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

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