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Linux/fs/dcache.c

  1 /*
  2  * fs/dcache.c
  3  *
  4  * Complete reimplementation
  5  * (C) 1997 Thomas Schoebel-Theuer,
  6  * with heavy changes by Linus Torvalds
  7  */
  8 
  9 /*
 10  * Notes on the allocation strategy:
 11  *
 12  * The dcache is a master of the icache - whenever a dcache entry
 13  * exists, the inode will always exist. "iput()" is done either when
 14  * the dcache entry is deleted or garbage collected.
 15  */
 16 
 17 #include <linux/syscalls.h>
 18 #include <linux/string.h>
 19 #include <linux/mm.h>
 20 #include <linux/fs.h>
 21 #include <linux/fsnotify.h>
 22 #include <linux/slab.h>
 23 #include <linux/init.h>
 24 #include <linux/hash.h>
 25 #include <linux/cache.h>
 26 #include <linux/export.h>
 27 #include <linux/mount.h>
 28 #include <linux/file.h>
 29 #include <asm/uaccess.h>
 30 #include <linux/security.h>
 31 #include <linux/seqlock.h>
 32 #include <linux/swap.h>
 33 #include <linux/bootmem.h>
 34 #include <linux/fs_struct.h>
 35 #include <linux/hardirq.h>
 36 #include <linux/bit_spinlock.h>
 37 #include <linux/rculist_bl.h>
 38 #include <linux/prefetch.h>
 39 #include <linux/ratelimit.h>
 40 #include <linux/list_lru.h>
 41 #include <linux/kasan.h>
 42 
 43 #include "internal.h"
 44 #include "mount.h"
 45 
 46 /*
 47  * Usage:
 48  * dcache->d_inode->i_lock protects:
 49  *   - i_dentry, d_u.d_alias, d_inode of aliases
 50  * dcache_hash_bucket lock protects:
 51  *   - the dcache hash table
 52  * s_anon bl list spinlock protects:
 53  *   - the s_anon list (see __d_drop)
 54  * dentry->d_sb->s_dentry_lru_lock protects:
 55  *   - the dcache lru lists and counters
 56  * d_lock protects:
 57  *   - d_flags
 58  *   - d_name
 59  *   - d_lru
 60  *   - d_count
 61  *   - d_unhashed()
 62  *   - d_parent and d_subdirs
 63  *   - childrens' d_child and d_parent
 64  *   - d_u.d_alias, d_inode
 65  *
 66  * Ordering:
 67  * dentry->d_inode->i_lock
 68  *   dentry->d_lock
 69  *     dentry->d_sb->s_dentry_lru_lock
 70  *     dcache_hash_bucket lock
 71  *     s_anon lock
 72  *
 73  * If there is an ancestor relationship:
 74  * dentry->d_parent->...->d_parent->d_lock
 75  *   ...
 76  *     dentry->d_parent->d_lock
 77  *       dentry->d_lock
 78  *
 79  * If no ancestor relationship:
 80  * if (dentry1 < dentry2)
 81  *   dentry1->d_lock
 82  *     dentry2->d_lock
 83  */
 84 int sysctl_vfs_cache_pressure __read_mostly = 100;
 85 EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
 86 
 87 __cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
 88 
 89 EXPORT_SYMBOL(rename_lock);
 90 
 91 static struct kmem_cache *dentry_cache __read_mostly;
 92 
 93 /*
 94  * This is the single most critical data structure when it comes
 95  * to the dcache: the hashtable for lookups. Somebody should try
 96  * to make this good - I've just made it work.
 97  *
 98  * This hash-function tries to avoid losing too many bits of hash
 99  * information, yet avoid using a prime hash-size or similar.
100  */
101 
102 static unsigned int d_hash_mask __read_mostly;
103 static unsigned int d_hash_shift __read_mostly;
104 
105 static struct hlist_bl_head *dentry_hashtable __read_mostly;
106 
107 static inline struct hlist_bl_head *d_hash(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 /*
1277  * Search for at least 1 mount point in the dentry's subdirs.
1278  * We descend to the next level whenever the d_subdirs
1279  * list is non-empty and continue searching.
1280  */
1281 
1282 static enum d_walk_ret check_mount(void *data, struct dentry *dentry)
1283 {
1284         int *ret = data;
1285         if (d_mountpoint(dentry)) {
1286                 *ret = 1;
1287                 return D_WALK_QUIT;
1288         }
1289         return D_WALK_CONTINUE;
1290 }
1291 
1292 /**
1293  * have_submounts - check for mounts over a dentry
1294  * @parent: dentry to check.
1295  *
1296  * Return true if the parent or its subdirectories contain
1297  * a mount point
1298  */
1299 int have_submounts(struct dentry *parent)
1300 {
1301         int ret = 0;
1302 
1303         d_walk(parent, &ret, check_mount, NULL);
1304 
1305         return ret;
1306 }
1307 EXPORT_SYMBOL(have_submounts);
1308 
1309 /*
1310  * Called by mount code to set a mountpoint and check if the mountpoint is
1311  * reachable (e.g. NFS can unhash a directory dentry and then the complete
1312  * subtree can become unreachable).
1313  *
1314  * Only one of d_invalidate() and d_set_mounted() must succeed.  For
1315  * this reason take rename_lock and d_lock on dentry and ancestors.
1316  */
1317 int d_set_mounted(struct dentry *dentry)
1318 {
1319         struct dentry *p;
1320         int ret = -ENOENT;
1321         write_seqlock(&rename_lock);
1322         for (p = dentry->d_parent; !IS_ROOT(p); p = p->d_parent) {
1323                 /* Need exclusion wrt. d_invalidate() */
1324                 spin_lock(&p->d_lock);
1325                 if (unlikely(d_unhashed(p))) {
1326                         spin_unlock(&p->d_lock);
1327                         goto out;
1328                 }
1329                 spin_unlock(&p->d_lock);
1330         }
1331         spin_lock(&dentry->d_lock);
1332         if (!d_unlinked(dentry)) {
1333                 dentry->d_flags |= DCACHE_MOUNTED;
1334                 ret = 0;
1335         }
1336         spin_unlock(&dentry->d_lock);
1337 out:
1338         write_sequnlock(&rename_lock);
1339         return ret;
1340 }
1341 
1342 /*
1343  * Search the dentry child list of the specified parent,
1344  * and move any unused dentries to the end of the unused
1345  * list for prune_dcache(). We descend to the next level
1346  * whenever the d_subdirs list is non-empty and continue
1347  * searching.
1348  *
1349  * It returns zero iff there are no unused children,
1350  * otherwise  it returns the number of children moved to
1351  * the end of the unused list. This may not be the total
1352  * number of unused children, because select_parent can
1353  * drop the lock and return early due to latency
1354  * constraints.
1355  */
1356 
1357 struct select_data {
1358         struct dentry *start;
1359         struct list_head dispose;
1360         int found;
1361 };
1362 
1363 static enum d_walk_ret select_collect(void *_data, struct dentry *dentry)
1364 {
1365         struct select_data *data = _data;
1366         enum d_walk_ret ret = D_WALK_CONTINUE;
1367 
1368         if (data->start == dentry)
1369                 goto out;
1370 
1371         if (dentry->d_flags & DCACHE_SHRINK_LIST) {
1372                 data->found++;
1373         } else {
1374                 if (dentry->d_flags & DCACHE_LRU_LIST)
1375                         d_lru_del(dentry);
1376                 if (!dentry->d_lockref.count) {
1377                         d_shrink_add(dentry, &data->dispose);
1378                         data->found++;
1379                 }
1380         }
1381         /*
1382          * We can return to the caller if we have found some (this
1383          * ensures forward progress). We'll be coming back to find
1384          * the rest.
1385          */
1386         if (!list_empty(&data->dispose))
1387                 ret = need_resched() ? D_WALK_QUIT : D_WALK_NORETRY;
1388 out:
1389         return ret;
1390 }
1391 
1392 /**
1393  * shrink_dcache_parent - prune dcache
1394  * @parent: parent of entries to prune
1395  *
1396  * Prune the dcache to remove unused children of the parent dentry.
1397  */
1398 void shrink_dcache_parent(struct dentry *parent)
1399 {
1400         for (;;) {
1401                 struct select_data data;
1402 
1403                 INIT_LIST_HEAD(&data.dispose);
1404                 data.start = parent;
1405                 data.found = 0;
1406 
1407                 d_walk(parent, &data, select_collect, NULL);
1408                 if (!data.found)
1409                         break;
1410 
1411                 shrink_dentry_list(&data.dispose);
1412                 cond_resched();
1413         }
1414 }
1415 EXPORT_SYMBOL(shrink_dcache_parent);
1416 
1417 static enum d_walk_ret umount_check(void *_data, struct dentry *dentry)
1418 {
1419         /* it has busy descendents; complain about those instead */
1420         if (!list_empty(&dentry->d_subdirs))
1421                 return D_WALK_CONTINUE;
1422 
1423         /* root with refcount 1 is fine */
1424         if (dentry == _data && dentry->d_lockref.count == 1)
1425                 return D_WALK_CONTINUE;
1426 
1427         printk(KERN_ERR "BUG: Dentry %p{i=%lx,n=%pd} "
1428                         " still in use (%d) [unmount of %s %s]\n",
1429                        dentry,
1430                        dentry->d_inode ?
1431                        dentry->d_inode->i_ino : 0UL,
1432                        dentry,
1433                        dentry->d_lockref.count,
1434                        dentry->d_sb->s_type->name,
1435                        dentry->d_sb->s_id);
1436         WARN_ON(1);
1437         return D_WALK_CONTINUE;
1438 }
1439 
1440 static void do_one_tree(struct dentry *dentry)
1441 {
1442         shrink_dcache_parent(dentry);
1443         d_walk(dentry, dentry, umount_check, NULL);
1444         d_drop(dentry);
1445         dput(dentry);
1446 }
1447 
1448 /*
1449  * destroy the dentries attached to a superblock on unmounting
1450  */
1451 void shrink_dcache_for_umount(struct super_block *sb)
1452 {
1453         struct dentry *dentry;
1454 
1455         WARN(down_read_trylock(&sb->s_umount), "s_umount should've been locked");
1456 
1457         dentry = sb->s_root;
1458         sb->s_root = NULL;
1459         do_one_tree(dentry);
1460 
1461         while (!hlist_bl_empty(&sb->s_anon)) {
1462                 dentry = dget(hlist_bl_entry(hlist_bl_first(&sb->s_anon), struct dentry, d_hash));
1463                 do_one_tree(dentry);
1464         }
1465 }
1466 
1467 struct detach_data {
1468         struct select_data select;
1469         struct dentry *mountpoint;
1470 };
1471 static enum d_walk_ret detach_and_collect(void *_data, struct dentry *dentry)
1472 {
1473         struct detach_data *data = _data;
1474 
1475         if (d_mountpoint(dentry)) {
1476                 __dget_dlock(dentry);
1477                 data->mountpoint = dentry;
1478                 return D_WALK_QUIT;
1479         }
1480 
1481         return select_collect(&data->select, dentry);
1482 }
1483 
1484 static void check_and_drop(void *_data)
1485 {
1486         struct detach_data *data = _data;
1487 
1488         if (!data->mountpoint && !data->select.found)
1489                 __d_drop(data->select.start);
1490 }
1491 
1492 /**
1493  * d_invalidate - detach submounts, prune dcache, and drop
1494  * @dentry: dentry to invalidate (aka detach, prune and drop)
1495  *
1496  * no dcache lock.
1497  *
1498  * The final d_drop is done as an atomic operation relative to
1499  * rename_lock ensuring there are no races with d_set_mounted.  This
1500  * ensures there are no unhashed dentries on the path to a mountpoint.
1501  */
1502 void d_invalidate(struct dentry *dentry)
1503 {
1504         /*
1505          * If it's already been dropped, return OK.
1506          */
1507         spin_lock(&dentry->d_lock);
1508         if (d_unhashed(dentry)) {
1509                 spin_unlock(&dentry->d_lock);
1510                 return;
1511         }
1512         spin_unlock(&dentry->d_lock);
1513 
1514         /* Negative dentries can be dropped without further checks */
1515         if (!dentry->d_inode) {
1516                 d_drop(dentry);
1517                 return;
1518         }
1519 
1520         for (;;) {
1521                 struct detach_data data;
1522 
1523                 data.mountpoint = NULL;
1524                 INIT_LIST_HEAD(&data.select.dispose);
1525                 data.select.start = dentry;
1526                 data.select.found = 0;
1527 
1528                 d_walk(dentry, &data, detach_and_collect, check_and_drop);
1529 
1530                 if (data.select.found)
1531                         shrink_dentry_list(&data.select.dispose);
1532 
1533                 if (data.mountpoint) {
1534                         detach_mounts(data.mountpoint);
1535                         dput(data.mountpoint);
1536                 }
1537 
1538                 if (!data.mountpoint && !data.select.found)
1539                         break;
1540 
1541                 cond_resched();
1542         }
1543 }
1544 EXPORT_SYMBOL(d_invalidate);
1545 
1546 /**
1547  * __d_alloc    -       allocate a dcache entry
1548  * @sb: filesystem it will belong to
1549  * @name: qstr of the name
1550  *
1551  * Allocates a dentry. It returns %NULL if there is insufficient memory
1552  * available. On a success the dentry is returned. The name passed in is
1553  * copied and the copy passed in may be reused after this call.
1554  */
1555  
1556 struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
1557 {
1558         struct dentry *dentry;
1559         char *dname;
1560         int err;
1561 
1562         dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
1563         if (!dentry)
1564                 return NULL;
1565 
1566         /*
1567          * We guarantee that the inline name is always NUL-terminated.
1568          * This way the memcpy() done by the name switching in rename
1569          * will still always have a NUL at the end, even if we might
1570          * be overwriting an internal NUL character
1571          */
1572         dentry->d_iname[DNAME_INLINE_LEN-1] = 0;
1573         if (unlikely(!name)) {
1574                 static const struct qstr anon = QSTR_INIT("/", 1);
1575                 name = &anon;
1576                 dname = dentry->d_iname;
1577         } else if (name->len > DNAME_INLINE_LEN-1) {
1578                 size_t size = offsetof(struct external_name, name[1]);
1579                 struct external_name *p = kmalloc(size + name->len,
1580                                                   GFP_KERNEL_ACCOUNT);
1581                 if (!p) {
1582                         kmem_cache_free(dentry_cache, dentry); 
1583                         return NULL;
1584                 }
1585                 atomic_set(&p->u.count, 1);
1586                 dname = p->name;
1587                 if (IS_ENABLED(CONFIG_DCACHE_WORD_ACCESS))
1588                         kasan_unpoison_shadow(dname,
1589                                 round_up(name->len + 1, sizeof(unsigned long)));
1590         } else  {
1591                 dname = dentry->d_iname;
1592         }       
1593 
1594         dentry->d_name.len = name->len;
1595         dentry->d_name.hash = name->hash;
1596         memcpy(dname, name->name, name->len);
1597         dname[name->len] = 0;
1598 
1599         /* Make sure we always see the terminating NUL character */
1600         smp_wmb();
1601         dentry->d_name.name = dname;
1602 
1603         dentry->d_lockref.count = 1;
1604         dentry->d_flags = 0;
1605         spin_lock_init(&dentry->d_lock);
1606         seqcount_init(&dentry->d_seq);
1607         dentry->d_inode = NULL;
1608         dentry->d_parent = dentry;
1609         dentry->d_sb = sb;
1610         dentry->d_op = NULL;
1611         dentry->d_fsdata = NULL;
1612         INIT_HLIST_BL_NODE(&dentry->d_hash);
1613         INIT_LIST_HEAD(&dentry->d_lru);
1614         INIT_LIST_HEAD(&dentry->d_subdirs);
1615         INIT_HLIST_NODE(&dentry->d_u.d_alias);
1616         INIT_LIST_HEAD(&dentry->d_child);
1617         d_set_d_op(dentry, dentry->d_sb->s_d_op);
1618 
1619         if (dentry->d_op && dentry->d_op->d_init) {
1620                 err = dentry->d_op->d_init(dentry);
1621                 if (err) {
1622                         if (dname_external(dentry))
1623                                 kfree(external_name(dentry));
1624                         kmem_cache_free(dentry_cache, dentry);
1625                         return NULL;
1626                 }
1627         }
1628 
1629         this_cpu_inc(nr_dentry);
1630 
1631         return dentry;
1632 }
1633 
1634 /**
1635  * d_alloc      -       allocate a dcache entry
1636  * @parent: parent of entry to allocate
1637  * @name: qstr of the name
1638  *
1639  * Allocates a dentry. It returns %NULL if there is insufficient memory
1640  * available. On a success the dentry is returned. The name passed in is
1641  * copied and the copy passed in may be reused after this call.
1642  */
1643 struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
1644 {
1645         struct dentry *dentry = __d_alloc(parent->d_sb, name);
1646         if (!dentry)
1647                 return NULL;
1648         dentry->d_flags |= DCACHE_RCUACCESS;
1649         spin_lock(&parent->d_lock);
1650         /*
1651          * don't need child lock because it is not subject
1652          * to concurrency here
1653          */
1654         __dget_dlock(parent);
1655         dentry->d_parent = parent;
1656         list_add(&dentry->d_child, &parent->d_subdirs);
1657         spin_unlock(&parent->d_lock);
1658 
1659         return dentry;
1660 }
1661 EXPORT_SYMBOL(d_alloc);
1662 
1663 struct dentry *d_alloc_cursor(struct dentry * parent)
1664 {
1665         struct dentry *dentry = __d_alloc(parent->d_sb, NULL);
1666         if (dentry) {
1667                 dentry->d_flags |= DCACHE_RCUACCESS | DCACHE_DENTRY_CURSOR;
1668                 dentry->d_parent = dget(parent);
1669         }
1670         return dentry;
1671 }
1672 
1673 /**
1674  * d_alloc_pseudo - allocate a dentry (for lookup-less filesystems)
1675  * @sb: the superblock
1676  * @name: qstr of the name
1677  *
1678  * For a filesystem that just pins its dentries in memory and never
1679  * performs lookups at all, return an unhashed IS_ROOT dentry.
1680  */
1681 struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
1682 {
1683         return __d_alloc(sb, name);
1684 }
1685 EXPORT_SYMBOL(d_alloc_pseudo);
1686 
1687 struct dentry *d_alloc_name(struct dentry *parent, const char *name)
1688 {
1689         struct qstr q;
1690 
1691         q.name = name;
1692         q.hash_len = hashlen_string(parent, name);
1693         return d_alloc(parent, &q);
1694 }
1695 EXPORT_SYMBOL(d_alloc_name);
1696 
1697 void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
1698 {
1699         WARN_ON_ONCE(dentry->d_op);
1700         WARN_ON_ONCE(dentry->d_flags & (DCACHE_OP_HASH  |
1701                                 DCACHE_OP_COMPARE       |
1702                                 DCACHE_OP_REVALIDATE    |
1703                                 DCACHE_OP_WEAK_REVALIDATE       |
1704                                 DCACHE_OP_DELETE        |
1705                                 DCACHE_OP_REAL));
1706         dentry->d_op = op;
1707         if (!op)
1708                 return;
1709         if (op->d_hash)
1710                 dentry->d_flags |= DCACHE_OP_HASH;
1711         if (op->d_compare)
1712                 dentry->d_flags |= DCACHE_OP_COMPARE;
1713         if (op->d_revalidate)
1714                 dentry->d_flags |= DCACHE_OP_REVALIDATE;
1715         if (op->d_weak_revalidate)
1716                 dentry->d_flags |= DCACHE_OP_WEAK_REVALIDATE;
1717         if (op->d_delete)
1718                 dentry->d_flags |= DCACHE_OP_DELETE;
1719         if (op->d_prune)
1720                 dentry->d_flags |= DCACHE_OP_PRUNE;
1721         if (op->d_real)
1722                 dentry->d_flags |= DCACHE_OP_REAL;
1723 
1724 }
1725 EXPORT_SYMBOL(d_set_d_op);
1726 
1727 
1728 /*
1729  * d_set_fallthru - Mark a dentry as falling through to a lower layer
1730  * @dentry - The dentry to mark
1731  *
1732  * Mark a dentry as falling through to the lower layer (as set with
1733  * d_pin_lower()).  This flag may be recorded on the medium.
1734  */
1735 void d_set_fallthru(struct dentry *dentry)
1736 {
1737         spin_lock(&dentry->d_lock);
1738         dentry->d_flags |= DCACHE_FALLTHRU;
1739         spin_unlock(&dentry->d_lock);
1740 }
1741 EXPORT_SYMBOL(d_set_fallthru);
1742 
1743 static unsigned d_flags_for_inode(struct inode *inode)
1744 {
1745         unsigned add_flags = DCACHE_REGULAR_TYPE;
1746 
1747         if (!inode)
1748                 return DCACHE_MISS_TYPE;
1749 
1750         if (S_ISDIR(inode->i_mode)) {
1751                 add_flags = DCACHE_DIRECTORY_TYPE;
1752                 if (unlikely(!(inode->i_opflags & IOP_LOOKUP))) {
1753                         if (unlikely(!inode->i_op->lookup))
1754                                 add_flags = DCACHE_AUTODIR_TYPE;
1755                         else
1756                                 inode->i_opflags |= IOP_LOOKUP;
1757                 }
1758                 goto type_determined;
1759         }
1760 
1761         if (unlikely(!(inode->i_opflags & IOP_NOFOLLOW))) {
1762                 if (unlikely(inode->i_op->get_link)) {
1763                         add_flags = DCACHE_SYMLINK_TYPE;
1764                         goto type_determined;
1765                 }
1766                 inode->i_opflags |= IOP_NOFOLLOW;
1767         }
1768 
1769         if (unlikely(!S_ISREG(inode->i_mode)))
1770                 add_flags = DCACHE_SPECIAL_TYPE;
1771 
1772 type_determined:
1773         if (unlikely(IS_AUTOMOUNT(inode)))
1774                 add_flags |= DCACHE_NEED_AUTOMOUNT;
1775         return add_flags;
1776 }
1777 
1778 static void __d_instantiate(struct dentry *dentry, struct inode *inode)
1779 {
1780         unsigned add_flags = d_flags_for_inode(inode);
1781         WARN_ON(d_in_lookup(dentry));
1782 
1783         spin_lock(&dentry->d_lock);
1784         hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
1785         raw_write_seqcount_begin(&dentry->d_seq);
1786         __d_set_inode_and_type(dentry, inode, add_flags);
1787         raw_write_seqcount_end(&dentry->d_seq);
1788         fsnotify_update_flags(dentry);
1789         spin_unlock(&dentry->d_lock);
1790 }
1791 
1792 /**
1793  * d_instantiate - fill in inode information for a dentry
1794  * @entry: dentry to complete
1795  * @inode: inode to attach to this dentry
1796  *
1797  * Fill in inode information in the entry.
1798  *
1799  * This turns negative dentries into productive full members
1800  * of society.
1801  *
1802  * NOTE! This assumes that the inode count has been incremented
1803  * (or otherwise set) by the caller to indicate that it is now
1804  * in use by the dcache.
1805  */
1806  
1807 void d_instantiate(struct dentry *entry, struct inode * inode)
1808 {
1809         BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
1810         if (inode) {
1811                 security_d_instantiate(entry, inode);
1812                 spin_lock(&inode->i_lock);
1813                 __d_instantiate(entry, inode);
1814                 spin_unlock(&inode->i_lock);
1815         }
1816 }
1817 EXPORT_SYMBOL(d_instantiate);
1818 
1819 /**
1820  * d_instantiate_no_diralias - instantiate a non-aliased dentry
1821  * @entry: dentry to complete
1822  * @inode: inode to attach to this dentry
1823  *
1824  * Fill in inode information in the entry.  If a directory alias is found, then
1825  * return an error (and drop inode).  Together with d_materialise_unique() this
1826  * guarantees that a directory inode may never have more than one alias.
1827  */
1828 int d_instantiate_no_diralias(struct dentry *entry, struct inode *inode)
1829 {
1830         BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
1831 
1832         security_d_instantiate(entry, inode);
1833         spin_lock(&inode->i_lock);
1834         if (S_ISDIR(inode->i_mode) && !hlist_empty(&inode->i_dentry)) {
1835                 spin_unlock(&inode->i_lock);
1836                 iput(inode);
1837                 return -EBUSY;
1838         }
1839         __d_instantiate(entry, inode);
1840         spin_unlock(&inode->i_lock);
1841 
1842         return 0;
1843 }
1844 EXPORT_SYMBOL(d_instantiate_no_diralias);
1845 
1846 struct dentry *d_make_root(struct inode *root_inode)
1847 {
1848         struct dentry *res = NULL;
1849 
1850         if (root_inode) {
1851                 res = __d_alloc(root_inode->i_sb, NULL);
1852                 if (res)
1853                         d_instantiate(res, root_inode);
1854                 else
1855                         iput(root_inode);
1856         }
1857         return res;
1858 }
1859 EXPORT_SYMBOL(d_make_root);
1860 
1861 static struct dentry * __d_find_any_alias(struct inode *inode)
1862 {
1863         struct dentry *alias;
1864 
1865         if (hlist_empty(&inode->i_dentry))
1866                 return NULL;
1867         alias = hlist_entry(inode->i_dentry.first, struct dentry, d_u.d_alias);
1868         __dget(alias);
1869         return alias;
1870 }
1871 
1872 /**
1873  * d_find_any_alias - find any alias for a given inode
1874  * @inode: inode to find an alias for
1875  *
1876  * If any aliases exist for the given inode, take and return a
1877  * reference for one of them.  If no aliases exist, return %NULL.
1878  */
1879 struct dentry *d_find_any_alias(struct inode *inode)
1880 {
1881         struct dentry *de;
1882 
1883         spin_lock(&inode->i_lock);
1884         de = __d_find_any_alias(inode);
1885         spin_unlock(&inode->i_lock);
1886         return de;
1887 }
1888 EXPORT_SYMBOL(d_find_any_alias);
1889 
1890 static struct dentry *__d_obtain_alias(struct inode *inode, int disconnected)
1891 {
1892         struct dentry *tmp;
1893         struct dentry *res;
1894         unsigned add_flags;
1895 
1896         if (!inode)
1897                 return ERR_PTR(-ESTALE);
1898         if (IS_ERR(inode))
1899                 return ERR_CAST(inode);
1900 
1901         res = d_find_any_alias(inode);
1902         if (res)
1903                 goto out_iput;
1904 
1905         tmp = __d_alloc(inode->i_sb, NULL);
1906         if (!tmp) {
1907                 res = ERR_PTR(-ENOMEM);
1908                 goto out_iput;
1909         }
1910 
1911         security_d_instantiate(tmp, inode);
1912         spin_lock(&inode->i_lock);
1913         res = __d_find_any_alias(inode);
1914         if (res) {
1915                 spin_unlock(&inode->i_lock);
1916                 dput(tmp);
1917                 goto out_iput;
1918         }
1919 
1920         /* attach a disconnected dentry */
1921         add_flags = d_flags_for_inode(inode);
1922 
1923         if (disconnected)
1924                 add_flags |= DCACHE_DISCONNECTED;
1925 
1926         spin_lock(&tmp->d_lock);
1927         __d_set_inode_and_type(tmp, inode, add_flags);
1928         hlist_add_head(&tmp->d_u.d_alias, &inode->i_dentry);
1929         hlist_bl_lock(&tmp->d_sb->s_anon);
1930         hlist_bl_add_head(&tmp->d_hash, &tmp->d_sb->s_anon);
1931         hlist_bl_unlock(&tmp->d_sb->s_anon);
1932         spin_unlock(&tmp->d_lock);
1933         spin_unlock(&inode->i_lock);
1934 
1935         return tmp;
1936 
1937  out_iput:
1938         iput(inode);
1939         return res;
1940 }
1941 
1942 /**
1943  * d_obtain_alias - find or allocate a DISCONNECTED dentry for a given inode
1944  * @inode: inode to allocate the dentry for
1945  *
1946  * Obtain a dentry for an inode resulting from NFS filehandle conversion or
1947  * similar open by handle operations.  The returned dentry may be anonymous,
1948  * or may have a full name (if the inode was already in the cache).
1949  *
1950  * When called on a directory inode, we must ensure that the inode only ever
1951  * has one dentry.  If a dentry is found, that is returned instead of
1952  * allocating a new one.
1953  *
1954  * On successful return, the reference to the inode has been transferred
1955  * to the dentry.  In case of an error the reference on the inode is released.
1956  * To make it easier to use in export operations a %NULL or IS_ERR inode may
1957  * be passed in and the error will be propagated to the return value,
1958  * with a %NULL @inode replaced by ERR_PTR(-ESTALE).
1959  */
1960 struct dentry *d_obtain_alias(struct inode *inode)
1961 {
1962         return __d_obtain_alias(inode, 1);
1963 }
1964 EXPORT_SYMBOL(d_obtain_alias);
1965 
1966 /**
1967  * d_obtain_root - find or allocate a dentry for a given inode
1968  * @inode: inode to allocate the dentry for
1969  *
1970  * Obtain an IS_ROOT dentry for the root of a filesystem.
1971  *
1972  * We must ensure that directory inodes only ever have one dentry.  If a
1973  * dentry is found, that is returned instead of allocating a new one.
1974  *
1975  * On successful return, the reference to the inode has been transferred
1976  * to the dentry.  In case of an error the reference on the inode is
1977  * released.  A %NULL or IS_ERR inode may be passed in and will be the
1978  * error will be propagate to the return value, with a %NULL @inode
1979  * replaced by ERR_PTR(-ESTALE).
1980  */
1981 struct dentry *d_obtain_root(struct inode *inode)
1982 {
1983         return __d_obtain_alias(inode, 0);
1984 }
1985 EXPORT_SYMBOL(d_obtain_root);
1986 
1987 /**
1988  * d_add_ci - lookup or allocate new dentry with case-exact name
1989  * @inode:  the inode case-insensitive lookup has found
1990  * @dentry: the negative dentry that was passed to the parent's lookup func
1991  * @name:   the case-exact name to be associated with the returned dentry
1992  *
1993  * This is to avoid filling the dcache with case-insensitive names to the
1994  * same inode, only the actual correct case is stored in the dcache for
1995  * case-insensitive filesystems.
1996  *
1997  * For a case-insensitive lookup match and if the the case-exact dentry
1998  * already exists in in the dcache, use it and return it.
1999  *
2000  * If no entry exists with the exact case name, allocate new dentry with
2001  * the exact case, and return the spliced entry.
2002  */
2003 struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
2004                         struct qstr *name)
2005 {
2006         struct dentry *found, *res;
2007 
2008         /*
2009          * First check if a dentry matching the name already exists,
2010          * if not go ahead and create it now.
2011          */
2012         found = d_hash_and_lookup(dentry->d_parent, name);
2013         if (found) {
2014                 iput(inode);
2015                 return found;
2016         }
2017         if (d_in_lookup(dentry)) {
2018                 found = d_alloc_parallel(dentry->d_parent, name,
2019                                         dentry->d_wait);
2020                 if (IS_ERR(found) || !d_in_lookup(found)) {
2021                         iput(inode);
2022                         return found;
2023                 }
2024         } else {
2025                 found = d_alloc(dentry->d_parent, name);
2026                 if (!found) {
2027                         iput(inode);
2028                         return ERR_PTR(-ENOMEM);
2029                 } 
2030         }
2031         res = d_splice_alias(inode, found);
2032         if (res) {
2033                 dput(found);
2034                 return res;
2035         }
2036         return found;
2037 }
2038 EXPORT_SYMBOL(d_add_ci);
2039 
2040 
2041 static inline bool d_same_name(const struct dentry *dentry,
2042                                 const struct dentry *parent,
2043                                 const struct qstr *name)
2044 {
2045         if (likely(!(parent->d_flags & DCACHE_OP_COMPARE))) {
2046                 if (dentry->d_name.len != name->len)
2047                         return false;
2048                 return dentry_cmp(dentry, name->name, name->len) == 0;
2049         }
2050         return parent->d_op->d_compare(dentry,
2051                                        dentry->d_name.len, dentry->d_name.name,
2052                                        name) == 0;
2053 }
2054 
2055 /**
2056  * __d_lookup_rcu - search for a dentry (racy, store-free)
2057  * @parent: parent dentry
2058  * @name: qstr of name we wish to find
2059  * @seqp: returns d_seq value at the point where the dentry was found
2060  * Returns: dentry, or NULL
2061  *
2062  * __d_lookup_rcu is the dcache lookup function for rcu-walk name
2063  * resolution (store-free path walking) design described in
2064  * Documentation/filesystems/path-lookup.txt.
2065  *
2066  * This is not to be used outside core vfs.
2067  *
2068  * __d_lookup_rcu must only be used in rcu-walk mode, ie. with vfsmount lock
2069  * held, and rcu_read_lock held. The returned dentry must not be stored into
2070  * without taking d_lock and checking d_seq sequence count against @seq
2071  * returned here.
2072  *
2073  * A refcount may be taken on the found dentry with the d_rcu_to_refcount
2074  * function.
2075  *
2076  * Alternatively, __d_lookup_rcu may be called again to look up the child of
2077  * the returned dentry, so long as its parent's seqlock is checked after the
2078  * child is looked up. Thus, an interlocking stepping of sequence lock checks
2079  * is formed, giving integrity down the path walk.
2080  *
2081  * NOTE! The caller *has* to check the resulting dentry against the sequence
2082  * number we've returned before using any of the resulting dentry state!
2083  */
2084 struct dentry *__d_lookup_rcu(const struct dentry *parent,
2085                                 const struct qstr *name,
2086                                 unsigned *seqp)
2087 {
2088         u64 hashlen = name->hash_len;
2089         const unsigned char *str = name->name;
2090         struct hlist_bl_head *b = d_hash(hashlen_hash(hashlen));
2091         struct hlist_bl_node *node;
2092         struct dentry *dentry;
2093 
2094         /*
2095          * Note: There is significant duplication with __d_lookup_rcu which is
2096          * required to prevent single threaded performance regressions
2097          * especially on architectures where smp_rmb (in seqcounts) are costly.
2098          * Keep the two functions in sync.
2099          */
2100 
2101         /*
2102          * The hash list is protected using RCU.
2103          *
2104          * Carefully use d_seq when comparing a candidate dentry, to avoid
2105          * races with d_move().
2106          *
2107          * It is possible that concurrent renames can mess up our list
2108          * walk here and result in missing our dentry, resulting in the
2109          * false-negative result. d_lookup() protects against concurrent
2110          * renames using rename_lock seqlock.
2111          *
2112          * See Documentation/filesystems/path-lookup.txt for more details.
2113          */
2114         hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
2115                 unsigned seq;
2116 
2117 seqretry:
2118                 /*
2119                  * The dentry sequence count protects us from concurrent
2120                  * renames, and thus protects parent and name fields.
2121                  *
2122                  * The caller must perform a seqcount check in order
2123                  * to do anything useful with the returned dentry.
2124                  *
2125                  * NOTE! We do a "raw" seqcount_begin here. That means that
2126                  * we don't wait for the sequence count to stabilize if it
2127                  * is in the middle of a sequence change. If we do the slow
2128                  * dentry compare, we will do seqretries until it is stable,
2129                  * and if we end up with a successful lookup, we actually
2130                  * want to exit RCU lookup anyway.
2131                  *
2132                  * Note that raw_seqcount_begin still *does* smp_rmb(), so
2133                  * we are still guaranteed NUL-termination of ->d_name.name.
2134                  */
2135                 seq = raw_seqcount_begin(&dentry->d_seq);
2136                 if (dentry->d_parent != parent)
2137                         continue;
2138                 if (d_unhashed(dentry))
2139                         continue;
2140 
2141                 if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
2142                         int tlen;
2143                         const char *tname;
2144                         if (dentry->d_name.hash != hashlen_hash(hashlen))
2145                                 continue;
2146                         tlen = dentry->d_name.len;
2147                         tname = dentry->d_name.name;
2148                         /* we want a consistent (name,len) pair */
2149                         if (read_seqcount_retry(&dentry->d_seq, seq)) {
2150                                 cpu_relax();
2151                                 goto seqretry;
2152                         }
2153                         if (parent->d_op->d_compare(dentry,
2154                                                     tlen, tname, name) != 0)
2155                                 continue;
2156                 } else {
2157                         if (dentry->d_name.hash_len != hashlen)
2158                                 continue;
2159                         if (dentry_cmp(dentry, str, hashlen_len(hashlen)) != 0)
2160                                 continue;
2161                 }
2162                 *seqp = seq;
2163                 return dentry;
2164         }
2165         return NULL;
2166 }
2167 
2168 /**
2169  * d_lookup - search for a dentry
2170  * @parent: parent dentry
2171  * @name: qstr of name we wish to find
2172  * Returns: dentry, or NULL
2173  *
2174  * d_lookup searches the children of the parent dentry for the name in
2175  * question. If the dentry is found its reference count is incremented and the
2176  * dentry is returned. The caller must use dput to free the entry when it has
2177  * finished using it. %NULL is returned if the dentry does not exist.
2178  */
2179 struct dentry *d_lookup(const struct dentry *parent, const struct qstr *name)
2180 {
2181         struct dentry *dentry;
2182         unsigned seq;
2183 
2184         do {
2185                 seq = read_seqbegin(&rename_lock);
2186                 dentry = __d_lookup(parent, name);
2187                 if (dentry)
2188                         break;
2189         } while (read_seqretry(&rename_lock, seq));
2190         return dentry;
2191 }
2192 EXPORT_SYMBOL(d_lookup);
2193 
2194 /**
2195  * __d_lookup - search for a dentry (racy)
2196  * @parent: parent dentry
2197  * @name: qstr of name we wish to find
2198  * Returns: dentry, or NULL
2199  *
2200  * __d_lookup is like d_lookup, however it may (rarely) return a
2201  * false-negative result due to unrelated rename activity.
2202  *
2203  * __d_lookup is slightly faster by avoiding rename_lock read seqlock,
2204  * however it must be used carefully, eg. with a following d_lookup in
2205  * the case of failure.
2206  *
2207  * __d_lookup callers must be commented.
2208  */
2209 struct dentry *__d_lookup(const struct dentry *parent, const struct qstr *name)
2210 {
2211         unsigned int hash = name->hash;
2212         struct hlist_bl_head *b = d_hash(hash);
2213         struct hlist_bl_node *node;
2214         struct dentry *found = NULL;
2215         struct dentry *dentry;
2216 
2217         /*
2218          * Note: There is significant duplication with __d_lookup_rcu which is
2219          * required to prevent single threaded performance regressions
2220          * especially on architectures where smp_rmb (in seqcounts) are costly.
2221          * Keep the two functions in sync.
2222          */
2223 
2224         /*
2225          * The hash list is protected using RCU.
2226          *
2227          * Take d_lock when comparing a candidate dentry, to avoid races
2228          * with d_move().
2229          *
2230          * It is possible that concurrent renames can mess up our list
2231          * walk here and result in missing our dentry, resulting in the
2232          * false-negative result. d_lookup() protects against concurrent
2233          * renames using rename_lock seqlock.
2234          *
2235          * See Documentation/filesystems/path-lookup.txt for more details.
2236          */
2237         rcu_read_lock();
2238         
2239         hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
2240 
2241                 if (dentry->d_name.hash != hash)
2242                         continue;
2243 
2244                 spin_lock(&dentry->d_lock);
2245                 if (dentry->d_parent != parent)
2246                         goto next;
2247                 if (d_unhashed(dentry))
2248                         goto next;
2249 
2250                 if (!d_same_name(dentry, parent, name))
2251                         goto next;
2252 
2253                 dentry->d_lockref.count++;
2254                 found = dentry;
2255                 spin_unlock(&dentry->d_lock);
2256                 break;
2257 next:
2258                 spin_unlock(&dentry->d_lock);
2259         }
2260         rcu_read_unlock();
2261 
2262         return found;
2263 }
2264 
2265 /**
2266  * d_hash_and_lookup - hash the qstr then search for a dentry
2267  * @dir: Directory to search in
2268  * @name: qstr of name we wish to find
2269  *
2270  * On lookup failure NULL is returned; on bad name - ERR_PTR(-error)
2271  */
2272 struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
2273 {
2274         /*
2275          * Check for a fs-specific hash function. Note that we must
2276          * calculate the standard hash first, as the d_op->d_hash()
2277          * routine may choose to leave the hash value unchanged.
2278          */
2279         name->hash = full_name_hash(dir, name->name, name->len);
2280         if (dir->d_flags & DCACHE_OP_HASH) {
2281                 int err = dir->d_op->d_hash(dir, name);
2282                 if (unlikely(err < 0))
2283                         return ERR_PTR(err);
2284         }
2285         return d_lookup(dir, name);
2286 }
2287 EXPORT_SYMBOL(d_hash_and_lookup);
2288 
2289 /*
2290  * When a file is deleted, we have two options:
2291  * - turn this dentry into a negative dentry
2292  * - unhash this dentry and free it.
2293  *
2294  * Usually, we want to just turn this into
2295  * a negative dentry, but if anybody else is
2296  * currently using the dentry or the inode
2297  * we can't do that and we fall back on removing
2298  * it from the hash queues and waiting for
2299  * it to be deleted later when it has no users
2300  */
2301  
2302 /**
2303  * d_delete - delete a dentry
2304  * @dentry: The dentry to delete
2305  *
2306  * Turn the dentry into a negative dentry if possible, otherwise
2307  * remove it from the hash queues so it can be deleted later
2308  */
2309  
2310 void d_delete(struct dentry * dentry)
2311 {
2312         struct inode *inode;
2313         int isdir = 0;
2314         /*
2315          * Are we the only user?
2316          */
2317 again:
2318         spin_lock(&dentry->d_lock);
2319         inode = dentry->d_inode;
2320         isdir = S_ISDIR(inode->i_mode);
2321         if (dentry->d_lockref.count == 1) {
2322                 if (!spin_trylock(&inode->i_lock)) {
2323                         spin_unlock(&dentry->d_lock);
2324                         cpu_relax();
2325                         goto again;
2326                 }
2327                 dentry->d_flags &= ~DCACHE_CANT_MOUNT;
2328                 dentry_unlink_inode(dentry);
2329                 fsnotify_nameremove(dentry, isdir);
2330                 return;
2331         }
2332 
2333         if (!d_unhashed(dentry))
2334                 __d_drop(dentry);
2335 
2336         spin_unlock(&dentry->d_lock);
2337 
2338         fsnotify_nameremove(dentry, isdir);
2339 }
2340 EXPORT_SYMBOL(d_delete);
2341 
2342 static void __d_rehash(struct dentry *entry)
2343 {
2344         struct hlist_bl_head *b = d_hash(entry->d_name.hash);
2345         BUG_ON(!d_unhashed(entry));
2346         hlist_bl_lock(b);
2347         hlist_bl_add_head_rcu(&entry->d_hash, b);
2348         hlist_bl_unlock(b);
2349 }
2350 
2351 /**
2352  * d_rehash     - add an entry back to the hash
2353  * @entry: dentry to add to the hash
2354  *
2355  * Adds a dentry to the hash according to its name.
2356  */
2357  
2358 void d_rehash(struct dentry * entry)
2359 {
2360         spin_lock(&entry->d_lock);
2361         __d_rehash(entry);
2362         spin_unlock(&entry->d_lock);
2363 }
2364 EXPORT_SYMBOL(d_rehash);
2365 
2366 static inline unsigned start_dir_add(struct inode *dir)
2367 {
2368 
2369         for (;;) {
2370                 unsigned n = dir->i_dir_seq;
2371                 if (!(n & 1) && cmpxchg(&dir->i_dir_seq, n, n + 1) == n)
2372                         return n;
2373                 cpu_relax();
2374         }
2375 }
2376 
2377 static inline void end_dir_add(struct inode *dir, unsigned n)
2378 {
2379         smp_store_release(&dir->i_dir_seq, n + 2);
2380 }
2381 
2382 static void d_wait_lookup(struct dentry *dentry)
2383 {
2384         if (d_in_lookup(dentry)) {
2385                 DECLARE_WAITQUEUE(wait, current);
2386                 add_wait_queue(dentry->d_wait, &wait);
2387                 do {
2388                         set_current_state(TASK_UNINTERRUPTIBLE);
2389                         spin_unlock(&dentry->d_lock);
2390                         schedule();
2391                         spin_lock(&dentry->d_lock);
2392                 } while (d_in_lookup(dentry));
2393         }
2394 }
2395 
2396 struct dentry *d_alloc_parallel(struct dentry *parent,
2397                                 const struct qstr *name,
2398                                 wait_queue_head_t *wq)
2399 {
2400         unsigned int hash = name->hash;
2401         struct hlist_bl_head *b = in_lookup_hash(parent, hash);
2402         struct hlist_bl_node *node;
2403         struct dentry *new = d_alloc(parent, name);
2404         struct dentry *dentry;
2405         unsigned seq, r_seq, d_seq;
2406 
2407         if (unlikely(!new))
2408                 return ERR_PTR(-ENOMEM);
2409 
2410 retry:
2411         rcu_read_lock();
2412         seq = smp_load_acquire(&parent->d_inode->i_dir_seq) & ~1;
2413         r_seq = read_seqbegin(&rename_lock);
2414         dentry = __d_lookup_rcu(parent, name, &d_seq);
2415         if (unlikely(dentry)) {
2416                 if (!lockref_get_not_dead(&dentry->d_lockref)) {
2417                         rcu_read_unlock();
2418                         goto retry;
2419                 }
2420                 if (read_seqcount_retry(&dentry->d_seq, d_seq)) {
2421                         rcu_read_unlock();
2422                         dput(dentry);
2423                         goto retry;
2424                 }
2425                 rcu_read_unlock();
2426                 dput(new);
2427                 return dentry;
2428         }
2429         if (unlikely(read_seqretry(&rename_lock, r_seq))) {
2430                 rcu_read_unlock();
2431                 goto retry;
2432         }
2433         hlist_bl_lock(b);
2434         if (unlikely(parent->d_inode->i_dir_seq != seq)) {
2435                 hlist_bl_unlock(b);
2436                 rcu_read_unlock();
2437                 goto retry;
2438         }
2439         /*
2440          * No changes for the parent since the beginning of d_lookup().
2441          * Since all removals from the chain happen with hlist_bl_lock(),
2442          * any potential in-lookup matches are going to stay here until
2443          * we unlock the chain.  All fields are stable in everything
2444          * we encounter.
2445          */
2446         hlist_bl_for_each_entry(dentry, node, b, d_u.d_in_lookup_hash) {
2447                 if (dentry->d_name.hash != hash)
2448                         continue;
2449                 if (dentry->d_parent != parent)
2450                         continue;
2451                 if (!d_same_name(dentry, parent, name))
2452                         continue;
2453                 hlist_bl_unlock(b);
2454                 /* now we can try to grab a reference */
2455                 if (!lockref_get_not_dead(&dentry->d_lockref)) {
2456                         rcu_read_unlock();
2457                         goto retry;
2458                 }
2459 
2460                 rcu_read_unlock();
2461                 /*
2462                  * somebody is likely to be still doing lookup for it;
2463                  * wait for them to finish
2464                  */
2465                 spin_lock(&dentry->d_lock);
2466                 d_wait_lookup(dentry);
2467                 /*
2468                  * it's not in-lookup anymore; in principle we should repeat
2469                  * everything from dcache lookup, but it's likely to be what
2470                  * d_lookup() would've found anyway.  If it is, just return it;
2471                  * otherwise we really have to repeat the whole thing.
2472                  */
2473                 if (unlikely(dentry->d_name.hash != hash))
2474                         goto mismatch;
2475                 if (unlikely(dentry->d_parent != parent))
2476                         goto mismatch;
2477                 if (unlikely(d_unhashed(dentry)))
2478                         goto mismatch;
2479                 if (unlikely(!d_same_name(dentry, parent, name)))
2480                         goto mismatch;
2481                 /* OK, it *is* a hashed match; return it */
2482                 spin_unlock(&dentry->d_lock);
2483                 dput(new);
2484                 return dentry;
2485         }
2486         rcu_read_unlock();
2487         /* we can't take ->d_lock here; it's OK, though. */
2488         new->d_flags |= DCACHE_PAR_LOOKUP;
2489         new->d_wait = wq;
2490         hlist_bl_add_head_rcu(&new->d_u.d_in_lookup_hash, b);
2491         hlist_bl_unlock(b);
2492         return new;
2493 mismatch:
2494         spin_unlock(&dentry->d_lock);
2495         dput(dentry);
2496         goto retry;
2497 }
2498 EXPORT_SYMBOL(d_alloc_parallel);
2499 
2500 void __d_lookup_done(struct dentry *dentry)
2501 {
2502         struct hlist_bl_head *b = in_lookup_hash(dentry->d_parent,
2503                                                  dentry->d_name.hash);
2504         hlist_bl_lock(b);
2505         dentry->d_flags &= ~DCACHE_PAR_LOOKUP;
2506         __hlist_bl_del(&dentry->d_u.d_in_lookup_hash);
2507         wake_up_all(dentry->d_wait);
2508         dentry->d_wait = NULL;
2509         hlist_bl_unlock(b);
2510         INIT_HLIST_NODE(&dentry->d_u.d_alias);
2511         INIT_LIST_HEAD(&dentry->d_lru);
2512 }
2513 EXPORT_SYMBOL(__d_lookup_done);
2514 
2515 /* inode->i_lock held if inode is non-NULL */
2516 
2517 static inline void __d_add(struct dentry *dentry, struct inode *inode)
2518 {
2519         struct inode *dir = NULL;
2520         unsigned n;
2521         spin_lock(&dentry->d_lock);
2522         if (unlikely(d_in_lookup(dentry))) {
2523                 dir = dentry->d_parent->d_inode;
2524                 n = start_dir_add(dir);
2525                 __d_lookup_done(dentry);
2526         }
2527         if (inode) {
2528                 unsigned add_flags = d_flags_for_inode(inode);
2529                 hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
2530                 raw_write_seqcount_begin(&dentry->d_seq);
2531                 __d_set_inode_and_type(dentry, inode, add_flags);
2532                 raw_write_seqcount_end(&dentry->d_seq);
2533                 fsnotify_update_flags(dentry);
2534         }
2535         __d_rehash(dentry);
2536         if (dir)
2537                 end_dir_add(dir, n);
2538         spin_unlock(&dentry->d_lock);
2539         if (inode)
2540                 spin_unlock(&inode->i_lock);
2541 }
2542 
2543 /**
2544  * d_add - add dentry to hash queues
2545  * @entry: dentry to add
2546  * @inode: The inode to attach to this dentry
2547  *
2548  * This adds the entry to the hash queues and initializes @inode.
2549  * The entry was actually filled in earlier during d_alloc().
2550  */
2551 
2552 void d_add(struct dentry *entry, struct inode *inode)
2553 {
2554         if (inode) {
2555                 security_d_instantiate(entry, inode);
2556                 spin_lock(&inode->i_lock);
2557         }
2558         __d_add(entry, inode);
2559 }
2560 EXPORT_SYMBOL(d_add);
2561 
2562 /**
2563  * d_exact_alias - find and hash an exact unhashed alias
2564  * @entry: dentry to add
2565  * @inode: The inode to go with this dentry
2566  *
2567  * If an unhashed dentry with the same name/parent and desired
2568  * inode already exists, hash and return it.  Otherwise, return
2569  * NULL.
2570  *
2571  * Parent directory should be locked.
2572  */
2573 struct dentry *d_exact_alias(struct dentry *entry, struct inode *inode)
2574 {
2575         struct dentry *alias;
2576         unsigned int hash = entry->d_name.hash;
2577 
2578         spin_lock(&inode->i_lock);
2579         hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
2580                 /*
2581                  * Don't need alias->d_lock here, because aliases with
2582                  * d_parent == entry->d_parent are not subject to name or
2583                  * parent changes, because the parent inode i_mutex is held.
2584                  */
2585                 if (alias->d_name.hash != hash)
2586                         continue;
2587                 if (alias->d_parent != entry->d_parent)
2588                         continue;
2589                 if (!d_same_name(alias, entry->d_parent, &entry->d_name))
2590                         continue;
2591                 spin_lock(&alias->d_lock);
2592                 if (!d_unhashed(alias)) {
2593                         spin_unlock(&alias->d_lock);
2594                         alias = NULL;
2595                 } else {
2596                         __dget_dlock(alias);
2597                         __d_rehash(alias);
2598                         spin_unlock(&alias->d_lock);
2599                 }
2600                 spin_unlock(&inode->i_lock);
2601                 return alias;
2602         }
2603         spin_unlock(&inode->i_lock);
2604         return NULL;
2605 }
2606 EXPORT_SYMBOL(d_exact_alias);
2607 
2608 /**
2609  * dentry_update_name_case - update case insensitive dentry with a new name
2610  * @dentry: dentry to be updated
2611  * @name: new name
2612  *
2613  * Update a case insensitive dentry with new case of name.
2614  *
2615  * dentry must have been returned by d_lookup with name @name. Old and new
2616  * name lengths must match (ie. no d_compare which allows mismatched name
2617  * lengths).
2618  *
2619  * Parent inode i_mutex must be held over d_lookup and into this call (to
2620  * keep renames and concurrent inserts, and readdir(2) away).
2621  */
2622 void dentry_update_name_case(struct dentry *dentry, const struct qstr *name)
2623 {
2624         BUG_ON(!inode_is_locked(dentry->d_parent->d_inode));
2625         BUG_ON(dentry->d_name.len != name->len); /* d_lookup gives this */
2626 
2627         spin_lock(&dentry->d_lock);
2628         write_seqcount_begin(&dentry->d_seq);
2629         memcpy((unsigned char *)dentry->d_name.name, name->name, name->len);
2630         write_seqcount_end(&dentry->d_seq);
2631         spin_unlock(&dentry->d_lock);
2632 }
2633 EXPORT_SYMBOL(dentry_update_name_case);
2634 
2635 static void swap_names(struct dentry *dentry, struct dentry *target)
2636 {
2637         if (unlikely(dname_external(target))) {
2638                 if (unlikely(dname_external(dentry))) {
2639                         /*
2640                          * Both external: swap the pointers
2641                          */
2642                         swap(target->d_name.name, dentry->d_name.name);
2643                 } else {
2644                         /*
2645                          * dentry:internal, target:external.  Steal target's
2646                          * storage and make target internal.
2647                          */
2648                         memcpy(target->d_iname, dentry->d_name.name,
2649                                         dentry->d_name.len + 1);
2650                         dentry->d_name.name = target->d_name.name;
2651                         target->d_name.name = target->d_iname;
2652                 }
2653         } else {
2654                 if (unlikely(dname_external(dentry))) {
2655                         /*
2656                          * dentry:external, target:internal.  Give dentry's
2657                          * storage to target and make dentry internal
2658                          */
2659                         memcpy(dentry->d_iname, target->d_name.name,
2660                                         target->d_name.len + 1);
2661                         target->d_name.name = dentry->d_name.name;
2662                         dentry->d_name.name = dentry->d_iname;
2663                 } else {
2664                         /*
2665                          * Both are internal.
2666                          */
2667                         unsigned int i;
2668                         BUILD_BUG_ON(!IS_ALIGNED(DNAME_INLINE_LEN, sizeof(long)));
2669                         kmemcheck_mark_initialized(dentry->d_iname, DNAME_INLINE_LEN);
2670                         kmemcheck_mark_initialized(target->d_iname, DNAME_INLINE_LEN);
2671                         for (i = 0; i < DNAME_INLINE_LEN / sizeof(long); i++) {
2672                                 swap(((long *) &dentry->d_iname)[i],
2673                                      ((long *) &target->d_iname)[i]);
2674                         }
2675                 }
2676         }
2677         swap(dentry->d_name.hash_len, target->d_name.hash_len);
2678 }
2679 
2680 static void copy_name(struct dentry *dentry, struct dentry *target)
2681 {
2682         struct external_name *old_name = NULL;
2683         if (unlikely(dname_external(dentry)))
2684                 old_name = external_name(dentry);
2685         if (unlikely(dname_external(target))) {
2686                 atomic_inc(&external_name(target)->u.count);
2687                 dentry->d_name = target->d_name;
2688         } else {
2689                 memcpy(dentry->d_iname, target->d_name.name,
2690                                 target->d_name.len + 1);
2691                 dentry->d_name.name = dentry->d_iname;
2692                 dentry->d_name.hash_len = target->d_name.hash_len;
2693         }
2694         if (old_name && likely(atomic_dec_and_test(&old_name->u.count)))
2695                 kfree_rcu(old_name, u.head);
2696 }
2697 
2698 static void dentry_lock_for_move(struct dentry *dentry, struct dentry *target)
2699 {
2700         /*
2701          * XXXX: do we really need to take target->d_lock?
2702          */
2703         if (IS_ROOT(dentry) || dentry->d_parent == target->d_parent)
2704                 spin_lock(&target->d_parent->d_lock);
2705         else {
2706                 if (d_ancestor(dentry->d_parent, target->d_parent)) {
2707                         spin_lock(&dentry->d_parent->d_lock);
2708                         spin_lock_nested(&target->d_parent->d_lock,
2709                                                 DENTRY_D_LOCK_NESTED);
2710                 } else {
2711                         spin_lock(&target->d_parent->d_lock);
2712                         spin_lock_nested(&dentry->d_parent->d_lock,
2713                                                 DENTRY_D_LOCK_NESTED);
2714                 }
2715         }
2716         if (target < dentry) {
2717                 spin_lock_nested(&target->d_lock, 2);
2718                 spin_lock_nested(&dentry->d_lock, 3);
2719         } else {
2720                 spin_lock_nested(&dentry->d_lock, 2);
2721                 spin_lock_nested(&target->d_lock, 3);
2722         }
2723 }
2724 
2725 static void dentry_unlock_for_move(struct dentry *dentry, struct dentry *target)
2726 {
2727         if (target->d_parent != dentry->d_parent)
2728                 spin_unlock(&dentry->d_parent->d_lock);
2729         if (target->d_parent != target)
2730                 spin_unlock(&target->d_parent->d_lock);
2731         spin_unlock(&target->d_lock);
2732         spin_unlock(&dentry->d_lock);
2733 }
2734 
2735 /*
2736  * When switching names, the actual string doesn't strictly have to
2737  * be preserved in the target - because we're dropping the target
2738  * anyway. As such, we can just do a simple memcpy() to copy over
2739  * the new name before we switch, unless we are going to rehash
2740  * it.  Note that if we *do* unhash the target, we are not allowed
2741  * to rehash it without giving it a new name/hash key - whether
2742  * we swap or overwrite the names here, resulting name won't match
2743  * the reality in filesystem; it's only there for d_path() purposes.
2744  * Note that all of this is happening under rename_lock, so the
2745  * any hash lookup seeing it in the middle of manipulations will
2746  * be discarded anyway.  So we do not care what happens to the hash
2747  * key in that case.
2748  */
2749 /*
2750  * __d_move - move a dentry
2751  * @dentry: entry to move
2752  * @target: new dentry
2753  * @exchange: exchange the two dentries
2754  *
2755  * Update the dcache to reflect the move of a file name. Negative
2756  * dcache entries should not be moved in this way. Caller must hold
2757  * rename_lock, the i_mutex of the source and target directories,
2758  * and the sb->s_vfs_rename_mutex if they differ. See lock_rename().
2759  */
2760 static void __d_move(struct dentry *dentry, struct dentry *target,
2761                      bool exchange)
2762 {
2763         struct inode *dir = NULL;
2764         unsigned n;
2765         if (!dentry->d_inode)
2766                 printk(KERN_WARNING "VFS: moving negative dcache entry\n");
2767 
2768         BUG_ON(d_ancestor(dentry, target));
2769         BUG_ON(d_ancestor(target, dentry));
2770 
2771         dentry_lock_for_move(dentry, target);
2772         if (unlikely(d_in_lookup(target))) {
2773                 dir = target->d_parent->d_inode;
2774                 n = start_dir_add(dir);
2775                 __d_lookup_done(target);
2776         }
2777 
2778         write_seqcount_begin(&dentry->d_seq);
2779         write_seqcount_begin_nested(&target->d_seq, DENTRY_D_LOCK_NESTED);
2780 
2781         /* unhash both */
2782         /* __d_drop does write_seqcount_barrier, but they're OK to nest. */
2783         __d_drop(dentry);
2784         __d_drop(target);
2785 
2786         /* Switch the names.. */
2787         if (exchange)
2788                 swap_names(dentry, target);
2789         else
2790                 copy_name(dentry, target);
2791 
2792         /* rehash in new place(s) */
2793         __d_rehash(dentry);
2794         if (exchange)
2795                 __d_rehash(target);
2796 
2797         /* ... and switch them in the tree */
2798         if (IS_ROOT(dentry)) {
2799                 /* splicing a tree */
2800                 dentry->d_flags |= DCACHE_RCUACCESS;
2801                 dentry->d_parent = target->d_parent;
2802                 target->d_parent = target;
2803                 list_del_init(&target->d_child);
2804                 list_move(&dentry->d_child, &dentry->d_parent->d_subdirs);
2805         } else {
2806                 /* swapping two dentries */
2807                 swap(dentry->d_parent, target->d_parent);
2808                 list_move(&target->d_child, &target->d_parent->d_subdirs);
2809                 list_move(&dentry->d_child, &dentry->d_parent->d_subdirs);
2810                 if (exchange)
2811                         fsnotify_update_flags(target);
2812                 fsnotify_update_flags(dentry);
2813         }
2814 
2815         write_seqcount_end(&target->d_seq);
2816         write_seqcount_end(&dentry->d_seq);
2817 
2818         if (dir)
2819                 end_dir_add(dir, n);
2820         dentry_unlock_for_move(dentry, target);
2821 }
2822 
2823 /*
2824  * d_move - move a dentry
2825  * @dentry: entry to move
2826  * @target: new dentry
2827  *
2828  * Update the dcache to reflect the move of a file name. Negative
2829  * dcache entries should not be moved in this way. See the locking
2830  * requirements for __d_move.
2831  */
2832 void d_move(struct dentry *dentry, struct dentry *target)
2833 {
2834         write_seqlock(&rename_lock);
2835         __d_move(dentry, target, false);
2836         write_sequnlock(&rename_lock);
2837 }
2838 EXPORT_SYMBOL(d_move);
2839 
2840 /*
2841  * d_exchange - exchange two dentries
2842  * @dentry1: first dentry
2843  * @dentry2: second dentry
2844  */
2845 void d_exchange(struct dentry *dentry1, struct dentry *dentry2)
2846 {
2847         write_seqlock(&rename_lock);
2848 
2849         WARN_ON(!dentry1->d_inode);
2850         WARN_ON(!dentry2->d_inode);
2851         WARN_ON(IS_ROOT(dentry1));
2852         WARN_ON(IS_ROOT(dentry2));
2853 
2854         __d_move(dentry1, dentry2, true);
2855 
2856         write_sequnlock(&rename_lock);
2857 }
2858 
2859 /**
2860  * d_ancestor - search for an ancestor
2861  * @p1: ancestor dentry
2862  * @p2: child dentry
2863  *
2864  * Returns the ancestor dentry of p2 which is a child of p1, if p1 is
2865  * an ancestor of p2, else NULL.
2866  */
2867 struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
2868 {
2869         struct dentry *p;
2870 
2871         for (p = p2; !IS_ROOT(p); p = p->d_parent) {
2872                 if (p->d_parent == p1)
2873                         return p;
2874         }
2875         return NULL;
2876 }
2877 
2878 /*
2879  * This helper attempts to cope with remotely renamed directories
2880  *
2881  * It assumes that the caller is already holding
2882  * dentry->d_parent->d_inode->i_mutex, and rename_lock
2883  *
2884  * Note: If ever the locking in lock_rename() changes, then please
2885  * remember to update this too...
2886  */
2887 static int __d_unalias(struct inode *inode,
2888                 struct dentry *dentry, struct dentry *alias)
2889 {
2890         struct mutex *m1 = NULL;
2891         struct rw_semaphore *m2 = NULL;
2892         int ret = -ESTALE;
2893 
2894         /* If alias and dentry share a parent, then no extra locks required */
2895         if (alias->d_parent == dentry->d_parent)
2896                 goto out_unalias;
2897 
2898         /* See lock_rename() */
2899         if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
2900                 goto out_err;
2901         m1 = &dentry->d_sb->s_vfs_rename_mutex;
2902         if (!inode_trylock_shared(alias->d_parent->d_inode))
2903                 goto out_err;
2904         m2 = &alias->d_parent->d_inode->i_rwsem;
2905 out_unalias:
2906         __d_move(alias, dentry, false);
2907         ret = 0;
2908 out_err:
2909         if (m2)
2910                 up_read(m2);
2911         if (m1)
2912                 mutex_unlock(m1);
2913         return ret;
2914 }
2915 
2916 /**
2917  * d_splice_alias - splice a disconnected dentry into the tree if one exists
2918  * @inode:  the inode which may have a disconnected dentry
2919  * @dentry: a negative dentry which we want to point to the inode.
2920  *
2921  * If inode is a directory and has an IS_ROOT alias, then d_move that in
2922  * place of the given dentry and return it, else simply d_add the inode
2923  * to the dentry and return NULL.
2924  *
2925  * If a non-IS_ROOT directory is found, the filesystem is corrupt, and
2926  * we should error out: directories can't have multiple aliases.
2927  *
2928  * This is needed in the lookup routine of any filesystem that is exportable
2929  * (via knfsd) so that we can build dcache paths to directories effectively.
2930  *
2931  * If a dentry was found and moved, then it is returned.  Otherwise NULL
2932  * is returned.  This matches the expected return value of ->lookup.
2933  *
2934  * Cluster filesystems may call this function with a negative, hashed dentry.
2935  * In that case, we know that the inode will be a regular file, and also this
2936  * will only occur during atomic_open. So we need to check for the dentry
2937  * being already hashed only in the final case.
2938  */
2939 struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
2940 {
2941         if (IS_ERR(inode))
2942                 return ERR_CAST(inode);
2943 
2944         BUG_ON(!d_unhashed(dentry));
2945 
2946         if (!inode)
2947                 goto out;
2948 
2949         security_d_instantiate(dentry, inode);
2950         spin_lock(&inode->i_lock);
2951         if (S_ISDIR(inode->i_mode)) {
2952                 struct dentry *new = __d_find_any_alias(inode);
2953                 if (unlikely(new)) {
2954                         /* The reference to new ensures it remains an alias */
2955                         spin_unlock(&inode->i_lock);
2956                         write_seqlock(&rename_lock);
2957                         if (unlikely(d_ancestor(new, dentry))) {
2958                                 write_sequnlock(&rename_lock);
2959                                 dput(new);
2960                                 new = ERR_PTR(-ELOOP);
2961                                 pr_warn_ratelimited(
2962                                         "VFS: Lookup of '%s' in %s %s"
2963                                         " would have caused loop\n",
2964                                         dentry->d_name.name,
2965                                         inode->i_sb->s_type->name,
2966                                         inode->i_sb->s_id);
2967                         } else if (!IS_ROOT(new)) {
2968                                 int err = __d_unalias(inode, dentry, new);
2969                                 write_sequnlock(&rename_lock);
2970                                 if (err) {
2971                                         dput(new);
2972                                         new = ERR_PTR(err);
2973                                 }
2974                         } else {
2975                                 __d_move(new, dentry, false);
2976                                 write_sequnlock(&rename_lock);
2977                         }
2978                         iput(inode);
2979                         return new;
2980                 }
2981         }
2982 out:
2983         __d_add(dentry, inode);
2984         return NULL;
2985 }
2986 EXPORT_SYMBOL(d_splice_alias);
2987 
2988 static int prepend(char **buffer, int *buflen, const char *str, int namelen)
2989 {
2990         *buflen -= namelen;
2991         if (*buflen < 0)
2992                 return -ENAMETOOLONG;
2993         *buffer -= namelen;
2994         memcpy(*buffer, str, namelen);
2995         return 0;
2996 }
2997 
2998 /**
2999  * prepend_name - prepend a pathname in front of current buffer pointer
3000  * @buffer: buffer pointer
3001  * @buflen: allocated length of the buffer
3002  * @name:   name string and length qstr structure
3003  *
3004  * With RCU path tracing, it may race with d_move(). Use ACCESS_ONCE() to
3005  * make sure that either the old or the new name pointer and length are
3006  * fetched. However, there may be mismatch between length and pointer.
3007  * The length cannot be trusted, we need to copy it byte-by-byte until
3008  * the length is reached or a null byte is found. It also prepends "/" at
3009  * the beginning of the name. The sequence number check at the caller will
3010  * retry it again when a d_move() does happen. So any garbage in the buffer
3011  * due to mismatched pointer and length will be discarded.
3012  *
3013  * Data dependency barrier is needed to make sure that we see that terminating
3014  * NUL.  Alpha strikes again, film at 11...
3015  */
3016 static int prepend_name(char **buffer, int *buflen, const struct qstr *name)
3017 {
3018         const char *dname = ACCESS_ONCE(name->name);
3019         u32 dlen = ACCESS_ONCE(name->len);
3020         char *p;
3021 
3022         smp_read_barrier_depends();
3023 
3024         *buflen -= dlen + 1;
3025         if (*buflen < 0)
3026                 return -ENAMETOOLONG;
3027         p = *buffer -= dlen + 1;
3028         *p++ = '/';
3029         while (dlen--) {
3030                 char c = *dname++;
3031                 if (!c)
3032                         break;
3033                 *p++ = c;
3034         }
3035         return 0;
3036 }
3037 
3038 /**
3039  * prepend_path - Prepend path string to a buffer
3040  * @path: the dentry/vfsmount to report
3041  * @root: root vfsmnt/dentry
3042  * @buffer: pointer to the end of the buffer
3043  * @buflen: pointer to buffer length
3044  *
3045  * The function will first try to write out the pathname without taking any
3046  * lock other than the RCU read lock to make sure that dentries won't go away.
3047  * It only checks the sequence number of the global rename_lock as any change
3048  * in the dentry's d_seq will be preceded by changes in the rename_lock
3049  * sequence number. If the sequence number had been changed, it will restart
3050  * the whole pathname back-tracing sequence again by taking the rename_lock.
3051  * In this case, there is no need to take the RCU read lock as the recursive
3052  * parent pointer references will keep the dentry chain alive as long as no
3053  * rename operation is performed.
3054  */
3055 static int prepend_path(const struct path *path,
3056                         const struct path *root,
3057                         char **buffer, int *buflen)
3058 {
3059         struct dentry *dentry;
3060         struct vfsmount *vfsmnt;
3061         struct mount *mnt;
3062         int error = 0;
3063         unsigned seq, m_seq = 0;
3064         char *bptr;
3065         int blen;
3066 
3067         rcu_read_lock();
3068 restart_mnt:
3069         read_seqbegin_or_lock(&mount_lock, &m_seq);
3070         seq = 0;
3071         rcu_read_lock();
3072 restart:
3073         bptr = *buffer;
3074         blen = *buflen;
3075         error = 0;
3076         dentry = path->dentry;
3077         vfsmnt = path->mnt;
3078         mnt = real_mount(vfsmnt);
3079         read_seqbegin_or_lock(&rename_lock, &seq);
3080         while (dentry != root->dentry || vfsmnt != root->mnt) {
3081                 struct dentry * parent;
3082 
3083                 if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
3084                         struct mount *parent = ACCESS_ONCE(mnt->mnt_parent);
3085                         /* Escaped? */
3086                         if (dentry != vfsmnt->mnt_root) {
3087                                 bptr = *buffer;
3088                                 blen = *buflen;
3089                                 error = 3;
3090                                 break;
3091                         }
3092                         /* Global root? */
3093                         if (mnt != parent) {
3094                                 dentry = ACCESS_ONCE(mnt->mnt_mountpoint);
3095                                 mnt = parent;
3096                                 vfsmnt = &mnt->mnt;
3097                                 continue;
3098                         }
3099                         if (!error)
3100                                 error = is_mounted(vfsmnt) ? 1 : 2;
3101                         break;
3102                 }
3103                 parent = dentry->d_parent;
3104                 prefetch(parent);
3105                 error = prepend_name(&bptr, &blen, &dentry->d_name);
3106                 if (error)
3107                         break;
3108 
3109                 dentry = parent;
3110         }
3111         if (!(seq & 1))
3112                 rcu_read_unlock();
3113         if (need_seqretry(&rename_lock, seq)) {
3114                 seq = 1;
3115                 goto restart;
3116         }
3117         done_seqretry(&rename_lock, seq);
3118 
3119         if (!(m_seq & 1))
3120                 rcu_read_unlock();
3121         if (need_seqretry(&mount_lock, m_seq)) {
3122                 m_seq = 1;
3123                 goto restart_mnt;
3124         }
3125         done_seqretry(&mount_lock, m_seq);
3126 
3127         if (error >= 0 && bptr == *buffer) {
3128                 if (--blen < 0)
3129                         error = -ENAMETOOLONG;
3130                 else
3131                         *--bptr = '/';
3132         }
3133         *buffer = bptr;
3134         *buflen = blen;
3135         return error;
3136 }
3137 
3138 /**
3139  * __d_path - return the path of a dentry
3140  * @path: the dentry/vfsmount to report
3141  * @root: root vfsmnt/dentry
3142  * @buf: buffer to return value in
3143  * @buflen: buffer length
3144  *
3145  * Convert a dentry into an ASCII path name.
3146  *
3147  * Returns a pointer into the buffer or an error code if the
3148  * path was too long.
3149  *
3150  * "buflen" should be positive.
3151  *
3152  * If the path is not reachable from the supplied root, return %NULL.
3153  */
3154 char *__d_path(const struct path *path,
3155                const struct path *root,
3156                char *buf, int buflen)
3157 {
3158         char *res = buf + buflen;
3159         int error;
3160 
3161         prepend(&res, &buflen, "\0", 1);
3162         error = prepend_path(path, root, &res, &buflen);
3163 
3164         if (error < 0)
3165                 return ERR_PTR(error);
3166         if (error > 0)
3167                 return NULL;
3168         return res;
3169 }
3170 
3171 char *d_absolute_path(const struct path *path,
3172                char *buf, int buflen)
3173 {
3174         struct path root = {};
3175         char *res = buf + buflen;
3176         int error;
3177 
3178         prepend(&res, &buflen, "\0", 1);
3179         error = prepend_path(path, &root, &res, &buflen);
3180 
3181         if (error > 1)
3182                 error = -EINVAL;
3183         if (error < 0)
3184                 return ERR_PTR(error);
3185         return res;
3186 }
3187 
3188 /*
3189  * same as __d_path but appends "(deleted)" for unlinked files.
3190  */
3191 static int path_with_deleted(const struct path *path,
3192                              const struct path *root,
3193                              char **buf, int *buflen)
3194 {
3195         prepend(buf, buflen, "\0", 1);
3196         if (d_unlinked(path->dentry)) {
3197                 int error = prepend(buf, buflen, " (deleted)", 10);
3198                 if (error)
3199                         return error;
3200         }
3201 
3202         return prepend_path(path, root, buf, buflen);
3203 }
3204 
3205 static int prepend_unreachable(char **buffer, int *buflen)
3206 {
3207         return prepend(buffer, buflen, "(unreachable)", 13);
3208 }
3209 
3210 static void get_fs_root_rcu(struct fs_struct *fs, struct path *root)
3211 {
3212         unsigned seq;
3213 
3214         do {
3215                 seq = read_seqcount_begin(&fs->seq);
3216                 *root = fs->root;
3217         } while (read_seqcount_retry(&fs->seq, seq));
3218 }
3219 
3220 /**
3221  * d_path - return the path of a dentry
3222  * @path: path to report
3223  * @buf: buffer to return value in
3224  * @buflen: buffer length
3225  *
3226  * Convert a dentry into an ASCII path name. If the entry has been deleted
3227  * the string " (deleted)" is appended. Note that this is ambiguous.
3228  *
3229  * Returns a pointer into the buffer or an error code if the path was
3230  * too long. Note: Callers should use the returned pointer, not the passed
3231  * in buffer, to use the name! The implementation often starts at an offset
3232  * into the buffer, and may leave 0 bytes at the start.
3233  *
3234  * "buflen" should be positive.
3235  */
3236 char *d_path(const struct path *path, char *buf, int buflen)
3237 {
3238         char *res = buf + buflen;
3239         struct path root;
3240         int error;
3241 
3242         /*
3243          * We have various synthetic filesystems that never get mounted.  On
3244          * these filesystems dentries are never used for lookup purposes, and
3245          * thus don't need to be hashed.  They also don't need a name until a
3246          * user wants to identify the object in /proc/pid/fd/.  The little hack
3247          * below allows us to generate a name for these objects on demand:
3248          *
3249          * Some pseudo inodes are mountable.  When they are mounted
3250          * path->dentry == path->mnt->mnt_root.  In that case don't call d_dname
3251          * and instead have d_path return the mounted path.
3252          */
3253         if (path->dentry->d_op && path->dentry->d_op->d_dname &&
3254             (!IS_ROOT(path->dentry) || path->dentry != path->mnt->mnt_root))
3255                 return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
3256 
3257         rcu_read_lock();
3258         get_fs_root_rcu(current->fs, &root);
3259         error = path_with_deleted(path, &root, &res, &buflen);
3260         rcu_read_unlock();
3261 
3262         if (error < 0)
3263                 res = ERR_PTR(error);
3264         return res;
3265 }
3266 EXPORT_SYMBOL(d_path);
3267 
3268 /*
3269  * Helper function for dentry_operations.d_dname() members
3270  */
3271 char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,
3272                         const char *fmt, ...)
3273 {
3274         va_list args;
3275         char temp[64];
3276         int sz;
3277 
3278         va_start(args, fmt);
3279         sz = vsnprintf(temp, sizeof(temp), fmt, args) + 1;
3280         va_end(args);
3281 
3282         if (sz > sizeof(temp) || sz > buflen)
3283                 return ERR_PTR(-ENAMETOOLONG);
3284 
3285         buffer += buflen - sz;
3286         return memcpy(buffer, temp, sz);
3287 }
3288 
3289 char *simple_dname(struct dentry *dentry, char *buffer, int buflen)
3290 {
3291         char *end = buffer + buflen;
3292         /* these dentries are never renamed, so d_lock is not needed */
3293         if (prepend(&end, &buflen, " (deleted)", 11) ||
3294             prepend(&end, &buflen, dentry->d_name.name, dentry->d_name.len) ||
3295             prepend(&end, &buflen, "/", 1))  
3296                 end = ERR_PTR(-ENAMETOOLONG);
3297         return end;
3298 }
3299 EXPORT_SYMBOL(simple_dname);
3300 
3301 /*
3302  * Write full pathname from the root of the filesystem into the buffer.
3303  */
3304 static char *__dentry_path(struct dentry *d, char *buf, int buflen)
3305 {
3306         struct dentry *dentry;
3307         char *end, *retval;
3308         int len, seq = 0;
3309         int error = 0;
3310 
3311         if (buflen < 2)
3312                 goto Elong;
3313 
3314         rcu_read_lock();
3315 restart:
3316         dentry = d;
3317         end = buf + buflen;
3318         len = buflen;
3319         prepend(&end, &len, "\0", 1);
3320         /* Get '/' right */
3321         retval = end-1;
3322         *retval = '/';
3323         read_seqbegin_or_lock(&rename_lock, &seq);
3324         while (!IS_ROOT(dentry)) {
3325                 struct dentry *parent = dentry->d_parent;
3326 
3327                 prefetch(parent);
3328                 error = prepend_name(&end, &len, &dentry->d_name);
3329                 if (error)
3330                         break;
3331 
3332                 retval = end;
3333                 dentry = parent;
3334         }
3335         if (!(seq & 1))
3336                 rcu_read_unlock();
3337         if (need_seqretry(&rename_lock, seq)) {
3338                 seq = 1;
3339                 goto restart;
3340         }
3341         done_seqretry(&rename_lock, seq);
3342         if (error)
3343                 goto Elong;
3344         return retval;
3345 Elong:
3346         return ERR_PTR(-ENAMETOOLONG);
3347 }
3348 
3349 char *dentry_path_raw(struct dentry *dentry, char *buf, int buflen)
3350 {
3351         return __dentry_path(dentry, buf, buflen);
3352 }
3353 EXPORT_SYMBOL(dentry_path_raw);
3354 
3355 char *dentry_path(struct dentry *dentry, char *buf, int buflen)
3356 {
3357         char *p = NULL;
3358         char *retval;
3359 
3360         if (d_unlinked(dentry)) {
3361                 p = buf + buflen;
3362                 if (prepend(&p, &buflen, "//deleted", 10) != 0)
3363                         goto Elong;
3364                 buflen++;
3365         }
3366         retval = __dentry_path(dentry, buf, buflen);
3367         if (!IS_ERR(retval) && p)
3368                 *p = '/';       /* restore '/' overriden with '\0' */
3369         return retval;
3370 Elong:
3371         return ERR_PTR(-ENAMETOOLONG);
3372 }
3373 
3374 static void get_fs_root_and_pwd_rcu(struct fs_struct *fs, struct path *root,
3375                                     struct path *pwd)
3376 {
3377         unsigned seq;
3378 
3379         do {
3380                 seq = read_seqcount_begin(&fs->seq);
3381                 *root = fs->root;
3382                 *pwd = fs->pwd;
3383         } while (read_seqcount_retry(&fs->seq, seq));
3384 }
3385 
3386 /*
3387  * NOTE! The user-level library version returns a
3388  * character pointer. The kernel system call just
3389  * returns the length of the buffer filled (which
3390  * includes the ending '\0' character), or a negative
3391  * error value. So libc would do something like
3392  *
3393  *      char *getcwd(char * buf, size_t size)
3394  *      {
3395  *              int retval;
3396  *
3397  *              retval = sys_getcwd(buf, size);
3398  *              if (retval >= 0)
3399  *                      return buf;
3400  *              errno = -retval;
3401  *              return NULL;
3402  *      }
3403  */
3404 SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
3405 {
3406         int error;
3407         struct path pwd, root;
3408         char *page = __getname();
3409 
3410         if (!page)
3411                 return -ENOMEM;
3412 
3413         rcu_read_lock();
3414         get_fs_root_and_pwd_rcu(current->fs, &root, &pwd);
3415 
3416         error = -ENOENT;
3417         if (!d_unlinked(pwd.dentry)) {
3418                 unsigned long len;
3419                 char *cwd = page + PATH_MAX;
3420                 int buflen = PATH_MAX;
3421 
3422                 prepend(&cwd, &buflen, "\0", 1);
3423                 error = prepend_path(&pwd, &root, &cwd, &buflen);
3424                 rcu_read_unlock();
3425 
3426                 if (error < 0)
3427                         goto out;
3428 
3429                 /* Unreachable from current root */
3430                 if (error > 0) {
3431                         error = prepend_unreachable(&cwd, &buflen);
3432                         if (error)
3433                                 goto out;
3434                 }
3435 
3436                 error = -ERANGE;
3437                 len = PATH_MAX + page - cwd;
3438                 if (len <= size) {
3439                         error = len;
3440                         if (copy_to_user(buf, cwd, len))
3441                                 error = -EFAULT;
3442                 }
3443         } else {
3444                 rcu_read_unlock();
3445         }
3446 
3447 out:
3448         __putname(page);
3449         return error;
3450 }
3451 
3452 /*
3453  * Test whether new_dentry is a subdirectory of old_dentry.
3454  *
3455  * Trivially implemented using the dcache structure
3456  */
3457 
3458 /**
3459  * is_subdir - is new dentry a subdirectory of old_dentry
3460  * @new_dentry: new dentry
3461  * @old_dentry: old dentry
3462  *
3463  * Returns true if new_dentry is a subdirectory of the parent (at any depth).
3464  * Returns false otherwise.
3465  * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
3466  */
3467   
3468 bool is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)
3469 {
3470         bool result;
3471         unsigned seq;
3472 
3473         if (new_dentry == old_dentry)
3474                 return true;
3475 
3476         do {
3477                 /* for restarting inner loop in case of seq retry */
3478                 seq = read_seqbegin(&rename_lock);
3479                 /*
3480                  * Need rcu_readlock to protect against the d_parent trashing
3481                  * due to d_move
3482                  */
3483                 rcu_read_lock();
3484                 if (d_ancestor(old_dentry, new_dentry))
3485                         result = true;
3486                 else
3487                         result = false;
3488                 rcu_read_unlock();
3489         } while (read_seqretry(&rename_lock, seq));
3490 
3491         return result;
3492 }
3493 
3494 static enum d_walk_ret d_genocide_kill(void *data, struct dentry *dentry)
3495 {
3496         struct dentry *root = data;
3497         if (dentry != root) {
3498                 if (d_unhashed(dentry) || !dentry->d_inode)
3499                         return D_WALK_SKIP;
3500 
3501                 if (!(dentry->d_flags & DCACHE_GENOCIDE)) {
3502                         dentry->d_flags |= DCACHE_GENOCIDE;
3503                         dentry->d_lockref.count--;
3504                 }
3505         }
3506         return D_WALK_CONTINUE;
3507 }
3508 
3509 void d_genocide(struct dentry *parent)
3510 {
3511         d_walk(parent, parent, d_genocide_kill, NULL);
3512 }
3513 
3514 void d_tmpfile(struct dentry *dentry, struct inode *inode)
3515 {
3516         inode_dec_link_count(inode);
3517         BUG_ON(dentry->d_name.name != dentry->d_iname ||
3518                 !hlist_unhashed(&dentry->d_u.d_alias) ||
3519                 !d_unlinked(dentry));
3520         spin_lock(&dentry->d_parent->d_lock);
3521         spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
3522         dentry->d_name.len = sprintf(dentry->d_iname, "#%llu",
3523                                 (unsigned long long)inode->i_ino);
3524         spin_unlock(&dentry->d_lock);
3525         spin_unlock(&dentry->d_parent->d_lock);
3526         d_instantiate(dentry, inode);
3527 }
3528 EXPORT_SYMBOL(d_tmpfile);
3529 
3530 static __initdata unsigned long dhash_entries;
3531 static int __init set_dhash_entries(char *str)
3532 {
3533         if (!str)
3534                 return 0;
3535         dhash_entries = simple_strtoul(str, &str, 0);
3536         return 1;
3537 }
3538 __setup("dhash_entries=", set_dhash_entries);
3539 
3540 static void __init dcache_init_early(void)
3541 {
3542         unsigned int loop;
3543 
3544         /* If hashes are distributed across NUMA nodes, defer
3545          * hash allocation until vmalloc space is available.
3546          */
3547         if (hashdist)
3548                 return;
3549 
3550         dentry_hashtable =
3551                 alloc_large_system_hash("Dentry cache",
3552                                         sizeof(struct hlist_bl_head),
3553                                         dhash_entries,
3554                                         13,
3555                                         HASH_EARLY,
3556                                         &d_hash_shift,
3557                                         &d_hash_mask,
3558                                         0,
3559                                         0);
3560 
3561         for (loop = 0; loop < (1U << d_hash_shift); loop++)
3562                 INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
3563 }
3564 
3565 static void __init dcache_init(void)
3566 {
3567         unsigned int loop;
3568 
3569         /* 
3570          * A constructor could be added for stable state like the lists,
3571          * but it is probably not worth it because of the cache nature
3572          * of the dcache. 
3573          */
3574         dentry_cache = KMEM_CACHE(dentry,
3575                 SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD|SLAB_ACCOUNT);
3576 
3577         /* Hash may have been set up in dcache_init_early */
3578         if (!hashdist)
3579                 return;
3580 
3581         dentry_hashtable =
3582                 alloc_large_system_hash("Dentry cache",
3583                                         sizeof(struct hlist_bl_head),
3584                                         dhash_entries,
3585                                         13,
3586                                         0,
3587                                         &d_hash_shift,
3588                                         &d_hash_mask,
3589                                         0,
3590                                         0);
3591 
3592         for (loop = 0; loop < (1U << d_hash_shift); loop++)
3593                 INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
3594 }
3595 
3596 /* SLAB cache for __getname() consumers */
3597 struct kmem_cache *names_cachep __read_mostly;
3598 EXPORT_SYMBOL(names_cachep);
3599 
3600 EXPORT_SYMBOL(d_genocide);
3601 
3602 void __init vfs_caches_init_early(void)
3603 {
3604         dcache_init_early();
3605         inode_init_early();
3606 }
3607 
3608 void __init vfs_caches_init(void)
3609 {
3610         names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
3611                         SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
3612 
3613         dcache_init();
3614         inode_init();
3615         files_init();
3616         files_maxfiles_init();
3617         mnt_init();
3618         bdev_cache_init();
3619         chrdev_init();
3620 }
3621 

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