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linux-2.6.16/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/config.h>
 18 #include <linux/syscalls.h>
 19 #include <linux/string.h>
 20 #include <linux/mm.h>
 21 #include <linux/fs.h>
 22 #include <linux/fsnotify.h>
 23 #include <linux/slab.h>
 24 #include <linux/init.h>
 25 #include <linux/smp_lock.h>
 26 #include <linux/hash.h>
 27 #include <linux/cache.h>
 28 #include <linux/module.h>
 29 #include <linux/mount.h>
 30 #include <linux/file.h>
 31 #include <asm/uaccess.h>
 32 #include <linux/security.h>
 33 #include <linux/seqlock.h>
 34 #include <linux/swap.h>
 35 #include <linux/bootmem.h>
 36 
 37 /* #define DCACHE_DEBUG 1 */
 38 
 39 int sysctl_vfs_cache_pressure = 100;
 40 EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
 41 
 42  __cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lock);
 43 static seqlock_t rename_lock __cacheline_aligned_in_smp = SEQLOCK_UNLOCKED;
 44 
 45 EXPORT_SYMBOL(dcache_lock);
 46 
 47 static kmem_cache_t *dentry_cache; 
 48 
 49 #define DNAME_INLINE_LEN (sizeof(struct dentry)-offsetof(struct dentry,d_iname))
 50 
 51 /*
 52  * This is the single most critical data structure when it comes
 53  * to the dcache: the hashtable for lookups. Somebody should try
 54  * to make this good - I've just made it work.
 55  *
 56  * This hash-function tries to avoid losing too many bits of hash
 57  * information, yet avoid using a prime hash-size or similar.
 58  */
 59 #define D_HASHBITS     d_hash_shift
 60 #define D_HASHMASK     d_hash_mask
 61 
 62 static unsigned int d_hash_mask;
 63 static unsigned int d_hash_shift;
 64 static struct hlist_head *dentry_hashtable;
 65 static LIST_HEAD(dentry_unused);
 66 
 67 /* Statistics gathering. */
 68 struct dentry_stat_t dentry_stat = {
 69         .age_limit = 45,
 70 };
 71 
 72 static void d_callback(struct rcu_head *head)
 73 {
 74         struct dentry * dentry = container_of(head, struct dentry, d_u.d_rcu);
 75 
 76         if (dname_external(dentry))
 77                 kfree(dentry->d_name.name);
 78         kmem_cache_free(dentry_cache, dentry); 
 79 }
 80 
 81 /*
 82  * no dcache_lock, please.  The caller must decrement dentry_stat.nr_dentry
 83  * inside dcache_lock.
 84  */
 85 static void d_free(struct dentry *dentry)
 86 {
 87         if (dentry->d_op && dentry->d_op->d_release)
 88                 dentry->d_op->d_release(dentry);
 89         call_rcu(&dentry->d_u.d_rcu, d_callback);
 90 }
 91 
 92 /*
 93  * Release the dentry's inode, using the filesystem
 94  * d_iput() operation if defined.
 95  * Called with dcache_lock and per dentry lock held, drops both.
 96  */
 97 static void dentry_iput(struct dentry * dentry)
 98 {
 99         struct inode *inode = dentry->d_inode;
100         if (inode) {
101                 dentry->d_inode = NULL;
102                 list_del_init(&dentry->d_alias);
103                 spin_unlock(&dentry->d_lock);
104                 spin_unlock(&dcache_lock);
105                 if (!inode->i_nlink)
106                         fsnotify_inoderemove(inode);
107                 if (dentry->d_op && dentry->d_op->d_iput)
108                         dentry->d_op->d_iput(dentry, inode);
109                 else
110                         iput(inode);
111         } else {
112                 spin_unlock(&dentry->d_lock);
113                 spin_unlock(&dcache_lock);
114         }
115 }
116 
117 /* 
118  * This is dput
119  *
120  * This is complicated by the fact that we do not want to put
121  * dentries that are no longer on any hash chain on the unused
122  * list: we'd much rather just get rid of them immediately.
123  *
124  * However, that implies that we have to traverse the dentry
125  * tree upwards to the parents which might _also_ now be
126  * scheduled for deletion (it may have been only waiting for
127  * its last child to go away).
128  *
129  * This tail recursion is done by hand as we don't want to depend
130  * on the compiler to always get this right (gcc generally doesn't).
131  * Real recursion would eat up our stack space.
132  */
133 
134 /*
135  * dput - release a dentry
136  * @dentry: dentry to release 
137  *
138  * Release a dentry. This will drop the usage count and if appropriate
139  * call the dentry unlink method as well as removing it from the queues and
140  * releasing its resources. If the parent dentries were scheduled for release
141  * they too may now get deleted.
142  *
143  * no dcache lock, please.
144  */
145 
146 void dput(struct dentry *dentry)
147 {
148         if (!dentry)
149                 return;
150 
151 repeat:
152         if (atomic_read(&dentry->d_count) == 1)
153                 might_sleep();
154         if (!atomic_dec_and_lock(&dentry->d_count, &dcache_lock))
155                 return;
156 
157         spin_lock(&dentry->d_lock);
158         if (atomic_read(&dentry->d_count)) {
159                 spin_unlock(&dentry->d_lock);
160                 spin_unlock(&dcache_lock);
161                 return;
162         }
163 
164         /*
165          * AV: ->d_delete() is _NOT_ allowed to block now.
166          */
167         if (dentry->d_op && dentry->d_op->d_delete) {
168                 if (dentry->d_op->d_delete(dentry))
169                         goto unhash_it;
170         }
171         /* Unreachable? Get rid of it */
172         if (d_unhashed(dentry))
173                 goto kill_it;
174         if (list_empty(&dentry->d_lru)) {
175                 dentry->d_flags |= DCACHE_REFERENCED;
176                 list_add(&dentry->d_lru, &dentry_unused);
177                 dentry_stat.nr_unused++;
178         }
179         spin_unlock(&dentry->d_lock);
180         spin_unlock(&dcache_lock);
181         return;
182 
183 unhash_it:
184         __d_drop(dentry);
185 
186 kill_it: {
187                 struct dentry *parent;
188 
189                 /* If dentry was on d_lru list
190                  * delete it from there
191                  */
192                 if (!list_empty(&dentry->d_lru)) {
193                         list_del(&dentry->d_lru);
194                         dentry_stat.nr_unused--;
195                 }
196                 list_del(&dentry->d_u.d_child);
197                 dentry_stat.nr_dentry--;        /* For d_free, below */
198                 /*drops the locks, at that point nobody can reach this dentry */
199                 dentry_iput(dentry);
200                 parent = dentry->d_parent;
201                 d_free(dentry);
202                 if (dentry == parent)
203                         return;
204                 dentry = parent;
205                 goto repeat;
206         }
207 }
208 
209 /**
210  * d_invalidate - invalidate a dentry
211  * @dentry: dentry to invalidate
212  *
213  * Try to invalidate the dentry if it turns out to be
214  * possible. If there are other dentries that can be
215  * reached through this one we can't delete it and we
216  * return -EBUSY. On success we return 0.
217  *
218  * no dcache lock.
219  */
220  
221 int d_invalidate(struct dentry * dentry)
222 {
223         /*
224          * If it's already been dropped, return OK.
225          */
226         spin_lock(&dcache_lock);
227         if (d_unhashed(dentry)) {
228                 spin_unlock(&dcache_lock);
229                 return 0;
230         }
231         /*
232          * Check whether to do a partial shrink_dcache
233          * to get rid of unused child entries.
234          */
235         if (!list_empty(&dentry->d_subdirs)) {
236                 spin_unlock(&dcache_lock);
237                 shrink_dcache_parent(dentry);
238                 spin_lock(&dcache_lock);
239         }
240 
241         /*
242          * Somebody else still using it?
243          *
244          * If it's a directory, we can't drop it
245          * for fear of somebody re-populating it
246          * with children (even though dropping it
247          * would make it unreachable from the root,
248          * we might still populate it if it was a
249          * working directory or similar).
250          */
251         spin_lock(&dentry->d_lock);
252         if (atomic_read(&dentry->d_count) > 1) {
253                 if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode)) {
254                         spin_unlock(&dentry->d_lock);
255                         spin_unlock(&dcache_lock);
256                         return -EBUSY;
257                 }
258         }
259 
260         __d_drop(dentry);
261         spin_unlock(&dentry->d_lock);
262         spin_unlock(&dcache_lock);
263         return 0;
264 }
265 
266 /* This should be called _only_ with dcache_lock held */
267 
268 static inline struct dentry * __dget_locked(struct dentry *dentry)
269 {
270         atomic_inc(&dentry->d_count);
271         if (!list_empty(&dentry->d_lru)) {
272                 dentry_stat.nr_unused--;
273                 list_del_init(&dentry->d_lru);
274         }
275         return dentry;
276 }
277 
278 struct dentry * dget_locked(struct dentry *dentry)
279 {
280         return __dget_locked(dentry);
281 }
282 
283 /**
284  * d_find_alias - grab a hashed alias of inode
285  * @inode: inode in question
286  * @want_discon:  flag, used by d_splice_alias, to request
287  *          that only a DISCONNECTED alias be returned.
288  *
289  * If inode has a hashed alias, or is a directory and has any alias,
290  * acquire the reference to alias and return it. Otherwise return NULL.
291  * Notice that if inode is a directory there can be only one alias and
292  * it can be unhashed only if it has no children, or if it is the root
293  * of a filesystem.
294  *
295  * If the inode has a DCACHE_DISCONNECTED alias, then prefer
296  * any other hashed alias over that one unless @want_discon is set,
297  * in which case only return a DCACHE_DISCONNECTED alias.
298  */
299 
300 static struct dentry * __d_find_alias(struct inode *inode, int want_discon)
301 {
302         struct list_head *head, *next, *tmp;
303         struct dentry *alias, *discon_alias=NULL;
304 
305         head = &inode->i_dentry;
306         next = inode->i_dentry.next;
307         while (next != head) {
308                 tmp = next;
309                 next = tmp->next;
310                 prefetch(next);
311                 alias = list_entry(tmp, struct dentry, d_alias);
312                 if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
313                         if (alias->d_flags & DCACHE_DISCONNECTED)
314                                 discon_alias = alias;
315                         else if (!want_discon) {
316                                 __dget_locked(alias);
317                                 return alias;
318                         }
319                 }
320         }
321         if (discon_alias)
322                 __dget_locked(discon_alias);
323         return discon_alias;
324 }
325 
326 struct dentry * d_find_alias(struct inode *inode)
327 {
328         struct dentry *de;
329         spin_lock(&dcache_lock);
330         de = __d_find_alias(inode, 0);
331         spin_unlock(&dcache_lock);
332         return de;
333 }
334 
335 /*
336  *      Try to kill dentries associated with this inode.
337  * WARNING: you must own a reference to inode.
338  */
339 void d_prune_aliases(struct inode *inode)
340 {
341         struct dentry *dentry;
342 restart:
343         spin_lock(&dcache_lock);
344         list_for_each_entry(dentry, &inode->i_dentry, d_alias) {
345                 spin_lock(&dentry->d_lock);
346                 if (!atomic_read(&dentry->d_count)) {
347                         __dget_locked(dentry);
348                         __d_drop(dentry);
349                         spin_unlock(&dentry->d_lock);
350                         spin_unlock(&dcache_lock);
351                         dput(dentry);
352                         goto restart;
353                 }
354                 spin_unlock(&dentry->d_lock);
355         }
356         spin_unlock(&dcache_lock);
357 }
358 
359 /*
360  * Throw away a dentry - free the inode, dput the parent.
361  * This requires that the LRU list has already been
362  * removed.
363  * Called with dcache_lock, drops it and then regains.
364  */
365 static inline void prune_one_dentry(struct dentry * dentry)
366 {
367         struct dentry * parent;
368 
369         __d_drop(dentry);
370         list_del(&dentry->d_u.d_child);
371         dentry_stat.nr_dentry--;        /* For d_free, below */
372         dentry_iput(dentry);
373         parent = dentry->d_parent;
374         d_free(dentry);
375         if (parent != dentry)
376                 dput(parent);
377         spin_lock(&dcache_lock);
378 }
379 
380 /**
381  * prune_dcache - shrink the dcache
382  * @count: number of entries to try and free
383  *
384  * Shrink the dcache. This is done when we need
385  * more memory, or simply when we need to unmount
386  * something (at which point we need to unuse
387  * all dentries).
388  *
389  * This function may fail to free any resources if
390  * all the dentries are in use.
391  */
392  
393 static void prune_dcache(int count)
394 {
395         spin_lock(&dcache_lock);
396         for (; count ; count--) {
397                 struct dentry *dentry;
398                 struct list_head *tmp;
399 
400                 cond_resched_lock(&dcache_lock);
401 
402                 tmp = dentry_unused.prev;
403                 if (tmp == &dentry_unused)
404                         break;
405                 list_del_init(tmp);
406                 prefetch(dentry_unused.prev);
407                 dentry_stat.nr_unused--;
408                 dentry = list_entry(tmp, struct dentry, d_lru);
409 
410                 spin_lock(&dentry->d_lock);
411                 /*
412                  * We found an inuse dentry which was not removed from
413                  * dentry_unused because of laziness during lookup.  Do not free
414                  * it - just keep it off the dentry_unused list.
415                  */
416                 if (atomic_read(&dentry->d_count)) {
417                         spin_unlock(&dentry->d_lock);
418                         continue;
419                 }
420                 /* If the dentry was recently referenced, don't free it. */
421                 if (dentry->d_flags & DCACHE_REFERENCED) {
422                         dentry->d_flags &= ~DCACHE_REFERENCED;
423                         list_add(&dentry->d_lru, &dentry_unused);
424                         dentry_stat.nr_unused++;
425                         spin_unlock(&dentry->d_lock);
426                         continue;
427                 }
428                 prune_one_dentry(dentry);
429         }
430         spin_unlock(&dcache_lock);
431 }
432 
433 /*
434  * Shrink the dcache for the specified super block.
435  * This allows us to unmount a device without disturbing
436  * the dcache for the other devices.
437  *
438  * This implementation makes just two traversals of the
439  * unused list.  On the first pass we move the selected
440  * dentries to the most recent end, and on the second
441  * pass we free them.  The second pass must restart after
442  * each dput(), but since the target dentries are all at
443  * the end, it's really just a single traversal.
444  */
445 
446 /**
447  * shrink_dcache_sb - shrink dcache for a superblock
448  * @sb: superblock
449  *
450  * Shrink the dcache for the specified super block. This
451  * is used to free the dcache before unmounting a file
452  * system
453  */
454 
455 void shrink_dcache_sb(struct super_block * sb)
456 {
457         struct list_head *tmp, *next;
458         struct dentry *dentry;
459 
460         /*
461          * Pass one ... move the dentries for the specified
462          * superblock to the most recent end of the unused list.
463          */
464         spin_lock(&dcache_lock);
465         list_for_each_safe(tmp, next, &dentry_unused) {
466                 dentry = list_entry(tmp, struct dentry, d_lru);
467                 if (dentry->d_sb != sb)
468                         continue;
469                 list_del(tmp);
470                 list_add(tmp, &dentry_unused);
471         }
472 
473         /*
474          * Pass two ... free the dentries for this superblock.
475          */
476 repeat:
477         list_for_each_safe(tmp, next, &dentry_unused) {
478                 dentry = list_entry(tmp, struct dentry, d_lru);
479                 if (dentry->d_sb != sb)
480                         continue;
481                 dentry_stat.nr_unused--;
482                 list_del_init(tmp);
483                 spin_lock(&dentry->d_lock);
484                 if (atomic_read(&dentry->d_count)) {
485                         spin_unlock(&dentry->d_lock);
486                         continue;
487                 }
488                 prune_one_dentry(dentry);
489                 goto repeat;
490         }
491         spin_unlock(&dcache_lock);
492 }
493 
494 /*
495  * Search for at least 1 mount point in the dentry's subdirs.
496  * We descend to the next level whenever the d_subdirs
497  * list is non-empty and continue searching.
498  */
499  
500 /**
501  * have_submounts - check for mounts over a dentry
502  * @parent: dentry to check.
503  *
504  * Return true if the parent or its subdirectories contain
505  * a mount point
506  */
507  
508 int have_submounts(struct dentry *parent)
509 {
510         struct dentry *this_parent = parent;
511         struct list_head *next;
512 
513         spin_lock(&dcache_lock);
514         if (d_mountpoint(parent))
515                 goto positive;
516 repeat:
517         next = this_parent->d_subdirs.next;
518 resume:
519         while (next != &this_parent->d_subdirs) {
520                 struct list_head *tmp = next;
521                 struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
522                 next = tmp->next;
523                 /* Have we found a mount point ? */
524                 if (d_mountpoint(dentry))
525                         goto positive;
526                 if (!list_empty(&dentry->d_subdirs)) {
527                         this_parent = dentry;
528                         goto repeat;
529                 }
530         }
531         /*
532          * All done at this level ... ascend and resume the search.
533          */
534         if (this_parent != parent) {
535                 next = this_parent->d_u.d_child.next;
536                 this_parent = this_parent->d_parent;
537                 goto resume;
538         }
539         spin_unlock(&dcache_lock);
540         return 0; /* No mount points found in tree */
541 positive:
542         spin_unlock(&dcache_lock);
543         return 1;
544 }
545 
546 /*
547  * Search the dentry child list for the specified parent,
548  * and move any unused dentries to the end of the unused
549  * list for prune_dcache(). We descend to the next level
550  * whenever the d_subdirs list is non-empty and continue
551  * searching.
552  *
553  * It returns zero iff there are no unused children,
554  * otherwise  it returns the number of children moved to
555  * the end of the unused list. This may not be the total
556  * number of unused children, because select_parent can
557  * drop the lock and return early due to latency
558  * constraints.
559  */
560 static int select_parent(struct dentry * parent)
561 {
562         struct dentry *this_parent = parent;
563         struct list_head *next;
564         int found = 0;
565 
566         spin_lock(&dcache_lock);
567 repeat:
568         next = this_parent->d_subdirs.next;
569 resume:
570         while (next != &this_parent->d_subdirs) {
571                 struct list_head *tmp = next;
572                 struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
573                 next = tmp->next;
574 
575                 if (!list_empty(&dentry->d_lru)) {
576                         dentry_stat.nr_unused--;
577                         list_del_init(&dentry->d_lru);
578                 }
579                 /* 
580                  * move only zero ref count dentries to the end 
581                  * of the unused list for prune_dcache
582                  */
583                 if (!atomic_read(&dentry->d_count)) {
584                         list_add(&dentry->d_lru, dentry_unused.prev);
585                         dentry_stat.nr_unused++;
586                         found++;
587                 }
588 
589                 /*
590                  * We can return to the caller if we have found some (this
591                  * ensures forward progress). We'll be coming back to find
592                  * the rest.
593                  */
594                 if (found && need_resched())
595                         goto out;
596 
597                 /*
598                  * Descend a level if the d_subdirs list is non-empty.
599                  */
600                 if (!list_empty(&dentry->d_subdirs)) {
601                         this_parent = dentry;
602 #ifdef DCACHE_DEBUG
603 printk(KERN_DEBUG "select_parent: descending to %s/%s, found=%d\n",
604 dentry->d_parent->d_name.name, dentry->d_name.name, found);
605 #endif
606                         goto repeat;
607                 }
608         }
609         /*
610          * All done at this level ... ascend and resume the search.
611          */
612         if (this_parent != parent) {
613                 next = this_parent->d_u.d_child.next;
614                 this_parent = this_parent->d_parent;
615 #ifdef DCACHE_DEBUG
616 printk(KERN_DEBUG "select_parent: ascending to %s/%s, found=%d\n",
617 this_parent->d_parent->d_name.name, this_parent->d_name.name, found);
618 #endif
619                 goto resume;
620         }
621 out:
622         spin_unlock(&dcache_lock);
623         return found;
624 }
625 
626 /**
627  * shrink_dcache_parent - prune dcache
628  * @parent: parent of entries to prune
629  *
630  * Prune the dcache to remove unused children of the parent dentry.
631  */
632  
633 void shrink_dcache_parent(struct dentry * parent)
634 {
635         int found;
636 
637         while ((found = select_parent(parent)) != 0)
638                 prune_dcache(found);
639 }
640 
641 /**
642  * shrink_dcache_anon - further prune the cache
643  * @head: head of d_hash list of dentries to prune
644  *
645  * Prune the dentries that are anonymous
646  *
647  * parsing d_hash list does not hlist_for_each_entry_rcu() as it
648  * done under dcache_lock.
649  *
650  */
651 void shrink_dcache_anon(struct hlist_head *head)
652 {
653         struct hlist_node *lp;
654         int found;
655         do {
656                 found = 0;
657                 spin_lock(&dcache_lock);
658                 hlist_for_each(lp, head) {
659                         struct dentry *this = hlist_entry(lp, struct dentry, d_hash);
660                         if (!list_empty(&this->d_lru)) {
661                                 dentry_stat.nr_unused--;
662                                 list_del_init(&this->d_lru);
663                         }
664 
665                         /* 
666                          * move only zero ref count dentries to the end 
667                          * of the unused list for prune_dcache
668                          */
669                         if (!atomic_read(&this->d_count)) {
670                                 list_add_tail(&this->d_lru, &dentry_unused);
671                                 dentry_stat.nr_unused++;
672                                 found++;
673                         }
674                 }
675                 spin_unlock(&dcache_lock);
676                 prune_dcache(found);
677         } while(found);
678 }
679 
680 /*
681  * Scan `nr' dentries and return the number which remain.
682  *
683  * We need to avoid reentering the filesystem if the caller is performing a
684  * GFP_NOFS allocation attempt.  One example deadlock is:
685  *
686  * ext2_new_block->getblk->GFP->shrink_dcache_memory->prune_dcache->
687  * prune_one_dentry->dput->dentry_iput->iput->inode->i_sb->s_op->put_inode->
688  * ext2_discard_prealloc->ext2_free_blocks->lock_super->DEADLOCK.
689  *
690  * In this case we return -1 to tell the caller that we baled.
691  */
692 static int shrink_dcache_memory(int nr, gfp_t gfp_mask)
693 {
694         if (nr) {
695                 if (!(gfp_mask & __GFP_FS))
696                         return -1;
697                 prune_dcache(nr);
698         }
699         return (dentry_stat.nr_unused / 100) * sysctl_vfs_cache_pressure;
700 }
701 
702 /**
703  * d_alloc      -       allocate a dcache entry
704  * @parent: parent of entry to allocate
705  * @name: qstr of the name
706  *
707  * Allocates a dentry. It returns %NULL if there is insufficient memory
708  * available. On a success the dentry is returned. The name passed in is
709  * copied and the copy passed in may be reused after this call.
710  */
711  
712 struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
713 {
714         struct dentry *dentry;
715         char *dname;
716 
717         dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL); 
718         if (!dentry)
719                 return NULL;
720 
721         if (name->len > DNAME_INLINE_LEN-1) {
722                 dname = kmalloc(name->len + 1, GFP_KERNEL);
723                 if (!dname) {
724                         kmem_cache_free(dentry_cache, dentry); 
725                         return NULL;
726                 }
727         } else  {
728                 dname = dentry->d_iname;
729         }       
730         dentry->d_name.name = dname;
731 
732         dentry->d_name.len = name->len;
733         dentry->d_name.hash = name->hash;
734         memcpy(dname, name->name, name->len);
735         dname[name->len] = 0;
736 
737         atomic_set(&dentry->d_count, 1);
738         dentry->d_flags = DCACHE_UNHASHED;
739         spin_lock_init(&dentry->d_lock);
740         dentry->d_inode = NULL;
741         dentry->d_parent = NULL;
742         dentry->d_sb = NULL;
743         dentry->d_op = NULL;
744         dentry->d_fsdata = NULL;
745         dentry->d_mounted = 0;
746 #ifdef CONFIG_PROFILING
747         dentry->d_cookie = NULL;
748 #endif
749         INIT_HLIST_NODE(&dentry->d_hash);
750         INIT_LIST_HEAD(&dentry->d_lru);
751         INIT_LIST_HEAD(&dentry->d_subdirs);
752         INIT_LIST_HEAD(&dentry->d_alias);
753 
754         if (parent) {
755                 dentry->d_parent = dget(parent);
756                 dentry->d_sb = parent->d_sb;
757         } else {
758                 INIT_LIST_HEAD(&dentry->d_u.d_child);
759         }
760 
761         spin_lock(&dcache_lock);
762         if (parent)
763                 list_add(&dentry->d_u.d_child, &parent->d_subdirs);
764         dentry_stat.nr_dentry++;
765         spin_unlock(&dcache_lock);
766 
767         return dentry;
768 }
769 
770 struct dentry *d_alloc_name(struct dentry *parent, const char *name)
771 {
772         struct qstr q;
773 
774         q.name = name;
775         q.len = strlen(name);
776         q.hash = full_name_hash(q.name, q.len);
777         return d_alloc(parent, &q);
778 }
779 
780 /**
781  * d_instantiate - fill in inode information for a dentry
782  * @entry: dentry to complete
783  * @inode: inode to attach to this dentry
784  *
785  * Fill in inode information in the entry.
786  *
787  * This turns negative dentries into productive full members
788  * of society.
789  *
790  * NOTE! This assumes that the inode count has been incremented
791  * (or otherwise set) by the caller to indicate that it is now
792  * in use by the dcache.
793  */
794  
795 void d_instantiate(struct dentry *entry, struct inode * inode)
796 {
797         if (!list_empty(&entry->d_alias)) BUG();
798         spin_lock(&dcache_lock);
799         if (inode)
800                 list_add(&entry->d_alias, &inode->i_dentry);
801         entry->d_inode = inode;
802         spin_unlock(&dcache_lock);
803         security_d_instantiate(entry, inode);
804 }
805 
806 /**
807  * d_instantiate_unique - instantiate a non-aliased dentry
808  * @entry: dentry to instantiate
809  * @inode: inode to attach to this dentry
810  *
811  * Fill in inode information in the entry. On success, it returns NULL.
812  * If an unhashed alias of "entry" already exists, then we return the
813  * aliased dentry instead and drop one reference to inode.
814  *
815  * Note that in order to avoid conflicts with rename() etc, the caller
816  * had better be holding the parent directory semaphore.
817  *
818  * This also assumes that the inode count has been incremented
819  * (or otherwise set) by the caller to indicate that it is now
820  * in use by the dcache.
821  */
822 struct dentry *d_instantiate_unique(struct dentry *entry, struct inode *inode)
823 {
824         struct dentry *alias;
825         int len = entry->d_name.len;
826         const char *name = entry->d_name.name;
827         unsigned int hash = entry->d_name.hash;
828 
829         BUG_ON(!list_empty(&entry->d_alias));
830         spin_lock(&dcache_lock);
831         if (!inode)
832                 goto do_negative;
833         list_for_each_entry(alias, &inode->i_dentry, d_alias) {
834                 struct qstr *qstr = &alias->d_name;
835 
836                 if (qstr->hash != hash)
837                         continue;
838                 if (alias->d_parent != entry->d_parent)
839                         continue;
840                 if (qstr->len != len)
841                         continue;
842                 if (memcmp(qstr->name, name, len))
843                         continue;
844                 dget_locked(alias);
845                 spin_unlock(&dcache_lock);
846                 BUG_ON(!d_unhashed(alias));
847                 iput(inode);
848                 return alias;
849         }
850         list_add(&entry->d_alias, &inode->i_dentry);
851 do_negative:
852         entry->d_inode = inode;
853         spin_unlock(&dcache_lock);
854         security_d_instantiate(entry, inode);
855         return NULL;
856 }
857 EXPORT_SYMBOL(d_instantiate_unique);
858 
859 /**
860  * d_alloc_root - allocate root dentry
861  * @root_inode: inode to allocate the root for
862  *
863  * Allocate a root ("/") dentry for the inode given. The inode is
864  * instantiated and returned. %NULL is returned if there is insufficient
865  * memory or the inode passed is %NULL.
866  */
867  
868 struct dentry * d_alloc_root(struct inode * root_inode)
869 {
870         struct dentry *res = NULL;
871 
872         if (root_inode) {
873                 static const struct qstr name = { .name = "/", .len = 1 };
874 
875                 res = d_alloc(NULL, &name);
876                 if (res) {
877                         res->d_sb = root_inode->i_sb;
878                         res->d_parent = res;
879                         d_instantiate(res, root_inode);
880                 }
881         }
882         return res;
883 }
884 
885 static inline struct hlist_head *d_hash(struct dentry *parent,
886                                         unsigned long hash)
887 {
888         hash += ((unsigned long) parent ^ GOLDEN_RATIO_PRIME) / L1_CACHE_BYTES;
889         hash = hash ^ ((hash ^ GOLDEN_RATIO_PRIME) >> D_HASHBITS);
890         return dentry_hashtable + (hash & D_HASHMASK);
891 }
892 
893 /**
894  * d_alloc_anon - allocate an anonymous dentry
895  * @inode: inode to allocate the dentry for
896  *
897  * This is similar to d_alloc_root.  It is used by filesystems when
898  * creating a dentry for a given inode, often in the process of 
899  * mapping a filehandle to a dentry.  The returned dentry may be
900  * anonymous, or may have a full name (if the inode was already
901  * in the cache).  The file system may need to make further
902  * efforts to connect this dentry into the dcache properly.
903  *
904  * When called on a directory inode, we must ensure that
905  * the inode only ever has one dentry.  If a dentry is
906  * found, that is returned instead of allocating a new one.
907  *
908  * On successful return, the reference to the inode has been transferred
909  * to the dentry.  If %NULL is returned (indicating kmalloc failure),
910  * the reference on the inode has not been released.
911  */
912 
913 struct dentry * d_alloc_anon(struct inode *inode)
914 {
915         static const struct qstr anonstring = { .name = "" };
916         struct dentry *tmp;
917         struct dentry *res;
918 
919         if ((res = d_find_alias(inode))) {
920                 iput(inode);
921                 return res;
922         }
923 
924         tmp = d_alloc(NULL, &anonstring);
925         if (!tmp)
926                 return NULL;
927 
928         tmp->d_parent = tmp; /* make sure dput doesn't croak */
929         
930         spin_lock(&dcache_lock);
931         res = __d_find_alias(inode, 0);
932         if (!res) {
933                 /* attach a disconnected dentry */
934                 res = tmp;
935                 tmp = NULL;
936                 spin_lock(&res->d_lock);
937                 res->d_sb = inode->i_sb;
938                 res->d_parent = res;
939                 res->d_inode = inode;
940                 res->d_flags |= DCACHE_DISCONNECTED;
941                 res->d_flags &= ~DCACHE_UNHASHED;
942                 list_add(&res->d_alias, &inode->i_dentry);
943                 hlist_add_head(&res->d_hash, &inode->i_sb->s_anon);
944                 spin_unlock(&res->d_lock);
945 
946                 inode = NULL; /* don't drop reference */
947         }
948         spin_unlock(&dcache_lock);
949 
950         if (inode)
951                 iput(inode);
952         if (tmp)
953                 dput(tmp);
954         return res;
955 }
956 
957 
958 /**
959  * d_splice_alias - splice a disconnected dentry into the tree if one exists
960  * @inode:  the inode which may have a disconnected dentry
961  * @dentry: a negative dentry which we want to point to the inode.
962  *
963  * If inode is a directory and has a 'disconnected' dentry (i.e. IS_ROOT and
964  * DCACHE_DISCONNECTED), then d_move that in place of the given dentry
965  * and return it, else simply d_add the inode to the dentry and return NULL.
966  *
967  * This is needed in the lookup routine of any filesystem that is exportable
968  * (via knfsd) so that we can build dcache paths to directories effectively.
969  *
970  * If a dentry was found and moved, then it is returned.  Otherwise NULL
971  * is returned.  This matches the expected return value of ->lookup.
972  *
973  */
974 struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
975 {
976         struct dentry *new = NULL;
977 
978         if (inode) {
979                 spin_lock(&dcache_lock);
980                 new = __d_find_alias(inode, 1);
981                 if (new) {
982                         BUG_ON(!(new->d_flags & DCACHE_DISCONNECTED));
983                         spin_unlock(&dcache_lock);
984                         security_d_instantiate(new, inode);
985                         d_rehash(dentry);
986                         d_move(new, dentry);
987                         iput(inode);
988                 } else {
989                         /* d_instantiate takes dcache_lock, so we do it by hand */
990                         list_add(&dentry->d_alias, &inode->i_dentry);
991                         dentry->d_inode = inode;
992                         spin_unlock(&dcache_lock);
993                         security_d_instantiate(dentry, inode);
994                         d_rehash(dentry);
995                 }
996         } else
997                 d_add(dentry, inode);
998         return new;
999 }
1000 
1001 
1002 /**
1003  * d_lookup - search for a dentry
1004  * @parent: parent dentry
1005  * @name: qstr of name we wish to find
1006  *
1007  * Searches the children of the parent dentry for the name in question. If
1008  * the dentry is found its reference count is incremented and the dentry
1009  * is returned. The caller must use d_put to free the entry when it has
1010  * finished using it. %NULL is returned on failure.
1011  *
1012  * __d_lookup is dcache_lock free. The hash list is protected using RCU.
1013  * Memory barriers are used while updating and doing lockless traversal. 
1014  * To avoid races with d_move while rename is happening, d_lock is used.
1015  *
1016  * Overflows in memcmp(), while d_move, are avoided by keeping the length
1017  * and name pointer in one structure pointed by d_qstr.
1018  *
1019  * rcu_read_lock() and rcu_read_unlock() are used to disable preemption while
1020  * lookup is going on.
1021  *
1022  * dentry_unused list is not updated even if lookup finds the required dentry
1023  * in there. It is updated in places such as prune_dcache, shrink_dcache_sb,
1024  * select_parent and __dget_locked. This laziness saves lookup from dcache_lock
1025  * acquisition.
1026  *
1027  * d_lookup() is protected against the concurrent renames in some unrelated
1028  * directory using the seqlockt_t rename_lock.
1029  */
1030 
1031 struct dentry * d_lookup(struct dentry * parent, struct qstr * name)
1032 {
1033         struct dentry * dentry = NULL;
1034         unsigned long seq;
1035 
1036         do {
1037                 seq = read_seqbegin(&rename_lock);
1038                 dentry = __d_lookup(parent, name);
1039                 if (dentry)
1040                         break;
1041         } while (read_seqretry(&rename_lock, seq));
1042         return dentry;
1043 }
1044 
1045 struct dentry * __d_lookup(struct dentry * parent, struct qstr * name)
1046 {
1047         unsigned int len = name->len;
1048         unsigned int hash = name->hash;
1049         const unsigned char *str = name->name;
1050         struct hlist_head *head = d_hash(parent,hash);
1051         struct dentry *found = NULL;
1052         struct hlist_node *node;
1053         struct dentry *dentry;
1054 
1055         rcu_read_lock();
1056         
1057         hlist_for_each_entry_rcu(dentry, node, head, d_hash) {
1058                 struct qstr *qstr;
1059 
1060                 if (dentry->d_name.hash != hash)
1061                         continue;
1062                 if (dentry->d_parent != parent)
1063                         continue;
1064 
1065                 spin_lock(&dentry->d_lock);
1066 
1067                 /*
1068                  * Recheck the dentry after taking the lock - d_move may have
1069                  * changed things.  Don't bother checking the hash because we're
1070                  * about to compare the whole name anyway.
1071                  */
1072                 if (dentry->d_parent != parent)
1073                         goto next;
1074 
1075                 /*
1076                  * It is safe to compare names since d_move() cannot
1077                  * change the qstr (protected by d_lock).
1078                  */
1079                 qstr = &dentry->d_name;
1080                 if (parent->d_op && parent->d_op->d_compare) {
1081                         if (parent->d_op->d_compare(parent, qstr, name))
1082                                 goto next;
1083                 } else {
1084                         if (qstr->len != len)
1085                                 goto next;
1086                         if (memcmp(qstr->name, str, len))
1087                                 goto next;
1088                 }
1089 
1090                 if (!d_unhashed(dentry)) {
1091                         atomic_inc(&dentry->d_count);
1092                         found = dentry;
1093                 }
1094                 spin_unlock(&dentry->d_lock);
1095                 break;
1096 next:
1097                 spin_unlock(&dentry->d_lock);
1098         }
1099         rcu_read_unlock();
1100 
1101         return found;
1102 }
1103 
1104 /**
1105  * d_validate - verify dentry provided from insecure source
1106  * @dentry: The dentry alleged to be valid child of @dparent
1107  * @dparent: The parent dentry (known to be valid)
1108  * @hash: Hash of the dentry
1109  * @len: Length of the name
1110  *
1111  * An insecure source has sent us a dentry, here we verify it and dget() it.
1112  * This is used by ncpfs in its readdir implementation.
1113  * Zero is returned in the dentry is invalid.
1114  */
1115  
1116 int d_validate(struct dentry *dentry, struct dentry *dparent)
1117 {
1118         struct hlist_head *base;
1119         struct hlist_node *lhp;
1120 
1121         /* Check whether the ptr might be valid at all.. */
1122         if (!kmem_ptr_validate(dentry_cache, dentry))
1123                 goto out;
1124 
1125         if (dentry->d_parent != dparent)
1126                 goto out;
1127 
1128         spin_lock(&dcache_lock);
1129         base = d_hash(dparent, dentry->d_name.hash);
1130         hlist_for_each(lhp,base) { 
1131                 /* hlist_for_each_entry_rcu() not required for d_hash list
1132                  * as it is parsed under dcache_lock
1133                  */
1134                 if (dentry == hlist_entry(lhp, struct dentry, d_hash)) {
1135                         __dget_locked(dentry);
1136                         spin_unlock(&dcache_lock);
1137                         return 1;
1138                 }
1139         }
1140         spin_unlock(&dcache_lock);
1141 out:
1142         return 0;
1143 }
1144 
1145 /*
1146  * When a file is deleted, we have two options:
1147  * - turn this dentry into a negative dentry
1148  * - unhash this dentry and free it.
1149  *
1150  * Usually, we want to just turn this into
1151  * a negative dentry, but if anybody else is
1152  * currently using the dentry or the inode
1153  * we can't do that and we fall back on removing
1154  * it from the hash queues and waiting for
1155  * it to be deleted later when it has no users
1156  */
1157  
1158 /**
1159  * d_delete - delete a dentry
1160  * @dentry: The dentry to delete
1161  *
1162  * Turn the dentry into a negative dentry if possible, otherwise
1163  * remove it from the hash queues so it can be deleted later
1164  */
1165  
1166 void d_delete(struct dentry * dentry)
1167 {
1168         int isdir = 0;
1169         /*
1170          * Are we the only user?
1171          */
1172         spin_lock(&dcache_lock);
1173         spin_lock(&dentry->d_lock);
1174         isdir = S_ISDIR(dentry->d_inode->i_mode);
1175         if (atomic_read(&dentry->d_count) == 1) {
1176                 dentry_iput(dentry);
1177                 fsnotify_nameremove(dentry, isdir);
1178                 return;
1179         }
1180 
1181         if (!d_unhashed(dentry))
1182                 __d_drop(dentry);
1183 
1184         spin_unlock(&dentry->d_lock);
1185         spin_unlock(&dcache_lock);
1186 
1187         fsnotify_nameremove(dentry, isdir);
1188 }
1189 
1190 static void __d_rehash(struct dentry * entry, struct hlist_head *list)
1191 {
1192 
1193         entry->d_flags &= ~DCACHE_UNHASHED;
1194         hlist_add_head_rcu(&entry->d_hash, list);
1195 }
1196 
1197 /**
1198  * d_rehash     - add an entry back to the hash
1199  * @entry: dentry to add to the hash
1200  *
1201  * Adds a dentry to the hash according to its name.
1202  */
1203  
1204 void d_rehash(struct dentry * entry)
1205 {
1206         struct hlist_head *list = d_hash(entry->d_parent, entry->d_name.hash);
1207 
1208         spin_lock(&dcache_lock);
1209         spin_lock(&entry->d_lock);
1210         __d_rehash(entry, list);
1211         spin_unlock(&entry->d_lock);
1212         spin_unlock(&dcache_lock);
1213 }
1214 
1215 #define do_switch(x,y) do { \
1216         __typeof__ (x) __tmp = x; \
1217         x = y; y = __tmp; } while (0)
1218 
1219 /*
1220  * When switching names, the actual string doesn't strictly have to
1221  * be preserved in the target - because we're dropping the target
1222  * anyway. As such, we can just do a simple memcpy() to copy over
1223  * the new name before we switch.
1224  *
1225  * Note that we have to be a lot more careful about getting the hash
1226  * switched - we have to switch the hash value properly even if it
1227  * then no longer matches the actual (corrupted) string of the target.
1228  * The hash value has to match the hash queue that the dentry is on..
1229  */
1230 static void switch_names(struct dentry *dentry, struct dentry *target)
1231 {
1232         if (dname_external(target)) {
1233                 if (dname_external(dentry)) {
1234                         /*
1235                          * Both external: swap the pointers
1236                          */
1237                         do_switch(target->d_name.name, dentry->d_name.name);
1238                 } else {
1239                         /*
1240                          * dentry:internal, target:external.  Steal target's
1241                          * storage and make target internal.
1242                          */
1243                         dentry->d_name.name = target->d_name.name;
1244                         target->d_name.name = target->d_iname;
1245                 }
1246         } else {
1247                 if (dname_external(dentry)) {
1248                         /*
1249                          * dentry:external, target:internal.  Give dentry's
1250                          * storage to target and make dentry internal
1251                          */
1252                         memcpy(dentry->d_iname, target->d_name.name,
1253                                         target->d_name.len + 1);
1254                         target->d_name.name = dentry->d_name.name;
1255                         dentry->d_name.name = dentry->d_iname;
1256                 } else {
1257                         /*
1258                          * Both are internal.  Just copy target to dentry
1259                          */
1260                         memcpy(dentry->d_iname, target->d_name.name,
1261                                         target->d_name.len + 1);
1262                 }
1263         }
1264 }
1265 
1266 /*
1267  * We cannibalize "target" when moving dentry on top of it,
1268  * because it's going to be thrown away anyway. We could be more
1269  * polite about it, though.
1270  *
1271  * This forceful removal will result in ugly /proc output if
1272  * somebody holds a file open that got deleted due to a rename.
1273  * We could be nicer about the deleted file, and let it show
1274  * up under the name it got deleted rather than the name that
1275  * deleted it.
1276  */
1277  
1278 /**
1279  * d_move - move a dentry
1280  * @dentry: entry to move
1281  * @target: new dentry
1282  *
1283  * Update the dcache to reflect the move of a file name. Negative
1284  * dcache entries should not be moved in this way.
1285  */
1286 
1287 void d_move(struct dentry * dentry, struct dentry * target)
1288 {
1289         struct hlist_head *list;
1290 
1291         if (!dentry->d_inode)
1292                 printk(KERN_WARNING "VFS: moving negative dcache entry\n");
1293 
1294         spin_lock(&dcache_lock);
1295         write_seqlock(&rename_lock);
1296         /*
1297          * XXXX: do we really need to take target->d_lock?
1298          */
1299         if (target < dentry) {
1300                 spin_lock(&target->d_lock);
1301                 spin_lock(&dentry->d_lock);
1302         } else {
1303                 spin_lock(&dentry->d_lock);
1304                 spin_lock(&target->d_lock);
1305         }
1306 
1307         /* Move the dentry to the target hash queue, if on different bucket */
1308         if (dentry->d_flags & DCACHE_UNHASHED)
1309                 goto already_unhashed;
1310 
1311         hlist_del_rcu(&dentry->d_hash);
1312 
1313 already_unhashed:
1314         list = d_hash(target->d_parent, target->d_name.hash);
1315         __d_rehash(dentry, list);
1316 
1317         /* Unhash the target: dput() will then get rid of it */
1318         __d_drop(target);
1319 
1320         list_del(&dentry->d_u.d_child);
1321         list_del(&target->d_u.d_child);
1322 
1323         /* Switch the names.. */
1324         switch_names(dentry, target);
1325         do_switch(dentry->d_name.len, target->d_name.len);
1326         do_switch(dentry->d_name.hash, target->d_name.hash);
1327 
1328         /* ... and switch the parents */
1329         if (IS_ROOT(dentry)) {
1330                 dentry->d_parent = target->d_parent;
1331                 target->d_parent = target;
1332                 INIT_LIST_HEAD(&target->d_u.d_child);
1333         } else {
1334                 do_switch(dentry->d_parent, target->d_parent);
1335 
1336                 /* And add them back to the (new) parent lists */
1337                 list_add(&target->d_u.d_child, &target->d_parent->d_subdirs);
1338         }
1339 
1340         list_add(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
1341         spin_unlock(&target->d_lock);
1342         spin_unlock(&dentry->d_lock);
1343         write_sequnlock(&rename_lock);
1344         spin_unlock(&dcache_lock);
1345 }
1346 
1347 /**
1348  * d_path - return the path of a dentry
1349  * @dentry: dentry to report
1350  * @vfsmnt: vfsmnt to which the dentry belongs
1351  * @root: root dentry
1352  * @rootmnt: vfsmnt to which the root dentry belongs
1353  * @buffer: buffer to return value in
1354  * @buflen: buffer length
1355  *
1356  * Convert a dentry into an ASCII path name. If the entry has been deleted
1357  * the string " (deleted)" is appended. Note that this is ambiguous.
1358  *
1359  * Returns the buffer or an error code if the path was too long.
1360  *
1361  * "buflen" should be positive. Caller holds the dcache_lock.
1362  */
1363 static char * __d_path( struct dentry *dentry, struct vfsmount *vfsmnt,
1364                         struct dentry *root, struct vfsmount *rootmnt,
1365                         char *buffer, int buflen)
1366 {
1367         char * end = buffer+buflen;
1368         char * retval;
1369         int namelen;
1370 
1371         *--end = '\0';
1372         buflen--;
1373         if (!IS_ROOT(dentry) && d_unhashed(dentry)) {
1374                 buflen -= 10;
1375                 end -= 10;
1376                 if (buflen < 0)
1377                         goto Elong;
1378                 memcpy(end, " (deleted)", 10);
1379         }
1380 
1381         if (buflen < 1)
1382                 goto Elong;
1383         /* Get '/' right */
1384         retval = end-1;
1385         *retval = '/';
1386 
1387         for (;;) {
1388                 struct dentry * parent;
1389 
1390                 if (dentry == root && vfsmnt == rootmnt)
1391                         break;
1392                 if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
1393                         /* Global root? */
1394                         spin_lock(&vfsmount_lock);
1395                         if (vfsmnt->mnt_parent == vfsmnt) {
1396                                 spin_unlock(&vfsmount_lock);
1397                                 goto global_root;
1398                         }
1399                         dentry = vfsmnt->mnt_mountpoint;
1400                         vfsmnt = vfsmnt->mnt_parent;
1401                         spin_unlock(&vfsmount_lock);
1402                         continue;
1403                 }
1404                 parent = dentry->d_parent;
1405                 prefetch(parent);
1406                 namelen = dentry->d_name.len;
1407                 buflen -= namelen + 1;
1408                 if (buflen < 0)
1409                         goto Elong;
1410                 end -= namelen;
1411                 memcpy(end, dentry->d_name.name, namelen);
1412                 *--end = '/';
1413                 retval = end;
1414                 dentry = parent;
1415         }
1416 
1417         return retval;
1418 
1419 global_root:
1420         namelen = dentry->d_name.len;
1421         buflen -= namelen;
1422         if (buflen < 0)
1423                 goto Elong;
1424         retval -= namelen-1;    /* hit the slash */
1425         memcpy(retval, dentry->d_name.name, namelen);
1426         return retval;
1427 Elong:
1428         return ERR_PTR(-ENAMETOOLONG);
1429 }
1430 
1431 /* write full pathname into buffer and return start of pathname */
1432 char * d_path(struct dentry *dentry, struct vfsmount *vfsmnt,
1433                                 char *buf, int buflen)
1434 {
1435         char *res;
1436         struct vfsmount *rootmnt;
1437         struct dentry *root;
1438 
1439         read_lock(&current->fs->lock);
1440         rootmnt = mntget(current->fs->rootmnt);
1441         root = dget(current->fs->root);
1442         read_unlock(&current->fs->lock);
1443         spin_lock(&dcache_lock);
1444         res = __d_path(dentry, vfsmnt, root, rootmnt, buf, buflen);
1445         spin_unlock(&dcache_lock);
1446         dput(root);
1447         mntput(rootmnt);
1448         return res;
1449 }
1450 
1451 /*
1452  * NOTE! The user-level library version returns a
1453  * character pointer. The kernel system call just
1454  * returns the length of the buffer filled (which
1455  * includes the ending '\0' character), or a negative
1456  * error value. So libc would do something like
1457  *
1458  *      char *getcwd(char * buf, size_t size)
1459  *      {
1460  *              int retval;
1461  *
1462  *              retval = sys_getcwd(buf, size);
1463  *              if (retval >= 0)
1464  *                      return buf;
1465  *              errno = -retval;
1466  *              return NULL;
1467  *      }
1468  */
1469 asmlinkage long sys_getcwd(char __user *buf, unsigned long size)
1470 {
1471         int error;
1472         struct vfsmount *pwdmnt, *rootmnt;
1473         struct dentry *pwd, *root;
1474         char *page = (char *) __get_free_page(GFP_USER);
1475 
1476         if (!page)
1477                 return -ENOMEM;
1478 
1479         read_lock(&current->fs->lock);
1480         pwdmnt = mntget(current->fs->pwdmnt);
1481         pwd = dget(current->fs->pwd);
1482         rootmnt = mntget(current->fs->rootmnt);
1483         root = dget(current->fs->root);
1484         read_unlock(&current->fs->lock);
1485 
1486         error = -ENOENT;
1487         /* Has the current directory has been unlinked? */
1488         spin_lock(&dcache_lock);
1489         if (pwd->d_parent == pwd || !d_unhashed(pwd)) {
1490                 unsigned long len;
1491                 char * cwd;
1492 
1493                 cwd = __d_path(pwd, pwdmnt, root, rootmnt, page, PAGE_SIZE);
1494                 spin_unlock(&dcache_lock);
1495 
1496                 error = PTR_ERR(cwd);
1497                 if (IS_ERR(cwd))
1498                         goto out;
1499 
1500                 error = -ERANGE;
1501                 len = PAGE_SIZE + page - cwd;
1502                 if (len <= size) {
1503                         error = len;
1504                         if (copy_to_user(buf, cwd, len))
1505                                 error = -EFAULT;
1506                 }
1507         } else
1508                 spin_unlock(&dcache_lock);
1509 
1510 out:
1511         dput(pwd);
1512         mntput(pwdmnt);
1513         dput(root);
1514         mntput(rootmnt);
1515         free_page((unsigned long) page);
1516         return error;
1517 }
1518 
1519 /*
1520  * Test whether new_dentry is a subdirectory of old_dentry.
1521  *
1522  * Trivially implemented using the dcache structure
1523  */
1524 
1525 /**
1526  * is_subdir - is new dentry a subdirectory of old_dentry
1527  * @new_dentry: new dentry
1528  * @old_dentry: old dentry
1529  *
1530  * Returns 1 if new_dentry is a subdirectory of the parent (at any depth).
1531  * Returns 0 otherwise.
1532  * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
1533  */
1534   
1535 int is_subdir(struct dentry * new_dentry, struct dentry * old_dentry)
1536 {
1537         int result;
1538         struct dentry * saved = new_dentry;
1539         unsigned long seq;
1540 
1541         /* need rcu_readlock to protect against the d_parent trashing due to
1542          * d_move
1543          */
1544         rcu_read_lock();
1545         do {
1546                 /* for restarting inner loop in case of seq retry */
1547                 new_dentry = saved;
1548                 result = 0;
1549                 seq = read_seqbegin(&rename_lock);
1550                 for (;;) {
1551                         if (new_dentry != old_dentry) {
1552                                 struct dentry * parent = new_dentry->d_parent;
1553                                 if (parent == new_dentry)
1554                                         break;
1555                                 new_dentry = parent;
1556                                 continue;
1557                         }
1558                         result = 1;
1559                         break;
1560                 }
1561         } while (read_seqretry(&rename_lock, seq));
1562         rcu_read_unlock();
1563 
1564         return result;
1565 }
1566 
1567 void d_genocide(struct dentry *root)
1568 {
1569         struct dentry *this_parent = root;
1570         struct list_head *next;
1571 
1572         spin_lock(&dcache_lock);
1573 repeat:
1574         next = this_parent->d_subdirs.next;
1575 resume:
1576         while (next != &this_parent->d_subdirs) {
1577                 struct list_head *tmp = next;
1578                 struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
1579                 next = tmp->next;
1580                 if (d_unhashed(dentry)||!dentry->d_inode)
1581                         continue;
1582                 if (!list_empty(&dentry->d_subdirs)) {
1583                         this_parent = dentry;
1584                         goto repeat;
1585                 }
1586                 atomic_dec(&dentry->d_count);
1587         }
1588         if (this_parent != root) {
1589                 next = this_parent->d_u.d_child.next;
1590                 atomic_dec(&this_parent->d_count);
1591                 this_parent = this_parent->d_parent;
1592                 goto resume;
1593         }
1594         spin_unlock(&dcache_lock);
1595 }
1596 
1597 /**
1598  * find_inode_number - check for dentry with name
1599  * @dir: directory to check
1600  * @name: Name to find.
1601  *
1602  * Check whether a dentry already exists for the given name,
1603  * and return the inode number if it has an inode. Otherwise
1604  * 0 is returned.
1605  *
1606  * This routine is used to post-process directory listings for
1607  * filesystems using synthetic inode numbers, and is necessary
1608  * to keep getcwd() working.
1609  */
1610  
1611 ino_t find_inode_number(struct dentry *dir, struct qstr *name)
1612 {
1613         struct dentry * dentry;
1614         ino_t ino = 0;
1615 
1616         /*
1617          * Check for a fs-specific hash function. Note that we must
1618          * calculate the standard hash first, as the d_op->d_hash()
1619          * routine may choose to leave the hash value unchanged.
1620          */
1621         name->hash = full_name_hash(name->name, name->len);
1622         if (dir->d_op && dir->d_op->d_hash)
1623         {
1624                 if (dir->d_op->d_hash(dir, name) != 0)
1625                         goto out;
1626         }
1627 
1628         dentry = d_lookup(dir, name);
1629         if (dentry)
1630         {
1631                 if (dentry->d_inode)
1632                         ino = dentry->d_inode->i_ino;
1633                 dput(dentry);
1634         }
1635 out:
1636         return ino;
1637 }
1638 
1639 static __initdata unsigned long dhash_entries;
1640 static int __init set_dhash_entries(char *str)
1641 {
1642         if (!str)
1643                 return 0;
1644         dhash_entries = simple_strtoul(str, &str, 0);
1645         return 1;
1646 }
1647 __setup("dhash_entries=", set_dhash_entries);
1648 
1649 static void __init dcache_init_early(void)
1650 {
1651         int loop;
1652 
1653         /* If hashes are distributed across NUMA nodes, defer
1654          * hash allocation until vmalloc space is available.
1655          */
1656         if (hashdist)
1657                 return;
1658 
1659         dentry_hashtable =
1660                 alloc_large_system_hash("Dentry cache",
1661                                         sizeof(struct hlist_head),
1662                                         dhash_entries,
1663                                         13,
1664                                         HASH_EARLY,
1665                                         &d_hash_shift,
1666                                         &d_hash_mask,
1667                                         0);
1668 
1669         for (loop = 0; loop < (1 << d_hash_shift); loop++)
1670                 INIT_HLIST_HEAD(&dentry_hashtable[loop]);
1671 }
1672 
1673 static void __init dcache_init(unsigned long mempages)
1674 {
1675         int loop;
1676 
1677         /* 
1678          * A constructor could be added for stable state like the lists,
1679          * but it is probably not worth it because of the cache nature
1680          * of the dcache. 
1681          */
1682         dentry_cache = kmem_cache_create("dentry_cache",
1683                                          sizeof(struct dentry),
1684                                          0,
1685                                          SLAB_RECLAIM_ACCOUNT|SLAB_PANIC,
1686                                          NULL, NULL);
1687         
1688         set_shrinker(DEFAULT_SEEKS, shrink_dcache_memory);
1689 
1690         /* Hash may have been set up in dcache_init_early */
1691         if (!hashdist)
1692                 return;
1693 
1694         dentry_hashtable =
1695                 alloc_large_system_hash("Dentry cache",
1696                                         sizeof(struct hlist_head),
1697                                         dhash_entries,
1698                                         13,
1699                                         0,
1700                                         &d_hash_shift,
1701                                         &d_hash_mask,
1702                                         0);
1703 
1704         for (loop = 0; loop < (1 << d_hash_shift); loop++)
1705                 INIT_HLIST_HEAD(&dentry_hashtable[loop]);
1706 }
1707 
1708 /* SLAB cache for __getname() consumers */
1709 kmem_cache_t *names_cachep;
1710 
1711 /* SLAB cache for file structures */
1712 kmem_cache_t *filp_cachep;
1713 
1714 EXPORT_SYMBOL(d_genocide);
1715 
1716 extern void bdev_cache_init(void);
1717 extern void chrdev_init(void);
1718 
1719 void __init vfs_caches_init_early(void)
1720 {
1721         dcache_init_early();
1722         inode_init_early();
1723 }
1724 
1725 void __init vfs_caches_init(unsigned long mempages)
1726 {
1727         unsigned long reserve;
1728 
1729         /* Base hash sizes on available memory, with a reserve equal to
1730            150% of current kernel size */
1731 
1732         reserve = min((mempages - nr_free_pages()) * 3/2, mempages - 1);
1733         mempages -= reserve;
1734 
1735         names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
1736                         SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
1737 
1738         filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
1739                         SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
1740 
1741         dcache_init(mempages);
1742         inode_init(mempages);
1743         files_init(mempages);
1744         mnt_init(mempages);
1745         bdev_cache_init();
1746         chrdev_init();
1747 }
1748 
1749 EXPORT_SYMBOL(d_alloc);
1750 EXPORT_SYMBOL(d_alloc_anon);
1751 EXPORT_SYMBOL(d_alloc_root);
1752 EXPORT_SYMBOL(d_delete);
1753 EXPORT_SYMBOL(d_find_alias);
1754 EXPORT_SYMBOL(d_instantiate);
1755 EXPORT_SYMBOL(d_invalidate);
1756 EXPORT_SYMBOL(d_lookup);
1757 EXPORT_SYMBOL(d_move);
1758 EXPORT_SYMBOL(d_path);
1759 EXPORT_SYMBOL(d_prune_aliases);
1760 EXPORT_SYMBOL(d_rehash);
1761 EXPORT_SYMBOL(d_splice_alias);
1762 EXPORT_SYMBOL(d_validate);
1763 EXPORT_SYMBOL(dget_locked);
1764 EXPORT_SYMBOL(dput);
1765 EXPORT_SYMBOL(find_inode_number);
1766 EXPORT_SYMBOL(have_submounts);
1767 EXPORT_SYMBOL(names_cachep);
1768 EXPORT_SYMBOL(shrink_dcache_parent);
1769 EXPORT_SYMBOL(shrink_dcache_sb);
1770 

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