IS_ROOT(dentry)) {
3167                 struct dentry *parent = dentry->d_parent;
3168 
3169                 prefetch(parent);
3170                 error = prepend_name(&end, &len, &dentry->d_name);
3171                 if (error)
3172                         break;
3173 
3174                 retval = end;
3175                 dentry = parent;
3176         }
3177         if (!(seq & 1))
3178                 rcu_read_unlock();
3179         if (need_seqretry(&rename_lock, seq)) {
3180                 seq = 1;
3181                 goto restart;
3182         }
3183         done_seqretry(&rename_lock, seq);
3184         if (error)
3185                 goto Elong;
3186         return retval;
3187 Elong:
3188         return ERR_PTR(-ENAMETOOLONG);
3189 }
3190 
3191 char *dentry_path_raw(struct dentry *dentry, char *buf, int buflen)
3192 {
3193         return __dentry_path(dentry, buf, buflen);
3194 }
3195 EXPORT_SYMBOL(dentry_path_raw);
3196 
3197 char *dentry_path(struct dentry *dentry, char *buf, int buflen)
3198 {
3199         char *p = NULL;
3200         char *retval;
3201 
3202         if (d_unlinked(dentry)) {
3203                 p = buf + buflen;
3204                 if (prepend(&p, &buflen, "//deleted", 10) != 0)
3205                         goto Elong;
3206                 buflen++;
3207         }
3208         retval = __dentry_path(dentry, buf, buflen);
3209         if (!IS_ERR(retval) && p)
3210                 *p = '/';       /* restore '/' overriden with '\0' */
3211         return retval;
3212 Elong:
3213         return ERR_PTR(-ENAMETOOLONG);
3214 }
3215 
3216 static void get_fs_root_and_pwd_rcu(struct fs_struct *fs, struct path *root,
3217                                     struct path *pwd)
3218 {
3219         unsigned seq;
3220 
3221         do {
3222                 seq = read_seqcount_begin(&fs->seq);
3223                 *root = fs->root;
3224                 *pwd = fs->pwd;
3225         } while (read_seqcount_retry(&fs->seq, seq));
3226 }
3227 
3228 /*
3229  * NOTE! The user-level library version returns a
3230  * character pointer. The kernel system call just
3231  * returns the length of the buffer filled (which
3232  * includes the ending '\0' character), or a negative
3233  * error value. So libc would do something like
3234  *
3235  *      char *getcwd(char * buf, size_t size)
3236  *      {
3237  *              int retval;
3238  *
3239  *              retval = sys_getcwd(buf, size);
3240  *              if (retval >= 0)
3241  *                      return buf;
3242  *              errno = -retval;
3243  *              return NULL;
3244  *      }
3245  */
3246 SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
3247 {
3248         int error;
3249         struct path pwd, root;
3250         char *page = __getname();
3251 
3252         if (!page)
3253                 return -ENOMEM;
3254 
3255         rcu_read_lock();
3256         get_fs_root_and_pwd_rcu(current->fs, &root, &pwd);
3257 
3258         error = -ENOENT;
3259         if (!d_unlinked(pwd.dentry)) {
3260                 unsigned long len;
3261                 char *cwd = page + PATH_MAX;
3262                 int buflen = PATH_MAX;
3263 
3264                 prepend(&cwd, &buflen, "\0", 1);
3265                 error = prepend_path(&pwd, &root, &cwd, &buflen);
3266                 rcu_read_unlock();
3267 
3268                 if (error < 0)
3269                         goto out;
3270 
3271                 /* Unreachable from current root */
3272                 if (error > 0) {
3273                         error = prepend_unreachable(&cwd, &buflen);
3274                         if (error)
3275                                 goto out;
3276                 }
3277 
3278                 error = -ERANGE;
3279                 len = PATH_MAX + page - cwd;
3280                 if (len <= size) {
3281                         error = len;
3282                         if (copy_to_user(buf, cwd, len))
3283                                 error = -EFAULT;
3284                 }
3285         } else {
3286                 rcu_read_unlock();
3287         }
3288 
3289 out:
3290         __putname(page);
3291         return error;
3292 }
3293 
3294 /*
3295  * Test whether new_dentry is a subdirectory of old_dentry.
3296  *
3297  * Trivially implemented using the dcache structure
3298  */
3299 
3300 /**
3301  * is_subdir - is new dentry a subdirectory of old_dentry
3302  * @new_dentry: new dentry
3303  * @old_dentry: old dentry
3304  *
3305  * Returns 1 if new_dentry is a subdirectory of the parent (at any depth).
3306  * Returns 0 otherwise.
3307  * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
3308  */
3309   
3310 int is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)
3311 {
3312         int result;
3313         unsigned seq;
3314 
3315         if (new_dentry == old_dentry)
3316                 return 1;
3317 
3318         do {
3319                 /* for restarting inner loop in case of seq retry */
3320                 seq = read_seqbegin(&rename_lock);
3321                 /*
3322                  * Need rcu_readlock to protect against the d_parent trashing
3323                  * due to d_move
3324                  */
3325                 rcu_read_lock();
3326                 if (d_ancestor(old_dentry, new_dentry))
3327                         result = 1;
3328                 else
3329                         result = 0;
3330                 rcu_read_unlock();
3331         } while (read_seqretry(&rename_lock, seq));
3332 
3333         return result;
3334 }
3335 
3336 static enum d_walk_ret d_genocide_kill(void *data, struct dentry *dentry)
3337 {
3338         struct dentry *root = data;
3339         if (dentry != root) {
3340                 if (d_unhashed(dentry) || !dentry->d_inode)
3341                         return D_WALK_SKIP;
3342 
3343                 if (!(dentry->d_flags & DCACHE_GENOCIDE)) {
3344                         dentry->d_flags |= DCACHE_GENOCIDE;
3345                         dentry->d_lockref.count--;
3346                 }
3347         }
3348         return D_WALK_CONTINUE;
3349 }
3350 
3351 void d_genocide(struct dentry *parent)
3352 {
3353         d_walk(parent, parent, d_genocide_kill, NULL);
3354 }
3355 
3356 void d_tmpfile(struct dentry *dentry, struct inode *inode)
3357 {
3358         inode_dec_link_count(inode);
3359         BUG_ON(dentry->d_name.name != dentry->d_iname ||
3360                 !hlist_unhashed(&dentry->d_u.d_alias) ||
3361                 !d_unlinked(dentry));
3362         spin_lock(&dentry->d_parent->d_lock);
3363         spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
3364         dentry->d_name.len = sprintf(dentry->d_iname, "#%llu",
3365                                 (unsigned long long)inode->i_ino);
3366         spin_unlock(&dentry->d_lock);
3367         spin_unlock(&dentry->d_parent->d_lock);
3368         d_instantiate(dentry, inode);
3369 }
3370 EXPORT_SYMBOL(d_tmpfile);
3371 
3372 static __initdata unsigned long dhash_entries;
3373 static int __init set_dhash_entries(char *str)
3374 {
3375         if (!str)
3376                 return 0;
3377         dhash_entries = simple_strtoul(str, &str, 0);
3378         return 1;
3379 }
3380 __setup("dhash_entries=", set_dhash_entries);
3381 
3382 static void __init dcache_init_early(void)
3383 {
3384         unsigned int loop;
3385 
3386         /* If hashes are distributed across NUMA nodes, defer
3387          * hash allocation until vmalloc space is available.
3388          */
3389         if (hashdist)
3390                 return;
3391 
3392         dentry_hashtable =
3393                 alloc_large_system_hash("Dentry cache",
3394                                         sizeof(struct hlist_bl_head),
3395                                         dhash_entries,
3396                                         13,
3397                                         HASH_EARLY,
3398                                         &d_hash_shift,
3399                                         &d_hash_mask,
3400                                         0,
3401                                         0);
3402 
3403         for (loop = 0; loop < (1U << d_hash_shift); loop++)
3404                 INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
3405 }
3406 
3407 static void __init dcache_init(void)
3408 {
3409         unsigned int loop;
3410 
3411         /* 
3412          * A constructor could be added for stable state like the lists,
3413          * but it is probably not worth it because of the cache nature
3414          * of the dcache. 
3415          */
3416         dentry_cache = KMEM_CACHE(dentry,
3417                 SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD);
3418 
3419         /* Hash may have been set up in dcache_init_early */
3420         if (!hashdist)
3421                 return;
3422 
3423         dentry_hashtable =
3424                 alloc_large_system_hash("Dentry cache",
3425                                         sizeof(struct hlist_bl_head),
3426                                         dhash_entries,
3427                                         13,
3428                                         0,
3429                                         &d_hash_shift,
3430                                         &d_hash_mask,
3431                                         0,
3432                                         0);
3433 
3434         for (loop = 0; loop < (1U << d_hash_shift); loop++)
3435                 INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
3436 }
3437 
3438 /* SLAB cache for __getname() consumers */
3439 struct kmem_cache *names_cachep __read_mostly;
3440 EXPORT_SYMBOL(names_cachep);
3441 
3442 EXPORT_SYMBOL(d_genocide);
3443 
3444 void __init vfs_caches_init_early(void)
3445 {
3446         dcache_init_early();
3447         inode_init_early();
3448 }
3449 
3450 void __init vfs_caches_init(unsigned long mempages)
3451 {
3452         unsigned long reserve;
3453 
3454         /* Base hash sizes on available memory, with a reserve equal to
3455            150% of current kernel size */
3456 
3457         reserve = min((mempages - nr_free_pages()) * 3/2, mempages - 1);
3458         mempages -= reserve;
3459 
3460         names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
3461                         SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
3462 
3463         dcache_init();
3464         inode_init();
3465         files_init(mempages);
3466         mnt_init();
3467         bdev_cache_init();
3468         chrdev_init();
3469 }
3470 

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