inode.c 44 KB
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/*
 * 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>
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#include <linux/rwsem.h>
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#include <linux/hash.h>
#include <linux/swap.h>
#include <linux/security.h>
#include <linux/pagemap.h>
#include <linux/cdev.h>
#include <linux/bootmem.h>
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#include <linux/fsnotify.h>
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#include <linux/mount.h>
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#include <linux/async.h>
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#include <linux/posix_acl.h>
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#include <linux/ima.h>
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/*
 * This is needed for the following functions:
 *  - inode_has_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

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static unsigned int i_hash_mask __read_mostly;
static unsigned int i_hash_shift __read_mostly;
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/*
 * 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.
 */

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static LIST_HEAD(inode_lru);
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static struct hlist_head *inode_hashtable __read_mostly;
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/*
 * 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);

/*
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 * iprune_sem provides exclusion between the kswapd or try_to_free_pages
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 * 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.
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 *
 * 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.
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 */
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static DECLARE_RWSEM(iprune_sem);
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/*
 * Statistics gathering..
 */
struct inodes_stat_t inodes_stat;

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static DEFINE_PER_CPU(unsigned int, nr_inodes);
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static struct kmem_cache *inode_cachep __read_mostly;
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static int get_nr_inodes(void)
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{
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	int i;
	int sum = 0;
	for_each_possible_cpu(i)
		sum += per_cpu(nr_inodes, i);
	return sum < 0 ? 0 : sum;
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}

static inline int get_nr_inodes_unused(void)
{
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	return inodes_stat.nr_unused;
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}

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

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

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

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/**
 * inode_init_always - perform inode structure intialisation
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 * @sb: superblock inode belongs to
 * @inode: inode to initialise
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 *
 * These are initializations that need to be done on every inode
 * allocation as the fields are not initialised by slab allocation.
 */
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int inode_init_always(struct super_block *sb, struct inode *inode)
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{
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	static const struct address_space_operations empty_aops;
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	static const struct inode_operations empty_iops;
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	static const struct file_operations empty_fops;
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	struct address_space *const mapping = &inode->i_data;
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	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;
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	inode->i_uid = 0;
	inode->i_gid = 0;
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	atomic_set(&inode->i_writecount, 0);
	inode->i_size = 0;
	inode->i_blocks = 0;
	inode->i_bytes = 0;
	inode->i_generation = 0;
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#ifdef CONFIG_QUOTA
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	memset(&inode->i_dquot, 0, sizeof(inode->i_dquot));
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#endif
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	inode->i_pipe = NULL;
	inode->i_bdev = NULL;
	inode->i_cdev = NULL;
	inode->i_rdev = 0;
	inode->dirtied_when = 0;
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	if (security_inode_alloc(inode))
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		goto out;
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	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;
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	mapping_set_gfp_mask(mapping, GFP_HIGHUSER_MOVABLE);
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	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;

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		bdi = sb->s_bdev->bd_inode->i_mapping->backing_dev_info;
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		mapping->backing_dev_info = bdi;
	}
	inode->i_private = NULL;
	inode->i_mapping = mapping;
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#ifdef CONFIG_FS_POSIX_ACL
	inode->i_acl = inode->i_default_acl = ACL_NOT_CACHED;
#endif
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#ifdef CONFIG_FSNOTIFY
	inode->i_fsnotify_mask = 0;
#endif

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	this_cpu_inc(nr_inodes);
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	return 0;
out:
	return -ENOMEM;
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}
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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);

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	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;
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}
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void __destroy_inode(struct inode *inode)
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{
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	BUG_ON(inode_has_buffers(inode));
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	security_inode_free(inode);
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	fsnotify_inode_delete(inode);
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#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
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	this_cpu_dec(nr_inodes);
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}
EXPORT_SYMBOL(__destroy_inode);

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

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

/*
 * 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);
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	INIT_LIST_HEAD(&inode->i_wb_list);
	INIT_LIST_HEAD(&inode->i_lru);
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	INIT_RADIX_TREE(&inode->i_data.page_tree, GFP_ATOMIC);
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	spin_lock_init(&inode->i_data.tree_lock);
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	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);
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#ifdef CONFIG_FSNOTIFY
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	INIT_HLIST_HEAD(&inode->i_fsnotify_marks);
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#endif
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}
EXPORT_SYMBOL(inode_init_once);

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

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

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static void inode_lru_list_add(struct inode *inode)
{
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	if (list_empty(&inode->i_lru)) {
		list_add(&inode->i_lru, &inode_lru);
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		inodes_stat.nr_unused++;
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	}
}
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static void inode_lru_list_del(struct inode *inode)
{
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	if (!list_empty(&inode->i_lru)) {
		list_del_init(&inode->i_lru);
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		inodes_stat.nr_unused--;
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	}
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}

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static inline void __inode_sb_list_add(struct inode *inode)
{
	list_add(&inode->i_sb_list, &inode->i_sb->s_inodes);
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}

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/**
 * inode_sb_list_add - add inode to the superblock list of inodes
 * @inode: inode to add
 */
void inode_sb_list_add(struct inode *inode)
{
	spin_lock(&inode_lock);
	__inode_sb_list_add(inode);
	spin_unlock(&inode_lock);
}
EXPORT_SYMBOL_GPL(inode_sb_list_add);

static inline void __inode_sb_list_del(struct inode *inode)
{
	list_del_init(&inode->i_sb_list);
}

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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;
}

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

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	spin_lock(&inode_lock);
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	hlist_add_head(&inode->i_hash, b);
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	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.
 */
static void __remove_inode_hash(struct inode *inode)
{
	hlist_del_init(&inode->i_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);

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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);
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	/* don't need i_lock here, no concurrent mods to i_state */
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	inode->i_state = I_FREEING | I_CLEAR;
}
EXPORT_SYMBOL(end_writeback);

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

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	if (op->evict_inode) {
		op->evict_inode(inode);
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	} else {
		if (inode->i_data.nrpages)
			truncate_inode_pages(&inode->i_data, 0);
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		end_writeback(inode);
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	}
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	if (S_ISBLK(inode->i_mode) && inode->i_bdev)
		bd_forget(inode);
	if (S_ISCHR(inode->i_mode) && inode->i_cdev)
		cd_forget(inode);
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}

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/*
 * dispose_list - dispose of the contents of a local list
 * @head: the head of the list to free
 *
 * Dispose-list gets a local list with local inodes in it, so it doesn't
 * need to worry about list corruption and SMP locks.
 */
static void dispose_list(struct list_head *head)
{
	while (!list_empty(head)) {
		struct inode *inode;

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		inode = list_first_entry(head, struct inode, i_lru);
		list_del_init(&inode->i_lru);
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		evict(inode);
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		spin_lock(&inode_lock);
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		__remove_inode_hash(inode);
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		__inode_sb_list_del(inode);
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		spin_unlock(&inode_lock);

		wake_up_inode(inode);
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		destroy_inode(inode);
	}
}

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/**
 * evict_inodes	- evict all evictable inodes for a superblock
 * @sb:		superblock to operate on
 *
 * Make sure that no inodes with zero refcount are retained.  This is
 * called by superblock shutdown after having MS_ACTIVE flag removed,
 * so any inode reaching zero refcount during or after that call will
 * be immediately evicted.
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 */
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void evict_inodes(struct super_block *sb)
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{
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	struct inode *inode, *next;
	LIST_HEAD(dispose);
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	down_write(&iprune_sem);
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	spin_lock(&inode_lock);
	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
		if (atomic_read(&inode->i_count))
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			continue;
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		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
			WARN_ON(1);
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			continue;
		}
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		inode->i_state |= I_FREEING;

		/*
		 * Move the inode off the IO lists and LRU once I_FREEING is
		 * set so that it won't get moved back on there if it is dirty.
		 */
		list_move(&inode->i_lru, &dispose);
		list_del_init(&inode->i_wb_list);
		if (!(inode->i_state & (I_DIRTY | I_SYNC)))
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			inodes_stat.nr_unused--;
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	}
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	spin_unlock(&inode_lock);

	dispose_list(&dispose);
	up_write(&iprune_sem);
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}

/**
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 * invalidate_inodes	- attempt to free all inodes on a superblock
 * @sb:		superblock to operate on
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 *
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 * Attempts to free all inodes for a given superblock.  If there were any
 * busy inodes return a non-zero value, else zero.
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 */
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int invalidate_inodes(struct super_block *sb)
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{
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	int busy = 0;
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	struct inode *inode, *next;
	LIST_HEAD(dispose);
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	down_write(&iprune_sem);
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	spin_lock(&inode_lock);
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	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
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		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE))
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			continue;
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		if (atomic_read(&inode->i_count)) {
			busy = 1;
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			continue;
		}
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		inode->i_state |= I_FREEING;
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		/*
		 * Move the inode off the IO lists and LRU once I_FREEING is
		 * set so that it won't get moved back on there if it is dirty.
		 */
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		list_move(&inode->i_lru, &dispose);
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		list_del_init(&inode->i_wb_list);
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		if (!(inode->i_state & (I_DIRTY | I_SYNC)))
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			inodes_stat.nr_unused--;
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	}
	spin_unlock(&inode_lock);

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	dispose_list(&dispose);
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	up_write(&iprune_sem);
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	return busy;
}

static int can_unuse(struct inode *inode)
{
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	if (inode->i_state & ~I_REFERENCED)
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		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;
}

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

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

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		if (list_empty(&inode_lru))
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			break;

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		inode = list_entry(inode_lru.prev, struct inode, i_lru);
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		/*
		 * Referenced or dirty inodes are still in use. Give them
		 * another pass through the LRU as we canot reclaim them now.
		 */
		if (atomic_read(&inode->i_count) ||
		    (inode->i_state & ~I_REFERENCED)) {
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			list_del_init(&inode->i_lru);
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			inodes_stat.nr_unused--;
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			continue;
		}

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

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			if (inode != list_entry(inode_lru.next,
						struct inode, i_lru))
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				continue;	/* wrong inode or list_empty */
			if (!can_unuse(inode))
				continue;
		}
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		WARN_ON(inode->i_state & I_NEW);
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		inode->i_state |= I_FREEING;
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		/*
		 * Move the inode off the IO lists and LRU once I_FREEING is
		 * set so that it won't get moved back on there if it is dirty.
		 */
		list_move(&inode->i_lru, &freeable);
		list_del_init(&inode->i_wb_list);
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		inodes_stat.nr_unused--;
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	}
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	if (current_is_kswapd())
		__count_vm_events(KSWAPD_INODESTEAL, reap);
	else
		__count_vm_events(PGINODESTEAL, reap);
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	spin_unlock(&inode_lock);

	dispose_list(&freeable);
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	up_read(&iprune_sem);
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}

/*
 * 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.
 */
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static int shrink_icache_memory(struct shrinker *shrink, int nr, gfp_t gfp_mask)
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{
	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..
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		 */
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		if (!(gfp_mask & __GFP_FS))
			return -1;
		prune_icache(nr);
	}
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	return (get_nr_inodes_unused() / 100) * sysctl_vfs_cache_pressure;
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}

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

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static void __wait_on_freeing_inode(struct inode *inode);
/*
 * Called with the inode lock held.
 */
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static struct inode *find_inode(struct super_block *sb,
				struct hlist_head *head,
				int (*test)(struct inode *, void *),
				void *data)
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{
	struct hlist_node *node;
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	struct inode *inode = NULL;
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repeat:
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	hlist_for_each_entry(inode, node, head, i_hash) {
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		if (inode->i_sb != sb)
			continue;
		if (!test(inode, data))
			continue;
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		if (inode->i_state & (I_FREEING|I_WILL_FREE)) {
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			__wait_on_freeing_inode(inode);
			goto repeat;
		}
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		__iget(inode);
		return inode;
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	}
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	return NULL;
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}

/*
 * find_inode_fast is the fast path version of find_inode, see the comment at
 * iget_locked for details.
 */
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static struct inode *find_inode_fast(struct super_block *sb,
				struct hlist_head *head, unsigned long ino)
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{
	struct hlist_node *node;
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	struct inode *inode = NULL;
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repeat:
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	hlist_for_each_entry(inode, node, head, i_hash) {
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		if (inode->i_ino != ino)
			continue;
		if (inode->i_sb != sb)
			continue;
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		if (inode->i_state & (I_FREEING|I_WILL_FREE)) {
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			__wait_on_freeing_inode(inode);
			goto repeat;
		}
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		__iget(inode);
		return inode;
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	}
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	return NULL;
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}

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/*
 * Each cpu owns a range of LAST_INO_BATCH numbers.
 * 'shared_last_ino' is dirtied only once out of LAST_INO_BATCH allocations,
 * to renew the exhausted range.
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 *
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 * This does not significantly increase overflow rate because every CPU can
 * consume at most LAST_INO_BATCH-1 unused inode numbers. So there is
 * NR_CPUS*(LAST_INO_BATCH-1) wastage. At 4096 and 1024, this is ~0.1% of the
 * 2^32 range, and is a worst-case. Even a 50% wastage would only increase
 * overflow rate by 2x, which does not seem too significant.
 *
 * On a 32bit, non LFS stat() call, glibc will generate an EOVERFLOW
 * error if st_ino won't fit in target struct field. Use 32bit counter
 * here to attempt to avoid that.
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 */
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#define LAST_INO_BATCH 1024
static DEFINE_PER_CPU(unsigned int, last_ino);

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unsigned int get_next_ino(void)
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{
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	unsigned int *p = &get_cpu_var(last_ino);
	unsigned int res = *p;
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#ifdef CONFIG_SMP
	if (unlikely((res & (LAST_INO_BATCH-1)) == 0)) {
		static atomic_t shared_last_ino;
		int next = atomic_add_return(LAST_INO_BATCH, &shared_last_ino);

		res = next - LAST_INO_BATCH;
	}
#endif

	*p = ++res;
	put_cpu_var(last_ino);
	return res;
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}
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EXPORT_SYMBOL(get_next_ino);
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/**
 *	new_inode 	- obtain an inode
 *	@sb: superblock
 *
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 *	Allocates a new inode for given superblock. The default gfp_mask
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 *	for allocations related to inode->i_mapping is GFP_HIGHUSER_MOVABLE.
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 *	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
 *
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 */
struct inode *new_inode(struct super_block *sb)
{
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	struct inode *inode;
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	spin_lock_prefetch(&inode_lock);
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	inode = alloc_inode(sb);
	if (inode) {
		spin_lock(&inode_lock);
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		__inode_sb_list_add(inode);
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		inode->i_state = 0;
		spin_unlock(&inode_lock);
	}
	return inode;
}
EXPORT_SYMBOL(new_inode);

void unlock_new_inode(struct inode *inode)
{
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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	if (S_ISDIR(inode->i_mode)) {
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		struct file_system_type *type = inode->i_sb->s_type;

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		/* 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);
		}
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	}
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#endif
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	/*
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	 * This is special!  We do not need the spinlock when clearing I_NEW,
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	 * 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
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	 * there can be no old holders that haven't tested I_NEW).
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	 * However we must emit the memory barrier so that other CPUs reliably
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	 * see the clearing of I_NEW after the other inode initialisation has
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	 * completed.
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	 */
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	smp_mb();
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	WARN_ON(!(inode->i_state & I_NEW));
	inode->i_state &= ~I_NEW;
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	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
 */
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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)
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{
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	struct inode *inode;
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	inode = alloc_inode(sb);
	if (inode) {
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		struct inode *old;
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		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;

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			hlist_add_head(&inode->i_hash, head);
			__inode_sb_list_add(inode);
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			inode->i_state = I_NEW;
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			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.
		 */
		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.
 */
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static struct inode *get_new_inode_fast(struct super_block *sb,
				struct hlist_head *head, unsigned long ino)
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{
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	struct inode *inode;
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	inode = alloc_inode(sb);
	if (inode) {
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		struct inode *old;
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		spin_lock(&inode_lock);
		/* We released the lock, so.. */
		old = find_inode_fast(sb, head, ino);
		if (!old) {
			inode->i_ino = ino;
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			hlist_add_head(&inode->i_hash, head);
			__inode_sb_list_add(inode);
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			inode->i_state = I_NEW;
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			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.
		 */
		spin_unlock(&inode_lock);
		destroy_inode(inode);
		inode = old;
		wait_on_inode(inode);
	}
	return inode;
}

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

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

	return 1;
}

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/**
 *	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)
{
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	/*
	 * 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.
	 */
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	static DEFINE_SPINLOCK(iunique_lock);
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	static unsigned int counter;
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	ino_t res;
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	spin_lock(&inode_lock);
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	spin_lock(&iunique_lock);
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	do {
		if (counter <= max_reserved)
			counter = max_reserved + 1;
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		res = counter++;
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	} while (!test_inode_iunique(sb, res));
	spin_unlock(&iunique_lock);
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	spin_unlock(&inode_lock);
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	return res;
}
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EXPORT_SYMBOL(iunique);

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

	spin_lock(&inode_lock);
	inode = find_inode(sb, head, test, data);
	if (inode) {
		spin_unlock(&inode_lock);
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		if (likely(wait))
			wait_on_inode(inode);
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		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.
 */
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static struct inode *ifind_fast(struct super_block *sb,
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		struct hlist_head *head, unsigned long ino)
{
	struct inode *inode;

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

/**
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 * ilookup5_nowait - search for an inode in the inode cache
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 * @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
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 * 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.
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 *
 * 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);

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	return ifind(sb, head, test, data, 1);
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}
EXPORT_SYMBOL(ilookup5);

/**
 * ilookup - search for an inode in the inode cache
 * @sb:		super block of file system to search