inode: Make unused inode LRU per superblock

[linux-3.10.git] / fs / inode.c

/*
 * (C) 1997 Linus Torvalds
 * (C) 1999 Andrea Arcangeli <andrea@suse.de> (dynamic inode allocation)
 */
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/dcache.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/writeback.h>
#include <linux/module.h>
#include <linux/backing-dev.h>
#include <linux/wait.h>
#include <linux/rwsem.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/fsnotify.h>
#include <linux/mount.h>
#include <linux/async.h>
#include <linux/posix_acl.h>
#include <linux/prefetch.h>
#include <linux/ima.h>
#include <linux/cred.h>
#include <linux/buffer_head.h> /* for inode_has_buffers */
#include "internal.h"

/*
 * Inode locking rules:
 *
 * inode->i_lock protects:
 *   inode->i_state, inode->i_hash, __iget()
 * inode_lru_lock protects:
 *   inode->i_sb->s_inode_lru, inode->i_lru
 * inode_sb_list_lock protects:
 *   sb->s_inodes, inode->i_sb_list
 * inode_wb_list_lock protects:
 *   bdi->wb.b_{dirty,io,more_io}, inode->i_wb_list
 * inode_hash_lock protects:
 *   inode_hashtable, inode->i_hash
 *
 * Lock ordering:
 *
 * inode_sb_list_lock
 *   inode->i_lock
 *     inode_lru_lock
 *
 * inode_wb_list_lock
 *   inode->i_lock
 *
 * inode_hash_lock
 *   inode_sb_list_lock
 *   inode->i_lock
 *
 * iunique_lock
 *   inode_hash_lock
 */

static unsigned int i_hash_mask __read_mostly;
static unsigned int i_hash_shift __read_mostly;
static struct hlist_head *inode_hashtable __read_mostly;
static __cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_hash_lock);

static DEFINE_SPINLOCK(inode_lru_lock);

__cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_sb_list_lock);
__cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_wb_list_lock);

/*
 * iprune_sem provides exclusion between the icache shrinking and the
 * umount path.
 *
 * We don't actually need it to protect anything in the umount path,
 * but only need to cycle through it to make sure any inode that
 * prune_icache took off the LRU list has been fully torn down by the
 * time we are past evict_inodes.
 */
static DECLARE_RWSEM(iprune_sem);

/*
 * Empty aops. Can be used for the cases where the user does not
 * define any of the address_space operations.
 */
const struct address_space_operations empty_aops = {
};
EXPORT_SYMBOL(empty_aops);

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

static DEFINE_PER_CPU(unsigned int, nr_inodes);
static DEFINE_PER_CPU(unsigned int, nr_unused);

static struct kmem_cache *inode_cachep __read_mostly;

static int get_nr_inodes(void)
{
        int i;
        int sum = 0;
        for_each_possible_cpu(i)
                sum += per_cpu(nr_inodes, i);
        return sum < 0 ? 0 : sum;
}

static inline int get_nr_inodes_unused(void)
{
        int i;
        int sum = 0;
        for_each_possible_cpu(i)
                sum += per_cpu(nr_unused, i);
        return sum < 0 ? 0 : sum;
}

int get_nr_dirty_inodes(void)
{
        /* not actually dirty inodes, but a wild approximation */
        int nr_dirty = get_nr_inodes() - get_nr_inodes_unused();
        return nr_dirty > 0 ? nr_dirty : 0;
}

/*
 * Handle nr_inode sysctl
 */
#ifdef CONFIG_SYSCTL
int proc_nr_inodes(ctl_table *table, int write,
                   void __user *buffer, size_t *lenp, loff_t *ppos)
{
        inodes_stat.nr_inodes = get_nr_inodes();
        inodes_stat.nr_unused = get_nr_inodes_unused();
        return proc_dointvec(table, write, buffer, lenp, ppos);
}
#endif

/**
 * inode_init_always - perform inode structure intialisation
 * @sb: superblock inode belongs to
 * @inode: inode to initialise
 *
 * These are initializations that need to be done on every inode
 * allocation as the fields are not initialised by slab allocation.
 */
int inode_init_always(struct super_block *sb, struct inode *inode)
{
        static const struct inode_operations empty_iops;
        static const struct file_operations empty_fops;
        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;
        inode->i_uid = 0;
        inode->i_gid = 0;
        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))
                goto out;
        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_MOVABLE);
        mapping->assoc_mapping = NULL;
        mapping->backing_dev_info = &default_backing_dev_info;
        mapping->writeback_index = 0;

        /*
         * 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->i_mapping->backing_dev_info;
                mapping->backing_dev_info = bdi;
        }
        inode->i_private = NULL;
        inode->i_mapping = mapping;
#ifdef CONFIG_FS_POSIX_ACL
        inode->i_acl = inode->i_default_acl = ACL_NOT_CACHED;
#endif

#ifdef CONFIG_FSNOTIFY
        inode->i_fsnotify_mask = 0;
#endif

        this_cpu_inc(nr_inodes);

        return 0;
out:
        return -ENOMEM;
}
EXPORT_SYMBOL(inode_init_always);

static struct inode *alloc_inode(struct super_block *sb)
{
        struct inode *inode;

        if (sb->s_op->alloc_inode)
                inode = sb->s_op->alloc_inode(sb);
        else
                inode = kmem_cache_alloc(inode_cachep, GFP_KERNEL);

        if (!inode)
                return NULL;

        if (unlikely(inode_init_always(sb, 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;
        }

        return inode;
}

void free_inode_nonrcu(struct inode *inode)
{
        kmem_cache_free(inode_cachep, inode);
}
EXPORT_SYMBOL(free_inode_nonrcu);

void __destroy_inode(struct inode *inode)
{
        BUG_ON(inode_has_buffers(inode));
        security_inode_free(inode);
        fsnotify_inode_delete(inode);
#ifdef CONFIG_FS_POSIX_ACL
        if (inode->i_acl && inode->i_acl != ACL_NOT_CACHED)
                posix_acl_release(inode->i_acl);
        if (inode->i_default_acl && inode->i_default_acl != ACL_NOT_CACHED)
                posix_acl_release(inode->i_default_acl);
#endif
        this_cpu_dec(nr_inodes);
}
EXPORT_SYMBOL(__destroy_inode);

static void i_callback(struct rcu_head *head)
{
        struct inode *inode = container_of(head, struct inode, i_rcu);
        INIT_LIST_HEAD(&inode->i_dentry);
        kmem_cache_free(inode_cachep, inode);
}

static void destroy_inode(struct inode *inode)
{
        BUG_ON(!list_empty(&inode->i_lru));
        __destroy_inode(inode);
        if (inode->i_sb->s_op->destroy_inode)
                inode->i_sb->s_op->destroy_inode(inode);
        else
                call_rcu(&inode->i_rcu, i_callback);
}

void address_space_init_once(struct address_space *mapping)
{
        memset(mapping, 0, sizeof(*mapping));
        INIT_RADIX_TREE(&mapping->page_tree, GFP_ATOMIC);
        spin_lock_init(&mapping->tree_lock);
        mutex_init(&mapping->i_mmap_mutex);
        INIT_LIST_HEAD(&mapping->private_list);
        spin_lock_init(&mapping->private_lock);
        INIT_RAW_PRIO_TREE_ROOT(&mapping->i_mmap);
        INIT_LIST_HEAD(&mapping->i_mmap_nonlinear);
}
EXPORT_SYMBOL(address_space_init_once);

/*
 * 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_LIST_HEAD(&inode->i_wb_list);
        INIT_LIST_HEAD(&inode->i_lru);
        address_space_init_once(&inode->i_data);
        i_size_ordered_init(inode);
#ifdef CONFIG_FSNOTIFY
        INIT_HLIST_HEAD(&inode->i_fsnotify_marks);
#endif
}
EXPORT_SYMBOL(inode_init_once);

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

        inode_init_once(inode);
}

/*
 * inode->i_lock must be held
 */
void __iget(struct inode *inode)
{
        atomic_inc(&inode->i_count);
}

/*
 * get additional reference to inode; caller must already hold one.
 */
void ihold(struct inode *inode)
{
        WARN_ON(atomic_inc_return(&inode->i_count) < 2);
}
EXPORT_SYMBOL(ihold);

static void inode_lru_list_add(struct inode *inode)
{
        spin_lock(&inode_lru_lock);
        if (list_empty(&inode->i_lru)) {
                list_add(&inode->i_lru, &inode->i_sb->s_inode_lru);
                inode->i_sb->s_nr_inodes_unused++;
                this_cpu_inc(nr_unused);
        }
        spin_unlock(&inode_lru_lock);
}

static void inode_lru_list_del(struct inode *inode)
{
        spin_lock(&inode_lru_lock);
        if (!list_empty(&inode->i_lru)) {
                list_del_init(&inode->i_lru);
                inode->i_sb->s_nr_inodes_unused--;
                this_cpu_dec(nr_unused);
        }
        spin_unlock(&inode_lru_lock);
}

/**
 * inode_sb_list_add - add inode to the superblock list of inodes
 * @inode: inode to add
 */
void inode_sb_list_add(struct inode *inode)
{
        spin_lock(&inode_sb_list_lock);
        list_add(&inode->i_sb_list, &inode->i_sb->s_inodes);
        spin_unlock(&inode_sb_list_lock);
}
EXPORT_SYMBOL_GPL(inode_sb_list_add);

static inline void inode_sb_list_del(struct inode *inode)
{
        spin_lock(&inode_sb_list_lock);
        list_del_init(&inode->i_sb_list);
        spin_unlock(&inode_sb_list_lock);
}

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_hash_shift);
        return tmp & i_hash_mask;
}

/**
 *      __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 *b = inode_hashtable + hash(inode->i_sb, hashval);

        spin_lock(&inode_hash_lock);
        spin_lock(&inode->i_lock);
        hlist_add_head(&inode->i_hash, b);
        spin_unlock(&inode->i_lock);
        spin_unlock(&inode_hash_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_hash_lock);
        spin_lock(&inode->i_lock);
        hlist_del_init(&inode->i_hash);
        spin_unlock(&inode->i_lock);
        spin_unlock(&inode_hash_lock);
}
EXPORT_SYMBOL(remove_inode_hash);

void end_writeback(struct inode *inode)
{
        might_sleep();
        /*
         * We have to cycle tree_lock here because reclaim can be still in the
         * process of removing the last page (in __delete_from_page_cache())
         * and we must not free mapping under it.
         */
        spin_lock_irq(&inode->i_data.tree_lock);
        BUG_ON(inode->i_data.nrpages);
        spin_unlock_irq(&inode->i_data.tree_lock);
        BUG_ON(!list_empty(&inode->i_data.private_list));
        BUG_ON(!(inode->i_state & I_FREEING));
        BUG_ON(inode->i_state & I_CLEAR);
        inode_sync_wait(inode);
        /* don't need i_lock here, no concurrent mods to i_state */
        inode->i_state = I_FREEING | I_CLEAR;
}
EXPORT_SYMBOL(end_writeback);

/*
 * Free the inode passed in, removing it from the lists it is still connected
 * to. We remove any pages still attached to the inode and wait for any IO that
 * is still in progress before finally destroying the inode.
 *
 * An inode must already be marked I_FREEING so that we avoid the inode being
 * moved back onto lists if we race with other code that manipulates the lists
 * (e.g. writeback_single_inode). The caller is responsible for setting this.
 *
 * An inode must already be removed from the LRU list before being evicted from
 * the cache. This should occur atomically with setting the I_FREEING state
 * flag, so no inodes here should ever be on the LRU when being evicted.
 */
static void evict(struct inode *inode)
{
        const struct super_operations *op = inode->i_sb->s_op;

        BUG_ON(!(inode->i_state & I_FREEING));
        BUG_ON(!list_empty(&inode->i_lru));

        inode_wb_list_del(inode);
        inode_sb_list_del(inode);

        if (op->evict_inode) {
                op->evict_inode(inode);
        } else {
                if (inode->i_data.nrpages)
                        truncate_inode_pages(&inode->i_data, 0);
                end_writeback(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);

        remove_inode_hash(inode);

        spin_lock(&inode->i_lock);
        wake_up_bit(&inode->i_state, __I_NEW);
        BUG_ON(inode->i_state != (I_FREEING | I_CLEAR));
        spin_unlock(&inode->i_lock);

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

                inode = list_first_entry(head, struct inode, i_lru);
                list_del_init(&inode->i_lru);

                evict(inode);
        }
}

/**
 * evict_inodes - evict all evictable inodes for a superblock
 * @sb:         superblock to operate on
 *
 * Make sure that no inodes with zero refcount are retained.  This is
 * called by superblock shutdown after having MS_ACTIVE flag removed,
 * so any inode reaching zero refcount during or after that call will
 * be immediately evicted.
 */
void evict_inodes(struct super_block *sb)
{
        struct inode *inode, *next;
        LIST_HEAD(dispose);

        spin_lock(&inode_sb_list_lock);
        list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
                if (atomic_read(&inode->i_count))
                        continue;

                spin_lock(&inode->i_lock);
                if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
                        spin_unlock(&inode->i_lock);
                        continue;
                }

                inode->i_state |= I_FREEING;
                inode_lru_list_del(inode);
                spin_unlock(&inode->i_lock);
                list_add(&inode->i_lru, &dispose);
        }
        spin_unlock(&inode_sb_list_lock);

        dispose_list(&dispose);

        /*
         * Cycle through iprune_sem to make sure any inode that prune_icache
         * moved off the list before we took the lock has been fully torn
         * down.
         */
        down_write(&iprune_sem);
        up_write(&iprune_sem);
}

/**
 * invalidate_inodes    - attempt to free all inodes on a superblock
 * @sb:         superblock to operate on
 * @kill_dirty: flag to guide handling of dirty inodes
 *
 * Attempts to free all inodes for a given superblock.  If there were any
 * busy inodes return a non-zero value, else zero.
 * If @kill_dirty is set, discard dirty inodes too, otherwise treat
 * them as busy.
 */
int invalidate_inodes(struct super_block *sb, bool kill_dirty)
{
        int busy = 0;
        struct inode *inode, *next;
        LIST_HEAD(dispose);

        spin_lock(&inode_sb_list_lock);
        list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
                spin_lock(&inode->i_lock);
                if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
                        spin_unlock(&inode->i_lock);
                        continue;
                }
                if (inode->i_state & I_DIRTY && !kill_dirty) {
                        spin_unlock(&inode->i_lock);
                        busy = 1;
                        continue;
                }
                if (atomic_read(&inode->i_count)) {
                        spin_unlock(&inode->i_lock);
                        busy = 1;
                        continue;
                }

                inode->i_state |= I_FREEING;
                inode_lru_list_del(inode);
                spin_unlock(&inode->i_lock);
                list_add(&inode->i_lru, &dispose);
        }
        spin_unlock(&inode_sb_list_lock);

        dispose_list(&dispose);

        return busy;
}

static int can_unuse(struct inode *inode)
{
        if (inode->i_state & ~I_REFERENCED)
                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_lru_lock by dispose_list().
 *
 * Any inodes which are pinned purely because of attached pagecache have their
 * pagecache removed.  If the inode has metadata buffers attached to
 * mapping->private_list then try to remove them.
 *
 * If the inode has the I_REFERENCED flag set, then it means that it has been
 * used recently - the flag is set in iput_final(). When we encounter such an
 * inode, clear the flag and move it to the back of the LRU so it gets another
 * pass through the LRU before it gets reclaimed. This is necessary because of
 * the fact we are doing lazy LRU updates to minimise lock contention so the
 * LRU does not have strict ordering. Hence we don't want to reclaim inodes
 * with this flag set because they are the inodes that are out of order.
 */
static void shrink_icache_sb(struct super_block *sb, int *nr_to_scan)
{
        LIST_HEAD(freeable);
        int nr_scanned;
        unsigned long reap = 0;

        spin_lock(&inode_lru_lock);
        for (nr_scanned = *nr_to_scan; nr_scanned >= 0; nr_scanned--) {
                struct inode *inode;

                if (list_empty(&sb->s_inode_lru))
                        break;

                inode = list_entry(sb->s_inode_lru.prev, struct inode, i_lru);

                /*
                 * we are inverting the inode_lru_lock/inode->i_lock here,
                 * so use a trylock. If we fail to get the lock, just move the
                 * inode to the back of the list so we don't spin on it.
                 */
                if (!spin_trylock(&inode->i_lock)) {
                        list_move(&inode->i_lru, &sb->s_inode_lru);
                        continue;
                }

                /*
                 * Referenced or dirty inodes are still in use. Give them
                 * another pass through the LRU as we canot reclaim them now.
                 */
                if (atomic_read(&inode->i_count) ||
                    (inode->i_state & ~I_REFERENCED)) {
                        list_del_init(&inode->i_lru);
                        spin_unlock(&inode->i_lock);
                        sb->s_nr_inodes_unused--;
                        this_cpu_dec(nr_unused);
                        continue;
                }

                /* recently referenced inodes get one more pass */
                if (inode->i_state & I_REFERENCED) {
                        inode->i_state &= ~I_REFERENCED;
                        list_move(&inode->i_lru, &sb->s_inode_lru);
                        spin_unlock(&inode->i_lock);
                        continue;
                }
                if (inode_has_buffers(inode) || inode->i_data.nrpages) {
                        __iget(inode);
                        spin_unlock(&inode->i_lock);
                        spin_unlock(&inode_lru_lock);
                        if (remove_inode_buffers(inode))
                                reap += invalidate_mapping_pages(&inode->i_data,
                                                                0, -1);
                        iput(inode);
                        spin_lock(&inode_lru_lock);

                        if (inode != list_entry(sb->s_inode_lru.next,
                                                struct inode, i_lru))
                                continue;       /* wrong inode or list_empty */
                        /* avoid lock inversions with trylock */
                        if (!spin_trylock(&inode->i_lock))
                                continue;
                        if (!can_unuse(inode)) {
                                spin_unlock(&inode->i_lock);
                                continue;
                        }
                }
                WARN_ON(inode->i_state & I_NEW);
                inode->i_state |= I_FREEING;
                spin_unlock(&inode->i_lock);

                list_move(&inode->i_lru, &freeable);
                sb->s_nr_inodes_unused--;
                this_cpu_dec(nr_unused);
        }
        if (current_is_kswapd())
                __count_vm_events(KSWAPD_INODESTEAL, reap);
        else
                __count_vm_events(PGINODESTEAL, reap);
        spin_unlock(&inode_lru_lock);
        *nr_to_scan = nr_scanned;

        dispose_list(&freeable);
}

static void prune_icache(int count)
{
        struct super_block *sb, *p = NULL;
        int w_count;
        int unused = inodes_stat.nr_unused;
        int prune_ratio;
        int pruned;

        if (unused == 0 || count == 0)
                return;
        down_read(&iprune_sem);
        if (count >= unused)
                prune_ratio = 1;
        else
                prune_ratio = unused / count;
        spin_lock(&sb_lock);
        list_for_each_entry(sb, &super_blocks, s_list) {
                if (list_empty(&sb->s_instances))
                        continue;
                if (sb->s_nr_inodes_unused == 0)
                        continue;
                sb->s_count++;
                /* Now, we reclaim unused dentrins with fairness.
                 * We reclaim them same percentage from each superblock.
                 * We calculate number of dentries to scan on this sb
                 * as follows, but the implementation is arranged to avoid
                 * overflows:
                 * number of dentries to scan on this sb =
                 * count * (number of dentries on this sb /
                 * number of dentries in the machine)
                 */
                spin_unlock(&sb_lock);
                if (prune_ratio != 1)
                        w_count = (sb->s_nr_inodes_unused / prune_ratio) + 1;
                else
                        w_count = sb->s_nr_inodes_unused;
                pruned = w_count;
                /*
                 * We need to be sure this filesystem isn't being unmounted,
                 * otherwise we could race with generic_shutdown_super(), and
                 * end up holding a reference to an inode while the filesystem
                 * is unmounted.  So we try to get s_umount, and make sure
                 * s_root isn't NULL.
                 */
                if (down_read_trylock(&sb->s_umount)) {
                        if ((sb->s_root != NULL) &&
                            (!list_empty(&sb->s_dentry_lru))) {
                                shrink_icache_sb(sb, &w_count);
                                pruned -= w_count;
                        }
                        up_read(&sb->s_umount);
                }
                spin_lock(&sb_lock);
                if (p)
                        __put_super(p);
                count -= pruned;
                p = sb;
                /* more work left to do? */
                if (count <= 0)
                        break;
        }
        if (p)
                __put_super(p);
        spin_unlock(&sb_lock);
        up_read(&iprune_sem);
}

/*
 * 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(struct shrinker *shrink,
                                struct shrink_control *sc)
{
        int nr = sc->nr_to_scan;
        gfp_t gfp_mask = sc->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 (get_nr_inodes_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.
 */
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) {
                spin_lock(&inode->i_lock);
                if (inode->i_sb != sb) {
                        spin_unlock(&inode->i_lock);
                        continue;
                }
                if (!test(inode, data)) {
                        spin_unlock(&inode->i_lock);
                        continue;
                }
                if (inode->i_state & (I_FREEING|I_WILL_FREE)) {
                        __wait_on_freeing_inode(inode);
                        goto repeat;
                }
                __iget(inode);
                spin_unlock(&inode->i_lock);
                return inode;
        }
        return 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) {
                spin_lock(&inode->i_lock);
                if (inode->i_ino != ino) {
                        spin_unlock(&inode->i_lock);
                        continue;
                }
                if (inode->i_sb != sb) {
                        spin_unlock(&inode->i_lock);
                        continue;
                }
                if (inode->i_state & (I_FREEING|I_WILL_FREE)) {
                        __wait_on_freeing_inode(inode);
                        goto repeat;
                }
                __iget(inode);
                spin_unlock(&inode->i_lock);
                return inode;
        }
        return NULL;
}

/*
 * Each cpu owns a range of LAST_INO_BATCH numbers.
 * 'shared_last_ino' is dirtied only once out of LAST_INO_BATCH allocations,
 * to renew the exhausted range.
 *
 * This does not significantly increase overflow rate because every CPU can
 * consume at most LAST_INO_BATCH-1 unused inode numbers. So there is
 * NR_CPUS*(LAST_INO_BATCH-1) wastage. At 4096 and 1024, this is ~0.1% of the
 * 2^32 range, and is a worst-case. Even a 50% wastage would only increase
 * overflow rate by 2x, which does not seem too significant.
 *
 * 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.
 */
#define LAST_INO_BATCH 1024
static DEFINE_PER_CPU(unsigned int, last_ino);

unsigned int get_next_ino(void)
{
        unsigned int *p = &get_cpu_var(last_ino);
        unsigned int res = *p;

#ifdef CONFIG_SMP
        if (unlikely((res & (LAST_INO_BATCH-1)) == 0)) {
                static atomic_t shared_last_ino;
                int next = atomic_add_return(LAST_INO_BATCH, &shared_last_ino);

                res = next - LAST_INO_BATCH;
        }
#endif

        *p = ++res;
        put_cpu_var(last_ino);
        return res;
}
EXPORT_SYMBOL(get_next_ino);

/**
 *      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_MOVABLE.
 *      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)
{
        struct inode *inode;

        spin_lock_prefetch(&inode_sb_list_lock);

        inode = alloc_inode(sb);
        if (inode) {
                spin_lock(&inode->i_lock);
                inode->i_state = 0;
                spin_unlock(&inode->i_lock);
                inode_sb_list_add(inode);
        }
        return inode;
}
EXPORT_SYMBOL(new_inode);

/**
 * unlock_new_inode - clear the I_NEW state and wake up any waiters
 * @inode:      new inode to unlock
 *
 * Called when the inode is fully initialised to clear the new state of the
 * inode and wake up anyone waiting for the inode to finish initialisation.
 */
void unlock_new_inode(struct inode *inode)
{
#ifdef CONFIG_DEBUG_LOCK_ALLOC
        if (S_ISDIR(inode->i_mode)) {
                struct file_system_type *type = inode->i_sb->s_type;

                /* Set new key only if filesystem hasn't already changed it */
                if (!lockdep_match_class(&inode->i_mutex,
                    &type->i_mutex_key)) {
                        /*
                         * 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
        spin_lock(&inode->i_lock);
        WARN_ON(!(inode->i_state & I_NEW));
        inode->i_state &= ~I_NEW;
        wake_up_bit(&inode->i_state, __I_NEW);
        spin_unlock(&inode->i_lock);
}
EXPORT_SYMBOL(unlock_new_inode);

/**
 * 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
 *
 * Search for the inode specified by @hashval and @data in the inode cache,
 * and if present it is return it 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, allocate a new inode and return it 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_hash_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;

        spin_lock(&inode_hash_lock);
        inode = find_inode(sb, head, test, data);
        spin_unlock(&inode_hash_lock);

        if (inode) {
                wait_on_inode(inode);
                return inode;
        }

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

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

                        spin_lock(&inode->i_lock);
                        inode->i_state = I_NEW;
                        hlist_add_head(&inode->i_hash, head);
                        spin_unlock(&inode->i_lock);
                        inode_sb_list_add(inode);
                        spin_unlock(&inode_hash_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.
                 */
                spin_unlock(&inode_hash_lock);
                destroy_inode(inode);
                inode = old;
                wait_on_inode(inode);
        }
        return inode;

set_failed:
        spin_unlock(&inode_hash_lock);
        destroy_inode(inode);
        return NULL;
}
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
 *
 * Search for the inode specified by @ino in the inode cache and if present
 * return it 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, allocate a new inode and return it 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;

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

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

                spin_lock(&inode_hash_lock);
                /* We released the lock, so.. */
                old = find_inode_fast(sb, head, ino);
                if (!old) {
                        inode->i_ino = ino;
                        spin_lock(&inode->i_lock);
                        inode->i_state = I_NEW;
                        hlist_add_head(&inode->i_hash, head);
                        spin_unlock(&inode->i_lock);
                        inode_sb_list_add(inode);
                        spin_unlock(&inode_hash_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.
                 */
                spin_unlock(&inode_hash_lock);
                destroy_inode(inode);
                inode = old;
                wait_on_inode(inode);
        }
        return inode;
}
EXPORT_SYMBOL(iget_locked);

/*
 * search the inode cache for a matching inode number.
 * If we find one, then the inode number we are trying to
 * allocate is not unique and so we should not use it.
 *
 * Returns 1 if the inode number is unique, 0 if it is not.
 */
static int test_inode_iunique(struct super_block *sb, unsigned long ino)
{
        struct hlist_head *b = inode_hashtable + hash(sb, ino);
        struct hlist_node *node;
        struct inode *inode;

        spin_lock(&inode_hash_lock);
        hlist_for_each_entry(inode, node, b, i_hash) {
                if (inode->i_ino == ino && inode->i_sb == sb) {
                        spin_unlock(&inode_hash_lock);
                        return 0;
                }
        }
        spin_unlock(&inode_hash_lock);

        return 1;
}

/**
 *      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 DEFINE_SPINLOCK(iunique_lock);
        static unsigned int counter;
        ino_t res;

        spin_lock(&iunique_lock);
        do {
                if (counter <= max_reserved)
                        counter = max_reserved + 1;
                res = counter++;
        } while (!test_inode_iunique(sb, res));
        spin_unlock(&iunique_lock);

        return res;
}
EXPORT_SYMBOL(iunique);

struct inode *igrab(struct inode *inode)
{
        spin_lock(&inode->i_lock);
        if (!(inode->i_state & (I_FREEING|I_WILL_FREE))) {
                __iget(inode);
                spin_unlock(&inode->i_lock);
        } else {
                spin_unlock(&inode->i_lock);
                /*
                 * 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;
        }
        return inode;
}
EXPORT_SYMBOL(igrab);

/**
 * 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
 *
 * Search for the inode specified by @hashval and @data in the inode cache.
 * If the inode is in the cache, the inode is returned with an incremented
 * reference count.
 *
 * Note: I_NEW 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.
 *
 * Note2: @test is called with the inode_hash_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);
        struct inode *inode;

        spin_lock(&inode_hash_lock);
        inode = find_inode(sb, head, test, data);
        spin_unlock(&inode_hash_lock);

        return inode;
}
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
 *
 * Search for the inode specified by @hashval and @data in the inode cache,
 * and if the inode is in the cache, return the inode with an incremented
 * reference count.  Waits on I_NEW before returning the inode.
 * returned with an incremented reference count.
 *
 * This is a generalized version of ilookup() for file systems where the
 * inode number is not sufficient for unique identification of an inode.
 *
 * Note: @test is called with the inode_hash_lock held, so can't sleep.
 */
struct inode *ilookup5(struct super_block *sb, unsigned long hashval,
                int (*test)(struct inode *, void *), void *data)
{
        struct inode *inode = ilookup5_nowait(sb, hashval, test, data);

        if (inode)
                wait_on_inode(inode);
        return inode;
}
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
 *
 * Search for the inode @ino in the inode cache, and if the inode is in the
 * cache, the inode is returned with an incremented reference count.
 */
struct inode *ilookup(struct super_block *sb, unsigned long ino)
{
        struct hlist_head *head = inode_hashtable + hash(sb, ino);
        struct inode *inode;

        spin_lock(&inode_hash_lock);
        inode = find_inode_fast(sb, head, ino);
        spin_unlock(&inode_hash_lock);

        if (inode)
                wait_on_inode(inode);
        return inode;
}
EXPORT_SYMBOL(ilookup);

int insert_inode_locked(struct inode *inode)
{
        struct super_block *sb = inode->i_sb;
        ino_t ino = inode->i_ino;
        struct hlist_head *head = inode_hashtable + hash(sb, ino);

        while (1) {
                struct hlist_node *node;
                struct inode *old = NULL;
                spin_lock(&inode_hash_lock);
                hlist_for_each_entry(old, node, head, i_hash) {
                        if (old->i_ino != ino)
                                continue;
                        if (old->i_sb != sb)
                                continue;
                        spin_lock(&old->i_lock);
                        if (old->i_state & (I_FREEING|I_WILL_FREE)) {
                                spin_unlock(&old->i_lock);
                                continue;
                        }
                        break;
                }
                if (likely(!node)) {
                        spin_lock(&inode->i_lock);
                        inode->i_state |= I_NEW;
                        hlist_add_head(&inode->i_hash, head);
                        spin_unlock(&inode->i_lock);
                        spin_unlock(&inode_hash_lock);
                        return 0;
                }
                __iget(old);
                spin_unlock(&old->i_lock);
                spin_unlock(&inode_hash_lock);
                wait_on_inode(old);
                if (unlikely(!inode_unhashed(old))) {
                        iput(old);
                        return -EBUSY;
                }
                iput(old);
        }
}
EXPORT_SYMBOL(insert_inode_locked);

int insert_inode_locked4(struct inode *inode, unsigned long hashval,
                int (*test)(struct inode *, void *), void *data)
{
        struct super_block *sb = inode->i_sb;
        struct hlist_head *head = inode_hashtable + hash(sb, hashval);

        while (1) {
                struct hlist_node *node;
                struct inode *old = NULL;

                spin_lock(&inode_hash_lock);
                hlist_for_each_entry(old, node, head, i_hash) {
                        if (old->i_sb != sb)
                                continue;
                        if (!test(old, data))
                                continue;
                        spin_lock(&old->i_lock);
                        if (old->i_state & (I_FREEING|I_WILL_FREE)) {
                                spin_unlock(&old->i_lock);
                                continue;
                        }
                        break;
                }
                if (likely(!node)) {
                        spin_lock(&inode->i_lock);
                        inode->i_state |= I_NEW;
                        hlist_add_head(&inode->i_hash, head);
                        spin_unlock(&inode->i_lock);
                        spin_unlock(&inode_hash_lock);
                        return 0;
                }
                __iget(old);
                spin_unlock(&old->i_lock);
                spin_unlock(&inode_hash_lock);
                wait_on_inode(old);
                if (unlikely(!inode_unhashed(old))) {
                        iput(old);
                        return -EBUSY;
                }
                iput(old);
        }
}
EXPORT_SYMBOL(insert_inode_locked4);


int generic_delete_inode(struct inode *inode)
{
        return 1;
}
EXPORT_SYMBOL(generic_delete_inode);

/*
 * Normal UNIX filesystem behaviour: delete the
 * inode when the usage count drops to zero, and
 * i_nlink is zero.
 */
int generic_drop_inode(struct inode *inode)
{
        return !inode->i_nlink || inode_unhashed(inode);
}
EXPORT_SYMBOL_GPL(generic_drop_inode);

/*
 * Called when we're dropping the last reference
 * to an inode.
 *
 * Call the FS "drop_inode()" function, defaulting to
 * the legacy UNIX filesystem behaviour.  If it tells
 * us to evict inode, do so.  Otherwise, retain inode
 * in cache if fs is alive, sync and evict if fs is
 * shutting down.
 */
static void iput_final(struct inode *inode)
{
        struct super_block *sb = inode->i_sb;
        const struct super_operations *op = inode->i_sb->s_op;
        int drop;

        WARN_ON(inode->i_state & I_NEW);

        if (op->drop_inode)
                drop = op->drop_inode(inode);
        else
                drop = generic_drop_inode(inode);

        if (!drop && (sb->s_flags & MS_ACTIVE)) {
                inode->i_state |= I_REFERENCED;
                if (!(inode->i_state & (I_DIRTY|I_SYNC)))
                        inode_lru_list_add(inode);
                spin_unlock(&inode->i_lock);
                return;
        }

        if (!drop) {
                inode->i_state |= I_WILL_FREE;
                spin_unlock(&inode->i_lock);
                write_inode_now(inode, 1);
                spin_lock(&inode->i_lock);
                WARN_ON(inode->i_state & I_NEW);
                inode->i_state &= ~I_WILL_FREE;
        }

        inode->i_state |= I_FREEING;
        inode_lru_list_del(inode);
        spin_unlock(&inode->i_lock);

        evict(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->i_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);

/*
 * With relative atime, only update atime if the previous atime is
 * earlier than either the ctime or mtime or if at least a day has
 * passed since the last atime update.
 */
static int relatime_need_update(struct vfsmount *mnt, struct inode *inode,
                             struct timespec now)
{

        if (!(mnt->mnt_flags & MNT_RELATIME))
                return 1;
        /*
         * Is mtime younger than atime? If yes, update atime:
         */
        if (timespec_compare(&inode->i_mtime, &inode->i_atime) >= 0)
                return 1;
        /*
         * Is ctime younger than atime? If yes, update atime:
         */
        if (timespec_compare(&inode->i_ctime, &inode->i_atime) >= 0)
                return 1;

        /*
         * Is the previous atime value older than a day? If yes,
         * update atime:
         */
        if ((long)(now.tv_sec - inode->i_atime.tv_sec) >= 24*60*60)
                return 1;
        /*
         * Good, we can skip the atime update:
         */
        return 0;
}

/**
 *      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 (inode->i_flags & S_NOATIME)
                return;
        if (IS_NOATIME(inode))
                return;
        if ((inode->i_sb->s_flags & MS_NODIRATIME) && S_ISDIR(inode->i_mode))
                return;

        if (mnt->mnt_flags & MNT_NOATIME)
                return;
        if ((mnt->mnt_flags & MNT_NODIRATIME) && S_ISDIR(inode->i_mode))
                return;

        now = current_fs_time(inode->i_sb);

        if (!relatime_need_update(mnt, inode, now))
                return;

        if (timespec_equal(&inode->i_atime, &now))
                return;

        if (mnt_want_write(mnt))
                return;

        inode->i_atime = now;
        mark_inode_dirty_sync(inode);
        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_NOCMTIME 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;
        enum { S_MTIME = 1, S_CTIME = 2, S_VERSION = 4 } sync_it = 0;

        /* First try to exhaust all avenues to not sync */
        if (IS_NOCMTIME(inode))
                return;

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

        if (!timespec_equal(&inode->i_ctime, &now))
                sync_it |= S_CTIME;

        if (IS_I_VERSION(inode))
                sync_it |= S_VERSION;

        if (!sync_it)
                return;

        /* Finally allowed to write? Takes lock. */
        if (mnt_want_write_file(file))
                return;

        /* Only change inode inside the lock region */
        if (sync_it & S_VERSION)
                inode_inc_iversion(inode);
        if (sync_it & S_CTIME)
                inode->i_ctime = now;
        if (sync_it & S_MTIME)
                inode->i_mtime = now;
        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;
}
EXPORT_SYMBOL(inode_wait);

/*
 * 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_NEW is not set initially, a call to
 * wake_up_bit(&inode->i_state, __I_NEW) after removing from the hash list
 * will DTRT.
 */
static void __wait_on_freeing_inode(struct inode *inode)
{
        wait_queue_head_t *wq;
        DEFINE_WAIT_BIT(wait, &inode->i_state, __I_NEW);
        wq = bit_waitqueue(&inode->i_state, __I_NEW);
        prepare_to_wait(wq, &wait.wait, TASK_UNINTERRUPTIBLE);
        spin_unlock(&inode->i_lock);
        spin_unlock(&inode_hash_lock);
        schedule();
        finish_wait(wq, &wait.wait);
        spin_lock(&inode_hash_lock);
}

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) for"
                                  " inode %s:%lu\n", mode, inode->i_sb->s_id,
                                  inode->i_ino);
}
EXPORT_SYMBOL(init_special_inode);

/**
 * inode_init_owner - Init uid,gid,mode for new inode according to posix standards
 * @inode: New inode
 * @dir: Directory inode
 * @mode: mode of the new inode
 */
void inode_init_owner(struct inode *inode, const struct inode *dir,
                        mode_t mode)
{
        inode->i_uid = current_fsuid();
        if (dir && dir->i_mode & S_ISGID) {
                inode->i_gid = dir->i_gid;
                if (S_ISDIR(mode))
                        mode |= S_ISGID;
        } else
                inode->i_gid = current_fsgid();
        inode->i_mode = mode;
}
EXPORT_SYMBOL(inode_init_owner);

/**
 * inode_owner_or_capable - check current task permissions to inode
 * @inode: inode being checked
 *
 * Return true if current either has CAP_FOWNER to the inode, or
 * owns the file.
 */
bool inode_owner_or_capable(const struct inode *inode)
{
        struct user_namespace *ns = inode_userns(inode);

        if (current_user_ns() == ns && current_fsuid() == inode->i_uid)
                return true;
        if (ns_capable(ns, CAP_FOWNER))
                return true;
        return false;
}
EXPORT_SYMBOL(inode_owner_or_capable);