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 <linux/bit_spinlock.h>
  37#include <linux/rculist_bl.h>
  38#include <linux/prefetch.h>
  39#include "internal.h"
  40
  41/*
  42 * Usage:
  43 * dcache->d_inode->i_lock protects:
  44 *   - i_dentry, d_alias, d_inode of aliases
  45 * dcache_hash_bucket lock protects:
  46 *   - the dcache hash table
  47 * s_anon bl list spinlock protects:
  48 *   - the s_anon list (see __d_drop)
  49 * dcache_lru_lock protects:
  50 *   - the dcache lru lists and counters
  51 * d_lock protects:
  52 *   - d_flags
  53 *   - d_name
  54 *   - d_lru
  55 *   - d_count
  56 *   - d_unhashed()
  57 *   - d_parent and d_subdirs
  58 *   - childrens' d_child and d_parent
  59 *   - d_alias, d_inode
  60 *
  61 * Ordering:
  62 * dentry->d_inode->i_lock
  63 *   dentry->d_lock
  64 *     dcache_lru_lock
  65 *     dcache_hash_bucket lock
  66 *     s_anon lock
  67 *
  68 * If there is an ancestor relationship:
  69 * dentry->d_parent->...->d_parent->d_lock
  70 *   ...
  71 *     dentry->d_parent->d_lock
  72 *       dentry->d_lock
  73 *
  74 * If no ancestor relationship:
  75 * if (dentry1 < dentry2)
  76 *   dentry1->d_lock
  77 *     dentry2->d_lock
  78 */
  79int sysctl_vfs_cache_pressure __read_mostly = 100;
  80EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
  81
  82static __cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lru_lock);
  83__cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
  84
  85EXPORT_SYMBOL(rename_lock);
  86
  87static struct kmem_cache *dentry_cache __read_mostly;
  88
  89/*
  90 * This is the single most critical data structure when it comes
  91 * to the dcache: the hashtable for lookups. Somebody should try
  92 * to make this good - I've just made it work.
  93 *
  94 * This hash-function tries to avoid losing too many bits of hash
  95 * information, yet avoid using a prime hash-size or similar.
  96 */
  97#define D_HASHBITS     d_hash_shift
  98#define D_HASHMASK     d_hash_mask
  99
 100static unsigned int d_hash_mask __read_mostly;
 101static unsigned int d_hash_shift __read_mostly;
 102
 103static struct hlist_bl_head *dentry_hashtable __read_mostly;
 104
 105static inline struct hlist_bl_head *d_hash(struct dentry *parent,
 106                                        unsigned long hash)
 107{
 108        hash += ((unsigned long) parent ^ GOLDEN_RATIO_PRIME) / L1_CACHE_BYTES;
 109        hash = hash ^ ((hash ^ GOLDEN_RATIO_PRIME) >> D_HASHBITS);
 110        return dentry_hashtable + (hash & D_HASHMASK);
 111}
 112
 113/* Statistics gathering. */
 114struct dentry_stat_t dentry_stat = {
 115        .age_limit = 45,
 116};
 117
 118static DEFINE_PER_CPU(unsigned int, nr_dentry);
 119
 120#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
 121static int get_nr_dentry(void)
 122{
 123        int i;
 124        int sum = 0;
 125        for_each_possible_cpu(i)
 126                sum += per_cpu(nr_dentry, i);
 127        return sum < 0 ? 0 : sum;
 128}
 129
 130int proc_nr_dentry(ctl_table *table, int write, void __user *buffer,
 131                   size_t *lenp, loff_t *ppos)
 132{
 133        dentry_stat.nr_dentry = get_nr_dentry();
 134        return proc_dointvec(table, write, buffer, lenp, ppos);
 135}
 136#endif
 137
 138static void __d_free(struct rcu_head *head)
 139{
 140        struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
 141
 142        WARN_ON(!list_empty(&dentry->d_alias));
 143        if (dname_external(dentry))
 144                kfree(dentry->d_name.name);
 145        kmem_cache_free(dentry_cache, dentry); 
 146}
 147
 148/*
 149 * no locks, please.
 150 */
 151static void d_free(struct dentry *dentry)
 152{
 153        BUG_ON(dentry->d_count);
 154        this_cpu_dec(nr_dentry);
 155        if (dentry->d_op && dentry->d_op->d_release)
 156                dentry->d_op->d_release(dentry);
 157
 158        /* if dentry was never visible to RCU, immediate free is OK */
 159        if (!(dentry->d_flags & DCACHE_RCUACCESS))
 160                __d_free(&dentry->d_u.d_rcu);
 161        else
 162                call_rcu(&dentry->d_u.d_rcu, __d_free);
 163}
 164
 165/**
 166 * dentry_rcuwalk_barrier - invalidate in-progress rcu-walk lookups
 167 * @dentry: the target dentry
 168 * After this call, in-progress rcu-walk path lookup will fail. This
 169 * should be called after unhashing, and after changing d_inode (if
 170 * the dentry has not already been unhashed).
 171 */
 172static inline void dentry_rcuwalk_barrier(struct dentry *dentry)
 173{
 174        assert_spin_locked(&dentry->d_lock);
 175        /* Go through a barrier */
 176        write_seqcount_barrier(&dentry->d_seq);
 177}
 178
 179/*
 180 * Release the dentry's inode, using the filesystem
 181 * d_iput() operation if defined. Dentry has no refcount
 182 * and is unhashed.
 183 */
 184static void dentry_iput(struct dentry * dentry)
 185        __releases(dentry->d_lock)
 186        __releases(dentry->d_inode->i_lock)
 187{
 188        struct inode *inode = dentry->d_inode;
 189        if (inode) {
 190                dentry->d_inode = NULL;
 191                list_del_init(&dentry->d_alias);
 192                spin_unlock(&dentry->d_lock);
 193                spin_unlock(&inode->i_lock);
 194                if (!inode->i_nlink)
 195                        fsnotify_inoderemove(inode);
 196                if (dentry->d_op && dentry->d_op->d_iput)
 197                        dentry->d_op->d_iput(dentry, inode);
 198                else
 199                        iput(inode);
 200        } else {
 201                spin_unlock(&dentry->d_lock);
 202        }
 203}
 204
 205/*
 206 * Release the dentry's inode, using the filesystem
 207 * d_iput() operation if defined. dentry remains in-use.
 208 */
 209static void dentry_unlink_inode(struct dentry * dentry)
 210        __releases(dentry->d_lock)
 211        __releases(dentry->d_inode->i_lock)
 212{
 213        struct inode *inode = dentry->d_inode;
 214        dentry->d_inode = NULL;
 215        list_del_init(&dentry->d_alias);
 216        dentry_rcuwalk_barrier(dentry);
 217        spin_unlock(&dentry->d_lock);
 218        spin_unlock(&inode->i_lock);
 219        if (!inode->i_nlink)
 220                fsnotify_inoderemove(inode);
 221        if (dentry->d_op && dentry->d_op->d_iput)
 222                dentry->d_op->d_iput(dentry, inode);
 223        else
 224                iput(inode);
 225}
 226
 227/*
 228 * dentry_lru_(add|del|move_tail) must be called with d_lock held.
 229 */
 230static void dentry_lru_add(struct dentry *dentry)
 231{
 232        if (list_empty(&dentry->d_lru)) {
 233                spin_lock(&dcache_lru_lock);
 234                list_add(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
 235                dentry->d_sb->s_nr_dentry_unused++;
 236                dentry_stat.nr_unused++;
 237                spin_unlock(&dcache_lru_lock);
 238        }
 239}
 240
 241static void __dentry_lru_del(struct dentry *dentry)
 242{
 243        list_del_init(&dentry->d_lru);
 244        dentry->d_sb->s_nr_dentry_unused--;
 245        dentry_stat.nr_unused--;
 246}
 247
 248static void dentry_lru_del(struct dentry *dentry)
 249{
 250        if (!list_empty(&dentry->d_lru)) {
 251                spin_lock(&dcache_lru_lock);
 252                __dentry_lru_del(dentry);
 253                spin_unlock(&dcache_lru_lock);
 254        }
 255}
 256
 257static void dentry_lru_move_tail(struct dentry *dentry)
 258{
 259        spin_lock(&dcache_lru_lock);
 260        if (list_empty(&dentry->d_lru)) {
 261                list_add_tail(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
 262                dentry->d_sb->s_nr_dentry_unused++;
 263                dentry_stat.nr_unused++;
 264        } else {
 265                list_move_tail(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
 266        }
 267        spin_unlock(&dcache_lru_lock);
 268}
 269
 270/**
 271 * d_kill - kill dentry and return parent
 272 * @dentry: dentry to kill
 273 * @parent: parent dentry
 274 *
 275 * The dentry must already be unhashed and removed from the LRU.
 276 *
 277 * If this is the root of the dentry tree, return NULL.
 278 *
 279 * dentry->d_lock and parent->d_lock must be held by caller, and are dropped by
 280 * d_kill.
 281 */
 282static struct dentry *d_kill(struct dentry *dentry, struct dentry *parent)
 283        __releases(dentry->d_lock)
 284        __releases(parent->d_lock)
 285        __releases(dentry->d_inode->i_lock)
 286{
 287        list_del(&dentry->d_u.d_child);
 288        /*
 289         * Inform try_to_ascend() that we are no longer attached to the
 290         * dentry tree
 291         */
 292        dentry->d_flags |= DCACHE_DISCONNECTED;
 293        if (parent)
 294                spin_unlock(&parent->d_lock);
 295        dentry_iput(dentry);
 296        /*
 297         * dentry_iput drops the locks, at which point nobody (except
 298         * transient RCU lookups) can reach this dentry.
 299         */
 300        d_free(dentry);
 301        return parent;
 302}
 303
 304/*
 305 * Unhash a dentry without inserting an RCU walk barrier or checking that
 306 * dentry->d_lock is locked.  The caller must take care of that, if
 307 * appropriate.
 308 */
 309static void __d_shrink(struct dentry *dentry)
 310{
 311        if (!d_unhashed(dentry)) {
 312                struct hlist_bl_head *b;
 313                if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED))
 314                        b = &dentry->d_sb->s_anon;
 315                else
 316                        b = d_hash(dentry->d_parent, dentry->d_name.hash);
 317
 318                hlist_bl_lock(b);
 319                __hlist_bl_del(&dentry->d_hash);
 320                dentry->d_hash.pprev = NULL;
 321                hlist_bl_unlock(b);
 322        }
 323}
 324
 325/**
 326 * d_drop - drop a dentry
 327 * @dentry: dentry to drop
 328 *
 329 * d_drop() unhashes the entry from the parent dentry hashes, so that it won't
 330 * be found through a VFS lookup any more. Note that this is different from
 331 * deleting the dentry - d_delete will try to mark the dentry negative if
 332 * possible, giving a successful _negative_ lookup, while d_drop will
 333 * just make the cache lookup fail.
 334 *
 335 * d_drop() is used mainly for stuff that wants to invalidate a dentry for some
 336 * reason (NFS timeouts or autofs deletes).
 337 *
 338 * __d_drop requires dentry->d_lock.
 339 */
 340void __d_drop(struct dentry *dentry)
 341{
 342        if (!d_unhashed(dentry)) {
 343                __d_shrink(dentry);
 344                dentry_rcuwalk_barrier(dentry);
 345        }
 346}
 347EXPORT_SYMBOL(__d_drop);
 348
 349void d_drop(struct dentry *dentry)
 350{
 351        spin_lock(&dentry->d_lock);
 352        __d_drop(dentry);
 353        spin_unlock(&dentry->d_lock);
 354}
 355EXPORT_SYMBOL(d_drop);
 356
 357/*
 358 * d_clear_need_lookup - drop a dentry from cache and clear the need lookup flag
 359 * @dentry: dentry to drop
 360 *
 361 * This is called when we do a lookup on a placeholder dentry that needed to be
 362 * looked up.  The dentry should have been hashed in order for it to be found by
 363 * the lookup code, but now needs to be unhashed while we do the actual lookup
 364 * and clear the DCACHE_NEED_LOOKUP flag.
 365 */
 366void d_clear_need_lookup(struct dentry *dentry)
 367{
 368        spin_lock(&dentry->d_lock);
 369        __d_drop(dentry);
 370        dentry->d_flags &= ~DCACHE_NEED_LOOKUP;
 371        spin_unlock(&dentry->d_lock);
 372}
 373EXPORT_SYMBOL(d_clear_need_lookup);
 374
 375/*
 376 * Finish off a dentry we've decided to kill.
 377 * dentry->d_lock must be held, returns with it unlocked.
 378 * If ref is non-zero, then decrement the refcount too.
 379 * Returns dentry requiring refcount drop, or NULL if we're done.
 380 */
 381static inline struct dentry *dentry_kill(struct dentry *dentry, int ref)
 382        __releases(dentry->d_lock)
 383{
 384        struct inode *inode;
 385        struct dentry *parent;
 386
 387        inode = dentry->d_inode;
 388        if (inode && !spin_trylock(&inode->i_lock)) {
 389relock:
 390                spin_unlock(&dentry->d_lock);
 391                cpu_relax();
 392                return dentry; /* try again with same dentry */
 393        }
 394        if (IS_ROOT(dentry))
 395                parent = NULL;
 396        else
 397                parent = dentry->d_parent;
 398        if (parent && !spin_trylock(&parent->d_lock)) {
 399                if (inode)
 400                        spin_unlock(&inode->i_lock);
 401                goto relock;
 402        }
 403
 404        if (ref)
 405                dentry->d_count--;
 406        /* if dentry was on the d_lru list delete it from there */
 407        dentry_lru_del(dentry);
 408        /* if it was on the hash then remove it */
 409        __d_drop(dentry);
 410        return d_kill(dentry, parent);
 411}
 412
 413/* 
 414 * This is dput
 415 *
 416 * This is complicated by the fact that we do not want to put
 417 * dentries that are no longer on any hash chain on the unused
 418 * list: we'd much rather just get rid of them immediately.
 419 *
 420 * However, that implies that we have to traverse the dentry
 421 * tree upwards to the parents which might _also_ now be
 422 * scheduled for deletion (it may have been only waiting for
 423 * its last child to go away).
 424 *
 425 * This tail recursion is done by hand as we don't want to depend
 426 * on the compiler to always get this right (gcc generally doesn't).
 427 * Real recursion would eat up our stack space.
 428 */
 429
 430/*
 431 * dput - release a dentry
 432 * @dentry: dentry to release 
 433 *
 434 * Release a dentry. This will drop the usage count and if appropriate
 435 * call the dentry unlink method as well as removing it from the queues and
 436 * releasing its resources. If the parent dentries were scheduled for release
 437 * they too may now get deleted.
 438 */
 439void dput(struct dentry *dentry)
 440{
 441        if (!dentry)
 442                return;
 443
 444repeat:
 445        if (dentry->d_count == 1)
 446                might_sleep();
 447        spin_lock(&dentry->d_lock);
 448        BUG_ON(!dentry->d_count);
 449        if (dentry->d_count > 1) {
 450                dentry->d_count--;
 451                spin_unlock(&dentry->d_lock);
 452                return;
 453        }
 454
 455        if (dentry->d_flags & DCACHE_OP_DELETE) {
 456                if (dentry->d_op->d_delete(dentry))
 457                        goto kill_it;
 458        }
 459
 460        /* Unreachable? Get rid of it */
 461        if (d_unhashed(dentry))
 462                goto kill_it;
 463
 464        /*
 465         * If this dentry needs lookup, don't set the referenced flag so that it
 466         * is more likely to be cleaned up by the dcache shrinker in case of
 467         * memory pressure.
 468         */
 469        if (!d_need_lookup(dentry))
 470                dentry->d_flags |= DCACHE_REFERENCED;
 471        dentry_lru_add(dentry);
 472
 473        dentry->d_count--;
 474        spin_unlock(&dentry->d_lock);
 475        return;
 476
 477kill_it:
 478        dentry = dentry_kill(dentry, 1);
 479        if (dentry)
 480                goto repeat;
 481}
 482EXPORT_SYMBOL(dput);
 483
 484/**
 485 * d_invalidate - invalidate a dentry
 486 * @dentry: dentry to invalidate
 487 *
 488 * Try to invalidate the dentry if it turns out to be
 489 * possible. If there are other dentries that can be
 490 * reached through this one we can't delete it and we
 491 * return -EBUSY. On success we return 0.
 492 *
 493 * no dcache lock.
 494 */
 495 
 496int d_invalidate(struct dentry * dentry)
 497{
 498        /*
 499         * If it's already been dropped, return OK.
 500         */
 501        spin_lock(&dentry->d_lock);
 502        if (d_unhashed(dentry)) {
 503                spin_unlock(&dentry->d_lock);
 504                return 0;
 505        }
 506        /*
 507         * Check whether to do a partial shrink_dcache
 508         * to get rid of unused child entries.
 509         */
 510        if (!list_empty(&dentry->d_subdirs)) {
 511                spin_unlock(&dentry->d_lock);
 512                shrink_dcache_parent(dentry);
 513                spin_lock(&dentry->d_lock);
 514        }
 515
 516        /*
 517         * Somebody else still using it?
 518         *
 519         * If it's a directory, we can't drop it
 520         * for fear of somebody re-populating it
 521         * with children (even though dropping it
 522         * would make it unreachable from the root,
 523         * we might still populate it if it was a
 524         * working directory or similar).
 525         */
 526        if (dentry->d_count > 1) {
 527                if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode)) {
 528                        spin_unlock(&dentry->d_lock);
 529                        return -EBUSY;
 530                }
 531        }
 532
 533        __d_drop(dentry);
 534        spin_unlock(&dentry->d_lock);
 535        return 0;
 536}
 537EXPORT_SYMBOL(d_invalidate);
 538
 539/* This must be called with d_lock held */
 540static inline void __dget_dlock(struct dentry *dentry)
 541{
 542        dentry->d_count++;
 543}
 544
 545static inline void __dget(struct dentry *dentry)
 546{
 547        spin_lock(&dentry->d_lock);
 548        __dget_dlock(dentry);
 549        spin_unlock(&dentry->d_lock);
 550}
 551
 552struct dentry *dget_parent(struct dentry *dentry)
 553{
 554        struct dentry *ret;
 555
 556repeat:
 557        /*
 558         * Don't need rcu_dereference because we re-check it was correct under
 559         * the lock.
 560         */
 561        rcu_read_lock();
 562        ret = dentry->d_parent;
 563        spin_lock(&ret->d_lock);
 564        if (unlikely(ret != dentry->d_parent)) {
 565                spin_unlock(&ret->d_lock);
 566                rcu_read_unlock();
 567                goto repeat;
 568        }
 569        rcu_read_unlock();
 570        BUG_ON(!ret->d_count);
 571        ret->d_count++;
 572        spin_unlock(&ret->d_lock);
 573        return ret;
 574}
 575EXPORT_SYMBOL(dget_parent);
 576
 577/**
 578 * d_find_alias - grab a hashed alias of inode
 579 * @inode: inode in question
 580 * @want_discon:  flag, used by d_splice_alias, to request
 581 *          that only a DISCONNECTED alias be returned.
 582 *
 583 * If inode has a hashed alias, or is a directory and has any alias,
 584 * acquire the reference to alias and return it. Otherwise return NULL.
 585 * Notice that if inode is a directory there can be only one alias and
 586 * it can be unhashed only if it has no children, or if it is the root
 587 * of a filesystem.
 588 *
 589 * If the inode has an IS_ROOT, DCACHE_DISCONNECTED alias, then prefer
 590 * any other hashed alias over that one unless @want_discon is set,
 591 * in which case only return an IS_ROOT, DCACHE_DISCONNECTED alias.
 592 */
 593static struct dentry *__d_find_alias(struct inode *inode, int want_discon)
 594{
 595        struct dentry *alias, *discon_alias;
 596
 597again:
 598        discon_alias = NULL;
 599        list_for_each_entry(alias, &inode->i_dentry, d_alias) {
 600                spin_lock(&alias->d_lock);
 601                if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
 602                        if (IS_ROOT(alias) &&
 603                            (alias->d_flags & DCACHE_DISCONNECTED)) {
 604                                discon_alias = alias;
 605                        } else if (!want_discon) {
 606                                __dget_dlock(alias);
 607                                spin_unlock(&alias->d_lock);
 608                                return alias;
 609                        }
 610                }
 611                spin_unlock(&alias->d_lock);
 612        }
 613        if (discon_alias) {
 614                alias = discon_alias;
 615                spin_lock(&alias->d_lock);
 616                if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
 617                        if (IS_ROOT(alias) &&
 618                            (alias->d_flags & DCACHE_DISCONNECTED)) {
 619                                __dget_dlock(alias);
 620                                spin_unlock(&alias->d_lock);
 621                                return alias;
 622                        }
 623                }
 624                spin_unlock(&alias->d_lock);
 625                goto again;
 626        }
 627        return NULL;
 628}
 629
 630struct dentry *d_find_alias(struct inode *inode)
 631{
 632        struct dentry *de = NULL;
 633
 634        if (!list_empty(&inode->i_dentry)) {
 635                spin_lock(&inode->i_lock);
 636                de = __d_find_alias(inode, 0);
 637                spin_unlock(&inode->i_lock);
 638        }
 639        return de;
 640}
 641EXPORT_SYMBOL(d_find_alias);
 642
 643/*
 644 *      Try to kill dentries associated with this inode.
 645 * WARNING: you must own a reference to inode.
 646 */
 647void d_prune_aliases(struct inode *inode)
 648{
 649        struct dentry *dentry;
 650restart:
 651        spin_lock(&inode->i_lock);
 652        list_for_each_entry(dentry, &inode->i_dentry, d_alias) {
 653                spin_lock(&dentry->d_lock);
 654                if (!dentry->d_count) {
 655                        __dget_dlock(dentry);
 656                        __d_drop(dentry);
 657                        spin_unlock(&dentry->d_lock);
 658                        spin_unlock(&inode->i_lock);
 659                        dput(dentry);
 660                        goto restart;
 661                }
 662                spin_unlock(&dentry->d_lock);
 663        }
 664        spin_unlock(&inode->i_lock);
 665}
 666EXPORT_SYMBOL(d_prune_aliases);
 667
 668/*
 669 * Try to throw away a dentry - free the inode, dput the parent.
 670 * Requires dentry->d_lock is held, and dentry->d_count == 0.
 671 * Releases dentry->d_lock.
 672 *
 673 * This may fail if locks cannot be acquired no problem, just try again.
 674 */
 675static void try_prune_one_dentry(struct dentry *dentry)
 676        __releases(dentry->d_lock)
 677{
 678        struct dentry *parent;
 679
 680        parent = dentry_kill(dentry, 0);
 681        /*
 682         * If dentry_kill returns NULL, we have nothing more to do.
 683         * if it returns the same dentry, trylocks failed. In either
 684         * case, just loop again.
 685         *
 686         * Otherwise, we need to prune ancestors too. This is necessary
 687         * to prevent quadratic behavior of shrink_dcache_parent(), but
 688         * is also expected to be beneficial in reducing dentry cache
 689         * fragmentation.
 690         */
 691        if (!parent)
 692                return;
 693        if (parent == dentry)
 694                return;
 695
 696        /* Prune ancestors. */
 697        dentry = parent;
 698        while (dentry) {
 699                spin_lock(&dentry->d_lock);
 700                if (dentry->d_count > 1) {
 701                        dentry->d_count--;
 702                        spin_unlock(&dentry->d_lock);
 703                        return;
 704                }
 705                dentry = dentry_kill(dentry, 1);
 706        }
 707}
 708
 709static void shrink_dentry_list(struct list_head *list)
 710{
 711        struct dentry *dentry;
 712
 713        rcu_read_lock();
 714        for (;;) {
 715                dentry = list_entry_rcu(list->prev, struct dentry, d_lru);
 716                if (&dentry->d_lru == list)
 717                        break; /* empty */
 718                spin_lock(&dentry->d_lock);
 719                if (dentry != list_entry(list->prev, struct dentry, d_lru)) {
 720                        spin_unlock(&dentry->d_lock);
 721                        continue;
 722                }
 723
 724                /*
 725                 * We found an inuse dentry which was not removed from
 726                 * the LRU because of laziness during lookup.  Do not free
 727                 * it - just keep it off the LRU list.
 728                 */
 729                if (dentry->d_count) {
 730                        dentry_lru_del(dentry);
 731                        spin_unlock(&dentry->d_lock);
 732                        continue;
 733                }
 734
 735                rcu_read_unlock();
 736
 737                try_prune_one_dentry(dentry);
 738
 739                rcu_read_lock();
 740        }
 741        rcu_read_unlock();
 742}
 743
 744/**
 745 * __shrink_dcache_sb - shrink the dentry LRU on a given superblock
 746 * @sb:         superblock to shrink dentry LRU.
 747 * @count:      number of entries to prune
 748 * @flags:      flags to control the dentry processing
 749 *
 750 * If flags contains DCACHE_REFERENCED reference dentries will not be pruned.
 751 */
 752static void __shrink_dcache_sb(struct super_block *sb, int count, int flags)
 753{
 754        struct dentry *dentry;
 755        LIST_HEAD(referenced);
 756        LIST_HEAD(tmp);
 757
 758relock:
 759        spin_lock(&dcache_lru_lock);
 760        while (!list_empty(&sb->s_dentry_lru)) {
 761                dentry = list_entry(sb->s_dentry_lru.prev,
 762                                struct dentry, d_lru);
 763                BUG_ON(dentry->d_sb != sb);
 764
 765                if (!spin_trylock(&dentry->d_lock)) {
 766                        spin_unlock(&dcache_lru_lock);
 767                        cpu_relax();
 768                        goto relock;
 769                }
 770
 771                /*
 772                 * If we are honouring the DCACHE_REFERENCED flag and the
 773                 * dentry has this flag set, don't free it.  Clear the flag
 774                 * and put it back on the LRU.
 775                 */
 776                if (flags & DCACHE_REFERENCED &&
 777                                dentry->d_flags & DCACHE_REFERENCED) {
 778                        dentry->d_flags &= ~DCACHE_REFERENCED;
 779                        list_move(&dentry->d_lru, &referenced);
 780                        spin_unlock(&dentry->d_lock);
 781                } else {
 782                        list_move_tail(&dentry->d_lru, &tmp);
 783                        spin_unlock(&dentry->d_lock);
 784                        if (!--count)
 785                                break;
 786                }
 787                cond_resched_lock(&dcache_lru_lock);
 788        }
 789        if (!list_empty(&referenced))
 790                list_splice(&referenced, &sb->s_dentry_lru);
 791        spin_unlock(&dcache_lru_lock);
 792
 793        shrink_dentry_list(&tmp);
 794}
 795
 796/**
 797 * prune_dcache_sb - shrink the dcache
 798 * @sb: superblock
 799 * @nr_to_scan: number of entries to try to free
 800 *
 801 * Attempt to shrink the superblock dcache LRU by @nr_to_scan entries. This is
 802 * done when we need more memory an called from the superblock shrinker
 803 * function.
 804 *
 805 * This function may fail to free any resources if all the dentries are in
 806 * use.
 807 */
 808void prune_dcache_sb(struct super_block *sb, int nr_to_scan)
 809{
 810        __shrink_dcache_sb(sb, nr_to_scan, DCACHE_REFERENCED);
 811}
 812
 813/**
 814 * shrink_dcache_sb - shrink dcache for a superblock
 815 * @sb: superblock
 816 *
 817 * Shrink the dcache for the specified super block. This is used to free
 818 * the dcache before unmounting a file system.
 819 */
 820void shrink_dcache_sb(struct super_block *sb)
 821{
 822        LIST_HEAD(tmp);
 823
 824        spin_lock(&dcache_lru_lock);
 825        while (!list_empty(&sb->s_dentry_lru)) {
 826                list_splice_init(&sb->s_dentry_lru, &tmp);
 827                spin_unlock(&dcache_lru_lock);
 828                shrink_dentry_list(&tmp);
 829                spin_lock(&dcache_lru_lock);
 830        }
 831        spin_unlock(&dcache_lru_lock);
 832}
 833EXPORT_SYMBOL(shrink_dcache_sb);
 834
 835/*
 836 * destroy a single subtree of dentries for unmount
 837 * - see the comments on shrink_dcache_for_umount() for a description of the
 838 *   locking
 839 */
 840static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
 841{
 842        struct dentry *parent;
 843
 844        BUG_ON(!IS_ROOT(dentry));
 845
 846        for (;;) {
 847                /* descend to the first leaf in the current subtree */
 848                while (!list_empty(&dentry->d_subdirs))
 849                        dentry = list_entry(dentry->d_subdirs.next,
 850                                            struct dentry, d_u.d_child);
 851
 852                /* consume the dentries from this leaf up through its parents
 853                 * until we find one with children or run out altogether */
 854                do {
 855                        struct inode *inode;
 856
 857                        /* detach from the system */
 858                        dentry_lru_del(dentry);
 859                        __d_shrink(dentry);
 860
 861                        if (dentry->d_count != 0) {
 862                                printk(KERN_ERR
 863                                       "BUG: Dentry %p{i=%lx,n=%s}"
 864                                       " still in use (%d)"
 865                                       " [unmount of %s %s]\n",
 866                                       dentry,
 867                                       dentry->d_inode ?
 868                                       dentry->d_inode->i_ino : 0UL,
 869                                       dentry->d_name.name,
 870                                       dentry->d_count,
 871                                       dentry->d_sb->s_type->name,
 872                                       dentry->d_sb->s_id);
 873                                BUG();
 874                        }
 875
 876                        if (IS_ROOT(dentry)) {
 877                                parent = NULL;
 878                                list_del(&dentry->d_u.d_child);
 879                        } else {
 880                                parent = dentry->d_parent;
 881                                parent->d_count--;
 882                                list_del(&dentry->d_u.d_child);
 883                        }
 884
 885                        inode = dentry->d_inode;
 886                        if (inode) {
 887                                dentry->d_inode = NULL;
 888                                list_del_init(&dentry->d_alias);
 889                                if (dentry->d_op && dentry->d_op->d_iput)
 890                                        dentry->d_op->d_iput(dentry, inode);
 891                                else
 892                                        iput(inode);
 893                        }
 894
 895                        d_free(dentry);
 896
 897                        /* finished when we fall off the top of the tree,
 898                         * otherwise we ascend to the parent and move to the
 899                         * next sibling if there is one */
 900                        if (!parent)
 901                                return;
 902                        dentry = parent;
 903                } while (list_empty(&dentry->d_subdirs));
 904
 905                dentry = list_entry(dentry->d_subdirs.next,
 906                                    struct dentry, d_u.d_child);
 907        }
 908}
 909
 910/*
 911 * destroy the dentries attached to a superblock on unmounting
 912 * - we don't need to use dentry->d_lock because:
 913 *   - the superblock is detached from all mountings and open files, so the
 914 *     dentry trees will not be rearranged by the VFS
 915 *   - s_umount is write-locked, so the memory pressure shrinker will ignore
 916 *     any dentries belonging to this superblock that it comes across
 917 *   - the filesystem itself is no longer permitted to rearrange the dentries
 918 *     in this superblock
 919 */
 920void shrink_dcache_for_umount(struct super_block *sb)
 921{
 922        struct dentry *dentry;
 923
 924        if (down_read_trylock(&sb->s_umount))
 925                BUG();
 926
 927        dentry = sb->s_root;
 928        sb->s_root = NULL;
 929        dentry->d_count--;
 930        shrink_dcache_for_umount_subtree(dentry);
 931
 932        while (!hlist_bl_empty(&sb->s_anon)) {
 933                dentry = hlist_bl_entry(hlist_bl_first(&sb->s_anon), struct dentry, d_hash);
 934                shrink_dcache_for_umount_subtree(dentry);
 935        }
 936}
 937
 938/*
 939 * This tries to ascend one level of parenthood, but
 940 * we can race with renaming, so we need to re-check
 941 * the parenthood after dropping the lock and check
 942 * that the sequence number still matches.
 943 */
 944static struct dentry *try_to_ascend(struct dentry *old, int locked, unsigned seq)
 945{
 946        struct dentry *new = old->d_parent;
 947
 948        rcu_read_lock();
 949        spin_unlock(&old->d_lock);
 950        spin_lock(&new->d_lock);
 951
 952        /*
 953         * might go back up the wrong parent if we have had a rename
 954         * or deletion
 955         */
 956        if (new != old->d_parent ||
 957                 (old->d_flags & DCACHE_DISCONNECTED) ||
 958                 (!locked && read_seqretry(&rename_lock, seq))) {
 959                spin_unlock(&new->d_lock);
 960                new = NULL;
 961        }
 962        rcu_read_unlock();
 963        return new;
 964}
 965
 966
 967/*
 968 * Search for at least 1 mount point in the dentry's subdirs.
 969 * We descend to the next level whenever the d_subdirs
 970 * list is non-empty and continue searching.
 971 */
 972 
 973/**
 974 * have_submounts - check for mounts over a dentry
 975 * @parent: dentry to check.
 976 *
 977 * Return true if the parent or its subdirectories contain
 978 * a mount point
 979 */
 980int have_submounts(struct dentry *parent)
 981{
 982        struct dentry *this_parent;
 983        struct list_head *next;
 984        unsigned seq;
 985        int locked = 0;
 986
 987        seq = read_seqbegin(&rename_lock);
 988again:
 989        this_parent = parent;
 990
 991        if (d_mountpoint(parent))
 992                goto positive;
 993        spin_lock(&this_parent->d_lock);
 994repeat:
 995        next = this_parent->d_subdirs.next;
 996resume:
 997        while (next != &this_parent->d_subdirs) {
 998                struct list_head *tmp = next;
 999                struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
1000                next = tmp->next;
1001
1002                spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
1003                /* Have we found a mount point ? */
1004                if (d_mountpoint(dentry)) {
1005                        spin_unlock(&dentry->d_lock);
1006                        spin_unlock(&this_parent->d_lock);
1007                        goto positive;
1008                }
1009                if (!list_empty(&dentry->d_subdirs)) {
1010                        spin_unlock(&this_parent->d_lock);
1011                        spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
1012                        this_parent = dentry;
1013                        spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
1014                        goto repeat;
1015                }
1016                spin_unlock(&dentry->d_lock);
1017        }
1018        /*
1019         * All done at this level ... ascend and resume the search.
1020         */
1021        if (this_parent != parent) {
1022                struct dentry *child = this_parent;
1023                this_parent = try_to_ascend(this_parent, locked, seq);
1024                if (!this_parent)
1025                        goto rename_retry;
1026                next = child->d_u.d_child.next;
1027                goto resume;
1028        }
1029        spin_unlock(&this_parent->d_lock);
1030        if (!locked && read_seqretry(&rename_lock, seq))
1031                goto rename_retry;
1032        if (locked)
1033                write_sequnlock(&rename_lock);
1034        return 0; /* No mount points found in tree */
1035positive:
1036        if (!locked && read_seqretry(&rename_lock, seq))
1037                goto rename_retry;
1038        if (locked)
1039                write_sequnlock(&rename_lock);
1040        return 1;
1041
1042rename_retry:
1043        locked = 1;
1044        write_seqlock(&rename_lock);
1045        goto again;
1046}
1047EXPORT_SYMBOL(have_submounts);
1048
1049/*
1050 * Search the dentry child list for the specified parent,
1051 * and move any unused dentries to the end of the unused
1052 * list for prune_dcache(). We descend to the next level
1053 * whenever the d_subdirs list is non-empty and continue
1054 * searching.
1055 *
1056 * It returns zero iff there are no unused children,
1057 * otherwise  it returns the number of children moved to
1058 * the end of the unused list. This may not be the total
1059 * number of unused children, because select_parent can
1060 * drop the lock and return early due to latency
1061 * constraints.
1062 */
1063static int select_parent(struct dentry * parent)
1064{
1065        struct dentry *this_parent;
1066        struct list_head *next;
1067        unsigned seq;
1068        int found = 0;
1069        int locked = 0;
1070
1071        seq = read_seqbegin(&rename_lock);
1072again:
1073        this_parent = parent;
1074        spin_lock(&this_parent->d_lock);
1075repeat:
1076        next = this_parent->d_subdirs.next;
1077resume:
1078        while (next != &this_parent->d_subdirs) {
1079                struct list_head *tmp = next;
1080                struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
1081                next = tmp->next;
1082
1083                spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
1084
1085                /* 
1086                 * move only zero ref count dentries to the end 
1087                 * of the unused list for prune_dcache
1088                 */
1089                if (!dentry->d_count) {
1090                        dentry_lru_move_tail(dentry);
1091                        found++;
1092                } else {
1093                        dentry_lru_del(dentry);
1094                }
1095
1096                /*
1097                 * We can return to the caller if we have found some (this
1098                 * ensures forward progress). We'll be coming back to find
1099                 * the rest.
1100                 */
1101                if (found && need_resched()) {
1102                        spin_unlock(&dentry->d_lock);
1103                        goto out;
1104                }
1105
1106                /*
1107                 * Descend a level if the d_subdirs list is non-empty.
1108                 */
1109                if (!list_empty(&dentry->d_subdirs)) {
1110                        spin_unlock(&this_parent->d_lock);
1111                        spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
1112                        this_parent = dentry;
1113                        spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
1114                        goto repeat;
1115                }
1116
1117                spin_unlock(&dentry->d_lock);
1118        }
1119        /*
1120         * All done at this level ... ascend and resume the search.
1121         */
1122        if (this_parent != parent) {
1123                struct dentry *child = this_parent;
1124                this_parent = try_to_ascend(this_parent, locked, seq);
1125                if (!this_parent)
1126                        goto rename_retry;
1127                next = child->d_u.d_child.next;
1128                goto resume;
1129        }
1130out:
1131        spin_unlock(&this_parent->d_lock);
1132        if (!locked && read_seqretry(&rename_lock, seq))
1133                goto rename_retry;
1134        if (locked)
1135                write_sequnlock(&rename_lock);
1136        return found;
1137
1138rename_retry:
1139        if (found)
1140                return found;
1141        locked = 1;
1142        write_seqlock(&rename_lock);
1143        goto again;
1144}
1145
1146/**
1147 * shrink_dcache_parent - prune dcache
1148 * @parent: parent of entries to prune
1149 *
1150 * Prune the dcache to remove unused children of the parent dentry.
1151 */
1152 
1153void shrink_dcache_parent(struct dentry * parent)
1154{
1155        struct super_block *sb = parent->d_sb;
1156        int found;
1157
1158        while ((found = select_parent(parent)) != 0)
1159                __shrink_dcache_sb(sb, found, 0);
1160}
1161EXPORT_SYMBOL(shrink_dcache_parent);
1162
1163/**
1164 * __d_alloc    -       allocate a dcache entry
1165 * @sb: filesystem it will belong to
1166 * @name: qstr of the name
1167 *
1168 * Allocates a dentry. It returns %NULL if there is insufficient memory
1169 * available. On a success the dentry is returned. The name passed in is
1170 * copied and the copy passed in may be reused after this call.
1171 */
1172 
1173struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
1174{
1175        struct dentry *dentry;
1176        char *dname;
1177
1178        dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
1179        if (!dentry)
1180                return NULL;
1181
1182        if (name->len > DNAME_INLINE_LEN-1) {
1183                dname = kmalloc(name->len + 1, GFP_KERNEL);
1184                if (!dname) {
1185                        kmem_cache_free(dentry_cache, dentry); 
1186                        return NULL;
1187                }
1188        } else  {
1189                dname = dentry->d_iname;
1190        }       
1191        dentry->d_name.name = dname;
1192
1193        dentry->d_name.len = name->len;
1194        dentry->d_name.hash = name->hash;
1195        memcpy(dname, name->name, name->len);
1196        dname[name->len] = 0;
1197
1198        dentry->d_count = 1;
1199        dentry->d_flags = 0;
1200        spin_lock_init(&dentry->d_lock);
1201        seqcount_init(&dentry->d_seq);
1202        dentry->d_inode = NULL;
1203        dentry->d_parent = dentry;
1204        dentry->d_sb = sb;
1205        dentry->d_op = NULL;
1206        dentry->d_fsdata = NULL;
1207        INIT_HLIST_BL_NODE(&dentry->d_hash);
1208        INIT_LIST_HEAD(&dentry->d_lru);
1209        INIT_LIST_HEAD(&dentry->d_subdirs);
1210        INIT_LIST_HEAD(&dentry->d_alias);
1211        INIT_LIST_HEAD(&dentry->d_u.d_child);
1212        d_set_d_op(dentry, dentry->d_sb->s_d_op);
1213
1214        this_cpu_inc(nr_dentry);
1215
1216        return dentry;
1217}
1218
1219/**
1220 * d_alloc      -       allocate a dcache entry
1221 * @parent: parent of entry to allocate
1222 * @name: qstr of the name
1223 *
1224 * Allocates a dentry. It returns %NULL if there is insufficient memory
1225 * available. On a success the dentry is returned. The name passed in is
1226 * copied and the copy passed in may be reused after this call.
1227 */
1228struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
1229{
1230        struct dentry *dentry = __d_alloc(parent->d_sb, name);
1231        if (!dentry)
1232                return NULL;
1233
1234        spin_lock(&parent->d_lock);
1235        /*
1236         * don't need child lock because it is not subject
1237         * to concurrency here
1238         */
1239        __dget_dlock(parent);
1240        dentry->d_parent = parent;
1241        list_add(&dentry->d_u.d_child, &parent->d_subdirs);
1242        spin_unlock(&parent->d_lock);
1243
1244        return dentry;
1245}
1246EXPORT_SYMBOL(d_alloc);
1247
1248struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
1249{
1250        struct dentry *dentry = __d_alloc(sb, name);
1251        if (dentry)
1252                dentry->d_flags |= DCACHE_DISCONNECTED;
1253        return dentry;
1254}
1255EXPORT_SYMBOL(d_alloc_pseudo);
1256
1257struct dentry *d_alloc_name(struct dentry *parent, const char *name)
1258{
1259        struct qstr q;
1260
1261        q.name = name;
1262        q.len = strlen(name);
1263        q.hash = full_name_hash(q.name, q.len);
1264        return d_alloc(parent, &q);
1265}
1266EXPORT_SYMBOL(d_alloc_name);
1267
1268void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
1269{
1270        WARN_ON_ONCE(dentry->d_op);
1271        WARN_ON_ONCE(dentry->d_flags & (DCACHE_OP_HASH  |
1272                                DCACHE_OP_COMPARE       |
1273                                DCACHE_OP_REVALIDATE    |
1274                                DCACHE_OP_DELETE ));
1275        dentry->d_op = op;
1276        if (!op)
1277                return;
1278        if (op->d_hash)
1279                dentry->d_flags |= DCACHE_OP_HASH;
1280        if (op->d_compare)
1281                dentry->d_flags |= DCACHE_OP_COMPARE;
1282        if (op->d_revalidate)
1283                dentry->d_flags |= DCACHE_OP_REVALIDATE;
1284        if (op->d_delete)
1285                dentry->d_flags |= DCACHE_OP_DELETE;
1286
1287}
1288EXPORT_SYMBOL(d_set_d_op);
1289
1290static void __d_instantiate(struct dentry *dentry, struct inode *inode)
1291{
1292        spin_lock(&dentry->d_lock);
1293        if (inode) {
1294                if (unlikely(IS_AUTOMOUNT(inode)))
1295                        dentry->d_flags |= DCACHE_NEED_AUTOMOUNT;
1296                list_add(&dentry->d_alias, &inode->i_dentry);
1297        }
1298        dentry->d_inode = inode;
1299        dentry_rcuwalk_barrier(dentry);
1300        spin_unlock(&dentry->d_lock);
1301        fsnotify_d_instantiate(dentry, inode);
1302}
1303
1304/**
1305 * d_instantiate - fill in inode information for a dentry
1306 * @entry: dentry to complete
1307 * @inode: inode to attach to this dentry
1308 *
1309 * Fill in inode information in the entry.
1310 *
1311 * This turns negative dentries into productive full members
1312 * of society.
1313 *
1314 * NOTE! This assumes that the inode count has been incremented
1315 * (or otherwise set) by the caller to indicate that it is now
1316 * in use by the dcache.
1317 */
1318 
1319void d_instantiate(struct dentry *entry, struct inode * inode)
1320{
1321        BUG_ON(!list_empty(&entry->d_alias));
1322        if (inode)
1323                spin_lock(&inode->i_lock);
1324        __d_instantiate(entry, inode);
1325        if (inode)
1326                spin_unlock(&inode->i_lock);
1327        security_d_instantiate(entry, inode);
1328}
1329EXPORT_SYMBOL(d_instantiate);
1330
1331/**
1332 * d_instantiate_unique - instantiate a non-aliased dentry
1333 * @entry: dentry to instantiate
1334 * @inode: inode to attach to this dentry
1335 *
1336 * Fill in inode information in the entry. On success, it returns NULL.
1337 * If an unhashed alias of "entry" already exists, then we return the
1338 * aliased dentry instead and drop one reference to inode.
1339 *
1340 * Note that in order to avoid conflicts with rename() etc, the caller
1341 * had better be holding the parent directory semaphore.
1342 *
1343 * This also assumes that the inode count has been incremented
1344 * (or otherwise set) by the caller to indicate that it is now
1345 * in use by the dcache.
1346 */
1347static struct dentry *__d_instantiate_unique(struct dentry *entry,
1348                                             struct inode *inode)
1349{
1350        struct dentry *alias;
1351        int len = entry->d_name.len;
1352        const char *name = entry->d_name.name;
1353        unsigned int hash = entry->d_name.hash;
1354
1355        if (!inode) {
1356                __d_instantiate(entry, NULL);
1357                return NULL;
1358        }
1359
1360        list_for_each_entry(alias, &inode->i_dentry, d_alias) {
1361                struct qstr *qstr = &alias->d_name;
1362
1363                /*
1364                 * Don't need alias->d_lock here, because aliases with
1365                 * d_parent == entry->d_parent are not subject to name or
1366                 * parent changes, because the parent inode i_mutex is held.
1367                 */
1368                if (qstr->hash != hash)
1369                        continue;
1370                if (alias->d_parent != entry->d_parent)
1371                        continue;
1372                if (dentry_cmp(qstr->name, qstr->len, name, len))
1373                        continue;
1374                __dget(alias);
1375                return alias;
1376        }
1377
1378        __d_instantiate(entry, inode);
1379        return NULL;
1380}
1381
1382struct dentry *d_instantiate_unique(struct dentry *entry, struct inode *inode)
1383{
1384        struct dentry *result;
1385
1386        BUG_ON(!list_empty(&entry->d_alias));
1387
1388        if (inode)
1389                spin_lock(&inode->i_lock);
1390        result = __d_instantiate_unique(entry, inode);
1391        if (inode)
1392                spin_unlock(&inode->i_lock);
1393
1394        if (!result) {
1395                security_d_instantiate(entry, inode);
1396                return NULL;
1397        }
1398
1399        BUG_ON(!d_unhashed(result));
1400        iput(inode);
1401        return result;
1402}
1403
1404EXPORT_SYMBOL(d_instantiate_unique);
1405
1406/**
1407 * d_alloc_root - allocate root dentry
1408 * @root_inode: inode to allocate the root for
1409 *
1410 * Allocate a root ("/") dentry for the inode given. The inode is
1411 * instantiated and returned. %NULL is returned if there is insufficient
1412 * memory or the inode passed is %NULL.
1413 */
1414 
1415struct dentry * d_alloc_root(struct inode * root_inode)
1416{
1417        struct dentry *res = NULL;
1418
1419        if (root_inode) {
1420                static const struct qstr name = { .name = "/", .len = 1 };
1421
1422                res = __d_alloc(root_inode->i_sb, &name);
1423                if (res)
1424                        d_instantiate(res, root_inode);
1425        }
1426        return res;
1427}
1428EXPORT_SYMBOL(d_alloc_root);
1429
1430static struct dentry * __d_find_any_alias(struct inode *inode)
1431{
1432        struct dentry *alias;
1433
1434        if (list_empty(&inode->i_dentry))
1435                return NULL;
1436        alias = list_first_entry(&inode->i_dentry, struct dentry, d_alias);
1437        __dget(alias);
1438        return alias;
1439}
1440
1441static struct dentry * d_find_any_alias(struct inode *inode)
1442{
1443        struct dentry *de;
1444
1445        spin_lock(&inode->i_lock);
1446        de = __d_find_any_alias(inode);
1447        spin_unlock(&inode->i_lock);
1448        return de;
1449}
1450
1451
1452/**
1453 * d_obtain_alias - find or allocate a dentry for a given inode
1454 * @inode: inode to allocate the dentry for
1455 *
1456 * Obtain a dentry for an inode resulting from NFS filehandle conversion or
1457 * similar open by handle operations.  The returned dentry may be anonymous,
1458 * or may have a full name (if the inode was already in the cache).
1459 *
1460 * When called on a directory inode, we must ensure that the inode only ever
1461 * has one dentry.  If a dentry is found, that is returned instead of
1462 * allocating a new one.
1463 *
1464 * On successful return, the reference to the inode has been transferred
1465 * to the dentry.  In case of an error the reference on the inode is released.
1466 * To make it easier to use in export operations a %NULL or IS_ERR inode may
1467 * be passed in and will be the error will be propagate to the return value,
1468 * with a %NULL @inode replaced by ERR_PTR(-ESTALE).
1469 */
1470struct dentry *d_obtain_alias(struct inode *inode)
1471{
1472        static const struct qstr anonstring = { .name = "" };
1473        struct dentry *tmp;
1474        struct dentry *res;
1475
1476        if (!inode)
1477                return ERR_PTR(-ESTALE);
1478        if (IS_ERR(inode))
1479                return ERR_CAST(inode);
1480
1481        res = d_find_any_alias(inode);
1482        if (res)
1483                goto out_iput;
1484
1485        tmp = __d_alloc(inode->i_sb, &anonstring);
1486        if (!tmp) {
1487                res = ERR_PTR(-ENOMEM);
1488                goto out_iput;
1489        }
1490
1491        spin_lock(&inode->i_lock);
1492        res = __d_find_any_alias(inode);
1493        if (res) {
1494                spin_unlock(&inode->i_lock);
1495                dput(tmp);
1496                goto out_iput;
1497        }
1498
1499        /* attach a disconnected dentry */
1500        spin_lock(&tmp->d_lock);
1501        tmp->d_inode = inode;
1502        tmp->d_flags |= DCACHE_DISCONNECTED;
1503        list_add(&tmp->d_alias, &inode->i_dentry);
1504        hlist_bl_lock(&tmp->d_sb->s_anon);
1505        hlist_bl_add_head(&tmp->d_hash, &tmp->d_sb->s_anon);
1506        hlist_bl_unlock(&tmp->d_sb->s_anon);
1507        spin_unlock(&tmp->d_lock);
1508        spin_unlock(&inode->i_lock);
1509        security_d_instantiate(tmp, inode);
1510
1511        return tmp;
1512
1513 out_iput:
1514        if (res && !IS_ERR(res))
1515                security_d_instantiate(res, inode);
1516        iput(inode);
1517        return res;
1518}
1519EXPORT_SYMBOL(d_obtain_alias);
1520
1521/**
1522 * d_splice_alias - splice a disconnected dentry into the tree if one exists
1523 * @inode:  the inode which may have a disconnected dentry
1524 * @dentry: a negative dentry which we want to point to the inode.
1525 *
1526 * If inode is a directory and has a 'disconnected' dentry (i.e. IS_ROOT and
1527 * DCACHE_DISCONNECTED), then d_move that in place of the given dentry
1528 * and return it, else simply d_add the inode to the dentry and return NULL.
1529 *
1530 * This is needed in the lookup routine of any filesystem that is exportable
1531 * (via knfsd) so that we can build dcache paths to directories effectively.
1532 *
1533 * If a dentry was found and moved, then it is returned.  Otherwise NULL
1534 * is returned.  This matches the expected return value of ->lookup.
1535 *
1536 */
1537struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
1538{
1539        struct dentry *new = NULL;
1540
1541        if (IS_ERR(inode))
1542                return ERR_CAST(inode);
1543
1544        if (inode && S_ISDIR(inode->i_mode)) {
1545                spin_lock(&inode->i_lock);
1546                new = __d_find_alias(inode, 1);
1547                if (new) {
1548                        BUG_ON(!(new->d_flags & DCACHE_DISCONNECTED));
1549                        spin_unlock(&inode->i_lock);
1550                        security_d_instantiate(new, inode);
1551                        d_move(new, dentry);
1552                        iput(inode);
1553                } else {
1554                        /* already taking inode->i_lock, so d_add() by hand */
1555                        __d_instantiate(dentry, inode);
1556                        spin_unlock(&inode->i_lock);
1557                        security_d_instantiate(dentry, inode);
1558                        d_rehash(dentry);
1559                }
1560        } else
1561                d_add(dentry, inode);
1562        return new;
1563}
1564EXPORT_SYMBOL(d_splice_alias);
1565
1566/**
1567 * d_add_ci - lookup or allocate new dentry with case-exact name
1568 * @inode:  the inode case-insensitive lookup has found
1569 * @dentry: the negative dentry that was passed to the parent's lookup func
1570 * @name:   the case-exact name to be associated with the returned dentry
1571 *
1572 * This is to avoid filling the dcache with case-insensitive names to the
1573 * same inode, only the actual correct case is stored in the dcache for
1574 * case-insensitive filesystems.
1575 *
1576 * For a case-insensitive lookup match and if the the case-exact dentry
1577 * already exists in in the dcache, use it and return it.
1578 *
1579 * If no entry exists with the exact case name, allocate new dentry with
1580 * the exact case, and return the spliced entry.
1581 */
1582struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
1583                        struct qstr *name)
1584{
1585        int error;
1586        struct dentry *found;
1587        struct dentry *new;
1588
1589        /*
1590         * First check if a dentry matching the name already exists,
1591         * if not go ahead and create it now.
1592         */
1593        found = d_hash_and_lookup(dentry->d_parent, name);
1594        if (!found) {
1595                new = d_alloc(dentry->d_parent, name);
1596                if (!new) {
1597                        error = -ENOMEM;
1598                        goto err_out;
1599                }
1600
1601                found = d_splice_alias(inode, new);
1602                if (found) {
1603                        dput(new);
1604                        return found;
1605                }
1606                return new;
1607        }
1608
1609        /*
1610         * If a matching dentry exists, and it's not negative use it.
1611         *
1612         * Decrement the reference count to balance the iget() done
1613         * earlier on.
1614         */
1615        if (found->d_inode) {
1616                if (unlikely(found->d_inode != inode)) {
1617                        /* This can't happen because bad inodes are unhashed. */
1618                        BUG_ON(!is_bad_inode(inode));
1619                        BUG_ON(!is_bad_inode(found->d_inode));
1620                }
1621                iput(inode);
1622                return found;
1623        }
1624
1625        /*
1626         * We are going to instantiate this dentry, unhash it and clear the
1627         * lookup flag so we can do that.
1628         */
1629        if (unlikely(d_need_lookup(found)))
1630                d_clear_need_lookup(found);
1631
1632        /*
1633         * Negative dentry: instantiate it unless the inode is a directory and
1634         * already has a dentry.
1635         */
1636        new = d_splice_alias(inode, found);
1637        if (new) {
1638                dput(found);
1639                found = new;
1640        }
1641        return found;
1642
1643err_out:
1644        iput(inode);
1645        return ERR_PTR(error);
1646}
1647EXPORT_SYMBOL(d_add_ci);
1648
1649/**
1650 * __d_lookup_rcu - search for a dentry (racy, store-free)
1651 * @parent: parent dentry
1652 * @name: qstr of name we wish to find
1653 * @seq: returns d_seq value at the point where the dentry was found
1654 * @inode: returns dentry->d_inode when the inode was found valid.
1655 * Returns: dentry, or NULL
1656 *
1657 * __d_lookup_rcu is the dcache lookup function for rcu-walk name
1658 * resolution (store-free path walking) design described in
1659 * Documentation/filesystems/path-lookup.txt.
1660 *
1661 * This is not to be used outside core vfs.
1662 *
1663 * __d_lookup_rcu must only be used in rcu-walk mode, ie. with vfsmount lock
1664 * held, and rcu_read_lock held. The returned dentry must not be stored into
1665 * without taking d_lock and checking d_seq sequence count against @seq
1666 * returned here.
1667 *
1668 * A refcount may be taken on the found dentry with the __d_rcu_to_refcount
1669 * function.
1670 *
1671 * Alternatively, __d_lookup_rcu may be called again to look up the child of
1672 * the returned dentry, so long as its parent's seqlock is checked after the
1673 * child is looked up. Thus, an interlocking stepping of sequence lock checks
1674 * is formed, giving integrity down the path walk.
1675 */
1676struct dentry *__d_lookup_rcu(struct dentry *parent, struct qstr *name,
1677                                unsigned *seq, struct inode **inode)
1678{
1679        unsigned int len = name->len;
1680        unsigned int hash = name->hash;
1681        const unsigned char *str = name->name;
1682        struct hlist_bl_head *b = d_hash(parent, hash);
1683        struct hlist_bl_node *node;
1684        struct dentry *dentry;
1685
1686        /*
1687         * Note: There is significant duplication with __d_lookup_rcu which is
1688         * required to prevent single threaded performance regressions
1689         * especially on architectures where smp_rmb (in seqcounts) are costly.
1690         * Keep the two functions in sync.
1691         */
1692
1693        /*
1694         * The hash list is protected using RCU.
1695         *
1696         * Carefully use d_seq when comparing a candidate dentry, to avoid
1697         * races with d_move().
1698         *
1699         * It is possible that concurrent renames can mess up our list
1700         * walk here and result in missing our dentry, resulting in the
1701         * false-negative result. d_lookup() protects against concurrent
1702         * renames using rename_lock seqlock.
1703         *
1704         * See Documentation/filesystems/path-lookup.txt for more details.
1705         */
1706        hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
1707                struct inode *i;
1708                const char *tname;
1709                int tlen;
1710
1711                if (dentry->d_name.hash != hash)
1712                        continue;
1713
1714seqretry:
1715                *seq = read_seqcount_begin(&dentry->d_seq);
1716                if (dentry->d_parent != parent)
1717                        continue;
1718                if (d_unhashed(dentry))
1719                        continue;
1720                tlen = dentry->d_name.len;
1721                tname = dentry->d_name.name;
1722                i = dentry->d_inode;
1723                prefetch(tname);
1724                /*
1725                 * This seqcount check is required to ensure name and
1726                 * len are loaded atomically, so as not to walk off the
1727                 * edge of memory when walking. If we could load this
1728                 * atomically some other way, we could drop this check.
1729                 */
1730                if (read_seqcount_retry(&dentry->d_seq, *seq))
1731                        goto seqretry;
1732                if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
1733                        if (parent->d_op->d_compare(parent, *inode,
1734                                                dentry, i,
1735                                                tlen, tname, name))
1736                                continue;
1737                } else {
1738                        if (dentry_cmp(tname, tlen, str, len))
1739                                continue;
1740                }
1741                /*
1742                 * No extra seqcount check is required after the name
1743                 * compare. The caller must perform a seqcount check in
1744                 * order to do anything useful with the returned dentry
1745                 * anyway.
1746                 */
1747                *inode = i;
1748                return dentry;
1749        }
1750        return NULL;
1751}
1752
1753/**
1754 * d_lookup - search for a dentry
1755 * @parent: parent dentry
1756 * @name: qstr of name we wish to find
1757 * Returns: dentry, or NULL
1758 *
1759 * d_lookup searches the children of the parent dentry for the name in
1760 * question. If the dentry is found its reference count is incremented and the
1761 * dentry is returned. The caller must use dput to free the entry when it has
1762 * finished using it. %NULL is returned if the dentry does not exist.
1763 */
1764struct dentry *d_lookup(struct dentry *parent, struct qstr *name)
1765{
1766        struct dentry *dentry;
1767        unsigned seq;
1768
1769        do {
1770                seq = read_seqbegin(&rename_lock);
1771                dentry = __d_lookup(parent, name);
1772                if (dentry)
1773                        break;
1774        } while (read_seqretry(&rename_lock, seq));
1775        return dentry;
1776}
1777EXPORT_SYMBOL(d_lookup);
1778
1779/**
1780 * __d_lookup - search for a dentry (racy)
1781 * @parent: parent dentry
1782 * @name: qstr of name we wish to find
1783 * Returns: dentry, or NULL
1784 *
1785 * __d_lookup is like d_lookup, however it may (rarely) return a
1786 * false-negative result due to unrelated rename activity.
1787 *
1788 * __d_lookup is slightly faster by avoiding rename_lock read seqlock,
1789 * however it must be used carefully, eg. with a following d_lookup in
1790 * the case of failure.
1791 *
1792 * __d_lookup callers must be commented.
1793 */
1794struct dentry *__d_lookup(struct dentry *parent, struct qstr *name)
1795{
1796        unsigned int len = name->len;
1797        unsigned int hash = name->hash;
1798        const unsigned char *str = name->name;
1799        struct hlist_bl_head *b = d_hash(parent, hash);
1800        struct hlist_bl_node *node;
1801        struct dentry *found = NULL;
1802        struct dentry *dentry;
1803
1804        /*
1805         * Note: There is significant duplication with __d_lookup_rcu which is
1806         * required to prevent single threaded performance regressions
1807         * especially on architectures where smp_rmb (in seqcounts) are costly.
1808         * Keep the two functions in sync.
1809         */
1810
1811        /*
1812         * The hash list is protected using RCU.
1813         *
1814         * Take d_lock when comparing a candidate dentry, to avoid races
1815         * with d_move().
1816         *
1817         * It is possible that concurrent renames can mess up our list
1818         * walk here and result in missing our dentry, resulting in the
1819         * false-negative result. d_lookup() protects against concurrent
1820         * renames using rename_lock seqlock.
1821         *
1822         * See Documentation/filesystems/path-lookup.txt for more details.
1823         */
1824        rcu_read_lock();
1825        
1826        hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
1827                const char *tname;
1828                int tlen;
1829
1830                if (dentry->d_name.hash != hash)
1831                        continue;
1832
1833                spin_lock(&dentry->d_lock);
1834                if (dentry->d_parent != parent)
1835                        goto next;
1836                if (d_unhashed(dentry))
1837                        goto next;
1838
1839                /*
1840                 * It is safe to compare names since d_move() cannot
1841                 * change the qstr (protected by d_lock).
1842                 */
1843                tlen = dentry->d_name.len;
1844                tname = dentry->d_name.name;
1845                if (parent->d_flags & DCACHE_OP_COMPARE) {
1846                        if (parent->d_op->d_compare(parent, parent->d_inode,
1847                                                dentry, dentry->d_inode,
1848                                                tlen, tname, name))
1849                                goto next;
1850                } else {
1851                        if (dentry_cmp(tname, tlen, str, len))
1852                                goto next;
1853                }
1854
1855                dentry->d_count++;
1856                found = dentry;
1857                spin_unlock(&dentry->d_lock);
1858                break;
1859next:
1860                spin_unlock(&dentry->d_lock);
1861        }
1862        rcu_read_unlock();
1863
1864        return found;
1865}
1866
1867/**
1868 * d_hash_and_lookup - hash the qstr then search for a dentry
1869 * @dir: Directory to search in
1870 * @name: qstr of name we wish to find
1871 *
1872 * On hash failure or on lookup failure NULL is returned.
1873 */
1874struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
1875{
1876        struct dentry *dentry = NULL;
1877
1878        /*
1879         * Check for a fs-specific hash function. Note that we must
1880         * calculate the standard hash first, as the d_op->d_hash()
1881         * routine may choose to leave the hash value unchanged.
1882         */
1883        name->hash = full_name_hash(name->name, name->len);
1884        if (dir->d_flags & DCACHE_OP_HASH) {
1885                if (dir->d_op->d_hash(dir, dir->d_inode, name) < 0)
1886                        goto out;
1887        }
1888        dentry = d_lookup(dir, name);
1889out:
1890        return dentry;
1891}
1892
1893/**
1894 * d_validate - verify dentry provided from insecure source (deprecated)
1895 * @dentry: The dentry alleged to be valid child of @dparent
1896 * @dparent: The parent dentry (known to be valid)
1897 *
1898 * An insecure source has sent us a dentry, here we verify it and dget() it.
1899 * This is used by ncpfs in its readdir implementation.
1900 * Zero is returned in the dentry is invalid.
1901 *
1902 * This function is slow for big directories, and deprecated, do not use it.
1903 */
1904int d_validate(struct dentry *dentry, struct dentry *dparent)
1905{
1906        struct dentry *child;
1907
1908        spin_lock(&dparent->d_lock);
1909        list_for_each_entry(child, &dparent->d_subdirs, d_u.d_child) {
1910                if (dentry == child) {
1911                        spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
1912                        __dget_dlock(dentry);
1913                        spin_unlock(&dentry->d_lock);
1914                        spin_unlock(&dparent->d_lock);
1915                        return 1;
1916                }
1917        }
1918        spin_unlock(&dparent->d_lock);
1919
1920        return 0;
1921}
1922EXPORT_SYMBOL(d_validate);
1923
1924/*
1925 * When a file is deleted, we have two options:
1926 * - turn this dentry into a negative dentry
1927 * - unhash this dentry and free it.
1928 *
1929 * Usually, we want to just turn this into
1930 * a negative dentry, but if anybody else is
1931 * currently using the dentry or the inode
1932 * we can't do that and we fall back on removing
1933 * it from the hash queues and waiting for
1934 * it to be deleted later when it has no users
1935 */
1936 
1937/**
1938 * d_delete - delete a dentry
1939 * @dentry: The dentry to delete
1940 *
1941 * Turn the dentry into a negative dentry if possible, otherwise
1942 * remove it from the hash queues so it can be deleted later
1943 */
1944 
1945void d_delete(struct dentry * dentry)
1946{
1947        struct inode *inode;
1948        int isdir = 0;
1949        /*
1950         * Are we the only user?
1951         */
1952again:
1953        spin_lock(&dentry->d_lock);
1954        inode = dentry->d_inode;
1955        isdir = S_ISDIR(inode->i_mode);
1956        if (dentry->d_count == 1) {
1957                if (inode && !spin_trylock(&inode->i_lock)) {
1958                        spin_unlock(&dentry->d_lock);
1959                        cpu_relax();
1960                        goto again;
1961                }
1962                dentry->d_flags &= ~DCACHE_CANT_MOUNT;
1963                dentry_unlink_inode(dentry);
1964                fsnotify_nameremove(dentry, isdir);
1965                return;
1966        }
1967
1968        if (!d_unhashed(dentry))
1969                __d_drop(dentry);
1970
1971        spin_unlock(&dentry->d_lock);
1972
1973        fsnotify_nameremove(dentry, isdir);
1974}
1975EXPORT_SYMBOL(d_delete);
1976
1977static void __d_rehash(struct dentry * entry, struct hlist_bl_head *b)
1978{
1979        BUG_ON(!d_unhashed(entry));
1980        hlist_bl_lock(b);
1981        entry->d_flags |= DCACHE_RCUACCESS;
1982        hlist_bl_add_head_rcu(&entry->d_hash, b);
1983        hlist_bl_unlock(b);
1984}
1985
1986static void _d_rehash(struct dentry * entry)
1987{
1988        __d_rehash(entry, d_hash(entry->d_parent, entry->d_name.hash));
1989}
1990
1991/**
1992 * d_rehash     - add an entry back to the hash
1993 * @entry: dentry to add to the hash
1994 *
1995 * Adds a dentry to the hash according to its name.
1996 */
1997 
1998void d_rehash(struct dentry * entry)
1999{
2000        spin_lock(&entry->d_lock);
2001        _d_rehash(entry);
2002        spin_unlock(&entry->d_lock);
2003}
2004EXPORT_SYMBOL(d_rehash);
2005
2006/**
2007 * dentry_update_name_case - update case insensitive dentry with a new name
2008 * @dentry: dentry to be updated
2009 * @name: new name
2010 *
2011 * Update a case insensitive dentry with new case of name.
2012 *
2013 * dentry must have been returned by d_lookup with name @name. Old and new
2014 * name lengths must match (ie. no d_compare which allows mismatched name
2015 * lengths).
2016 *
2017 * Parent inode i_mutex must be held over d_lookup and into this call (to
2018 * keep renames and concurrent inserts, and readdir(2) away).
2019 */
2020void dentry_update_name_case(struct dentry *dentry, struct qstr *name)
2021{
2022        BUG_ON(!mutex_is_locked(&dentry->d_parent->d_inode->i_mutex));
2023        BUG_ON(dentry->d_name.len != name->len); /* d_lookup gives this */
2024
2025        spin_lock(&dentry->d_lock);
2026        write_seqcount_begin(&dentry->d_seq);
2027        memcpy((unsigned char *)dentry->d_name.name, name->name, name->len);
2028        write_seqcount_end(&dentry->d_seq);
2029        spin_unlock(&dentry->d_lock);
2030}
2031EXPORT_SYMBOL(dentry_update_name_case);
2032
2033static void switch_names(struct dentry *dentry, struct dentry *target)
2034{
2035        if (dname_external(target)) {
2036                if (dname_external(dentry)) {
2037                        /*
2038                         * Both external: swap the pointers
2039                         */
2040                        swap(target->d_name.name, dentry->d_name.name);
2041                } else {
2042                        /*
2043                         * dentry:internal, target:external.  Steal target's
2044                         * storage and make target internal.
2045                         */
2046                        memcpy(target->d_iname, dentry->d_name.name,
2047                                        dentry->d_name.len + 1);
2048                        dentry->d_name.name = target->d_name.name;
2049                        target->d_name.name = target->d_iname;
2050                }
2051        } else {
2052                if (dname_external(dentry)) {
2053                        /*
2054                         * dentry:external, target:internal.  Give dentry's
2055                         * storage to target and make dentry internal
2056                         */
2057                        memcpy(dentry->d_iname, target->d_name.name,
2058                                        target->d_name.len + 1);
2059                        target->d_name.name = dentry->d_name.name;
2060                        dentry->d_name.name = dentry->d_iname;
2061                } else {
2062                        /*
2063                         * Both are internal.  Just copy target to dentry
2064                         */
2065                        memcpy(dentry->d_iname, target->d_name.name,
2066                                        target->d_name.len + 1);
2067                        dentry->d_name.len = target->d_name.len;
2068                        return;
2069                }
2070        }
2071        swap(dentry->d_name.len, target->d_name.len);
2072}
2073
2074static void dentry_lock_for_move(struct dentry *dentry, struct dentry *target)
2075{
2076        /*
2077         * XXXX: do we really need to take target->d_lock?
2078         */
2079        if (IS_ROOT(dentry) || dentry->d_parent == target->d_parent)
2080                spin_lock(&target->d_parent->d_lock);
2081        else {
2082                if (d_ancestor(dentry->d_parent, target->d_parent)) {
2083                        spin_lock(&dentry->d_parent->d_lock);
2084                        spin_lock_nested(&target->d_parent->d_lock,
2085                                                DENTRY_D_LOCK_NESTED);
2086                } else {
2087                        spin_lock(&target->d_parent->d_lock);
2088                        spin_lock_nested(&dentry->d_parent->d_lock,
2089                                                DENTRY_D_LOCK_NESTED);
2090                }
2091        }
2092        if (target < dentry) {
2093                spin_lock_nested(&target->d_lock, 2);
2094                spin_lock_nested(&dentry->d_lock, 3);
2095        } else {
2096                spin_lock_nested(&dentry->d_lock, 2);
2097                spin_lock_nested(&target->d_lock, 3);
2098        }
2099}
2100
2101static void dentry_unlock_parents_for_move(struct dentry *dentry,
2102                                        struct dentry *target)
2103{
2104        if (target->d_parent != dentry->d_parent)
2105                spin_unlock(&dentry->d_parent->d_lock);
2106        if (target->d_parent != target)
2107                spin_unlock(&target->d_parent->d_lock);
2108}
2109
2110/*
2111 * When switching names, the actual string doesn't strictly have to
2112 * be preserved in the target - because we're dropping the target
2113 * anyway. As such, we can just do a simple memcpy() to copy over
2114 * the new name before we switch.
2115 *
2116 * Note that we have to be a lot more careful about getting the hash
2117 * switched - we have to switch the hash value properly even if it
2118 * then no longer matches the actual (corrupted) string of the target.
2119 * The hash value has to match the hash queue that the dentry is on..
2120 */
2121/*
2122 * __d_move - move a dentry
2123 * @dentry: entry to move
2124 * @target: new dentry
2125 *
2126 * Update the dcache to reflect the move of a file name. Negative
2127 * dcache entries should not be moved in this way. Caller must hold
2128 * rename_lock, the i_mutex of the source and target directories,
2129 * and the sb->s_vfs_rename_mutex if they differ. See lock_rename().
2130 */
2131static void __d_move(struct dentry * dentry, struct dentry * target)
2132{
2133        if (!dentry->d_inode)
2134                printk(KERN_WARNING "VFS: moving negative dcache entry\n");
2135
2136        BUG_ON(d_ancestor(dentry, target));
2137        BUG_ON(d_ancestor(target, dentry));
2138
2139        dentry_lock_for_move(dentry, target);
2140
2141        write_seqcount_begin(&dentry->d_seq);
2142        write_seqcount_begin(&target->d_seq);
2143
2144        /* __d_drop does write_seqcount_barrier, but they're OK to nest. */
2145
2146        /*
2147         * Move the dentry to the target hash queue. Don't bother checking
2148         * for the same hash queue because of how unlikely it is.
2149         */
2150        __d_drop(dentry);
2151        __d_rehash(dentry, d_hash(target->d_parent, target->d_name.hash));
2152
2153        /* Unhash the target: dput() will then get rid of it */
2154        __d_drop(target);
2155
2156        list_del(&dentry->d_u.d_child);
2157        list_del(&target->d_u.d_child);
2158
2159        /* Switch the names.. */
2160        switch_names(dentry, target);
2161        swap(dentry->d_name.hash, target->d_name.hash);
2162
2163        /* ... and switch the parents */
2164        if (IS_ROOT(dentry)) {
2165                dentry->d_parent = target->d_parent;
2166                target->d_parent = target;
2167                INIT_LIST_HEAD(&target->d_u.d_child);
2168        } else {
2169                swap(dentry->d_parent, target->d_parent);
2170
2171                /* And add them back to the (new) parent lists */
2172                list_add(&target->d_u.d_child, &target->d_parent->d_subdirs);
2173        }
2174
2175        list_add(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
2176
2177        write_seqcount_end(&target->d_seq);
2178        write_seqcount_end(&dentry->d_seq);
2179
2180        dentry_unlock_parents_for_move(dentry, target);
2181        spin_unlock(&target->d_lock);
2182        fsnotify_d_move(dentry);
2183        spin_unlock(&dentry->d_lock);
2184}
2185
2186/*
2187 * d_move - move a dentry
2188 * @dentry: entry to move
2189 * @target: new dentry
2190 *
2191 * Update the dcache to reflect the move of a file name. Negative
2192 * dcache entries should not be moved in this way. See the locking
2193 * requirements for __d_move.
2194 */
2195void d_move(struct dentry *dentry, struct dentry *target)
2196{
2197        write_seqlock(&rename_lock);
2198        __d_move(dentry, target);
2199        write_sequnlock(&rename_lock);
2200}
2201EXPORT_SYMBOL(d_move);
2202
2203/**
2204 * d_ancestor - search for an ancestor
2205 * @p1: ancestor dentry
2206 * @p2: child dentry
2207 *
2208 * Returns the ancestor dentry of p2 which is a child of p1, if p1 is
2209 * an ancestor of p2, else NULL.
2210 */
2211struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
2212{
2213        struct dentry *p;
2214
2215        for (p = p2; !IS_ROOT(p); p = p->d_parent) {
2216                if (p->d_parent == p1)
2217                        return p;
2218        }
2219        return NULL;
2220}
2221
2222/*
2223 * This helper attempts to cope with remotely renamed directories
2224 *
2225 * It assumes that the caller is already holding
2226 * dentry->d_parent->d_inode->i_mutex, inode->i_lock and rename_lock
2227 *
2228 * Note: If ever the locking in lock_rename() changes, then please
2229 * remember to update this too...
2230 */
2231static struct dentry *__d_unalias(struct inode *inode,
2232                struct dentry *dentry, struct dentry *alias)
2233{
2234        struct mutex *m1 = NULL, *m2 = NULL;
2235        struct dentry *ret;
2236
2237        /* If alias and dentry share a parent, then no extra locks required */
2238        if (alias->d_parent == dentry->d_parent)
2239                goto out_unalias;
2240
2241        /* See lock_rename() */
2242        ret = ERR_PTR(-EBUSY);
2243        if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
2244                goto out_err;
2245        m1 = &dentry->d_sb->s_vfs_rename_mutex;
2246        if (!mutex_trylock(&alias->d_parent->d_inode->i_mutex))
2247                goto out_err;
2248        m2 = &alias->d_parent->d_inode->i_mutex;
2249out_unalias:
2250        __d_move(alias, dentry);
2251        ret = alias;
2252out_err:
2253        spin_unlock(&inode->i_lock);
2254        if (m2)
2255                mutex_unlock(m2);
2256        if (m1)
2257                mutex_unlock(m1);
2258        return ret;
2259}
2260
2261/*
2262 * Prepare an anonymous dentry for life in the superblock's dentry tree as a
2263 * named dentry in place of the dentry to be replaced.
2264 * returns with anon->d_lock held!
2265 */
2266static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
2267{
2268        struct dentry *dparent, *aparent;
2269
2270        dentry_lock_for_move(anon, dentry);
2271
2272        write_seqcount_begin(&dentry->d_seq);
2273        write_seqcount_begin(&anon->d_seq);
2274
2275        dparent = dentry->d_parent;
2276        aparent = anon->d_parent;
2277
2278        switch_names(dentry, anon);
2279        swap(dentry->d_name.hash, anon->d_name.hash);
2280
2281        dentry->d_parent = (aparent == anon) ? dentry : aparent;
2282        list_del(&dentry->d_u.d_child);
2283        if (!IS_ROOT(dentry))
2284                list_add(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
2285        else
2286                INIT_LIST_HEAD(&dentry->d_u.d_child);
2287
2288        anon->d_parent = (dparent == dentry) ? anon : dparent;
2289        list_del(&anon->d_u.d_child);
2290        if (!IS_ROOT(anon))
2291                list_add(&anon->d_u.d_child, &anon->d_parent->d_subdirs);
2292        else
2293                INIT_LIST_HEAD(&anon->d_u.d_child);
2294
2295        write_seqcount_end(&dentry->d_seq);
2296        write_seqcount_end(&anon->d_seq);
2297
2298        dentry_unlock_parents_for_move(anon, dentry);
2299        spin_unlock(&dentry->d_lock);
2300
2301        /* anon->d_lock still locked, returns locked */
2302        anon->d_flags &= ~DCACHE_DISCONNECTED;
2303}
2304
2305/**
2306 * d_materialise_unique - introduce an inode into the tree
2307 * @dentry: candidate dentry
2308 * @inode: inode to bind to the dentry, to which aliases may be attached
2309 *
2310 * Introduces an dentry into the tree, substituting an extant disconnected
2311 * root directory alias in its place if there is one. Caller must hold the
2312 * i_mutex of the parent directory.
2313 */
2314struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode)
2315{
2316        struct dentry *actual;
2317
2318        BUG_ON(!d_unhashed(dentry));
2319
2320        if (!inode) {
2321                actual = dentry;
2322                __d_instantiate(dentry, NULL);
2323                d_rehash(actual);
2324                goto out_nolock;
2325        }
2326
2327        spin_lock(&inode->i_lock);
2328
2329        if (S_ISDIR(inode->i_mode)) {
2330                struct dentry *alias;
2331
2332                /* Does an aliased dentry already exist? */
2333                alias = __d_find_alias(inode, 0);
2334                if (alias) {
2335                        actual = alias;
2336                        write_seqlock(&rename_lock);
2337
2338                        if (d_ancestor(alias, dentry)) {
2339                                /* Check for loops */
2340                                actual = ERR_PTR(-ELOOP);
2341                        } else if (IS_ROOT(alias)) {
2342                                /* Is this an anonymous mountpoint that we
2343                                 * could splice into our tree? */
2344                                __d_materialise_dentry(dentry, alias);
2345                                write_sequnlock(&rename_lock);
2346                                __d_drop(alias);
2347                                goto found;
2348                        } else {
2349                                /* Nope, but we must(!) avoid directory
2350                                 * aliasing */
2351                                actual = __d_unalias(inode, dentry, alias);
2352                        }
2353                        write_sequnlock(&rename_lock);
2354                        if (IS_ERR(actual))
2355                                dput(alias);
2356                        goto out_nolock;
2357                }
2358        }
2359
2360        /* Add a unique reference */
2361        actual = __d_instantiate_unique(dentry, inode);
2362        if (!actual)
2363                actual = dentry;
2364        else
2365                BUG_ON(!d_unhashed(actual));
2366
2367        spin_lock(&actual->d_lock);
2368found:
2369        _d_rehash(actual);
2370        spin_unlock(&actual->d_lock);
2371        spin_unlock(&inode->i_lock);
2372out_nolock:
2373        if (actual == dentry) {
2374                security_d_instantiate(dentry, inode);
2375                return NULL;
2376        }
2377
2378        iput(inode);
2379        return actual;
2380}
2381EXPORT_SYMBOL_GPL(d_materialise_unique);
2382
2383static int prepend(char **buffer, int *buflen, const char *str, int namelen)
2384{
2385        *buflen -= namelen;
2386        if (*buflen < 0)
2387                return -ENAMETOOLONG;
2388        *buffer -= namelen;
2389        memcpy(*buffer, str, namelen);
2390        return 0;
2391}
2392
2393static int prepend_name(char **buffer, int *buflen, struct qstr *name)
2394{
2395        return prepend(buffer, buflen, name->name, name->len);
2396}
2397
2398/**
2399 * prepend_path - Prepend path string to a buffer
2400 * @path: the dentry/vfsmount to report
2401 * @root: root vfsmnt/dentry
2402 * @buffer: pointer to the end of the buffer
2403 * @buflen: pointer to buffer length
2404 *
2405 * Caller holds the rename_lock.
2406 */
2407static int prepend_path(const struct path *path,
2408                        const struct path *root,
2409                        char **buffer, int *buflen)
2410{
2411        struct dentry *dentry = path->dentry;
2412        struct vfsmount *vfsmnt = path->mnt;
2413        bool slash = false;
2414        int error = 0;
2415
2416        br_read_lock(vfsmount_lock);
2417        while (dentry != root->dentry || vfsmnt != root->mnt) {
2418                struct dentry * parent;
2419
2420                if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
2421                        /* Global root? */
2422                        if (vfsmnt->mnt_parent == vfsmnt) {
2423                                goto global_root;
2424                        }
2425                        dentry = vfsmnt->mnt_mountpoint;
2426                        vfsmnt = vfsmnt->mnt_parent;
2427                        continue;
2428                }
2429                parent = dentry->d_parent;
2430                prefetch(parent);
2431                spin_lock(&dentry->d_lock);
2432                error = prepend_name(buffer, buflen, &dentry->d_name);
2433                spin_unlock(&dentry->d_lock);
2434                if (!error)
2435                        error = prepend(buffer, buflen, "/", 1);
2436                if (error)
2437                        break;
2438
2439                slash = true;
2440                dentry = parent;
2441        }
2442
2443        if (!error && !slash)
2444                error = prepend(buffer, buflen, "/", 1);
2445
2446out:
2447        br_read_unlock(vfsmount_lock);
2448        return error;
2449
2450global_root:
2451        /*
2452         * Filesystems needing to implement special "root names"
2453         * should do so with ->d_dname()
2454         */
2455        if (IS_ROOT(dentry) &&
2456            (dentry->d_name.len != 1 || dentry->d_name.name[0] != '/')) {
2457                WARN(1, "Root dentry has weird name <%.*s>\n",
2458                     (int) dentry->d_name.len, dentry->d_name.name);
2459        }
2460        if (!slash)
2461                error = prepend(buffer, buflen, "/", 1);
2462        if (!error)
2463                error = vfsmnt->mnt_ns ? 1 : 2;
2464        goto out;
2465}
2466
2467/**
2468 * __d_path - return the path of a dentry
2469 * @path: the dentry/vfsmount to report
2470 * @root: root vfsmnt/dentry
2471 * @buf: buffer to return value in
2472 * @buflen: buffer length
2473 *
2474 * Convert a dentry into an ASCII path name.
2475 *
2476 * Returns a pointer into the buffer or an error code if the
2477 * path was too long.
2478 *
2479 * "buflen" should be positive.
2480 *
2481 * If the path is not reachable from the supplied root, return %NULL.
2482 */
2483char *__d_path(const struct path *path,
2484               const struct path *root,
2485               char *buf, int buflen)
2486{
2487        char *res = buf + buflen;
2488        int error;
2489
2490        prepend(&res, &buflen, "\0", 1);
2491        write_seqlock(&rename_lock);
2492        error = prepend_path(path, root, &res, &buflen);
2493        write_sequnlock(&rename_lock);
2494
2495        if (error < 0)
2496                return ERR_PTR(error);
2497        if (error > 0)
2498                return NULL;
2499        return res;
2500}
2501
2502char *d_absolute_path(const struct path *path,
2503               char *buf, int buflen)
2504{
2505        struct path root = {};
2506        char *res = buf + buflen;
2507        int error;
2508
2509        prepend(&res, &buflen, "\0", 1);
2510        write_seqlock(&rename_lock);
2511        error = prepend_path(path, &root, &res, &buflen);
2512        write_sequnlock(&rename_lock);
2513
2514        if (error > 1)
2515                error = -EINVAL;
2516        if (error < 0)
2517                return ERR_PTR(error);
2518        return res;
2519}
2520
2521/*
2522 * same as __d_path but appends "(deleted)" for unlinked files.
2523 */
2524static int path_with_deleted(const struct path *path,
2525                             const struct path *root,
2526                             char **buf, int *buflen)
2527{
2528        prepend(buf, buflen, "\0", 1);
2529        if (d_unlinked(path->dentry)) {
2530                int error = prepend(buf, buflen, " (deleted)", 10);
2531                if (error)
2532                        return error;
2533        }
2534
2535        return prepend_path(path, root, buf, buflen);
2536}
2537
2538static int prepend_unreachable(char **buffer, int *buflen)
2539{
2540        return prepend(buffer, buflen, "(unreachable)", 13);
2541}
2542
2543/**
2544 * d_path - return the path of a dentry
2545 * @path: path to report
2546 * @buf: buffer to return value in
2547 * @buflen: buffer length
2548 *
2549 * Convert a dentry into an ASCII path name. If the entry has been deleted
2550 * the string " (deleted)" is appended. Note that this is ambiguous.
2551 *
2552 * Returns a pointer into the buffer or an error code if the path was
2553 * too long. Note: Callers should use the returned pointer, not the passed
2554 * in buffer, to use the name! The implementation often starts at an offset
2555 * into the buffer, and may leave 0 bytes at the start.
2556 *
2557 * "buflen" should be positive.
2558 */
2559char *d_path(const struct path *path, char *buf, int buflen)
2560{
2561        char *res = buf + buflen;
2562        struct path root;
2563        int error;
2564
2565        /*
2566         * We have various synthetic filesystems that never get mounted.  On
2567         * these filesystems dentries are never used for lookup purposes, and
2568         * thus don't need to be hashed.  They also don't need a name until a
2569         * user wants to identify the object in /proc/pid/fd/.  The little hack
2570         * below allows us to generate a name for these objects on demand:
2571         */
2572        if (path->dentry->d_op && path->dentry->d_op->d_dname)
2573                return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
2574
2575        get_fs_root(current->fs, &root);
2576        write_seqlock(&rename_lock);
2577        error = path_with_deleted(path, &root, &res, &buflen);
2578        if (error < 0)
2579                res = ERR_PTR(error);
2580        write_sequnlock(&rename_lock);
2581        path_put(&root);
2582        return res;
2583}
2584EXPORT_SYMBOL(d_path);
2585
2586/**
2587 * d_path_with_unreachable - return the path of a dentry
2588 * @path: path to report
2589 * @buf: buffer to return value in
2590 * @buflen: buffer length
2591 *
2592 * The difference from d_path() is that this prepends "(unreachable)"
2593 * to paths which are unreachable from the current process' root.
2594 */
2595char *d_path_with_unreachable(const struct path *path, char *buf, int buflen)
2596{
2597        char *res = buf + buflen;
2598        struct path root;
2599        int error;
2600
2601        if (path->dentry->d_op && path->dentry->d_op->d_dname)
2602                return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
2603
2604        get_fs_root(current->fs, &root);
2605        write_seqlock(&rename_lock);
2606        error = path_with_deleted(path, &root, &res, &buflen);
2607        if (error > 0)
2608                error = prepend_unreachable(&res, &buflen);
2609        write_sequnlock(&rename_lock);
2610        path_put(&root);
2611        if (error)
2612                res =  ERR_PTR(error);
2613
2614        return res;
2615}
2616
2617/*
2618 * Helper function for dentry_operations.d_dname() members
2619 */
2620char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,
2621                        const char *fmt, ...)
2622{
2623        va_list args;
2624        char temp[64];
2625        int sz;
2626
2627        va_start(args, fmt);
2628        sz = vsnprintf(temp, sizeof(temp), fmt, args) + 1;
2629        va_end(args);
2630
2631        if (sz > sizeof(temp) || sz > buflen)
2632                return ERR_PTR(-ENAMETOOLONG);
2633
2634        buffer += buflen - sz;
2635        return memcpy(buffer, temp, sz);
2636}
2637
2638/*
2639 * Write full pathname from the root of the filesystem into the buffer.
2640 */
2641static char *__dentry_path(struct dentry *dentry, char *buf, int buflen)
2642{
2643        char *end = buf + buflen;
2644        char *retval;
2645
2646        prepend(&end, &buflen, "\0", 1);
2647        if (buflen < 1)
2648                goto Elong;
2649        /* Get '/' right */
2650        retval = end-1;
2651        *retval = '/';
2652
2653        while (!IS_ROOT(dentry)) {
2654                struct dentry *parent = dentry->d_parent;
2655                int error;
2656
2657                prefetch(parent);
2658                spin_lock(&dentry->d_lock);
2659                error = prepend_name(&end, &buflen, &dentry->d_name);
2660                spin_unlock(&dentry->d_lock);
2661                if (error != 0 || prepend(&end, &buflen, "/", 1) != 0)
2662                        goto Elong;
2663
2664                retval = end;
2665                dentry = parent;
2666        }
2667        return retval;
2668Elong:
2669        return ERR_PTR(-ENAMETOOLONG);
2670}
2671
2672char *dentry_path_raw(struct dentry *dentry, char *buf, int buflen)
2673{
2674        char *retval;
2675
2676        write_seqlock(&rename_lock);
2677        retval = __dentry_path(dentry, buf, buflen);
2678        write_sequnlock(&rename_lock);
2679
2680        return retval;
2681}
2682EXPORT_SYMBOL(dentry_path_raw);
2683
2684char *dentry_path(struct dentry *dentry, char *buf, int buflen)
2685{
2686        char *p = NULL;
2687        char *retval;
2688
2689        write_seqlock(&rename_lock);
2690        if (d_unlinked(dentry)) {
2691                p = buf + buflen;
2692                if (prepend(&p, &buflen, "//deleted", 10) != 0)
2693                        goto Elong;
2694                buflen++;
2695        }
2696        retval = __dentry_path(dentry, buf, buflen);
2697        write_sequnlock(&rename_lock);
2698        if (!IS_ERR(retval) && p)
2699                *p = '/';       /* restore '/' overriden with '\0' */
2700        return retval;
2701Elong:
2702        return ERR_PTR(-ENAMETOOLONG);
2703}
2704
2705/*
2706 * NOTE! The user-level library version returns a
2707 * character pointer. The kernel system call just
2708 * returns the length of the buffer filled (which
2709 * includes the ending '\0' character), or a negative
2710 * error value. So libc would do something like
2711 *
2712 *      char *getcwd(char * buf, size_t size)
2713 *      {
2714 *              int retval;
2715 *
2716 *              retval = sys_getcwd(buf, size);
2717 *              if (retval >= 0)
2718 *                      return buf;
2719 *              errno = -retval;
2720 *              return NULL;
2721 *      }
2722 */
2723SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
2724{
2725        int error;
2726        struct path pwd, root;
2727        char *page = (char *) __get_free_page(GFP_USER);
2728
2729        if (!page)
2730                return -ENOMEM;
2731
2732        get_fs_root_and_pwd(current->fs, &root, &pwd);
2733
2734        error = -ENOENT;
2735        write_seqlock(&rename_lock);
2736        if (!d_unlinked(pwd.dentry)) {
2737                unsigned long len;
2738                char *cwd = page + PAGE_SIZE;
2739                int buflen = PAGE_SIZE;
2740
2741                prepend(&cwd, &buflen, "\0", 1);
2742                error = prepend_path(&pwd, &root, &cwd, &buflen);
2743                write_sequnlock(&rename_lock);
2744
2745                if (error < 0)
2746                        goto out;
2747
2748                /* Unreachable from current root */
2749                if (error > 0) {
2750                        error = prepend_unreachable(&cwd, &buflen);
2751                        if (error)
2752                                goto out;
2753                }
2754
2755                error = -ERANGE;
2756                len = PAGE_SIZE + page - cwd;
2757                if (len <= size) {
2758                        error = len;
2759                        if (copy_to_user(buf, cwd, len))
2760                                error = -EFAULT;
2761                }
2762        } else {
2763                write_sequnlock(&rename_lock);
2764        }
2765
2766out:
2767        path_put(&pwd);
2768        path_put(&root);
2769        free_page((unsigned long) page);
2770        return error;
2771}
2772
2773/*
2774 * Test whether new_dentry is a subdirectory of old_dentry.
2775 *
2776 * Trivially implemented using the dcache structure
2777 */
2778
2779/**
2780 * is_subdir - is new dentry a subdirectory of old_dentry
2781 * @new_dentry: new dentry
2782 * @old_dentry: old dentry
2783 *
2784 * Returns 1 if new_dentry is a subdirectory of the parent (at any depth).
2785 * Returns 0 otherwise.
2786 * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
2787 */
2788  
2789int is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)
2790{
2791        int result;
2792        unsigned seq;
2793
2794        if (new_dentry == old_dentry)
2795                return 1;
2796
2797        do {
2798                /* for restarting inner loop in case of seq retry */
2799                seq = read_seqbegin(&rename_lock);
2800                /*
2801                 * Need rcu_readlock to protect against the d_parent trashing
2802                 * due to d_move
2803                 */
2804                rcu_read_lock();
2805                if (d_ancestor(old_dentry, new_dentry))
2806                        result = 1;
2807                else
2808                        result = 0;
2809                rcu_read_unlock();
2810        } while (read_seqretry(&rename_lock, seq));
2811
2812        return result;
2813}
2814
2815int path_is_under(struct path *path1, struct path *path2)
2816{
2817        struct vfsmount *mnt = path1->mnt;
2818        struct dentry *dentry = path1->dentry;
2819        int res;
2820
2821        br_read_lock(vfsmount_lock);
2822        if (mnt != path2->mnt) {
2823                for (;;) {
2824                        if (mnt->mnt_parent == mnt) {
2825                                br_read_unlock(vfsmount_lock);
2826                                return 0;
2827                        }
2828                        if (mnt->mnt_parent == path2->mnt)
2829                                break;
2830                        mnt = mnt->mnt_parent;
2831                }
2832                dentry = mnt->mnt_mountpoint;
2833        }
2834        res = is_subdir(dentry, path2->dentry);
2835        br_read_unlock(vfsmount_lock);
2836        return res;
2837}
2838EXPORT_SYMBOL(path_is_under);
2839
2840void d_genocide(struct dentry *root)
2841{
2842        struct dentry *this_parent;
2843        struct list_head *next;
2844        unsigned seq;
2845        int locked = 0;
2846
2847        seq = read_seqbegin(&rename_lock);
2848again:
2849        this_parent = root;
2850        spin_lock(&this_parent->d_lock);
2851repeat:
2852        next = this_parent->d_subdirs.next;
2853resume:
2854        while (next != &this_parent->d_subdirs) {
2855                struct list_head *tmp = next;
2856                struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
2857                next = tmp->next;
2858
2859                spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
2860                if (d_unhashed(dentry) || !dentry->d_inode) {
2861                        spin_unlock(&dentry->d_lock);
2862                        continue;
2863                }
2864                if (!list_empty(&dentry->d_subdirs)) {
2865                        spin_unlock(&this_parent->d_lock);
2866                        spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
2867                        this_parent = dentry;
2868                        spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
2869                        goto repeat;
2870                }
2871                if (!(dentry->d_flags & DCACHE_GENOCIDE)) {
2872                        dentry->d_flags |= DCACHE_GENOCIDE;
2873                        dentry->d_count--;
2874                }
2875                spin_unlock(&dentry->d_lock);
2876        }
2877        if (this_parent != root) {
2878                struct dentry *child = this_parent;
2879                if (!(this_parent->d_flags & DCACHE_GENOCIDE)) {
2880                        this_parent->d_flags |= DCACHE_GENOCIDE;
2881                        this_parent->d_count--;
2882                }
2883                this_parent = try_to_ascend(this_parent, locked, seq);
2884                if (!this_parent)
2885                        goto rename_retry;
2886                next = child->d_u.d_child.next;
2887                goto resume;
2888        }
2889        spin_unlock(&this_parent->d_lock);
2890        if (!locked && read_seqretry(&rename_lock, seq))
2891                goto rename_retry;
2892        if (locked)
2893                write_sequnlock(&rename_lock);
2894        return;
2895
2896rename_retry:
2897        locked = 1;
2898        write_seqlock(&rename_lock);
2899        goto again;
2900}
2901
2902/**
2903 * find_inode_number - check for dentry with name
2904 * @dir: directory to check
2905 * @name: Name to find.
2906 *
2907 * Check whether a dentry already exists for the given name,
2908 * and return the inode number if it has an inode. Otherwise
2909 * 0 is returned.
2910 *
2911 * This routine is used to post-process directory listings for
2912 * filesystems using synthetic inode numbers, and is necessary
2913 * to keep getcwd() working.
2914 */
2915 
2916ino_t find_inode_number(struct dentry *dir, struct qstr *name)
2917{
2918        struct dentry * dentry;
2919        ino_t ino = 0;
2920
2921        dentry = d_hash_and_lookup(dir, name);
2922        if (dentry) {
2923                if (dentry->d_inode)
2924                        ino = dentry->d_inode->i_ino;
2925                dput(dentry);
2926        }
2927        return ino;
2928}
2929EXPORT_SYMBOL(find_inode_number);
2930
2931static __initdata unsigned long dhash_entries;
2932static int __init set_dhash_entries(char *str)
2933{
2934        if (!str)
2935                return 0;
2936        dhash_entries = simple_strtoul(str, &str, 0);
2937        return 1;
2938}
2939__setup("dhash_entries=", set_dhash_entries);
2940
2941static void __init dcache_init_early(void)
2942{
2943        int loop;
2944
2945        /* If hashes are distributed across NUMA nodes, defer
2946         * hash allocation until vmalloc space is available.
2947         */
2948        if (hashdist)
2949                return;
2950
2951        dentry_hashtable =
2952                alloc_large_system_hash("Dentry cache",
2953                                        sizeof(struct hlist_bl_head),
2954                                        dhash_entries,
2955                                        13,
2956                                        HASH_EARLY,
2957                                        &d_hash_shift,
2958                                        &d_hash_mask,
2959                                        0);
2960
2961        for (loop = 0; loop < (1 << d_hash_shift); loop++)
2962                INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
2963}
2964
2965static void __init dcache_init(void)
2966{
2967        int loop;
2968
2969        /* 
2970         * A constructor could be added for stable state like the lists,
2971         * but it is probably not worth it because of the cache nature
2972         * of the dcache. 
2973         */
2974        dentry_cache = KMEM_CACHE(dentry,
2975                SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD);
2976
2977        /* Hash may have been set up in dcache_init_early */
2978        if (!hashdist)
2979                return;
2980
2981        dentry_hashtable =
2982                alloc_large_system_hash("Dentry cache",
2983                                        sizeof(struct hlist_bl_head),
2984                                        dhash_entries,
2985                                        13,
2986                                        0,
2987                                        &d_hash_shift,
2988                                        &d_hash_mask,
2989                                        0);
2990
2991        for (loop = 0; loop < (1 << d_hash_shift); loop++)
2992                INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
2993}
2994
2995/* SLAB cache for __getname() consumers */
2996struct kmem_cache *names_cachep __read_mostly;
2997EXPORT_SYMBOL(names_cachep);
2998
2999EXPORT_SYMBOL(d_genocide);
3000
3001void __init vfs_caches_init_early(void)
3002{
3003        dcache_init_early();
3004        inode_init_early();
3005}
3006
3007void __init vfs_caches_init(unsigned long mempages)
3008{
3009        unsigned long reserve;
3010
3011        /* Base hash sizes on available memory, with a reserve equal to
3012           150% of current kernel size */
3013
3014        reserve = min((mempages - nr_free_pages()) * 3/2, mempages - 1);
3015        mempages -= reserve;
3016
3017        names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
3018                        SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
3019
3020        dcache_init();
3021        inode_init();
3022        files_init(mempages);
3023        mnt_init();
3024        bdev_cache_init();
3025        chrdev_init();
3026}
3027
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