mtd: davinci: fix comment to match the code

[linux-2.6/cjktty.git] / 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/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>

/*
 * 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_sem provides exclusion between the kswapd or try_to_free_pages
 * icache shrinking path, and the umount path.  Without this exclusion,
 * by the time prune_icache calls iput for the inode whose pages it has
 * been invalidating, or by the time it calls clear_inode & destroy_inode
 * from its final dispose_list, the struct super_block they refer to
 * (for inode->i_sb->s_op) may already have been freed and reused.
 *
 * We make this an rwsem because the fastpath is icache shrinking. In
 * some cases a filesystem may be doing a significant amount of work in
 * its inode reclaim code, so this should improve parallelism.
 */
static DECLARE_RWSEM(iprune_sem);

/*
 * 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_NEW);
}

/**
 * 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 address_space_operations empty_aops;
        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

        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 __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
}
EXPORT_SYMBOL(__destroy_inode);

void destroy_inode(struct inode *inode)
{
        __destroy_inode(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);
        spin_lock_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_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_lock must be held
 */
void __iget(struct inode *inode)
{
        if (atomic_inc_return(&inode->i_count) != 1)
                return;

        if (!(inode->i_state & (I_DIRTY|I_SYNC)))
                list_move(&inode->i_list, &inode_in_use);
        inodes_stat.nr_unused--;
}

void end_writeback(struct inode *inode)
{
        might_sleep();
        BUG_ON(inode->i_data.nrpages);
        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);
        inode->i_state = I_FREEING | I_CLEAR;
}
EXPORT_SYMBOL(end_writeback);

static void evict(struct inode *inode)
{
        const struct super_operations *op = inode->i_sb->s_op;

        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);
}

/*
 * 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);

                evict(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_sem 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);
                if (inode->i_state & I_NEW)
                        continue;
                invalidate_inode_buffers(inode);
                if (!atomic_read(&inode->i_count)) {
                        list_move(&inode->i_list, dispose);
                        WARN_ON(inode->i_state & I_NEW);
                        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);

        down_write(&iprune_sem);
        spin_lock(&inode_lock);
        fsnotify_unmount_inodes(&sb->s_inodes);
        busy = invalidate_list(&sb->s_inodes, &throw_away);
        spin_unlock(&inode_lock);

        dispose_list(&throw_away);
        up_write(&iprune_sem);

        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;

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

                if (list_empty(&inode_unused))
                        break;

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

                if (inode->i_state || atomic_read(&inode->i_count)) {
                        list_move(&inode->i_list, &inode_unused);
                        continue;
                }
                if (inode_has_buffers(inode) || inode->i_data.nrpages) {
                        __iget(inode);
                        spin_unlock(&inode_lock);
                        if (remove_inode_buffers(inode))
                                reap += invalidate_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);
                WARN_ON(inode->i_state & I_NEW);
                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);
        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, 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_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_WILL_FREE)) {
                        __wait_on_freeing_inode(inode);
                        goto repeat;
                }
                break;
        }
        return node ? inode : NULL;
}

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;
}

static inline void
__inode_add_to_lists(struct super_block *sb, struct hlist_head *head,
                        struct inode *inode)
{
        inodes_stat.nr_inodes++;
        list_add(&inode->i_list, &inode_in_use);
        list_add(&inode->i_sb_list, &sb->s_inodes);
        if (head)
                hlist_add_head(&inode->i_hash, head);
}

/**
 * inode_add_to_lists - add a new inode to relevant lists
 * @sb: superblock inode belongs to
 * @inode: inode to mark in use
 *
 * When an inode is allocated it needs to be accounted for, added to the in use
 * list, the owning superblock and the inode hash. This needs to be done under
 * the inode_lock, so export a function to do this rather than the inode lock
 * itself. We calculate the hash list to add to here so it is all internal
 * which requires the caller to have already set up the inode number in the
 * inode to add.
 */
void inode_add_to_lists(struct super_block *sb, struct inode *inode)
{
        struct hlist_head *head = inode_hashtable + hash(sb, inode->i_ino);

        spin_lock(&inode_lock);
        __inode_add_to_lists(sb, head, inode);
        spin_unlock(&inode_lock);
}
EXPORT_SYMBOL_GPL(inode_add_to_lists);

/**
 *      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)
{
        /*
         * 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);
                __inode_add_to_lists(sb, NULL, inode);
                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;

                /* 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
        /*
         * This is special!  We do not need the spinlock when clearing I_NEW,
         * 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_NEW).
         * However we must emit the memory barrier so that other CPUs reliably
         * see the clearing of I_NEW after the other inode initialisation has
         * completed.
         */
        smp_mb();
        WARN_ON(!(inode->i_state & I_NEW));
        inode->i_state &= ~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;

                        __inode_add_to_lists(sb, head, inode);
                        inode->i_state = 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;
                        __inode_add_to_lists(sb, head, inode);
                        inode->i_state = 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;
}

/**
 *      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_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);

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);

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

        inode->i_state |= I_NEW;

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

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

/**
 *      __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);

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 || hlist_unhashed(&inode->i_hash);
}
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;

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

        if (!drop) {
                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;
                }
                WARN_ON(inode->i_state & I_NEW);
                inode->i_state |= I_WILL_FREE;
                spin_unlock(&inode_lock);
                write_inode_now(inode, 1);
                spin_lock(&inode_lock);
                WARN_ON(inode->i_state & I_NEW);
                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);
        WARN_ON(inode->i_state & I_NEW);
        inode->i_state |= I_FREEING;
        inodes_stat.nr_inodes--;
        spin_unlock(&inode_lock);
        evict(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_FREEING | I_CLEAR));
        destroy_inode(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);

/*
 * 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_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_NEW);
        wq = bit_waitqueue(&inode->i_state, __I_NEW);
        prepare_to_wait(wq, &wait.wait, TASK_UNINTERRUPTIBLE);
        spin_unlock(&inode_lock);
        schedule();
        finish_wait(wq, &wait.wait);
        spin_lock(&inode_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);

/**
 * 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);