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

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