net/tcp/linux-2.6.26/fs/inode.c

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

#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>
#include <linux/bootmem.h>
#include <linux/inotify.h>
#include <linux/mount.h>

/*
 * This is needed for the following functions:
 *  - inode_has_buffers
 *  - invalidate_inode_buffers
 *  - 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 __read_mostly;
static unsigned int i_hash_shift __read_mostly;

/*
 * 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 __read_mostly;

/*
 * 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..
 */
DEFINE_SPINLOCK(inode_lock);

/*
 * iprune_mutex 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 DEFINE_MUTEX(iprune_mutex);

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

static struct kmem_cache * inode_cachep __read_mostly;

static void wake_up_inode(struct inode *inode)
{
    /*
     * Prevent speculative execution through spin_unlock(&inode_lock);
     */
    smp_mb();
    wake_up_bit(&inode->i_state, __I_LOCK);
}

static struct inode *alloc_inode(struct super_block *sb)
{
    static const struct address_space_operations empty_aops;
    static struct inode_operations empty_iops;
    static const 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, GFP_KERNEL);

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

        inode->i_sb = sb;
        inode->i_blkbits = sb->s_blocksize_bits;
        inode->i_flags = 0;
        atomic_set(&inode->i_count, 1);
        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->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;
        }

        spin_lock_init(&inode->i_lock);
        lockdep_set_class(&inode->i_lock, &sb->s_type->i_lock_key);

        mutex_init(&inode->i_mutex);
        lockdep_set_class(&inode->i_mutex, &sb->s_type->i_mutex_key);

        init_rwsem(&inode->i_alloc_sem);
        lockdep_set_class(&inode->i_alloc_sem, &sb->s_type->i_alloc_sem_key);

        mapping->a_ops = &empty_aops;
         mapping->host = inode;
        mapping->flags = 0;
        mapping_set_gfp_mask(mapping, GFP_HIGHUSER_PAGECACHE);
        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;
        }
        inode->i_private = NULL;
        inode->i_mapping = mapping;
    }
    return inode;
}

void destroy_inode(struct inode *inode) 
{
    BUG_ON(inode_has_buffers(inode));
    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);
    INIT_RADIX_TREE(&inode->i_data.page_tree, GFP_ATOMIC);
    rwlock_init(&inode->i_data.tree_lock);
    spin_lock_init(&inode->i_data.i_mmap_lock);
    INIT_LIST_HEAD(&inode->i_data.private_list);
    spin_lock_init(&inode->i_data.private_lock);
    INIT_RAW_PRIO_TREE_ROOT(&inode->i_data.i_mmap);
    INIT_LIST_HEAD(&inode->i_data.i_mmap_nonlinear);
    i_size_ordered_init(inode);
#ifdef CONFIG_INOTIFY
    INIT_LIST_HEAD(&inode->inotify_watches);
    mutex_init(&inode->inotify_mutex);
#endif
}

EXPORT_SYMBOL(inode_init_once);

static void init_once(struct kmem_cache * cachep, void *foo)
{
    struct inode * inode = (struct inode *) foo;

    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_SYNC)))
        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)
{
    might_sleep();
    invalidate_inode_buffers(inode);
       
    BUG_ON(inode->i_data.nrpages);
    BUG_ON(!(inode->i_state & I_FREEING));
    BUG_ON(inode->i_state & I_CLEAR);
    inode_sync_wait(inode);
    DQUOT_DROP(inode);
    if (inode->i_sb->s_op->clear_inode)
        inode->i_sb->s_op->clear_inode(inode);
    if (S_ISBLK(inode->i_mode) && inode->i_bdev)
        bd_forget(inode);
    if (S_ISCHR(inode->i_mode) && 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_first_entry(head, struct inode, i_list);
        list_del(&inode->i_list);

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

        spin_lock(&inode_lock);
        hlist_del_init(&inode->i_hash);
        list_del_init(&inode->i_sb_list);
        spin_unlock(&inode_lock);

        wake_up_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 list_head *dispose)
{
    struct list_head *next;
    int busy = 0, count = 0;

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

        /*
         * We can reschedule here without worrying about the list's
         * consistency because the per-sb list of inodes must not
         * change during umount anymore, and because iprune_mutex keeps
         * shrink_icache_memory() away.
         */
        cond_resched_lock(&inode_lock);

        next = next->next;
        if (tmp == head)
            break;
        inode = list_entry(tmp, struct inode, i_sb_list);
        invalidate_inode_buffers(inode);
        if (!atomic_read(&inode->i_count)) {
            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;
}

/**
 *    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);

    mutex_lock(&iprune_mutex);
    spin_lock(&inode_lock);
    inotify_unmount_inodes(&sb->s_inodes);
    busy = invalidate_list(&sb->s_inodes, &throw_away);
    spin_unlock(&inode_lock);

    dispose_list(&throw_away);
    mutex_unlock(&iprune_mutex);

    return busy;
}

EXPORT_SYMBOL(invalidate_inodes);

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;

    mutex_lock(&iprune_mutex);
    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_mapping_pages(&inode->i_data,
                                0, -1);
            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;
        }
        list_move(&inode->i_list, &freeable);
        inode->i_state |= I_FREEING;
        nr_pruned++;
    }
    inodes_stat.nr_unused -= nr_pruned;
    if (current_is_kswapd())
        __count_vm_events(KSWAPD_INODESTEAL, reap);
    else
        __count_vm_events(PGINODESTEAL, reap);
    spin_unlock(&inode_lock);

    dispose_list(&freeable);
    mutex_unlock(&iprune_mutex);
}

/*
 * 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, gfp_t 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))
            return -1;
        prune_icache(nr);
    }
    return (inodes_stat.nr_unused / 100) * sysctl_vfs_cache_pressure;
}

static struct shrinker icache_shrinker = {
    .shrink = shrink_icache_memory,
    .seeks = DEFAULT_SEEKS,
};

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_entry(inode, node, head, i_hash) {
        if (inode->i_sb != sb)
            continue;
        if (!test(inode, data))
            continue;
        if (inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE)) {
            __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_entry(inode, node, head, i_hash) {
        if (inode->i_ino != ino)
            continue;
        if (inode->i_sb != sb)
            continue;
        if (inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE)) {
            __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. The default gfp_mask
 *    for allocations related to inode->i_mapping is GFP_HIGHUSER_PAGECACHE.
 *    If HIGHMEM pages are unsuitable or it is known that pages allocated
 *    for the page cache are not reclaimable or migratable,
 *    mapping_set_gfp_mask() must be called with suitable flags on the
 *    newly created inode's mapping
 *
 */
struct inode *new_inode(struct super_block *sb)
{
    /*
     * On a 32bit, non LFS stat() call, glibc will generate an EOVERFLOW
     * error if st_ino won't fit in target struct field. Use 32bit counter
     * here to attempt to avoid that.
     */
    static unsigned int 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);
        list_add(&inode->i_sb_list, &sb->s_inodes);
        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)
{
#ifdef CONFIG_DEBUG_LOCK_ALLOC
    if (inode->i_mode & S_IFDIR) {
        struct file_system_type *type = inode->i_sb->s_type;

        /*
         * ensure nobody is actually holding i_mutex
         */
        mutex_destroy(&inode->i_mutex);
        mutex_init(&inode->i_mutex);
        lockdep_set_class(&inode->i_mutex, &type->i_mutex_dir_key);
    }
#endif
    /*
     * 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);
            list_add(&inode->i_sb_list, &sb->s_inodes);
            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);
            list_add(&inode->i_sb_list, &sb->s_inodes);
            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 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)
{
    /*
     * On a 32bit, non LFS stat() call, glibc will generate an EOVERFLOW
     * error if st_ino won't fit in target struct field. Use 32bit counter
     * here to attempt to avoid that.
     */
    static unsigned int counter;
    struct inode *inode;
    struct hlist_head *head;
    ino_t res;

    spin_lock(&inode_lock);
    do {
        if (counter <= max_reserved)
            counter = max_reserved + 1;
        res = counter++;
        head = inode_hashtable + hash(sb, res);
        inode = find_inode_fast(sb, head, res);
    } while (inode != NULL);
    spin_unlock(&inode_lock);

    return res;
}
EXPORT_SYMBOL(iunique);

struct inode *igrab(struct inode *inode)
{
    spin_lock(&inode_lock);
    if (!(inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE)))
        __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
 * @wait:    if true wait for the inode to be unlocked, if false do not
 *
 * 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 struct inode *ifind(struct super_block *sb,
        struct hlist_head *head, int (*test)(struct inode *, void *),
        void *data, const int wait)
{
    struct inode *inode;

    spin_lock(&inode_lock);
    inode = find_inode(sb, head, test, data);
    if (inode) {
        __iget(inode);
        spin_unlock(&inode_lock);
        if (likely(wait))
            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 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_nowait - 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.  Note, the inode lock is not waited upon so you have to be
 * very careful what you do with the returned inode.  You probably should be
 * using ilookup5() instead.
 *
 * Otherwise NULL is returned.
 *
 * Note, @test is called with the inode_lock held, so can't sleep.
 */
struct inode *ilookup5_nowait(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, 0);
}

EXPORT_SYMBOL(ilookup5_nowait);

/**
 * 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 lock is waited upon and 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, 1);
}

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
 *
 * 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, 1);
    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
 *
 * 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)
{
    const struct super_operations *op = inode->i_sb->s_op;

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

    security_inode_delete(inode);

    if (op->delete_inode) {
        void (*delete)(struct inode *) = op->delete_inode;
        if (!is_bad_inode(inode))
            DQUOT_INIT(inode);
        /* Filesystems implementing their own
         * s_op->delete_inode are required to call
         * truncate_inode_pages and clear_inode()
         * internally */
        delete(inode);
    } else {
        truncate_inode_pages(&inode->i_data, 0);
        clear_inode(inode);
    }
    spin_lock(&inode_lock);
    hlist_del_init(&inode->i_hash);
    spin_unlock(&inode_lock);
    wake_up_inode(inode);
    BUG_ON(inode->i_state != I_CLEAR);
    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_SYNC)))
            list_move(&inode->i_list, &inode_unused);
        inodes_stat.nr_unused++;
        if (sb->s_flags & MS_ACTIVE) {
            spin_unlock(&inode_lock);
            return;
        }
        inode->i_state |= I_WILL_FREE;
        spin_unlock(&inode_lock);
        write_inode_now(inode, 1);
        spin_lock(&inode_lock);
        inode->i_state &= ~I_WILL_FREE;
        inodes_stat.nr_unused--;
        hlist_del_init(&inode->i_hash);
    }
    list_del_init(&inode->i_list);
    list_del_init(&inode->i_sb_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);
    wake_up_inode(inode);
    destroy_inode(inode);
}

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

EXPORT_SYMBOL_GPL(generic_drop_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)
{
    const 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 then freed and may also be destroyed.
 *
 *    Consequently, iput() can sleep.
 */
void iput(struct inode *inode)
{
    if (inode) {
        BUG_ON(inode->i_state == I_CLEAR);

        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);

/**
 *    touch_atime    -    update the access time
 *    @mnt: mount the inode is accessed on
 *    @dentry: dentry 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 touch_atime(struct vfsmount *mnt, struct dentry *dentry)
{
    struct inode *inode = dentry->d_inode;
    struct timespec now;

    if (mnt_want_write(mnt))
        return;
    if (inode->i_flags & S_NOATIME)
        goto out;
    if (IS_NOATIME(inode))
        goto out;
    if ((inode->i_sb->s_flags & MS_NODIRATIME) && S_ISDIR(inode->i_mode))
        goto out;

    if (mnt->mnt_flags & MNT_NOATIME)
        goto out;
    if ((mnt->mnt_flags & MNT_NODIRATIME) && S_ISDIR(inode->i_mode))
        goto out;
    if (mnt->mnt_flags & MNT_RELATIME) {
        /*
         * With relative atime, only update atime if the previous
         * atime is earlier than either the ctime or mtime.
         */
        if (timespec_compare(&inode->i_mtime, &inode->i_atime) < 0 &&
            timespec_compare(&inode->i_ctime, &inode->i_atime) < 0)
            goto out;
    }

    now = current_fs_time(inode->i_sb);
    if (timespec_equal(&inode->i_atime, &now))
        goto out;

    inode->i_atime = now;
    mark_inode_dirty_sync(inode);
out:
    mnt_drop_write(mnt);
}
EXPORT_SYMBOL(touch_atime);

/**
 *    file_update_time    -    update mtime and ctime time
 *    @file: file accessed
 *
 *    Update the mtime and ctime members of an inode and mark the inode
 *    for writeback.  Note that this function is meant exclusively for
 *    usage in the file write path of filesystems, and filesystems may
 *    choose to explicitly ignore update via this function with the
 *    S_NOCTIME inode flag, e.g. for network filesystem where these
 *    timestamps are handled by the server.
 */

void file_update_time(struct file *file)
{
    struct inode *inode = file->f_path.dentry->d_inode;
    struct timespec now;
    int sync_it = 0;
    int err;

    if (IS_NOCMTIME(inode))
        return;

    err = mnt_want_write(file->f_path.mnt);
    if (err)
        return;

    now = current_fs_time(inode->i_sb);
    if (!timespec_equal(&inode->i_mtime, &now)) {
        inode->i_mtime = now;
        sync_it = 1;
    }

    if (!timespec_equal(&inode->i_ctime, &now)) {
        inode->i_ctime = now;
        sync_it = 1;
    }

    if (IS_I_VERSION(inode)) {
        inode_inc_iversion(inode);
        sync_it = 1;
    }

    if (sync_it)
        mark_inode_dirty_sync(inode);
    mnt_drop_write(file->f_path.mnt);
}

EXPORT_SYMBOL(file_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);

int inode_wait(void *word)
{
    schedule();
    return 0;
}

/*
 * 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 function waits
 * until the deletion _might_ have completed.  Callers are responsible
 * to recheck inode state.
 *
 * It doesn't matter if I_LOCK is not set initially, a call to
 * wake_up_inode() after removing from the hash list will DTRT.
 *
 * This is called with inode_lock held.
 */
static void __wait_on_freeing_inode(struct inode *inode)
{
    wait_queue_head_t *wq;
    DEFINE_WAIT_BIT(wait, &inode->i_state, __I_LOCK);
    wq = bit_waitqueue(&inode->i_state, __I_LOCK);
    prepare_to_wait(wq, &wait.wait, TASK_UNINTERRUPTIBLE);
    spin_unlock(&inode_lock);
    schedule();
    finish_wait(wq, &wait.wait);
    spin_lock(&inode_lock);
}

/*
 * We rarely want to lock two inodes that do not have a parent/child
 * relationship (such as directory, child inode) simultaneously. The
 * vast majority of file systems should be able to get along fine
 * without this. Do not use these functions except as a last resort.
 */
void inode_double_lock(struct inode *inode1, struct inode *inode2)
{
    if (inode1 == NULL || inode2 == NULL || inode1 == inode2) {
        if (inode1)
            mutex_lock(&inode1->i_mutex);
        else if (inode2)
            mutex_lock(&inode2->i_mutex);
        return;
    }

    if (inode1 < inode2) {
        mutex_lock_nested(&inode1->i_mutex, I_MUTEX_PARENT);
        mutex_lock_nested(&inode2->i_mutex, I_MUTEX_CHILD);
    } else {
        mutex_lock_nested(&inode2->i_mutex, I_MUTEX_PARENT);
        mutex_lock_nested(&inode1->i_mutex, I_MUTEX_CHILD);
    }
}
EXPORT_SYMBOL(inode_double_lock);

void inode_double_unlock(struct inode *inode1, struct inode *inode2)
{
    if (inode1)
        mutex_unlock(&inode1->i_mutex);

    if (inode2 && inode2 != inode1)
        mutex_unlock(&inode2->i_mutex);
}
EXPORT_SYMBOL(inode_double_unlock);

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_early(void)
{
    int loop;

    /* If hashes are distributed across NUMA nodes, defer
     * hash allocation until vmalloc space is available.
     */
    if (hashdist)
        return;

    inode_hashtable =
        alloc_large_system_hash("Inode-cache",
                    sizeof(struct hlist_head),
                    ihash_entries,
                    14,
                    HASH_EARLY,
                    &i_hash_shift,
                    &i_hash_mask,
                    0);

    for (loop = 0; loop < (1 << i_hash_shift); loop++)
        INIT_HLIST_HEAD(&inode_hashtable[loop]);
}

void __init inode_init(void)
{
    int loop;

    /* inode slab cache */
    inode_cachep = kmem_cache_create("inode_cache",
                     sizeof(struct inode),
                     0,
                     (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
                     SLAB_MEM_SPREAD),
                     init_once);
    register_shrinker(&icache_shrinker);

    /* Hash may have been set up in inode_init_early */
    if (!hashdist)
        return;

    inode_hashtable =
        alloc_large_system_hash("Inode-cache",
                    sizeof(struct hlist_head),
                    ihash_entries,
                    14,
                    0,
                    &i_hash_shift,
                    &i_hash_mask,
                    0);

    for (loop = 0; loop < (1 << i_hash_shift); loop++)
        INIT_HLIST_HEAD(&inode_hashtable[loop]);
}

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);