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Linux/fs/dcache.c

  1 /*
  2  * fs/dcache.c
  3  *
  4  * Complete reimplementation
  5  * (C) 1997 Thomas Schoebel-Theuer,
  6  * with heavy changes by Linus Torvalds
  7  */
  8 
  9 /*
 10  * Notes on the allocation strategy:
 11  *
 12  * The dcache is a master of the icache - whenever a dcache entry
 13  * exists, the inode will always exist. "iput()" is done either when
 14  * the dcache entry is deleted or garbage collected.
 15  */
 16 
 17 #include <linux/syscalls.h>
 18 #include <linux/string.h>
 19 #include <linux/mm.h>
 20 #include <linux/fs.h>
 21 #include <linux/fsnotify.h>
 22 #include <linux/slab.h>
 23 #include <linux/init.h>
 24 #include <linux/hash.h>
 25 #include <linux/cache.h>
 26 #include <linux/export.h>
 27 #include <linux/mount.h>
 28 #include <linux/file.h>
 29 #include <asm/uaccess.h>
 30 #include <linux/security.h>
 31 #include <linux/seqlock.h>
 32 #include <linux/swap.h>
 33 #include <linux/bootmem.h>
 34 #include <linux/fs_struct.h>
 35 #include <linux/hardirq.h>
 36 #include <linux/bit_spinlock.h>
 37 #include <linux/rculist_bl.h>
 38 #include <linux/prefetch.h>
 39 #include <linux/ratelimit.h>
 40 #include <linux/list_lru.h>
 41 #include "internal.h"
 42 #include "mount.h"
 43 
 44 /*
 45  * Usage:
 46  * dcache->d_inode->i_lock protects:
 47  *   - i_dentry, d_alias, d_inode of aliases
 48  * dcache_hash_bucket lock protects:
 49  *   - the dcache hash table
 50  * s_anon bl list spinlock protects:
 51  *   - the s_anon list (see __d_drop)
 52  * dentry->d_sb->s_dentry_lru_lock protects:
 53  *   - the dcache lru lists and counters
 54  * d_lock protects:
 55  *   - d_flags
 56  *   - d_name
 57  *   - d_lru
 58  *   - d_count
 59  *   - d_unhashed()
 60  *   - d_parent and d_subdirs
 61  *   - childrens' d_child and d_parent
 62  *   - d_alias, d_inode
 63  *
 64  * Ordering:
 65  * dentry->d_inode->i_lock
 66  *   dentry->d_lock
 67  *     dentry->d_sb->s_dentry_lru_lock
 68  *     dcache_hash_bucket lock
 69  *     s_anon lock
 70  *
 71  * If there is an ancestor relationship:
 72  * dentry->d_parent->...->d_parent->d_lock
 73  *   ...
 74  *     dentry->d_parent->d_lock
 75  *       dentry->d_lock
 76  *
 77  * If no ancestor relationship:
 78  * if (dentry1 < dentry2)
 79  *   dentry1->d_lock
 80  *     dentry2->d_lock
 81  */
 82 int sysctl_vfs_cache_pressure __read_mostly = 100;
 83 EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
 84 
 85 __cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
 86 
 87 EXPORT_SYMBOL(rename_lock);
 88 
 89 static struct kmem_cache *dentry_cache __read_mostly;
 90 
 91 /*
 92  * This is the single most critical data structure when it comes
 93  * to the dcache: the hashtable for lookups. Somebody should try
 94  * to make this good - I've just made it work.
 95  *
 96  * This hash-function tries to avoid losing too many bits of hash
 97  * information, yet avoid using a prime hash-size or similar.
 98  */
 99 
100 static unsigned int d_hash_mask __read_mostly;
101 static unsigned int d_hash_shift __read_mostly;
102 
103 static struct hlist_bl_head *dentry_hashtable __read_mostly;
104 
105 static inline struct hlist_bl_head *d_hash(const struct dentry *parent,
106                                         unsigned int hash)
107 {
108         hash += (unsigned long) parent / L1_CACHE_BYTES;
109         return dentry_hashtable + hash_32(hash, d_hash_shift);
110 }
111 
112 /* Statistics gathering. */
113 struct dentry_stat_t dentry_stat = {
114         .age_limit = 45,
115 };
116 
117 static DEFINE_PER_CPU(long, nr_dentry);
118 static DEFINE_PER_CPU(long, nr_dentry_unused);
119 
120 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
121 
122 /*
123  * Here we resort to our own counters instead of using generic per-cpu counters
124  * for consistency with what the vfs inode code does. We are expected to harvest
125  * better code and performance by having our own specialized counters.
126  *
127  * Please note that the loop is done over all possible CPUs, not over all online
128  * CPUs. The reason for this is that we don't want to play games with CPUs going
129  * on and off. If one of them goes off, we will just keep their counters.
130  *
131  * glommer: See cffbc8a for details, and if you ever intend to change this,
132  * please update all vfs counters to match.
133  */
134 static long get_nr_dentry(void)
135 {
136         int i;
137         long sum = 0;
138         for_each_possible_cpu(i)
139                 sum += per_cpu(nr_dentry, i);
140         return sum < 0 ? 0 : sum;
141 }
142 
143 static long get_nr_dentry_unused(void)
144 {
145         int i;
146         long sum = 0;
147         for_each_possible_cpu(i)
148                 sum += per_cpu(nr_dentry_unused, i);
149         return sum < 0 ? 0 : sum;
150 }
151 
152 int proc_nr_dentry(struct ctl_table *table, int write, void __user *buffer,
153                    size_t *lenp, loff_t *ppos)
154 {
155         dentry_stat.nr_dentry = get_nr_dentry();
156         dentry_stat.nr_unused = get_nr_dentry_unused();
157         return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
158 }
159 #endif
160 
161 /*
162  * Compare 2 name strings, return 0 if they match, otherwise non-zero.
163  * The strings are both count bytes long, and count is non-zero.
164  */
165 #ifdef CONFIG_DCACHE_WORD_ACCESS
166 
167 #include <asm/word-at-a-time.h>
168 /*
169  * NOTE! 'cs' and 'scount' come from a dentry, so it has a
170  * aligned allocation for this particular component. We don't
171  * strictly need the load_unaligned_zeropad() safety, but it
172  * doesn't hurt either.
173  *
174  * In contrast, 'ct' and 'tcount' can be from a pathname, and do
175  * need the careful unaligned handling.
176  */
177 static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
178 {
179         unsigned long a,b,mask;
180 
181         for (;;) {
182                 a = *(unsigned long *)cs;
183                 b = load_unaligned_zeropad(ct);
184                 if (tcount < sizeof(unsigned long))
185                         break;
186                 if (unlikely(a != b))
187                         return 1;
188                 cs += sizeof(unsigned long);
189                 ct += sizeof(unsigned long);
190                 tcount -= sizeof(unsigned long);
191                 if (!tcount)
192                         return 0;
193         }
194         mask = bytemask_from_count(tcount);
195         return unlikely(!!((a ^ b) & mask));
196 }
197 
198 #else
199 
200 static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
201 {
202         do {
203                 if (*cs != *ct)
204                         return 1;
205                 cs++;
206                 ct++;
207                 tcount--;
208         } while (tcount);
209         return 0;
210 }
211 
212 #endif
213 
214 static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
215 {
216         const unsigned char *cs;
217         /*
218          * Be careful about RCU walk racing with rename:
219          * use ACCESS_ONCE to fetch the name pointer.
220          *
221          * NOTE! Even if a rename will mean that the length
222          * was not loaded atomically, we don't care. The
223          * RCU walk will check the sequence count eventually,
224          * and catch it. And we won't overrun the buffer,
225          * because we're reading the name pointer atomically,
226          * and a dentry name is guaranteed to be properly
227          * terminated with a NUL byte.
228          *
229          * End result: even if 'len' is wrong, we'll exit
230          * early because the data cannot match (there can
231          * be no NUL in the ct/tcount data)
232          */
233         cs = ACCESS_ONCE(dentry->d_name.name);
234         smp_read_barrier_depends();
235         return dentry_string_cmp(cs, ct, tcount);
236 }
237 
238 struct external_name {
239         union {
240                 atomic_t count;
241                 struct rcu_head head;
242         } u;
243         unsigned char name[];
244 };
245 
246 static inline struct external_name *external_name(struct dentry *dentry)
247 {
248         return container_of(dentry->d_name.name, struct external_name, name[0]);
249 }
250 
251 static void __d_free(struct rcu_head *head)
252 {
253         struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
254 
255         WARN_ON(!hlist_unhashed(&dentry->d_alias));
256         kmem_cache_free(dentry_cache, dentry); 
257 }
258 
259 static void __d_free_external(struct rcu_head *head)
260 {
261         struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
262         WARN_ON(!hlist_unhashed(&dentry->d_alias));
263         kfree(external_name(dentry));
264         kmem_cache_free(dentry_cache, dentry); 
265 }
266 
267 static inline int dname_external(const struct dentry *dentry)
268 {
269         return dentry->d_name.name != dentry->d_iname;
270 }
271 
272 static void dentry_free(struct dentry *dentry)
273 {
274         if (unlikely(dname_external(dentry))) {
275                 struct external_name *p = external_name(dentry);
276                 if (likely(atomic_dec_and_test(&p->u.count))) {
277                         call_rcu(&dentry->d_u.d_rcu, __d_free_external);
278                         return;
279                 }
280         }
281         /* if dentry was never visible to RCU, immediate free is OK */
282         if (!(dentry->d_flags & DCACHE_RCUACCESS))
283                 __d_free(&dentry->d_u.d_rcu);
284         else
285                 call_rcu(&dentry->d_u.d_rcu, __d_free);
286 }
287 
288 /**
289  * dentry_rcuwalk_barrier - invalidate in-progress rcu-walk lookups
290  * @dentry: the target dentry
291  * After this call, in-progress rcu-walk path lookup will fail. This
292  * should be called after unhashing, and after changing d_inode (if
293  * the dentry has not already been unhashed).
294  */
295 static inline void dentry_rcuwalk_barrier(struct dentry *dentry)
296 {
297         assert_spin_locked(&dentry->d_lock);
298         /* Go through a barrier */
299         write_seqcount_barrier(&dentry->d_seq);
300 }
301 
302 /*
303  * Release the dentry's inode, using the filesystem
304  * d_iput() operation if defined. Dentry has no refcount
305  * and is unhashed.
306  */
307 static void dentry_iput(struct dentry * dentry)
308         __releases(dentry->d_lock)
309         __releases(dentry->d_inode->i_lock)
310 {
311         struct inode *inode = dentry->d_inode;
312         if (inode) {
313                 dentry->d_inode = NULL;
314                 hlist_del_init(&dentry->d_alias);
315                 spin_unlock(&dentry->d_lock);
316                 spin_unlock(&inode->i_lock);
317                 if (!inode->i_nlink)
318                         fsnotify_inoderemove(inode);
319                 if (dentry->d_op && dentry->d_op->d_iput)
320                         dentry->d_op->d_iput(dentry, inode);
321                 else
322                         iput(inode);
323         } else {
324                 spin_unlock(&dentry->d_lock);
325         }
326 }
327 
328 /*
329  * Release the dentry's inode, using the filesystem
330  * d_iput() operation if defined. dentry remains in-use.
331  */
332 static void dentry_unlink_inode(struct dentry * dentry)
333         __releases(dentry->d_lock)
334         __releases(dentry->d_inode->i_lock)
335 {
336         struct inode *inode = dentry->d_inode;
337         __d_clear_type(dentry);
338         dentry->d_inode = NULL;
339         hlist_del_init(&dentry->d_alias);
340         dentry_rcuwalk_barrier(dentry);
341         spin_unlock(&dentry->d_lock);
342         spin_unlock(&inode->i_lock);
343         if (!inode->i_nlink)
344                 fsnotify_inoderemove(inode);
345         if (dentry->d_op && dentry->d_op->d_iput)
346                 dentry->d_op->d_iput(dentry, inode);
347         else
348                 iput(inode);
349 }
350 
351 /*
352  * The DCACHE_LRU_LIST bit is set whenever the 'd_lru' entry
353  * is in use - which includes both the "real" per-superblock
354  * LRU list _and_ the DCACHE_SHRINK_LIST use.
355  *
356  * The DCACHE_SHRINK_LIST bit is set whenever the dentry is
357  * on the shrink list (ie not on the superblock LRU list).
358  *
359  * The per-cpu "nr_dentry_unused" counters are updated with
360  * the DCACHE_LRU_LIST bit.
361  *
362  * These helper functions make sure we always follow the
363  * rules. d_lock must be held by the caller.
364  */
365 #define D_FLAG_VERIFY(dentry,x) WARN_ON_ONCE(((dentry)->d_flags & (DCACHE_LRU_LIST | DCACHE_SHRINK_LIST)) != (x))
366 static void d_lru_add(struct dentry *dentry)
367 {
368         D_FLAG_VERIFY(dentry, 0);
369         dentry->d_flags |= DCACHE_LRU_LIST;
370         this_cpu_inc(nr_dentry_unused);
371         WARN_ON_ONCE(!list_lru_add(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
372 }
373 
374 static void d_lru_del(struct dentry *dentry)
375 {
376         D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
377         dentry->d_flags &= ~DCACHE_LRU_LIST;
378         this_cpu_dec(nr_dentry_unused);
379         WARN_ON_ONCE(!list_lru_del(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
380 }
381 
382 static void d_shrink_del(struct dentry *dentry)
383 {
384         D_FLAG_VERIFY(dentry, DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
385         list_del_init(&dentry->d_lru);
386         dentry->d_flags &= ~(DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
387         this_cpu_dec(nr_dentry_unused);
388 }
389 
390 static void d_shrink_add(struct dentry *dentry, struct list_head *list)
391 {
392         D_FLAG_VERIFY(dentry, 0);
393         list_add(&dentry->d_lru, list);
394         dentry->d_flags |= DCACHE_SHRINK_LIST | DCACHE_LRU_LIST;
395         this_cpu_inc(nr_dentry_unused);
396 }
397 
398 /*
399  * These can only be called under the global LRU lock, ie during the
400  * callback for freeing the LRU list. "isolate" removes it from the
401  * LRU lists entirely, while shrink_move moves it to the indicated
402  * private list.
403  */
404 static void d_lru_isolate(struct dentry *dentry)
405 {
406         D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
407         dentry->d_flags &= ~DCACHE_LRU_LIST;
408         this_cpu_dec(nr_dentry_unused);
409         list_del_init(&dentry->d_lru);
410 }
411 
412 static void d_lru_shrink_move(struct dentry *dentry, struct list_head *list)
413 {
414         D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
415         dentry->d_flags |= DCACHE_SHRINK_LIST;
416         list_move_tail(&dentry->d_lru, list);
417 }
418 
419 /*
420  * dentry_lru_(add|del)_list) must be called with d_lock held.
421  */
422 static void dentry_lru_add(struct dentry *dentry)
423 {
424         if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST)))
425                 d_lru_add(dentry);
426 }
427 
428 /**
429  * d_drop - drop a dentry
430  * @dentry: dentry to drop
431  *
432  * d_drop() unhashes the entry from the parent dentry hashes, so that it won't
433  * be found through a VFS lookup any more. Note that this is different from
434  * deleting the dentry - d_delete will try to mark the dentry negative if
435  * possible, giving a successful _negative_ lookup, while d_drop will
436  * just make the cache lookup fail.
437  *
438  * d_drop() is used mainly for stuff that wants to invalidate a dentry for some
439  * reason (NFS timeouts or autofs deletes).
440  *
441  * __d_drop requires dentry->d_lock.
442  */
443 void __d_drop(struct dentry *dentry)
444 {
445         if (!d_unhashed(dentry)) {
446                 struct hlist_bl_head *b;
447                 /*
448                  * Hashed dentries are normally on the dentry hashtable,
449                  * with the exception of those newly allocated by
450                  * d_obtain_alias, which are always IS_ROOT:
451                  */
452                 if (unlikely(IS_ROOT(dentry)))
453                         b = &dentry->d_sb->s_anon;
454                 else
455                         b = d_hash(dentry->d_parent, dentry->d_name.hash);
456 
457                 hlist_bl_lock(b);
458                 __hlist_bl_del(&dentry->d_hash);
459                 dentry->d_hash.pprev = NULL;
460                 hlist_bl_unlock(b);
461                 dentry_rcuwalk_barrier(dentry);
462         }
463 }
464 EXPORT_SYMBOL(__d_drop);
465 
466 void d_drop(struct dentry *dentry)
467 {
468         spin_lock(&dentry->d_lock);
469         __d_drop(dentry);
470         spin_unlock(&dentry->d_lock);
471 }
472 EXPORT_SYMBOL(d_drop);
473 
474 static void __dentry_kill(struct dentry *dentry)
475 {
476         struct dentry *parent = NULL;
477         bool can_free = true;
478         if (!IS_ROOT(dentry))
479                 parent = dentry->d_parent;
480 
481         /*
482          * The dentry is now unrecoverably dead to the world.
483          */
484         lockref_mark_dead(&dentry->d_lockref);
485 
486         /*
487          * inform the fs via d_prune that this dentry is about to be
488          * unhashed and destroyed.
489          */
490         if (dentry->d_flags & DCACHE_OP_PRUNE)
491                 dentry->d_op->d_prune(dentry);
492 
493         if (dentry->d_flags & DCACHE_LRU_LIST) {
494                 if (!(dentry->d_flags & DCACHE_SHRINK_LIST))
495                         d_lru_del(dentry);
496         }
497         /* if it was on the hash then remove it */
498         __d_drop(dentry);
499         list_del(&dentry->d_u.d_child);
500         /*
501          * Inform d_walk() that we are no longer attached to the
502          * dentry tree
503          */
504         dentry->d_flags |= DCACHE_DENTRY_KILLED;
505         if (parent)
506                 spin_unlock(&parent->d_lock);
507         dentry_iput(dentry);
508         /*
509          * dentry_iput drops the locks, at which point nobody (except
510          * transient RCU lookups) can reach this dentry.
511          */
512         BUG_ON((int)dentry->d_lockref.count > 0);
513         this_cpu_dec(nr_dentry);
514         if (dentry->d_op && dentry->d_op->d_release)
515                 dentry->d_op->d_release(dentry);
516 
517         spin_lock(&dentry->d_lock);
518         if (dentry->d_flags & DCACHE_SHRINK_LIST) {
519                 dentry->d_flags |= DCACHE_MAY_FREE;
520                 can_free = false;
521         }
522         spin_unlock(&dentry->d_lock);
523         if (likely(can_free))
524                 dentry_free(dentry);
525 }
526 
527 /*
528  * Finish off a dentry we've decided to kill.
529  * dentry->d_lock must be held, returns with it unlocked.
530  * If ref is non-zero, then decrement the refcount too.
531  * Returns dentry requiring refcount drop, or NULL if we're done.
532  */
533 static struct dentry *dentry_kill(struct dentry *dentry)
534         __releases(dentry->d_lock)
535 {
536         struct inode *inode = dentry->d_inode;
537         struct dentry *parent = NULL;
538 
539         if (inode && unlikely(!spin_trylock(&inode->i_lock)))
540                 goto failed;
541 
542         if (!IS_ROOT(dentry)) {
543                 parent = dentry->d_parent;
544                 if (unlikely(!spin_trylock(&parent->d_lock))) {
545                         if (inode)
546                                 spin_unlock(&inode->i_lock);
547                         goto failed;
548                 }
549         }
550 
551         __dentry_kill(dentry);
552         return parent;
553 
554 failed:
555         spin_unlock(&dentry->d_lock);
556         cpu_relax();
557         return dentry; /* try again with same dentry */
558 }
559 
560 static inline struct dentry *lock_parent(struct dentry *dentry)
561 {
562         struct dentry *parent = dentry->d_parent;
563         if (IS_ROOT(dentry))
564                 return NULL;
565         if (unlikely((int)dentry->d_lockref.count < 0))
566                 return NULL;
567         if (likely(spin_trylock(&parent->d_lock)))
568                 return parent;
569         rcu_read_lock();
570         spin_unlock(&dentry->d_lock);
571 again:
572         parent = ACCESS_ONCE(dentry->d_parent);
573         spin_lock(&parent->d_lock);
574         /*
575          * We can't blindly lock dentry until we are sure
576          * that we won't violate the locking order.
577          * Any changes of dentry->d_parent must have
578          * been done with parent->d_lock held, so
579          * spin_lock() above is enough of a barrier
580          * for checking if it's still our child.
581          */
582         if (unlikely(parent != dentry->d_parent)) {
583                 spin_unlock(&parent->d_lock);
584                 goto again;
585         }
586         rcu_read_unlock();
587         if (parent != dentry)
588                 spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
589         else
590                 parent = NULL;
591         return parent;
592 }
593 
594 /* 
595  * This is dput
596  *
597  * This is complicated by the fact that we do not want to put
598  * dentries that are no longer on any hash chain on the unused
599  * list: we'd much rather just get rid of them immediately.
600  *
601  * However, that implies that we have to traverse the dentry
602  * tree upwards to the parents which might _also_ now be
603  * scheduled for deletion (it may have been only waiting for
604  * its last child to go away).
605  *
606  * This tail recursion is done by hand as we don't want to depend
607  * on the compiler to always get this right (gcc generally doesn't).
608  * Real recursion would eat up our stack space.
609  */
610 
611 /*
612  * dput - release a dentry
613  * @dentry: dentry to release 
614  *
615  * Release a dentry. This will drop the usage count and if appropriate
616  * call the dentry unlink method as well as removing it from the queues and
617  * releasing its resources. If the parent dentries were scheduled for release
618  * they too may now get deleted.
619  */
620 void dput(struct dentry *dentry)
621 {
622         if (unlikely(!dentry))
623                 return;
624 
625 repeat:
626         if (lockref_put_or_lock(&dentry->d_lockref))
627                 return;
628 
629         /* Unreachable? Get rid of it */
630         if (unlikely(d_unhashed(dentry)))
631                 goto kill_it;
632 
633         if (unlikely(dentry->d_flags & DCACHE_OP_DELETE)) {
634                 if (dentry->d_op->d_delete(dentry))
635                         goto kill_it;
636         }
637 
638         if (!(dentry->d_flags & DCACHE_REFERENCED))
639                 dentry->d_flags |= DCACHE_REFERENCED;
640         dentry_lru_add(dentry);
641 
642         dentry->d_lockref.count--;
643         spin_unlock(&dentry->d_lock);
644         return;
645 
646 kill_it:
647         dentry = dentry_kill(dentry);
648         if (dentry)
649                 goto repeat;
650 }
651 EXPORT_SYMBOL(dput);
652 
653 
654 /* This must be called with d_lock held */
655 static inline void __dget_dlock(struct dentry *dentry)
656 {
657         dentry->d_lockref.count++;
658 }
659 
660 static inline void __dget(struct dentry *dentry)
661 {
662         lockref_get(&dentry->d_lockref);
663 }
664 
665 struct dentry *dget_parent(struct dentry *dentry)
666 {
667         int gotref;
668         struct dentry *ret;
669 
670         /*
671          * Do optimistic parent lookup without any
672          * locking.
673          */
674         rcu_read_lock();
675         ret = ACCESS_ONCE(dentry->d_parent);
676         gotref = lockref_get_not_zero(&ret->d_lockref);
677         rcu_read_unlock();
678         if (likely(gotref)) {
679                 if (likely(ret == ACCESS_ONCE(dentry->d_parent)))
680                         return ret;
681                 dput(ret);
682         }
683 
684 repeat:
685         /*
686          * Don't need rcu_dereference because we re-check it was correct under
687          * the lock.
688          */
689         rcu_read_lock();
690         ret = dentry->d_parent;
691         spin_lock(&ret->d_lock);
692         if (unlikely(ret != dentry->d_parent)) {
693                 spin_unlock(&ret->d_lock);
694                 rcu_read_unlock();
695                 goto repeat;
696         }
697         rcu_read_unlock();
698         BUG_ON(!ret->d_lockref.count);
699         ret->d_lockref.count++;
700         spin_unlock(&ret->d_lock);
701         return ret;
702 }
703 EXPORT_SYMBOL(dget_parent);
704 
705 /**
706  * d_find_alias - grab a hashed alias of inode
707  * @inode: inode in question
708  *
709  * If inode has a hashed alias, or is a directory and has any alias,
710  * acquire the reference to alias and return it. Otherwise return NULL.
711  * Notice that if inode is a directory there can be only one alias and
712  * it can be unhashed only if it has no children, or if it is the root
713  * of a filesystem, or if the directory was renamed and d_revalidate
714  * was the first vfs operation to notice.
715  *
716  * If the inode has an IS_ROOT, DCACHE_DISCONNECTED alias, then prefer
717  * any other hashed alias over that one.
718  */
719 static struct dentry *__d_find_alias(struct inode *inode)
720 {
721         struct dentry *alias, *discon_alias;
722 
723 again:
724         discon_alias = NULL;
725         hlist_for_each_entry(alias, &inode->i_dentry, d_alias) {
726                 spin_lock(&alias->d_lock);
727                 if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
728                         if (IS_ROOT(alias) &&
729                             (alias->d_flags & DCACHE_DISCONNECTED)) {
730                                 discon_alias = alias;
731                         } else {
732                                 __dget_dlock(alias);
733                                 spin_unlock(&alias->d_lock);
734                                 return alias;
735                         }
736                 }
737                 spin_unlock(&alias->d_lock);
738         }
739         if (discon_alias) {
740                 alias = discon_alias;
741                 spin_lock(&alias->d_lock);
742                 if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
743                         __dget_dlock(alias);
744                         spin_unlock(&alias->d_lock);
745                         return alias;
746                 }
747                 spin_unlock(&alias->d_lock);
748                 goto again;
749         }
750         return NULL;
751 }
752 
753 struct dentry *d_find_alias(struct inode *inode)
754 {
755         struct dentry *de = NULL;
756 
757         if (!hlist_empty(&inode->i_dentry)) {
758                 spin_lock(&inode->i_lock);
759                 de = __d_find_alias(inode);
760                 spin_unlock(&inode->i_lock);
761         }
762         return de;
763 }
764 EXPORT_SYMBOL(d_find_alias);
765 
766 /*
767  *      Try to kill dentries associated with this inode.
768  * WARNING: you must own a reference to inode.
769  */
770 void d_prune_aliases(struct inode *inode)
771 {
772         struct dentry *dentry;
773 restart:
774         spin_lock(&inode->i_lock);
775         hlist_for_each_entry(dentry, &inode->i_dentry, d_alias) {
776                 spin_lock(&dentry->d_lock);
777                 if (!dentry->d_lockref.count) {
778                         struct dentry *parent = lock_parent(dentry);
779                         if (likely(!dentry->d_lockref.count)) {
780                                 __dentry_kill(dentry);
781                                 dput(parent);
782                                 goto restart;
783                         }
784                         if (parent)
785                                 spin_unlock(&parent->d_lock);
786                 }
787                 spin_unlock(&dentry->d_lock);
788         }
789         spin_unlock(&inode->i_lock);
790 }
791 EXPORT_SYMBOL(d_prune_aliases);
792 
793 static void shrink_dentry_list(struct list_head *list)
794 {
795         struct dentry *dentry, *parent;
796 
797         while (!list_empty(list)) {
798                 struct inode *inode;
799                 dentry = list_entry(list->prev, struct dentry, d_lru);
800                 spin_lock(&dentry->d_lock);
801                 parent = lock_parent(dentry);
802 
803                 /*
804                  * The dispose list is isolated and dentries are not accounted
805                  * to the LRU here, so we can simply remove it from the list
806                  * here regardless of whether it is referenced or not.
807                  */
808                 d_shrink_del(dentry);
809 
810                 /*
811                  * We found an inuse dentry which was not removed from
812                  * the LRU because of laziness during lookup. Do not free it.
813                  */
814                 if ((int)dentry->d_lockref.count > 0) {
815                         spin_unlock(&dentry->d_lock);
816                         if (parent)
817                                 spin_unlock(&parent->d_lock);
818                         continue;
819                 }
820 
821 
822                 if (unlikely(dentry->d_flags & DCACHE_DENTRY_KILLED)) {
823                         bool can_free = dentry->d_flags & DCACHE_MAY_FREE;
824                         spin_unlock(&dentry->d_lock);
825                         if (parent)
826                                 spin_unlock(&parent->d_lock);
827                         if (can_free)
828                                 dentry_free(dentry);
829                         continue;
830                 }
831 
832                 inode = dentry->d_inode;
833                 if (inode && unlikely(!spin_trylock(&inode->i_lock))) {
834                         d_shrink_add(dentry, list);
835                         spin_unlock(&dentry->d_lock);
836                         if (parent)
837                                 spin_unlock(&parent->d_lock);
838                         continue;
839                 }
840 
841                 __dentry_kill(dentry);
842 
843                 /*
844                  * We need to prune ancestors too. This is necessary to prevent
845                  * quadratic behavior of shrink_dcache_parent(), but is also
846                  * expected to be beneficial in reducing dentry cache
847                  * fragmentation.
848                  */
849                 dentry = parent;
850                 while (dentry && !lockref_put_or_lock(&dentry->d_lockref)) {
851                         parent = lock_parent(dentry);
852                         if (dentry->d_lockref.count != 1) {
853                                 dentry->d_lockref.count--;
854                                 spin_unlock(&dentry->d_lock);
855                                 if (parent)
856                                         spin_unlock(&parent->d_lock);
857                                 break;
858                         }
859                         inode = dentry->d_inode;        /* can't be NULL */
860                         if (unlikely(!spin_trylock(&inode->i_lock))) {
861                                 spin_unlock(&dentry->d_lock);
862                                 if (parent)
863                                         spin_unlock(&parent->d_lock);
864                                 cpu_relax();
865                                 continue;
866                         }
867                         __dentry_kill(dentry);
868                         dentry = parent;
869                 }
870         }
871 }
872 
873 static enum lru_status
874 dentry_lru_isolate(struct list_head *item, spinlock_t *lru_lock, void *arg)
875 {
876         struct list_head *freeable = arg;
877         struct dentry   *dentry = container_of(item, struct dentry, d_lru);
878 
879 
880         /*
881          * we are inverting the lru lock/dentry->d_lock here,
882          * so use a trylock. If we fail to get the lock, just skip
883          * it
884          */
885         if (!spin_trylock(&dentry->d_lock))
886                 return LRU_SKIP;
887 
888         /*
889          * Referenced dentries are still in use. If they have active
890          * counts, just remove them from the LRU. Otherwise give them
891          * another pass through the LRU.
892          */
893         if (dentry->d_lockref.count) {
894                 d_lru_isolate(dentry);
895                 spin_unlock(&dentry->d_lock);
896                 return LRU_REMOVED;
897         }
898 
899         if (dentry->d_flags & DCACHE_REFERENCED) {
900                 dentry->d_flags &= ~DCACHE_REFERENCED;
901                 spin_unlock(&dentry->d_lock);
902 
903                 /*
904                  * The list move itself will be made by the common LRU code. At
905                  * this point, we've dropped the dentry->d_lock but keep the
906                  * lru lock. This is safe to do, since every list movement is
907                  * protected by the lru lock even if both locks are held.
908                  *
909                  * This is guaranteed by the fact that all LRU management
910                  * functions are intermediated by the LRU API calls like
911                  * list_lru_add and list_lru_del. List movement in this file
912                  * only ever occur through this functions or through callbacks
913                  * like this one, that are called from the LRU API.
914                  *
915                  * The only exceptions to this are functions like
916                  * shrink_dentry_list, and code that first checks for the
917                  * DCACHE_SHRINK_LIST flag.  Those are guaranteed to be
918                  * operating only with stack provided lists after they are
919                  * properly isolated from the main list.  It is thus, always a
920                  * local access.
921                  */
922                 return LRU_ROTATE;
923         }
924 
925         d_lru_shrink_move(dentry, freeable);
926         spin_unlock(&dentry->d_lock);
927 
928         return LRU_REMOVED;
929 }
930 
931 /**
932  * prune_dcache_sb - shrink the dcache
933  * @sb: superblock
934  * @nr_to_scan : number of entries to try to free
935  * @nid: which node to scan for freeable entities
936  *
937  * Attempt to shrink the superblock dcache LRU by @nr_to_scan entries. This is
938  * done when we need more memory an called from the superblock shrinker
939  * function.
940  *
941  * This function may fail to free any resources if all the dentries are in
942  * use.
943  */
944 long prune_dcache_sb(struct super_block *sb, unsigned long nr_to_scan,
945                      int nid)
946 {
947         LIST_HEAD(dispose);
948         long freed;
949 
950         freed = list_lru_walk_node(&sb->s_dentry_lru, nid, dentry_lru_isolate,
951                                        &dispose, &nr_to_scan);
952         shrink_dentry_list(&dispose);
953         return freed;
954 }
955 
956 static enum lru_status dentry_lru_isolate_shrink(struct list_head *item,
957                                                 spinlock_t *lru_lock, void *arg)
958 {
959         struct list_head *freeable = arg;
960         struct dentry   *dentry = container_of(item, struct dentry, d_lru);
961 
962         /*
963          * we are inverting the lru lock/dentry->d_lock here,
964          * so use a trylock. If we fail to get the lock, just skip
965          * it
966          */
967         if (!spin_trylock(&dentry->d_lock))
968                 return LRU_SKIP;
969 
970         d_lru_shrink_move(dentry, freeable);
971         spin_unlock(&dentry->d_lock);
972 
973         return LRU_REMOVED;
974 }
975 
976 
977 /**
978  * shrink_dcache_sb - shrink dcache for a superblock
979  * @sb: superblock
980  *
981  * Shrink the dcache for the specified super block. This is used to free
982  * the dcache before unmounting a file system.
983  */
984 void shrink_dcache_sb(struct super_block *sb)
985 {
986         long freed;
987 
988         do {
989                 LIST_HEAD(dispose);
990 
991                 freed = list_lru_walk(&sb->s_dentry_lru,
992                         dentry_lru_isolate_shrink, &dispose, UINT_MAX);
993 
994                 this_cpu_sub(nr_dentry_unused, freed);
995                 shrink_dentry_list(&dispose);
996         } while (freed > 0);
997 }
998 EXPORT_SYMBOL(shrink_dcache_sb);
999 
1000 /**
1001  * enum d_walk_ret - action to talke during tree walk
1002  * @D_WALK_CONTINUE:    contrinue walk
1003  * @D_WALK_QUIT:        quit walk
1004  * @D_WALK_NORETRY:     quit when retry is needed
1005  * @D_WALK_SKIP:        skip this dentry and its children
1006  */
1007 enum d_walk_ret {
1008         D_WALK_CONTINUE,
1009         D_WALK_QUIT,
1010         D_WALK_NORETRY,
1011         D_WALK_SKIP,
1012 };
1013 
1014 /**
1015  * d_walk - walk the dentry tree
1016  * @parent:     start of walk
1017  * @data:       data passed to @enter() and @finish()
1018  * @enter:      callback when first entering the dentry
1019  * @finish:     callback when successfully finished the walk
1020  *
1021  * The @enter() and @finish() callbacks are called with d_lock held.
1022  */
1023 static void d_walk(struct dentry *parent, void *data,
1024                    enum d_walk_ret (*enter)(void *, struct dentry *),
1025                    void (*finish)(void *))
1026 {
1027         struct dentry *this_parent;
1028         struct list_head *next;
1029         unsigned seq = 0;
1030         enum d_walk_ret ret;
1031         bool retry = true;
1032 
1033 again:
1034         read_seqbegin_or_lock(&rename_lock, &seq);
1035         this_parent = parent;
1036         spin_lock(&this_parent->d_lock);
1037 
1038         ret = enter(data, this_parent);
1039         switch (ret) {
1040         case D_WALK_CONTINUE:
1041                 break;
1042         case D_WALK_QUIT:
1043         case D_WALK_SKIP:
1044                 goto out_unlock;
1045         case D_WALK_NORETRY:
1046                 retry = false;
1047                 break;
1048         }
1049 repeat:
1050         next = this_parent->d_subdirs.next;
1051 resume:
1052         while (next != &this_parent->d_subdirs) {
1053                 struct list_head *tmp = next;
1054                 struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
1055                 next = tmp->next;
1056 
1057                 spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
1058 
1059                 ret = enter(data, dentry);
1060                 switch (ret) {
1061                 case D_WALK_CONTINUE:
1062                         break;
1063                 case D_WALK_QUIT:
1064                         spin_unlock(&dentry->d_lock);
1065                         goto out_unlock;
1066                 case D_WALK_NORETRY:
1067                         retry = false;
1068                         break;
1069                 case D_WALK_SKIP:
1070                         spin_unlock(&dentry->d_lock);
1071                         continue;
1072                 }
1073 
1074                 if (!list_empty(&dentry->d_subdirs)) {
1075                         spin_unlock(&this_parent->d_lock);
1076                         spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
1077                         this_parent = dentry;
1078                         spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
1079                         goto repeat;
1080                 }
1081                 spin_unlock(&dentry->d_lock);
1082         }
1083         /*
1084          * All done at this level ... ascend and resume the search.
1085          */
1086         if (this_parent != parent) {
1087                 struct dentry *child = this_parent;
1088                 this_parent = child->d_parent;
1089 
1090                 rcu_read_lock();
1091                 spin_unlock(&child->d_lock);
1092                 spin_lock(&this_parent->d_lock);
1093 
1094                 /*
1095                  * might go back up the wrong parent if we have had a rename
1096                  * or deletion
1097                  */
1098                 if (this_parent != child->d_parent ||
1099                          (child->d_flags & DCACHE_DENTRY_KILLED) ||
1100                          need_seqretry(&rename_lock, seq)) {
1101                         spin_unlock(&this_parent->d_lock);
1102                         rcu_read_unlock();
1103                         goto rename_retry;
1104                 }
1105                 rcu_read_unlock();
1106                 next = child->d_u.d_child.next;
1107                 goto resume;
1108         }
1109         if (need_seqretry(&rename_lock, seq)) {
1110                 spin_unlock(&this_parent->d_lock);
1111                 goto rename_retry;
1112         }
1113         if (finish)
1114                 finish(data);
1115 
1116 out_unlock:
1117         spin_unlock(&this_parent->d_lock);
1118         done_seqretry(&rename_lock, seq);
1119         return;
1120 
1121 rename_retry:
1122         if (!retry)
1123                 return;
1124         seq = 1;
1125         goto again;
1126 }
1127 
1128 /*
1129  * Search for at least 1 mount point in the dentry's subdirs.
1130  * We descend to the next level whenever the d_subdirs
1131  * list is non-empty and continue searching.
1132  */
1133 
1134 static enum d_walk_ret check_mount(void *data, struct dentry *dentry)
1135 {
1136         int *ret = data;
1137         if (d_mountpoint(dentry)) {
1138                 *ret = 1;
1139                 return D_WALK_QUIT;
1140         }
1141         return D_WALK_CONTINUE;
1142 }
1143 
1144 /**
1145  * have_submounts - check for mounts over a dentry
1146  * @parent: dentry to check.
1147  *
1148  * Return true if the parent or its subdirectories contain
1149  * a mount point
1150  */
1151 int have_submounts(struct dentry *parent)
1152 {
1153         int ret = 0;
1154 
1155         d_walk(parent, &ret, check_mount, NULL);
1156 
1157         return ret;
1158 }
1159 EXPORT_SYMBOL(have_submounts);
1160 
1161 /*
1162  * Called by mount code to set a mountpoint and check if the mountpoint is
1163  * reachable (e.g. NFS can unhash a directory dentry and then the complete
1164  * subtree can become unreachable).
1165  *
1166  * Only one of d_invalidate() and d_set_mounted() must succeed.  For
1167  * this reason take rename_lock and d_lock on dentry and ancestors.
1168  */
1169 int d_set_mounted(struct dentry *dentry)
1170 {
1171         struct dentry *p;
1172         int ret = -ENOENT;
1173         write_seqlock(&rename_lock);
1174         for (p = dentry->d_parent; !IS_ROOT(p); p = p->d_parent) {
1175                 /* Need exclusion wrt. d_invalidate() */
1176                 spin_lock(&p->d_lock);
1177                 if (unlikely(d_unhashed(p))) {
1178                         spin_unlock(&p->d_lock);
1179                         goto out;
1180                 }
1181                 spin_unlock(&p->d_lock);
1182         }
1183         spin_lock(&dentry->d_lock);
1184         if (!d_unlinked(dentry)) {
1185                 dentry->d_flags |= DCACHE_MOUNTED;
1186                 ret = 0;
1187         }
1188         spin_unlock(&dentry->d_lock);
1189 out:
1190         write_sequnlock(&rename_lock);
1191         return ret;
1192 }
1193 
1194 /*
1195  * Search the dentry child list of the specified parent,
1196  * and move any unused dentries to the end of the unused
1197  * list for prune_dcache(). We descend to the next level
1198  * whenever the d_subdirs list is non-empty and continue
1199  * searching.
1200  *
1201  * It returns zero iff there are no unused children,
1202  * otherwise  it returns the number of children moved to
1203  * the end of the unused list. This may not be the total
1204  * number of unused children, because select_parent can
1205  * drop the lock and return early due to latency
1206  * constraints.
1207  */
1208 
1209 struct select_data {
1210         struct dentry *start;
1211         struct list_head dispose;
1212         int found;
1213 };
1214 
1215 static enum d_walk_ret select_collect(void *_data, struct dentry *dentry)
1216 {
1217         struct select_data *data = _data;
1218         enum d_walk_ret ret = D_WALK_CONTINUE;
1219 
1220         if (data->start == dentry)
1221                 goto out;
1222 
1223         if (dentry->d_flags & DCACHE_SHRINK_LIST) {
1224                 data->found++;
1225         } else {
1226                 if (dentry->d_flags & DCACHE_LRU_LIST)
1227                         d_lru_del(dentry);
1228                 if (!dentry->d_lockref.count) {
1229                         d_shrink_add(dentry, &data->dispose);
1230                         data->found++;
1231                 }
1232         }
1233         /*
1234          * We can return to the caller if we have found some (this
1235          * ensures forward progress). We'll be coming back to find
1236          * the rest.
1237          */
1238         if (!list_empty(&data->dispose))
1239                 ret = need_resched() ? D_WALK_QUIT : D_WALK_NORETRY;
1240 out:
1241         return ret;
1242 }
1243 
1244 /**
1245  * shrink_dcache_parent - prune dcache
1246  * @parent: parent of entries to prune
1247  *
1248  * Prune the dcache to remove unused children of the parent dentry.
1249  */
1250 void shrink_dcache_parent(struct dentry *parent)
1251 {
1252         for (;;) {
1253                 struct select_data data;
1254 
1255                 INIT_LIST_HEAD(&data.dispose);
1256                 data.start = parent;
1257                 data.found = 0;
1258 
1259                 d_walk(parent, &data, select_collect, NULL);
1260                 if (!data.found)
1261                         break;
1262 
1263                 shrink_dentry_list(&data.dispose);
1264                 cond_resched();
1265         }
1266 }
1267 EXPORT_SYMBOL(shrink_dcache_parent);
1268 
1269 static enum d_walk_ret umount_check(void *_data, struct dentry *dentry)
1270 {
1271         /* it has busy descendents; complain about those instead */
1272         if (!list_empty(&dentry->d_subdirs))
1273                 return D_WALK_CONTINUE;
1274 
1275         /* root with refcount 1 is fine */
1276         if (dentry == _data && dentry->d_lockref.count == 1)
1277                 return D_WALK_CONTINUE;
1278 
1279         printk(KERN_ERR "BUG: Dentry %p{i=%lx,n=%pd} "
1280                         " still in use (%d) [unmount of %s %s]\n",
1281                        dentry,
1282                        dentry->d_inode ?
1283                        dentry->d_inode->i_ino : 0UL,
1284                        dentry,
1285                        dentry->d_lockref.count,
1286                        dentry->d_sb->s_type->name,
1287                        dentry->d_sb->s_id);
1288         WARN_ON(1);
1289         return D_WALK_CONTINUE;
1290 }
1291 
1292 static void do_one_tree(struct dentry *dentry)
1293 {
1294         shrink_dcache_parent(dentry);
1295         d_walk(dentry, dentry, umount_check, NULL);
1296         d_drop(dentry);
1297         dput(dentry);
1298 }
1299 
1300 /*
1301  * destroy the dentries attached to a superblock on unmounting
1302  */
1303 void shrink_dcache_for_umount(struct super_block *sb)
1304 {
1305         struct dentry *dentry;
1306 
1307         WARN(down_read_trylock(&sb->s_umount), "s_umount should've been locked");
1308 
1309         dentry = sb->s_root;
1310         sb->s_root = NULL;
1311         do_one_tree(dentry);
1312 
1313         while (!hlist_bl_empty(&sb->s_anon)) {
1314                 dentry = dget(hlist_bl_entry(hlist_bl_first(&sb->s_anon), struct dentry, d_hash));
1315                 do_one_tree(dentry);
1316         }
1317 }
1318 
1319 struct detach_data {
1320         struct select_data select;
1321         struct dentry *mountpoint;
1322 };
1323 static enum d_walk_ret detach_and_collect(void *_data, struct dentry *dentry)
1324 {
1325         struct detach_data *data = _data;
1326 
1327         if (d_mountpoint(dentry)) {
1328                 __dget_dlock(dentry);
1329                 data->mountpoint = dentry;
1330                 return D_WALK_QUIT;
1331         }
1332 
1333         return select_collect(&data->select, dentry);
1334 }
1335 
1336 static void check_and_drop(void *_data)
1337 {
1338         struct detach_data *data = _data;
1339 
1340         if (!data->mountpoint && !data->select.found)
1341                 __d_drop(data->select.start);
1342 }
1343 
1344 /**
1345  * d_invalidate - detach submounts, prune dcache, and drop
1346  * @dentry: dentry to invalidate (aka detach, prune and drop)
1347  *
1348  * no dcache lock.
1349  *
1350  * The final d_drop is done as an atomic operation relative to
1351  * rename_lock ensuring there are no races with d_set_mounted.  This
1352  * ensures there are no unhashed dentries on the path to a mountpoint.
1353  */
1354 void d_invalidate(struct dentry *dentry)
1355 {
1356         /*
1357          * If it's already been dropped, return OK.
1358          */
1359         spin_lock(&dentry->d_lock);
1360         if (d_unhashed(dentry)) {
1361                 spin_unlock(&dentry->d_lock);
1362                 return;
1363         }
1364         spin_unlock(&dentry->d_lock);
1365 
1366         /* Negative dentries can be dropped without further checks */
1367         if (!dentry->d_inode) {
1368                 d_drop(dentry);
1369                 return;
1370         }
1371 
1372         for (;;) {
1373                 struct detach_data data;
1374 
1375                 data.mountpoint = NULL;
1376                 INIT_LIST_HEAD(&data.select.dispose);
1377                 data.select.start = dentry;
1378                 data.select.found = 0;
1379 
1380                 d_walk(dentry, &data, detach_and_collect, check_and_drop);
1381 
1382                 if (data.select.found)
1383                         shrink_dentry_list(&data.select.dispose);
1384 
1385                 if (data.mountpoint) {
1386                         detach_mounts(data.mountpoint);
1387                         dput(data.mountpoint);
1388                 }
1389 
1390                 if (!data.mountpoint && !data.select.found)
1391                         break;
1392 
1393                 cond_resched();
1394         }
1395 }
1396 EXPORT_SYMBOL(d_invalidate);
1397 
1398 /**
1399  * __d_alloc    -       allocate a dcache entry
1400  * @sb: filesystem it will belong to
1401  * @name: qstr of the name
1402  *
1403  * Allocates a dentry. It returns %NULL if there is insufficient memory
1404  * available. On a success the dentry is returned. The name passed in is
1405  * copied and the copy passed in may be reused after this call.
1406  */
1407  
1408 struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
1409 {
1410         struct dentry *dentry;
1411         char *dname;
1412 
1413         dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
1414         if (!dentry)
1415                 return NULL;
1416 
1417         /*
1418          * We guarantee that the inline name is always NUL-terminated.
1419          * This way the memcpy() done by the name switching in rename
1420          * will still always have a NUL at the end, even if we might
1421          * be overwriting an internal NUL character
1422          */
1423         dentry->d_iname[DNAME_INLINE_LEN-1] = 0;
1424         if (name->len > DNAME_INLINE_LEN-1) {
1425                 size_t size = offsetof(struct external_name, name[1]);
1426                 struct external_name *p = kmalloc(size + name->len, GFP_KERNEL);
1427                 if (!p) {
1428                         kmem_cache_free(dentry_cache, dentry); 
1429                         return NULL;
1430                 }
1431                 atomic_set(&p->u.count, 1);
1432                 dname = p->name;
1433         } else  {
1434                 dname = dentry->d_iname;
1435         }       
1436 
1437         dentry->d_name.len = name->len;
1438         dentry->d_name.hash = name->hash;
1439         memcpy(dname, name->name, name->len);
1440         dname[name->len] = 0;
1441 
1442         /* Make sure we always see the terminating NUL character */
1443         smp_wmb();
1444         dentry->d_name.name = dname;
1445 
1446         dentry->d_lockref.count = 1;
1447         dentry->d_flags = 0;
1448         spin_lock_init(&dentry->d_lock);
1449         seqcount_init(&dentry->d_seq);
1450         dentry->d_inode = NULL;
1451         dentry->d_parent = dentry;
1452         dentry->d_sb = sb;
1453         dentry->d_op = NULL;
1454         dentry->d_fsdata = NULL;
1455         INIT_HLIST_BL_NODE(&dentry->d_hash);
1456         INIT_LIST_HEAD(&dentry->d_lru);
1457         INIT_LIST_HEAD(&dentry->d_subdirs);
1458         INIT_HLIST_NODE(&dentry->d_alias);
1459         INIT_LIST_HEAD(&dentry->d_u.d_child);
1460         d_set_d_op(dentry, dentry->d_sb->s_d_op);
1461 
1462         this_cpu_inc(nr_dentry);
1463 
1464         return dentry;
1465 }
1466 
1467 /**
1468  * d_alloc      -       allocate a dcache entry
1469  * @parent: parent of entry to allocate
1470  * @name: qstr of the name
1471  *
1472  * Allocates a dentry. It returns %NULL if there is insufficient memory
1473  * available. On a success the dentry is returned. The name passed in is
1474  * copied and the copy passed in may be reused after this call.
1475  */
1476 struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
1477 {
1478         struct dentry *dentry = __d_alloc(parent->d_sb, name);
1479         if (!dentry)
1480                 return NULL;
1481 
1482         spin_lock(&parent->d_lock);
1483         /*
1484          * don't need child lock because it is not subject
1485          * to concurrency here
1486          */
1487         __dget_dlock(parent);
1488         dentry->d_parent = parent;
1489         list_add(&dentry->d_u.d_child, &parent->d_subdirs);
1490         spin_unlock(&parent->d_lock);
1491 
1492         return dentry;
1493 }
1494 EXPORT_SYMBOL(d_alloc);
1495 
1496 /**
1497  * d_alloc_pseudo - allocate a dentry (for lookup-less filesystems)
1498  * @sb: the superblock
1499  * @name: qstr of the name
1500  *
1501  * For a filesystem that just pins its dentries in memory and never
1502  * performs lookups at all, return an unhashed IS_ROOT dentry.
1503  */
1504 struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
1505 {
1506         return __d_alloc(sb, name);
1507 }
1508 EXPORT_SYMBOL(d_alloc_pseudo);
1509 
1510 struct dentry *d_alloc_name(struct dentry *parent, const char *name)
1511 {
1512         struct qstr q;
1513 
1514         q.name = name;
1515         q.len = strlen(name);
1516         q.hash = full_name_hash(q.name, q.len);
1517         return d_alloc(parent, &q);
1518 }
1519 EXPORT_SYMBOL(d_alloc_name);
1520 
1521 void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
1522 {
1523         WARN_ON_ONCE(dentry->d_op);
1524         WARN_ON_ONCE(dentry->d_flags & (DCACHE_OP_HASH  |
1525                                 DCACHE_OP_COMPARE       |
1526                                 DCACHE_OP_REVALIDATE    |
1527                                 DCACHE_OP_WEAK_REVALIDATE       |
1528                                 DCACHE_OP_DELETE ));
1529         dentry->d_op = op;
1530         if (!op)
1531                 return;
1532         if (op->d_hash)
1533                 dentry->d_flags |= DCACHE_OP_HASH;
1534         if (op->d_compare)
1535                 dentry->d_flags |= DCACHE_OP_COMPARE;
1536         if (op->d_revalidate)
1537                 dentry->d_flags |= DCACHE_OP_REVALIDATE;
1538         if (op->d_weak_revalidate)
1539                 dentry->d_flags |= DCACHE_OP_WEAK_REVALIDATE;
1540         if (op->d_delete)
1541                 dentry->d_flags |= DCACHE_OP_DELETE;
1542         if (op->d_prune)
1543                 dentry->d_flags |= DCACHE_OP_PRUNE;
1544 
1545 }
1546 EXPORT_SYMBOL(d_set_d_op);
1547 
1548 static unsigned d_flags_for_inode(struct inode *inode)
1549 {
1550         unsigned add_flags = DCACHE_FILE_TYPE;
1551 
1552         if (!inode)
1553                 return DCACHE_MISS_TYPE;
1554 
1555         if (S_ISDIR(inode->i_mode)) {
1556                 add_flags = DCACHE_DIRECTORY_TYPE;
1557                 if (unlikely(!(inode->i_opflags & IOP_LOOKUP))) {
1558                         if (unlikely(!inode->i_op->lookup))
1559                                 add_flags = DCACHE_AUTODIR_TYPE;
1560                         else
1561                                 inode->i_opflags |= IOP_LOOKUP;
1562                 }
1563         } else if (unlikely(!(inode->i_opflags & IOP_NOFOLLOW))) {
1564                 if (unlikely(inode->i_op->follow_link))
1565                         add_flags = DCACHE_SYMLINK_TYPE;
1566                 else
1567                         inode->i_opflags |= IOP_NOFOLLOW;
1568         }
1569 
1570         if (unlikely(IS_AUTOMOUNT(inode)))
1571                 add_flags |= DCACHE_NEED_AUTOMOUNT;
1572         return add_flags;
1573 }
1574 
1575 static void __d_instantiate(struct dentry *dentry, struct inode *inode)
1576 {
1577         unsigned add_flags = d_flags_for_inode(inode);
1578 
1579         spin_lock(&dentry->d_lock);
1580         __d_set_type(dentry, add_flags);
1581         if (inode)
1582                 hlist_add_head(&dentry->d_alias, &inode->i_dentry);
1583         dentry->d_inode = inode;
1584         dentry_rcuwalk_barrier(dentry);
1585         spin_unlock(&dentry->d_lock);
1586         fsnotify_d_instantiate(dentry, inode);
1587 }
1588 
1589 /**
1590  * d_instantiate - fill in inode information for a dentry
1591  * @entry: dentry to complete
1592  * @inode: inode to attach to this dentry
1593  *
1594  * Fill in inode information in the entry.
1595  *
1596  * This turns negative dentries into productive full members
1597  * of society.
1598  *
1599  * NOTE! This assumes that the inode count has been incremented
1600  * (or otherwise set) by the caller to indicate that it is now
1601  * in use by the dcache.
1602  */
1603  
1604 void d_instantiate(struct dentry *entry, struct inode * inode)
1605 {
1606         BUG_ON(!hlist_unhashed(&entry->d_alias));
1607         if (inode)
1608                 spin_lock(&inode->i_lock);
1609         __d_instantiate(entry, inode);
1610         if (inode)
1611                 spin_unlock(&inode->i_lock);
1612         security_d_instantiate(entry, inode);
1613 }
1614 EXPORT_SYMBOL(d_instantiate);
1615 
1616 /**
1617  * d_instantiate_unique - instantiate a non-aliased dentry
1618  * @entry: dentry to instantiate
1619  * @inode: inode to attach to this dentry
1620  *
1621  * Fill in inode information in the entry. On success, it returns NULL.
1622  * If an unhashed alias of "entry" already exists, then we return the
1623  * aliased dentry instead and drop one reference to inode.
1624  *
1625  * Note that in order to avoid conflicts with rename() etc, the caller
1626  * had better be holding the parent directory semaphore.
1627  *
1628  * This also assumes that the inode count has been incremented
1629  * (or otherwise set) by the caller to indicate that it is now
1630  * in use by the dcache.
1631  */
1632 static struct dentry *__d_instantiate_unique(struct dentry *entry,
1633                                              struct inode *inode)
1634 {
1635         struct dentry *alias;
1636         int len = entry->d_name.len;
1637         const char *name = entry->d_name.name;
1638         unsigned int hash = entry->d_name.hash;
1639 
1640         if (!inode) {
1641                 __d_instantiate(entry, NULL);
1642                 return NULL;
1643         }
1644 
1645         hlist_for_each_entry(alias, &inode->i_dentry, d_alias) {
1646                 /*
1647                  * Don't need alias->d_lock here, because aliases with
1648                  * d_parent == entry->d_parent are not subject to name or
1649                  * parent changes, because the parent inode i_mutex is held.
1650                  */
1651                 if (alias->d_name.hash != hash)
1652                         continue;
1653                 if (alias->d_parent != entry->d_parent)
1654                         continue;
1655                 if (alias->d_name.len != len)
1656                         continue;
1657                 if (dentry_cmp(alias, name, len))
1658                         continue;
1659                 __dget(alias);
1660                 return alias;
1661         }
1662 
1663         __d_instantiate(entry, inode);
1664         return NULL;
1665 }
1666 
1667 struct dentry *d_instantiate_unique(struct dentry *entry, struct inode *inode)
1668 {
1669         struct dentry *result;
1670 
1671         BUG_ON(!hlist_unhashed(&entry->d_alias));
1672 
1673         if (inode)
1674                 spin_lock(&inode->i_lock);
1675         result = __d_instantiate_unique(entry, inode);
1676         if (inode)
1677                 spin_unlock(&inode->i_lock);
1678 
1679         if (!result) {
1680                 security_d_instantiate(entry, inode);
1681                 return NULL;
1682         }
1683 
1684         BUG_ON(!d_unhashed(result));
1685         iput(inode);
1686         return result;
1687 }
1688 
1689 EXPORT_SYMBOL(d_instantiate_unique);
1690 
1691 /**
1692  * d_instantiate_no_diralias - instantiate a non-aliased dentry
1693  * @entry: dentry to complete
1694  * @inode: inode to attach to this dentry
1695  *
1696  * Fill in inode information in the entry.  If a directory alias is found, then
1697  * return an error (and drop inode).  Together with d_materialise_unique() this
1698  * guarantees that a directory inode may never have more than one alias.
1699  */
1700 int d_instantiate_no_diralias(struct dentry *entry, struct inode *inode)
1701 {
1702         BUG_ON(!hlist_unhashed(&entry->d_alias));
1703 
1704         spin_lock(&inode->i_lock);
1705         if (S_ISDIR(inode->i_mode) && !hlist_empty(&inode->i_dentry)) {
1706                 spin_unlock(&inode->i_lock);
1707                 iput(inode);
1708                 return -EBUSY;
1709         }
1710         __d_instantiate(entry, inode);
1711         spin_unlock(&inode->i_lock);
1712         security_d_instantiate(entry, inode);
1713 
1714         return 0;
1715 }
1716 EXPORT_SYMBOL(d_instantiate_no_diralias);
1717 
1718 struct dentry *d_make_root(struct inode *root_inode)
1719 {
1720         struct dentry *res = NULL;
1721 
1722         if (root_inode) {
1723                 static const struct qstr name = QSTR_INIT("/", 1);
1724 
1725                 res = __d_alloc(root_inode->i_sb, &name);
1726                 if (res)
1727                         d_instantiate(res, root_inode);
1728                 else
1729                         iput(root_inode);
1730         }
1731         return res;
1732 }
1733 EXPORT_SYMBOL(d_make_root);
1734 
1735 static struct dentry * __d_find_any_alias(struct inode *inode)
1736 {
1737         struct dentry *alias;
1738 
1739         if (hlist_empty(&inode->i_dentry))
1740                 return NULL;
1741         alias = hlist_entry(inode->i_dentry.first, struct dentry, d_alias);
1742         __dget(alias);
1743         return alias;
1744 }
1745 
1746 /**
1747  * d_find_any_alias - find any alias for a given inode
1748  * @inode: inode to find an alias for
1749  *
1750  * If any aliases exist for the given inode, take and return a
1751  * reference for one of them.  If no aliases exist, return %NULL.
1752  */
1753 struct dentry *d_find_any_alias(struct inode *inode)
1754 {
1755         struct dentry *de;
1756 
1757         spin_lock(&inode->i_lock);
1758         de = __d_find_any_alias(inode);
1759         spin_unlock(&inode->i_lock);
1760         return de;
1761 }
1762 EXPORT_SYMBOL(d_find_any_alias);
1763 
1764 static struct dentry *__d_obtain_alias(struct inode *inode, int disconnected)
1765 {
1766         static const struct qstr anonstring = QSTR_INIT("/", 1);
1767         struct dentry *tmp;
1768         struct dentry *res;
1769         unsigned add_flags;
1770 
1771         if (!inode)
1772                 return ERR_PTR(-ESTALE);
1773         if (IS_ERR(inode))
1774                 return ERR_CAST(inode);
1775 
1776         res = d_find_any_alias(inode);
1777         if (res)
1778                 goto out_iput;
1779 
1780         tmp = __d_alloc(inode->i_sb, &anonstring);
1781         if (!tmp) {
1782                 res = ERR_PTR(-ENOMEM);
1783                 goto out_iput;
1784         }
1785 
1786         spin_lock(&inode->i_lock);
1787         res = __d_find_any_alias(inode);
1788         if (res) {
1789                 spin_unlock(&inode->i_lock);
1790                 dput(tmp);
1791                 goto out_iput;
1792         }
1793 
1794         /* attach a disconnected dentry */
1795         add_flags = d_flags_for_inode(inode);
1796 
1797         if (disconnected)
1798                 add_flags |= DCACHE_DISCONNECTED;
1799 
1800         spin_lock(&tmp->d_lock);
1801         tmp->d_inode = inode;
1802         tmp->d_flags |= add_flags;
1803         hlist_add_head(&tmp->d_alias, &inode->i_dentry);
1804         hlist_bl_lock(&tmp->d_sb->s_anon);
1805         hlist_bl_add_head(&tmp->d_hash, &tmp->d_sb->s_anon);
1806         hlist_bl_unlock(&tmp->d_sb->s_anon);
1807         spin_unlock(&tmp->d_lock);
1808         spin_unlock(&inode->i_lock);
1809         security_d_instantiate(tmp, inode);
1810 
1811         return tmp;
1812 
1813  out_iput:
1814         if (res && !IS_ERR(res))
1815                 security_d_instantiate(res, inode);
1816         iput(inode);
1817         return res;
1818 }
1819 
1820 /**
1821  * d_obtain_alias - find or allocate a DISCONNECTED dentry for a given inode
1822  * @inode: inode to allocate the dentry for
1823  *
1824  * Obtain a dentry for an inode resulting from NFS filehandle conversion or
1825  * similar open by handle operations.  The returned dentry may be anonymous,
1826  * or may have a full name (if the inode was already in the cache).
1827  *
1828  * When called on a directory inode, we must ensure that the inode only ever
1829  * has one dentry.  If a dentry is found, that is returned instead of
1830  * allocating a new one.
1831  *
1832  * On successful return, the reference to the inode has been transferred
1833  * to the dentry.  In case of an error the reference on the inode is released.
1834  * To make it easier to use in export operations a %NULL or IS_ERR inode may
1835  * be passed in and the error will be propagated to the return value,
1836  * with a %NULL @inode replaced by ERR_PTR(-ESTALE).
1837  */
1838 struct dentry *d_obtain_alias(struct inode *inode)
1839 {
1840         return __d_obtain_alias(inode, 1);
1841 }
1842 EXPORT_SYMBOL(d_obtain_alias);
1843 
1844 /**
1845  * d_obtain_root - find or allocate a dentry for a given inode
1846  * @inode: inode to allocate the dentry for
1847  *
1848  * Obtain an IS_ROOT dentry for the root of a filesystem.
1849  *
1850  * We must ensure that directory inodes only ever have one dentry.  If a
1851  * dentry is found, that is returned instead of allocating a new one.
1852  *
1853  * On successful return, the reference to the inode has been transferred
1854  * to the dentry.  In case of an error the reference on the inode is
1855  * released.  A %NULL or IS_ERR inode may be passed in and will be the
1856  * error will be propagate to the return value, with a %NULL @inode
1857  * replaced by ERR_PTR(-ESTALE).
1858  */
1859 struct dentry *d_obtain_root(struct inode *inode)
1860 {
1861         return __d_obtain_alias(inode, 0);
1862 }
1863 EXPORT_SYMBOL(d_obtain_root);
1864 
1865 /**
1866  * d_add_ci - lookup or allocate new dentry with case-exact name
1867  * @inode:  the inode case-insensitive lookup has found
1868  * @dentry: the negative dentry that was passed to the parent's lookup func
1869  * @name:   the case-exact name to be associated with the returned dentry
1870  *
1871  * This is to avoid filling the dcache with case-insensitive names to the
1872  * same inode, only the actual correct case is stored in the dcache for
1873  * case-insensitive filesystems.
1874  *
1875  * For a case-insensitive lookup match and if the the case-exact dentry
1876  * already exists in in the dcache, use it and return it.
1877  *
1878  * If no entry exists with the exact case name, allocate new dentry with
1879  * the exact case, and return the spliced entry.
1880  */
1881 struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
1882                         struct qstr *name)
1883 {
1884         struct dentry *found;
1885         struct dentry *new;
1886 
1887         /*
1888          * First check if a dentry matching the name already exists,
1889          * if not go ahead and create it now.
1890          */
1891         found = d_hash_and_lookup(dentry->d_parent, name);
1892         if (unlikely(IS_ERR(found)))
1893                 goto err_out;
1894         if (!found) {
1895                 new = d_alloc(dentry->d_parent, name);
1896                 if (!new) {
1897                         found = ERR_PTR(-ENOMEM);
1898                         goto err_out;
1899                 }
1900 
1901                 found = d_splice_alias(inode, new);
1902                 if (found) {
1903                         dput(new);
1904                         return found;
1905                 }
1906                 return new;
1907         }
1908 
1909         /*
1910          * If a matching dentry exists, and it's not negative use it.
1911          *
1912          * Decrement the reference count to balance the iget() done
1913          * earlier on.
1914          */
1915         if (found->d_inode) {
1916                 if (unlikely(found->d_inode != inode)) {
1917                         /* This can't happen because bad inodes are unhashed. */
1918                         BUG_ON(!is_bad_inode(inode));
1919                         BUG_ON(!is_bad_inode(found->d_inode));
1920                 }
1921                 iput(inode);
1922                 return found;
1923         }
1924 
1925         /*
1926          * Negative dentry: instantiate it unless the inode is a directory and
1927          * already has a dentry.
1928          */
1929         new = d_splice_alias(inode, found);
1930         if (new) {
1931                 dput(found);
1932                 found = new;
1933         }
1934         return found;
1935 
1936 err_out:
1937         iput(inode);
1938         return found;
1939 }
1940 EXPORT_SYMBOL(d_add_ci);
1941 
1942 /*
1943  * Do the slow-case of the dentry name compare.
1944  *
1945  * Unlike the dentry_cmp() function, we need to atomically
1946  * load the name and length information, so that the
1947  * filesystem can rely on them, and can use the 'name' and
1948  * 'len' information without worrying about walking off the
1949  * end of memory etc.
1950  *
1951  * Thus the read_seqcount_retry() and the "duplicate" info
1952  * in arguments (the low-level filesystem should not look
1953  * at the dentry inode or name contents directly, since
1954  * rename can change them while we're in RCU mode).
1955  */
1956 enum slow_d_compare {
1957         D_COMP_OK,
1958         D_COMP_NOMATCH,
1959         D_COMP_SEQRETRY,
1960 };
1961 
1962 static noinline enum slow_d_compare slow_dentry_cmp(
1963                 const struct dentry *parent,
1964                 struct dentry *dentry,
1965                 unsigned int seq,
1966                 const struct qstr *name)
1967 {
1968         int tlen = dentry->d_name.len;
1969         const char *tname = dentry->d_name.name;
1970 
1971         if (read_seqcount_retry(&dentry->d_seq, seq)) {
1972                 cpu_relax();
1973                 return D_COMP_SEQRETRY;
1974         }
1975         if (parent->d_op->d_compare(parent, dentry, tlen, tname, name))
1976                 return D_COMP_NOMATCH;
1977         return D_COMP_OK;
1978 }
1979 
1980 /**
1981  * __d_lookup_rcu - search for a dentry (racy, store-free)
1982  * @parent: parent dentry
1983  * @name: qstr of name we wish to find
1984  * @seqp: returns d_seq value at the point where the dentry was found
1985  * Returns: dentry, or NULL
1986  *
1987  * __d_lookup_rcu is the dcache lookup function for rcu-walk name
1988  * resolution (store-free path walking) design described in
1989  * Documentation/filesystems/path-lookup.txt.
1990  *
1991  * This is not to be used outside core vfs.
1992  *
1993  * __d_lookup_rcu must only be used in rcu-walk mode, ie. with vfsmount lock
1994  * held, and rcu_read_lock held. The returned dentry must not be stored into
1995  * without taking d_lock and checking d_seq sequence count against @seq
1996  * returned here.
1997  *
1998  * A refcount may be taken on the found dentry with the d_rcu_to_refcount
1999  * function.
2000  *
2001  * Alternatively, __d_lookup_rcu may be called again to look up the child of
2002  * the returned dentry, so long as its parent's seqlock is checked after the
2003  * child is looked up. Thus, an interlocking stepping of sequence lock checks
2004  * is formed, giving integrity down the path walk.
2005  *
2006  * NOTE! The caller *has* to check the resulting dentry against the sequence
2007  * number we've returned before using any of the resulting dentry state!
2008  */
2009 struct dentry *__d_lookup_rcu(const struct dentry *parent,
2010                                 const struct qstr *name,
2011                                 unsigned *seqp)
2012 {
2013         u64 hashlen = name->hash_len;
2014         const unsigned char *str = name->name;
2015         struct hlist_bl_head *b = d_hash(parent, hashlen_hash(hashlen));
2016         struct hlist_bl_node *node;
2017         struct dentry *dentry;
2018 
2019         /*
2020          * Note: There is significant duplication with __d_lookup_rcu which is
2021          * required to prevent single threaded performance regressions
2022          * especially on architectures where smp_rmb (in seqcounts) are costly.
2023          * Keep the two functions in sync.
2024          */
2025 
2026         /*
2027          * The hash list is protected using RCU.
2028          *
2029          * Carefully use d_seq when comparing a candidate dentry, to avoid
2030          * races with d_move().
2031          *
2032          * It is possible that concurrent renames can mess up our list
2033          * walk here and result in missing our dentry, resulting in the
2034          * false-negative result. d_lookup() protects against concurrent
2035          * renames using rename_lock seqlock.
2036          *
2037          * See Documentation/filesystems/path-lookup.txt for more details.
2038          */
2039         hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
2040                 unsigned seq;
2041 
2042 seqretry:
2043                 /*
2044                  * The dentry sequence count protects us from concurrent
2045                  * renames, and thus protects parent and name fields.
2046                  *
2047                  * The caller must perform a seqcount check in order
2048                  * to do anything useful with the returned dentry.
2049                  *
2050                  * NOTE! We do a "raw" seqcount_begin here. That means that
2051                  * we don't wait for the sequence count to stabilize if it
2052                  * is in the middle of a sequence change. If we do the slow
2053                  * dentry compare, we will do seqretries until it is stable,
2054                  * and if we end up with a successful lookup, we actually
2055                  * want to exit RCU lookup anyway.
2056                  */
2057                 seq = raw_seqcount_begin(&dentry->d_seq);
2058                 if (dentry->d_parent != parent)
2059                         continue;
2060                 if (d_unhashed(dentry))
2061                         continue;
2062 
2063                 if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
2064                         if (dentry->d_name.hash != hashlen_hash(hashlen))
2065                                 continue;
2066                         *seqp = seq;
2067                         switch (slow_dentry_cmp(parent, dentry, seq, name)) {
2068                         case D_COMP_OK:
2069                                 return dentry;
2070                         case D_COMP_NOMATCH:
2071                                 continue;
2072                         default:
2073                                 goto seqretry;
2074                         }
2075                 }
2076 
2077                 if (dentry->d_name.hash_len != hashlen)
2078                         continue;
2079                 *seqp = seq;
2080                 if (!dentry_cmp(dentry, str, hashlen_len(hashlen)))
2081                         return dentry;
2082         }
2083         return NULL;
2084 }
2085 
2086 /**
2087  * d_lookup - search for a dentry
2088  * @parent: parent dentry
2089  * @name: qstr of name we wish to find
2090  * Returns: dentry, or NULL
2091  *
2092  * d_lookup searches the children of the parent dentry for the name in
2093  * question. If the dentry is found its reference count is incremented and the
2094  * dentry is returned. The caller must use dput to free the entry when it has
2095  * finished using it. %NULL is returned if the dentry does not exist.
2096  */
2097 struct dentry *d_lookup(const struct dentry *parent, const struct qstr *name)
2098 {
2099         struct dentry *dentry;
2100         unsigned seq;
2101 
2102         do {
2103                 seq = read_seqbegin(&rename_lock);
2104                 dentry = __d_lookup(parent, name);
2105                 if (dentry)
2106                         break;
2107         } while (read_seqretry(&rename_lock, seq));
2108         return dentry;
2109 }
2110 EXPORT_SYMBOL(d_lookup);
2111 
2112 /**
2113  * __d_lookup - search for a dentry (racy)
2114  * @parent: parent dentry
2115  * @name: qstr of name we wish to find
2116  * Returns: dentry, or NULL
2117  *
2118  * __d_lookup is like d_lookup, however it may (rarely) return a
2119  * false-negative result due to unrelated rename activity.
2120  *
2121  * __d_lookup is slightly faster by avoiding rename_lock read seqlock,
2122  * however it must be used carefully, eg. with a following d_lookup in
2123  * the case of failure.
2124  *
2125  * __d_lookup callers must be commented.
2126  */
2127 struct dentry *__d_lookup(const struct dentry *parent, const struct qstr *name)
2128 {
2129         unsigned int len = name->len;
2130         unsigned int hash = name->hash;
2131         const unsigned char *str = name->name;
2132         struct hlist_bl_head *b = d_hash(parent, hash);
2133         struct hlist_bl_node *node;
2134         struct dentry *found = NULL;
2135         struct dentry *dentry;
2136 
2137         /*
2138          * Note: There is significant duplication with __d_lookup_rcu which is
2139          * required to prevent single threaded performance regressions
2140          * especially on architectures where smp_rmb (in seqcounts) are costly.
2141          * Keep the two functions in sync.
2142          */
2143 
2144         /*
2145          * The hash list is protected using RCU.
2146          *
2147          * Take d_lock when comparing a candidate dentry, to avoid races
2148          * with d_move().
2149          *
2150          * It is possible that concurrent renames can mess up our list
2151          * walk here and result in missing our dentry, resulting in the
2152          * false-negative result. d_lookup() protects against concurrent
2153          * renames using rename_lock seqlock.
2154          *
2155          * See Documentation/filesystems/path-lookup.txt for more details.
2156          */
2157         rcu_read_lock();
2158         
2159         hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
2160 
2161                 if (dentry->d_name.hash != hash)
2162                         continue;
2163 
2164                 spin_lock(&dentry->d_lock);
2165                 if (dentry->d_parent != parent)
2166                         goto next;
2167                 if (d_unhashed(dentry))
2168                         goto next;
2169 
2170                 /*
2171                  * It is safe to compare names since d_move() cannot
2172                  * change the qstr (protected by d_lock).
2173                  */
2174                 if (parent->d_flags & DCACHE_OP_COMPARE) {
2175                         int tlen = dentry->d_name.len;
2176                         const char *tname = dentry->d_name.name;
2177                         if (parent->d_op->d_compare(parent, dentry, tlen, tname, name))
2178                                 goto next;
2179                 } else {
2180                         if (dentry->d_name.len != len)
2181                                 goto next;
2182                         if (dentry_cmp(dentry, str, len))
2183                                 goto next;
2184                 }
2185 
2186                 dentry->d_lockref.count++;
2187                 found = dentry;
2188                 spin_unlock(&dentry->d_lock);
2189                 break;
2190 next:
2191                 spin_unlock(&dentry->d_lock);
2192         }
2193         rcu_read_unlock();
2194 
2195         return found;
2196 }
2197 
2198 /**
2199  * d_hash_and_lookup - hash the qstr then search for a dentry
2200  * @dir: Directory to search in
2201  * @name: qstr of name we wish to find
2202  *
2203  * On lookup failure NULL is returned; on bad name - ERR_PTR(-error)
2204  */
2205 struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
2206 {
2207         /*
2208          * Check for a fs-specific hash function. Note that we must
2209          * calculate the standard hash first, as the d_op->d_hash()
2210          * routine may choose to leave the hash value unchanged.
2211          */
2212         name->hash = full_name_hash(name->name, name->len);
2213         if (dir->d_flags & DCACHE_OP_HASH) {
2214                 int err = dir->d_op->d_hash(dir, name);
2215                 if (unlikely(err < 0))
2216                         return ERR_PTR(err);
2217         }
2218         return d_lookup(dir, name);
2219 }
2220 EXPORT_SYMBOL(d_hash_and_lookup);
2221 
2222 /**
2223  * d_validate - verify dentry provided from insecure source (deprecated)
2224  * @dentry: The dentry alleged to be valid child of @dparent
2225  * @dparent: The parent dentry (known to be valid)
2226  *
2227  * An insecure source has sent us a dentry, here we verify it and dget() it.
2228  * This is used by ncpfs in its readdir implementation.
2229  * Zero is returned in the dentry is invalid.
2230  *
2231  * This function is slow for big directories, and deprecated, do not use it.
2232  */
2233 int d_validate(struct dentry *dentry, struct dentry *dparent)
2234 {
2235         struct dentry *child;
2236 
2237         spin_lock(&dparent->d_lock);
2238         list_for_each_entry(child, &dparent->d_subdirs, d_u.d_child) {
2239                 if (dentry == child) {
2240                         spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
2241                         __dget_dlock(dentry);
2242                         spin_unlock(&dentry->d_lock);
2243                         spin_unlock(&dparent->d_lock);
2244                         return 1;
2245                 }
2246         }
2247         spin_unlock(&dparent->d_lock);
2248 
2249         return 0;
2250 }
2251 EXPORT_SYMBOL(d_validate);
2252 
2253 /*
2254  * When a file is deleted, we have two options:
2255  * - turn this dentry into a negative dentry
2256  * - unhash this dentry and free it.
2257  *
2258  * Usually, we want to just turn this into
2259  * a negative dentry, but if anybody else is
2260  * currently using the dentry or the inode
2261  * we can't do that and we fall back on removing
2262  * it from the hash queues and waiting for
2263  * it to be deleted later when it has no users
2264  */
2265  
2266 /**
2267  * d_delete - delete a dentry
2268  * @dentry: The dentry to delete
2269  *
2270  * Turn the dentry into a negative dentry if possible, otherwise
2271  * remove it from the hash queues so it can be deleted later
2272  */
2273  
2274 void d_delete(struct dentry * dentry)
2275 {
2276         struct inode *inode;
2277         int isdir = 0;
2278         /*
2279          * Are we the only user?
2280          */
2281 again:
2282         spin_lock(&dentry->d_lock);
2283         inode = dentry->d_inode;
2284         isdir = S_ISDIR(inode->i_mode);
2285         if (dentry->d_lockref.count == 1) {
2286                 if (!spin_trylock(&inode->i_lock)) {
2287                         spin_unlock(&dentry->d_lock);
2288                         cpu_relax();
2289                         goto again;
2290                 }
2291                 dentry->d_flags &= ~DCACHE_CANT_MOUNT;
2292                 dentry_unlink_inode(dentry);
2293                 fsnotify_nameremove(dentry, isdir);
2294                 return;
2295         }
2296 
2297         if (!d_unhashed(dentry))
2298                 __d_drop(dentry);
2299 
2300         spin_unlock(&dentry->d_lock);
2301 
2302         fsnotify_nameremove(dentry, isdir);
2303 }
2304 EXPORT_SYMBOL(d_delete);
2305 
2306 static void __d_rehash(struct dentry * entry, struct hlist_bl_head *b)
2307 {
2308         BUG_ON(!d_unhashed(entry));
2309         hlist_bl_lock(b);
2310         entry->d_flags |= DCACHE_RCUACCESS;
2311         hlist_bl_add_head_rcu(&entry->d_hash, b);
2312         hlist_bl_unlock(b);
2313 }
2314 
2315 static void _d_rehash(struct dentry * entry)
2316 {
2317         __d_rehash(entry, d_hash(entry->d_parent, entry->d_name.hash));
2318 }
2319 
2320 /**
2321  * d_rehash     - add an entry back to the hash
2322  * @entry: dentry to add to the hash
2323  *
2324  * Adds a dentry to the hash according to its name.
2325  */
2326  
2327 void d_rehash(struct dentry * entry)
2328 {
2329         spin_lock(&entry->d_lock);
2330         _d_rehash(entry);
2331         spin_unlock(&entry->d_lock);
2332 }
2333 EXPORT_SYMBOL(d_rehash);
2334 
2335 /**
2336  * dentry_update_name_case - update case insensitive dentry with a new name
2337  * @dentry: dentry to be updated
2338  * @name: new name
2339  *
2340  * Update a case insensitive dentry with new case of name.
2341  *
2342  * dentry must have been returned by d_lookup with name @name. Old and new
2343  * name lengths must match (ie. no d_compare which allows mismatched name
2344  * lengths).
2345  *
2346  * Parent inode i_mutex must be held over d_lookup and into this call (to
2347  * keep renames and concurrent inserts, and readdir(2) away).
2348  */
2349 void dentry_update_name_case(struct dentry *dentry, struct qstr *name)
2350 {
2351         BUG_ON(!mutex_is_locked(&dentry->d_parent->d_inode->i_mutex));
2352         BUG_ON(dentry->d_name.len != name->len); /* d_lookup gives this */
2353 
2354         spin_lock(&dentry->d_lock);
2355         write_seqcount_begin(&dentry->d_seq);
2356         memcpy((unsigned char *)dentry->d_name.name, name->name, name->len);
2357         write_seqcount_end(&dentry->d_seq);
2358         spin_unlock(&dentry->d_lock);
2359 }
2360 EXPORT_SYMBOL(dentry_update_name_case);
2361 
2362 static void swap_names(struct dentry *dentry, struct dentry *target)
2363 {
2364         if (unlikely(dname_external(target))) {
2365                 if (unlikely(dname_external(dentry))) {
2366                         /*
2367                          * Both external: swap the pointers
2368                          */
2369                         swap(target->d_name.name, dentry->d_name.name);
2370                 } else {
2371                         /*
2372                          * dentry:internal, target:external.  Steal target's
2373                          * storage and make target internal.
2374                          */
2375                         memcpy(target->d_iname, dentry->d_name.name,
2376                                         dentry->d_name.len + 1);
2377                         dentry->d_name.name = target->d_name.name;
2378                         target->d_name.name = target->d_iname;
2379                 }
2380         } else {
2381                 if (unlikely(dname_external(dentry))) {
2382                         /*
2383                          * dentry:external, target:internal.  Give dentry's
2384                          * storage to target and make dentry internal
2385                          */
2386                         memcpy(dentry->d_iname, target->d_name.name,
2387                                         target->d_name.len + 1);
2388                         target->d_name.name = dentry->d_name.name;
2389                         dentry->d_name.name = dentry->d_iname;
2390                 } else {
2391                         /*
2392                          * Both are internal.
2393                          */
2394                         unsigned int i;
2395                         BUILD_BUG_ON(!IS_ALIGNED(DNAME_INLINE_LEN, sizeof(long)));
2396                         for (i = 0; i < DNAME_INLINE_LEN / sizeof(long); i++) {
2397                                 swap(((long *) &dentry->d_iname)[i],
2398                                      ((long *) &target->d_iname)[i]);
2399                         }
2400                 }
2401         }
2402         swap(dentry->d_name.hash_len, target->d_name.hash_len);
2403 }
2404 
2405 static void copy_name(struct dentry *dentry, struct dentry *target)
2406 {
2407         struct external_name *old_name = NULL;
2408         if (unlikely(dname_external(dentry)))
2409                 old_name = external_name(dentry);
2410         if (unlikely(dname_external(target))) {
2411                 atomic_inc(&external_name(target)->u.count);
2412                 dentry->d_name = target->d_name;
2413         } else {
2414                 memcpy(dentry->d_iname, target->d_name.name,
2415                                 target->d_name.len + 1);
2416                 dentry->d_name.name = dentry->d_iname;
2417                 dentry->d_name.hash_len = target->d_name.hash_len;
2418         }
2419         if (old_name && likely(atomic_dec_and_test(&old_name->u.count)))
2420                 kfree_rcu(old_name, u.head);
2421 }
2422 
2423 static void dentry_lock_for_move(struct dentry *dentry, struct dentry *target)
2424 {
2425         /*
2426          * XXXX: do we really need to take target->d_lock?
2427          */
2428         if (IS_ROOT(dentry) || dentry->d_parent == target->d_parent)
2429                 spin_lock(&target->d_parent->d_lock);
2430         else {
2431                 if (d_ancestor(dentry->d_parent, target->d_parent)) {
2432                         spin_lock(&dentry->d_parent->d_lock);
2433                         spin_lock_nested(&target->d_parent->d_lock,
2434                                                 DENTRY_D_LOCK_NESTED);
2435                 } else {
2436                         spin_lock(&target->d_parent->d_lock);
2437                         spin_lock_nested(&dentry->d_parent->d_lock,
2438                                                 DENTRY_D_LOCK_NESTED);
2439                 }
2440         }
2441         if (target < dentry) {
2442                 spin_lock_nested(&target->d_lock, 2);
2443                 spin_lock_nested(&dentry->d_lock, 3);
2444         } else {
2445                 spin_lock_nested(&dentry->d_lock, 2);
2446                 spin_lock_nested(&target->d_lock, 3);
2447         }
2448 }
2449 
2450 static void dentry_unlock_for_move(struct dentry *dentry, struct dentry *target)
2451 {
2452         if (target->d_parent != dentry->d_parent)
2453                 spin_unlock(&dentry->d_parent->d_lock);
2454         if (target->d_parent != target)
2455                 spin_unlock(&target->d_parent->d_lock);
2456         spin_unlock(&target->d_lock);
2457         spin_unlock(&dentry->d_lock);
2458 }
2459 
2460 /*
2461  * When switching names, the actual string doesn't strictly have to
2462  * be preserved in the target - because we're dropping the target
2463  * anyway. As such, we can just do a simple memcpy() to copy over
2464  * the new name before we switch, unless we are going to rehash
2465  * it.  Note that if we *do* unhash the target, we are not allowed
2466  * to rehash it without giving it a new name/hash key - whether
2467  * we swap or overwrite the names here, resulting name won't match
2468  * the reality in filesystem; it's only there for d_path() purposes.
2469  * Note that all of this is happening under rename_lock, so the
2470  * any hash lookup seeing it in the middle of manipulations will
2471  * be discarded anyway.  So we do not care what happens to the hash
2472  * key in that case.
2473  */
2474 /*
2475  * __d_move - move a dentry
2476  * @dentry: entry to move
2477  * @target: new dentry
2478  * @exchange: exchange the two dentries
2479  *
2480  * Update the dcache to reflect the move of a file name. Negative
2481  * dcache entries should not be moved in this way. Caller must hold
2482  * rename_lock, the i_mutex of the source and target directories,
2483  * and the sb->s_vfs_rename_mutex if they differ. See lock_rename().
2484  */
2485 static void __d_move(struct dentry *dentry, struct dentry *target,
2486                      bool exchange)
2487 {
2488         if (!dentry->d_inode)
2489                 printk(KERN_WARNING "VFS: moving negative dcache entry\n");
2490 
2491         BUG_ON(d_ancestor(dentry, target));
2492         BUG_ON(d_ancestor(target, dentry));
2493 
2494         dentry_lock_for_move(dentry, target);
2495 
2496         write_seqcount_begin(&dentry->d_seq);
2497         write_seqcount_begin_nested(&target->d_seq, DENTRY_D_LOCK_NESTED);
2498 
2499         /* __d_drop does write_seqcount_barrier, but they're OK to nest. */
2500 
2501         /*
2502          * Move the dentry to the target hash queue. Don't bother checking
2503          * for the same hash queue because of how unlikely it is.
2504          */
2505         __d_drop(dentry);
2506         __d_rehash(dentry, d_hash(target->d_parent, target->d_name.hash));
2507 
2508         /*
2509          * Unhash the target (d_delete() is not usable here).  If exchanging
2510          * the two dentries, then rehash onto the other's hash queue.
2511          */
2512         __d_drop(target);
2513         if (exchange) {
2514                 __d_rehash(target,
2515                            d_hash(dentry->d_parent, dentry->d_name.hash));
2516         }
2517 
2518         /* Switch the names.. */
2519         if (exchange)
2520                 swap_names(dentry, target);
2521         else
2522                 copy_name(dentry, target);
2523 
2524         /* ... and switch them in the tree */
2525         if (IS_ROOT(dentry)) {
2526                 /* splicing a tree */
2527                 dentry->d_parent = target->d_parent;
2528                 target->d_parent = target;
2529                 list_del_init(&target->d_u.d_child);
2530                 list_move(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
2531         } else {
2532                 /* swapping two dentries */
2533                 swap(dentry->d_parent, target->d_parent);
2534                 list_move(&target->d_u.d_child, &target->d_parent->d_subdirs);
2535                 list_move(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
2536                 if (exchange)
2537                         fsnotify_d_move(target);
2538                 fsnotify_d_move(dentry);
2539         }
2540 
2541         write_seqcount_end(&target->d_seq);
2542         write_seqcount_end(&dentry->d_seq);
2543 
2544         dentry_unlock_for_move(dentry, target);
2545 }
2546 
2547 /*
2548  * d_move - move a dentry
2549  * @dentry: entry to move
2550  * @target: new dentry
2551  *
2552  * Update the dcache to reflect the move of a file name. Negative
2553  * dcache entries should not be moved in this way. See the locking
2554  * requirements for __d_move.
2555  */
2556 void d_move(struct dentry *dentry, struct dentry *target)
2557 {
2558         write_seqlock(&rename_lock);
2559         __d_move(dentry, target, false);
2560         write_sequnlock(&rename_lock);
2561 }
2562 EXPORT_SYMBOL(d_move);
2563 
2564 /*
2565  * d_exchange - exchange two dentries
2566  * @dentry1: first dentry
2567  * @dentry2: second dentry
2568  */
2569 void d_exchange(struct dentry *dentry1, struct dentry *dentry2)
2570 {
2571         write_seqlock(&rename_lock);
2572 
2573         WARN_ON(!dentry1->d_inode);
2574         WARN_ON(!dentry2->d_inode);
2575         WARN_ON(IS_ROOT(dentry1));
2576         WARN_ON(IS_ROOT(dentry2));
2577 
2578         __d_move(dentry1, dentry2, true);
2579 
2580         write_sequnlock(&rename_lock);
2581 }
2582 
2583 /**
2584  * d_ancestor - search for an ancestor
2585  * @p1: ancestor dentry
2586  * @p2: child dentry
2587  *
2588  * Returns the ancestor dentry of p2 which is a child of p1, if p1 is
2589  * an ancestor of p2, else NULL.
2590  */
2591 struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
2592 {
2593         struct dentry *p;
2594 
2595         for (p = p2; !IS_ROOT(p); p = p->d_parent) {
2596                 if (p->d_parent == p1)
2597                         return p;
2598         }
2599         return NULL;
2600 }
2601 
2602 /*
2603  * This helper attempts to cope with remotely renamed directories
2604  *
2605  * It assumes that the caller is already holding
2606  * dentry->d_parent->d_inode->i_mutex, inode->i_lock and rename_lock
2607  *
2608  * Note: If ever the locking in lock_rename() changes, then please
2609  * remember to update this too...
2610  */
2611 static struct dentry *__d_unalias(struct inode *inode,
2612                 struct dentry *dentry, struct dentry *alias)
2613 {
2614         struct mutex *m1 = NULL, *m2 = NULL;
2615         struct dentry *ret = ERR_PTR(-EBUSY);
2616 
2617         /* If alias and dentry share a parent, then no extra locks required */
2618         if (alias->d_parent == dentry->d_parent)
2619                 goto out_unalias;
2620 
2621         /* See lock_rename() */
2622         if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
2623                 goto out_err;
2624         m1 = &dentry->d_sb->s_vfs_rename_mutex;
2625         if (!mutex_trylock(&alias->d_parent->d_inode->i_mutex))
2626                 goto out_err;
2627         m2 = &alias->d_parent->d_inode->i_mutex;
2628 out_unalias:
2629         __d_move(alias, dentry, false);
2630         ret = alias;
2631 out_err:
2632         spin_unlock(&inode->i_lock);
2633         if (m2)
2634                 mutex_unlock(m2);
2635         if (m1)
2636                 mutex_unlock(m1);
2637         return ret;
2638 }
2639 
2640 /**
2641  * d_splice_alias - splice a disconnected dentry into the tree if one exists
2642  * @inode:  the inode which may have a disconnected dentry
2643  * @dentry: a negative dentry which we want to point to the inode.
2644  *
2645  * If inode is a directory and has an IS_ROOT alias, then d_move that in
2646  * place of the given dentry and return it, else simply d_add the inode
2647  * to the dentry and return NULL.
2648  *
2649  * If a non-IS_ROOT directory is found, the filesystem is corrupt, and
2650  * we should error out: directories can't have multiple aliases.
2651  *
2652  * This is needed in the lookup routine of any filesystem that is exportable
2653  * (via knfsd) so that we can build dcache paths to directories effectively.
2654  *
2655  * If a dentry was found and moved, then it is returned.  Otherwise NULL
2656  * is returned.  This matches the expected return value of ->lookup.
2657  *
2658  * Cluster filesystems may call this function with a negative, hashed dentry.
2659  * In that case, we know that the inode will be a regular file, and also this
2660  * will only occur during atomic_open. So we need to check for the dentry
2661  * being already hashed only in the final case.
2662  */
2663 struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
2664 {
2665         struct dentry *new = NULL;
2666 
2667         if (IS_ERR(inode))
2668                 return ERR_CAST(inode);
2669 
2670         if (inode && S_ISDIR(inode->i_mode)) {
2671                 spin_lock(&inode->i_lock);
2672                 new = __d_find_any_alias(inode);
2673                 if (new) {
2674                         if (!IS_ROOT(new)) {
2675                                 spin_unlock(&inode->i_lock);
2676                                 dput(new);
2677                                 iput(inode);
2678                                 return ERR_PTR(-EIO);
2679                         }
2680                         if (d_ancestor(new, dentry)) {
2681                                 spin_unlock(&inode->i_lock);
2682                                 dput(new);
2683                                 iput(inode);
2684                                 return ERR_PTR(-EIO);
2685                         }
2686                         write_seqlock(&rename_lock);
2687                         __d_move(new, dentry, false);
2688                         write_sequnlock(&rename_lock);
2689                         spin_unlock(&inode->i_lock);
2690                         security_d_instantiate(new, inode);
2691                         iput(inode);
2692                 } else {
2693                         /* already taking inode->i_lock, so d_add() by hand */
2694                         __d_instantiate(dentry, inode);
2695                         spin_unlock(&inode->i_lock);
2696                         security_d_instantiate(dentry, inode);
2697                         d_rehash(dentry);
2698                 }
2699         } else {
2700                 d_instantiate(dentry, inode);
2701                 if (d_unhashed(dentry))
2702                         d_rehash(dentry);
2703         }
2704         return new;
2705 }
2706 EXPORT_SYMBOL(d_splice_alias);
2707 
2708 /**
2709  * d_materialise_unique - introduce an inode into the tree
2710  * @dentry: candidate dentry
2711  * @inode: inode to bind to the dentry, to which aliases may be attached
2712  *
2713  * Introduces an dentry into the tree, substituting an extant disconnected
2714  * root directory alias in its place if there is one. Caller must hold the
2715  * i_mutex of the parent directory.
2716  */
2717 struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode)
2718 {
2719         struct dentry *actual;
2720 
2721         BUG_ON(!d_unhashed(dentry));
2722 
2723         if (!inode) {
2724                 actual = dentry;
2725                 __d_instantiate(dentry, NULL);
2726                 d_rehash(actual);
2727                 goto out_nolock;
2728         }
2729 
2730         spin_lock(&inode->i_lock);
2731 
2732         if (S_ISDIR(inode->i_mode)) {
2733                 struct dentry *alias;
2734 
2735                 /* Does an aliased dentry already exist? */
2736                 alias = __d_find_alias(inode);
2737                 if (alias) {
2738                         actual = alias;
2739                         write_seqlock(&rename_lock);
2740 
2741                         if (d_ancestor(alias, dentry)) {
2742                                 /* Check for loops */
2743                                 actual = ERR_PTR(-ELOOP);
2744                                 spin_unlock(&inode->i_lock);
2745                         } else if (IS_ROOT(alias)) {
2746                                 /* Is this an anonymous mountpoint that we
2747                                  * could splice into our tree? */
2748                                 __d_move(alias, dentry, false);
2749                                 write_sequnlock(&rename_lock);
2750                                 goto found;
2751                         } else {
2752                                 /* Nope, but we must(!) avoid directory
2753                                  * aliasing. This drops inode->i_lock */
2754                                 actual = __d_unalias(inode, dentry, alias);
2755                         }
2756                         write_sequnlock(&rename_lock);
2757                         if (IS_ERR(actual)) {
2758                                 if (PTR_ERR(actual) == -ELOOP)
2759                                         pr_warn_ratelimited(
2760                                                 "VFS: Lookup of '%s' in %s %s"
2761                                                 " would have caused loop\n",
2762                                                 dentry->d_name.name,
2763                                                 inode->i_sb->s_type->name,
2764                                                 inode->i_sb->s_id);
2765                                 dput(alias);
2766                         }
2767                         goto out_nolock;
2768                 }
2769         }
2770 
2771         /* Add a unique reference */
2772         actual = __d_instantiate_unique(dentry, inode);
2773         if (!actual)
2774                 actual = dentry;
2775 
2776         d_rehash(actual);
2777 found:
2778         spin_unlock(&inode->i_lock);
2779 out_nolock:
2780         if (actual == dentry) {
2781                 security_d_instantiate(dentry, inode);
2782                 return NULL;
2783         }
2784 
2785         iput(inode);
2786         return actual;
2787 }
2788 EXPORT_SYMBOL_GPL(d_materialise_unique);
2789 
2790 static int prepend(char **buffer, int *buflen, const char *str, int namelen)
2791 {
2792         *buflen -= namelen;
2793         if (*buflen < 0)
2794                 return -ENAMETOOLONG;
2795         *buffer -= namelen;
2796         memcpy(*buffer, str, namelen);
2797         return 0;
2798 }
2799 
2800 /**
2801  * prepend_name - prepend a pathname in front of current buffer pointer
2802  * @buffer: buffer pointer
2803  * @buflen: allocated length of the buffer
2804  * @name:   name string and length qstr structure
2805  *
2806  * With RCU path tracing, it may race with d_move(). Use ACCESS_ONCE() to
2807  * make sure that either the old or the new name pointer and length are
2808  * fetched. However, there may be mismatch between length and pointer.
2809  * The length cannot be trusted, we need to copy it byte-by-byte until
2810  * the length is reached or a null byte is found. It also prepends "/" at
2811  * the beginning of the name. The sequence number check at the caller will
2812  * retry it again when a d_move() does happen. So any garbage in the buffer
2813  * due to mismatched pointer and length will be discarded.
2814  *
2815  * Data dependency barrier is needed to make sure that we see that terminating
2816  * NUL.  Alpha strikes again, film at 11...
2817  */
2818 static int prepend_name(char **buffer, int *buflen, struct qstr *name)
2819 {
2820         const char *dname = ACCESS_ONCE(name->name);
2821         u32 dlen = ACCESS_ONCE(name->len);
2822         char *p;
2823 
2824         smp_read_barrier_depends();
2825 
2826         *buflen -= dlen + 1;
2827         if (*buflen < 0)
2828                 return -ENAMETOOLONG;
2829         p = *buffer -= dlen + 1;
2830         *p++ = '/';
2831         while (dlen--) {
2832                 char c = *dname++;
2833                 if (!c)
2834                         break;
2835                 *p++ = c;
2836         }
2837         return 0;
2838 }
2839 
2840 /**
2841  * prepend_path - Prepend path string to a buffer
2842  * @path: the dentry/vfsmount to report
2843  * @root: root vfsmnt/dentry
2844  * @buffer: pointer to the end of the buffer
2845  * @buflen: pointer to buffer length
2846  *
2847  * The function will first try to write out the pathname without taking any
2848  * lock other than the RCU read lock to make sure that dentries won't go away.
2849  * It only checks the sequence number of the global rename_lock as any change
2850  * in the dentry's d_seq will be preceded by changes in the rename_lock
2851  * sequence number. If the sequence number had been changed, it will restart
2852  * the whole pathname back-tracing sequence again by taking the rename_lock.
2853  * In this case, there is no need to take the RCU read lock as the recursive
2854  * parent pointer references will keep the dentry chain alive as long as no
2855  * rename operation is performed.
2856  */
2857 static int prepend_path(const struct path *path,
2858                         const struct path *root,
2859                         char **buffer, int *buflen)
2860 {
2861         struct dentry *dentry;
2862         struct vfsmount *vfsmnt;
2863         struct mount *mnt;
2864         int error = 0;
2865         unsigned seq, m_seq = 0;
2866         char *bptr;
2867         int blen;
2868 
2869         rcu_read_lock();
2870 restart_mnt:
2871         read_seqbegin_or_lock(&mount_lock, &m_seq);
2872         seq = 0;
2873         rcu_read_lock();
2874 restart:
2875         bptr = *buffer;
2876         blen = *buflen;
2877         error = 0;
2878         dentry = path->dentry;
2879         vfsmnt = path->mnt;
2880         mnt = real_mount(vfsmnt);
2881         read_seqbegin_or_lock(&rename_lock, &seq);
2882         while (dentry != root->dentry || vfsmnt != root->mnt) {
2883                 struct dentry * parent;
2884 
2885                 if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
2886                         struct mount *parent = ACCESS_ONCE(mnt->mnt_parent);
2887                         /* Global root? */
2888                         if (mnt != parent) {
2889                                 dentry = ACCESS_ONCE(mnt->mnt_mountpoint);
2890                                 mnt = parent;
2891                                 vfsmnt = &mnt->mnt;
2892                                 continue;
2893                         }
2894                         /*
2895                          * Filesystems needing to implement special "root names"
2896                          * should do so with ->d_dname()
2897                          */
2898                         if (IS_ROOT(dentry) &&
2899                            (dentry->d_name.len != 1 ||
2900                             dentry->d_name.name[0] != '/')) {
2901                                 WARN(1, "Root dentry has weird name <%.*s>\n",
2902                                      (int) dentry->d_name.len,
2903                                      dentry->d_name.name);
2904                         }
2905                         if (!error)
2906                                 error = is_mounted(vfsmnt) ? 1 : 2;
2907                         break;
2908                 }
2909                 parent = dentry->d_parent;
2910                 prefetch(parent);
2911                 error = prepend_name(&bptr, &blen, &dentry->d_name);
2912                 if (error)
2913                         break;
2914 
2915                 dentry = parent;
2916         }
2917         if (!(seq & 1))
2918                 rcu_read_unlock();
2919         if (need_seqretry(&rename_lock, seq)) {
2920                 seq = 1;
2921                 goto restart;
2922         }
2923         done_seqretry(&rename_lock, seq);
2924 
2925         if (!(m_seq & 1))
2926                 rcu_read_unlock();
2927         if (need_seqretry(&mount_lock, m_seq)) {
2928                 m_seq = 1;
2929                 goto restart_mnt;
2930         }
2931         done_seqretry(&mount_lock, m_seq);
2932 
2933         if (error >= 0 && bptr == *buffer) {
2934                 if (--blen < 0)
2935                         error = -ENAMETOOLONG;
2936                 else
2937                         *--bptr = '/';
2938         }
2939         *buffer = bptr;
2940         *buflen = blen;
2941         return error;
2942 }
2943 
2944 /**
2945  * __d_path - return the path of a dentry
2946  * @path: the dentry/vfsmount to report
2947  * @root: root vfsmnt/dentry
2948  * @buf: buffer to return value in
2949  * @buflen: buffer length
2950  *
2951  * Convert a dentry into an ASCII path name.
2952  *
2953  * Returns a pointer into the buffer or an error code if the
2954  * path was too long.
2955  *
2956  * "buflen" should be positive.
2957  *
2958  * If the path is not reachable from the supplied root, return %NULL.
2959  */
2960 char *__d_path(const struct path *path,
2961                const struct path *root,
2962                char *buf, int buflen)
2963 {
2964         char *res = buf + buflen;
2965         int error;
2966 
2967         prepend(&res, &buflen, "\0", 1);
2968         error = prepend_path(path, root, &res, &buflen);
2969 
2970         if (error < 0)
2971                 return ERR_PTR(error);
2972         if (error > 0)
2973                 return NULL;
2974         return res;
2975 }
2976 
2977 char *d_absolute_path(const struct path *path,
2978                char *buf, int buflen)
2979 {
2980         struct path root = {};
2981         char *res = buf + buflen;
2982         int error;
2983 
2984         prepend(&res, &buflen, "\0", 1);
2985         error = prepend_path(path, &root, &res, &buflen);
2986 
2987         if (error > 1)
2988                 error = -EINVAL;
2989         if (error < 0)
2990                 return ERR_PTR(error);
2991         return res;
2992 }
2993 
2994 /*
2995  * same as __d_path but appends "(deleted)" for unlinked files.
2996  */
2997 static int path_with_deleted(const struct path *path,
2998                              const struct path *root,
2999                              char **buf, int *buflen)
3000 {
3001         prepend(buf, buflen, "\0", 1);
3002         if (d_unlinked(path->dentry)) {
3003                 int error = prepend(buf, buflen, " (deleted)", 10);
3004                 if (error)
3005                         return error;
3006         }
3007 
3008         return prepend_path(path, root, buf, buflen);
3009 }
3010 
3011 static int prepend_unreachable(char **buffer, int *buflen)
3012 {
3013         return prepend(buffer, buflen, "(unreachable)", 13);
3014 }
3015 
3016 static void get_fs_root_rcu(struct fs_struct *fs, struct path *root)
3017 {
3018         unsigned seq;
3019 
3020         do {
3021                 seq = read_seqcount_begin(&fs->seq);
3022                 *root = fs->root;
3023         } while (read_seqcount_retry(&fs->seq, seq));
3024 }
3025 
3026 /**
3027  * d_path - return the path of a dentry
3028  * @path: path to report
3029  * @buf: buffer to return value in
3030  * @buflen: buffer length
3031  *
3032  * Convert a dentry into an ASCII path name. If the entry has been deleted
3033  * the string " (deleted)" is appended. Note that this is ambiguous.
3034  *
3035  * Returns a pointer into the buffer or an error code if the path was
3036  * too long. Note: Callers should use the returned pointer, not the passed
3037  * in buffer, to use the name! The implementation often starts at an offset
3038  * into the buffer, and may leave 0 bytes at the start.
3039  *
3040  * "buflen" should be positive.
3041  */
3042 char *d_path(const struct path *path, char *buf, int buflen)
3043 {
3044         char *res = buf + buflen;
3045         struct path root;
3046         int error;
3047 
3048         /*
3049          * We have various synthetic filesystems that never get mounted.  On
3050          * these filesystems dentries are never used for lookup purposes, and
3051          * thus don't need to be hashed.  They also don't need a name until a
3052          * user wants to identify the object in /proc/pid/fd/.  The little hack
3053          * below allows us to generate a name for these objects on demand:
3054          *
3055          * Some pseudo inodes are mountable.  When they are mounted
3056          * path->dentry == path->mnt->mnt_root.  In that case don't call d_dname
3057          * and instead have d_path return the mounted path.
3058          */
3059         if (path->dentry->d_op && path->dentry->d_op->d_dname &&
3060             (!IS_ROOT(path->dentry) || path->dentry != path->mnt->mnt_root))
3061                 return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
3062 
3063         rcu_read_lock();
3064         get_fs_root_rcu(current->fs, &root);
3065         error = path_with_deleted(path, &root, &res, &buflen);
3066         rcu_read_unlock();
3067 
3068         if (error < 0)
3069                 res = ERR_PTR(error);
3070         return res;
3071 }
3072 EXPORT_SYMBOL(d_path);
3073 
3074 /*
3075  * Helper function for dentry_operations.d_dname() members
3076  */
3077 char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,
3078                         const char *fmt, ...)
3079 {
3080         va_list args;
3081         char temp[64];
3082         int sz;
3083 
3084         va_start(args, fmt);
3085         sz = vsnprintf(temp, sizeof(temp), fmt, args) + 1;
3086         va_end(args);
3087 
3088         if (sz > sizeof(temp) || sz > buflen)
3089                 return ERR_PTR(-ENAMETOOLONG);
3090 
3091         buffer += buflen - sz;
3092         return memcpy(buffer, temp, sz);
3093 }
3094 
3095 char *simple_dname(struct dentry *dentry, char *buffer, int buflen)
3096 {
3097         char *end = buffer + buflen;
3098         /* these dentries are never renamed, so d_lock is not needed */
3099         if (prepend(&end, &buflen, " (deleted)", 11) ||
3100             prepend(&end, &buflen, dentry->d_name.name, dentry->d_name.len) ||
3101             prepend(&end, &buflen, "/", 1))  
3102                 end = ERR_PTR(-ENAMETOOLONG);
3103         return end;
3104 }
3105 EXPORT_SYMBOL(simple_dname);
3106 
3107 /*
3108  * Write full pathname from the root of the filesystem into the buffer.
3109  */
3110 static char *__dentry_path(struct dentry *d, char *buf, int buflen)
3111 {
3112         struct dentry *dentry;
3113         char *end, *retval;
3114         int len, seq = 0;
3115         int error = 0;
3116 
3117         if (buflen < 2)
3118                 goto Elong;
3119 
3120         rcu_read_lock();
3121 restart:
3122         dentry = d;
3123         end = buf + buflen;
3124         len = buflen;
3125         prepend(&end, &len, "\0", 1);
3126         /* Get '/' right */
3127         retval = end-1;
3128         *retval = '/';
3129         read_seqbegin_or_lock(&rename_lock, &seq);
3130         while (!IS_ROOT(dentry)) {
3131                 struct dentry *parent = dentry->d_parent;
3132 
3133                 prefetch(parent);
3134                 error = prepend_name(&end, &len, &dentry->d_name);
3135                 if (error)
3136                         break;
3137 
3138                 retval = end;
3139                 dentry = parent;
3140         }
3141         if (!(seq & 1))
3142                 rcu_read_unlock();
3143         if (need_seqretry(&rename_lock, seq)) {
3144                 seq = 1;
3145                 goto restart;
3146         }
3147         done_seqretry(&rename_lock, seq);
3148         if (error)
3149                 goto Elong;
3150         return retval;
3151 Elong:
3152         return ERR_PTR(-ENAMETOOLONG);
3153 }
3154 
3155 char *dentry_path_raw(struct dentry *dentry, char *buf, int buflen)
3156 {
3157         return __dentry_path(dentry, buf, buflen);
3158 }
3159 EXPORT_SYMBOL(dentry_path_raw);
3160 
3161 char *dentry_path(struct dentry *dentry, char *buf, int buflen)
3162 {
3163         char *p = NULL;
3164         char *retval;
3165 
3166         if (d_unlinked(dentry)) {
3167                 p = buf + buflen;
3168                 if (prepend(&p, &buflen, "//deleted", 10) != 0)
3169                         goto Elong;
3170                 buflen++;
3171         }
3172         retval = __dentry_path(dentry, buf, buflen);
3173         if (!IS_ERR(retval) && p)
3174                 *p = '/';       /* restore '/' overriden with '\0' */
3175         return retval;
3176 Elong:
3177         return ERR_PTR(-ENAMETOOLONG);
3178 }
3179 
3180 static void get_fs_root_and_pwd_rcu(struct fs_struct *fs, struct path *root,
3181                                     struct path *pwd)
3182 {
3183         unsigned seq;
3184 
3185         do {
3186                 seq = read_seqcount_begin(&fs->seq);
3187                 *root = fs->root;
3188                 *pwd = fs->pwd;
3189         } while (read_seqcount_retry(&fs->seq, seq));
3190 }
3191 
3192 /*
3193  * NOTE! The user-level library version returns a
3194  * character pointer. The kernel system call just
3195  * returns the length of the buffer filled (which
3196  * includes the ending '\0' character), or a negative
3197  * error value. So libc would do something like
3198  *
3199  *      char *getcwd(char * buf, size_t size)
3200  *      {
3201  *              int retval;
3202  *
3203  *              retval = sys_getcwd(buf, size);
3204  *              if (retval >= 0)
3205  *                      return buf;
3206  *              errno = -retval;
3207  *              return NULL;
3208  *      }
3209  */
3210 SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
3211 {
3212         int error;
3213         struct path pwd, root;
3214         char *page = __getname();
3215 
3216         if (!page)
3217                 return -ENOMEM;
3218 
3219         rcu_read_lock();
3220         get_fs_root_and_pwd_rcu(current->fs, &root, &pwd);
3221 
3222         error = -ENOENT;
3223         if (!d_unlinked(pwd.dentry)) {
3224                 unsigned long len;
3225                 char *cwd = page + PATH_MAX;
3226                 int buflen = PATH_MAX;
3227 
3228                 prepend(&cwd, &buflen, "\0", 1);
3229                 error = prepend_path(&pwd, &root, &cwd, &buflen);
3230                 rcu_read_unlock();
3231 
3232                 if (error < 0)
3233                         goto out;
3234 
3235                 /* Unreachable from current root */
3236                 if (error > 0) {
3237                         error = prepend_unreachable(&cwd, &buflen);
3238                         if (error)
3239                                 goto out;
3240                 }
3241 
3242                 error = -ERANGE;
3243                 len = PATH_MAX + page - cwd;
3244                 if (len <= size) {
3245                         error = len;
3246                         if (copy_to_user(buf, cwd, len))
3247                                 error = -EFAULT;
3248                 }
3249         } else {
3250                 rcu_read_unlock();
3251         }
3252 
3253 out:
3254         __putname(page);
3255         return error;
3256 }
3257 
3258 /*
3259  * Test whether new_dentry is a subdirectory of old_dentry.
3260  *
3261  * Trivially implemented using the dcache structure
3262  */
3263 
3264 /**
3265  * is_subdir - is new dentry a subdirectory of old_dentry
3266  * @new_dentry: new dentry
3267  * @old_dentry: old dentry
3268  *
3269  * Returns 1 if new_dentry is a subdirectory of the parent (at any depth).
3270  * Returns 0 otherwise.
3271  * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
3272  */
3273   
3274 int is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)
3275 {
3276         int result;
3277         unsigned seq;
3278 
3279         if (new_dentry == old_dentry)
3280                 return 1;
3281 
3282         do {
3283                 /* for restarting inner loop in case of seq retry */
3284                 seq = read_seqbegin(&rename_lock);
3285                 /*
3286                  * Need rcu_readlock to protect against the d_parent trashing
3287                  * due to d_move
3288                  */
3289                 rcu_read_lock();
3290                 if (d_ancestor(old_dentry, new_dentry))
3291                         result = 1;
3292                 else
3293                         result = 0;
3294                 rcu_read_unlock();
3295         } while (read_seqretry(&rename_lock, seq));
3296 
3297         return result;
3298 }
3299 
3300 static enum d_walk_ret d_genocide_kill(void *data, struct dentry *dentry)
3301 {
3302         struct dentry *root = data;
3303         if (dentry != root) {
3304                 if (d_unhashed(dentry) || !dentry->d_inode)
3305                         return D_WALK_SKIP;
3306 
3307                 if (!(dentry->d_flags & DCACHE_GENOCIDE)) {
3308                         dentry->d_flags |= DCACHE_GENOCIDE;
3309                         dentry->d_lockref.count--;
3310                 }
3311         }
3312         return D_WALK_CONTINUE;
3313 }
3314 
3315 void d_genocide(struct dentry *parent)
3316 {
3317         d_walk(parent, parent, d_genocide_kill, NULL);
3318 }
3319 
3320 void d_tmpfile(struct dentry *dentry, struct inode *inode)
3321 {
3322         inode_dec_link_count(inode);
3323         BUG_ON(dentry->d_name.name != dentry->d_iname ||
3324                 !hlist_unhashed(&dentry->d_alias) ||
3325                 !d_unlinked(dentry));
3326         spin_lock(&dentry->d_parent->d_lock);
3327         spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
3328         dentry->d_name.len = sprintf(dentry->d_iname, "#%llu",
3329                                 (unsigned long long)inode->i_ino);
3330         spin_unlock(&dentry->d_lock);
3331         spin_unlock(&dentry->d_parent->d_lock);
3332         d_instantiate(dentry, inode);
3333 }
3334 EXPORT_SYMBOL(d_tmpfile);
3335 
3336 static __initdata unsigned long dhash_entries;
3337 static int __init set_dhash_entries(char *str)
3338 {
3339         if (!str)
3340                 return 0;
3341         dhash_entries = simple_strtoul(str, &str, 0);
3342         return 1;
3343 }
3344 __setup("dhash_entries=", set_dhash_entries);
3345 
3346 static void __init dcache_init_early(void)
3347 {
3348         unsigned int loop;
3349 
3350         /* If hashes are distributed across NUMA nodes, defer
3351          * hash allocation until vmalloc space is available.
3352          */
3353         if (hashdist)
3354                 return;
3355 
3356         dentry_hashtable =
3357                 alloc_large_system_hash("Dentry cache",
3358                                         sizeof(struct hlist_bl_head),
3359                                         dhash_entries,
3360                                         13,
3361                                         HASH_EARLY,
3362                                         &d_hash_shift,
3363                                         &d_hash_mask,
3364                                         0,
3365                                         0);
3366 
3367         for (loop = 0; loop < (1U << d_hash_shift); loop++)
3368                 INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
3369 }
3370 
3371 static void __init dcache_init(void)
3372 {
3373         unsigned int loop;
3374 
3375         /* 
3376          * A constructor could be added for stable state like the lists,
3377          * but it is probably not worth it because of the cache nature
3378          * of the dcache. 
3379          */
3380         dentry_cache = KMEM_CACHE(dentry,
3381                 SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD);
3382 
3383         /* Hash may have been set up in dcache_init_early */
3384         if (!hashdist)
3385                 return;
3386 
3387         dentry_hashtable =
3388                 alloc_large_system_hash("Dentry cache",
3389                                         sizeof(struct hlist_bl_head),
3390                                         dhash_entries,
3391                                         13,
3392                                         0,
3393                                         &d_hash_shift,
3394                                         &d_hash_mask,
3395                                         0,
3396                                         0);
3397 
3398         for (loop = 0; loop < (1U << d_hash_shift); loop++)
3399                 INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
3400 }
3401 
3402 /* SLAB cache for __getname() consumers */
3403 struct kmem_cache *names_cachep __read_mostly;
3404 EXPORT_SYMBOL(names_cachep);
3405 
3406 EXPORT_SYMBOL(d_genocide);
3407 
3408 void __init vfs_caches_init_early(void)
3409 {
3410         dcache_init_early();
3411         inode_init_early();
3412 }
3413 
3414 void __init vfs_caches_init(unsigned long mempages)
3415 {
3416         unsigned long reserve;
3417 
3418         /* Base hash sizes on available memory, with a reserve equal to
3419            150% of current kernel size */
3420 
3421         reserve = min((mempages - nr_free_pages()) * 3/2, mempages - 1);
3422         mempages -= reserve;
3423 
3424         names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
3425                         SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
3426 
3427         dcache_init();
3428         inode_init();
3429         files_init(mempages);
3430         mnt_init();
3431         bdev_cache_init();
3432         chrdev_init();
3433 }
3434 

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