linux/fs/dcache.c
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   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/module.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 "internal.h"
  37
  38int sysctl_vfs_cache_pressure __read_mostly = 100;
  39EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
  40
  41 __cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lock);
  42__cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
  43
  44EXPORT_SYMBOL(dcache_lock);
  45
  46static struct kmem_cache *dentry_cache __read_mostly;
  47
  48#define DNAME_INLINE_LEN (sizeof(struct dentry)-offsetof(struct dentry,d_iname))
  49
  50/*
  51 * This is the single most critical data structure when it comes
  52 * to the dcache: the hashtable for lookups. Somebody should try
  53 * to make this good - I've just made it work.
  54 *
  55 * This hash-function tries to avoid losing too many bits of hash
  56 * information, yet avoid using a prime hash-size or similar.
  57 */
  58#define D_HASHBITS     d_hash_shift
  59#define D_HASHMASK     d_hash_mask
  60
  61static unsigned int d_hash_mask __read_mostly;
  62static unsigned int d_hash_shift __read_mostly;
  63static struct hlist_head *dentry_hashtable __read_mostly;
  64
  65/* Statistics gathering. */
  66struct dentry_stat_t dentry_stat = {
  67        .age_limit = 45,
  68};
  69
  70static void __d_free(struct dentry *dentry)
  71{
  72        WARN_ON(!list_empty(&dentry->d_alias));
  73        if (dname_external(dentry))
  74                kfree(dentry->d_name.name);
  75        kmem_cache_free(dentry_cache, dentry); 
  76}
  77
  78static void d_callback(struct rcu_head *head)
  79{
  80        struct dentry * dentry = container_of(head, struct dentry, d_u.d_rcu);
  81        __d_free(dentry);
  82}
  83
  84/*
  85 * no dcache_lock, please.  The caller must decrement dentry_stat.nr_dentry
  86 * inside dcache_lock.
  87 */
  88static void d_free(struct dentry *dentry)
  89{
  90        if (dentry->d_op && dentry->d_op->d_release)
  91                dentry->d_op->d_release(dentry);
  92        /* if dentry was never inserted into hash, immediate free is OK */
  93        if (hlist_unhashed(&dentry->d_hash))
  94                __d_free(dentry);
  95        else
  96                call_rcu(&dentry->d_u.d_rcu, d_callback);
  97}
  98
  99/*
 100 * Release the dentry's inode, using the filesystem
 101 * d_iput() operation if defined.
 102 */
 103static void dentry_iput(struct dentry * dentry)
 104        __releases(dentry->d_lock)
 105        __releases(dcache_lock)
 106{
 107        struct inode *inode = dentry->d_inode;
 108        if (inode) {
 109                dentry->d_inode = NULL;
 110                list_del_init(&dentry->d_alias);
 111                spin_unlock(&dentry->d_lock);
 112                spin_unlock(&dcache_lock);
 113                if (!inode->i_nlink)
 114                        fsnotify_inoderemove(inode);
 115                if (dentry->d_op && dentry->d_op->d_iput)
 116                        dentry->d_op->d_iput(dentry, inode);
 117                else
 118                        iput(inode);
 119        } else {
 120                spin_unlock(&dentry->d_lock);
 121                spin_unlock(&dcache_lock);
 122        }
 123}
 124
 125/*
 126 * dentry_lru_(add|add_tail|del|del_init) must be called with dcache_lock held.
 127 */
 128static void dentry_lru_add(struct dentry *dentry)
 129{
 130        list_add(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
 131        dentry->d_sb->s_nr_dentry_unused++;
 132        dentry_stat.nr_unused++;
 133}
 134
 135static void dentry_lru_add_tail(struct dentry *dentry)
 136{
 137        list_add_tail(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
 138        dentry->d_sb->s_nr_dentry_unused++;
 139        dentry_stat.nr_unused++;
 140}
 141
 142static void dentry_lru_del(struct dentry *dentry)
 143{
 144        if (!list_empty(&dentry->d_lru)) {
 145                list_del(&dentry->d_lru);
 146                dentry->d_sb->s_nr_dentry_unused--;
 147                dentry_stat.nr_unused--;
 148        }
 149}
 150
 151static void dentry_lru_del_init(struct dentry *dentry)
 152{
 153        if (likely(!list_empty(&dentry->d_lru))) {
 154                list_del_init(&dentry->d_lru);
 155                dentry->d_sb->s_nr_dentry_unused--;
 156                dentry_stat.nr_unused--;
 157        }
 158}
 159
 160/**
 161 * d_kill - kill dentry and return parent
 162 * @dentry: dentry to kill
 163 *
 164 * The dentry must already be unhashed and removed from the LRU.
 165 *
 166 * If this is the root of the dentry tree, return NULL.
 167 */
 168static struct dentry *d_kill(struct dentry *dentry)
 169        __releases(dentry->d_lock)
 170        __releases(dcache_lock)
 171{
 172        struct dentry *parent;
 173
 174        list_del(&dentry->d_u.d_child);
 175        dentry_stat.nr_dentry--;        /* For d_free, below */
 176        /*drops the locks, at that point nobody can reach this dentry */
 177        dentry_iput(dentry);
 178        if (IS_ROOT(dentry))
 179                parent = NULL;
 180        else
 181                parent = dentry->d_parent;
 182        d_free(dentry);
 183        return parent;
 184}
 185
 186/* 
 187 * This is dput
 188 *
 189 * This is complicated by the fact that we do not want to put
 190 * dentries that are no longer on any hash chain on the unused
 191 * list: we'd much rather just get rid of them immediately.
 192 *
 193 * However, that implies that we have to traverse the dentry
 194 * tree upwards to the parents which might _also_ now be
 195 * scheduled for deletion (it may have been only waiting for
 196 * its last child to go away).
 197 *
 198 * This tail recursion is done by hand as we don't want to depend
 199 * on the compiler to always get this right (gcc generally doesn't).
 200 * Real recursion would eat up our stack space.
 201 */
 202
 203/*
 204 * dput - release a dentry
 205 * @dentry: dentry to release 
 206 *
 207 * Release a dentry. This will drop the usage count and if appropriate
 208 * call the dentry unlink method as well as removing it from the queues and
 209 * releasing its resources. If the parent dentries were scheduled for release
 210 * they too may now get deleted.
 211 *
 212 * no dcache lock, please.
 213 */
 214
 215void dput(struct dentry *dentry)
 216{
 217        if (!dentry)
 218                return;
 219
 220repeat:
 221        if (atomic_read(&dentry->d_count) == 1)
 222                might_sleep();
 223        if (!atomic_dec_and_lock(&dentry->d_count, &dcache_lock))
 224                return;
 225
 226        spin_lock(&dentry->d_lock);
 227        if (atomic_read(&dentry->d_count)) {
 228                spin_unlock(&dentry->d_lock);
 229                spin_unlock(&dcache_lock);
 230                return;
 231        }
 232
 233        /*
 234         * AV: ->d_delete() is _NOT_ allowed to block now.
 235         */
 236        if (dentry->d_op && dentry->d_op->d_delete) {
 237                if (dentry->d_op->d_delete(dentry))
 238                        goto unhash_it;
 239        }
 240        /* Unreachable? Get rid of it */
 241        if (d_unhashed(dentry))
 242                goto kill_it;
 243        if (list_empty(&dentry->d_lru)) {
 244                dentry->d_flags |= DCACHE_REFERENCED;
 245                dentry_lru_add(dentry);
 246        }
 247        spin_unlock(&dentry->d_lock);
 248        spin_unlock(&dcache_lock);
 249        return;
 250
 251unhash_it:
 252        __d_drop(dentry);
 253kill_it:
 254        /* if dentry was on the d_lru list delete it from there */
 255        dentry_lru_del(dentry);
 256        dentry = d_kill(dentry);
 257        if (dentry)
 258                goto repeat;
 259}
 260
 261/**
 262 * d_invalidate - invalidate a dentry
 263 * @dentry: dentry to invalidate
 264 *
 265 * Try to invalidate the dentry if it turns out to be
 266 * possible. If there are other dentries that can be
 267 * reached through this one we can't delete it and we
 268 * return -EBUSY. On success we return 0.
 269 *
 270 * no dcache lock.
 271 */
 272 
 273int d_invalidate(struct dentry * dentry)
 274{
 275        /*
 276         * If it's already been dropped, return OK.
 277         */
 278        spin_lock(&dcache_lock);
 279        if (d_unhashed(dentry)) {
 280                spin_unlock(&dcache_lock);
 281                return 0;
 282        }
 283        /*
 284         * Check whether to do a partial shrink_dcache
 285         * to get rid of unused child entries.
 286         */
 287        if (!list_empty(&dentry->d_subdirs)) {
 288                spin_unlock(&dcache_lock);
 289                shrink_dcache_parent(dentry);
 290                spin_lock(&dcache_lock);
 291        }
 292
 293        /*
 294         * Somebody else still using it?
 295         *
 296         * If it's a directory, we can't drop it
 297         * for fear of somebody re-populating it
 298         * with children (even though dropping it
 299         * would make it unreachable from the root,
 300         * we might still populate it if it was a
 301         * working directory or similar).
 302         */
 303        spin_lock(&dentry->d_lock);
 304        if (atomic_read(&dentry->d_count) > 1) {
 305                if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode)) {
 306                        spin_unlock(&dentry->d_lock);
 307                        spin_unlock(&dcache_lock);
 308                        return -EBUSY;
 309                }
 310        }
 311
 312        __d_drop(dentry);
 313        spin_unlock(&dentry->d_lock);
 314        spin_unlock(&dcache_lock);
 315        return 0;
 316}
 317
 318/* This should be called _only_ with dcache_lock held */
 319
 320static inline struct dentry * __dget_locked(struct dentry *dentry)
 321{
 322        atomic_inc(&dentry->d_count);
 323        dentry_lru_del_init(dentry);
 324        return dentry;
 325}
 326
 327struct dentry * dget_locked(struct dentry *dentry)
 328{
 329        return __dget_locked(dentry);
 330}
 331
 332/**
 333 * d_find_alias - grab a hashed alias of inode
 334 * @inode: inode in question
 335 * @want_discon:  flag, used by d_splice_alias, to request
 336 *          that only a DISCONNECTED alias be returned.
 337 *
 338 * If inode has a hashed alias, or is a directory and has any alias,
 339 * acquire the reference to alias and return it. Otherwise return NULL.
 340 * Notice that if inode is a directory there can be only one alias and
 341 * it can be unhashed only if it has no children, or if it is the root
 342 * of a filesystem.
 343 *
 344 * If the inode has an IS_ROOT, DCACHE_DISCONNECTED alias, then prefer
 345 * any other hashed alias over that one unless @want_discon is set,
 346 * in which case only return an IS_ROOT, DCACHE_DISCONNECTED alias.
 347 */
 348
 349static struct dentry * __d_find_alias(struct inode *inode, int want_discon)
 350{
 351        struct list_head *head, *next, *tmp;
 352        struct dentry *alias, *discon_alias=NULL;
 353
 354        head = &inode->i_dentry;
 355        next = inode->i_dentry.next;
 356        while (next != head) {
 357                tmp = next;
 358                next = tmp->next;
 359                prefetch(next);
 360                alias = list_entry(tmp, struct dentry, d_alias);
 361                if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
 362                        if (IS_ROOT(alias) &&
 363                            (alias->d_flags & DCACHE_DISCONNECTED))
 364                                discon_alias = alias;
 365                        else if (!want_discon) {
 366                                __dget_locked(alias);
 367                                return alias;
 368                        }
 369                }
 370        }
 371        if (discon_alias)
 372                __dget_locked(discon_alias);
 373        return discon_alias;
 374}
 375
 376struct dentry * d_find_alias(struct inode *inode)
 377{
 378        struct dentry *de = NULL;
 379
 380        if (!list_empty(&inode->i_dentry)) {
 381                spin_lock(&dcache_lock);
 382                de = __d_find_alias(inode, 0);
 383                spin_unlock(&dcache_lock);
 384        }
 385        return de;
 386}
 387
 388/*
 389 *      Try to kill dentries associated with this inode.
 390 * WARNING: you must own a reference to inode.
 391 */
 392void d_prune_aliases(struct inode *inode)
 393{
 394        struct dentry *dentry;
 395restart:
 396        spin_lock(&dcache_lock);
 397        list_for_each_entry(dentry, &inode->i_dentry, d_alias) {
 398                spin_lock(&dentry->d_lock);
 399                if (!atomic_read(&dentry->d_count)) {
 400                        __dget_locked(dentry);
 401                        __d_drop(dentry);
 402                        spin_unlock(&dentry->d_lock);
 403                        spin_unlock(&dcache_lock);
 404                        dput(dentry);
 405                        goto restart;
 406                }
 407                spin_unlock(&dentry->d_lock);
 408        }
 409        spin_unlock(&dcache_lock);
 410}
 411
 412/*
 413 * Throw away a dentry - free the inode, dput the parent.  This requires that
 414 * the LRU list has already been removed.
 415 *
 416 * Try to prune ancestors as well.  This is necessary to prevent
 417 * quadratic behavior of shrink_dcache_parent(), but is also expected
 418 * to be beneficial in reducing dentry cache fragmentation.
 419 */
 420static void prune_one_dentry(struct dentry * dentry)
 421        __releases(dentry->d_lock)
 422        __releases(dcache_lock)
 423        __acquires(dcache_lock)
 424{
 425        __d_drop(dentry);
 426        dentry = d_kill(dentry);
 427
 428        /*
 429         * Prune ancestors.  Locking is simpler than in dput(),
 430         * because dcache_lock needs to be taken anyway.
 431         */
 432        spin_lock(&dcache_lock);
 433        while (dentry) {
 434                if (!atomic_dec_and_lock(&dentry->d_count, &dentry->d_lock))
 435                        return;
 436
 437                if (dentry->d_op && dentry->d_op->d_delete)
 438                        dentry->d_op->d_delete(dentry);
 439                dentry_lru_del_init(dentry);
 440                __d_drop(dentry);
 441                dentry = d_kill(dentry);
 442                spin_lock(&dcache_lock);
 443        }
 444}
 445
 446/*
 447 * Shrink the dentry LRU on a given superblock.
 448 * @sb   : superblock to shrink dentry LRU.
 449 * @count: If count is NULL, we prune all dentries on superblock.
 450 * @flags: If flags is non-zero, we need to do special processing based on
 451 * which flags are set. This means we don't need to maintain multiple
 452 * similar copies of this loop.
 453 */
 454static void __shrink_dcache_sb(struct super_block *sb, int *count, int flags)
 455{
 456        LIST_HEAD(referenced);
 457        LIST_HEAD(tmp);
 458        struct dentry *dentry;
 459        int cnt = 0;
 460
 461        BUG_ON(!sb);
 462        BUG_ON((flags & DCACHE_REFERENCED) && count == NULL);
 463        spin_lock(&dcache_lock);
 464        if (count != NULL)
 465                /* called from prune_dcache() and shrink_dcache_parent() */
 466                cnt = *count;
 467restart:
 468        if (count == NULL)
 469                list_splice_init(&sb->s_dentry_lru, &tmp);
 470        else {
 471                while (!list_empty(&sb->s_dentry_lru)) {
 472                        dentry = list_entry(sb->s_dentry_lru.prev,
 473                                        struct dentry, d_lru);
 474                        BUG_ON(dentry->d_sb != sb);
 475
 476                        spin_lock(&dentry->d_lock);
 477                        /*
 478                         * If we are honouring the DCACHE_REFERENCED flag and
 479                         * the dentry has this flag set, don't free it. Clear
 480                         * the flag and put it back on the LRU.
 481                         */
 482                        if ((flags & DCACHE_REFERENCED)
 483                                && (dentry->d_flags & DCACHE_REFERENCED)) {
 484                                dentry->d_flags &= ~DCACHE_REFERENCED;
 485                                list_move(&dentry->d_lru, &referenced);
 486                                spin_unlock(&dentry->d_lock);
 487                        } else {
 488                                list_move_tail(&dentry->d_lru, &tmp);
 489                                spin_unlock(&dentry->d_lock);
 490                                cnt--;
 491                                if (!cnt)
 492                                        break;
 493                        }
 494                        cond_resched_lock(&dcache_lock);
 495                }
 496        }
 497        while (!list_empty(&tmp)) {
 498                dentry = list_entry(tmp.prev, struct dentry, d_lru);
 499                dentry_lru_del_init(dentry);
 500                spin_lock(&dentry->d_lock);
 501                /*
 502                 * We found an inuse dentry which was not removed from
 503                 * the LRU because of laziness during lookup.  Do not free
 504                 * it - just keep it off the LRU list.
 505                 */
 506                if (atomic_read(&dentry->d_count)) {
 507                        spin_unlock(&dentry->d_lock);
 508                        continue;
 509                }
 510                prune_one_dentry(dentry);
 511                /* dentry->d_lock was dropped in prune_one_dentry() */
 512                cond_resched_lock(&dcache_lock);
 513        }
 514        if (count == NULL && !list_empty(&sb->s_dentry_lru))
 515                goto restart;
 516        if (count != NULL)
 517                *count = cnt;
 518        if (!list_empty(&referenced))
 519                list_splice(&referenced, &sb->s_dentry_lru);
 520        spin_unlock(&dcache_lock);
 521}
 522
 523/**
 524 * prune_dcache - shrink the dcache
 525 * @count: number of entries to try to free
 526 *
 527 * Shrink the dcache. This is done when we need more memory, or simply when we
 528 * need to unmount something (at which point we need to unuse all dentries).
 529 *
 530 * This function may fail to free any resources if all the dentries are in use.
 531 */
 532static void prune_dcache(int count)
 533{
 534        struct super_block *sb;
 535        int w_count;
 536        int unused = dentry_stat.nr_unused;
 537        int prune_ratio;
 538        int pruned;
 539
 540        if (unused == 0 || count == 0)
 541                return;
 542        spin_lock(&dcache_lock);
 543restart:
 544        if (count >= unused)
 545                prune_ratio = 1;
 546        else
 547                prune_ratio = unused / count;
 548        spin_lock(&sb_lock);
 549        list_for_each_entry(sb, &super_blocks, s_list) {
 550                if (sb->s_nr_dentry_unused == 0)
 551                        continue;
 552                sb->s_count++;
 553                /* Now, we reclaim unused dentrins with fairness.
 554                 * We reclaim them same percentage from each superblock.
 555                 * We calculate number of dentries to scan on this sb
 556                 * as follows, but the implementation is arranged to avoid
 557                 * overflows:
 558                 * number of dentries to scan on this sb =
 559                 * count * (number of dentries on this sb /
 560                 * number of dentries in the machine)
 561                 */
 562                spin_unlock(&sb_lock);
 563                if (prune_ratio != 1)
 564                        w_count = (sb->s_nr_dentry_unused / prune_ratio) + 1;
 565                else
 566                        w_count = sb->s_nr_dentry_unused;
 567                pruned = w_count;
 568                /*
 569                 * We need to be sure this filesystem isn't being unmounted,
 570                 * otherwise we could race with generic_shutdown_super(), and
 571                 * end up holding a reference to an inode while the filesystem
 572                 * is unmounted.  So we try to get s_umount, and make sure
 573                 * s_root isn't NULL.
 574                 */
 575                if (down_read_trylock(&sb->s_umount)) {
 576                        if ((sb->s_root != NULL) &&
 577                            (!list_empty(&sb->s_dentry_lru))) {
 578                                spin_unlock(&dcache_lock);
 579                                __shrink_dcache_sb(sb, &w_count,
 580                                                DCACHE_REFERENCED);
 581                                pruned -= w_count;
 582                                spin_lock(&dcache_lock);
 583                        }
 584                        up_read(&sb->s_umount);
 585                }
 586                spin_lock(&sb_lock);
 587                count -= pruned;
 588                /*
 589                 * restart only when sb is no longer on the list and
 590                 * we have more work to do.
 591                 */
 592                if (__put_super_and_need_restart(sb) && count > 0) {
 593                        spin_unlock(&sb_lock);
 594                        goto restart;
 595                }
 596        }
 597        spin_unlock(&sb_lock);
 598        spin_unlock(&dcache_lock);
 599}
 600
 601/**
 602 * shrink_dcache_sb - shrink dcache for a superblock
 603 * @sb: superblock
 604 *
 605 * Shrink the dcache for the specified super block. This
 606 * is used to free the dcache before unmounting a file
 607 * system
 608 */
 609void shrink_dcache_sb(struct super_block * sb)
 610{
 611        __shrink_dcache_sb(sb, NULL, 0);
 612}
 613
 614/*
 615 * destroy a single subtree of dentries for unmount
 616 * - see the comments on shrink_dcache_for_umount() for a description of the
 617 *   locking
 618 */
 619static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
 620{
 621        struct dentry *parent;
 622        unsigned detached = 0;
 623
 624        BUG_ON(!IS_ROOT(dentry));
 625
 626        /* detach this root from the system */
 627        spin_lock(&dcache_lock);
 628        dentry_lru_del_init(dentry);
 629        __d_drop(dentry);
 630        spin_unlock(&dcache_lock);
 631
 632        for (;;) {
 633                /* descend to the first leaf in the current subtree */
 634                while (!list_empty(&dentry->d_subdirs)) {
 635                        struct dentry *loop;
 636
 637                        /* this is a branch with children - detach all of them
 638                         * from the system in one go */
 639                        spin_lock(&dcache_lock);
 640                        list_for_each_entry(loop, &dentry->d_subdirs,
 641                                            d_u.d_child) {
 642                                dentry_lru_del_init(loop);
 643                                __d_drop(loop);
 644                                cond_resched_lock(&dcache_lock);
 645                        }
 646                        spin_unlock(&dcache_lock);
 647
 648                        /* move to the first child */
 649                        dentry = list_entry(dentry->d_subdirs.next,
 650                                            struct dentry, d_u.d_child);
 651                }
 652
 653                /* consume the dentries from this leaf up through its parents
 654                 * until we find one with children or run out altogether */
 655                do {
 656                        struct inode *inode;
 657
 658                        if (atomic_read(&dentry->d_count) != 0) {
 659                                printk(KERN_ERR
 660                                       "BUG: Dentry %p{i=%lx,n=%s}"
 661                                       " still in use (%d)"
 662                                       " [unmount of %s %s]\n",
 663                                       dentry,
 664                                       dentry->d_inode ?
 665                                       dentry->d_inode->i_ino : 0UL,
 666                                       dentry->d_name.name,
 667                                       atomic_read(&dentry->d_count),
 668                                       dentry->d_sb->s_type->name,
 669                                       dentry->d_sb->s_id);
 670                                BUG();
 671                        }
 672
 673                        if (IS_ROOT(dentry))
 674                                parent = NULL;
 675                        else {
 676                                parent = dentry->d_parent;
 677                                atomic_dec(&parent->d_count);
 678                        }
 679
 680                        list_del(&dentry->d_u.d_child);
 681                        detached++;
 682
 683                        inode = dentry->d_inode;
 684                        if (inode) {
 685                                dentry->d_inode = NULL;
 686                                list_del_init(&dentry->d_alias);
 687                                if (dentry->d_op && dentry->d_op->d_iput)
 688                                        dentry->d_op->d_iput(dentry, inode);
 689                                else
 690                                        iput(inode);
 691                        }
 692
 693                        d_free(dentry);
 694
 695                        /* finished when we fall off the top of the tree,
 696                         * otherwise we ascend to the parent and move to the
 697                         * next sibling if there is one */
 698                        if (!parent)
 699                                goto out;
 700
 701                        dentry = parent;
 702
 703                } while (list_empty(&dentry->d_subdirs));
 704
 705                dentry = list_entry(dentry->d_subdirs.next,
 706                                    struct dentry, d_u.d_child);
 707        }
 708out:
 709        /* several dentries were freed, need to correct nr_dentry */
 710        spin_lock(&dcache_lock);
 711        dentry_stat.nr_dentry -= detached;
 712        spin_unlock(&dcache_lock);
 713}
 714
 715/*
 716 * destroy the dentries attached to a superblock on unmounting
 717 * - we don't need to use dentry->d_lock, and only need dcache_lock when
 718 *   removing the dentry from the system lists and hashes because:
 719 *   - the superblock is detached from all mountings and open files, so the
 720 *     dentry trees will not be rearranged by the VFS
 721 *   - s_umount is write-locked, so the memory pressure shrinker will ignore
 722 *     any dentries belonging to this superblock that it comes across
 723 *   - the filesystem itself is no longer permitted to rearrange the dentries
 724 *     in this superblock
 725 */
 726void shrink_dcache_for_umount(struct super_block *sb)
 727{
 728        struct dentry *dentry;
 729
 730        if (down_read_trylock(&sb->s_umount))
 731                BUG();
 732
 733        dentry = sb->s_root;
 734        sb->s_root = NULL;
 735        atomic_dec(&dentry->d_count);
 736        shrink_dcache_for_umount_subtree(dentry);
 737
 738        while (!hlist_empty(&sb->s_anon)) {
 739                dentry = hlist_entry(sb->s_anon.first, struct dentry, d_hash);
 740                shrink_dcache_for_umount_subtree(dentry);
 741        }
 742}
 743
 744/*
 745 * Search for at least 1 mount point in the dentry's subdirs.
 746 * We descend to the next level whenever the d_subdirs
 747 * list is non-empty and continue searching.
 748 */
 749 
 750/**
 751 * have_submounts - check for mounts over a dentry
 752 * @parent: dentry to check.
 753 *
 754 * Return true if the parent or its subdirectories contain
 755 * a mount point
 756 */
 757 
 758int have_submounts(struct dentry *parent)
 759{
 760        struct dentry *this_parent = parent;
 761        struct list_head *next;
 762
 763        spin_lock(&dcache_lock);
 764        if (d_mountpoint(parent))
 765                goto positive;
 766repeat:
 767        next = this_parent->d_subdirs.next;
 768resume:
 769        while (next != &this_parent->d_subdirs) {
 770                struct list_head *tmp = next;
 771                struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
 772                next = tmp->next;
 773                /* Have we found a mount point ? */
 774                if (d_mountpoint(dentry))
 775                        goto positive;
 776                if (!list_empty(&dentry->d_subdirs)) {
 777                        this_parent = dentry;
 778                        goto repeat;
 779                }
 780        }
 781        /*
 782         * All done at this level ... ascend and resume the search.
 783         */
 784        if (this_parent != parent) {
 785                next = this_parent->d_u.d_child.next;
 786                this_parent = this_parent->d_parent;
 787                goto resume;
 788        }
 789        spin_unlock(&dcache_lock);
 790        return 0; /* No mount points found in tree */
 791positive:
 792        spin_unlock(&dcache_lock);
 793        return 1;
 794}
 795
 796/*
 797 * Search the dentry child list for the specified parent,
 798 * and move any unused dentries to the end of the unused
 799 * list for prune_dcache(). We descend to the next level
 800 * whenever the d_subdirs list is non-empty and continue
 801 * searching.
 802 *
 803 * It returns zero iff there are no unused children,
 804 * otherwise  it returns the number of children moved to
 805 * the end of the unused list. This may not be the total
 806 * number of unused children, because select_parent can
 807 * drop the lock and return early due to latency
 808 * constraints.
 809 */
 810static int select_parent(struct dentry * parent)
 811{
 812        struct dentry *this_parent = parent;
 813        struct list_head *next;
 814        int found = 0;
 815
 816        spin_lock(&dcache_lock);
 817repeat:
 818        next = this_parent->d_subdirs.next;
 819resume:
 820        while (next != &this_parent->d_subdirs) {
 821                struct list_head *tmp = next;
 822                struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
 823                next = tmp->next;
 824
 825                dentry_lru_del_init(dentry);
 826                /* 
 827                 * move only zero ref count dentries to the end 
 828                 * of the unused list for prune_dcache
 829                 */
 830                if (!atomic_read(&dentry->d_count)) {
 831                        dentry_lru_add_tail(dentry);
 832                        found++;
 833                }
 834
 835                /*
 836                 * We can return to the caller if we have found some (this
 837                 * ensures forward progress). We'll be coming back to find
 838                 * the rest.
 839                 */
 840                if (found && need_resched())
 841                        goto out;
 842
 843                /*
 844                 * Descend a level if the d_subdirs list is non-empty.
 845                 */
 846                if (!list_empty(&dentry->d_subdirs)) {
 847                        this_parent = dentry;
 848                        goto repeat;
 849                }
 850        }
 851        /*
 852         * All done at this level ... ascend and resume the search.
 853         */
 854        if (this_parent != parent) {
 855                next = this_parent->d_u.d_child.next;
 856                this_parent = this_parent->d_parent;
 857                goto resume;
 858        }
 859out:
 860        spin_unlock(&dcache_lock);
 861        return found;
 862}
 863
 864/**
 865 * shrink_dcache_parent - prune dcache
 866 * @parent: parent of entries to prune
 867 *
 868 * Prune the dcache to remove unused children of the parent dentry.
 869 */
 870 
 871void shrink_dcache_parent(struct dentry * parent)
 872{
 873        struct super_block *sb = parent->d_sb;
 874        int found;
 875
 876        while ((found = select_parent(parent)) != 0)
 877                __shrink_dcache_sb(sb, &found, 0);
 878}
 879
 880/*
 881 * Scan `nr' dentries and return the number which remain.
 882 *
 883 * We need to avoid reentering the filesystem if the caller is performing a
 884 * GFP_NOFS allocation attempt.  One example deadlock is:
 885 *
 886 * ext2_new_block->getblk->GFP->shrink_dcache_memory->prune_dcache->
 887 * prune_one_dentry->dput->dentry_iput->iput->inode->i_sb->s_op->put_inode->
 888 * ext2_discard_prealloc->ext2_free_blocks->lock_super->DEADLOCK.
 889 *
 890 * In this case we return -1 to tell the caller that we baled.
 891 */
 892static int shrink_dcache_memory(int nr, gfp_t gfp_mask)
 893{
 894        if (nr) {
 895                if (!(gfp_mask & __GFP_FS))
 896                        return -1;
 897                prune_dcache(nr);
 898        }
 899        return (dentry_stat.nr_unused / 100) * sysctl_vfs_cache_pressure;
 900}
 901
 902static struct shrinker dcache_shrinker = {
 903        .shrink = shrink_dcache_memory,
 904        .seeks = DEFAULT_SEEKS,
 905};
 906
 907/**
 908 * d_alloc      -       allocate a dcache entry
 909 * @parent: parent of entry to allocate
 910 * @name: qstr of the name
 911 *
 912 * Allocates a dentry. It returns %NULL if there is insufficient memory
 913 * available. On a success the dentry is returned. The name passed in is
 914 * copied and the copy passed in may be reused after this call.
 915 */
 916 
 917struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
 918{
 919        struct dentry *dentry;
 920        char *dname;
 921
 922        dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
 923        if (!dentry)
 924                return NULL;
 925
 926        if (name->len > DNAME_INLINE_LEN-1) {
 927                dname = kmalloc(name->len + 1, GFP_KERNEL);
 928                if (!dname) {
 929                        kmem_cache_free(dentry_cache, dentry); 
 930                        return NULL;
 931                }
 932        } else  {
 933                dname = dentry->d_iname;
 934        }       
 935        dentry->d_name.name = dname;
 936
 937        dentry->d_name.len = name->len;
 938        dentry->d_name.hash = name->hash;
 939        memcpy(dname, name->name, name->len);
 940        dname[name->len] = 0;
 941
 942        atomic_set(&dentry->d_count, 1);
 943        dentry->d_flags = DCACHE_UNHASHED;
 944        spin_lock_init(&dentry->d_lock);
 945        dentry->d_inode = NULL;
 946        dentry->d_parent = NULL;
 947        dentry->d_sb = NULL;
 948        dentry->d_op = NULL;
 949        dentry->d_fsdata = NULL;
 950        dentry->d_mounted = 0;
 951        INIT_HLIST_NODE(&dentry->d_hash);
 952        INIT_LIST_HEAD(&dentry->d_lru);
 953        INIT_LIST_HEAD(&dentry->d_subdirs);
 954        INIT_LIST_HEAD(&dentry->d_alias);
 955
 956        if (parent) {
 957                dentry->d_parent = dget(parent);
 958                dentry->d_sb = parent->d_sb;
 959        } else {
 960                INIT_LIST_HEAD(&dentry->d_u.d_child);
 961        }
 962
 963        spin_lock(&dcache_lock);
 964        if (parent)
 965                list_add(&dentry->d_u.d_child, &parent->d_subdirs);
 966        dentry_stat.nr_dentry++;
 967        spin_unlock(&dcache_lock);
 968
 969        return dentry;
 970}
 971
 972struct dentry *d_alloc_name(struct dentry *parent, const char *name)
 973{
 974        struct qstr q;
 975
 976        q.name = name;
 977        q.len = strlen(name);
 978        q.hash = full_name_hash(q.name, q.len);
 979        return d_alloc(parent, &q);
 980}
 981
 982/* the caller must hold dcache_lock */
 983static void __d_instantiate(struct dentry *dentry, struct inode *inode)
 984{
 985        if (inode)
 986                list_add(&dentry->d_alias, &inode->i_dentry);
 987        dentry->d_inode = inode;
 988        fsnotify_d_instantiate(dentry, inode);
 989}
 990
 991/**
 992 * d_instantiate - fill in inode information for a dentry
 993 * @entry: dentry to complete
 994 * @inode: inode to attach to this dentry
 995 *
 996 * Fill in inode information in the entry.
 997 *
 998 * This turns negative dentries into productive full members
 999 * of society.
1000 *
1001 * NOTE! This assumes that the inode count has been incremented
1002 * (or otherwise set) by the caller to indicate that it is now
1003 * in use by the dcache.
1004 */
1005 
1006void d_instantiate(struct dentry *entry, struct inode * inode)
1007{
1008        BUG_ON(!list_empty(&entry->d_alias));
1009        spin_lock(&dcache_lock);
1010        __d_instantiate(entry, inode);
1011        spin_unlock(&dcache_lock);
1012        security_d_instantiate(entry, inode);
1013}
1014
1015/**
1016 * d_instantiate_unique - instantiate a non-aliased dentry
1017 * @entry: dentry to instantiate
1018 * @inode: inode to attach to this dentry
1019 *
1020 * Fill in inode information in the entry. On success, it returns NULL.
1021 * If an unhashed alias of "entry" already exists, then we return the
1022 * aliased dentry instead and drop one reference to inode.
1023 *
1024 * Note that in order to avoid conflicts with rename() etc, the caller
1025 * had better be holding the parent directory semaphore.
1026 *
1027 * This also assumes that the inode count has been incremented
1028 * (or otherwise set) by the caller to indicate that it is now
1029 * in use by the dcache.
1030 */
1031static struct dentry *__d_instantiate_unique(struct dentry *entry,
1032                                             struct inode *inode)
1033{
1034        struct dentry *alias;
1035        int len = entry->d_name.len;
1036        const char *name = entry->d_name.name;
1037        unsigned int hash = entry->d_name.hash;
1038
1039        if (!inode) {
1040                __d_instantiate(entry, NULL);
1041                return NULL;
1042        }
1043
1044        list_for_each_entry(alias, &inode->i_dentry, d_alias) {
1045                struct qstr *qstr = &alias->d_name;
1046
1047                if (qstr->hash != hash)
1048                        continue;
1049                if (alias->d_parent != entry->d_parent)
1050                        continue;
1051                if (qstr->len != len)
1052                        continue;
1053                if (memcmp(qstr->name, name, len))
1054                        continue;
1055                dget_locked(alias);
1056                return alias;
1057        }
1058
1059        __d_instantiate(entry, inode);
1060        return NULL;
1061}
1062
1063struct dentry *d_instantiate_unique(struct dentry *entry, struct inode *inode)
1064{
1065        struct dentry *result;
1066
1067        BUG_ON(!list_empty(&entry->d_alias));
1068
1069        spin_lock(&dcache_lock);
1070        result = __d_instantiate_unique(entry, inode);
1071        spin_unlock(&dcache_lock);
1072
1073        if (!result) {
1074                security_d_instantiate(entry, inode);
1075                return NULL;
1076        }
1077
1078        BUG_ON(!d_unhashed(result));
1079        iput(inode);
1080        return result;
1081}
1082
1083EXPORT_SYMBOL(d_instantiate_unique);
1084
1085/**
1086 * d_alloc_root - allocate root dentry
1087 * @root_inode: inode to allocate the root for
1088 *
1089 * Allocate a root ("/") dentry for the inode given. The inode is
1090 * instantiated and returned. %NULL is returned if there is insufficient
1091 * memory or the inode passed is %NULL.
1092 */
1093 
1094struct dentry * d_alloc_root(struct inode * root_inode)
1095{
1096        struct dentry *res = NULL;
1097
1098        if (root_inode) {
1099                static const struct qstr name = { .name = "/", .len = 1 };
1100
1101                res = d_alloc(NULL, &name);
1102                if (res) {
1103                        res->d_sb = root_inode->i_sb;
1104                        res->d_parent = res;
1105                        d_instantiate(res, root_inode);
1106                }
1107        }
1108        return res;
1109}
1110
1111static inline struct hlist_head *d_hash(struct dentry *parent,
1112                                        unsigned long hash)
1113{
1114        hash += ((unsigned long) parent ^ GOLDEN_RATIO_PRIME) / L1_CACHE_BYTES;
1115        hash = hash ^ ((hash ^ GOLDEN_RATIO_PRIME) >> D_HASHBITS);
1116        return dentry_hashtable + (hash & D_HASHMASK);
1117}
1118
1119/**
1120 * d_obtain_alias - find or allocate a dentry for a given inode
1121 * @inode: inode to allocate the dentry for
1122 *
1123 * Obtain a dentry for an inode resulting from NFS filehandle conversion or
1124 * similar open by handle operations.  The returned dentry may be anonymous,
1125 * or may have a full name (if the inode was already in the cache).
1126 *
1127 * When called on a directory inode, we must ensure that the inode only ever
1128 * has one dentry.  If a dentry is found, that is returned instead of
1129 * allocating a new one.
1130 *
1131 * On successful return, the reference to the inode has been transferred
1132 * to the dentry.  In case of an error the reference on the inode is released.
1133 * To make it easier to use in export operations a %NULL or IS_ERR inode may
1134 * be passed in and will be the error will be propagate to the return value,
1135 * with a %NULL @inode replaced by ERR_PTR(-ESTALE).
1136 */
1137struct dentry *d_obtain_alias(struct inode *inode)
1138{
1139        static const struct qstr anonstring = { .name = "" };
1140        struct dentry *tmp;
1141        struct dentry *res;
1142
1143        if (!inode)
1144                return ERR_PTR(-ESTALE);
1145        if (IS_ERR(inode))
1146                return ERR_CAST(inode);
1147
1148        res = d_find_alias(inode);
1149        if (res)
1150                goto out_iput;
1151
1152        tmp = d_alloc(NULL, &anonstring);
1153        if (!tmp) {
1154                res = ERR_PTR(-ENOMEM);
1155                goto out_iput;
1156        }
1157        tmp->d_parent = tmp; /* make sure dput doesn't croak */
1158
1159        spin_lock(&dcache_lock);
1160        res = __d_find_alias(inode, 0);
1161        if (res) {
1162                spin_unlock(&dcache_lock);
1163                dput(tmp);
1164                goto out_iput;
1165        }
1166
1167        /* attach a disconnected dentry */
1168        spin_lock(&tmp->d_lock);
1169        tmp->d_sb = inode->i_sb;
1170        tmp->d_inode = inode;
1171        tmp->d_flags |= DCACHE_DISCONNECTED;
1172        tmp->d_flags &= ~DCACHE_UNHASHED;
1173        list_add(&tmp->d_alias, &inode->i_dentry);
1174        hlist_add_head(&tmp->d_hash, &inode->i_sb->s_anon);
1175        spin_unlock(&tmp->d_lock);
1176
1177        spin_unlock(&dcache_lock);
1178        return tmp;
1179
1180 out_iput:
1181        iput(inode);
1182        return res;
1183}
1184EXPORT_SYMBOL(d_obtain_alias);
1185
1186/**
1187 * d_splice_alias - splice a disconnected dentry into the tree if one exists
1188 * @inode:  the inode which may have a disconnected dentry
1189 * @dentry: a negative dentry which we want to point to the inode.
1190 *
1191 * If inode is a directory and has a 'disconnected' dentry (i.e. IS_ROOT and
1192 * DCACHE_DISCONNECTED), then d_move that in place of the given dentry
1193 * and return it, else simply d_add the inode to the dentry and return NULL.
1194 *
1195 * This is needed in the lookup routine of any filesystem that is exportable
1196 * (via knfsd) so that we can build dcache paths to directories effectively.
1197 *
1198 * If a dentry was found and moved, then it is returned.  Otherwise NULL
1199 * is returned.  This matches the expected return value of ->lookup.
1200 *
1201 */
1202struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
1203{
1204        struct dentry *new = NULL;
1205
1206        if (inode && S_ISDIR(inode->i_mode)) {
1207                spin_lock(&dcache_lock);
1208                new = __d_find_alias(inode, 1);
1209                if (new) {
1210                        BUG_ON(!(new->d_flags & DCACHE_DISCONNECTED));
1211                        spin_unlock(&dcache_lock);
1212                        security_d_instantiate(new, inode);
1213                        d_rehash(dentry);
1214                        d_move(new, dentry);
1215                        iput(inode);
1216                } else {
1217                        /* already taking dcache_lock, so d_add() by hand */
1218                        __d_instantiate(dentry, inode);
1219                        spin_unlock(&dcache_lock);
1220                        security_d_instantiate(dentry, inode);
1221                        d_rehash(dentry);
1222                }
1223        } else
1224                d_add(dentry, inode);
1225        return new;
1226}
1227
1228/**
1229 * d_add_ci - lookup or allocate new dentry with case-exact name
1230 * @inode:  the inode case-insensitive lookup has found
1231 * @dentry: the negative dentry that was passed to the parent's lookup func
1232 * @name:   the case-exact name to be associated with the returned dentry
1233 *
1234 * This is to avoid filling the dcache with case-insensitive names to the
1235 * same inode, only the actual correct case is stored in the dcache for
1236 * case-insensitive filesystems.
1237 *
1238 * For a case-insensitive lookup match and if the the case-exact dentry
1239 * already exists in in the dcache, use it and return it.
1240 *
1241 * If no entry exists with the exact case name, allocate new dentry with
1242 * the exact case, and return the spliced entry.
1243 */
1244struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
1245                        struct qstr *name)
1246{
1247        int error;
1248        struct dentry *found;
1249        struct dentry *new;
1250
1251        /*
1252         * First check if a dentry matching the name already exists,
1253         * if not go ahead and create it now.
1254         */
1255        found = d_hash_and_lookup(dentry->d_parent, name);
1256        if (!found) {
1257                new = d_alloc(dentry->d_parent, name);
1258                if (!new) {
1259                        error = -ENOMEM;
1260                        goto err_out;
1261                }
1262
1263                found = d_splice_alias(inode, new);
1264                if (found) {
1265                        dput(new);
1266                        return found;
1267                }
1268                return new;
1269        }
1270
1271        /*
1272         * If a matching dentry exists, and it's not negative use it.
1273         *
1274         * Decrement the reference count to balance the iget() done
1275         * earlier on.
1276         */
1277        if (found->d_inode) {
1278                if (unlikely(found->d_inode != inode)) {
1279                        /* This can't happen because bad inodes are unhashed. */
1280                        BUG_ON(!is_bad_inode(inode));
1281                        BUG_ON(!is_bad_inode(found->d_inode));
1282                }
1283                iput(inode);
1284                return found;
1285        }
1286
1287        /*
1288         * Negative dentry: instantiate it unless the inode is a directory and
1289         * already has a dentry.
1290         */
1291        spin_lock(&dcache_lock);
1292        if (!S_ISDIR(inode->i_mode) || list_empty(&inode->i_dentry)) {
1293                __d_instantiate(found, inode);
1294                spin_unlock(&dcache_lock);
1295                security_d_instantiate(found, inode);
1296                return found;
1297        }
1298
1299        /*
1300         * In case a directory already has a (disconnected) entry grab a
1301         * reference to it, move it in place and use it.
1302         */
1303        new = list_entry(inode->i_dentry.next, struct dentry, d_alias);
1304        dget_locked(new);
1305        spin_unlock(&dcache_lock);
1306        security_d_instantiate(found, inode);
1307        d_move(new, found);
1308        iput(inode);
1309        dput(found);
1310        return new;
1311
1312err_out:
1313        iput(inode);
1314        return ERR_PTR(error);
1315}
1316
1317/**
1318 * d_lookup - search for a dentry
1319 * @parent: parent dentry
1320 * @name: qstr of name we wish to find
1321 *
1322 * Searches the children of the parent dentry for the name in question. If
1323 * the dentry is found its reference count is incremented and the dentry
1324 * is returned. The caller must use dput to free the entry when it has
1325 * finished using it. %NULL is returned on failure.
1326 *
1327 * __d_lookup is dcache_lock free. The hash list is protected using RCU.
1328 * Memory barriers are used while updating and doing lockless traversal. 
1329 * To avoid races with d_move while rename is happening, d_lock is used.
1330 *
1331 * Overflows in memcmp(), while d_move, are avoided by keeping the length
1332 * and name pointer in one structure pointed by d_qstr.
1333 *
1334 * rcu_read_lock() and rcu_read_unlock() are used to disable preemption while
1335 * lookup is going on.
1336 *
1337 * The dentry unused LRU is not updated even if lookup finds the required dentry
1338 * in there. It is updated in places such as prune_dcache, shrink_dcache_sb,
1339 * select_parent and __dget_locked. This laziness saves lookup from dcache_lock
1340 * acquisition.
1341 *
1342 * d_lookup() is protected against the concurrent renames in some unrelated
1343 * directory using the seqlockt_t rename_lock.
1344 */
1345
1346struct dentry * d_lookup(struct dentry * parent, struct qstr * name)
1347{
1348        struct dentry * dentry = NULL;
1349        unsigned long seq;
1350
1351        do {
1352                seq = read_seqbegin(&rename_lock);
1353                dentry = __d_lookup(parent, name);
1354                if (dentry)
1355                        break;
1356        } while (read_seqretry(&rename_lock, seq));
1357        return dentry;
1358}
1359
1360struct dentry * __d_lookup(struct dentry * parent, struct qstr * name)
1361{
1362        unsigned int len = name->len;
1363        unsigned int hash = name->hash;
1364        const unsigned char *str = name->name;
1365        struct hlist_head *head = d_hash(parent,hash);
1366        struct dentry *found = NULL;
1367        struct hlist_node *node;
1368        struct dentry *dentry;
1369
1370        rcu_read_lock();
1371        
1372        hlist_for_each_entry_rcu(dentry, node, head, d_hash) {
1373                struct qstr *qstr;
1374
1375                if (dentry->d_name.hash != hash)
1376                        continue;
1377                if (dentry->d_parent != parent)
1378                        continue;
1379
1380                spin_lock(&dentry->d_lock);
1381
1382                /*
1383                 * Recheck the dentry after taking the lock - d_move may have
1384                 * changed things.  Don't bother checking the hash because we're
1385                 * about to compare the whole name anyway.
1386                 */
1387                if (dentry->d_parent != parent)
1388                        goto next;
1389
1390                /* non-existing due to RCU? */
1391                if (d_unhashed(dentry))
1392                        goto next;
1393
1394                /*
1395                 * It is safe to compare names since d_move() cannot
1396                 * change the qstr (protected by d_lock).
1397                 */
1398                qstr = &dentry->d_name;
1399                if (parent->d_op && parent->d_op->d_compare) {
1400                        if (parent->d_op->d_compare(parent, qstr, name))
1401                                goto next;
1402                } else {
1403                        if (qstr->len != len)
1404                                goto next;
1405                        if (memcmp(qstr->name, str, len))
1406                                goto next;
1407                }
1408
1409                atomic_inc(&dentry->d_count);
1410                found = dentry;
1411                spin_unlock(&dentry->d_lock);
1412                break;
1413next:
1414                spin_unlock(&dentry->d_lock);
1415        }
1416        rcu_read_unlock();
1417
1418        return found;
1419}
1420
1421/**
1422 * d_hash_and_lookup - hash the qstr then search for a dentry
1423 * @dir: Directory to search in
1424 * @name: qstr of name we wish to find
1425 *
1426 * On hash failure or on lookup failure NULL is returned.
1427 */
1428struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
1429{
1430        struct dentry *dentry = NULL;
1431
1432        /*
1433         * Check for a fs-specific hash function. Note that we must
1434         * calculate the standard hash first, as the d_op->d_hash()
1435         * routine may choose to leave the hash value unchanged.
1436         */
1437        name->hash = full_name_hash(name->name, name->len);
1438        if (dir->d_op && dir->d_op->d_hash) {
1439                if (dir->d_op->d_hash(dir, name) < 0)
1440                        goto out;
1441        }
1442        dentry = d_lookup(dir, name);
1443out:
1444        return dentry;
1445}
1446
1447/**
1448 * d_validate - verify dentry provided from insecure source
1449 * @dentry: The dentry alleged to be valid child of @dparent
1450 * @dparent: The parent dentry (known to be valid)
1451 *
1452 * An insecure source has sent us a dentry, here we verify it and dget() it.
1453 * This is used by ncpfs in its readdir implementation.
1454 * Zero is returned in the dentry is invalid.
1455 */
1456 
1457int d_validate(struct dentry *dentry, struct dentry *dparent)
1458{
1459        struct hlist_head *base;
1460        struct hlist_node *lhp;
1461
1462        /* Check whether the ptr might be valid at all.. */
1463        if (!kmem_ptr_validate(dentry_cache, dentry))
1464                goto out;
1465
1466        if (dentry->d_parent != dparent)
1467                goto out;
1468
1469        spin_lock(&dcache_lock);
1470        base = d_hash(dparent, dentry->d_name.hash);
1471        hlist_for_each(lhp,base) { 
1472                /* hlist_for_each_entry_rcu() not required for d_hash list
1473                 * as it is parsed under dcache_lock
1474                 */
1475                if (dentry == hlist_entry(lhp, struct dentry, d_hash)) {
1476                        __dget_locked(dentry);
1477                        spin_unlock(&dcache_lock);
1478                        return 1;
1479                }
1480        }
1481        spin_unlock(&dcache_lock);
1482out:
1483        return 0;
1484}
1485
1486/*
1487 * When a file is deleted, we have two options:
1488 * - turn this dentry into a negative dentry
1489 * - unhash this dentry and free it.
1490 *
1491 * Usually, we want to just turn this into
1492 * a negative dentry, but if anybody else is
1493 * currently using the dentry or the inode
1494 * we can't do that and we fall back on removing
1495 * it from the hash queues and waiting for
1496 * it to be deleted later when it has no users
1497 */
1498 
1499/**
1500 * d_delete - delete a dentry
1501 * @dentry: The dentry to delete
1502 *
1503 * Turn the dentry into a negative dentry if possible, otherwise
1504 * remove it from the hash queues so it can be deleted later
1505 */
1506 
1507void d_delete(struct dentry * dentry)
1508{
1509        int isdir = 0;
1510        /*
1511         * Are we the only user?
1512         */
1513        spin_lock(&dcache_lock);
1514        spin_lock(&dentry->d_lock);
1515        isdir = S_ISDIR(dentry->d_inode->i_mode);
1516        if (atomic_read(&dentry->d_count) == 1) {
1517                dentry_iput(dentry);
1518                fsnotify_nameremove(dentry, isdir);
1519                return;
1520        }
1521
1522        if (!d_unhashed(dentry))
1523                __d_drop(dentry);
1524
1525        spin_unlock(&dentry->d_lock);
1526        spin_unlock(&dcache_lock);
1527
1528        fsnotify_nameremove(dentry, isdir);
1529}
1530
1531static void __d_rehash(struct dentry * entry, struct hlist_head *list)
1532{
1533
1534        entry->d_flags &= ~DCACHE_UNHASHED;
1535        hlist_add_head_rcu(&entry->d_hash, list);
1536}
1537
1538static void _d_rehash(struct dentry * entry)
1539{
1540        __d_rehash(entry, d_hash(entry->d_parent, entry->d_name.hash));
1541}
1542
1543/**
1544 * d_rehash     - add an entry back to the hash
1545 * @entry: dentry to add to the hash
1546 *
1547 * Adds a dentry to the hash according to its name.
1548 */
1549 
1550void d_rehash(struct dentry * entry)
1551{
1552        spin_lock(&dcache_lock);
1553        spin_lock(&entry->d_lock);
1554        _d_rehash(entry);
1555        spin_unlock(&entry->d_lock);
1556        spin_unlock(&dcache_lock);
1557}
1558
1559/*
1560 * When switching names, the actual string doesn't strictly have to
1561 * be preserved in the target - because we're dropping the target
1562 * anyway. As such, we can just do a simple memcpy() to copy over
1563 * the new name before we switch.
1564 *
1565 * Note that we have to be a lot more careful about getting the hash
1566 * switched - we have to switch the hash value properly even if it
1567 * then no longer matches the actual (corrupted) string of the target.
1568 * The hash value has to match the hash queue that the dentry is on..
1569 */
1570static void switch_names(struct dentry *dentry, struct dentry *target)
1571{
1572        if (dname_external(target)) {
1573                if (dname_external(dentry)) {
1574                        /*
1575                         * Both external: swap the pointers
1576                         */
1577                        swap(target->d_name.name, dentry->d_name.name);
1578                } else {
1579                        /*
1580                         * dentry:internal, target:external.  Steal target's
1581                         * storage and make target internal.
1582                         */
1583                        memcpy(target->d_iname, dentry->d_name.name,
1584                                        dentry->d_name.len + 1);
1585                        dentry->d_name.name = target->d_name.name;
1586                        target->d_name.name = target->d_iname;
1587                }
1588        } else {
1589                if (dname_external(dentry)) {
1590                        /*
1591                         * dentry:external, target:internal.  Give dentry's
1592                         * storage to target and make dentry internal
1593                         */
1594                        memcpy(dentry->d_iname, target->d_name.name,
1595                                        target->d_name.len + 1);
1596                        target->d_name.name = dentry->d_name.name;
1597                        dentry->d_name.name = dentry->d_iname;
1598                } else {
1599                        /*
1600                         * Both are internal.  Just copy target to dentry
1601                         */
1602                        memcpy(dentry->d_iname, target->d_name.name,
1603                                        target->d_name.len + 1);
1604                        dentry->d_name.len = target->d_name.len;
1605                        return;
1606                }
1607        }
1608        swap(dentry->d_name.len, target->d_name.len);
1609}
1610
1611/*
1612 * We cannibalize "target" when moving dentry on top of it,
1613 * because it's going to be thrown away anyway. We could be more
1614 * polite about it, though.
1615 *
1616 * This forceful removal will result in ugly /proc output if
1617 * somebody holds a file open that got deleted due to a rename.
1618 * We could be nicer about the deleted file, and let it show
1619 * up under the name it had before it was deleted rather than
1620 * under the original name of the file that was moved on top of it.
1621 */
1622 
1623/*
1624 * d_move_locked - move a dentry
1625 * @dentry: entry to move
1626 * @target: new dentry
1627 *
1628 * Update the dcache to reflect the move of a file name. Negative
1629 * dcache entries should not be moved in this way.
1630 */
1631static void d_move_locked(struct dentry * dentry, struct dentry * target)
1632{
1633        struct hlist_head *list;
1634
1635        if (!dentry->d_inode)
1636                printk(KERN_WARNING "VFS: moving negative dcache entry\n");
1637
1638        write_seqlock(&rename_lock);
1639        /*
1640         * XXXX: do we really need to take target->d_lock?
1641         */
1642        if (target < dentry) {
1643                spin_lock(&target->d_lock);
1644                spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
1645        } else {
1646                spin_lock(&dentry->d_lock);
1647                spin_lock_nested(&target->d_lock, DENTRY_D_LOCK_NESTED);
1648        }
1649
1650        /* Move the dentry to the target hash queue, if on different bucket */
1651        if (d_unhashed(dentry))
1652                goto already_unhashed;
1653
1654        hlist_del_rcu(&dentry->d_hash);
1655
1656already_unhashed:
1657        list = d_hash(target->d_parent, target->d_name.hash);
1658        __d_rehash(dentry, list);
1659
1660        /* Unhash the target: dput() will then get rid of it */
1661        __d_drop(target);
1662
1663        list_del(&dentry->d_u.d_child);
1664        list_del(&target->d_u.d_child);
1665
1666        /* Switch the names.. */
1667        switch_names(dentry, target);
1668        swap(dentry->d_name.hash, target->d_name.hash);
1669
1670        /* ... and switch the parents */
1671        if (IS_ROOT(dentry)) {
1672                dentry->d_parent = target->d_parent;
1673                target->d_parent = target;
1674                INIT_LIST_HEAD(&target->d_u.d_child);
1675        } else {
1676                swap(dentry->d_parent, target->d_parent);
1677
1678                /* And add them back to the (new) parent lists */
1679                list_add(&target->d_u.d_child, &target->d_parent->d_subdirs);
1680        }
1681
1682        list_add(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
1683        spin_unlock(&target->d_lock);
1684        fsnotify_d_move(dentry);
1685        spin_unlock(&dentry->d_lock);
1686        write_sequnlock(&rename_lock);
1687}
1688
1689/**
1690 * d_move - move a dentry
1691 * @dentry: entry to move
1692 * @target: new dentry
1693 *
1694 * Update the dcache to reflect the move of a file name. Negative
1695 * dcache entries should not be moved in this way.
1696 */
1697
1698void d_move(struct dentry * dentry, struct dentry * target)
1699{
1700        spin_lock(&dcache_lock);
1701        d_move_locked(dentry, target);
1702        spin_unlock(&dcache_lock);
1703}
1704
1705/**
1706 * d_ancestor - search for an ancestor
1707 * @p1: ancestor dentry
1708 * @p2: child dentry
1709 *
1710 * Returns the ancestor dentry of p2 which is a child of p1, if p1 is
1711 * an ancestor of p2, else NULL.
1712 */
1713struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
1714{
1715        struct dentry *p;
1716
1717        for (p = p2; !IS_ROOT(p); p = p->d_parent) {
1718                if (p->d_parent == p1)
1719                        return p;
1720        }
1721        return NULL;
1722}
1723
1724/*
1725 * This helper attempts to cope with remotely renamed directories
1726 *
1727 * It assumes that the caller is already holding
1728 * dentry->d_parent->d_inode->i_mutex and the dcache_lock
1729 *
1730 * Note: If ever the locking in lock_rename() changes, then please
1731 * remember to update this too...
1732 */
1733static struct dentry *__d_unalias(struct dentry *dentry, struct dentry *alias)
1734        __releases(dcache_lock)
1735{
1736        struct mutex *m1 = NULL, *m2 = NULL;
1737        struct dentry *ret;
1738
1739        /* If alias and dentry share a parent, then no extra locks required */
1740        if (alias->d_parent == dentry->d_parent)
1741                goto out_unalias;
1742
1743        /* Check for loops */
1744        ret = ERR_PTR(-ELOOP);
1745        if (d_ancestor(alias, dentry))
1746                goto out_err;
1747
1748        /* See lock_rename() */
1749        ret = ERR_PTR(-EBUSY);
1750        if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
1751                goto out_err;
1752        m1 = &dentry->d_sb->s_vfs_rename_mutex;
1753        if (!mutex_trylock(&alias->d_parent->d_inode->i_mutex))
1754                goto out_err;
1755        m2 = &alias->d_parent->d_inode->i_mutex;
1756out_unalias:
1757        d_move_locked(alias, dentry);
1758        ret = alias;
1759out_err:
1760        spin_unlock(&dcache_lock);
1761        if (m2)
1762                mutex_unlock(m2);
1763        if (m1)
1764                mutex_unlock(m1);
1765        return ret;
1766}
1767
1768/*
1769 * Prepare an anonymous dentry for life in the superblock's dentry tree as a
1770 * named dentry in place of the dentry to be replaced.
1771 */
1772static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
1773{
1774        struct dentry *dparent, *aparent;
1775
1776        switch_names(dentry, anon);
1777        swap(dentry->d_name.hash, anon->d_name.hash);
1778
1779        dparent = dentry->d_parent;
1780        aparent = anon->d_parent;
1781
1782        dentry->d_parent = (aparent == anon) ? dentry : aparent;
1783        list_del(&dentry->d_u.d_child);
1784        if (!IS_ROOT(dentry))
1785                list_add(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
1786        else
1787                INIT_LIST_HEAD(&dentry->d_u.d_child);
1788
1789        anon->d_parent = (dparent == dentry) ? anon : dparent;
1790        list_del(&anon->d_u.d_child);
1791        if (!IS_ROOT(anon))
1792                list_add(&anon->d_u.d_child, &anon->d_parent->d_subdirs);
1793        else
1794                INIT_LIST_HEAD(&anon->d_u.d_child);
1795
1796        anon->d_flags &= ~DCACHE_DISCONNECTED;
1797}
1798
1799/**
1800 * d_materialise_unique - introduce an inode into the tree
1801 * @dentry: candidate dentry
1802 * @inode: inode to bind to the dentry, to which aliases may be attached
1803 *
1804 * Introduces an dentry into the tree, substituting an extant disconnected
1805 * root directory alias in its place if there is one
1806 */
1807struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode)
1808{
1809        struct dentry *actual;
1810
1811        BUG_ON(!d_unhashed(dentry));
1812
1813        spin_lock(&dcache_lock);
1814
1815        if (!inode) {
1816                actual = dentry;
1817                __d_instantiate(dentry, NULL);
1818                goto found_lock;
1819        }
1820
1821        if (S_ISDIR(inode->i_mode)) {
1822                struct dentry *alias;
1823
1824                /* Does an aliased dentry already exist? */
1825                alias = __d_find_alias(inode, 0);
1826                if (alias) {
1827                        actual = alias;
1828                        /* Is this an anonymous mountpoint that we could splice
1829                         * into our tree? */
1830                        if (IS_ROOT(alias)) {
1831                                spin_lock(&alias->d_lock);
1832                                __d_materialise_dentry(dentry, alias);
1833                                __d_drop(alias);
1834                                goto found;
1835                        }
1836                        /* Nope, but we must(!) avoid directory aliasing */
1837                        actual = __d_unalias(dentry, alias);
1838                        if (IS_ERR(actual))
1839                                dput(alias);
1840                        goto out_nolock;
1841                }
1842        }
1843
1844        /* Add a unique reference */
1845        actual = __d_instantiate_unique(dentry, inode);
1846        if (!actual)
1847                actual = dentry;
1848        else if (unlikely(!d_unhashed(actual)))
1849                goto shouldnt_be_hashed;
1850
1851found_lock:
1852        spin_lock(&actual->d_lock);
1853found:
1854        _d_rehash(actual);
1855        spin_unlock(&actual->d_lock);
1856        spin_unlock(&dcache_lock);
1857out_nolock:
1858        if (actual == dentry) {
1859                security_d_instantiate(dentry, inode);
1860                return NULL;
1861        }
1862
1863        iput(inode);
1864        return actual;
1865
1866shouldnt_be_hashed:
1867        spin_unlock(&dcache_lock);
1868        BUG();
1869}
1870
1871static int prepend(char **buffer, int *buflen, const char *str, int namelen)
1872{
1873        *buflen -= namelen;
1874        if (*buflen < 0)
1875                return -ENAMETOOLONG;
1876        *buffer -= namelen;
1877        memcpy(*buffer, str, namelen);
1878        return 0;
1879}
1880
1881static int prepend_name(char **buffer, int *buflen, struct qstr *name)
1882{
1883        return prepend(buffer, buflen, name->name, name->len);
1884}
1885
1886/**
1887 * __d_path - return the path of a dentry
1888 * @path: the dentry/vfsmount to report
1889 * @root: root vfsmnt/dentry (may be modified by this function)
1890 * @buffer: buffer to return value in
1891 * @buflen: buffer length
1892 *
1893 * Convert a dentry into an ASCII path name. If the entry has been deleted
1894 * the string " (deleted)" is appended. Note that this is ambiguous.
1895 *
1896 * Returns a pointer into the buffer or an error code if the
1897 * path was too long.
1898 *
1899 * "buflen" should be positive. Caller holds the dcache_lock.
1900 *
1901 * If path is not reachable from the supplied root, then the value of
1902 * root is changed (without modifying refcounts).
1903 */
1904char *__d_path(const struct path *path, struct path *root,
1905               char *buffer, int buflen)
1906{
1907        struct dentry *dentry = path->dentry;
1908        struct vfsmount *vfsmnt = path->mnt;
1909        char *end = buffer + buflen;
1910        char *retval;
1911
1912        spin_lock(&vfsmount_lock);
1913        prepend(&end, &buflen, "\0", 1);
1914        if (d_unlinked(dentry) &&
1915                (prepend(&end, &buflen, " (deleted)", 10) != 0))
1916                        goto Elong;
1917
1918        if (buflen < 1)
1919                goto Elong;
1920        /* Get '/' right */
1921        retval = end-1;
1922        *retval = '/';
1923
1924        for (;;) {
1925                struct dentry * parent;
1926
1927                if (dentry == root->dentry && vfsmnt == root->mnt)
1928                        break;
1929                if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
1930                        /* Global root? */
1931                        if (vfsmnt->mnt_parent == vfsmnt) {
1932                                goto global_root;
1933                        }
1934                        dentry = vfsmnt->mnt_mountpoint;
1935                        vfsmnt = vfsmnt->mnt_parent;
1936                        continue;
1937                }
1938                parent = dentry->d_parent;
1939                prefetch(parent);
1940                if ((prepend_name(&end, &buflen, &dentry->d_name) != 0) ||
1941                    (prepend(&end, &buflen, "/", 1) != 0))
1942                        goto Elong;
1943                retval = end;
1944                dentry = parent;
1945        }
1946
1947out:
1948        spin_unlock(&vfsmount_lock);
1949        return retval;
1950
1951global_root:
1952        retval += 1;    /* hit the slash */
1953        if (prepend_name(&retval, &buflen, &dentry->d_name) != 0)
1954                goto Elong;
1955        root->mnt = vfsmnt;
1956        root->dentry = dentry;
1957        goto out;
1958
1959Elong:
1960        retval = ERR_PTR(-ENAMETOOLONG);
1961        goto out;
1962}
1963
1964/**
1965 * d_path - return the path of a dentry
1966 * @path: path to report
1967 * @buf: buffer to return value in
1968 * @buflen: buffer length
1969 *
1970 * Convert a dentry into an ASCII path name. If the entry has been deleted
1971 * the string " (deleted)" is appended. Note that this is ambiguous.
1972 *
1973 * Returns a pointer into the buffer or an error code if the path was
1974 * too long. Note: Callers should use the returned pointer, not the passed
1975 * in buffer, to use the name! The implementation often starts at an offset
1976 * into the buffer, and may leave 0 bytes at the start.
1977 *
1978 * "buflen" should be positive.
1979 */
1980char *d_path(const struct path *path, char *buf, int buflen)
1981{
1982        char *res;
1983        struct path root;
1984        struct path tmp;
1985
1986        /*
1987         * We have various synthetic filesystems that never get mounted.  On
1988         * these filesystems dentries are never used for lookup purposes, and
1989         * thus don't need to be hashed.  They also don't need a name until a
1990         * user wants to identify the object in /proc/pid/fd/.  The little hack
1991         * below allows us to generate a name for these objects on demand:
1992         */
1993        if (path->dentry->d_op && path->dentry->d_op->d_dname)
1994                return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
1995
1996        read_lock(&current->fs->lock);
1997        root = current->fs->root;
1998        path_get(&root);
1999        read_unlock(&current->fs->lock);
2000        spin_lock(&dcache_lock);
2001        tmp = root;
2002        res = __d_path(path, &tmp, buf, buflen);
2003        spin_unlock(&dcache_lock);
2004        path_put(&root);
2005        return res;
2006}
2007
2008/*
2009 * Helper function for dentry_operations.d_dname() members
2010 */
2011char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,
2012                        const char *fmt, ...)
2013{
2014        va_list args;
2015        char temp[64];
2016        int sz;
2017
2018        va_start(args, fmt);
2019        sz = vsnprintf(temp, sizeof(temp), fmt, args) + 1;
2020        va_end(args);
2021
2022        if (sz > sizeof(temp) || sz > buflen)
2023                return ERR_PTR(-ENAMETOOLONG);
2024
2025        buffer += buflen - sz;
2026        return memcpy(buffer, temp, sz);
2027}
2028
2029/*
2030 * Write full pathname from the root of the filesystem into the buffer.
2031 */
2032char *dentry_path(struct dentry *dentry, char *buf, int buflen)
2033{
2034        char *end = buf + buflen;
2035        char *retval;
2036
2037        spin_lock(&dcache_lock);
2038        prepend(&end, &buflen, "\0", 1);
2039        if (d_unlinked(dentry) &&
2040                (prepend(&end, &buflen, "//deleted", 9) != 0))
2041                        goto Elong;
2042        if (buflen < 1)
2043                goto Elong;
2044        /* Get '/' right */
2045        retval = end-1;
2046        *retval = '/';
2047
2048        while (!IS_ROOT(dentry)) {
2049                struct dentry *parent = dentry->d_parent;
2050
2051                prefetch(parent);
2052                if ((prepend_name(&end, &buflen, &dentry->d_name) != 0) ||
2053                    (prepend(&end, &buflen, "/", 1) != 0))
2054                        goto Elong;
2055
2056                retval = end;
2057                dentry = parent;
2058        }
2059        spin_unlock(&dcache_lock);
2060        return retval;
2061Elong:
2062        spin_unlock(&dcache_lock);
2063        return ERR_PTR(-ENAMETOOLONG);
2064}
2065
2066/*
2067 * NOTE! The user-level library version returns a
2068 * character pointer. The kernel system call just
2069 * returns the length of the buffer filled (which
2070 * includes the ending '\0' character), or a negative
2071 * error value. So libc would do something like
2072 *
2073 *      char *getcwd(char * buf, size_t size)
2074 *      {
2075 *              int retval;
2076 *
2077 *              retval = sys_getcwd(buf, size);
2078 *              if (retval >= 0)
2079 *                      return buf;
2080 *              errno = -retval;
2081 *              return NULL;
2082 *      }
2083 */
2084SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
2085{
2086        int error;
2087        struct path pwd, root;
2088        char *page = (char *) __get_free_page(GFP_USER);
2089
2090        if (!page)
2091                return -ENOMEM;
2092
2093        read_lock(&current->fs->lock);
2094        pwd = current->fs->pwd;
2095        path_get(&pwd);
2096        root = current->fs->root;
2097        path_get(&root);
2098        read_unlock(&current->fs->lock);
2099
2100        error = -ENOENT;
2101        spin_lock(&dcache_lock);
2102        if (!d_unlinked(pwd.dentry)) {
2103                unsigned long len;
2104                struct path tmp = root;
2105                char * cwd;
2106
2107                cwd = __d_path(&pwd, &tmp, page, PAGE_SIZE);
2108                spin_unlock(&dcache_lock);
2109
2110                error = PTR_ERR(cwd);
2111                if (IS_ERR(cwd))
2112                        goto out;
2113
2114                error = -ERANGE;
2115                len = PAGE_SIZE + page - cwd;
2116                if (len <= size) {
2117                        error = len;
2118                        if (copy_to_user(buf, cwd, len))
2119                                error = -EFAULT;
2120                }
2121        } else
2122                spin_unlock(&dcache_lock);
2123
2124out:
2125        path_put(&pwd);
2126        path_put(&root);
2127        free_page((unsigned long) page);
2128        return error;
2129}
2130
2131/*
2132 * Test whether new_dentry is a subdirectory of old_dentry.
2133 *
2134 * Trivially implemented using the dcache structure
2135 */
2136
2137/**
2138 * is_subdir - is new dentry a subdirectory of old_dentry
2139 * @new_dentry: new dentry
2140 * @old_dentry: old dentry
2141 *
2142 * Returns 1 if new_dentry is a subdirectory of the parent (at any depth).
2143 * Returns 0 otherwise.
2144 * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
2145 */
2146  
2147int is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)
2148{
2149        int result;
2150        unsigned long seq;
2151
2152        if (new_dentry == old_dentry)
2153                return 1;
2154
2155        /*
2156         * Need rcu_readlock to protect against the d_parent trashing
2157         * due to d_move
2158         */
2159        rcu_read_lock();
2160        do {
2161                /* for restarting inner loop in case of seq retry */
2162                seq = read_seqbegin(&rename_lock);
2163                if (d_ancestor(old_dentry, new_dentry))
2164                        result = 1;
2165                else
2166                        result = 0;
2167        } while (read_seqretry(&rename_lock, seq));
2168        rcu_read_unlock();
2169
2170        return result;
2171}
2172
2173void d_genocide(struct dentry *root)
2174{
2175        struct dentry *this_parent = root;
2176        struct list_head *next;
2177
2178        spin_lock(&dcache_lock);
2179repeat:
2180        next = this_parent->d_subdirs.next;
2181resume:
2182        while (next != &this_parent->d_subdirs) {
2183                struct list_head *tmp = next;
2184                struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
2185                next = tmp->next;
2186                if (d_unhashed(dentry)||!dentry->d_inode)
2187                        continue;
2188                if (!list_empty(&dentry->d_subdirs)) {
2189                        this_parent = dentry;
2190                        goto repeat;
2191                }
2192                atomic_dec(&dentry->d_count);
2193        }
2194        if (this_parent != root) {
2195                next = this_parent->d_u.d_child.next;
2196                atomic_dec(&this_parent->d_count);
2197                this_parent = this_parent->d_parent;
2198                goto resume;
2199        }
2200        spin_unlock(&dcache_lock);
2201}
2202
2203/**
2204 * find_inode_number - check for dentry with name
2205 * @dir: directory to check
2206 * @name: Name to find.
2207 *
2208 * Check whether a dentry already exists for the given name,
2209 * and return the inode number if it has an inode. Otherwise
2210 * 0 is returned.
2211 *
2212 * This routine is used to post-process directory listings for
2213 * filesystems using synthetic inode numbers, and is necessary
2214 * to keep getcwd() working.
2215 */
2216 
2217ino_t find_inode_number(struct dentry *dir, struct qstr *name)
2218{
2219        struct dentry * dentry;
2220        ino_t ino = 0;
2221
2222        dentry = d_hash_and_lookup(dir, name);
2223        if (dentry) {
2224                if (dentry->d_inode)
2225                        ino = dentry->d_inode->i_ino;
2226                dput(dentry);
2227        }
2228        return ino;
2229}
2230
2231static __initdata unsigned long dhash_entries;
2232static int __init set_dhash_entries(char *str)
2233{
2234        if (!str)
2235                return 0;
2236        dhash_entries = simple_strtoul(str, &str, 0);
2237        return 1;
2238}
2239__setup("dhash_entries=", set_dhash_entries);
2240
2241static void __init dcache_init_early(void)
2242{
2243        int loop;
2244
2245        /* If hashes are distributed across NUMA nodes, defer
2246         * hash allocation until vmalloc space is available.
2247         */
2248        if (hashdist)
2249                return;
2250
2251        dentry_hashtable =
2252                alloc_large_system_hash("Dentry cache",
2253                                        sizeof(struct hlist_head),
2254                                        dhash_entries,
2255                                        13,
2256                                        HASH_EARLY,
2257                                        &d_hash_shift,
2258                                        &d_hash_mask,
2259                                        0);
2260
2261        for (loop = 0; loop < (1 << d_hash_shift); loop++)
2262                INIT_HLIST_HEAD(&dentry_hashtable[loop]);
2263}
2264
2265static void __init dcache_init(void)
2266{
2267        int loop;
2268
2269        /* 
2270         * A constructor could be added for stable state like the lists,
2271         * but it is probably not worth it because of the cache nature
2272         * of the dcache. 
2273         */
2274        dentry_cache = KMEM_CACHE(dentry,
2275                SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD);
2276        
2277        register_shrinker(&dcache_shrinker);
2278
2279        /* Hash may have been set up in dcache_init_early */
2280        if (!hashdist)
2281                return;
2282
2283        dentry_hashtable =
2284                alloc_large_system_hash("Dentry cache",
2285                                        sizeof(struct hlist_head),
2286                                        dhash_entries,
2287                                        13,
2288                                        0,
2289                                        &d_hash_shift,
2290                                        &d_hash_mask,
2291                                        0);
2292
2293        for (loop = 0; loop < (1 << d_hash_shift); loop++)
2294                INIT_HLIST_HEAD(&dentry_hashtable[loop]);
2295}
2296
2297/* SLAB cache for __getname() consumers */
2298struct kmem_cache *names_cachep __read_mostly;
2299
2300EXPORT_SYMBOL(d_genocide);
2301
2302void __init vfs_caches_init_early(void)
2303{
2304        dcache_init_early();
2305        inode_init_early();
2306}
2307
2308void __init vfs_caches_init(unsigned long mempages)
2309{
2310        unsigned long reserve;
2311
2312        /* Base hash sizes on available memory, with a reserve equal to
2313           150% of current kernel size */
2314
2315        reserve = min((mempages - nr_free_pages()) * 3/2, mempages - 1);
2316        mempages -= reserve;
2317
2318        names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
2319                        SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
2320
2321        dcache_init();
2322        inode_init();
2323        files_init(mempages);
2324        mnt_init();
2325        bdev_cache_init();
2326        chrdev_init();
2327}
2328
2329EXPORT_SYMBOL(d_alloc);
2330EXPORT_SYMBOL(d_alloc_root);
2331EXPORT_SYMBOL(d_delete);
2332EXPORT_SYMBOL(d_find_alias);
2333EXPORT_SYMBOL(d_instantiate);
2334EXPORT_SYMBOL(d_invalidate);
2335EXPORT_SYMBOL(d_lookup);
2336EXPORT_SYMBOL(d_move);
2337EXPORT_SYMBOL_GPL(d_materialise_unique);
2338EXPORT_SYMBOL(d_path);
2339EXPORT_SYMBOL(d_prune_aliases);
2340EXPORT_SYMBOL(d_rehash);
2341EXPORT_SYMBOL(d_splice_alias);
2342EXPORT_SYMBOL(d_add_ci);
2343EXPORT_SYMBOL(d_validate);
2344EXPORT_SYMBOL(dget_locked);
2345EXPORT_SYMBOL(dput);
2346EXPORT_SYMBOL(find_inode_number);
2347EXPORT_SYMBOL(have_submounts);
2348EXPORT_SYMBOL(names_cachep);
2349EXPORT_SYMBOL(shrink_dcache_parent);
2350EXPORT_SYMBOL(shrink_dcache_sb);
2351
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