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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 <linux/uaccess.h>
 30 #include <linux/security.h>
 31 #include <linux/seqlock.h>
 32 #include <linux/swap.h>
 33 #include <linux/bootmem.h>
 34 #include <linux/fs_struct.h>
 35 #include <linux/hardirq.h>
 36 #include <linux/bit_spinlock.h>
 37 #include <linux/rculist_bl.h>
 38 #include <linux/prefetch.h>
 39 #include <linux/ratelimit.h>
 40 #include <linux/list_lru.h>
 41 #include <linux/kasan.h>
 42 
 43 #include "internal.h"
 44 #include "mount.h"
 45 
 46 /*
 47  * Usage:
 48  * dcache->d_inode->i_lock protects:
 49  *   - i_dentry, d_u.d_alias, d_inode of aliases
 50  * dcache_hash_bucket lock protects:
 51  *   - the dcache hash table
 52  * s_anon bl list spinlock protects:
 53  *   - the s_anon list (see __d_drop)
 54  * dentry->d_sb->s_dentry_lru_lock protects:
 55  *   - the dcache lru lists and counters
 56  * d_lock protects:
 57  *   - d_flags
 58  *   - d_name
 59  *   - d_lru
 60  *   - d_count
 61  *   - d_unhashed()
 62  *   - d_parent and d_subdirs
 63  *   - childrens' d_child and d_parent
 64  *   - d_u.d_alias, d_inode
 65  *
 66  * Ordering:
 67  * dentry->d_inode->i_lock
 68  *   dentry->d_lock
 69  *     dentry->d_sb->s_dentry_lru_lock
 70  *     dcache_hash_bucket lock
 71  *     s_anon lock
 72  *
 73  * If there is an ancestor relationship:
 74  * dentry->d_parent->...->d_parent->d_lock
 75  *   ...
 76  *     dentry->d_parent->d_lock
 77  *       dentry->d_lock
 78  *
 79  * If no ancestor relationship:
 80  * if (dentry1 < dentry2)
 81  *   dentry1->d_lock
 82  *     dentry2->d_lock
 83  */
 84 int sysctl_vfs_cache_pressure __read_mostly = 100;
 85 EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
 86 
 87 __cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
 88 
 89 EXPORT_SYMBOL(rename_lock);
 90 
 91 static struct kmem_cache *dentry_cache __read_mostly;
 92 
 93 /*
 94  * This is the single most critical data structure when it comes
 95  * to the dcache: the hashtable for lookups. Somebody should try
 96  * to make this good - I've just made it work.
 97  *
 98  * This hash-function tries to avoid losing too many bits of hash
 99  * information, yet avoid using a prime hash-size or similar.
100  */
101 
102 static unsigned int d_hash_mask __read_mostly;
103 static unsigned int d_hash_shift __read_mostly;
104 
105 static struct hlist_bl_head *dentry_hashtable __read_mostly;
106 
107 static inline struct hlist_bl_head *d_hash(unsigned int hash)
108 {
109         return dentry_hashtable + (hash >> (32 - d_hash_shift));
110 }
111 
112 #define IN_LOOKUP_SHIFT 10
113 static struct hlist_bl_head in_lookup_hashtable[1 << IN_LOOKUP_SHIFT];
114 
115 static inline struct hlist_bl_head *in_lookup_hash(const struct dentry *parent,
116                                         unsigned int hash)
117 {
118         hash += (unsigned long) parent / L1_CACHE_BYTES;
119         return in_lookup_hashtable + hash_32(hash, IN_LOOKUP_SHIFT);
120 }
121 
122 
123 /* Statistics gathering. */
124 struct dentry_stat_t dentry_stat = {
125         .age_limit = 45,
126 };
127 
128 static DEFINE_PER_CPU(long, nr_dentry);
129 static DEFINE_PER_CPU(long, nr_dentry_unused);
130 
131 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
132 
133 /*
134  * Here we resort to our own counters instead of using generic per-cpu counters
135  * for consistency with what the vfs inode code does. We are expected to harvest
136  * better code and performance by having our own specialized counters.
137  *
138  * Please note that the loop is done over all possible CPUs, not over all online
139  * CPUs. The reason for this is that we don't want to play games with CPUs going
140  * on and off. If one of them goes off, we will just keep their counters.
141  *
142  * glommer: See cffbc8a for details, and if you ever intend to change this,
143  * please update all vfs counters to match.
144  */
145 static long get_nr_dentry(void)
146 {
147         int i;
148         long sum = 0;
149         for_each_possible_cpu(i)
150                 sum += per_cpu(nr_dentry, i);
151         return sum < 0 ? 0 : sum;
152 }
153 
154 static long get_nr_dentry_unused(void)
155 {
156         int i;
157         long sum = 0;
158         for_each_possible_cpu(i)
159                 sum += per_cpu(nr_dentry_unused, i);
160         return sum < 0 ? 0 : sum;
161 }
162 
163 int proc_nr_dentry(struct ctl_table *table, int write, void __user *buffer,
164                    size_t *lenp, loff_t *ppos)
165 {
166         dentry_stat.nr_dentry = get_nr_dentry();
167         dentry_stat.nr_unused = get_nr_dentry_unused();
168         return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
169 }
170 #endif
171 
172 /*
173  * Compare 2 name strings, return 0 if they match, otherwise non-zero.
174  * The strings are both count bytes long, and count is non-zero.
175  */
176 #ifdef CONFIG_DCACHE_WORD_ACCESS
177 
178 #include <asm/word-at-a-time.h>
179 /*
180  * NOTE! 'cs' and 'scount' come from a dentry, so it has a
181  * aligned allocation for this particular component. We don't
182  * strictly need the load_unaligned_zeropad() safety, but it
183  * doesn't hurt either.
184  *
185  * In contrast, 'ct' and 'tcount' can be from a pathname, and do
186  * need the careful unaligned handling.
187  */
188 static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
189 {
190         unsigned long a,b,mask;
191 
192         for (;;) {
193                 a = *(unsigned long *)cs;
194                 b = load_unaligned_zeropad(ct);
195                 if (tcount < sizeof(unsigned long))
196                         break;
197                 if (unlikely(a != b))
198                         return 1;
199                 cs += sizeof(unsigned long);
200                 ct += sizeof(unsigned long);
201                 tcount -= sizeof(unsigned long);
202                 if (!tcount)
203                         return 0;
204         }
205         mask = bytemask_from_count(tcount);
206         return unlikely(!!((a ^ b) & mask));
207 }
208 
209 #else
210 
211 static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
212 {
213         do {
214                 if (*cs != *ct)
215                         return 1;
216                 cs++;
217                 ct++;
218                 tcount--;
219         } while (tcount);
220         return 0;
221 }
222 
223 #endif
224 
225 static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
226 {
227         /*
228          * Be careful about RCU walk racing with rename:
229          * use 'lockless_dereference' to fetch the name pointer.
230          *
231          * NOTE! Even if a rename will mean that the length
232          * was not loaded atomically, we don't care. The
233          * RCU walk will check the sequence count eventually,
234          * and catch it. And we won't overrun the buffer,
235          * because we're reading the name pointer atomically,
236          * and a dentry name is guaranteed to be properly
237          * terminated with a NUL byte.
238          *
239          * End result: even if 'len' is wrong, we'll exit
240          * early because the data cannot match (there can
241          * be no NUL in the ct/tcount data)
242          */
243         const unsigned char *cs = lockless_dereference(dentry->d_name.name);
244 
245         return dentry_string_cmp(cs, ct, tcount);
246 }
247 
248 struct external_name {
249         union {
250                 atomic_t count;
251                 struct rcu_head head;
252         } u;
253         unsigned char name[];
254 };
255 
256 static inline struct external_name *external_name(struct dentry *dentry)
257 {
258         return container_of(dentry->d_name.name, struct external_name, name[0]);
259 }
260 
261 static void __d_free(struct rcu_head *head)
262 {
263         struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
264 
265         kmem_cache_free(dentry_cache, dentry); 
266 }
267 
268 static void __d_free_external(struct rcu_head *head)
269 {
270         struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
271         kfree(external_name(dentry));
272         kmem_cache_free(dentry_cache, dentry); 
273 }
274 
275 static inline int dname_external(const struct dentry *dentry)
276 {
277         return dentry->d_name.name != dentry->d_iname;
278 }
279 
280 static inline void __d_set_inode_and_type(struct dentry *dentry,
281                                           struct inode *inode,
282                                           unsigned type_flags)
283 {
284         unsigned flags;
285 
286         dentry->d_inode = inode;
287         flags = READ_ONCE(dentry->d_flags);
288         flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
289         flags |= type_flags;
290         WRITE_ONCE(dentry->d_flags, flags);
291 }
292 
293 static inline void __d_clear_type_and_inode(struct dentry *dentry)
294 {
295         unsigned flags = READ_ONCE(dentry->d_flags);
296 
297         flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
298         WRITE_ONCE(dentry->d_flags, flags);
299         dentry->d_inode = NULL;
300 }
301 
302 static void dentry_free(struct dentry *dentry)
303 {
304         WARN_ON(!hlist_unhashed(&dentry->d_u.d_alias));
305         if (unlikely(dname_external(dentry))) {
306                 struct external_name *p = external_name(dentry);
307                 if (likely(atomic_dec_and_test(&p->u.count))) {
308                         call_rcu(&dentry->d_u.d_rcu, __d_free_external);
309                         return;
310                 }
311         }
312         /* if dentry was never visible to RCU, immediate free is OK */
313         if (!(dentry->d_flags & DCACHE_RCUACCESS))
314                 __d_free(&dentry->d_u.d_rcu);
315         else
316                 call_rcu(&dentry->d_u.d_rcu, __d_free);
317 }
318 
319 /*
320  * Release the dentry's inode, using the filesystem
321  * d_iput() operation if defined.
322  */
323 static void dentry_unlink_inode(struct dentry * dentry)
324         __releases(dentry->d_lock)
325         __releases(dentry->d_inode->i_lock)
326 {
327         struct inode *inode = dentry->d_inode;
328         bool hashed = !d_unhashed(dentry);
329 
330         if (hashed)
331                 raw_write_seqcount_begin(&dentry->d_seq);
332         __d_clear_type_and_inode(dentry);
333         hlist_del_init(&dentry->d_u.d_alias);
334         if (hashed)
335                 raw_write_seqcount_end(&dentry->d_seq);
336         spin_unlock(&dentry->d_lock);
337         spin_unlock(&inode->i_lock);
338         if (!inode->i_nlink)
339                 fsnotify_inoderemove(inode);
340         if (dentry->d_op && dentry->d_op->d_iput)
341                 dentry->d_op->d_iput(dentry, inode);
342         else
343                 iput(inode);
344 }
345 
346 /*
347  * The DCACHE_LRU_LIST bit is set whenever the 'd_lru' entry
348  * is in use - which includes both the "real" per-superblock
349  * LRU list _and_ the DCACHE_SHRINK_LIST use.
350  *
351  * The DCACHE_SHRINK_LIST bit is set whenever the dentry is
352  * on the shrink list (ie not on the superblock LRU list).
353  *
354  * The per-cpu "nr_dentry_unused" counters are updated with
355  * the DCACHE_LRU_LIST bit.
356  *
357  * These helper functions make sure we always follow the
358  * rules. d_lock must be held by the caller.
359  */
360 #define D_FLAG_VERIFY(dentry,x) WARN_ON_ONCE(((dentry)->d_flags & (DCACHE_LRU_LIST | DCACHE_SHRINK_LIST)) != (x))
361 static void d_lru_add(struct dentry *dentry)
362 {
363         D_FLAG_VERIFY(dentry, 0);
364         dentry->d_flags |= DCACHE_LRU_LIST;
365         this_cpu_inc(nr_dentry_unused);
366         WARN_ON_ONCE(!list_lru_add(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
367 }
368 
369 static void d_lru_del(struct dentry *dentry)
370 {
371         D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
372         dentry->d_flags &= ~DCACHE_LRU_LIST;
373         this_cpu_dec(nr_dentry_unused);
374         WARN_ON_ONCE(!list_lru_del(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
375 }
376 
377 static void d_shrink_del(struct dentry *dentry)
378 {
379         D_FLAG_VERIFY(dentry, DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
380         list_del_init(&dentry->d_lru);
381         dentry->d_flags &= ~(DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
382         this_cpu_dec(nr_dentry_unused);
383 }
384 
385 static void d_shrink_add(struct dentry *dentry, struct list_head *list)
386 {
387         D_FLAG_VERIFY(dentry, 0);
388         list_add(&dentry->d_lru, list);
389         dentry->d_flags |= DCACHE_SHRINK_LIST | DCACHE_LRU_LIST;
390         this_cpu_inc(nr_dentry_unused);
391 }
392 
393 /*
394  * These can only be called under the global LRU lock, ie during the
395  * callback for freeing the LRU list. "isolate" removes it from the
396  * LRU lists entirely, while shrink_move moves it to the indicated
397  * private list.
398  */
399 static void d_lru_isolate(struct list_lru_one *lru, struct dentry *dentry)
400 {
401         D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
402         dentry->d_flags &= ~DCACHE_LRU_LIST;
403         this_cpu_dec(nr_dentry_unused);
404         list_lru_isolate(lru, &dentry->d_lru);
405 }
406 
407 static void d_lru_shrink_move(struct list_lru_one *lru, struct dentry *dentry,
408                               struct list_head *list)
409 {
410         D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
411         dentry->d_flags |= DCACHE_SHRINK_LIST;
412         list_lru_isolate_move(lru, &dentry->d_lru, list);
413 }
414 
415 /*
416  * dentry_lru_(add|del)_list) must be called with d_lock held.
417  */
418 static void dentry_lru_add(struct dentry *dentry)
419 {
420         if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST)))
421                 d_lru_add(dentry);
422 }
423 
424 /**
425  * d_drop - drop a dentry
426  * @dentry: dentry to drop
427  *
428  * d_drop() unhashes the entry from the parent dentry hashes, so that it won't
429  * be found through a VFS lookup any more. Note that this is different from
430  * deleting the dentry - d_delete will try to mark the dentry negative if
431  * possible, giving a successful _negative_ lookup, while d_drop will
432  * just make the cache lookup fail.
433  *
434  * d_drop() is used mainly for stuff that wants to invalidate a dentry for some
435  * reason (NFS timeouts or autofs deletes).
436  *
437  * __d_drop requires dentry->d_lock.
438  */
439 void __d_drop(struct dentry *dentry)
440 {
441         if (!d_unhashed(dentry)) {
442                 struct hlist_bl_head *b;
443                 /*
444                  * Hashed dentries are normally on the dentry hashtable,
445                  * with the exception of those newly allocated by
446                  * d_obtain_alias, which are always IS_ROOT:
447                  */
448                 if (unlikely(IS_ROOT(dentry)))
449                         b = &dentry->d_sb->s_anon;
450                 else
451                         b = d_hash(dentry->d_name.hash);
452 
453                 hlist_bl_lock(b);
454                 __hlist_bl_del(&dentry->d_hash);
455                 dentry->d_hash.pprev = NULL;
456                 hlist_bl_unlock(b);
457                 /* After this call, in-progress rcu-walk path lookup will fail. */
458                 write_seqcount_invalidate(&dentry->d_seq);
459         }
460 }
461 EXPORT_SYMBOL(__d_drop);
462 
463 void d_drop(struct dentry *dentry)
464 {
465         spin_lock(&dentry->d_lock);
466         __d_drop(dentry);
467         spin_unlock(&dentry->d_lock);
468 }
469 EXPORT_SYMBOL(d_drop);
470 
471 static inline void dentry_unlist(struct dentry *dentry, struct dentry *parent)
472 {
473         struct dentry *next;
474         /*
475          * Inform d_walk() and shrink_dentry_list() that we are no longer
476          * attached to the dentry tree
477          */
478         dentry->d_flags |= DCACHE_DENTRY_KILLED;
479         if (unlikely(list_empty(&dentry->d_child)))
480                 return;
481         __list_del_entry(&dentry->d_child);
482         /*
483          * Cursors can move around the list of children.  While we'd been
484          * a normal list member, it didn't matter - ->d_child.next would've
485          * been updated.  However, from now on it won't be and for the
486          * things like d_walk() it might end up with a nasty surprise.
487          * Normally d_walk() doesn't care about cursors moving around -
488          * ->d_lock on parent prevents that and since a cursor has no children
489          * of its own, we get through it without ever unlocking the parent.
490          * There is one exception, though - if we ascend from a child that
491          * gets killed as soon as we unlock it, the next sibling is found
492          * using the value left in its ->d_child.next.  And if _that_
493          * pointed to a cursor, and cursor got moved (e.g. by lseek())
494          * before d_walk() regains parent->d_lock, we'll end up skipping
495          * everything the cursor had been moved past.
496          *
497          * Solution: make sure that the pointer left behind in ->d_child.next
498          * points to something that won't be moving around.  I.e. skip the
499          * cursors.
500          */
501         while (dentry->d_child.next != &parent->d_subdirs) {
502                 next = list_entry(dentry->d_child.next, struct dentry, d_child);
503                 if (likely(!(next->d_flags & DCACHE_DENTRY_CURSOR)))
504                         break;
505                 dentry->d_child.next = next->d_child.next;
506         }
507 }
508 
509 static void __dentry_kill(struct dentry *dentry)
510 {
511         struct dentry *parent = NULL;
512         bool can_free = true;
513         if (!IS_ROOT(dentry))
514                 parent = dentry->d_parent;
515 
516         /*
517          * The dentry is now unrecoverably dead to the world.
518          */
519         lockref_mark_dead(&dentry->d_lockref);
520 
521         /*
522          * inform the fs via d_prune that this dentry is about to be
523          * unhashed and destroyed.
524          */
525         if (dentry->d_flags & DCACHE_OP_PRUNE)
526                 dentry->d_op->d_prune(dentry);
527 
528         if (dentry->d_flags & DCACHE_LRU_LIST) {
529                 if (!(dentry->d_flags & DCACHE_SHRINK_LIST))
530                         d_lru_del(dentry);
531         }
532         /* if it was on the hash then remove it */
533         __d_drop(dentry);
534         dentry_unlist(dentry, parent);
535         if (parent)
536                 spin_unlock(&parent->d_lock);
537         if (dentry->d_inode)
538                 dentry_unlink_inode(dentry);
539         else
540                 spin_unlock(&dentry->d_lock);
541         this_cpu_dec(nr_dentry);
542         if (dentry->d_op && dentry->d_op->d_release)
543                 dentry->d_op->d_release(dentry);
544 
545         spin_lock(&dentry->d_lock);
546         if (dentry->d_flags & DCACHE_SHRINK_LIST) {
547                 dentry->d_flags |= DCACHE_MAY_FREE;
548                 can_free = false;
549         }
550         spin_unlock(&dentry->d_lock);
551         if (likely(can_free))
552                 dentry_free(dentry);
553 }
554 
555 /*
556  * Finish off a dentry we've decided to kill.
557  * dentry->d_lock must be held, returns with it unlocked.
558  * If ref is non-zero, then decrement the refcount too.
559  * Returns dentry requiring refcount drop, or NULL if we're done.
560  */
561 static struct dentry *dentry_kill(struct dentry *dentry)
562         __releases(dentry->d_lock)
563 {
564         struct inode *inode = dentry->d_inode;
565         struct dentry *parent = NULL;
566 
567         if (inode && unlikely(!spin_trylock(&inode->i_lock)))
568                 goto failed;
569 
570         if (!IS_ROOT(dentry)) {
571                 parent = dentry->d_parent;
572                 if (unlikely(!spin_trylock(&parent->d_lock))) {
573                         if (inode)
574                                 spin_unlock(&inode->i_lock);
575                         goto failed;
576                 }
577         }
578 
579         __dentry_kill(dentry);
580         return parent;
581 
582 failed:
583         spin_unlock(&dentry->d_lock);
584         return dentry; /* try again with same dentry */
585 }
586 
587 static inline struct dentry *lock_parent(struct dentry *dentry)
588 {
589         struct dentry *parent = dentry->d_parent;
590         if (IS_ROOT(dentry))
591                 return NULL;
592         if (unlikely(dentry->d_lockref.count < 0))
593                 return NULL;
594         if (likely(spin_trylock(&parent->d_lock)))
595                 return parent;
596         rcu_read_lock();
597         spin_unlock(&dentry->d_lock);
598 again:
599         parent = ACCESS_ONCE(dentry->d_parent);
600         spin_lock(&parent->d_lock);
601         /*
602          * We can't blindly lock dentry until we are sure
603          * that we won't violate the locking order.
604          * Any changes of dentry->d_parent must have
605          * been done with parent->d_lock held, so
606          * spin_lock() above is enough of a barrier
607          * for checking if it's still our child.
608          */
609         if (unlikely(parent != dentry->d_parent)) {
610                 spin_unlock(&parent->d_lock);
611                 goto again;
612         }
613         rcu_read_unlock();
614         if (parent != dentry)
615                 spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
616         else
617                 parent = NULL;
618         return parent;
619 }
620 
621 /*
622  * Try to do a lockless dput(), and return whether that was successful.
623  *
624  * If unsuccessful, we return false, having already taken the dentry lock.
625  *
626  * The caller needs to hold the RCU read lock, so that the dentry is
627  * guaranteed to stay around even if the refcount goes down to zero!
628  */
629 static inline bool fast_dput(struct dentry *dentry)
630 {
631         int ret;
632         unsigned int d_flags;
633 
634         /*
635          * If we have a d_op->d_delete() operation, we sould not
636          * let the dentry count go to zero, so use "put_or_lock".
637          */
638         if (unlikely(dentry->d_flags & DCACHE_OP_DELETE))
639                 return lockref_put_or_lock(&dentry->d_lockref);
640 
641         /*
642          * .. otherwise, we can try to just decrement the
643          * lockref optimistically.
644          */
645         ret = lockref_put_return(&dentry->d_lockref);
646 
647         /*
648          * If the lockref_put_return() failed due to the lock being held
649          * by somebody else, the fast path has failed. We will need to
650          * get the lock, and then check the count again.
651          */
652         if (unlikely(ret < 0)) {
653                 spin_lock(&dentry->d_lock);
654                 if (dentry->d_lockref.count > 1) {
655                         dentry->d_lockref.count--;
656                         spin_unlock(&dentry->d_lock);
657                         return 1;
658                 }
659                 return 0;
660         }
661 
662         /*
663          * If we weren't the last ref, we're done.
664          */
665         if (ret)
666                 return 1;
667 
668         /*
669          * Careful, careful. The reference count went down
670          * to zero, but we don't hold the dentry lock, so
671          * somebody else could get it again, and do another
672          * dput(), and we need to not race with that.
673          *
674          * However, there is a very special and common case
675          * where we don't care, because there is nothing to
676          * do: the dentry is still hashed, it does not have
677          * a 'delete' op, and it's referenced and already on
678          * the LRU list.
679          *
680          * NOTE! Since we aren't locked, these values are
681          * not "stable". However, it is sufficient that at
682          * some point after we dropped the reference the
683          * dentry was hashed and the flags had the proper
684          * value. Other dentry users may have re-gotten
685          * a reference to the dentry and change that, but
686          * our work is done - we can leave the dentry
687          * around with a zero refcount.
688          */
689         smp_rmb();
690         d_flags = ACCESS_ONCE(dentry->d_flags);
691         d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED;
692 
693         /* Nothing to do? Dropping the reference was all we needed? */
694         if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry))
695                 return 1;
696 
697         /*
698          * Not the fast normal case? Get the lock. We've already decremented
699          * the refcount, but we'll need to re-check the situation after
700          * getting the lock.
701          */
702         spin_lock(&dentry->d_lock);
703 
704         /*
705          * Did somebody else grab a reference to it in the meantime, and
706          * we're no longer the last user after all? Alternatively, somebody
707          * else could have killed it and marked it dead. Either way, we
708          * don't need to do anything else.
709          */
710         if (dentry->d_lockref.count) {
711                 spin_unlock(&dentry->d_lock);
712                 return 1;
713         }
714 
715         /*
716          * Re-get the reference we optimistically dropped. We hold the
717          * lock, and we just tested that it was zero, so we can just
718          * set it to 1.
719          */
720         dentry->d_lockref.count = 1;
721         return 0;
722 }
723 
724 
725 /* 
726  * This is dput
727  *
728  * This is complicated by the fact that we do not want to put
729  * dentries that are no longer on any hash chain on the unused
730  * list: we'd much rather just get rid of them immediately.
731  *
732  * However, that implies that we have to traverse the dentry
733  * tree upwards to the parents which might _also_ now be
734  * scheduled for deletion (it may have been only waiting for
735  * its last child to go away).
736  *
737  * This tail recursion is done by hand as we don't want to depend
738  * on the compiler to always get this right (gcc generally doesn't).
739  * Real recursion would eat up our stack space.
740  */
741 
742 /*
743  * dput - release a dentry
744  * @dentry: dentry to release 
745  *
746  * Release a dentry. This will drop the usage count and if appropriate
747  * call the dentry unlink method as well as removing it from the queues and
748  * releasing its resources. If the parent dentries were scheduled for release
749  * they too may now get deleted.
750  */
751 void dput(struct dentry *dentry)
752 {
753         if (unlikely(!dentry))
754                 return;
755 
756 repeat:
757         might_sleep();
758 
759         rcu_read_lock();
760         if (likely(fast_dput(dentry))) {
761                 rcu_read_unlock();
762                 return;
763         }
764 
765         /* Slow case: now with the dentry lock held */
766         rcu_read_unlock();
767 
768         WARN_ON(d_in_lookup(dentry));
769 
770         /* Unreachable? Get rid of it */
771         if (unlikely(d_unhashed(dentry)))
772                 goto kill_it;
773 
774         if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED))
775                 goto kill_it;
776 
777         if (unlikely(dentry->d_flags & DCACHE_OP_DELETE)) {
778                 if (dentry->d_op->d_delete(dentry))
779                         goto kill_it;
780         }
781 
782         if (!(dentry->d_flags & DCACHE_REFERENCED))
783                 dentry->d_flags |= DCACHE_REFERENCED;
784         dentry_lru_add(dentry);
785 
786         dentry->d_lockref.count--;
787         spin_unlock(&dentry->d_lock);
788         return;
789 
790 kill_it:
791         dentry = dentry_kill(dentry);
792         if (dentry) {
793                 cond_resched();
794                 goto repeat;
795         }
796 }
797 EXPORT_SYMBOL(dput);
798 
799 
800 /* This must be called with d_lock held */
801 static inline void __dget_dlock(struct dentry *dentry)
802 {
803         dentry->d_lockref.count++;
804 }
805 
806 static inline void __dget(struct dentry *dentry)
807 {
808         lockref_get(&dentry->d_lockref);
809 }
810 
811 struct dentry *dget_parent(struct dentry *dentry)
812 {
813         int gotref;
814         struct dentry *ret;
815 
816         /*
817          * Do optimistic parent lookup without any
818          * locking.
819          */
820         rcu_read_lock();
821         ret = ACCESS_ONCE(dentry->d_parent);
822         gotref = lockref_get_not_zero(&ret->d_lockref);
823         rcu_read_unlock();
824         if (likely(gotref)) {
825                 if (likely(ret == ACCESS_ONCE(dentry->d_parent)))
826                         return ret;
827                 dput(ret);
828         }
829 
830 repeat:
831         /*
832          * Don't need rcu_dereference because we re-check it was correct under
833          * the lock.
834          */
835         rcu_read_lock();
836         ret = dentry->d_parent;
837         spin_lock(&ret->d_lock);
838         if (unlikely(ret != dentry->d_parent)) {
839                 spin_unlock(&ret->d_lock);
840                 rcu_read_unlock();
841                 goto repeat;
842         }
843         rcu_read_unlock();
844         BUG_ON(!ret->d_lockref.count);
845         ret->d_lockref.count++;
846         spin_unlock(&ret->d_lock);
847         return ret;
848 }
849 EXPORT_SYMBOL(dget_parent);
850 
851 /**
852  * d_find_alias - grab a hashed alias of inode
853  * @inode: inode in question
854  *
855  * If inode has a hashed alias, or is a directory and has any alias,
856  * acquire the reference to alias and return it. Otherwise return NULL.
857  * Notice that if inode is a directory there can be only one alias and
858  * it can be unhashed only if it has no children, or if it is the root
859  * of a filesystem, or if the directory was renamed and d_revalidate
860  * was the first vfs operation to notice.
861  *
862  * If the inode has an IS_ROOT, DCACHE_DISCONNECTED alias, then prefer
863  * any other hashed alias over that one.
864  */
865 static struct dentry *__d_find_alias(struct inode *inode)
866 {
867         struct dentry *alias, *discon_alias;
868 
869 again:
870         discon_alias = NULL;
871         hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
872                 spin_lock(&alias->d_lock);
873                 if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
874                         if (IS_ROOT(alias) &&
875                             (alias->d_flags & DCACHE_DISCONNECTED)) {
876                                 discon_alias = alias;
877                         } else {
878                                 __dget_dlock(alias);
879                                 spin_unlock(&alias->d_lock);
880                                 return alias;
881                         }
882                 }
883                 spin_unlock(&alias->d_lock);
884         }
885         if (discon_alias) {
886                 alias = discon_alias;
887                 spin_lock(&alias->d_lock);
888                 if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
889                         __dget_dlock(alias);
890                         spin_unlock(&alias->d_lock);
891                         return alias;
892                 }
893                 spin_unlock(&alias->d_lock);
894                 goto again;
895         }
896         return NULL;
897 }
898 
899 struct dentry *d_find_alias(struct inode *inode)
900 {
901         struct dentry *de = NULL;
902 
903         if (!hlist_empty(&inode->i_dentry)) {
904                 spin_lock(&inode->i_lock);
905                 de = __d_find_alias(inode);
906                 spin_unlock(&inode->i_lock);
907         }
908         return de;
909 }
910 EXPORT_SYMBOL(d_find_alias);
911 
912 /*
913  *      Try to kill dentries associated with this inode.
914  * WARNING: you must own a reference to inode.
915  */
916 void d_prune_aliases(struct inode *inode)
917 {
918         struct dentry *dentry;
919 restart:
920         spin_lock(&inode->i_lock);
921         hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias) {
922                 spin_lock(&dentry->d_lock);
923                 if (!dentry->d_lockref.count) {
924                         struct dentry *parent = lock_parent(dentry);
925                         if (likely(!dentry->d_lockref.count)) {
926                                 __dentry_kill(dentry);
927                                 dput(parent);
928                                 goto restart;
929                         }
930                         if (parent)
931                                 spin_unlock(&parent->d_lock);
932                 }
933                 spin_unlock(&dentry->d_lock);
934         }
935         spin_unlock(&inode->i_lock);
936 }
937 EXPORT_SYMBOL(d_prune_aliases);
938 
939 static void shrink_dentry_list(struct list_head *list)
940 {
941         struct dentry *dentry, *parent;
942 
943         while (!list_empty(list)) {
944                 struct inode *inode;
945                 dentry = list_entry(list->prev, struct dentry, d_lru);
946                 spin_lock(&dentry->d_lock);
947                 parent = lock_parent(dentry);
948 
949                 /*
950                  * The dispose list is isolated and dentries are not accounted
951                  * to the LRU here, so we can simply remove it from the list
952                  * here regardless of whether it is referenced or not.
953                  */
954                 d_shrink_del(dentry);
955 
956                 /*
957                  * We found an inuse dentry which was not removed from
958                  * the LRU because of laziness during lookup. Do not free it.
959                  */
960                 if (dentry->d_lockref.count > 0) {
961                         spin_unlock(&dentry->d_lock);
962                         if (parent)
963                                 spin_unlock(&parent->d_lock);
964                         continue;
965                 }
966 
967 
968                 if (unlikely(dentry->d_flags & DCACHE_DENTRY_KILLED)) {
969                         bool can_free = dentry->d_flags & DCACHE_MAY_FREE;
970                         spin_unlock(&dentry->d_lock);
971                         if (parent)
972                                 spin_unlock(&parent->d_lock);
973                         if (can_free)
974                                 dentry_free(dentry);
975                         continue;
976                 }
977 
978                 inode = dentry->d_inode;
979                 if (inode && unlikely(!spin_trylock(&inode->i_lock))) {
980                         d_shrink_add(dentry, list);
981                         spin_unlock(&dentry->d_lock);
982                         if (parent)
983                                 spin_unlock(&parent->d_lock);
984                         continue;
985                 }
986 
987                 __dentry_kill(dentry);
988 
989                 /*
990                  * We need to prune ancestors too. This is necessary to prevent
991                  * quadratic behavior of shrink_dcache_parent(), but is also
992                  * expected to be beneficial in reducing dentry cache
993                  * fragmentation.
994                  */
995                 dentry = parent;
996                 while (dentry && !lockref_put_or_lock(&dentry->d_lockref)) {
997                         parent = lock_parent(dentry);
998                         if (dentry->d_lockref.count != 1) {
999                                 dentry->d_lockref.count--;
1000                                 spin_unlock(&dentry->d_lock);
1001                                 if (parent)
1002                                         spin_unlock(&parent->d_lock);
1003                                 break;
1004                         }
1005                         inode = dentry->d_inode;        /* can't be NULL */
1006                         if (unlikely(!spin_trylock(&inode->i_lock))) {
1007                                 spin_unlock(&dentry->d_lock);
1008                                 if (parent)
1009                                         spin_unlock(&parent->d_lock);
1010                                 cpu_relax();
1011                                 continue;
1012                         }
1013                         __dentry_kill(dentry);
1014                         dentry = parent;
1015                 }
1016         }
1017 }
1018 
1019 static enum lru_status dentry_lru_isolate(struct list_head *item,
1020                 struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
1021 {
1022         struct list_head *freeable = arg;
1023         struct dentry   *dentry = container_of(item, struct dentry, d_lru);
1024 
1025 
1026         /*
1027          * we are inverting the lru lock/dentry->d_lock here,
1028          * so use a trylock. If we fail to get the lock, just skip
1029          * it
1030          */
1031         if (!spin_trylock(&dentry->d_lock))
1032                 return LRU_SKIP;
1033 
1034         /*
1035          * Referenced dentries are still in use. If they have active
1036          * counts, just remove them from the LRU. Otherwise give them
1037          * another pass through the LRU.
1038          */
1039         if (dentry->d_lockref.count) {
1040                 d_lru_isolate(lru, dentry);
1041                 spin_unlock(&dentry->d_lock);
1042                 return LRU_REMOVED;
1043         }
1044 
1045         if (dentry->d_flags & DCACHE_REFERENCED) {
1046                 dentry->d_flags &= ~DCACHE_REFERENCED;
1047                 spin_unlock(&dentry->d_lock);
1048 
1049                 /*
1050                  * The list move itself will be made by the common LRU code. At
1051                  * this point, we've dropped the dentry->d_lock but keep the
1052                  * lru lock. This is safe to do, since every list movement is
1053                  * protected by the lru lock even if both locks are held.
1054                  *
1055                  * This is guaranteed by the fact that all LRU management
1056                  * functions are intermediated by the LRU API calls like
1057                  * list_lru_add and list_lru_del. List movement in this file
1058                  * only ever occur through this functions or through callbacks
1059                  * like this one, that are called from the LRU API.
1060                  *
1061                  * The only exceptions to this are functions like
1062                  * shrink_dentry_list, and code that first checks for the
1063                  * DCACHE_SHRINK_LIST flag.  Those are guaranteed to be
1064                  * operating only with stack provided lists after they are
1065                  * properly isolated from the main list.  It is thus, always a
1066                  * local access.
1067                  */
1068                 return LRU_ROTATE;
1069         }
1070 
1071         d_lru_shrink_move(lru, dentry, freeable);
1072         spin_unlock(&dentry->d_lock);
1073 
1074         return LRU_REMOVED;
1075 }
1076 
1077 /**
1078  * prune_dcache_sb - shrink the dcache
1079  * @sb: superblock
1080  * @sc: shrink control, passed to list_lru_shrink_walk()
1081  *
1082  * Attempt to shrink the superblock dcache LRU by @sc->nr_to_scan entries. This
1083  * is done when we need more memory and called from the superblock shrinker
1084  * function.
1085  *
1086  * This function may fail to free any resources if all the dentries are in
1087  * use.
1088  */
1089 long prune_dcache_sb(struct super_block *sb, struct shrink_control *sc)
1090 {
1091         LIST_HEAD(dispose);
1092         long freed;
1093 
1094         freed = list_lru_shrink_walk(&sb->s_dentry_lru, sc,
1095                                      dentry_lru_isolate, &dispose);
1096         shrink_dentry_list(&dispose);
1097         return freed;
1098 }
1099 
1100 static enum lru_status dentry_lru_isolate_shrink(struct list_head *item,
1101                 struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
1102 {
1103         struct list_head *freeable = arg;
1104         struct dentry   *dentry = container_of(item, struct dentry, d_lru);
1105 
1106         /*
1107          * we are inverting the lru lock/dentry->d_lock here,
1108          * so use a trylock. If we fail to get the lock, just skip
1109          * it
1110          */
1111         if (!spin_trylock(&dentry->d_lock))
1112                 return LRU_SKIP;
1113 
1114         d_lru_shrink_move(lru, dentry, freeable);
1115         spin_unlock(&dentry->d_lock);
1116 
1117         return LRU_REMOVED;
1118 }
1119 
1120 
1121 /**
1122  * shrink_dcache_sb - shrink dcache for a superblock
1123  * @sb: superblock
1124  *
1125  * Shrink the dcache for the specified super block. This is used to free
1126  * the dcache before unmounting a file system.
1127  */
1128 void shrink_dcache_sb(struct super_block *sb)
1129 {
1130         long freed;
1131 
1132         do {
1133                 LIST_HEAD(dispose);
1134 
1135                 freed = list_lru_walk(&sb->s_dentry_lru,
1136                         dentry_lru_isolate_shrink, &dispose, UINT_MAX);
1137 
1138                 this_cpu_sub(nr_dentry_unused, freed);
1139                 shrink_dentry_list(&dispose);
1140         } while (freed > 0);
1141 }
1142 EXPORT_SYMBOL(shrink_dcache_sb);
1143 
1144 /**
1145  * enum d_walk_ret - action to talke during tree walk
1146  * @D_WALK_CONTINUE:    contrinue walk
1147  * @D_WALK_QUIT:        quit walk
1148  * @D_WALK_NORETRY:     quit when retry is needed
1149  * @D_WALK_SKIP:        skip this dentry and its children
1150  */
1151 enum d_walk_ret {
1152         D_WALK_CONTINUE,
1153         D_WALK_QUIT,
1154         D_WALK_NORETRY,
1155         D_WALK_SKIP,
1156 };
1157 
1158 /**
1159  * d_walk - walk the dentry tree
1160  * @parent:     start of walk
1161  * @data:       data passed to @enter() and @finish()
1162  * @enter:      callback when first entering the dentry
1163  * @finish:     callback when successfully finished the walk
1164  *
1165  * The @enter() and @finish() callbacks are called with d_lock held.
1166  */
1167 static void d_walk(struct dentry *parent, void *data,
1168                    enum d_walk_ret (*enter)(void *, struct dentry *),
1169                    void (*finish)(void *))
1170 {
1171         struct dentry *this_parent;
1172         struct list_head *next;
1173         unsigned seq = 0;
1174         enum d_walk_ret ret;
1175         bool retry = true;
1176 
1177 again:
1178         read_seqbegin_or_lock(&rename_lock, &seq);
1179         this_parent = parent;
1180         spin_lock(&this_parent->d_lock);
1181 
1182         ret = enter(data, this_parent);
1183         switch (ret) {
1184         case D_WALK_CONTINUE:
1185                 break;
1186         case D_WALK_QUIT:
1187         case D_WALK_SKIP:
1188                 goto out_unlock;
1189         case D_WALK_NORETRY:
1190                 retry = false;
1191                 break;
1192         }
1193 repeat:
1194         next = this_parent->d_subdirs.next;
1195 resume:
1196         while (next != &this_parent->d_subdirs) {
1197                 struct list_head *tmp = next;
1198                 struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
1199                 next = tmp->next;
1200 
1201                 if (unlikely(dentry->d_flags & DCACHE_DENTRY_CURSOR))
1202                         continue;
1203 
1204                 spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
1205 
1206                 ret = enter(data, dentry);
1207                 switch (ret) {
1208                 case D_WALK_CONTINUE:
1209                         break;
1210                 case D_WALK_QUIT:
1211                         spin_unlock(&dentry->d_lock);
1212                         goto out_unlock;
1213                 case D_WALK_NORETRY:
1214                         retry = false;
1215                         break;
1216                 case D_WALK_SKIP:
1217                         spin_unlock(&dentry->d_lock);
1218                         continue;
1219                 }
1220 
1221                 if (!list_empty(&dentry->d_subdirs)) {
1222                         spin_unlock(&this_parent->d_lock);
1223                         spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
1224                         this_parent = dentry;
1225                         spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
1226                         goto repeat;
1227                 }
1228                 spin_unlock(&dentry->d_lock);
1229         }
1230         /*
1231          * All done at this level ... ascend and resume the search.
1232          */
1233         rcu_read_lock();
1234 ascend:
1235         if (this_parent != parent) {
1236                 struct dentry *child = this_parent;
1237                 this_parent = child->d_parent;
1238 
1239                 spin_unlock(&child->d_lock);
1240                 spin_lock(&this_parent->d_lock);
1241 
1242                 /* might go back up the wrong parent if we have had a rename. */
1243                 if (need_seqretry(&rename_lock, seq))
1244                         goto rename_retry;
1245                 /* go into the first sibling still alive */
1246                 do {
1247                         next = child->d_child.next;
1248                         if (next == &this_parent->d_subdirs)
1249                                 goto ascend;
1250                         child = list_entry(next, struct dentry, d_child);
1251                 } while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED));
1252                 rcu_read_unlock();
1253                 goto resume;
1254         }
1255         if (need_seqretry(&rename_lock, seq))
1256                 goto rename_retry;
1257         rcu_read_unlock();
1258         if (finish)
1259                 finish(data);
1260 
1261 out_unlock:
1262         spin_unlock(&this_parent->d_lock);
1263         done_seqretry(&rename_lock, seq);
1264         return;
1265 
1266 rename_retry:
1267         spin_unlock(&this_parent->d_lock);
1268         rcu_read_unlock();
1269         BUG_ON(seq & 1);
1270         if (!retry)
1271                 return;
1272         seq = 1;
1273         goto again;
1274 }
1275 
1276 struct check_mount {
1277         struct vfsmount *mnt;
1278         unsigned int mounted;
1279 };
1280 
1281 static enum d_walk_ret path_check_mount(void *data, struct dentry *dentry)
1282 {
1283         struct check_mount *info = data;
1284         struct path path = { .mnt = info->mnt, .dentry = dentry };
1285 
1286         if (likely(!d_mountpoint(dentry)))
1287                 return D_WALK_CONTINUE;
1288         if (__path_is_mountpoint(&path)) {
1289                 info->mounted = 1;
1290                 return D_WALK_QUIT;
1291         }
1292         return D_WALK_CONTINUE;
1293 }
1294 
1295 /**
1296  * path_has_submounts - check for mounts over a dentry in the
1297  *                      current namespace.
1298  * @parent: path to check.
1299  *
1300  * Return true if the parent or its subdirectories contain
1301  * a mount point in the current namespace.
1302  */
1303 int path_has_submounts(const struct path *parent)
1304 {
1305         struct check_mount data = { .mnt = parent->mnt, .mounted = 0 };
1306 
1307         read_seqlock_excl(&mount_lock);
1308         d_walk(parent->dentry, &data, path_check_mount, NULL);
1309         read_sequnlock_excl(&mount_lock);
1310 
1311         return data.mounted;
1312 }
1313 EXPORT_SYMBOL(path_has_submounts);
1314 
1315 /*
1316  * Called by mount code to set a mountpoint and check if the mountpoint is
1317  * reachable (e.g. NFS can unhash a directory dentry and then the complete
1318  * subtree can become unreachable).
1319  *
1320  * Only one of d_invalidate() and d_set_mounted() must succeed.  For
1321  * this reason take rename_lock and d_lock on dentry and ancestors.
1322  */
1323 int d_set_mounted(struct dentry *dentry)
1324 {
1325         struct dentry *p;
1326         int ret = -ENOENT;
1327         write_seqlock(&rename_lock);
1328         for (p = dentry->d_parent; !IS_ROOT(p); p = p->d_parent) {
1329                 /* Need exclusion wrt. d_invalidate() */
1330                 spin_lock(&p->d_lock);
1331                 if (unlikely(d_unhashed(p))) {
1332                         spin_unlock(&p->d_lock);
1333                         goto out;
1334                 }
1335                 spin_unlock(&p->d_lock);
1336         }
1337         spin_lock(&dentry->d_lock);
1338         if (!d_unlinked(dentry)) {
1339                 ret = -EBUSY;
1340                 if (!d_mountpoint(dentry)) {
1341                         dentry->d_flags |= DCACHE_MOUNTED;
1342                         ret = 0;
1343                 }
1344         }
1345         spin_unlock(&dentry->d_lock);
1346 out:
1347         write_sequnlock(&rename_lock);
1348         return ret;
1349 }
1350 
1351 /*
1352  * Search the dentry child list of the specified parent,
1353  * and move any unused dentries to the end of the unused
1354  * list for prune_dcache(). We descend to the next level
1355  * whenever the d_subdirs list is non-empty and continue
1356  * searching.
1357  *
1358  * It returns zero iff there are no unused children,
1359  * otherwise  it returns the number of children moved to
1360  * the end of the unused list. This may not be the total
1361  * number of unused children, because select_parent can
1362  * drop the lock and return early due to latency
1363  * constraints.
1364  */
1365 
1366 struct select_data {
1367         struct dentry *start;
1368         struct list_head dispose;
1369         int found;
1370 };
1371 
1372 static enum d_walk_ret select_collect(void *_data, struct dentry *dentry)
1373 {
1374         struct select_data *data = _data;
1375         enum d_walk_ret ret = D_WALK_CONTINUE;
1376 
1377         if (data->start == dentry)
1378                 goto out;
1379 
1380         if (dentry->d_flags & DCACHE_SHRINK_LIST) {
1381                 data->found++;
1382         } else {
1383                 if (dentry->d_flags & DCACHE_LRU_LIST)
1384                         d_lru_del(dentry);
1385                 if (!dentry->d_lockref.count) {
1386                         d_shrink_add(dentry, &data->dispose);
1387                         data->found++;
1388                 }
1389         }
1390         /*
1391          * We can return to the caller if we have found some (this
1392          * ensures forward progress). We'll be coming back to find
1393          * the rest.
1394          */
1395         if (!list_empty(&data->dispose))
1396                 ret = need_resched() ? D_WALK_QUIT : D_WALK_NORETRY;
1397 out:
1398         return ret;
1399 }
1400 
1401 /**
1402  * shrink_dcache_parent - prune dcache
1403  * @parent: parent of entries to prune
1404  *
1405  * Prune the dcache to remove unused children of the parent dentry.
1406  */
1407 void shrink_dcache_parent(struct dentry *parent)
1408 {
1409         for (;;) {
1410                 struct select_data data;
1411 
1412                 INIT_LIST_HEAD(&data.dispose);
1413                 data.start = parent;
1414                 data.found = 0;
1415 
1416                 d_walk(parent, &data, select_collect, NULL);
1417                 if (!data.found)
1418                         break;
1419 
1420                 shrink_dentry_list(&data.dispose);
1421                 cond_resched();
1422         }
1423 }
1424 EXPORT_SYMBOL(shrink_dcache_parent);
1425 
1426 static enum d_walk_ret umount_check(void *_data, struct dentry *dentry)
1427 {
1428         /* it has busy descendents; complain about those instead */
1429         if (!list_empty(&dentry->d_subdirs))
1430                 return D_WALK_CONTINUE;
1431 
1432         /* root with refcount 1 is fine */
1433         if (dentry == _data && dentry->d_lockref.count == 1)
1434                 return D_WALK_CONTINUE;
1435 
1436         printk(KERN_ERR "BUG: Dentry %p{i=%lx,n=%pd} "
1437                         " still in use (%d) [unmount of %s %s]\n",
1438                        dentry,
1439                        dentry->d_inode ?
1440                        dentry->d_inode->i_ino : 0UL,
1441                        dentry,
1442                        dentry->d_lockref.count,
1443                        dentry->d_sb->s_type->name,
1444                        dentry->d_sb->s_id);
1445         WARN_ON(1);
1446         return D_WALK_CONTINUE;
1447 }
1448 
1449 static void do_one_tree(struct dentry *dentry)
1450 {
1451         shrink_dcache_parent(dentry);
1452         d_walk(dentry, dentry, umount_check, NULL);
1453         d_drop(dentry);
1454         dput(dentry);
1455 }
1456 
1457 /*
1458  * destroy the dentries attached to a superblock on unmounting
1459  */
1460 void shrink_dcache_for_umount(struct super_block *sb)
1461 {
1462         struct dentry *dentry;
1463 
1464         WARN(down_read_trylock(&sb->s_umount), "s_umount should've been locked");
1465 
1466         dentry = sb->s_root;
1467         sb->s_root = NULL;
1468         do_one_tree(dentry);
1469 
1470         while (!hlist_bl_empty(&sb->s_anon)) {
1471                 dentry = dget(hlist_bl_entry(hlist_bl_first(&sb->s_anon), struct dentry, d_hash));
1472                 do_one_tree(dentry);
1473         }
1474 }
1475 
1476 struct detach_data {
1477         struct select_data select;
1478         struct dentry *mountpoint;
1479 };
1480 static enum d_walk_ret detach_and_collect(void *_data, struct dentry *dentry)
1481 {
1482         struct detach_data *data = _data;
1483 
1484         if (d_mountpoint(dentry)) {
1485                 __dget_dlock(dentry);
1486                 data->mountpoint = dentry;
1487                 return D_WALK_QUIT;
1488         }
1489 
1490         return select_collect(&data->select, dentry);
1491 }
1492 
1493 static void check_and_drop(void *_data)
1494 {
1495         struct detach_data *data = _data;
1496 
1497         if (!data->mountpoint && !data->select.found)
1498                 __d_drop(data->select.start);
1499 }
1500 
1501 /**
1502  * d_invalidate - detach submounts, prune dcache, and drop
1503  * @dentry: dentry to invalidate (aka detach, prune and drop)
1504  *
1505  * no dcache lock.
1506  *
1507  * The final d_drop is done as an atomic operation relative to
1508  * rename_lock ensuring there are no races with d_set_mounted.  This
1509  * ensures there are no unhashed dentries on the path to a mountpoint.
1510  */
1511 void d_invalidate(struct dentry *dentry)
1512 {
1513         /*
1514          * If it's already been dropped, return OK.
1515          */
1516         spin_lock(&dentry->d_lock);
1517         if (d_unhashed(dentry)) {
1518                 spin_unlock(&dentry->d_lock);
1519                 return;
1520         }
1521         spin_unlock(&dentry->d_lock);
1522 
1523         /* Negative dentries can be dropped without further checks */
1524         if (!dentry->d_inode) {
1525                 d_drop(dentry);
1526                 return;
1527         }
1528 
1529         for (;;) {
1530                 struct detach_data data;
1531 
1532                 data.mountpoint = NULL;
1533                 INIT_LIST_HEAD(&data.select.dispose);
1534                 data.select.start = dentry;
1535                 data.select.found = 0;
1536 
1537                 d_walk(dentry, &data, detach_and_collect, check_and_drop);
1538 
1539                 if (data.select.found)
1540                         shrink_dentry_list(&data.select.dispose);
1541 
1542                 if (data.mountpoint) {
1543                         detach_mounts(data.mountpoint);
1544                         dput(data.mountpoint);
1545                 }
1546 
1547                 if (!data.mountpoint && !data.select.found)
1548                         break;
1549 
1550                 cond_resched();
1551         }
1552 }
1553 EXPORT_SYMBOL(d_invalidate);
1554 
1555 /**
1556  * __d_alloc    -       allocate a dcache entry
1557  * @sb: filesystem it will belong to
1558  * @name: qstr of the name
1559  *
1560  * Allocates a dentry. It returns %NULL if there is insufficient memory
1561  * available. On a success the dentry is returned. The name passed in is
1562  * copied and the copy passed in may be reused after this call.
1563  */
1564  
1565 struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
1566 {
1567         struct dentry *dentry;
1568         char *dname;
1569         int err;
1570 
1571         dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
1572         if (!dentry)
1573                 return NULL;
1574 
1575         /*
1576          * We guarantee that the inline name is always NUL-terminated.
1577          * This way the memcpy() done by the name switching in rename
1578          * will still always have a NUL at the end, even if we might
1579          * be overwriting an internal NUL character
1580          */
1581         dentry->d_iname[DNAME_INLINE_LEN-1] = 0;
1582         if (unlikely(!name)) {
1583                 static const struct qstr anon = QSTR_INIT("/", 1);
1584                 name = &anon;
1585                 dname = dentry->d_iname;
1586         } else if (name->len > DNAME_INLINE_LEN-1) {
1587                 size_t size = offsetof(struct external_name, name[1]);
1588                 struct external_name *p = kmalloc(size + name->len,
1589                                                   GFP_KERNEL_ACCOUNT);
1590                 if (!p) {
1591                         kmem_cache_free(dentry_cache, dentry); 
1592                         return NULL;
1593                 }
1594                 atomic_set(&p->u.count, 1);
1595                 dname = p->name;
1596                 if (IS_ENABLED(CONFIG_DCACHE_WORD_ACCESS))
1597                         kasan_unpoison_shadow(dname,
1598                                 round_up(name->len + 1, sizeof(unsigned long)));
1599         } else  {
1600                 dname = dentry->d_iname;
1601         }       
1602 
1603         dentry->d_name.len = name->len;
1604         dentry->d_name.hash = name->hash;
1605         memcpy(dname, name->name, name->len);
1606         dname[name->len] = 0;
1607 
1608         /* Make sure we always see the terminating NUL character */
1609         smp_wmb();
1610         dentry->d_name.name = dname;
1611 
1612         dentry->d_lockref.count = 1;
1613         dentry->d_flags = 0;
1614         spin_lock_init(&dentry->d_lock);
1615         seqcount_init(&dentry->d_seq);
1616         dentry->d_inode = NULL;
1617         dentry->d_parent = dentry;
1618         dentry->d_sb = sb;
1619         dentry->d_op = NULL;
1620         dentry->d_fsdata = NULL;
1621         INIT_HLIST_BL_NODE(&dentry->d_hash);
1622         INIT_LIST_HEAD(&dentry->d_lru);
1623         INIT_LIST_HEAD(&dentry->d_subdirs);
1624         INIT_HLIST_NODE(&dentry->d_u.d_alias);
1625         INIT_LIST_HEAD(&dentry->d_child);
1626         d_set_d_op(dentry, dentry->d_sb->s_d_op);
1627 
1628         if (dentry->d_op && dentry->d_op->d_init) {
1629                 err = dentry->d_op->d_init(dentry);
1630                 if (err) {
1631                         if (dname_external(dentry))
1632                                 kfree(external_name(dentry));
1633                         kmem_cache_free(dentry_cache, dentry);
1634                         return NULL;
1635                 }
1636         }
1637 
1638         this_cpu_inc(nr_dentry);
1639 
1640         return dentry;
1641 }
1642 
1643 /**
1644  * d_alloc      -       allocate a dcache entry
1645  * @parent: parent of entry to allocate
1646  * @name: qstr of the name
1647  *
1648  * Allocates a dentry. It returns %NULL if there is insufficient memory
1649  * available. On a success the dentry is returned. The name passed in is
1650  * copied and the copy passed in may be reused after this call.
1651  */
1652 struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
1653 {
1654         struct dentry *dentry = __d_alloc(parent->d_sb, name);
1655         if (!dentry)
1656                 return NULL;
1657         dentry->d_flags |= DCACHE_RCUACCESS;
1658         spin_lock(&parent->d_lock);
1659         /*
1660          * don't need child lock because it is not subject
1661          * to concurrency here
1662          */
1663         __dget_dlock(parent);
1664         dentry->d_parent = parent;
1665         list_add(&dentry->d_child, &parent->d_subdirs);
1666         spin_unlock(&parent->d_lock);
1667 
1668         return dentry;
1669 }
1670 EXPORT_SYMBOL(d_alloc);
1671 
1672 struct dentry *d_alloc_cursor(struct dentry * parent)
1673 {
1674         struct dentry *dentry = __d_alloc(parent->d_sb, NULL);
1675         if (dentry) {
1676                 dentry->d_flags |= DCACHE_RCUACCESS | DCACHE_DENTRY_CURSOR;
1677                 dentry->d_parent = dget(parent);
1678         }
1679         return dentry;
1680 }
1681 
1682 /**
1683  * d_alloc_pseudo - allocate a dentry (for lookup-less filesystems)
1684  * @sb: the superblock
1685  * @name: qstr of the name
1686  *
1687  * For a filesystem that just pins its dentries in memory and never
1688  * performs lookups at all, return an unhashed IS_ROOT dentry.
1689  */
1690 struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
1691 {
1692         return __d_alloc(sb, name);
1693 }
1694 EXPORT_SYMBOL(d_alloc_pseudo);
1695 
1696 struct dentry *d_alloc_name(struct dentry *parent, const char *name)
1697 {
1698         struct qstr q;
1699 
1700         q.name = name;
1701         q.hash_len = hashlen_string(parent, name);
1702         return d_alloc(parent, &q);
1703 }
1704 EXPORT_SYMBOL(d_alloc_name);
1705 
1706 void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
1707 {
1708         WARN_ON_ONCE(dentry->d_op);
1709         WARN_ON_ONCE(dentry->d_flags & (DCACHE_OP_HASH  |
1710                                 DCACHE_OP_COMPARE       |
1711                                 DCACHE_OP_REVALIDATE    |
1712                                 DCACHE_OP_WEAK_REVALIDATE       |
1713                                 DCACHE_OP_DELETE        |
1714                                 DCACHE_OP_REAL));
1715         dentry->d_op = op;
1716         if (!op)
1717                 return;
1718         if (op->d_hash)
1719                 dentry->d_flags |= DCACHE_OP_HASH;
1720         if (op->d_compare)
1721                 dentry->d_flags |= DCACHE_OP_COMPARE;
1722         if (op->d_revalidate)
1723                 dentry->d_flags |= DCACHE_OP_REVALIDATE;
1724         if (op->d_weak_revalidate)
1725                 dentry->d_flags |= DCACHE_OP_WEAK_REVALIDATE;
1726         if (op->d_delete)
1727                 dentry->d_flags |= DCACHE_OP_DELETE;
1728         if (op->d_prune)
1729                 dentry->d_flags |= DCACHE_OP_PRUNE;
1730         if (op->d_real)
1731                 dentry->d_flags |= DCACHE_OP_REAL;
1732 
1733 }
1734 EXPORT_SYMBOL(d_set_d_op);
1735 
1736 
1737 /*
1738  * d_set_fallthru - Mark a dentry as falling through to a lower layer
1739  * @dentry - The dentry to mark
1740  *
1741  * Mark a dentry as falling through to the lower layer (as set with
1742  * d_pin_lower()).  This flag may be recorded on the medium.
1743  */
1744 void d_set_fallthru(struct dentry *dentry)
1745 {
1746         spin_lock(&dentry->d_lock);
1747         dentry->d_flags |= DCACHE_FALLTHRU;
1748         spin_unlock(&dentry->d_lock);
1749 }
1750 EXPORT_SYMBOL(d_set_fallthru);
1751 
1752 static unsigned d_flags_for_inode(struct inode *inode)
1753 {
1754         unsigned add_flags = DCACHE_REGULAR_TYPE;
1755 
1756         if (!inode)
1757                 return DCACHE_MISS_TYPE;
1758 
1759         if (S_ISDIR(inode->i_mode)) {
1760                 add_flags = DCACHE_DIRECTORY_TYPE;
1761                 if (unlikely(!(inode->i_opflags & IOP_LOOKUP))) {
1762                         if (unlikely(!inode->i_op->lookup))
1763                                 add_flags = DCACHE_AUTODIR_TYPE;
1764                         else
1765                                 inode->i_opflags |= IOP_LOOKUP;
1766                 }
1767                 goto type_determined;
1768         }
1769 
1770         if (unlikely(!(inode->i_opflags & IOP_NOFOLLOW))) {
1771                 if (unlikely(inode->i_op->get_link)) {
1772                         add_flags = DCACHE_SYMLINK_TYPE;
1773                         goto type_determined;
1774                 }
1775                 inode->i_opflags |= IOP_NOFOLLOW;
1776         }
1777 
1778         if (unlikely(!S_ISREG(inode->i_mode)))
1779                 add_flags = DCACHE_SPECIAL_TYPE;
1780 
1781 type_determined:
1782         if (unlikely(IS_AUTOMOUNT(inode)))
1783                 add_flags |= DCACHE_NEED_AUTOMOUNT;
1784         return add_flags;
1785 }
1786 
1787 static void __d_instantiate(struct dentry *dentry, struct inode *inode)
1788 {
1789         unsigned add_flags = d_flags_for_inode(inode);
1790         WARN_ON(d_in_lookup(dentry));
1791 
1792         spin_lock(&dentry->d_lock);
1793         hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
1794         raw_write_seqcount_begin(&dentry->d_seq);
1795         __d_set_inode_and_type(dentry, inode, add_flags);
1796         raw_write_seqcount_end(&dentry->d_seq);
1797         fsnotify_update_flags(dentry);
1798         spin_unlock(&dentry->d_lock);
1799 }
1800 
1801 /**
1802  * d_instantiate - fill in inode information for a dentry
1803  * @entry: dentry to complete
1804  * @inode: inode to attach to this dentry
1805  *
1806  * Fill in inode information in the entry.
1807  *
1808  * This turns negative dentries into productive full members
1809  * of society.
1810  *
1811  * NOTE! This assumes that the inode count has been incremented
1812  * (or otherwise set) by the caller to indicate that it is now
1813  * in use by the dcache.
1814  */
1815  
1816 void d_instantiate(struct dentry *entry, struct inode * inode)
1817 {
1818         BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
1819         if (inode) {
1820                 security_d_instantiate(entry, inode);
1821                 spin_lock(&inode->i_lock);
1822                 __d_instantiate(entry, inode);
1823                 spin_unlock(&inode->i_lock);
1824         }
1825 }
1826 EXPORT_SYMBOL(d_instantiate);
1827 
1828 /**
1829  * d_instantiate_no_diralias - instantiate a non-aliased dentry
1830  * @entry: dentry to complete
1831  * @inode: inode to attach to this dentry
1832  *
1833  * Fill in inode information in the entry.  If a directory alias is found, then
1834  * return an error (and drop inode).  Together with d_materialise_unique() this
1835  * guarantees that a directory inode may never have more than one alias.
1836  */
1837 int d_instantiate_no_diralias(struct dentry *entry, struct inode *inode)
1838 {
1839         BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
1840 
1841         security_d_instantiate(entry, inode);
1842         spin_lock(&inode->i_lock);
1843         if (S_ISDIR(inode->i_mode) && !hlist_empty(&inode->i_dentry)) {
1844                 spin_unlock(&inode->i_lock);
1845                 iput(inode);
1846                 return -EBUSY;
1847         }
1848         __d_instantiate(entry, inode);
1849         spin_unlock(&inode->i_lock);
1850 
1851         return 0;
1852 }
1853 EXPORT_SYMBOL(d_instantiate_no_diralias);
1854 
1855 struct dentry *d_make_root(struct inode *root_inode)
1856 {
1857         struct dentry *res = NULL;
1858 
1859         if (root_inode) {
1860                 res = __d_alloc(root_inode->i_sb, NULL);
1861                 if (res)
1862                         d_instantiate(res, root_inode);
1863                 else
1864                         iput(root_inode);
1865         }
1866         return res;
1867 }
1868 EXPORT_SYMBOL(d_make_root);
1869 
1870 static struct dentry * __d_find_any_alias(struct inode *inode)
1871 {
1872         struct dentry *alias;
1873 
1874         if (hlist_empty(&inode->i_dentry))
1875                 return NULL;
1876         alias = hlist_entry(inode->i_dentry.first, struct dentry, d_u.d_alias);
1877         __dget(alias);
1878         return alias;
1879 }
1880 
1881 /**
1882  * d_find_any_alias - find any alias for a given inode
1883  * @inode: inode to find an alias for
1884  *
1885  * If any aliases exist for the given inode, take and return a
1886  * reference for one of them.  If no aliases exist, return %NULL.
1887  */
1888 struct dentry *d_find_any_alias(struct inode *inode)
1889 {
1890         struct dentry *de;
1891 
1892         spin_lock(&inode->i_lock);
1893         de = __d_find_any_alias(inode);
1894         spin_unlock(&inode->i_lock);
1895         return de;
1896 }
1897 EXPORT_SYMBOL(d_find_any_alias);
1898 
1899 static struct dentry *__d_obtain_alias(struct inode *inode, int disconnected)
1900 {
1901         struct dentry *tmp;
1902         struct dentry *res;
1903         unsigned add_flags;
1904 
1905         if (!inode)
1906                 return ERR_PTR(-ESTALE);
1907         if (IS_ERR(inode))
1908                 return ERR_CAST(inode);
1909 
1910         res = d_find_any_alias(inode);
1911         if (res)
1912                 goto out_iput;
1913 
1914         tmp = __d_alloc(inode->i_sb, NULL);
1915         if (!tmp) {
1916                 res = ERR_PTR(-ENOMEM);
1917                 goto out_iput;
1918         }
1919 
1920         security_d_instantiate(tmp, inode);
1921         spin_lock(&inode->i_lock);
1922         res = __d_find_any_alias(inode);
1923         if (res) {
1924                 spin_unlock(&inode->i_lock);
1925                 dput(tmp);
1926                 goto out_iput;
1927         }
1928 
1929         /* attach a disconnected dentry */
1930         add_flags = d_flags_for_inode(inode);
1931 
1932         if (disconnected)
1933                 add_flags |= DCACHE_DISCONNECTED;
1934 
1935         spin_lock(&tmp->d_lock);
1936         __d_set_inode_and_type(tmp, inode, add_flags);
1937         hlist_add_head(&tmp->d_u.d_alias, &inode->i_dentry);
1938         hlist_bl_lock(&tmp->d_sb->s_anon);
1939         hlist_bl_add_head(&tmp->d_hash, &tmp->d_sb->s_anon);
1940         hlist_bl_unlock(&tmp->d_sb->s_anon);
1941         spin_unlock(&tmp->d_lock);
1942         spin_unlock(&inode->i_lock);
1943 
1944         return tmp;
1945 
1946  out_iput:
1947         iput(inode);
1948         return res;
1949 }
1950 
1951 /**
1952  * d_obtain_alias - find or allocate a DISCONNECTED dentry for a given inode
1953  * @inode: inode to allocate the dentry for
1954  *
1955  * Obtain a dentry for an inode resulting from NFS filehandle conversion or
1956  * similar open by handle operations.  The returned dentry may be anonymous,
1957  * or may have a full name (if the inode was already in the cache).
1958  *
1959  * When called on a directory inode, we must ensure that the inode only ever
1960  * has one dentry.  If a dentry is found, that is returned instead of
1961  * allocating a new one.
1962  *
1963  * On successful return, the reference to the inode has been transferred
1964  * to the dentry.  In case of an error the reference on the inode is released.
1965  * To make it easier to use in export operations a %NULL or IS_ERR inode may
1966  * be passed in and the error will be propagated to the return value,
1967  * with a %NULL @inode replaced by ERR_PTR(-ESTALE).
1968  */
1969 struct dentry *d_obtain_alias(struct inode *inode)
1970 {
1971         return __d_obtain_alias(inode, 1);
1972 }
1973 EXPORT_SYMBOL(d_obtain_alias);
1974 
1975 /**
1976  * d_obtain_root - find or allocate a dentry for a given inode
1977  * @inode: inode to allocate the dentry for
1978  *
1979  * Obtain an IS_ROOT dentry for the root of a filesystem.
1980  *
1981  * We must ensure that directory inodes only ever have one dentry.  If a
1982  * dentry is found, that is returned instead of allocating a new one.
1983  *
1984  * On successful return, the reference to the inode has been transferred
1985  * to the dentry.  In case of an error the reference on the inode is
1986  * released.  A %NULL or IS_ERR inode may be passed in and will be the
1987  * error will be propagate to the return value, with a %NULL @inode
1988  * replaced by ERR_PTR(-ESTALE).
1989  */
1990 struct dentry *d_obtain_root(struct inode *inode)
1991 {
1992         return __d_obtain_alias(inode, 0);
1993 }
1994 EXPORT_SYMBOL(d_obtain_root);
1995 
1996 /**
1997  * d_add_ci - lookup or allocate new dentry with case-exact name
1998  * @inode:  the inode case-insensitive lookup has found
1999  * @dentry: the negative dentry that was passed to the parent's lookup func
2000  * @name:   the case-exact name to be associated with the returned dentry
2001  *
2002  * This is to avoid filling the dcache with case-insensitive names to the
2003  * same inode, only the actual correct case is stored in the dcache for
2004  * case-insensitive filesystems.
2005  *
2006  * For a case-insensitive lookup match and if the the case-exact dentry
2007  * already exists in in the dcache, use it and return it.
2008  *
2009  * If no entry exists with the exact case name, allocate new dentry with
2010  * the exact case, and return the spliced entry.
2011  */
2012 struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
2013                         struct qstr *name)
2014 {
2015         struct dentry *found, *res;
2016 
2017         /*
2018          * First check if a dentry matching the name already exists,
2019          * if not go ahead and create it now.
2020          */
2021         found = d_hash_and_lookup(dentry->d_parent, name);
2022         if (found) {
2023                 iput(inode);
2024                 return found;
2025         }
2026         if (d_in_lookup(dentry)) {
2027                 found = d_alloc_parallel(dentry->d_parent, name,
2028                                         dentry->d_wait);
2029                 if (IS_ERR(found) || !d_in_lookup(found)) {
2030                         iput(inode);
2031                         return found;
2032                 }
2033         } else {
2034                 found = d_alloc(dentry->d_parent, name);
2035                 if (!found) {
2036                         iput(inode);
2037                         return ERR_PTR(-ENOMEM);
2038                 } 
2039         }
2040         res = d_splice_alias(inode, found);
2041         if (res) {
2042                 dput(found);
2043                 return res;
2044         }
2045         return found;
2046 }
2047 EXPORT_SYMBOL(d_add_ci);
2048 
2049 
2050 static inline bool d_same_name(const struct dentry *dentry,
2051                                 const struct dentry *parent,
2052                                 const struct qstr *name)
2053 {
2054         if (likely(!(parent->d_flags & DCACHE_OP_COMPARE))) {
2055                 if (dentry->d_name.len != name->len)
2056                         return false;
2057                 return dentry_cmp(dentry, name->name, name->len) == 0;
2058         }
2059         return parent->d_op->d_compare(dentry,
2060                                        dentry->d_name.len, dentry->d_name.name,
2061                                        name) == 0;
2062 }
2063 
2064 /**
2065  * __d_lookup_rcu - search for a dentry (racy, store-free)
2066  * @parent: parent dentry
2067  * @name: qstr of name we wish to find
2068  * @seqp: returns d_seq value at the point where the dentry was found
2069  * Returns: dentry, or NULL
2070  *
2071  * __d_lookup_rcu is the dcache lookup function for rcu-walk name
2072  * resolution (store-free path walking) design described in
2073  * Documentation/filesystems/path-lookup.txt.
2074  *
2075  * This is not to be used outside core vfs.
2076  *
2077  * __d_lookup_rcu must only be used in rcu-walk mode, ie. with vfsmount lock
2078  * held, and rcu_read_lock held. The returned dentry must not be stored into
2079  * without taking d_lock and checking d_seq sequence count against @seq
2080  * returned here.
2081  *
2082  * A refcount may be taken on the found dentry with the d_rcu_to_refcount
2083  * function.
2084  *
2085  * Alternatively, __d_lookup_rcu may be called again to look up the child of
2086  * the returned dentry, so long as its parent's seqlock is checked after the
2087  * child is looked up. Thus, an interlocking stepping of sequence lock checks
2088  * is formed, giving integrity down the path walk.
2089  *
2090  * NOTE! The caller *has* to check the resulting dentry against the sequence
2091  * number we've returned before using any of the resulting dentry state!
2092  */
2093 struct dentry *__d_lookup_rcu(const struct dentry *parent,
2094                                 const struct qstr *name,
2095                                 unsigned *seqp)
2096 {
2097         u64 hashlen = name->hash_len;
2098         const unsigned char *str = name->name;
2099         struct hlist_bl_head *b = d_hash(hashlen_hash(hashlen));
2100         struct hlist_bl_node *node;
2101         struct dentry *dentry;
2102 
2103         /*
2104          * Note: There is significant duplication with __d_lookup_rcu which is
2105          * required to prevent single threaded performance regressions
2106          * especially on architectures where smp_rmb (in seqcounts) are costly.
2107          * Keep the two functions in sync.
2108          */
2109 
2110         /*
2111          * The hash list is protected using RCU.
2112          *
2113          * Carefully use d_seq when comparing a candidate dentry, to avoid
2114          * races with d_move().
2115          *
2116          * It is possible that concurrent renames can mess up our list
2117          * walk here and result in missing our dentry, resulting in the
2118          * false-negative result. d_lookup() protects against concurrent
2119          * renames using rename_lock seqlock.
2120          *
2121          * See Documentation/filesystems/path-lookup.txt for more details.
2122          */
2123         hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
2124                 unsigned seq;
2125 
2126 seqretry:
2127                 /*
2128                  * The dentry sequence count protects us from concurrent
2129                  * renames, and thus protects parent and name fields.
2130                  *
2131                  * The caller must perform a seqcount check in order
2132                  * to do anything useful with the returned dentry.
2133                  *
2134                  * NOTE! We do a "raw" seqcount_begin here. That means that
2135                  * we don't wait for the sequence count to stabilize if it
2136                  * is in the middle of a sequence change. If we do the slow
2137                  * dentry compare, we will do seqretries until it is stable,
2138                  * and if we end up with a successful lookup, we actually
2139                  * want to exit RCU lookup anyway.
2140                  *
2141                  * Note that raw_seqcount_begin still *does* smp_rmb(), so
2142                  * we are still guaranteed NUL-termination of ->d_name.name.
2143                  */
2144                 seq = raw_seqcount_begin(&dentry->d_seq);
2145                 if (dentry->d_parent != parent)
2146                         continue;
2147                 if (d_unhashed(dentry))
2148                         continue;
2149 
2150                 if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
2151                         int tlen;
2152                         const char *tname;
2153                         if (dentry->d_name.hash != hashlen_hash(hashlen))
2154                                 continue;
2155                         tlen = dentry->d_name.len;
2156                         tname = dentry->d_name.name;
2157                         /* we want a consistent (name,len) pair */
2158                         if (read_seqcount_retry(&dentry->d_seq, seq)) {
2159                                 cpu_relax();
2160                                 goto seqretry;
2161                         }
2162                         if (parent->d_op->d_compare(dentry,
2163                                                     tlen, tname, name) != 0)
2164                                 continue;
2165                 } else {
2166                         if (dentry->d_name.hash_len != hashlen)
2167                                 continue;
2168                         if (dentry_cmp(dentry, str, hashlen_len(hashlen)) != 0)
2169                                 continue;
2170                 }
2171                 *seqp = seq;
2172                 return dentry;
2173         }
2174         return NULL;
2175 }
2176 
2177 /**
2178  * d_lookup - search for a dentry
2179  * @parent: parent dentry
2180  * @name: qstr of name we wish to find
2181  * Returns: dentry, or NULL
2182  *
2183  * d_lookup searches the children of the parent dentry for the name in
2184  * question. If the dentry is found its reference count is incremented and the
2185  * dentry is returned. The caller must use dput to free the entry when it has
2186  * finished using it. %NULL is returned if the dentry does not exist.
2187  */
2188 struct dentry *d_lookup(const struct dentry *parent, const struct qstr *name)
2189 {
2190         struct dentry *dentry;
2191         unsigned seq;
2192 
2193         do {
2194                 seq = read_seqbegin(&rename_lock);
2195                 dentry = __d_lookup(parent, name);
2196                 if (dentry)
2197                         break;
2198         } while (read_seqretry(&rename_lock, seq));
2199         return dentry;
2200 }
2201 EXPORT_SYMBOL(d_lookup);
2202 
2203 /**
2204  * __d_lookup - search for a dentry (racy)
2205  * @parent: parent dentry
2206  * @name: qstr of name we wish to find
2207  * Returns: dentry, or NULL
2208  *
2209  * __d_lookup is like d_lookup, however it may (rarely) return a
2210  * false-negative result due to unrelated rename activity.
2211  *
2212  * __d_lookup is slightly faster by avoiding rename_lock read seqlock,
2213  * however it must be used carefully, eg. with a following d_lookup in
2214  * the case of failure.
2215  *
2216  * __d_lookup callers must be commented.
2217  */
2218 struct dentry *__d_lookup(const struct dentry *parent, const struct qstr *name)
2219 {
2220         unsigned int hash = name->hash;
2221         struct hlist_bl_head *b = d_hash(hash);
2222         struct hlist_bl_node *node;
2223         struct dentry *found = NULL;
2224         struct dentry *dentry;
2225 
2226         /*
2227          * Note: There is significant duplication with __d_lookup_rcu which is
2228          * required to prevent single threaded performance regressions
2229          * especially on architectures where smp_rmb (in seqcounts) are costly.
2230          * Keep the two functions in sync.
2231          */
2232 
2233         /*
2234          * The hash list is protected using RCU.
2235          *
2236          * Take d_lock when comparing a candidate dentry, to avoid races
2237          * with d_move().
2238          *
2239          * It is possible that concurrent renames can mess up our list
2240          * walk here and result in missing our dentry, resulting in the
2241          * false-negative result. d_lookup() protects against concurrent
2242          * renames using rename_lock seqlock.
2243          *
2244          * See Documentation/filesystems/path-lookup.txt for more details.
2245          */
2246         rcu_read_lock();
2247         
2248         hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
2249 
2250                 if (dentry->d_name.hash != hash)
2251                         continue;
2252 
2253                 spin_lock(&dentry->d_lock);
2254                 if (dentry->d_parent != parent)
2255                         goto next;
2256                 if (d_unhashed(dentry))
2257                         goto next;
2258 
2259                 if (!d_same_name(dentry, parent, name))
2260                         goto next;
2261 
2262                 dentry->d_lockref.count++;
2263                 found = dentry;
2264                 spin_unlock(&dentry->d_lock);
2265                 break;
2266 next:
2267                 spin_unlock(&dentry->d_lock);
2268         }
2269         rcu_read_unlock();
2270 
2271         return found;
2272 }
2273 
2274 /**
2275  * d_hash_and_lookup - hash the qstr then search for a dentry
2276  * @dir: Directory to search in
2277  * @name: qstr of name we wish to find
2278  *
2279  * On lookup failure NULL is returned; on bad name - ERR_PTR(-error)
2280  */
2281 struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
2282 {
2283         /*
2284          * Check for a fs-specific hash function. Note that we must
2285          * calculate the standard hash first, as the d_op->d_hash()
2286          * routine may choose to leave the hash value unchanged.
2287          */
2288         name->hash = full_name_hash(dir, name->name, name->len);
2289         if (dir->d_flags & DCACHE_OP_HASH) {
2290                 int err = dir->d_op->d_hash(dir, name);
2291                 if (unlikely(err < 0))
2292                         return ERR_PTR(err);
2293         }
2294         return d_lookup(dir, name);
2295 }
2296 EXPORT_SYMBOL(d_hash_and_lookup);
2297 
2298 /*
2299  * When a file is deleted, we have two options:
2300  * - turn this dentry into a negative dentry
2301  * - unhash this dentry and free it.
2302  *
2303  * Usually, we want to just turn this into
2304  * a negative dentry, but if anybody else is
2305  * currently using the dentry or the inode
2306  * we can't do that and we fall back on removing
2307  * it from the hash queues and waiting for
2308  * it to be deleted later when it has no users
2309  */
2310  
2311 /**
2312  * d_delete - delete a dentry
2313  * @dentry: The dentry to delete
2314  *
2315  * Turn the dentry into a negative dentry if possible, otherwise
2316  * remove it from the hash queues so it can be deleted later
2317  */
2318  
2319 void d_delete(struct dentry * dentry)
2320 {
2321         struct inode *inode;
2322         int isdir = 0;
2323         /*
2324          * Are we the only user?
2325          */
2326 again:
2327         spin_lock(&dentry->d_lock);
2328         inode = dentry->d_inode;
2329         isdir = S_ISDIR(inode->i_mode);
2330         if (dentry->d_lockref.count == 1) {
2331                 if (!spin_trylock(&inode->i_lock)) {
2332                         spin_unlock(&dentry->d_lock);
2333                         cpu_relax();
2334                         goto again;
2335                 }
2336                 dentry->d_flags &= ~DCACHE_CANT_MOUNT;
2337                 dentry_unlink_inode(dentry);
2338                 fsnotify_nameremove(dentry, isdir);
2339                 return;
2340         }
2341 
2342         if (!d_unhashed(dentry))
2343                 __d_drop(dentry);
2344 
2345         spin_unlock(&dentry->d_lock);
2346 
2347         fsnotify_nameremove(dentry, isdir);
2348 }
2349 EXPORT_SYMBOL(d_delete);
2350 
2351 static void __d_rehash(struct dentry *entry)
2352 {
2353         struct hlist_bl_head *b = d_hash(entry->d_name.hash);
2354         BUG_ON(!d_unhashed(entry));
2355         hlist_bl_lock(b);
2356         hlist_bl_add_head_rcu(&entry->d_hash, b);
2357         hlist_bl_unlock(b);
2358 }
2359 
2360 /**
2361  * d_rehash     - add an entry back to the hash
2362  * @entry: dentry to add to the hash
2363  *
2364  * Adds a dentry to the hash according to its name.
2365  */
2366  
2367 void d_rehash(struct dentry * entry)
2368 {
2369         spin_lock(&entry->d_lock);
2370         __d_rehash(entry);
2371         spin_unlock(&entry->d_lock);
2372 }
2373 EXPORT_SYMBOL(d_rehash);
2374 
2375 static inline unsigned start_dir_add(struct inode *dir)
2376 {
2377 
2378         for (;;) {
2379                 unsigned n = dir->i_dir_seq;
2380                 if (!(n & 1) && cmpxchg(&dir->i_dir_seq, n, n + 1) == n)
2381                         return n;
2382                 cpu_relax();
2383         }
2384 }
2385 
2386 static inline void end_dir_add(struct inode *dir, unsigned n)
2387 {
2388         smp_store_release(&dir->i_dir_seq, n + 2);
2389 }
2390 
2391 static void d_wait_lookup(struct dentry *dentry)
2392 {
2393         if (d_in_lookup(dentry)) {
2394                 DECLARE_WAITQUEUE(wait, current);
2395                 add_wait_queue(dentry->d_wait, &wait);
2396                 do {
2397                         set_current_state(TASK_UNINTERRUPTIBLE);
2398                         spin_unlock(&dentry->d_lock);
2399                         schedule();
2400                         spin_lock(&dentry->d_lock);
2401                 } while (d_in_lookup(dentry));
2402         }
2403 }
2404 
2405 struct dentry *d_alloc_parallel(struct dentry *parent,
2406                                 const struct qstr *name,
2407                                 wait_queue_head_t *wq)
2408 {
2409         unsigned int hash = name->hash;
2410         struct hlist_bl_head *b = in_lookup_hash(parent, hash);
2411         struct hlist_bl_node *node;
2412         struct dentry *new = d_alloc(parent, name);
2413         struct dentry *dentry;
2414         unsigned seq, r_seq, d_seq;
2415 
2416         if (unlikely(!new))
2417                 return ERR_PTR(-ENOMEM);
2418 
2419 retry:
2420         rcu_read_lock();
2421         seq = smp_load_acquire(&parent->d_inode->i_dir_seq) & ~1;
2422         r_seq = read_seqbegin(&rename_lock);
2423         dentry = __d_lookup_rcu(parent, name, &d_seq);
2424         if (unlikely(dentry)) {
2425                 if (!lockref_get_not_dead(&dentry->d_lockref)) {
2426                         rcu_read_unlock();
2427                         goto retry;
2428                 }
2429                 if (read_seqcount_retry(&dentry->d_seq, d_seq)) {
2430                         rcu_read_unlock();
2431                         dput(dentry);
2432                         goto retry;
2433                 }
2434                 rcu_read_unlock();
2435                 dput(new);
2436                 return dentry;
2437         }
2438         if (unlikely(read_seqretry(&rename_lock, r_seq))) {
2439                 rcu_read_unlock();
2440                 goto retry;
2441         }
2442         hlist_bl_lock(b);
2443         if (unlikely(parent->d_inode->i_dir_seq != seq)) {
2444                 hlist_bl_unlock(b);
2445                 rcu_read_unlock();
2446                 goto retry;
2447         }
2448         /*
2449          * No changes for the parent since the beginning of d_lookup().
2450          * Since all removals from the chain happen with hlist_bl_lock(),
2451          * any potential in-lookup matches are going to stay here until
2452          * we unlock the chain.  All fields are stable in everything
2453          * we encounter.
2454          */
2455         hlist_bl_for_each_entry(dentry, node, b, d_u.d_in_lookup_hash) {
2456                 if (dentry->d_name.hash != hash)
2457                         continue;
2458                 if (dentry->d_parent != parent)
2459                         continue;
2460                 if (!d_same_name(dentry, parent, name))
2461                         continue;
2462                 hlist_bl_unlock(b);
2463                 /* now we can try to grab a reference */
2464                 if (!lockref_get_not_dead(&dentry->d_lockref)) {
2465                         rcu_read_unlock();
2466                         goto retry;
2467                 }
2468 
2469                 rcu_read_unlock();
2470                 /*
2471                  * somebody is likely to be still doing lookup for it;
2472                  * wait for them to finish
2473                  */
2474                 spin_lock(&dentry->d_lock);
2475                 d_wait_lookup(dentry);
2476                 /*
2477                  * it's not in-lookup anymore; in principle we should repeat
2478                  * everything from dcache lookup, but it's likely to be what
2479                  * d_lookup() would've found anyway.  If it is, just return it;
2480                  * otherwise we really have to repeat the whole thing.
2481                  */
2482                 if (unlikely(dentry->d_name.hash != hash))
2483                         goto mismatch;
2484                 if (unlikely(dentry->d_parent != parent))
2485                         goto mismatch;
2486                 if (unlikely(d_unhashed(dentry)))
2487                         goto mismatch;
2488                 if (unlikely(!d_same_name(dentry, parent, name)))
2489                         goto mismatch;
2490                 /* OK, it *is* a hashed match; return it */
2491                 spin_unlock(&dentry->d_lock);
2492                 dput(new);
2493                 return dentry;
2494         }
2495         rcu_read_unlock();
2496         /* we can't take ->d_lock here; it's OK, though. */
2497         new->d_flags |= DCACHE_PAR_LOOKUP;
2498         new->d_wait = wq;
2499         hlist_bl_add_head_rcu(&new->d_u.d_in_lookup_hash, b);
2500         hlist_bl_unlock(b);
2501         return new;
2502 mismatch:
2503         spin_unlock(&dentry->d_lock);
2504         dput(dentry);
2505         goto retry;
2506 }
2507 EXPORT_SYMBOL(d_alloc_parallel);
2508 
2509 void __d_lookup_done(struct dentry *dentry)
2510 {
2511         struct hlist_bl_head *b = in_lookup_hash(dentry->d_parent,
2512                                                  dentry->d_name.hash);
2513         hlist_bl_lock(b);
2514         dentry->d_flags &= ~DCACHE_PAR_LOOKUP;
2515         __hlist_bl_del(&dentry->d_u.d_in_lookup_hash);
2516         wake_up_all(dentry->d_wait);
2517         dentry->d_wait = NULL;
2518         hlist_bl_unlock(b);
2519         INIT_HLIST_NODE(&dentry->d_u.d_alias);
2520         INIT_LIST_HEAD(&dentry->d_lru);
2521 }
2522 EXPORT_SYMBOL(__d_lookup_done);
2523 
2524 /* inode->i_lock held if inode is non-NULL */
2525 
2526 static inline void __d_add(struct dentry *dentry, struct inode *inode)
2527 {
2528         struct inode *dir = NULL;
2529         unsigned n;
2530         spin_lock(&dentry->d_lock);
2531         if (unlikely(d_in_lookup(dentry))) {
2532                 dir = dentry->d_parent->d_inode;
2533                 n = start_dir_add(dir);
2534                 __d_lookup_done(dentry);
2535         }
2536         if (inode) {
2537                 unsigned add_flags = d_flags_for_inode(inode);
2538                 hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
2539                 raw_write_seqcount_begin(&dentry->d_seq);
2540                 __d_set_inode_and_type(dentry, inode, add_flags);
2541                 raw_write_seqcount_end(&dentry->d_seq);
2542                 fsnotify_update_flags(dentry);
2543         }
2544         __d_rehash(dentry);
2545         if (dir)
2546                 end_dir_add(dir, n);
2547         spin_unlock(&dentry->d_lock);
2548         if (inode)
2549                 spin_unlock(&inode->i_lock);
2550 }
2551 
2552 /**
2553  * d_add - add dentry to hash queues
2554  * @entry: dentry to add
2555  * @inode: The inode to attach to this dentry
2556  *
2557  * This adds the entry to the hash queues and initializes @inode.
2558  * The entry was actually filled in earlier during d_alloc().
2559  */
2560 
2561 void d_add(struct dentry *entry, struct inode *inode)
2562 {
2563         if (inode) {
2564                 security_d_instantiate(entry, inode);
2565                 spin_lock(&inode->i_lock);
2566         }
2567         __d_add(entry, inode);
2568 }
2569 EXPORT_SYMBOL(d_add);
2570 
2571 /**
2572  * d_exact_alias - find and hash an exact unhashed alias
2573  * @entry: dentry to add
2574  * @inode: The inode to go with this dentry
2575  *
2576  * If an unhashed dentry with the same name/parent and desired
2577  * inode already exists, hash and return it.  Otherwise, return
2578  * NULL.
2579  *
2580  * Parent directory should be locked.
2581  */
2582 struct dentry *d_exact_alias(struct dentry *entry, struct inode *inode)
2583 {
2584         struct dentry *alias;
2585         unsigned int hash = entry->d_name.hash;
2586 
2587         spin_lock(&inode->i_lock);
2588         hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
2589                 /*
2590                  * Don't need alias->d_lock here, because aliases with
2591                  * d_parent == entry->d_parent are not subject to name or
2592                  * parent changes, because the parent inode i_mutex is held.
2593                  */
2594                 if (alias->d_name.hash != hash)
2595                         continue;
2596                 if (alias->d_parent != entry->d_parent)
2597                         continue;
2598                 if (!d_same_name(alias, entry->d_parent, &entry->d_name))
2599                         continue;
2600                 spin_lock(&alias->d_lock);
2601                 if (!d_unhashed(alias)) {
2602                         spin_unlock(&alias->d_lock);
2603                         alias = NULL;
2604                 } else {
2605                         __dget_dlock(alias);
2606                         __d_rehash(alias);
2607                         spin_unlock(&alias->d_lock);
2608                 }
2609                 spin_unlock(&inode->i_lock);
2610                 return alias;
2611         }
2612         spin_unlock(&inode->i_lock);
2613         return NULL;
2614 }
2615 EXPORT_SYMBOL(d_exact_alias);
2616 
2617 /**
2618  * dentry_update_name_case - update case insensitive dentry with a new name
2619  * @dentry: dentry to be updated
2620  * @name: new name
2621  *
2622  * Update a case insensitive dentry with new case of name.
2623  *
2624  * dentry must have been returned by d_lookup with name @name. Old and new
2625  * name lengths must match (ie. no d_compare which allows mismatched name
2626  * lengths).
2627  *
2628  * Parent inode i_mutex must be held over d_lookup and into this call (to
2629  * keep renames and concurrent inserts, and readdir(2) away).
2630  */
2631 void dentry_update_name_case(struct dentry *dentry, const struct qstr *name)
2632 {
2633         BUG_ON(!inode_is_locked(dentry->d_parent->d_inode));
2634         BUG_ON(dentry->d_name.len != name->len); /* d_lookup gives this */
2635 
2636         spin_lock(&dentry->d_lock);
2637         write_seqcount_begin(&dentry->d_seq);
2638         memcpy((unsigned char *)dentry->d_name.name, name->name, name->len);
2639         write_seqcount_end(&dentry->d_seq);
2640         spin_unlock(&dentry->d_lock);
2641 }
2642 EXPORT_SYMBOL(dentry_update_name_case);
2643 
2644 static void swap_names(struct dentry *dentry, struct dentry *target)
2645 {
2646         if (unlikely(dname_external(target))) {
2647                 if (unlikely(dname_external(dentry))) {
2648                         /*
2649                          * Both external: swap the pointers
2650                          */
2651                         swap(target->d_name.name, dentry->d_name.name);
2652                 } else {
2653                         /*
2654                          * dentry:internal, target:external.  Steal target's
2655                          * storage and make target internal.
2656                          */
2657                         memcpy(target->d_iname, dentry->d_name.name,
2658                                         dentry->d_name.len + 1);
2659                         dentry->d_name.name = target->d_name.name;
2660                         target->d_name.name = target->d_iname;
2661                 }
2662         } else {
2663                 if (unlikely(dname_external(dentry))) {
2664                         /*
2665                          * dentry:external, target:internal.  Give dentry's
2666                          * storage to target and make dentry internal
2667                          */
2668                         memcpy(dentry->d_iname, target->d_name.name,
2669                                         target->d_name.len + 1);
2670                         target->d_name.name = dentry->d_name.name;
2671                         dentry->d_name.name = dentry->d_iname;
2672                 } else {
2673                         /*
2674                          * Both are internal.
2675                          */
2676                         unsigned int i;
2677                         BUILD_BUG_ON(!IS_ALIGNED(DNAME_INLINE_LEN, sizeof(long)));
2678                         kmemcheck_mark_initialized(dentry->d_iname, DNAME_INLINE_LEN);
2679                         kmemcheck_mark_initialized(target->d_iname, DNAME_INLINE_LEN);
2680                         for (i = 0; i < DNAME_INLINE_LEN / sizeof(long); i++) {
2681                                 swap(((long *) &dentry->d_iname)[i],
2682                                      ((long *) &target->d_iname)[i]);
2683                         }
2684                 }
2685         }
2686         swap(dentry->d_name.hash_len, target->d_name.hash_len);
2687 }
2688 
2689 static void copy_name(struct dentry *dentry, struct dentry *target)
2690 {
2691         struct external_name *old_name = NULL;
2692         if (unlikely(dname_external(dentry)))
2693                 old_name = external_name(dentry);
2694         if (unlikely(dname_external(target))) {
2695                 atomic_inc(&external_name(target)->u.count);
2696                 dentry->d_name = target->d_name;
2697         } else {
2698                 memcpy(dentry->d_iname, target->d_name.name,
2699                                 target->d_name.len + 1);
2700                 dentry->d_name.name = dentry->d_iname;
2701                 dentry->d_name.hash_len = target->d_name.hash_len;
2702         }
2703         if (old_name && likely(atomic_dec_and_test(&old_name->u.count)))
2704                 kfree_rcu(old_name, u.head);
2705 }
2706 
2707 static void dentry_lock_for_move(struct dentry *dentry, struct dentry *target)
2708 {
2709         /*
2710          * XXXX: do we really need to take target->d_lock?
2711          */
2712         if (IS_ROOT(dentry) || dentry->d_parent == target->d_parent)
2713                 spin_lock(&target->d_parent->d_lock);
2714         else {
2715                 if (d_ancestor(dentry->d_parent, target->d_parent)) {
2716                         spin_lock(&dentry->d_parent->d_lock);
2717                         spin_lock_nested(&target->d_parent->d_lock,
2718                                                 DENTRY_D_LOCK_NESTED);
2719                 } else {
2720                         spin_lock(&target->d_parent->d_lock);
2721                         spin_lock_nested(&dentry->d_parent->d_lock,
2722                                                 DENTRY_D_LOCK_NESTED);
2723                 }
2724         }
2725         if (target < dentry) {
2726                 spin_lock_nested(&target->d_lock, 2);
2727                 spin_lock_nested(&dentry->d_lock, 3);
2728         } else {
2729                 spin_lock_nested(&dentry->d_lock, 2);
2730                 spin_lock_nested(&target->d_lock, 3);
2731         }
2732 }
2733 
2734 static void dentry_unlock_for_move(struct dentry *dentry, struct dentry *target)
2735 {
2736         if (target->d_parent != dentry->d_parent)
2737                 spin_unlock(&dentry->d_parent->d_lock);
2738         if (target->d_parent != target)
2739                 spin_unlock(&target->d_parent->d_lock);
2740         spin_unlock(&target->d_lock);
2741         spin_unlock(&dentry->d_lock);
2742 }
2743 
2744 /*
2745  * When switching names, the actual string doesn't strictly have to
2746  * be preserved in the target - because we're dropping the target
2747  * anyway. As such, we can just do a simple memcpy() to copy over
2748  * the new name before we switch, unless we are going to rehash
2749  * it.  Note that if we *do* unhash the target, we are not allowed
2750  * to rehash it without giving it a new name/hash key - whether
2751  * we swap or overwrite the names here, resulting name won't match
2752  * the reality in filesystem; it's only there for d_path() purposes.
2753  * Note that all of this is happening under rename_lock, so the
2754  * any hash lookup seeing it in the middle of manipulations will
2755  * be discarded anyway.  So we do not care what happens to the hash
2756  * key in that case.
2757  */
2758 /*
2759  * __d_move - move a dentry
2760  * @dentry: entry to move
2761  * @target: new dentry
2762  * @exchange: exchange the two dentries
2763  *
2764  * Update the dcache to reflect the move of a file name. Negative
2765  * dcache entries should not be moved in this way. Caller must hold
2766  * rename_lock, the i_mutex of the source and target directories,
2767  * and the sb->s_vfs_rename_mutex if they differ. See lock_rename().
2768  */
2769 static void __d_move(struct dentry *dentry, struct dentry *target,
2770                      bool exchange)
2771 {
2772         struct inode *dir = NULL;
2773         unsigned n;
2774         if (!dentry->d_inode)
2775                 printk(KERN_WARNING "VFS: moving negative dcache entry\n");
2776 
2777         BUG_ON(d_ancestor(dentry, target));
2778         BUG_ON(d_ancestor(target, dentry));
2779 
2780         dentry_lock_for_move(dentry, target);
2781         if (unlikely(d_in_lookup(target))) {
2782                 dir = target->d_parent->d_inode;
2783                 n = start_dir_add(dir);
2784                 __d_lookup_done(target);
2785         }
2786 
2787         write_seqcount_begin(&dentry->d_seq);
2788         write_seqcount_begin_nested(&target->d_seq, DENTRY_D_LOCK_NESTED);
2789 
2790         /* unhash both */
2791         /* __d_drop does write_seqcount_barrier, but they're OK to nest. */
2792         __d_drop(dentry);
2793         __d_drop(target);
2794 
2795         /* Switch the names.. */
2796         if (exchange)
2797                 swap_names(dentry, target);
2798         else
2799                 copy_name(dentry, target);
2800 
2801         /* rehash in new place(s) */
2802         __d_rehash(dentry);
2803         if (exchange)
2804                 __d_rehash(target);
2805 
2806         /* ... and switch them in the tree */
2807         if (IS_ROOT(dentry)) {
2808                 /* splicing a tree */
2809                 dentry->d_flags |= DCACHE_RCUACCESS;
2810                 dentry->d_parent = target->d_parent;
2811                 target->d_parent = target;
2812                 list_del_init(&target->d_child);
2813                 list_move(&dentry->d_child, &dentry->d_parent->d_subdirs);
2814         } else {
2815                 /* swapping two dentries */
2816                 swap(dentry->d_parent, target->d_parent);
2817                 list_move(&target->d_child, &target->d_parent->d_subdirs);
2818                 list_move(&dentry->d_child, &dentry->d_parent->d_subdirs);
2819                 if (exchange)
2820                         fsnotify_update_flags(target);
2821                 fsnotify_update_flags(dentry);
2822         }
2823 
2824         write_seqcount_end(&target->d_seq);
2825         write_seqcount_end(&dentry->d_seq);
2826 
2827         if (dir)
2828                 end_dir_add(dir, n);
2829         dentry_unlock_for_move(dentry, target);
2830 }
2831 
2832 /*
2833  * d_move - move a dentry
2834  * @dentry: entry to move
2835  * @target: new dentry
2836  *
2837  * Update the dcache to reflect the move of a file name. Negative
2838  * dcache entries should not be moved in this way. See the locking
2839  * requirements for __d_move.
2840  */
2841 void d_move(struct dentry *dentry, struct dentry *target)
2842 {
2843         write_seqlock(&rename_lock);
2844         __d_move(dentry, target, false);
2845         write_sequnlock(&rename_lock);
2846 }
2847 EXPORT_SYMBOL(d_move);
2848 
2849 /*
2850  * d_exchange - exchange two dentries
2851  * @dentry1: first dentry
2852  * @dentry2: second dentry
2853  */
2854 void d_exchange(struct dentry *dentry1, struct dentry *dentry2)
2855 {
2856         write_seqlock(&rename_lock);
2857 
2858         WARN_ON(!dentry1->d_inode);
2859         WARN_ON(!dentry2->d_inode);
2860         WARN_ON(IS_ROOT(dentry1));
2861         WARN_ON(IS_ROOT(dentry2));
2862 
2863         __d_move(dentry1, dentry2, true);
2864 
2865         write_sequnlock(&rename_lock);
2866 }
2867 
2868 /**
2869  * d_ancestor - search for an ancestor
2870  * @p1: ancestor dentry
2871  * @p2: child dentry
2872  *
2873  * Returns the ancestor dentry of p2 which is a child of p1, if p1 is
2874  * an ancestor of p2, else NULL.
2875  */
2876 struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
2877 {
2878         struct dentry *p;
2879 
2880         for (p = p2; !IS_ROOT(p); p = p->d_parent) {
2881                 if (p->d_parent == p1)
2882                         return p;
2883         }
2884         return NULL;
2885 }
2886 
2887 /*
2888  * This helper attempts to cope with remotely renamed directories
2889  *
2890  * It assumes that the caller is already holding
2891  * dentry->d_parent->d_inode->i_mutex, and rename_lock
2892  *
2893  * Note: If ever the locking in lock_rename() changes, then please
2894  * remember to update this too...
2895  */
2896 static int __d_unalias(struct inode *inode,
2897                 struct dentry *dentry, struct dentry *alias)
2898 {
2899         struct mutex *m1 = NULL;
2900         struct rw_semaphore *m2 = NULL;
2901         int ret = -ESTALE;
2902 
2903         /* If alias and dentry share a parent, then no extra locks required */
2904         if (alias->d_parent == dentry->d_parent)
2905                 goto out_unalias;
2906 
2907         /* See lock_rename() */
2908         if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
2909                 goto out_err;
2910         m1 = &dentry->d_sb->s_vfs_rename_mutex;
2911         if (!inode_trylock_shared(alias->d_parent->d_inode))
2912                 goto out_err;
2913         m2 = &alias->d_parent->d_inode->i_rwsem;
2914 out_unalias:
2915         __d_move(alias, dentry, false);
2916         ret = 0;
2917 out_err:
2918         if (m2)
2919                 up_read(m2);
2920         if (m1)
2921                 mutex_unlock(m1);
2922         return ret;
2923 }
2924 
2925 /**
2926  * d_splice_alias - splice a disconnected dentry into the tree if one exists
2927  * @inode:  the inode which may have a disconnected dentry
2928  * @dentry: a negative dentry which we want to point to the inode.
2929  *
2930  * If inode is a directory and has an IS_ROOT alias, then d_move that in
2931  * place of the given dentry and return it, else simply d_add the inode
2932  * to the dentry and return NULL.
2933  *
2934  * If a non-IS_ROOT directory is found, the filesystem is corrupt, and
2935  * we should error out: directories can't have multiple aliases.
2936  *
2937  * This is needed in the lookup routine of any filesystem that is exportable
2938  * (via knfsd) so that we can build dcache paths to directories effectively.
2939  *
2940  * If a dentry was found and moved, then it is returned.  Otherwise NULL
2941  * is returned.  This matches the expected return value of ->lookup.
2942  *
2943  * Cluster filesystems may call this function with a negative, hashed dentry.
2944  * In that case, we know that the inode will be a regular file, and also this
2945  * will only occur during atomic_open. So we need to check for the dentry
2946  * being already hashed only in the final case.
2947  */
2948 struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
2949 {
2950         if (IS_ERR(inode))
2951                 return ERR_CAST(inode);
2952 
2953         BUG_ON(!d_unhashed(dentry));
2954 
2955         if (!inode)
2956                 goto out;
2957 
2958         security_d_instantiate(dentry, inode);
2959         spin_lock(&inode->i_lock);
2960         if (S_ISDIR(inode->i_mode)) {
2961                 struct dentry *new = __d_find_any_alias(inode);
2962                 if (unlikely(new)) {
2963                         /* The reference to new ensures it remains an alias */
2964                         spin_unlock(&inode->i_lock);
2965                         write_seqlock(&rename_lock);
2966                         if (unlikely(d_ancestor(new, dentry))) {
2967                                 write_sequnlock(&rename_lock);
2968                                 dput(new);
2969                                 new = ERR_PTR(-ELOOP);
2970                                 pr_warn_ratelimited(
2971                                         "VFS: Lookup of '%s' in %s %s"
2972                                         " would have caused loop\n",
2973                                         dentry->d_name.name,
2974                                         inode->i_sb->s_type->name,
2975                                         inode->i_sb->s_id);
2976                         } else if (!IS_ROOT(new)) {
2977                                 int err = __d_unalias(inode, dentry, new);
2978                                 write_sequnlock(&rename_lock);
2979                                 if (err) {
2980                                         dput(new);
2981                                         new = ERR_PTR(err);
2982                                 }
2983                         } else {
2984                                 __d_move(new, dentry, false);
2985                                 write_sequnlock(&rename_lock);
2986                         }
2987                         iput(inode);
2988                         return new;
2989                 }
2990         }
2991 out:
2992         __d_add(dentry, inode);
2993         return NULL;
2994 }
2995 EXPORT_SYMBOL(d_splice_alias);
2996 
2997 static int prepend(char **buffer, int *buflen, const char *str, int namelen)
2998 {
2999         *buflen -= namelen;
3000         if (*buflen < 0)
3001                 return -ENAMETOOLONG;
3002         *buffer -= namelen;
3003         memcpy(*buffer, str, namelen);
3004         return 0;
3005 }
3006 
3007 /**
3008  * prepend_name - prepend a pathname in front of current buffer pointer
3009  * @buffer: buffer pointer
3010  * @buflen: allocated length of the buffer
3011  * @name:   name string and length qstr structure
3012  *
3013  * With RCU path tracing, it may race with d_move(). Use ACCESS_ONCE() to
3014  * make sure that either the old or the new name pointer and length are
3015  * fetched. However, there may be mismatch between length and pointer.
3016  * The length cannot be trusted, we need to copy it byte-by-byte until
3017  * the length is reached or a null byte is found. It also prepends "/" at
3018  * the beginning of the name. The sequence number check at the caller will
3019  * retry it again when a d_move() does happen. So any garbage in the buffer
3020  * due to mismatched pointer and length will be discarded.
3021  *
3022  * Data dependency barrier is needed to make sure that we see that terminating
3023  * NUL.  Alpha strikes again, film at 11...
3024  */
3025 static int prepend_name(char **buffer, int *buflen, const struct qstr *name)
3026 {
3027         const char *dname = ACCESS_ONCE(name->name);
3028         u32 dlen = ACCESS_ONCE(name->len);
3029         char *p;
3030 
3031         smp_read_barrier_depends();
3032 
3033         *buflen -= dlen + 1;
3034         if (*buflen < 0)
3035                 return -ENAMETOOLONG;
3036         p = *buffer -= dlen + 1;
3037         *p++ = '/';
3038         while (dlen--) {
3039                 char c = *dname++;
3040                 if (!c)
3041                         break;
3042                 *p++ = c;
3043         }
3044         return 0;
3045 }
3046 
3047 /**
3048  * prepend_path - Prepend path string to a buffer
3049  * @path: the dentry/vfsmount to report
3050  * @root: root vfsmnt/dentry
3051  * @buffer: pointer to the end of the buffer
3052  * @buflen: pointer to buffer length
3053  *
3054  * The function will first try to write out the pathname without taking any
3055  * lock other than the RCU read lock to make sure that dentries won't go away.
3056  * It only checks the sequence number of the global rename_lock as any change
3057  * in the dentry's d_seq will be preceded by changes in the rename_lock
3058  * sequence number. If the sequence number had been changed, it will restart
3059  * the whole pathname back-tracing sequence again by taking the rename_lock.
3060  * In this case, there is no need to take the RCU read lock as the recursive
3061  * parent pointer references will keep the dentry chain alive as long as no
3062  * rename operation is performed.
3063  */
3064 static int prepend_path(const struct path *path,
3065                         const struct path *root,
3066                         char **buffer, int *buflen)
3067 {
3068         struct dentry *dentry;
3069         struct vfsmount *vfsmnt;
3070         struct mount *mnt;
3071         int error = 0;
3072         unsigned seq, m_seq = 0;
3073         char *bptr;
3074         int blen;
3075 
3076         rcu_read_lock();
3077 restart_mnt:
3078         read_seqbegin_or_lock(&mount_lock, &m_seq);
3079         seq = 0;
3080         rcu_read_lock();
3081 restart:
3082         bptr = *buffer;
3083         blen = *buflen;
3084         error = 0;
3085         dentry = path->dentry;
3086         vfsmnt = path->mnt;
3087         mnt = real_mount(vfsmnt);
3088         read_seqbegin_or_lock(&rename_lock, &seq);
3089         while (dentry != root->dentry || vfsmnt != root->mnt) {
3090                 struct dentry * parent;
3091 
3092                 if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
3093                         struct mount *parent = ACCESS_ONCE(mnt->mnt_parent);
3094                         /* Escaped? */
3095                         if (dentry != vfsmnt->mnt_root) {
3096                                 bptr = *buffer;
3097                                 blen = *buflen;
3098                                 error = 3;
3099                                 break;
3100                         }
3101                         /* Global root? */
3102                         if (mnt != parent) {
3103                                 dentry = ACCESS_ONCE(mnt->mnt_mountpoint);
3104                                 mnt = parent;
3105                                 vfsmnt = &mnt->mnt;
3106                                 continue;
3107                         }
3108                         if (!error)
3109                                 error = is_mounted(vfsmnt) ? 1 : 2;
3110                         break;
3111                 }
3112                 parent = dentry->d_parent;
3113                 prefetch(parent);
3114                 error = prepend_name(&bptr, &blen, &dentry->d_name);
3115                 if (error)
3116                         break;
3117 
3118                 dentry = parent;
3119         }
3120         if (!(seq & 1))
3121                 rcu_read_unlock();
3122         if (need_seqretry(&rename_lock, seq)) {
3123                 seq = 1;
3124                 goto restart;
3125         }
3126         done_seqretry(&rename_lock, seq);
3127 
3128         if (!(m_seq & 1))
3129                 rcu_read_unlock();
3130         if (need_seqretry(&mount_lock, m_seq)) {
3131                 m_seq = 1;
3132                 goto restart_mnt;
3133         }
3134         done_seqretry(&mount_lock, m_seq);
3135 
3136         if (error >= 0 && bptr == *buffer) {
3137                 if (--blen < 0)
3138                         error = -ENAMETOOLONG;
3139                 else
3140                         *--bptr = '/';
3141         }
3142         *buffer = bptr;
3143         *buflen = blen;
3144         return error;
3145 }
3146 
3147 /**
3148  * __d_path - return the path of a dentry
3149  * @path: the dentry/vfsmount to report
3150  * @root: root vfsmnt/dentry
3151  * @buf: buffer to return value in
3152  * @buflen: buffer length
3153  *
3154  * Convert a dentry into an ASCII path name.
3155  *
3156  * Returns a pointer into the buffer or an error code if the
3157  * path was too long.
3158  *
3159  * "buflen" should be positive.
3160  *
3161  * If the path is not reachable from the supplied root, return %NULL.
3162  */
3163 char *__d_path(const struct path *path,
3164                const struct path *root,
3165                char *buf, int buflen)
3166 {
3167         char *res = buf + buflen;
3168         int error;
3169 
3170         prepend(&res, &buflen, "\0", 1);
3171         error = prepend_path(path, root, &res, &buflen);
3172 
3173         if (error < 0)
3174                 return ERR_PTR(error);
3175         if (error > 0)
3176                 return NULL;
3177         return res;
3178 }
3179 
3180 char *d_absolute_path(const struct path *path,
3181                char *buf, int buflen)
3182 {
3183         struct path root = {};
3184         char *res = buf + buflen;
3185         int error;
3186 
3187         prepend(&res, &buflen, "\0", 1);
3188         error = prepend_path(path, &root, &res, &buflen);
3189 
3190         if (error > 1)
3191                 error = -EINVAL;
3192         if (error < 0)
3193                 return ERR_PTR(error);
3194         return res;
3195 }
3196 
3197 /*
3198  * same as __d_path but appends "(deleted)" for unlinked files.
3199  */
3200 static int path_with_deleted(const struct path *path,
3201                              const struct path *root,
3202                              char **buf, int *buflen)
3203 {
3204         prepend(buf, buflen, "\0", 1);
3205         if (d_unlinked(path->dentry)) {
3206                 int error = prepend(buf, buflen, " (deleted)", 10);
3207                 if (error)
3208                         return error;
3209         }
3210 
3211         return prepend_path(path, root, buf, buflen);
3212 }
3213 
3214 static int prepend_unreachable(char **buffer, int *buflen)
3215 {
3216         return prepend(buffer, buflen, "(unreachable)", 13);
3217 }
3218 
3219 static void get_fs_root_rcu(struct fs_struct *fs, struct path *root)
3220 {
3221         unsigned seq;
3222 
3223         do {
3224                 seq = read_seqcount_begin(&fs->seq);
3225                 *root = fs->root;
3226         } while (read_seqcount_retry(&fs->seq, seq));
3227 }
3228 
3229 /**
3230  * d_path - return the path of a dentry
3231  * @path: path to report
3232  * @buf: buffer to return value in
3233  * @buflen: buffer length
3234  *
3235  * Convert a dentry into an ASCII path name. If the entry has been deleted
3236  * the string " (deleted)" is appended. Note that this is ambiguous.
3237  *
3238  * Returns a pointer into the buffer or an error code if the path was
3239  * too long. Note: Callers should use the returned pointer, not the passed
3240  * in buffer, to use the name! The implementation often starts at an offset
3241  * into the buffer, and may leave 0 bytes at the start.
3242  *
3243  * "buflen" should be positive.
3244  */
3245 char *d_path(const struct path *path, char *buf, int buflen)
3246 {
3247         char *res = buf + buflen;
3248         struct path root;
3249         int error;
3250 
3251         /*
3252          * We have various synthetic filesystems that never get mounted.  On
3253          * these filesystems dentries are never used for lookup purposes, and
3254          * thus don't need to be hashed.  They also don't need a name until a
3255          * user wants to identify the object in /proc/pid/fd/.  The little hack
3256          * below allows us to generate a name for these objects on demand:
3257          *
3258          * Some pseudo inodes are mountable.  When they are mounted
3259          * path->dentry == path->mnt->mnt_root.  In that case don't call d_dname
3260          * and instead have d_path return the mounted path.
3261          */
3262         if (path->dentry->d_op && path->dentry->d_op->d_dname &&
3263             (!IS_ROOT(path->dentry) || path->dentry != path->mnt->mnt_root))
3264                 return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
3265 
3266         rcu_read_lock();
3267         get_fs_root_rcu(current->fs, &root);
3268         error = path_with_deleted(path, &root, &res, &buflen);
3269         rcu_read_unlock();
3270 
3271         if (error < 0)
3272                 res = ERR_PTR(error);
3273         return res;
3274 }
3275 EXPORT_SYMBOL(d_path);
3276 
3277 /*
3278  * Helper function for dentry_operations.d_dname() members
3279  */
3280 char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,
3281                         const char *fmt, ...)
3282 {
3283         va_list args;
3284         char temp[64];
3285         int sz;
3286 
3287         va_start(args, fmt);
3288         sz = vsnprintf(temp, sizeof(temp), fmt, args) + 1;
3289         va_end(args);
3290 
3291         if (sz > sizeof(temp) || sz > buflen)
3292                 return ERR_PTR(-ENAMETOOLONG);
3293 
3294         buffer += buflen - sz;
3295         return memcpy(buffer, temp, sz);
3296 }
3297 
3298 char *simple_dname(struct dentry *dentry, char *buffer, int buflen)
3299 {
3300         char *end = buffer + buflen;
3301         /* these dentries are never renamed, so d_lock is not needed */
3302         if (prepend(&end, &buflen, " (deleted)", 11) ||
3303             prepend(&end, &buflen, dentry->d_name.name, dentry->d_name.len) ||
3304             prepend(&end, &buflen, "/", 1))  
3305                 end = ERR_PTR(-ENAMETOOLONG);
3306         return end;
3307 }
3308 EXPORT_SYMBOL(simple_dname);
3309 
3310 /*
3311  * Write full pathname from the root of the filesystem into the buffer.
3312  */
3313 static char *__dentry_path(struct dentry *d, char *buf, int buflen)
3314 {
3315         struct dentry *dentry;
3316         char *end, *retval;
3317         int len, seq = 0;
3318         int error = 0;
3319 
3320         if (buflen < 2)
3321                 goto Elong;
3322 
3323         rcu_read_lock();
3324 restart:
3325         dentry = d;
3326         end = buf + buflen;
3327         len = buflen;
3328         prepend(&end, &len, "\0", 1);
3329         /* Get '/' right */
3330         retval = end-1;
3331         *retval = '/';
3332         read_seqbegin_or_lock(&rename_lock, &seq);
3333         while (!IS_ROOT(dentry)) {
3334                 struct dentry *parent = dentry->d_parent;
3335 
3336                 prefetch(parent);
3337                 error = prepend_name(&end, &len, &dentry->d_name);
3338                 if (error)
3339                         break;
3340 
3341                 retval = end;
3342                 dentry = parent;
3343         }
3344         if (!(seq & 1))
3345                 rcu_read_unlock();
3346         if (need_seqretry(&rename_lock, seq)) {
3347                 seq = 1;
3348                 goto restart;
3349         }
3350         done_seqretry(&rename_lock, seq);
3351         if (error)
3352                 goto Elong;
3353         return retval;
3354 Elong:
3355         return ERR_PTR(-ENAMETOOLONG);
3356 }
3357 
3358 char *dentry_path_raw(struct dentry *dentry, char *buf, int buflen)
3359 {
3360         return __dentry_path(dentry, buf, buflen);
3361 }
3362 EXPORT_SYMBOL(dentry_path_raw);
3363 
3364 char *dentry_path(struct dentry *dentry, char *buf, int buflen)
3365 {
3366         char *p = NULL;
3367         char *retval;
3368 
3369         if (d_unlinked(dentry)) {
3370                 p = buf + buflen;
3371                 if (prepend(&p, &buflen, "//deleted", 10) != 0)
3372                         goto Elong;
3373                 buflen++;
3374         }
3375         retval = __dentry_path(dentry, buf, buflen);
3376         if (!IS_ERR(retval) && p)
3377                 *p = '/';       /* restore '/' overriden with '\0' */
3378         return retval;
3379 Elong:
3380         return ERR_PTR(-ENAMETOOLONG);
3381 }
3382 
3383 static void get_fs_root_and_pwd_rcu(struct fs_struct *fs, struct path *root,
3384                                     struct path *pwd)
3385 {
3386         unsigned seq;
3387 
3388         do {
3389                 seq = read_seqcount_begin(&fs->seq);
3390                 *root = fs->root;
3391                 *pwd = fs->pwd;
3392         } while (read_seqcount_retry(&fs->seq, seq));
3393 }
3394 
3395 /*
3396  * NOTE! The user-level library version returns a
3397  * character pointer. The kernel system call just
3398  * returns the length of the buffer filled (which
3399  * includes the ending '\0' character), or a negative
3400  * error value. So libc would do something like
3401  *
3402  *      char *getcwd(char * buf, size_t size)
3403  *      {
3404  *              int retval;
3405  *
3406  *              retval = sys_getcwd(buf, size);
3407  *              if (retval >= 0)
3408  *                      return buf;
3409  *              errno = -retval;
3410  *              return NULL;
3411  *      }
3412  */
3413 SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
3414 {
3415         int error;
3416         struct path pwd, root;
3417         char *page = __getname();
3418 
3419         if (!page)
3420                 return -ENOMEM;
3421 
3422         rcu_read_lock();
3423         get_fs_root_and_pwd_rcu(current->fs, &root, &pwd);
3424 
3425         error = -ENOENT;
3426         if (!d_unlinked(pwd.dentry)) {
3427                 unsigned long len;
3428                 char *cwd = page + PATH_MAX;
3429                 int buflen = PATH_MAX;
3430 
3431                 prepend(&cwd, &buflen, "\0", 1);
3432                 error = prepend_path(&pwd, &root, &cwd, &buflen);
3433                 rcu_read_unlock();
3434 
3435                 if (error < 0)
3436                         goto out;
3437 
3438                 /* Unreachable from current root */
3439                 if (error > 0) {
3440                         error = prepend_unreachable(&cwd, &buflen);
3441                         if (error)
3442                                 goto out;
3443                 }
3444 
3445                 error = -ERANGE;
3446                 len = PATH_MAX + page - cwd;
3447                 if (len <= size) {
3448                         error = len;
3449                         if (copy_to_user(buf, cwd, len))
3450                                 error = -EFAULT;
3451                 }
3452         } else {
3453                 rcu_read_unlock();
3454         }
3455 
3456 out:
3457         __putname(page);
3458         return error;
3459 }
3460 
3461 /*
3462  * Test whether new_dentry is a subdirectory of old_dentry.
3463  *
3464  * Trivially implemented using the dcache structure
3465  */
3466 
3467 /**
3468  * is_subdir - is new dentry a subdirectory of old_dentry
3469  * @new_dentry: new dentry
3470  * @old_dentry: old dentry
3471  *
3472  * Returns true if new_dentry is a subdirectory of the parent (at any depth).
3473  * Returns false otherwise.
3474  * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
3475  */
3476   
3477 bool is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)
3478 {
3479         bool result;
3480         unsigned seq;
3481 
3482         if (new_dentry == old_dentry)
3483                 return true;
3484 
3485         do {
3486                 /* for restarting inner loop in case of seq retry */
3487                 seq = read_seqbegin(&rename_lock);
3488                 /*
3489                  * Need rcu_readlock to protect against the d_parent trashing
3490                  * due to d_move
3491                  */
3492                 rcu_read_lock();
3493                 if (d_ancestor(old_dentry, new_dentry))
3494                         result = true;
3495                 else
3496                         result = false;
3497                 rcu_read_unlock();
3498         } while (read_seqretry(&rename_lock, seq));
3499 
3500         return result;
3501 }
3502 
3503 static enum d_walk_ret d_genocide_kill(void *data, struct dentry *dentry)
3504 {
3505         struct dentry *root = data;
3506         if (dentry != root) {
3507                 if (d_unhashed(dentry) || !dentry->d_inode)
3508                         return D_WALK_SKIP;
3509 
3510                 if (!(dentry->d_flags & DCACHE_GENOCIDE)) {
3511                         dentry->d_flags |= DCACHE_GENOCIDE;
3512                         dentry->d_lockref.count--;
3513                 }
3514         }
3515         return D_WALK_CONTINUE;
3516 }
3517 
3518 void d_genocide(struct dentry *parent)
3519 {
3520         d_walk(parent, parent, d_genocide_kill, NULL);
3521 }
3522 
3523 void d_tmpfile(struct dentry *dentry, struct inode *inode)
3524 {
3525         inode_dec_link_count(inode);
3526         BUG_ON(dentry->d_name.name != dentry->d_iname ||
3527                 !hlist_unhashed(&dentry->d_u.d_alias) ||
3528                 !d_unlinked(dentry));
3529         spin_lock(&dentry->d_parent->d_lock);
3530         spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
3531         dentry->d_name.len = sprintf(dentry->d_iname, "#%llu",
3532                                 (unsigned long long)inode->i_ino);
3533         spin_unlock(&dentry->d_lock);
3534         spin_unlock(&dentry->d_parent->d_lock);
3535         d_instantiate(dentry, inode);
3536 }
3537 EXPORT_SYMBOL(d_tmpfile);
3538 
3539 static __initdata unsigned long dhash_entries;
3540 static int __init set_dhash_entries(char *str)
3541 {
3542         if (!str)
3543                 return 0;
3544         dhash_entries = simple_strtoul(str, &str, 0);
3545         return 1;
3546 }
3547 __setup("dhash_entries=", set_dhash_entries);
3548 
3549 static void __init dcache_init_early(void)
3550 {
3551         unsigned int loop;
3552 
3553         /* If hashes are distributed across NUMA nodes, defer
3554          * hash allocation until vmalloc space is available.
3555          */
3556         if (hashdist)
3557                 return;
3558 
3559         dentry_hashtable =
3560                 alloc_large_system_hash("Dentry cache",
3561                                         sizeof(struct hlist_bl_head),
3562                                         dhash_entries,
3563                                         13,
3564                                         HASH_EARLY,
3565                                         &d_hash_shift,
3566                                         &d_hash_mask,
3567                                         0,
3568                                         0);
3569 
3570         for (loop = 0; loop < (1U << d_hash_shift); loop++)
3571                 INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
3572 }
3573 
3574 static void __init dcache_init(void)
3575 {
3576         unsigned int loop;
3577 
3578         /* 
3579          * A constructor could be added for stable state like the lists,
3580          * but it is probably not worth it because of the cache nature
3581          * of the dcache. 
3582          */
3583         dentry_cache = KMEM_CACHE(dentry,
3584                 SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD|SLAB_ACCOUNT);
3585 
3586         /* Hash may have been set up in dcache_init_early */
3587         if (!hashdist)
3588                 return;
3589 
3590         dentry_hashtable =
3591                 alloc_large_system_hash("Dentry cache",
3592                                         sizeof(struct hlist_bl_head),
3593                                         dhash_entries,
3594                                         13,
3595                                         0,
3596                                         &d_hash_shift,
3597                                         &d_hash_mask,
3598                                         0,
3599                                         0);
3600 
3601         for (loop = 0; loop < (1U << d_hash_shift); loop++)
3602                 INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
3603 }
3604 
3605 /* SLAB cache for __getname() consumers */
3606 struct kmem_cache *names_cachep __read_mostly;
3607 EXPORT_SYMBOL(names_cachep);
3608 
3609 EXPORT_SYMBOL(d_genocide);
3610 
3611 void __init vfs_caches_init_early(void)
3612 {
3613         dcache_init_early();
3614         inode_init_early();
3615 }
3616 
3617 void __init vfs_caches_init(void)
3618 {
3619         names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
3620                         SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
3621 
3622         dcache_init();
3623         inode_init();
3624         files_init();
3625         files_maxfiles_init();
3626         mnt_init();
3627         bdev_cache_init();
3628         chrdev_init();
3629 }
3630 

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