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32 results

io_tables.h

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  • inode.c 36.49 KiB
    /*
     * linux/fs/inode.c
     *
     * (C) 1997 Linus Torvalds
     */
    
    #include <linux/config.h>
    #include <linux/fs.h>
    #include <linux/mm.h>
    #include <linux/dcache.h>
    #include <linux/init.h>
    #include <linux/quotaops.h>
    #include <linux/slab.h>
    #include <linux/writeback.h>
    #include <linux/module.h>
    #include <linux/backing-dev.h>
    #include <linux/wait.h>
    #include <linux/hash.h>
    #include <linux/swap.h>
    #include <linux/security.h>
    #include <linux/pagemap.h>
    #include <linux/cdev.h>
    #include <linux/bootmem.h>
    #include <linux/inotify.h>
    #include <linux/mount.h>
    
    /*
     * This is needed for the following functions:
     *  - inode_has_buffers
     *  - invalidate_inode_buffers
     *  - invalidate_bdev
     *
     * FIXME: remove all knowledge of the buffer layer from this file
     */
    #include <linux/buffer_head.h>
    
    /*
     * New inode.c implementation.
     *
     * This implementation has the basic premise of trying
     * to be extremely low-overhead and SMP-safe, yet be
     * simple enough to be "obviously correct".
     *
     * Famous last words.
     */
    
    /* inode dynamic allocation 1999, Andrea Arcangeli <andrea@suse.de> */
    
    /* #define INODE_PARANOIA 1 */
    /* #define INODE_DEBUG 1 */
    
    /*
     * Inode lookup is no longer as critical as it used to be:
     * most of the lookups are going to be through the dcache.
     */
    #define I_HASHBITS	i_hash_shift
    #define I_HASHMASK	i_hash_mask
    
    static unsigned int i_hash_mask __read_mostly;
    static unsigned int i_hash_shift __read_mostly;
    
    /*
     * Each inode can be on two separate lists. One is
     * the hash list of the inode, used for lookups. The
     * other linked list is the "type" list:
     *  "in_use" - valid inode, i_count > 0, i_nlink > 0
     *  "dirty"  - as "in_use" but also dirty
     *  "unused" - valid inode, i_count = 0
     *
     * A "dirty" list is maintained for each super block,
     * allowing for low-overhead inode sync() operations.
     */
    
    LIST_HEAD(inode_in_use);
    LIST_HEAD(inode_unused);
    static struct hlist_head *inode_hashtable __read_mostly;
    
    /*
     * A simple spinlock to protect the list manipulations.
     *
     * NOTE! You also have to own the lock if you change
     * the i_state of an inode while it is in use..
     */
    DEFINE_SPINLOCK(inode_lock);
    
    /*
     * iprune_mutex provides exclusion between the kswapd or try_to_free_pages
     * icache shrinking path, and the umount path.  Without this exclusion,
     * by the time prune_icache calls iput for the inode whose pages it has
     * been invalidating, or by the time it calls clear_inode & destroy_inode
     * from its final dispose_list, the struct super_block they refer to
     * (for inode->i_sb->s_op) may already have been freed and reused.
     */
    static DEFINE_MUTEX(iprune_mutex);
    
    /*
     * Statistics gathering..
     */
    struct inodes_stat_t inodes_stat;
    
    static kmem_cache_t * inode_cachep __read_mostly;
    
    static struct inode *alloc_inode(struct super_block *sb)
    {
    	static struct address_space_operations empty_aops;
    	static struct inode_operations empty_iops;
    	static const struct file_operations empty_fops;
    	struct inode *inode;
    
    	if (sb->s_op->alloc_inode)
    		inode = sb->s_op->alloc_inode(sb);
    	else
    		inode = (struct inode *) kmem_cache_alloc(inode_cachep, SLAB_KERNEL);
    
    	if (inode) {
    		struct address_space * const mapping = &inode->i_data;
    
    		inode->i_sb = sb;
    		inode->i_blkbits = sb->s_blocksize_bits;
    		inode->i_flags = 0;
    		atomic_set(&inode->i_count, 1);
    		inode->i_op = &empty_iops;
    		inode->i_fop = &empty_fops;
    		inode->i_nlink = 1;
    		atomic_set(&inode->i_writecount, 0);
    		inode->i_size = 0;
    		inode->i_blocks = 0;
    		inode->i_bytes = 0;
    		inode->i_generation = 0;
    #ifdef CONFIG_QUOTA
    		memset(&inode->i_dquot, 0, sizeof(inode->i_dquot));
    #endif
    		inode->i_pipe = NULL;
    		inode->i_bdev = NULL;
    		inode->i_cdev = NULL;
    		inode->i_rdev = 0;
    		inode->i_security = NULL;
    		inode->dirtied_when = 0;
    		if (security_inode_alloc(inode)) {
    			if (inode->i_sb->s_op->destroy_inode)
    				inode->i_sb->s_op->destroy_inode(inode);
    			else
    				kmem_cache_free(inode_cachep, (inode));
    			return NULL;
    		}
    
    		mapping->a_ops = &empty_aops;
     		mapping->host = inode;
    		mapping->flags = 0;
    		mapping_set_gfp_mask(mapping, GFP_HIGHUSER);
    		mapping->assoc_mapping = NULL;
    		mapping->backing_dev_info = &default_backing_dev_info;
    
    		/*
    		 * If the block_device provides a backing_dev_info for client
    		 * inodes then use that.  Otherwise the inode share the bdev's
    		 * backing_dev_info.
    		 */
    		if (sb->s_bdev) {
    			struct backing_dev_info *bdi;
    
    			bdi = sb->s_bdev->bd_inode_backing_dev_info;
    			if (!bdi)
    				bdi = sb->s_bdev->bd_inode->i_mapping->backing_dev_info;
    			mapping->backing_dev_info = bdi;
    		}
    		memset(&inode->u, 0, sizeof(inode->u));
    		inode->i_mapping = mapping;
    	}
    	return inode;
    }
    
    void destroy_inode(struct inode *inode) 
    {
    	BUG_ON(inode_has_buffers(inode));
    	security_inode_free(inode);
    	if (inode->i_sb->s_op->destroy_inode)
    		inode->i_sb->s_op->destroy_inode(inode);
    	else
    		kmem_cache_free(inode_cachep, (inode));
    }
    
    
    /*
     * These are initializations that only need to be done
     * once, because the fields are idempotent across use
     * of the inode, so let the slab aware of that.
     */
    void inode_init_once(struct inode *inode)
    {
    	memset(inode, 0, sizeof(*inode));
    	INIT_HLIST_NODE(&inode->i_hash);
    	INIT_LIST_HEAD(&inode->i_dentry);
    	INIT_LIST_HEAD(&inode->i_devices);
    	mutex_init(&inode->i_mutex);
    	init_rwsem(&inode->i_alloc_sem);
    	INIT_RADIX_TREE(&inode->i_data.page_tree, GFP_ATOMIC);
    	rwlock_init(&inode->i_data.tree_lock);
    	spin_lock_init(&inode->i_data.i_mmap_lock);
    	INIT_LIST_HEAD(&inode->i_data.private_list);
    	spin_lock_init(&inode->i_data.private_lock);
    	INIT_RAW_PRIO_TREE_ROOT(&inode->i_data.i_mmap);
    	INIT_LIST_HEAD(&inode->i_data.i_mmap_nonlinear);
    	spin_lock_init(&inode->i_lock);
    	i_size_ordered_init(inode);
    #ifdef CONFIG_INOTIFY
    	INIT_LIST_HEAD(&inode->inotify_watches);
    	mutex_init(&inode->inotify_mutex);
    #endif
    }
    
    EXPORT_SYMBOL(inode_init_once);
    
    static void init_once(void * foo, kmem_cache_t * cachep, unsigned long flags)
    {
    	struct inode * inode = (struct inode *) foo;
    
    	if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
    	    SLAB_CTOR_CONSTRUCTOR)
    		inode_init_once(inode);
    }
    
    /*
     * inode_lock must be held
     */
    void __iget(struct inode * inode)
    {
    	if (atomic_read(&inode->i_count)) {
    		atomic_inc(&inode->i_count);
    		return;
    	}
    	atomic_inc(&inode->i_count);
    	if (!(inode->i_state & (I_DIRTY|I_LOCK)))
    		list_move(&inode->i_list, &inode_in_use);
    	inodes_stat.nr_unused--;
    }
    
    /**
     * clear_inode - clear an inode
     * @inode: inode to clear
     *
     * This is called by the filesystem to tell us
     * that the inode is no longer useful. We just
     * terminate it with extreme prejudice.
     */
    void clear_inode(struct inode *inode)
    {
    	might_sleep();
    	invalidate_inode_buffers(inode);
           
    	BUG_ON(inode->i_data.nrpages);
    	BUG_ON(!(inode->i_state & I_FREEING));
    	BUG_ON(inode->i_state & I_CLEAR);
    	wait_on_inode(inode);
    	DQUOT_DROP(inode);
    	if (inode->i_sb && inode->i_sb->s_op->clear_inode)
    		inode->i_sb->s_op->clear_inode(inode);
    	if (inode->i_bdev)
    		bd_forget(inode);
    	if (inode->i_cdev)
    		cd_forget(inode);
    	inode->i_state = I_CLEAR;
    }
    
    EXPORT_SYMBOL(clear_inode);
    
    /*
     * dispose_list - dispose of the contents of a local list
     * @head: the head of the list to free
     *
     * Dispose-list gets a local list with local inodes in it, so it doesn't
     * need to worry about list corruption and SMP locks.
     */
    static void dispose_list(struct list_head *head)
    {
    	int nr_disposed = 0;
    
    	while (!list_empty(head)) {
    		struct inode *inode;
    
    		inode = list_entry(head->next, struct inode, i_list);
    		list_del(&inode->i_list);
    
    		if (inode->i_data.nrpages)
    			truncate_inode_pages(&inode->i_data, 0);
    		clear_inode(inode);
    
    		spin_lock(&inode_lock);
    		hlist_del_init(&inode->i_hash);
    		list_del_init(&inode->i_sb_list);
    		spin_unlock(&inode_lock);
    
    		wake_up_inode(inode);
    		destroy_inode(inode);
    		nr_disposed++;
    	}
    	spin_lock(&inode_lock);
    	inodes_stat.nr_inodes -= nr_disposed;
    	spin_unlock(&inode_lock);
    }
    
    /*
     * Invalidate all inodes for a device.
     */
    static int invalidate_list(struct list_head *head, struct list_head *dispose)
    {
    	struct list_head *next;
    	int busy = 0, count = 0;
    
    	next = head->next;
    	for (;;) {
    		struct list_head * tmp = next;
    		struct inode * inode;
    
    		/*
    		 * We can reschedule here without worrying about the list's
    		 * consistency because the per-sb list of inodes must not
    		 * change during umount anymore, and because iprune_mutex keeps
    		 * shrink_icache_memory() away.
    		 */
    		cond_resched_lock(&inode_lock);
    
    		next = next->next;
    		if (tmp == head)
    			break;
    		inode = list_entry(tmp, struct inode, i_sb_list);
    		invalidate_inode_buffers(inode);
    		if (!atomic_read(&inode->i_count)) {
    			list_move(&inode->i_list, dispose);
    			inode->i_state |= I_FREEING;
    			count++;
    			continue;
    		}
    		busy = 1;
    	}
    	/* only unused inodes may be cached with i_count zero */
    	inodes_stat.nr_unused -= count;
    	return busy;
    }
    
    /**
     *	invalidate_inodes	- discard the inodes on a device
     *	@sb: superblock
     *
     *	Discard all of the inodes for a given superblock. If the discard
     *	fails because there are busy inodes then a non zero value is returned.
     *	If the discard is successful all the inodes have been discarded.
     */
    int invalidate_inodes(struct super_block * sb)
    {
    	int busy;
    	LIST_HEAD(throw_away);
    
    	mutex_lock(&iprune_mutex);
    	spin_lock(&inode_lock);
    	inotify_unmount_inodes(&sb->s_inodes);
    	busy = invalidate_list(&sb->s_inodes, &throw_away);
    	spin_unlock(&inode_lock);
    
    	dispose_list(&throw_away);
    	mutex_unlock(&iprune_mutex);
    
    	return busy;
    }
    
    EXPORT_SYMBOL(invalidate_inodes);
     
    int __invalidate_device(struct block_device *bdev)
    {
    	struct super_block *sb = get_super(bdev);
    	int res = 0;
    
    	if (sb) {
    		/*
    		 * no need to lock the super, get_super holds the
    		 * read mutex so the filesystem cannot go away
    		 * under us (->put_super runs with the write lock
    		 * hold).
    		 */
    		shrink_dcache_sb(sb);
    		res = invalidate_inodes(sb);
    		drop_super(sb);
    	}
    	invalidate_bdev(bdev, 0);
    	return res;
    }
    EXPORT_SYMBOL(__invalidate_device);
    
    static int can_unuse(struct inode *inode)
    {
    	if (inode->i_state)
    		return 0;
    	if (inode_has_buffers(inode))
    		return 0;
    	if (atomic_read(&inode->i_count))
    		return 0;
    	if (inode->i_data.nrpages)
    		return 0;
    	return 1;
    }
    
    /*
     * Scan `goal' inodes on the unused list for freeable ones. They are moved to
     * a temporary list and then are freed outside inode_lock by dispose_list().
     *
     * Any inodes which are pinned purely because of attached pagecache have their
     * pagecache removed.  We expect the final iput() on that inode to add it to
     * the front of the inode_unused list.  So look for it there and if the
     * inode is still freeable, proceed.  The right inode is found 99.9% of the
     * time in testing on a 4-way.
     *
     * If the inode has metadata buffers attached to mapping->private_list then
     * try to remove them.
     */
    static void prune_icache(int nr_to_scan)
    {
    	LIST_HEAD(freeable);
    	int nr_pruned = 0;
    	int nr_scanned;
    	unsigned long reap = 0;
    
    	mutex_lock(&iprune_mutex);
    	spin_lock(&inode_lock);
    	for (nr_scanned = 0; nr_scanned < nr_to_scan; nr_scanned++) {
    		struct inode *inode;
    
    		if (list_empty(&inode_unused))
    			break;
    
    		inode = list_entry(inode_unused.prev, struct inode, i_list);
    
    		if (inode->i_state || atomic_read(&inode->i_count)) {
    			list_move(&inode->i_list, &inode_unused);
    			continue;
    		}
    		if (inode_has_buffers(inode) || inode->i_data.nrpages) {
    			__iget(inode);
    			spin_unlock(&inode_lock);
    			if (remove_inode_buffers(inode))
    				reap += invalidate_inode_pages(&inode->i_data);
    			iput(inode);
    			spin_lock(&inode_lock);
    
    			if (inode != list_entry(inode_unused.next,
    						struct inode, i_list))
    				continue;	/* wrong inode or list_empty */
    			if (!can_unuse(inode))
    				continue;
    		}
    		list_move(&inode->i_list, &freeable);
    		inode->i_state |= I_FREEING;
    		nr_pruned++;
    	}
    	inodes_stat.nr_unused -= nr_pruned;
    	spin_unlock(&inode_lock);
    
    	dispose_list(&freeable);
    	mutex_unlock(&iprune_mutex);
    
    	if (current_is_kswapd())
    		mod_page_state(kswapd_inodesteal, reap);
    	else
    		mod_page_state(pginodesteal, reap);
    }
    
    /*
     * shrink_icache_memory() will attempt to reclaim some unused inodes.  Here,
     * "unused" means that no dentries are referring to the inodes: the files are
     * not open and the dcache references to those inodes have already been
     * reclaimed.
     *
     * This function is passed the number of inodes to scan, and it returns the
     * total number of remaining possibly-reclaimable inodes.
     */
    static int shrink_icache_memory(int nr, 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 void __wait_on_freeing_inode(struct inode *inode);
    /*
     * Called with the inode lock held.
     * NOTE: we are not increasing the inode-refcount, you must call __iget()
     * by hand after calling find_inode now! This simplifies iunique and won't
     * add any additional branch in the common code.
     */
    static struct inode * find_inode(struct super_block * sb, struct hlist_head *head, int (*test)(struct inode *, void *), void *data)
    {
    	struct hlist_node *node;
    	struct inode * inode = NULL;
    
    repeat:
    	hlist_for_each (node, head) { 
    		inode = hlist_entry(node, struct inode, i_hash);
    		if (inode->i_sb != sb)
    			continue;
    		if (!test(inode, data))
    			continue;
    		if (inode->i_state & (I_FREEING|I_CLEAR|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 (node, head) {
    		inode = hlist_entry(node, struct inode, i_hash);
    		if (inode->i_ino != ino)
    			continue;
    		if (inode->i_sb != sb)
    			continue;
    		if (inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE)) {
    			__wait_on_freeing_inode(inode);
    			goto repeat;
    		}
    		break;
    	}
    	return node ? inode : NULL;
    }
    
    /**
     *	new_inode 	- obtain an inode
     *	@sb: superblock
     *
     *	Allocates a new inode for given superblock.
     */
    struct inode *new_inode(struct super_block *sb)
    {
    	static unsigned long last_ino;
    	struct inode * inode;
    
    	spin_lock_prefetch(&inode_lock);
    	
    	inode = alloc_inode(sb);
    	if (inode) {
    		spin_lock(&inode_lock);
    		inodes_stat.nr_inodes++;
    		list_add(&inode->i_list, &inode_in_use);
    		list_add(&inode->i_sb_list, &sb->s_inodes);
    		inode->i_ino = ++last_ino;
    		inode->i_state = 0;
    		spin_unlock(&inode_lock);
    	}
    	return inode;
    }
    
    EXPORT_SYMBOL(new_inode);
    
    void unlock_new_inode(struct inode *inode)
    {
    	/*
    	 * This is special!  We do not need the spinlock
    	 * when clearing I_LOCK, because we're guaranteed
    	 * that nobody else tries to do anything about the
    	 * state of the inode when it is locked, as we
    	 * just created it (so there can be no old holders
    	 * that haven't tested I_LOCK).
    	 */
    	inode->i_state &= ~(I_LOCK|I_NEW);
    	wake_up_inode(inode);
    }
    
    EXPORT_SYMBOL(unlock_new_inode);
    
    /*
     * This is called without the inode lock held.. Be careful.
     *
     * We no longer cache the sb_flags in i_flags - see fs.h
     *	-- rmk@arm.uk.linux.org
     */
    static struct inode * get_new_inode(struct super_block *sb, struct hlist_head *head, int (*test)(struct inode *, void *), int (*set)(struct inode *, void *), void *data)
    {
    	struct inode * inode;
    
    	inode = alloc_inode(sb);
    	if (inode) {
    		struct inode * old;
    
    		spin_lock(&inode_lock);
    		/* We released the lock, so.. */
    		old = find_inode(sb, head, test, data);
    		if (!old) {
    			if (set(inode, data))
    				goto set_failed;
    
    			inodes_stat.nr_inodes++;
    			list_add(&inode->i_list, &inode_in_use);
    			list_add(&inode->i_sb_list, &sb->s_inodes);
    			hlist_add_head(&inode->i_hash, head);
    			inode->i_state = I_LOCK|I_NEW;
    			spin_unlock(&inode_lock);
    
    			/* Return the locked inode with I_NEW set, the
    			 * caller is responsible for filling in the contents
    			 */
    			return inode;
    		}
    
    		/*
    		 * Uhhuh, somebody else created the same inode under
    		 * us. Use the old inode instead of the one we just
    		 * allocated.
    		 */
    		__iget(old);
    		spin_unlock(&inode_lock);
    		destroy_inode(inode);
    		inode = old;
    		wait_on_inode(inode);
    	}
    	return inode;
    
    set_failed:
    	spin_unlock(&inode_lock);
    	destroy_inode(inode);
    	return NULL;
    }
    
    /*
     * get_new_inode_fast is the fast path version of get_new_inode, see the
     * comment at iget_locked for details.
     */
    static struct inode * get_new_inode_fast(struct super_block *sb, struct hlist_head *head, unsigned long ino)
    {
    	struct inode * inode;
    
    	inode = alloc_inode(sb);
    	if (inode) {
    		struct inode * old;
    
    		spin_lock(&inode_lock);
    		/* We released the lock, so.. */
    		old = find_inode_fast(sb, head, ino);
    		if (!old) {
    			inode->i_ino = ino;
    			inodes_stat.nr_inodes++;
    			list_add(&inode->i_list, &inode_in_use);
    			list_add(&inode->i_sb_list, &sb->s_inodes);
    			hlist_add_head(&inode->i_hash, head);
    			inode->i_state = I_LOCK|I_NEW;
    			spin_unlock(&inode_lock);
    
    			/* Return the locked inode with I_NEW set, the
    			 * caller is responsible for filling in the contents
    			 */
    			return inode;
    		}
    
    		/*
    		 * Uhhuh, somebody else created the same inode under
    		 * us. Use the old inode instead of the one we just
    		 * allocated.
    		 */
    		__iget(old);
    		spin_unlock(&inode_lock);
    		destroy_inode(inode);
    		inode = old;
    		wait_on_inode(inode);
    	}
    	return inode;
    }
    
    static inline unsigned long hash(struct super_block *sb, unsigned long hashval)
    {
    	unsigned long tmp;
    
    	tmp = (hashval * (unsigned long)sb) ^ (GOLDEN_RATIO_PRIME + hashval) /
    			L1_CACHE_BYTES;
    	tmp = tmp ^ ((tmp ^ GOLDEN_RATIO_PRIME) >> I_HASHBITS);
    	return tmp & I_HASHMASK;
    }
    
    /**
     *	iunique - get a unique inode number
     *	@sb: superblock
     *	@max_reserved: highest reserved inode number
     *
     *	Obtain an inode number that is unique on the system for a given
     *	superblock. This is used by file systems that have no natural
     *	permanent inode numbering system. An inode number is returned that
     *	is higher than the reserved limit but unique.
     *
     *	BUGS:
     *	With a large number of inodes live on the file system this function
     *	currently becomes quite slow.
     */
    ino_t iunique(struct super_block *sb, ino_t max_reserved)
    {
    	static ino_t counter;
    	struct inode *inode;
    	struct hlist_head * head;
    	ino_t res;
    	spin_lock(&inode_lock);
    retry:
    	if (counter > max_reserved) {
    		head = inode_hashtable + hash(sb,counter);
    		res = counter++;
    		inode = find_inode_fast(sb, head, res);
    		if (!inode) {
    			spin_unlock(&inode_lock);
    			return res;
    		}
    	} else {
    		counter = max_reserved + 1;
    	}
    	goto retry;
    	
    }
    
    EXPORT_SYMBOL(iunique);
    
    struct inode *igrab(struct inode *inode)
    {
    	spin_lock(&inode_lock);
    	if (!(inode->i_state & (I_FREEING|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
     *
     * This is iget() without the read_inode() portion of get_new_inode().
     *
     * iget5_locked() uses ifind() to search for the inode specified by @hashval
     * and @data in the inode cache and if present it is returned with an increased
     * reference count. This is a generalized version of iget_locked() for file
     * systems where the inode number is not sufficient for unique identification
     * of an inode.
     *
     * If the inode is not in cache, get_new_inode() is called to allocate a new
     * inode and this is returned locked, hashed, and with the I_NEW flag set. The
     * file system gets to fill it in before unlocking it via unlock_new_inode().
     *
     * Note both @test and @set are called with the inode_lock held, so can't sleep.
     */
    struct inode *iget5_locked(struct super_block *sb, unsigned long hashval,
    		int (*test)(struct inode *, void *),
    		int (*set)(struct inode *, void *), void *data)
    {
    	struct hlist_head *head = inode_hashtable + hash(sb, hashval);
    	struct inode *inode;
    
    	inode = ifind(sb, head, test, data, 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
     *
     * This is iget() without the read_inode() portion of get_new_inode_fast().
     *
     * iget_locked() uses ifind_fast() to search for the inode specified by @ino in
     * the inode cache and if present it is returned with an increased reference
     * count. This is for file systems where the inode number is sufficient for
     * unique identification of an inode.
     *
     * If the inode is not in cache, get_new_inode_fast() is called to allocate a
     * new inode and this is returned locked, hashed, and with the I_NEW flag set.
     * The file system gets to fill it in before unlocking it via
     * unlock_new_inode().
     */
    struct inode *iget_locked(struct super_block *sb, unsigned long ino)
    {
    	struct hlist_head *head = inode_hashtable + hash(sb, ino);
    	struct inode *inode;
    
    	inode = ifind_fast(sb, head, ino);
    	if (inode)
    		return inode;
    	/*
    	 * get_new_inode_fast() will do the right thing, re-trying the search
    	 * in case it had to block at any point.
    	 */
    	return get_new_inode_fast(sb, head, ino);
    }
    
    EXPORT_SYMBOL(iget_locked);
    
    /**
     *	__insert_inode_hash - hash an inode
     *	@inode: unhashed inode
     *	@hashval: unsigned long value used to locate this object in the
     *		inode_hashtable.
     *
     *	Add an inode to the inode hash for this superblock.
     */
    void __insert_inode_hash(struct inode *inode, unsigned long hashval)
    {
    	struct hlist_head *head = inode_hashtable + hash(inode->i_sb, hashval);
    	spin_lock(&inode_lock);
    	hlist_add_head(&inode->i_hash, head);
    	spin_unlock(&inode_lock);
    }
    
    EXPORT_SYMBOL(__insert_inode_hash);
    
    /**
     *	remove_inode_hash - remove an inode from the hash
     *	@inode: inode to unhash
     *
     *	Remove an inode from the superblock.
     */
    void remove_inode_hash(struct inode *inode)
    {
    	spin_lock(&inode_lock);
    	hlist_del_init(&inode->i_hash);
    	spin_unlock(&inode_lock);
    }
    
    EXPORT_SYMBOL(remove_inode_hash);
    
    /*
     * Tell the filesystem that this inode is no longer of any interest and should
     * be completely destroyed.
     *
     * We leave the inode in the inode hash table until *after* the filesystem's
     * ->delete_inode completes.  This ensures that an iget (such as nfsd might
     * instigate) will always find up-to-date information either in the hash or on
     * disk.
     *
     * I_FREEING is set so that no-one will take a new reference to the inode while
     * it is being deleted.
     */
    void generic_delete_inode(struct inode *inode)
    {
    	struct super_operations *op = inode->i_sb->s_op;
    
    	list_del_init(&inode->i_list);
    	list_del_init(&inode->i_sb_list);
    	inode->i_state|=I_FREEING;
    	inodes_stat.nr_inodes--;
    	spin_unlock(&inode_lock);
    
    	security_inode_delete(inode);
    
    	if (op->delete_inode) {
    		void (*delete)(struct inode *) = op->delete_inode;
    		if (!is_bad_inode(inode))
    			DQUOT_INIT(inode);
    		/* Filesystems implementing their own
    		 * s_op->delete_inode are required to call
    		 * truncate_inode_pages and clear_inode()
    		 * internally */
    		delete(inode);
    	} else {
    		truncate_inode_pages(&inode->i_data, 0);
    		clear_inode(inode);
    	}
    	spin_lock(&inode_lock);
    	hlist_del_init(&inode->i_hash);
    	spin_unlock(&inode_lock);
    	wake_up_inode(inode);
    	BUG_ON(inode->i_state != I_CLEAR);
    	destroy_inode(inode);
    }
    
    EXPORT_SYMBOL(generic_delete_inode);
    
    static void generic_forget_inode(struct inode *inode)
    {
    	struct super_block *sb = inode->i_sb;
    
    	if (!hlist_unhashed(&inode->i_hash)) {
    		if (!(inode->i_state & (I_DIRTY|I_LOCK)))
    			list_move(&inode->i_list, &inode_unused);
    		inodes_stat.nr_unused++;
    		if (!sb || (sb->s_flags & MS_ACTIVE)) {
    			spin_unlock(&inode_lock);
    			return;
    		}
    		inode->i_state |= I_WILL_FREE;
    		spin_unlock(&inode_lock);
    		write_inode_now(inode, 1);
    		spin_lock(&inode_lock);
    		inode->i_state &= ~I_WILL_FREE;
    		inodes_stat.nr_unused--;
    		hlist_del_init(&inode->i_hash);
    	}
    	list_del_init(&inode->i_list);
    	list_del_init(&inode->i_sb_list);
    	inode->i_state |= I_FREEING;
    	inodes_stat.nr_inodes--;
    	spin_unlock(&inode_lock);
    	if (inode->i_data.nrpages)
    		truncate_inode_pages(&inode->i_data, 0);
    	clear_inode(inode);
    	wake_up_inode(inode);
    	destroy_inode(inode);
    }
    
    /*
     * Normal UNIX filesystem behaviour: delete the
     * inode when the usage count drops to zero, and
     * i_nlink is zero.
     */
    void generic_drop_inode(struct inode *inode)
    {
    	if (!inode->i_nlink)
    		generic_delete_inode(inode);
    	else
    		generic_forget_inode(inode);
    }
    
    EXPORT_SYMBOL_GPL(generic_drop_inode);
    
    /*
     * Called when we're dropping the last reference
     * to an inode. 
     *
     * Call the FS "drop()" function, defaulting to
     * the legacy UNIX filesystem behaviour..
     *
     * NOTE! NOTE! NOTE! We're called with the inode lock
     * held, and the drop function is supposed to release
     * the lock!
     */
    static inline void iput_final(struct inode *inode)
    {
    	struct super_operations *op = inode->i_sb->s_op;
    	void (*drop)(struct inode *) = generic_drop_inode;
    
    	if (op && op->drop_inode)
    		drop = op->drop_inode;
    	drop(inode);
    }
    
    /**
     *	iput	- put an inode 
     *	@inode: inode to put
     *
     *	Puts an inode, dropping its usage count. If the inode use count hits
     *	zero, the inode is then freed and may also be destroyed.
     *
     *	Consequently, iput() can sleep.
     */
    void iput(struct inode *inode)
    {
    	if (inode) {
    		struct super_operations *op = inode->i_sb->s_op;
    
    		BUG_ON(inode->i_state == I_CLEAR);
    
    		if (op && op->put_inode)
    			op->put_inode(inode);
    
    		if (atomic_dec_and_lock(&inode->i_count, &inode_lock))
    			iput_final(inode);
    	}
    }
    
    EXPORT_SYMBOL(iput);
    
    /**
     *	bmap	- find a block number in a file
     *	@inode: inode of file
     *	@block: block to find
     *
     *	Returns the block number on the device holding the inode that
     *	is the disk block number for the block of the file requested.
     *	That is, asked for block 4 of inode 1 the function will return the
     *	disk block relative to the disk start that holds that block of the 
     *	file.
     */
    sector_t bmap(struct inode * inode, sector_t block)
    {
    	sector_t res = 0;
    	if (inode->i_mapping->a_ops->bmap)
    		res = inode->i_mapping->a_ops->bmap(inode->i_mapping, block);
    	return res;
    }
    
    EXPORT_SYMBOL(bmap);
    
    /**
     *	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 (IS_RDONLY(inode))
    		return;
    
    	if ((inode->i_flags & S_NOATIME) ||
    	    (inode->i_sb->s_flags & MS_NOATIME) ||
    	    ((inode->i_sb->s_flags & MS_NODIRATIME) && S_ISDIR(inode->i_mode)))
    		return;
    
    	/*
    	 * We may have a NULL vfsmount when coming from NFSD
    	 */
    	if (mnt &&
    	    ((mnt->mnt_flags & MNT_NOATIME) ||
    	     ((mnt->mnt_flags & MNT_NODIRATIME) && S_ISDIR(inode->i_mode))))
    		return;
    
    	now = current_fs_time(inode->i_sb);
    	if (!timespec_equal(&inode->i_atime, &now)) {
    		inode->i_atime = now;
    		mark_inode_dirty_sync(inode);
    	}
    }
    
    EXPORT_SYMBOL(touch_atime);
    
    /**
     *	file_update_time	-	update mtime and ctime time
     *	@file: file accessed
     *
     *	Update the mtime and ctime members of an inode and mark the inode
     *	for writeback.  Note that this function is meant exclusively for
     *	usage in the file write path of filesystems, and filesystems may
     *	choose to explicitly ignore update via this function with the
     *	S_NOCTIME inode flag, e.g. for network filesystem where these
     *	timestamps are handled by the server.
     */
    
    void file_update_time(struct file *file)
    {
    	struct inode *inode = file->f_dentry->d_inode;
    	struct timespec now;
    	int sync_it = 0;
    
    	if (IS_NOCMTIME(inode))
    		return;
    	if (IS_RDONLY(inode))
    		return;
    
    	now = current_fs_time(inode->i_sb);
    	if (!timespec_equal(&inode->i_mtime, &now))
    		sync_it = 1;
    	inode->i_mtime = now;
    
    	if (!timespec_equal(&inode->i_ctime, &now))
    		sync_it = 1;
    	inode->i_ctime = now;
    
    	if (sync_it)
    		mark_inode_dirty_sync(inode);
    }
    
    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);
    
    /*
     *	Quota functions that want to walk the inode lists..
     */
    #ifdef CONFIG_QUOTA
    
    /* Function back in dquot.c */
    int remove_inode_dquot_ref(struct inode *, int, struct list_head *);
    
    void remove_dquot_ref(struct super_block *sb, int type,
    			struct list_head *tofree_head)
    {
    	struct inode *inode;
    
    	if (!sb->dq_op)
    		return;	/* nothing to do */
    	spin_lock(&inode_lock);	/* This lock is for inodes code */
    
    	/*
    	 * We don't have to lock against quota code - test IS_QUOTAINIT is
    	 * just for speedup...
    	 */
    	list_for_each_entry(inode, &sb->s_inodes, i_sb_list)
    		if (!IS_NOQUOTA(inode))
    			remove_inode_dquot_ref(inode, type, tofree_head);
    
    	spin_unlock(&inode_lock);
    }
    
    #endif
    
    int inode_wait(void *word)
    {
    	schedule();
    	return 0;
    }
    
    /*
     * If we try to find an inode in the inode hash while it is being
     * deleted, we have to wait until the filesystem completes its
     * deletion before reporting that it isn't found.  This function waits
     * until the deletion _might_ have completed.  Callers are responsible
     * to recheck inode state.
     *
     * It doesn't matter if I_LOCK is not set initially, a call to
     * wake_up_inode() after removing from the hash list will DTRT.
     *
     * This is called with inode_lock held.
     */
    static void __wait_on_freeing_inode(struct inode *inode)
    {
    	wait_queue_head_t *wq;
    	DEFINE_WAIT_BIT(wait, &inode->i_state, __I_LOCK);
    	wq = bit_waitqueue(&inode->i_state, __I_LOCK);
    	prepare_to_wait(wq, &wait.wait, TASK_UNINTERRUPTIBLE);
    	spin_unlock(&inode_lock);
    	schedule();
    	finish_wait(wq, &wait.wait);
    	spin_lock(&inode_lock);
    }
    
    void wake_up_inode(struct inode *inode)
    {
    	/*
    	 * Prevent speculative execution through spin_unlock(&inode_lock);
    	 */
    	smp_mb();
    	wake_up_bit(&inode->i_state, __I_LOCK);
    }
    
    static __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(unsigned long mempages)
    {
    	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,
    					 NULL);
    	set_shrinker(DEFAULT_SEEKS, shrink_icache_memory);
    
    	/* Hash may have been set up in inode_init_early */
    	if (!hashdist)
    		return;
    
    	inode_hashtable =
    		alloc_large_system_hash("Inode-cache",
    					sizeof(struct hlist_head),
    					ihash_entries,
    					14,
    					0,
    					&i_hash_shift,
    					&i_hash_mask,
    					0);
    
    	for (loop = 0; loop < (1 << i_hash_shift); loop++)
    		INIT_HLIST_HEAD(&inode_hashtable[loop]);
    }
    
    void init_special_inode(struct inode *inode, umode_t mode, dev_t rdev)
    {
    	inode->i_mode = mode;
    	if (S_ISCHR(mode)) {
    		inode->i_fop = &def_chr_fops;
    		inode->i_rdev = rdev;
    	} else if (S_ISBLK(mode)) {
    		inode->i_fop = &def_blk_fops;
    		inode->i_rdev = rdev;
    	} else if (S_ISFIFO(mode))
    		inode->i_fop = &def_fifo_fops;
    	else if (S_ISSOCK(mode))
    		inode->i_fop = &bad_sock_fops;
    	else
    		printk(KERN_DEBUG "init_special_inode: bogus i_mode (%o)\n",
    		       mode);
    }
    EXPORT_SYMBOL(init_special_inode);