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

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