/*
 * 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/security.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 list_head *inode_hashtable;
static LIST_HEAD(anon_hash_chain); /* for inodes with NULL i_sb */

/*
 * 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;

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

static kmem_cache_t * inode_cachep;

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_security = NULL;
                if (security_ops->inode_alloc_security(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;
                }
                inode->i_sb = sb;
                inode->i_dev = sb->s_dev;
                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;
                memset(&inode->i_dquot, 0, sizeof(inode->i_dquot));
                inode->i_pipe = NULL;
                inode->i_bdev = NULL;
                inode->i_cdev = NULL;

                mapping->a_ops = &empty_aops;
                mapping->host = inode;
                mapping->gfp_mask = GFP_HIGHUSER;
                mapping->dirtied_when = 0;
                mapping->assoc_mapping = NULL;
                mapping->backing_dev_info = &default_backing_dev_info;
                if (sb->s_bdev)
                        inode->i_data.backing_dev_info = sb->s_bdev->bd_inode->i_mapping->backing_dev_info;
                memset(&inode->u, 0, sizeof(inode->u));
                inode->i_mapping = mapping;
        }
        return inode;
}

static void destroy_inode(struct inode *inode) 
{
        if (inode_has_buffers(inode))
                BUG();
        security_ops->inode_free_security(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_LIST_HEAD(&inode->i_hash);
        INIT_LIST_HEAD(&inode->i_data.clean_pages);
        INIT_LIST_HEAD(&inode->i_data.dirty_pages);
        INIT_LIST_HEAD(&inode->i_data.locked_pages);
        INIT_LIST_HEAD(&inode->i_data.io_pages);
        INIT_LIST_HEAD(&inode->i_dentry);
        INIT_LIST_HEAD(&inode->i_devices);
        sema_init(&inode->i_sem, 1);
        INIT_RADIX_TREE(&inode->i_data.page_tree, GFP_ATOMIC);
        rwlock_init(&inode->i_data.page_lock);
        spin_lock_init(&inode->i_data.i_shared_lock);
        INIT_LIST_HEAD(&inode->i_data.private_list);
        spin_lock_init(&inode->i_data.private_lock);
        INIT_LIST_HEAD(&inode->i_data.i_mmap);
        INIT_LIST_HEAD(&inode->i_data.i_mmap_shared);
}

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_del(&inode->i_list);
                list_add(&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 && inode->i_sb->s_op->clear_inode)
                inode->i_sb->s_op->clear_inode(inode);
        if (inode->i_bdev)
                bd_forget(inode);
        else if (inode->i_cdev) {
                cdput(inode->i_cdev);
                inode->i_cdev = NULL;
        }
        inode->i_state = I_CLEAR;
}

/*
 * 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)
{
        struct list_head * inode_entry;
        struct inode * inode;

        while ((inode_entry = head->next) != head)
        {
                list_del(inode_entry);

                inode = list_entry(inode_entry, struct inode, i_list);
                if (inode->i_data.nrpages)
                        truncate_inode_pages(&inode->i_data, 0);
                clear_inode(inode);
                destroy_inode(inode);
                inodes_stat.nr_inodes--;
        }
}

/*
 * 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)) {
                        list_del_init(&inode->i_hash);
                        list_del(&inode->i_list);
                        list_add(&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);

        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);

        return busy;
}
 
int invalidate_device(kdev_t dev, int do_sync)
{
        struct super_block *sb;
        struct block_device *bdev = bdget(kdev_t_to_nr(dev));
        int res;

        if (!bdev)
                return 0;

        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);
        bdput(bdev);
        return res;
}


/*
 * This is called with the inode lock held. It searches
 * the in-use for freeable inodes, which are moved to a
 * temporary list and then placed on the unused list by
 * dispose_list. 
 *
 * We don't expect to have to call this very often.
 *
 * N.B. The spinlock is released during the call to
 *      dispose_list.
 */
#define CAN_UNUSE(inode) \
        ((((inode)->i_state | (inode)->i_data.nrpages) == 0)  && \
         !inode_has_buffers(inode))
#define INODE(entry)    (list_entry(entry, struct inode, i_list))

void prune_icache(int goal)
{
        LIST_HEAD(list);
        struct list_head *entry, *freeable = &list;
        int count;
        struct inode * inode;

        spin_lock(&inode_lock);

        count = 0;
        entry = inode_unused.prev;
        while (entry != &inode_unused)
        {
                struct list_head *tmp = entry;

                entry = entry->prev;
                inode = INODE(tmp);
                if (inode->i_state & (I_FREEING|I_CLEAR|I_LOCK))
                        continue;
                if (!CAN_UNUSE(inode))
                        continue;
                if (atomic_read(&inode->i_count))
                        continue;
                list_del(tmp);
                list_del_init(&inode->i_hash);
                list_add(tmp, freeable);
                inode->i_state |= I_FREEING;
                count++;
                if (!--goal)
                        break;
        }
        inodes_stat.nr_unused -= count;
        spin_unlock(&inode_lock);

        dispose_list(freeable);
}

/*
 * This is called from kswapd when we think we need some
 * more memory, but aren't really sure how much. So we
 * carefully try to free a _bit_ of our icache, but not
 * too much.
 *
 * Priority:
 *   1 - very urgent: shrink everything
 *  ...
 *   6 - base-level: try to shrink a bit.
 */
int shrink_icache_memory(int priority, int gfp_mask)
{
        int count = 0;

        /*
         * 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))
                return 0;

        count = inodes_stat.nr_unused / priority;

        prune_icache(count);
        kmem_cache_shrink(inode_cachep);
        return 0;
}

/*
 * 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 list_head *head, int (*test)(struct inode *, void *), void *data)
{
        struct list_head *tmp;
        struct inode * inode;

        tmp = head;
        for (;;) {
                tmp = tmp->next;
                inode = NULL;
                if (tmp == head)
                        break;
                inode = list_entry(tmp, struct inode, i_hash);
                if (inode->i_sb != sb)
                        continue;
                if (!test(inode, data))
                        continue;
                break;
        }
        return inode;
}

/*
 * 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 list_head *head, unsigned long ino)
{
        struct list_head *tmp;
        struct inode * inode;

        tmp = head;
        for (;;) {
                tmp = tmp->next;
                inode = NULL;
                if (tmp == head)
                        break;
                inode = list_entry(tmp, struct inode, i_hash);
                if (inode->i_ino != ino)
                        continue;
                if (inode->i_sb != sb)
                        continue;
                break;
        }
        return inode;
}

/**
 *      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;
}

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);
}


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

/* Yeah, I know about quadratic hash. Maybe, later. */

/**
 *      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 = 0;
        struct inode *inode;
        struct list_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;
        
}

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;
}

/*
 * This is iget without the read_inode portion of get_new_inode
 * the filesystem gets back a new locked and hashed inode and gets
 * to fill it in before unlocking it via unlock_new_inode().
 */
struct inode *iget5_locked(struct super_block *sb, unsigned long hashval, int (*test)(struct inode *, void *), int (*set)(struct inode *, void *), void *data)
{
        struct list_head * head = inode_hashtable + hash(sb, hashval);
        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);

        /*
         * 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);
}

/*
 * Because most filesystems are based on 32-bit unique inode numbers some
 * functions are duplicated to keep iget_locked as a fast path. We can avoid
 * unnecessary pointer dereferences and function calls for this specific
 * case. The duplicated functions (find_inode_fast and get_new_inode_fast)
 * have the same pre- and post-conditions as their original counterparts.
 */
struct inode *iget_locked(struct super_block *sb, unsigned long ino)
{
        struct list_head * head = inode_hashtable + hash(sb, 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);

        /*
         * 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(iget5_locked);
EXPORT_SYMBOL(iget_locked);
EXPORT_SYMBOL(unlock_new_inode);

/**
 *      __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. If the inode
 *      has no superblock it is added to a separate anonymous chain.
 */
 
void __insert_inode_hash(struct inode *inode, unsigned long hashval)
{
        struct list_head *head = &anon_hash_chain;
        if (inode->i_sb)
                head = inode_hashtable + hash(inode->i_sb, hashval);
        spin_lock(&inode_lock);
        list_add(&inode->i_hash, head);
        spin_unlock(&inode_lock);
}

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

void generic_delete_inode(struct inode *inode)
{
        struct super_operations *op = inode->i_sb->s_op;

        list_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);

        security_ops->inode_delete(inode);

        if (op && 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);
        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 (!list_empty(&inode->i_hash)) {
                if (!(inode->i_state & (I_DIRTY|I_LOCK))) {
                        list_del(&inode->i_list);
                        list_add(&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--;
                list_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);
        }
}

/**
 *      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.
 */
 
int bmap(struct inode * inode, int block)
{
        int res = 0;
        if (inode->i_mapping->a_ops->bmap)
                res = inode->i_mapping->a_ops->bmap(inode->i_mapping, block);
        return res;
}

/**
 *      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)
{
        if (inode->i_atime == CURRENT_TIME)
                return;
        if (IS_NOATIME(inode))
                return;
        if (IS_NODIRATIME(inode) && S_ISDIR(inode->i_mode))
                return;
        if (IS_RDONLY(inode))
                return;
        inode->i_atime = CURRENT_TIME;
        mark_inode_dirty_sync(inode);
}

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

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

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

        if (!sb->dq_op)
                return; /* nothing to do */
        /* We have to be protected against other CPUs */
        lock_kernel();          /* This lock is for quota code */
        spin_lock(&inode_lock); /* This lock is for inodes code */
 
        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);
        unlock_kernel();

        put_dquot_list(&tofree_head);
}

#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);
        current->state = TASK_RUNNING;
}

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);
}

/*
 * Initialize the waitqueues and inode hash table.
 */
void __init inode_init(unsigned long mempages)
{
        struct list_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);

        mempages >>= (14 - PAGE_SHIFT);
        mempages *= sizeof(struct list_head);
        for (order = 0; ((1UL << order) << PAGE_SHIFT) < mempages; order++)
                ;

        do {
                unsigned long tmp;

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

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

                inode_hashtable = (struct list_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_LIST_HEAD(head);
                head++;
                i--;
        } while (i);

        /* inode slab cache */
        inode_cachep = kmem_cache_create("inode_cache", sizeof(struct inode),
                                         0, SLAB_HWCACHE_ALIGN, init_once,
                                         NULL);
        if (!inode_cachep)
                panic("cannot create inode slab cache");
}