[linux-2.6.git] / fs / inode.c

/*
 * linux/fs/inode.c
 *
 * (C) 1997 Linus Torvalds
 */

#include <linux/config.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/dcache.h>
#include <linux/init.h>
#include <linux/quotaops.h>
#include <linux/slab.h>
#include <linux/writeback.h>
#include <linux/module.h>
#include <linux/backing-dev.h>
#include <linux/wait.h>
#include <linux/hash.h>
#include <linux/swap.h>
#include <linux/security.h>
#include <linux/pagemap.h>
#include <linux/cdev.h>

/*
 * This is needed for the following functions:
 *  - inode_has_buffers
 *  - invalidate_inode_buffers
 *  - fsync_bdev
 *  - invalidate_bdev
 *
 * FIXME: remove all knowledge of the buffer layer from this file
 */
#include <linux/buffer_head.h>

/*
 * New inode.c implementation.
 *
 * This implementation has the basic premise of trying
 * to be extremely low-overhead and SMP-safe, yet be
 * simple enough to be "obviously correct".
 *
 * Famous last words.
 */

/* inode dynamic allocation 1999, Andrea Arcangeli <andrea@suse.de> */

/* #define INODE_PARANOIA 1 */
/* #define INODE_DEBUG 1 */

/*
 * Inode lookup is no longer as critical as it used to be:
 * most of the lookups are going to be through the dcache.
 */
#define I_HASHBITS      i_hash_shift
#define I_HASHMASK      i_hash_mask

static unsigned int i_hash_mask;
static unsigned int i_hash_shift;

/*
 * Each inode can be on two separate lists. One is
 * the hash list of the inode, used for lookups. The
 * other linked list is the "type" list:
 *  "in_use" - valid inode, i_count > 0, i_nlink > 0
 *  "dirty"  - as "in_use" but also dirty
 *  "unused" - valid inode, i_count = 0
 *
 * A "dirty" list is maintained for each super block,
 * allowing for low-overhead inode sync() operations.
 */

LIST_HEAD(inode_in_use);
LIST_HEAD(inode_unused);
static struct hlist_head *inode_hashtable;

/*
 * A simple spinlock to protect the list manipulations.
 *
 * NOTE! You also have to own the lock if you change
 * the i_state of an inode while it is in use..
 */
spinlock_t inode_lock = SPIN_LOCK_UNLOCKED;

/*
 * iprune_sem provides exclusion between the kswapd or try_to_free_pages
 * icache shrinking path, and the umount path.  Without this exclusion,
 * by the time prune_icache calls iput for the inode whose pages it has
 * been invalidating, or by the time it calls clear_inode & destroy_inode
 * from its final dispose_list, the struct super_block they refer to
 * (for inode->i_sb->s_op) may already have been freed and reused.
 */
static DECLARE_MUTEX(iprune_sem);

/*
 * Statistics gathering..
 */
struct inodes_stat_t inodes_stat;

static kmem_cache_t * inode_cachep;

static void prune_icache(int nr_to_scan);


#define INODE_UNUSED_THRESHOLD 15000
#define PRUNE_BATCH_COUNT 32

void try_to_clip_inodes(void)
{
        unsigned long count = 0; 
        /* if there are a LOT of unused inodes in cache, better shrink a few first */
        
        /* check lockless first to not take the lock always here; racing occasionally isn't a big deal */
        if (inodes_stat.nr_unused > INODE_UNUSED_THRESHOLD) {
                spin_lock(&inode_lock);
                if (inodes_stat.nr_unused > INODE_UNUSED_THRESHOLD)
                        count = inodes_stat.nr_unused - INODE_UNUSED_THRESHOLD;
                spin_unlock(&inode_lock);
                if (count)
                        prune_icache(count);
        }
}


static struct inode *alloc_inode(struct super_block *sb)
{
        static struct address_space_operations empty_aops;
        static struct inode_operations empty_iops;
        static struct file_operations empty_fops;
        struct inode *inode;
        
        if (sb->s_op->alloc_inode)
                inode = sb->s_op->alloc_inode(sb);
        else
                inode = (struct inode *) kmem_cache_alloc(inode_cachep, SLAB_KERNEL);

        if (inode) {
                struct address_space * const mapping = &inode->i_data;

                inode->i_sb = sb;
                if (sb->s_flags & MS_TAGXID)
                        inode->i_xid = current->xid;
                else
                        inode->i_xid = 0;       /* maybe xid -1 would be better? */
                // inode->i_dqh = dqhget(sb->s_dqh);
                inode->i_blkbits = sb->s_blocksize_bits;
                inode->i_flags = 0;
                atomic_set(&inode->i_count, 1);
                inode->i_sock = 0;
                inode->i_op = &empty_iops;
                inode->i_fop = &empty_fops;
                inode->i_nlink = 1;
                atomic_set(&inode->i_writecount, 0);
                inode->i_size = 0;
                inode->i_blocks = 0;
                inode->i_bytes = 0;
                inode->i_generation = 0;
#ifdef CONFIG_QUOTA
                memset(&inode->i_dquot, 0, sizeof(inode->i_dquot));
#endif
                inode->i_pipe = NULL;
                inode->i_bdev = NULL;
                inode->i_cdev = NULL;
                inode->i_rdev = 0;
                // inode->i_xid = 0;    /* maybe not too wise ... */
                inode->i_security = NULL;
                inode->dirtied_when = 0;
                if (security_inode_alloc(inode)) {
                        if (inode->i_sb->s_op->destroy_inode)
                                inode->i_sb->s_op->destroy_inode(inode);
                        else
                                kmem_cache_free(inode_cachep, (inode));
                        return NULL;
                }

                mapping->a_ops = &empty_aops;
                mapping->host = inode;
                mapping->flags = 0;
                mapping_set_gfp_mask(mapping, GFP_HIGHUSER);
                mapping->assoc_mapping = NULL;
                mapping->backing_dev_info = &default_backing_dev_info;

                /*
                 * If the block_device provides a backing_dev_info for client
                 * inodes then use that.  Otherwise the inode share the bdev's
                 * backing_dev_info.
                 */
                if (sb->s_bdev) {
                        struct backing_dev_info *bdi;

                        bdi = sb->s_bdev->bd_inode_backing_dev_info;
                        if (!bdi)
                                bdi = sb->s_bdev->bd_inode->i_mapping->backing_dev_info;
                        mapping->backing_dev_info = bdi;
                }
                memset(&inode->u, 0, sizeof(inode->u));
                inode->i_mapping = mapping;
        }
        return inode;
}

void destroy_inode(struct inode *inode) 
{
        if (inode_has_buffers(inode))
                BUG();
        security_inode_free(inode);
        if (inode->i_sb->s_op->destroy_inode)
                inode->i_sb->s_op->destroy_inode(inode);
        else
                kmem_cache_free(inode_cachep, (inode));
}


/*
 * These are initializations that only need to be done
 * once, because the fields are idempotent across use
 * of the inode, so let the slab aware of that.
 */
void inode_init_once(struct inode *inode)
{
        memset(inode, 0, sizeof(*inode));
        INIT_HLIST_NODE(&inode->i_hash);
        INIT_LIST_HEAD(&inode->i_dentry);
        INIT_LIST_HEAD(&inode->i_devices);
        sema_init(&inode->i_sem, 1);
        init_rwsem(&inode->i_alloc_sem);
        INIT_RADIX_TREE(&inode->i_data.page_tree, GFP_ATOMIC);
        spin_lock_init(&inode->i_data.tree_lock);
        spin_lock_init(&inode->i_data.i_mmap_lock);
        atomic_set(&inode->i_data.truncate_count, 0);
        INIT_LIST_HEAD(&inode->i_data.private_list);
        spin_lock_init(&inode->i_data.private_lock);
        INIT_PRIO_TREE_ROOT(&inode->i_data.i_mmap);
        INIT_LIST_HEAD(&inode->i_data.i_mmap_nonlinear);
        spin_lock_init(&inode->i_lock);
        i_size_ordered_init(inode);
}

EXPORT_SYMBOL(inode_init_once);

static void init_once(void * foo, kmem_cache_t * cachep, unsigned long flags)
{
        struct inode * inode = (struct inode *) foo;

        if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
            SLAB_CTOR_CONSTRUCTOR)
                inode_init_once(inode);
}

/*
 * inode_lock must be held
 */
void __iget(struct inode * inode)
{
        if (atomic_read(&inode->i_count)) {
                atomic_inc(&inode->i_count);
                return;
        }
        atomic_inc(&inode->i_count);
        if (!(inode->i_state & (I_DIRTY|I_LOCK)))
                list_move(&inode->i_list, &inode_in_use);
        inodes_stat.nr_unused--;
}

/**
 * clear_inode - clear an inode
 * @inode: inode to clear
 *
 * This is called by the filesystem to tell us
 * that the inode is no longer useful. We just
 * terminate it with extreme prejudice.
 */
void clear_inode(struct inode *inode)
{
        invalidate_inode_buffers(inode);
       
        if (inode->i_data.nrpages)
                BUG();
        if (!(inode->i_state & I_FREEING))
                BUG();
        if (inode->i_state & I_CLEAR)
                BUG();
        wait_on_inode(inode);
        DQUOT_DROP(inode);
        if (inode->i_sb && inode->i_sb->s_op->clear_inode)
                inode->i_sb->s_op->clear_inode(inode);
        if (inode->i_bdev)
                bd_forget(inode);
        if (inode->i_cdev)
                cd_forget(inode);
        inode->i_state = I_CLEAR;
}

EXPORT_SYMBOL(clear_inode);

/*
 * dispose_list - dispose of the contents of a local list
 * @head: the head of the list to free
 *
 * Dispose-list gets a local list with local inodes in it, so it doesn't
 * need to worry about list corruption and SMP locks.
 */
static void dispose_list(struct list_head *head)
{
        int nr_disposed = 0;

        while (!list_empty(head)) {
                struct inode *inode;

                inode = list_entry(head->next, struct inode, i_list);
                list_del(&inode->i_list);

                if (inode->i_data.nrpages)
                        truncate_inode_pages(&inode->i_data, 0);
                clear_inode(inode);
                destroy_inode(inode);
                nr_disposed++;
        }
        spin_lock(&inode_lock);
        inodes_stat.nr_inodes -= nr_disposed;
        spin_unlock(&inode_lock);
}

/*
 * Invalidate all inodes for a device.
 */
static int invalidate_list(struct list_head *head, struct super_block * sb, struct list_head * dispose)
{
        struct list_head *next;
        int busy = 0, count = 0;

        next = head->next;
        for (;;) {
                struct list_head * tmp = next;
                struct inode * inode;

                next = next->next;
                if (tmp == head)
                        break;
                inode = list_entry(tmp, struct inode, i_list);
                if (inode->i_sb != sb)
                        continue;
                invalidate_inode_buffers(inode);
                if (!atomic_read(&inode->i_count)) {
                        hlist_del_init(&inode->i_hash);
                        list_move(&inode->i_list, dispose);
                        inode->i_state |= I_FREEING;
                        count++;
                        continue;
                }
                busy = 1;
        }
        /* only unused inodes may be cached with i_count zero */
        inodes_stat.nr_unused -= count;
        return busy;
}

/*
 * This is a two-stage process. First we collect all
 * offending inodes onto the throw-away list, and in
 * the second stage we actually dispose of them. This
 * is because we don't want to sleep while messing
 * with the global lists..
 */
 
/**
 *      invalidate_inodes       - discard the inodes on a device
 *      @sb: superblock
 *
 *      Discard all of the inodes for a given superblock. If the discard
 *      fails because there are busy inodes then a non zero value is returned.
 *      If the discard is successful all the inodes have been discarded.
 */
int invalidate_inodes(struct super_block * sb)
{
        int busy;
        LIST_HEAD(throw_away);

        down(&iprune_sem);
        spin_lock(&inode_lock);
        busy = invalidate_list(&inode_in_use, sb, &throw_away);
        busy |= invalidate_list(&inode_unused, sb, &throw_away);
        busy |= invalidate_list(&sb->s_dirty, sb, &throw_away);
        busy |= invalidate_list(&sb->s_io, sb, &throw_away);
        spin_unlock(&inode_lock);

        dispose_list(&throw_away);
        up(&iprune_sem);

        return busy;
}

EXPORT_SYMBOL(invalidate_inodes);
 
int __invalidate_device(struct block_device *bdev, int do_sync)
{
        struct super_block *sb;
        int res;

        if (do_sync)
                fsync_bdev(bdev);

        res = 0;
        sb = get_super(bdev);
        if (sb) {
                /*
                 * no need to lock the super, get_super holds the
                 * read semaphore so the filesystem cannot go away
                 * under us (->put_super runs with the write lock
                 * hold).
                 */
                shrink_dcache_sb(sb);
                res = invalidate_inodes(sb);
                drop_super(sb);
        }
        invalidate_bdev(bdev, 0);
        return res;
}

EXPORT_SYMBOL(__invalidate_device);

static int can_unuse(struct inode *inode)
{
        if (inode->i_state)
                return 0;
        if (inode_has_buffers(inode))
                return 0;
        if (atomic_read(&inode->i_count))
                return 0;
        if (inode->i_data.nrpages)
                return 0;
        return 1;
}

/*
 * Scan `goal' inodes on the unused list for freeable ones. They are moved to
 * a temporary list and then are freed outside inode_lock by dispose_list().
 *
 * Any inodes which are pinned purely because of attached pagecache have their
 * pagecache removed.  We expect the final iput() on that inode to add it to
 * the front of the inode_unused list.  So look for it there and if the
 * inode is still freeable, proceed.  The right inode is found 99.9% of the
 * time in testing on a 4-way.
 *
 * If the inode has metadata buffers attached to mapping->private_list then
 * try to remove them.
 */
static void prune_icache(int nr_to_scan)
{
        LIST_HEAD(freeable);
        int nr_pruned = 0;
        int nr_scanned;
        unsigned long reap = 0;

        down(&iprune_sem);
        spin_lock(&inode_lock);
        for (nr_scanned = 0; nr_scanned < nr_to_scan; nr_scanned++) {
                struct inode *inode;

                if (list_empty(&inode_unused))
                        break;

                inode = list_entry(inode_unused.prev, struct inode, i_list);

                if (inode->i_state || atomic_read(&inode->i_count)) {
                        list_move(&inode->i_list, &inode_unused);
                        continue;
                }
                if (inode_has_buffers(inode) || inode->i_data.nrpages) {
                        __iget(inode);
                        spin_unlock(&inode_lock);
                        if (remove_inode_buffers(inode))
                                reap += invalidate_inode_pages(&inode->i_data);
                        iput(inode);
                        spin_lock(&inode_lock);

                        if (inode != list_entry(inode_unused.next,
                                                struct inode, i_list))
                                continue;       /* wrong inode or list_empty */
                        if (!can_unuse(inode))
                                continue;
                }
                hlist_del_init(&inode->i_hash);
                list_move(&inode->i_list, &freeable);
                inode->i_state |= I_FREEING;
                nr_pruned++;
        }
        inodes_stat.nr_unused -= nr_pruned;
        spin_unlock(&inode_lock);

        dispose_list(&freeable);
        up(&iprune_sem);

        if (current_is_kswapd())
                mod_page_state(kswapd_inodesteal, reap);
        else
                mod_page_state(pginodesteal, reap);
}

/*
 * shrink_icache_memory() will attempt to reclaim some unused inodes.  Here,
 * "unused" means that no dentries are referring to the inodes: the files are
 * not open and the dcache references to those inodes have already been
 * reclaimed.
 *
 * This function is passed the number of inodes to scan, and it returns the
 * total number of remaining possibly-reclaimable inodes.
 */
static int shrink_icache_memory(int nr, unsigned int gfp_mask)
{
        if (nr) {
                /*
                 * Nasty deadlock avoidance.  We may hold various FS locks,
                 * and we don't want to recurse into the FS that called us
                 * in clear_inode() and friends..
                 */
                if (gfp_mask & __GFP_FS)
                        prune_icache(nr);
        }
        return inodes_stat.nr_unused;
}

static void __wait_on_freeing_inode(struct inode *inode);
/*
 * Called with the inode lock held.
 * NOTE: we are not increasing the inode-refcount, you must call __iget()
 * by hand after calling find_inode now! This simplifies iunique and won't
 * add any additional branch in the common code.
 */
static struct inode * find_inode(struct super_block * sb, struct hlist_head *head, int (*test)(struct inode *, void *), void *data)
{
        struct hlist_node *node;
        struct inode * inode = NULL;

repeat:
        hlist_for_each (node, head) { 
                inode = hlist_entry(node, struct inode, i_hash);
                if (inode->i_sb != sb)
                        continue;
                if (!test(inode, data))
                        continue;
                if (inode->i_state & (I_FREEING|I_CLEAR)) {
                        __wait_on_freeing_inode(inode);
                        goto repeat;
                }
                break;
        }
        return node ? inode : NULL;
}

/*
 * find_inode_fast is the fast path version of find_inode, see the comment at
 * iget_locked for details.
 */
static struct inode * find_inode_fast(struct super_block * sb, struct hlist_head *head, unsigned long ino)
{
        struct hlist_node *node;
        struct inode * inode = NULL;

repeat:
        hlist_for_each (node, head) {
                inode = hlist_entry(node, struct inode, i_hash);
                if (inode->i_ino != ino)
                        continue;
                if (inode->i_sb != sb)
                        continue;
                if (inode->i_state & (I_FREEING|I_CLEAR)) {
                        __wait_on_freeing_inode(inode);
                        goto repeat;
                }
                break;
        }
        return node ? inode : NULL;
}

/**
 *      new_inode       - obtain an inode
 *      @sb: superblock
 *
 *      Allocates a new inode for given superblock.
 */
struct inode *new_inode(struct super_block *sb)
{
        static unsigned long last_ino;
        struct inode * inode;

        spin_lock_prefetch(&inode_lock);
        
        inode = alloc_inode(sb);
        if (inode) {
                spin_lock(&inode_lock);
                inodes_stat.nr_inodes++;
                list_add(&inode->i_list, &inode_in_use);
                inode->i_ino = ++last_ino;
                inode->i_state = 0;
                spin_unlock(&inode_lock);
        }
        return inode;
}

EXPORT_SYMBOL(new_inode);

void unlock_new_inode(struct inode *inode)
{
        /*
         * This is special!  We do not need the spinlock
         * when clearing I_LOCK, because we're guaranteed
         * that nobody else tries to do anything about the
         * state of the inode when it is locked, as we
         * just created it (so there can be no old holders
         * that haven't tested I_LOCK).
         */
        inode->i_state &= ~(I_LOCK|I_NEW);
        wake_up_inode(inode);
}

EXPORT_SYMBOL(unlock_new_inode);

/*
 * This is called without the inode lock held.. Be careful.
 *
 * We no longer cache the sb_flags in i_flags - see fs.h
 *      -- rmk@arm.uk.linux.org
 */
static struct inode * get_new_inode(struct super_block *sb, struct hlist_head *head, int (*test)(struct inode *, void *), int (*set)(struct inode *, void *), void *data)
{
        struct inode * inode;

        inode = alloc_inode(sb);
        if (inode) {
                struct inode * old;

                spin_lock(&inode_lock);
                /* We released the lock, so.. */
                old = find_inode(sb, head, test, data);
                if (!old) {
                        if (set(inode, data))
                                goto set_failed;

                        inodes_stat.nr_inodes++;
                        list_add(&inode->i_list, &inode_in_use);
                        hlist_add_head(&inode->i_hash, head);
                        inode->i_state = I_LOCK|I_NEW;
                        spin_unlock(&inode_lock);

                        /* Return the locked inode with I_NEW set, the
                         * caller is responsible for filling in the contents
                         */
                        return inode;
                }

                /*
                 * Uhhuh, somebody else created the same inode under
                 * us. Use the old inode instead of the one we just
                 * allocated.
                 */
                __iget(old);
                spin_unlock(&inode_lock);
                destroy_inode(inode);
                inode = old;
                wait_on_inode(inode);
        }
        return inode;

set_failed:
        spin_unlock(&inode_lock);
        destroy_inode(inode);
        return NULL;
}

/*
 * get_new_inode_fast is the fast path version of get_new_inode, see the
 * comment at iget_locked for details.
 */
static struct inode * get_new_inode_fast(struct super_block *sb, struct hlist_head *head, unsigned long ino)
{
        struct inode * inode;

        inode = alloc_inode(sb);
        if (inode) {
                struct inode * old;

                spin_lock(&inode_lock);
                /* We released the lock, so.. */
                old = find_inode_fast(sb, head, ino);
                if (!old) {
                        inode->i_ino = ino;
                        inodes_stat.nr_inodes++;
                        list_add(&inode->i_list, &inode_in_use);
                        hlist_add_head(&inode->i_hash, head);
                        inode->i_state = I_LOCK|I_NEW;
                        spin_unlock(&inode_lock);

                        /* Return the locked inode with I_NEW set, the
                         * caller is responsible for filling in the contents
                         */
                        return inode;
                }

                /*
                 * Uhhuh, somebody else created the same inode under
                 * us. Use the old inode instead of the one we just
                 * allocated.
                 */
                __iget(old);
                spin_unlock(&inode_lock);
                destroy_inode(inode);
                inode = old;
                wait_on_inode(inode);
        }
        return inode;
}

static inline unsigned long hash(struct super_block *sb, unsigned long hashval)
{
        unsigned long tmp;

        tmp = (hashval * (unsigned long)sb) ^ (GOLDEN_RATIO_PRIME + hashval) /
                        L1_CACHE_BYTES;
        tmp = tmp ^ ((tmp ^ GOLDEN_RATIO_PRIME) >> I_HASHBITS);
        return tmp & I_HASHMASK;
}

/**
 *      iunique - get a unique inode number
 *      @sb: superblock
 *      @max_reserved: highest reserved inode number
 *
 *      Obtain an inode number that is unique on the system for a given
 *      superblock. This is used by file systems that have no natural
 *      permanent inode numbering system. An inode number is returned that
 *      is higher than the reserved limit but unique.
 *
 *      BUGS:
 *      With a large number of inodes live on the file system this function
 *      currently becomes quite slow.
 */
ino_t iunique(struct super_block *sb, ino_t max_reserved)
{
        static ino_t counter;
        struct inode *inode;
        struct hlist_head * head;
        ino_t res;
        spin_lock(&inode_lock);
retry:
        if (counter > max_reserved) {
                head = inode_hashtable + hash(sb,counter);
                res = counter++;
                inode = find_inode_fast(sb, head, res);
                if (!inode) {
                        spin_unlock(&inode_lock);
                        return res;
                }
        } else {
                counter = max_reserved + 1;
        }
        goto retry;
        
}

EXPORT_SYMBOL(iunique);

struct inode *igrab(struct inode *inode)
{
        spin_lock(&inode_lock);
        if (!(inode->i_state & I_FREEING))
                __iget(inode);
        else
                /*
                 * Handle the case where s_op->clear_inode is not been
                 * called yet, and somebody is calling igrab
                 * while the inode is getting freed.
                 */
                inode = NULL;
        spin_unlock(&inode_lock);
        return inode;
}

EXPORT_SYMBOL(igrab);

/**
 * ifind - internal function, you want ilookup5() or iget5().
 * @sb:         super block of file system to search
 * @head:       the head of the list to search
 * @test:       callback used for comparisons between inodes
 * @data:       opaque data pointer to pass to @test
 *
 * ifind() searches for the inode specified by @data in the inode
 * cache. This is a generalized version of ifind_fast() for file systems where
 * the inode number is not sufficient for unique identification of an inode.
 *
 * If the inode is in the cache, the inode is returned with an incremented
 * reference count.
 *
 * Otherwise NULL is returned.
 *
 * Note, @test is called with the inode_lock held, so can't sleep.
 */
static inline struct inode *ifind(struct super_block *sb,
                struct hlist_head *head, int (*test)(struct inode *, void *),
                void *data)
{
        struct inode *inode;

        spin_lock(&inode_lock);
        inode = find_inode(sb, head, test, data);
        if (inode) {
                __iget(inode);
                spin_unlock(&inode_lock);
                wait_on_inode(inode);
                return inode;
        }
        spin_unlock(&inode_lock);
        return NULL;
}

/**
 * ifind_fast - internal function, you want ilookup() or iget().
 * @sb:         super block of file system to search
 * @head:       head of the list to search
 * @ino:        inode number to search for
 *
 * ifind_fast() searches for the inode @ino in the inode cache. This is for
 * file systems where the inode number is sufficient for unique identification
 * of an inode.
 *
 * If the inode is in the cache, the inode is returned with an incremented
 * reference count.
 *
 * Otherwise NULL is returned.
 */
static inline struct inode *ifind_fast(struct super_block *sb,
                struct hlist_head *head, unsigned long ino)
{
        struct inode *inode;

        spin_lock(&inode_lock);
        inode = find_inode_fast(sb, head, ino);
        if (inode) {
                __iget(inode);
                spin_unlock(&inode_lock);
                wait_on_inode(inode);
                return inode;
        }
        spin_unlock(&inode_lock);
        return NULL;
}

/**
 * ilookup5 - search for an inode in the inode cache
 * @sb:         super block of file system to search
 * @hashval:    hash value (usually inode number) to search for
 * @test:       callback used for comparisons between inodes
 * @data:       opaque data pointer to pass to @test
 *
 * ilookup5() uses ifind() to search for the inode specified by @hashval and
 * @data in the inode cache. This is a generalized version of ilookup() for
 * file systems where the inode number is not sufficient for unique
 * identification of an inode.
 *
 * If the inode is in the cache, the inode is returned with an incremented
 * reference count.
 *
 * Otherwise NULL is returned.
 *
 * Note, @test is called with the inode_lock held, so can't sleep.
 */
struct inode *ilookup5(struct super_block *sb, unsigned long hashval,
                int (*test)(struct inode *, void *), void *data)
{
        struct hlist_head *head = inode_hashtable + hash(sb, hashval);

        return ifind(sb, head, test, data);
}

EXPORT_SYMBOL(ilookup5);

/**
 * ilookup - search for an inode in the inode cache
 * @sb:         super block of file system to search
 * @ino:        inode number to search for
 *
 * ilookup() uses ifind_fast() to search for the inode @ino in the inode cache.
 * This is for file systems where the inode number is sufficient for unique
 * identification of an inode.
 *
 * If the inode is in the cache, the inode is returned with an incremented
 * reference count.
 *
 * Otherwise NULL is returned.
 */
struct inode *ilookup(struct super_block *sb, unsigned long ino)
{
        struct hlist_head *head = inode_hashtable + hash(sb, ino);

        return ifind_fast(sb, head, ino);
}

EXPORT_SYMBOL(ilookup);

/**
 * iget5_locked - obtain an inode from a mounted file system
 * @sb:         super block of file system
 * @hashval:    hash value (usually inode number) to get
 * @test:       callback used for comparisons between inodes
 * @set:        callback used to initialize a new struct inode
 * @data:       opaque data pointer to pass to @test and @set
 *
 * This is iget() without the read_inode() portion of get_new_inode().
 *
 * iget5_locked() uses ifind() to search for the inode specified by @hashval
 * and @data in the inode cache and if present it is returned with an increased
 * reference count. This is a generalized version of iget_locked() for file
 * systems where the inode number is not sufficient for unique identification
 * of an inode.
 *
 * If the inode is not in cache, get_new_inode() is called to allocate a new
 * inode and this is returned locked, hashed, and with the I_NEW flag set. The
 * file system gets to fill it in before unlocking it via unlock_new_inode().
 *
 * Note both @test and @set are called with the inode_lock held, so can't sleep.
 */
struct inode *iget5_locked(struct super_block *sb, unsigned long hashval,
                int (*test)(struct inode *, void *),
                int (*set)(struct inode *, void *), void *data)
{
        struct hlist_head *head = inode_hashtable + hash(sb, hashval);
        struct inode *inode;

        inode = ifind(sb, head, test, data);
        if (inode)
                return inode;
        /*
         * get_new_inode() will do the right thing, re-trying the search
         * in case it had to block at any point.
         */
        return get_new_inode(sb, head, test, set, data);
}

EXPORT_SYMBOL(iget5_locked);

/**
 * iget_locked - obtain an inode from a mounted file system
 * @sb:         super block of file system
 * @ino:        inode number to get
 *
 * This is iget() without the read_inode() portion of get_new_inode_fast().
 *
 * iget_locked() uses ifind_fast() to search for the inode specified by @ino in
 * the inode cache and if present it is returned with an increased reference
 * count. This is for file systems where the inode number is sufficient for
 * unique identification of an inode.
 *
 * If the inode is not in cache, get_new_inode_fast() is called to allocate a
 * new inode and this is returned locked, hashed, and with the I_NEW flag set.
 * The file system gets to fill it in before unlocking it via
 * unlock_new_inode().
 */
struct inode *iget_locked(struct super_block *sb, unsigned long ino)
{
        struct hlist_head *head = inode_hashtable + hash(sb, ino);
        struct inode *inode;

        inode = ifind_fast(sb, head, ino);
        if (inode)
                return inode;
        /*
         * get_new_inode_fast() will do the right thing, re-trying the search
         * in case it had to block at any point.
         */
        return get_new_inode_fast(sb, head, ino);
}

EXPORT_SYMBOL(iget_locked);

/**
 *      __insert_inode_hash - hash an inode
 *      @inode: unhashed inode
 *      @hashval: unsigned long value used to locate this object in the
 *              inode_hashtable.
 *
 *      Add an inode to the inode hash for this superblock.
 */
void __insert_inode_hash(struct inode *inode, unsigned long hashval)
{
        struct hlist_head *head = inode_hashtable + hash(inode->i_sb, hashval);
        spin_lock(&inode_lock);
        hlist_add_head(&inode->i_hash, head);
        spin_unlock(&inode_lock);
}

EXPORT_SYMBOL(__insert_inode_hash);

/**
 *      remove_inode_hash - remove an inode from the hash
 *      @inode: inode to unhash
 *
 *      Remove an inode from the superblock.
 */
void remove_inode_hash(struct inode *inode)
{
        spin_lock(&inode_lock);
        hlist_del_init(&inode->i_hash);
        spin_unlock(&inode_lock);
}

EXPORT_SYMBOL(remove_inode_hash);

/*
 * Tell the filesystem that this inode is no longer of any interest and should
 * be completely destroyed.
 *
 * We leave the inode in the inode hash table until *after* the filesystem's
 * ->delete_inode completes.  This ensures that an iget (such as nfsd might
 * instigate) will always find up-to-date information either in the hash or on
 * disk.
 *
 * I_FREEING is set so that no-one will take a new reference to the inode while
 * it is being deleted.
 */
void generic_delete_inode(struct inode *inode)
{
        struct super_operations *op = inode->i_sb->s_op;

        list_del_init(&inode->i_list);
        inode->i_state|=I_FREEING;
        inodes_stat.nr_inodes--;
        spin_unlock(&inode_lock);

        if (inode->i_data.nrpages)
                truncate_inode_pages(&inode->i_data, 0);

        security_inode_delete(inode);

        if (op->delete_inode) {
                void (*delete)(struct inode *) = op->delete_inode;
                if (!is_bad_inode(inode))
                        DQUOT_INIT(inode);
                /* s_op->delete_inode internally recalls clear_inode() */
                delete(inode);
        } else
                clear_inode(inode);
        spin_lock(&inode_lock);
        hlist_del_init(&inode->i_hash);
        spin_unlock(&inode_lock);
        wake_up_inode(inode);
        if (inode->i_state != I_CLEAR)
                BUG();
        destroy_inode(inode);
}

EXPORT_SYMBOL(generic_delete_inode);

static void generic_forget_inode(struct inode *inode)
{
        struct super_block *sb = inode->i_sb;

        if (!hlist_unhashed(&inode->i_hash)) {
                if (!(inode->i_state & (I_DIRTY|I_LOCK)))
                        list_move(&inode->i_list, &inode_unused);
                inodes_stat.nr_unused++;
                spin_unlock(&inode_lock);
                if (!sb || (sb->s_flags & MS_ACTIVE))
                        return;
                write_inode_now(inode, 1);
                spin_lock(&inode_lock);
                inodes_stat.nr_unused--;
                hlist_del_init(&inode->i_hash);
        }
        list_del_init(&inode->i_list);
        inode->i_state|=I_FREEING;
        inodes_stat.nr_inodes--;
        spin_unlock(&inode_lock);
        if (inode->i_data.nrpages)
                truncate_inode_pages(&inode->i_data, 0);
        clear_inode(inode);
        destroy_inode(inode);
}

/*
 * Normal UNIX filesystem behaviour: delete the
 * inode when the usage count drops to zero, and
 * i_nlink is zero.
 */
static void generic_drop_inode(struct inode *inode)
{
        if (!inode->i_nlink)
                generic_delete_inode(inode);
        else
                generic_forget_inode(inode);
}

/*
 * Called when we're dropping the last reference
 * to an inode. 
 *
 * Call the FS "drop()" function, defaulting to
 * the legacy UNIX filesystem behaviour..
 *
 * NOTE! NOTE! NOTE! We're called with the inode lock
 * held, and the drop function is supposed to release
 * the lock!
 */
static inline void iput_final(struct inode *inode)
{
        struct super_operations *op = inode->i_sb->s_op;
        void (*drop)(struct inode *) = generic_drop_inode;

        if (op && op->drop_inode)
                drop = op->drop_inode;
        drop(inode);
}

/**
 *      iput    - put an inode 
 *      @inode: inode to put
 *
 *      Puts an inode, dropping its usage count. If the inode use count hits
 *      zero the inode is also then freed and may be destroyed.
 */
void iput(struct inode *inode)
{
        if (inode) {
                struct super_operations *op = inode->i_sb->s_op;

                if (inode->i_state == I_CLEAR)
                        BUG();

                if (op && op->put_inode)
                        op->put_inode(inode);

                if (atomic_dec_and_lock(&inode->i_count, &inode_lock))
                        iput_final(inode);
        }
}

EXPORT_SYMBOL(iput);

/**
 *      bmap    - find a block number in a file
 *      @inode: inode of file
 *      @block: block to find
 *
 *      Returns the block number on the device holding the inode that
 *      is the disk block number for the block of the file requested.
 *      That is, asked for block 4 of inode 1 the function will return the
 *      disk block relative to the disk start that holds that block of the 
 *      file.
 */
sector_t bmap(struct inode * inode, sector_t block)
{
        sector_t res = 0;
        if (inode->i_mapping->a_ops->bmap)
                res = inode->i_mapping->a_ops->bmap(inode->i_mapping, block);
        return res;
}

EXPORT_SYMBOL(bmap);

/*
 * Return true if the filesystem which backs this inode considers the two
 * passed timespecs to be sufficiently different to warrant flushing the
 * altered time out to disk.
 */
static int inode_times_differ(struct inode *inode,
                        struct timespec *old, struct timespec *new)
{
        if (IS_ONE_SECOND(inode))
                return old->tv_sec != new->tv_sec;
        return !timespec_equal(old, new);
}

/**
 *      update_atime    -       update the access time
 *      @inode: inode accessed
 *
 *      Update the accessed time on an inode and mark it for writeback.
 *      This function automatically handles read only file systems and media,
 *      as well as the "noatime" flag and inode specific "noatime" markers.
 */
void update_atime(struct inode *inode)
{
        struct timespec now;

        if (IS_NOATIME(inode))
                return;
        if (IS_NODIRATIME(inode) && S_ISDIR(inode->i_mode))
                return;
        if (IS_RDONLY(inode))
                return;

        now = current_kernel_time();
        if (inode_times_differ(inode, &inode->i_atime, &now)) {
                inode->i_atime = now;
                mark_inode_dirty_sync(inode);
        } else {
                if (!timespec_equal(&inode->i_atime, &now))
                        inode->i_atime = now;
        }
}

EXPORT_SYMBOL(update_atime);

/**
 *      inode_update_time       -       update mtime and ctime time
 *      @inode: inode accessed
 *      @ctime_too: update ctime too
 *
 *      Update the mtime time on an inode and mark it for writeback.
 *      When ctime_too is specified update the ctime too.
 */

void inode_update_time(struct inode *inode, int ctime_too)
{
        struct timespec now;
        int sync_it = 0;

        if (IS_NOCMTIME(inode))
                return;
        if (IS_RDONLY(inode))
                return;

        now = current_kernel_time();

        if (inode_times_differ(inode, &inode->i_mtime, &now))
                sync_it = 1;
        inode->i_mtime = now;

        if (ctime_too) {
                if (inode_times_differ(inode, &inode->i_ctime, &now))
                        sync_it = 1;
                inode->i_ctime = now;
        }
        if (sync_it)
                mark_inode_dirty_sync(inode);
}

EXPORT_SYMBOL(inode_update_time);

int inode_needs_sync(struct inode *inode)
{
        if (IS_SYNC(inode))
                return 1;
        if (S_ISDIR(inode->i_mode) && IS_DIRSYNC(inode))
                return 1;
        return 0;
}

EXPORT_SYMBOL(inode_needs_sync);

/*
 *      Quota functions that want to walk the inode lists..
 */
#ifdef CONFIG_QUOTA

/* Function back in dquot.c */
int remove_inode_dquot_ref(struct inode *, int, struct list_head *);

void remove_dquot_ref(struct super_block *sb, int type, struct list_head *tofree_head)
{
        struct inode *inode;
        struct list_head *act_head;

        if (!sb->dq_op)
                return; /* nothing to do */
        spin_lock(&inode_lock); /* This lock is for inodes code */
        /* We don't have to lock against quota code - test IS_QUOTAINIT is just for speedup... */
 
        list_for_each(act_head, &inode_in_use) {
                inode = list_entry(act_head, struct inode, i_list);
                if (inode->i_sb == sb && IS_QUOTAINIT(inode))
                        remove_inode_dquot_ref(inode, type, tofree_head);
        }
        list_for_each(act_head, &inode_unused) {
                inode = list_entry(act_head, struct inode, i_list);
                if (inode->i_sb == sb && IS_QUOTAINIT(inode))
                        remove_inode_dquot_ref(inode, type, tofree_head);
        }
        list_for_each(act_head, &sb->s_dirty) {
                inode = list_entry(act_head, struct inode, i_list);
                if (IS_QUOTAINIT(inode))
                        remove_inode_dquot_ref(inode, type, tofree_head);
        }
        list_for_each(act_head, &sb->s_io) {
                inode = list_entry(act_head, struct inode, i_list);
                if (IS_QUOTAINIT(inode))
                        remove_inode_dquot_ref(inode, type, tofree_head);
        }
        spin_unlock(&inode_lock);
}

#endif

/*
 * Hashed waitqueues for wait_on_inode().  The table is pretty small - the
 * kernel doesn't lock many inodes at the same time.
 */
#define I_WAIT_TABLE_ORDER      3
static struct i_wait_queue_head {
        wait_queue_head_t wqh;
} ____cacheline_aligned_in_smp i_wait_queue_heads[1<<I_WAIT_TABLE_ORDER];

/*
 * Return the address of the waitqueue_head to be used for this inode
 */
static wait_queue_head_t *i_waitq_head(struct inode *inode)
{
        return &i_wait_queue_heads[hash_ptr(inode, I_WAIT_TABLE_ORDER)].wqh;
}

void __wait_on_inode(struct inode *inode)
{
        DECLARE_WAITQUEUE(wait, current);
        wait_queue_head_t *wq = i_waitq_head(inode);

        add_wait_queue(wq, &wait);
repeat:
        set_current_state(TASK_UNINTERRUPTIBLE);
        if (inode->i_state & I_LOCK) {
                schedule();
                goto repeat;
        }
        remove_wait_queue(wq, &wait);
        __set_current_state(TASK_RUNNING);
}

/*
 * If we try to find an inode in the inode hash while it is being deleted, we
 * have to wait until the filesystem completes its deletion before reporting
 * that it isn't found.  This is because iget will immediately call
 * ->read_inode, and we want to be sure that evidence of the deletion is found
 * by ->read_inode.
 *
 * This call might return early if an inode which shares the waitq is woken up.
 * This is most easily handled by the caller which will loop around again
 * looking for the inode.
 *
 * This is called with inode_lock held.
 */
static void __wait_on_freeing_inode(struct inode *inode)
{
        DECLARE_WAITQUEUE(wait, current);
        wait_queue_head_t *wq = i_waitq_head(inode);

        add_wait_queue(wq, &wait);
        set_current_state(TASK_UNINTERRUPTIBLE);
        spin_unlock(&inode_lock);
        schedule();
        remove_wait_queue(wq, &wait);
        spin_lock(&inode_lock);
}

void wake_up_inode(struct inode *inode)
{
        wait_queue_head_t *wq = i_waitq_head(inode);

        /*
         * Prevent speculative execution through spin_unlock(&inode_lock);
         */
        smp_mb();
        if (waitqueue_active(wq))
                wake_up_all(wq);
}

static __initdata unsigned long ihash_entries;
static int __init set_ihash_entries(char *str)
{
        if (!str)
                return 0;
        ihash_entries = simple_strtoul(str, &str, 0);
        return 1;
}
__setup("ihash_entries=", set_ihash_entries);

/*
 * Initialize the waitqueues and inode hash table.
 */
void __init inode_init(unsigned long mempages)
{
        struct hlist_head *head;
        unsigned long order;
        unsigned int nr_hash;
        int i;

        for (i = 0; i < ARRAY_SIZE(i_wait_queue_heads); i++)
                init_waitqueue_head(&i_wait_queue_heads[i].wqh);

        if (!ihash_entries)
                ihash_entries = PAGE_SHIFT < 14 ?
                                mempages >> (14 - PAGE_SHIFT) :
                                mempages << (PAGE_SHIFT - 14);

        ihash_entries *= sizeof(struct hlist_head);
        for (order = 0; ((1UL << order) << PAGE_SHIFT) < ihash_entries; order++)
                ;
                
        if (order > 5)
                order = 5;

        do {
                unsigned long tmp;

                nr_hash = (1UL << order) * PAGE_SIZE /
                        sizeof(struct hlist_head);
                i_hash_mask = (nr_hash - 1);

                tmp = nr_hash;
                i_hash_shift = 0;
                while ((tmp >>= 1UL) != 0UL)
                        i_hash_shift++;

                inode_hashtable = (struct hlist_head *)
                        __get_free_pages(GFP_ATOMIC, order);
        } while (inode_hashtable == NULL && --order >= 0);

        printk("Inode-cache hash table entries: %d (order: %ld, %ld bytes)\n",
                        nr_hash, order, (PAGE_SIZE << order));

        if (!inode_hashtable)
                panic("Failed to allocate inode hash table\n");

        head = inode_hashtable;
        i = nr_hash;
        do {
                INIT_HLIST_HEAD(head);
                head++;
                i--;
        } while (i);

        /* inode slab cache */
        inode_cachep = kmem_cache_create("inode_cache", sizeof(struct inode),
                                0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, init_once,
                                NULL);
        set_shrinker(DEFAULT_SEEKS, shrink_icache_memory);
}

void init_special_inode(struct inode *inode, umode_t mode, dev_t rdev)
{
        inode->i_mode = mode;
        if (S_ISCHR(mode)) {
                inode->i_fop = &def_chr_fops;
                inode->i_rdev = rdev;
        } else if (S_ISBLK(mode)) {
                inode->i_fop = &def_blk_fops;
                inode->i_rdev = rdev;
        } else if (S_ISFIFO(mode))
                inode->i_fop = &def_fifo_fops;
        else if (S_ISSOCK(mode))
                inode->i_fop = &bad_sock_fops;
        else
                printk(KERN_DEBUG "init_special_inode: bogus i_mode (%o)\n",
                       mode);
}
EXPORT_SYMBOL(init_special_inode);