// SPDX-License-Identifier: GPL-2.0-only

  /*

   * (C) 1997 Linus Torvalds

   * (C) 1999 Andrea Arcangeli <andrea@suse.de> (dynamic inode allocation)

   */

  #include <linux/export.h>

  #include <linux/fs.h>
  #include <linux/mm.h>

  #include <linux/backing-dev.h>

  #include <linux/hash.h>
  #include <linux/swap.h>
  #include <linux/security.h>

  #include <linux/cdev.h>

  #include <linux/memblock.h>

  #include <linux/fscrypt.h>

  #include <linux/fsnotify.h>

  #include <linux/mount.h>

  #include <linux/posix_acl.h>

  #include <linux/prefetch.h>

  #include <linux/buffer_head.h> /* for inode_has_buffers */

  #include <linux/ratelimit.h>

  #include <linux/list_lru.h>

  #include <linux/iversion.h>

  #include <trace/events/writeback.h>

  #include "internal.h"

  
  /*

   * Inode locking rules:

   *
   * inode->i_lock protects:
   *   inode->i_state, inode->i_hash, __iget()

   * Inode LRU list locks protect:

   *   inode->i_sb->s_inode_lru, inode->i_lru

   * inode->i_sb->s_inode_list_lock protects:
   *   inode->i_sb->s_inodes, inode->i_sb_list

   * bdi->wb.list_lock protects:

   *   bdi->wb.b_{dirty,io,more_io,dirty_time}, inode->i_io_list

   * inode_hash_lock protects:
   *   inode_hashtable, inode->i_hash

   *
   * Lock ordering:

   *

   * inode->i_sb->s_inode_list_lock

   *   inode->i_lock

   *     Inode LRU list locks

   *

   * bdi->wb.list_lock

   *   inode->i_lock

   *
   * inode_hash_lock

   *   inode->i_sb->s_inode_list_lock

   *   inode->i_lock
   *
   * iunique_lock
   *   inode_hash_lock

   */

  static unsigned int i_hash_mask __read_mostly;
  static unsigned int i_hash_shift __read_mostly;

  static struct hlist_head *inode_hashtable __read_mostly;
  static __cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_hash_lock);

  /*

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

   * Statistics gathering..
   */
  struct inodes_stat_t inodes_stat;

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

  static struct kmem_cache *inode_cachep __read_mostly;

  static long get_nr_inodes(void)

  {

  	int i;

  	long sum = 0;

  	for_each_possible_cpu(i)
  		sum += per_cpu(nr_inodes, i);
  	return sum < 0 ? 0 : sum;

  }

  static inline long get_nr_inodes_unused(void)

  {

  	int i;

  	long sum = 0;

  	for_each_possible_cpu(i)
  		sum += per_cpu(nr_unused, i);
  	return sum < 0 ? 0 : sum;

  }

  long get_nr_dirty_inodes(void)

  {

  	/* not actually dirty inodes, but a wild approximation */

  	long 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(struct ctl_table *table, int write,

  		   void *buffer, size_t *lenp, loff_t *ppos)

  {
  	inodes_stat.nr_inodes = get_nr_inodes();

  	inodes_stat.nr_unused = get_nr_inodes_unused();

  	return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);

  }
  #endif

  static int no_open(struct inode *inode, struct file *file)
  {
  	return -ENXIO;
  }

  /**

   * inode_init_always - perform inode structure initialisation

   * @sb: superblock inode belongs to
   * @inode: inode to initialise

   *
   * These are initializations that need to be done on every inode
   * allocation as the fields are not initialised by slab allocation.
   */

  int inode_init_always(struct super_block *sb, struct inode *inode)

  {

  	static const struct inode_operations empty_iops;

  	static const struct file_operations no_open_fops = {.open = no_open};

  	struct address_space *const mapping = &inode->i_data;

  
  	inode->i_sb = sb;
  	inode->i_blkbits = sb->s_blocksize_bits;
  	inode->i_flags = 0;

  	atomic64_set(&inode->i_sequence, 0);

  	atomic_set(&inode->i_count, 1);
  	inode->i_op = &empty_iops;

  	inode->i_fop = &no_open_fops;

  	inode->__i_nlink = 1;

  	inode->i_opflags = 0;

  	if (sb->s_xattr)
  		inode->i_opflags |= IOP_XATTR;

  	i_uid_write(inode, 0);
  	i_gid_write(inode, 0);

  	atomic_set(&inode->i_writecount, 0);
  	inode->i_size = 0;

  	inode->i_write_hint = WRITE_LIFE_NOT_SET;

  	inode->i_blocks = 0;
  	inode->i_bytes = 0;
  	inode->i_generation = 0;

  	inode->i_pipe = NULL;
  	inode->i_bdev = NULL;
  	inode->i_cdev = NULL;

  	inode->i_link = NULL;

  	inode->i_dir_seq = 0;

  	inode->i_rdev = 0;
  	inode->dirtied_when = 0;

  #ifdef CONFIG_CGROUP_WRITEBACK
  	inode->i_wb_frn_winner = 0;
  	inode->i_wb_frn_avg_time = 0;
  	inode->i_wb_frn_history = 0;
  #endif

  	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);

  	init_rwsem(&inode->i_rwsem);
  	lockdep_set_class(&inode->i_rwsem, &sb->s_type->i_mutex_key);

  	atomic_set(&inode->i_dio_count, 0);

  
  	mapping->a_ops = &empty_aops;
  	mapping->host = inode;
  	mapping->flags = 0;

  	if (sb->s_type->fs_flags & FS_THP_SUPPORT)
  		__set_bit(AS_THP_SUPPORT, &mapping->flags);

  	mapping->wb_err = 0;

  	atomic_set(&mapping->i_mmap_writable, 0);

  #ifdef CONFIG_READ_ONLY_THP_FOR_FS
  	atomic_set(&mapping->nr_thps, 0);
  #endif

  	mapping_set_gfp_mask(mapping, GFP_HIGHUSER_MOVABLE);

  	mapping->private_data = NULL;

  	mapping->writeback_index = 0;

  	inode->i_private = NULL;
  	inode->i_mapping = mapping;

  	INIT_HLIST_HEAD(&inode->i_dentry);	/* buggered by rcu freeing */

  #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

  	inode->i_flctx = NULL;

  	this_cpu_inc(nr_inodes);

  	return 0;

  out:
  	return -ENOMEM;

  }

  EXPORT_SYMBOL(inode_init_always);

  void free_inode_nonrcu(struct inode *inode)
  {
  	kmem_cache_free(inode_cachep, inode);
  }
  EXPORT_SYMBOL(free_inode_nonrcu);
  
  static void i_callback(struct rcu_head *head)
  {
  	struct inode *inode = container_of(head, struct inode, i_rcu);
  	if (inode->free_inode)
  		inode->free_inode(inode);
  	else
  		free_inode_nonrcu(inode);
  }

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

  	const struct super_operations *ops = sb->s_op;

  	struct inode *inode;

  	if (ops->alloc_inode)
  		inode = ops->alloc_inode(sb);

  	else
  		inode = kmem_cache_alloc(inode_cachep, GFP_KERNEL);

  	if (!inode)
  		return NULL;
  
  	if (unlikely(inode_init_always(sb, inode))) {

  		if (ops->destroy_inode) {
  			ops->destroy_inode(inode);
  			if (!ops->free_inode)
  				return NULL;
  		}
  		inode->free_inode = ops->free_inode;
  		i_callback(&inode->i_rcu);

  		return NULL;
  	}
  
  	return inode;

  }

  void __destroy_inode(struct inode *inode)

  {

  	BUG_ON(inode_has_buffers(inode));

  	inode_detach_wb(inode);

  	security_inode_free(inode);

  	fsnotify_inode_delete(inode);

  	locks_free_lock_context(inode);

  	if (!inode->i_nlink) {
  		WARN_ON(atomic_long_read(&inode->i_sb->s_remove_count) == 0);
  		atomic_long_dec(&inode->i_sb->s_remove_count);
  	}

  #ifdef CONFIG_FS_POSIX_ACL

  	if (inode->i_acl && !is_uncached_acl(inode->i_acl))

  		posix_acl_release(inode->i_acl);

  	if (inode->i_default_acl && !is_uncached_acl(inode->i_default_acl))

  		posix_acl_release(inode->i_default_acl);
  #endif

  	this_cpu_dec(nr_inodes);

  }
  EXPORT_SYMBOL(__destroy_inode);

  static void destroy_inode(struct inode *inode)

  {

  	const struct super_operations *ops = inode->i_sb->s_op;

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

  	__destroy_inode(inode);

  	if (ops->destroy_inode) {
  		ops->destroy_inode(inode);
  		if (!ops->free_inode)
  			return;
  	}
  	inode->free_inode = ops->free_inode;
  	call_rcu(&inode->i_rcu, i_callback);

  }

  /**
   * drop_nlink - directly drop an inode's link count
   * @inode: inode
   *
   * This is a low-level filesystem helper to replace any
   * direct filesystem manipulation of i_nlink.  In cases
   * where we are attempting to track writes to the
   * filesystem, a decrement to zero means an imminent
   * write when the file is truncated and actually unlinked
   * on the filesystem.
   */
  void drop_nlink(struct inode *inode)
  {
  	WARN_ON(inode->i_nlink == 0);
  	inode->__i_nlink--;
  	if (!inode->i_nlink)
  		atomic_long_inc(&inode->i_sb->s_remove_count);
  }
  EXPORT_SYMBOL(drop_nlink);
  
  /**
   * clear_nlink - directly zero an inode's link count
   * @inode: inode
   *
   * This is a low-level filesystem helper to replace any
   * direct filesystem manipulation of i_nlink.  See
   * drop_nlink() for why we care about i_nlink hitting zero.
   */
  void clear_nlink(struct inode *inode)
  {
  	if (inode->i_nlink) {
  		inode->__i_nlink = 0;
  		atomic_long_inc(&inode->i_sb->s_remove_count);
  	}
  }
  EXPORT_SYMBOL(clear_nlink);
  
  /**
   * set_nlink - directly set an inode's link count
   * @inode: inode
   * @nlink: new nlink (should be non-zero)
   *
   * This is a low-level filesystem helper to replace any
   * direct filesystem manipulation of i_nlink.
   */
  void set_nlink(struct inode *inode, unsigned int nlink)
  {
  	if (!nlink) {

  		clear_nlink(inode);
  	} else {
  		/* Yes, some filesystems do change nlink from zero to one */
  		if (inode->i_nlink == 0)
  			atomic_long_dec(&inode->i_sb->s_remove_count);
  
  		inode->__i_nlink = nlink;
  	}
  }
  EXPORT_SYMBOL(set_nlink);
  
  /**
   * inc_nlink - directly increment an inode's link count
   * @inode: inode
   *
   * This is a low-level filesystem helper to replace any
   * direct filesystem manipulation of i_nlink.  Currently,
   * it is only here for parity with dec_nlink().
   */
  void inc_nlink(struct inode *inode)
  {

  	if (unlikely(inode->i_nlink == 0)) {
  		WARN_ON(!(inode->i_state & I_LINKABLE));

  		atomic_long_dec(&inode->i_sb->s_remove_count);

  	}

  
  	inode->__i_nlink++;
  }
  EXPORT_SYMBOL(inc_nlink);

  static void __address_space_init_once(struct address_space *mapping)

  {

  	xa_init_flags(&mapping->i_pages, XA_FLAGS_LOCK_IRQ | XA_FLAGS_ACCOUNT);

  	init_rwsem(&mapping->i_mmap_rwsem);

  	INIT_LIST_HEAD(&mapping->private_list);
  	spin_lock_init(&mapping->private_lock);

  	mapping->i_mmap = RB_ROOT_CACHED;

  }

  
  void address_space_init_once(struct address_space *mapping)
  {
  	memset(mapping, 0, sizeof(*mapping));
  	__address_space_init_once(mapping);
  }

  EXPORT_SYMBOL(address_space_init_once);

  /*
   * These are initializations that only need to be done
   * once, because the fields are idempotent across use
   * of the inode, so let the slab aware of that.
   */
  void inode_init_once(struct inode *inode)
  {
  	memset(inode, 0, sizeof(*inode));
  	INIT_HLIST_NODE(&inode->i_hash);

  	INIT_LIST_HEAD(&inode->i_devices);

  	INIT_LIST_HEAD(&inode->i_io_list);

  	INIT_LIST_HEAD(&inode->i_wb_list);

  	INIT_LIST_HEAD(&inode->i_lru);

  	__address_space_init_once(&inode->i_data);

  	i_size_ordered_init(inode);
  }

  EXPORT_SYMBOL(inode_init_once);

  static void init_once(void *foo)

  {

  	struct inode *inode = (struct inode *) foo;

  	inode_init_once(inode);

  }
  
  /*

   * inode->i_lock must be held

   */

  void __iget(struct inode *inode)

  {

  	atomic_inc(&inode->i_count);
  }

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

  static void inode_lru_list_add(struct inode *inode)
  {

  	if (list_lru_add(&inode->i_sb->s_inode_lru, &inode->i_lru))

  		this_cpu_inc(nr_unused);

  	else
  		inode->i_state |= I_REFERENCED;

  }

  /*
   * Add inode to LRU if needed (inode is unused and clean).
   *
   * Needs inode->i_lock held.
   */
  void inode_add_lru(struct inode *inode)
  {

  	if (!(inode->i_state & (I_DIRTY_ALL | I_SYNC |
  				I_FREEING | I_WILL_FREE)) &&

  	    !atomic_read(&inode->i_count) && inode->i_sb->s_flags & SB_ACTIVE)

  		inode_lru_list_add(inode);
  }

  static void inode_lru_list_del(struct inode *inode)
  {

  
  	if (list_lru_del(&inode->i_sb->s_inode_lru, &inode->i_lru))

  		this_cpu_dec(nr_unused);

  }

  /**
   * 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->i_sb->s_inode_list_lock);

  	list_add(&inode->i_sb_list, &inode->i_sb->s_inodes);

  	spin_unlock(&inode->i_sb->s_inode_list_lock);

  }
  EXPORT_SYMBOL_GPL(inode_sb_list_add);

  static inline void inode_sb_list_del(struct inode *inode)

  {

  	if (!list_empty(&inode->i_sb_list)) {

  		spin_lock(&inode->i_sb->s_inode_list_lock);

  		list_del_init(&inode->i_sb_list);

  		spin_unlock(&inode->i_sb->s_inode_list_lock);

  	}

  }

  static unsigned long hash(struct super_block *sb, unsigned long hashval)
  {
  	unsigned long tmp;
  
  	tmp = (hashval * (unsigned long)sb) ^ (GOLDEN_RATIO_PRIME + hashval) /
  			L1_CACHE_BYTES;

  	tmp = tmp ^ ((tmp ^ GOLDEN_RATIO_PRIME) >> i_hash_shift);
  	return tmp & i_hash_mask;

  }
  
  /**
   *	__insert_inode_hash - hash an inode
   *	@inode: unhashed inode
   *	@hashval: unsigned long value used to locate this object in the
   *		inode_hashtable.
   *
   *	Add an inode to the inode hash for this superblock.
   */
  void __insert_inode_hash(struct inode *inode, unsigned long hashval)
  {

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

  	spin_lock(&inode_hash_lock);

  	spin_lock(&inode->i_lock);

  	hlist_add_head_rcu(&inode->i_hash, b);

  	spin_unlock(&inode->i_lock);

  	spin_unlock(&inode_hash_lock);

  }
  EXPORT_SYMBOL(__insert_inode_hash);
  
  /**

   *	__remove_inode_hash - remove an inode from the hash

   *	@inode: inode to unhash
   *
   *	Remove an inode from the superblock.
   */

  void __remove_inode_hash(struct inode *inode)

  {

  	spin_lock(&inode_hash_lock);

  	spin_lock(&inode->i_lock);

  	hlist_del_init_rcu(&inode->i_hash);

  	spin_unlock(&inode->i_lock);

  	spin_unlock(&inode_hash_lock);

  }

  EXPORT_SYMBOL(__remove_inode_hash);

  void clear_inode(struct inode *inode)

  {

  	/*

  	 * We have to cycle the i_pages lock here because reclaim can be in the

  	 * process of removing the last page (in __delete_from_page_cache())

  	 * and we must not free the mapping under it.

  	 */

  	xa_lock_irq(&inode->i_data.i_pages);

  	BUG_ON(inode->i_data.nrpages);

  	BUG_ON(inode->i_data.nrexceptional);

  	xa_unlock_irq(&inode->i_data.i_pages);

  	BUG_ON(!list_empty(&inode->i_data.private_list));
  	BUG_ON(!(inode->i_state & I_FREEING));
  	BUG_ON(inode->i_state & I_CLEAR);

  	BUG_ON(!list_empty(&inode->i_wb_list));

  	/* don't need i_lock here, no concurrent mods to i_state */

  	inode->i_state = I_FREEING | I_CLEAR;
  }

  EXPORT_SYMBOL(clear_inode);

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

  static void evict(struct inode *inode)

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

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

  	if (!list_empty(&inode->i_io_list))
  		inode_io_list_del(inode);

  	inode_sb_list_del(inode);

  	/*
  	 * Wait for flusher thread to be done with the inode so that filesystem
  	 * does not start destroying it while writeback is still running. Since
  	 * the inode has I_FREEING set, flusher thread won't start new work on
  	 * the inode.  We just have to wait for running writeback to finish.
  	 */
  	inode_wait_for_writeback(inode);

  	if (op->evict_inode) {
  		op->evict_inode(inode);

  	} else {

  		truncate_inode_pages_final(&inode->i_data);

  		clear_inode(inode);

  	}

  	if (S_ISBLK(inode->i_mode) && inode->i_bdev)
  		bd_forget(inode);
  	if (S_ISCHR(inode->i_mode) && inode->i_cdev)
  		cd_forget(inode);

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

  }

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

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

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

  		evict(inode);

  		cond_resched();

  	}

  }

  /**

   * 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 SB_ACTIVE flag removed,

   * so any inode reaching zero refcount during or after that call will
   * be immediately evicted.

   */

  void evict_inodes(struct super_block *sb)

  {

  	struct inode *inode, *next;
  	LIST_HEAD(dispose);

  again:

  	spin_lock(&sb->s_inode_list_lock);

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

  			continue;

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

  			continue;

  		}

  
  		inode->i_state |= I_FREEING;

  		inode_lru_list_del(inode);

  		spin_unlock(&inode->i_lock);

  		list_add(&inode->i_lru, &dispose);

  
  		/*
  		 * We can have a ton of inodes to evict at unmount time given
  		 * enough memory, check to see if we need to go to sleep for a
  		 * bit so we don't livelock.
  		 */
  		if (need_resched()) {
  			spin_unlock(&sb->s_inode_list_lock);
  			cond_resched();
  			dispose_list(&dispose);
  			goto again;
  		}

  	}

  	spin_unlock(&sb->s_inode_list_lock);

  
  	dispose_list(&dispose);

  }

  EXPORT_SYMBOL_GPL(evict_inodes);

  /**

   * invalidate_inodes	- attempt to free all inodes on a superblock
   * @sb:		superblock to operate on

   * @kill_dirty: flag to guide handling of dirty inodes

   *

   * Attempts to free all inodes for a given superblock.  If there were any
   * busy inodes return a non-zero value, else zero.

   * If @kill_dirty is set, discard dirty inodes too, otherwise treat
   * them as busy.

   */

  int invalidate_inodes(struct super_block *sb, bool kill_dirty)

  {

  	int busy = 0;

  	struct inode *inode, *next;
  	LIST_HEAD(dispose);

  again:

  	spin_lock(&sb->s_inode_list_lock);

  	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {

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

  			continue;

  		}

  		if (inode->i_state & I_DIRTY_ALL && !kill_dirty) {

  			spin_unlock(&inode->i_lock);

  			busy = 1;
  			continue;
  		}

  		if (atomic_read(&inode->i_count)) {

  			spin_unlock(&inode->i_lock);

  			busy = 1;

  			continue;
  		}

  		inode->i_state |= I_FREEING;

  		inode_lru_list_del(inode);

  		spin_unlock(&inode->i_lock);

  		list_add(&inode->i_lru, &dispose);

  		if (need_resched()) {
  			spin_unlock(&sb->s_inode_list_lock);
  			cond_resched();
  			dispose_list(&dispose);
  			goto again;
  		}

  	}

  	spin_unlock(&sb->s_inode_list_lock);

  	dispose_list(&dispose);

  
  	return busy;
  }

  /*

   * Isolate the inode from the LRU in preparation for freeing it.

   *
   * Any inodes which are pinned purely because of attached pagecache have their

   * pagecache removed.  If the inode has metadata buffers attached to
   * mapping->private_list then try to remove them.

   *

   * If the inode has the I_REFERENCED flag set, then it means that it has been
   * used recently - the flag is set in iput_final(). When we encounter such an
   * inode, clear the flag and move it to the back of the LRU so it gets another
   * pass through the LRU before it gets reclaimed. This is necessary because of
   * the fact we are doing lazy LRU updates to minimise lock contention so the
   * LRU does not have strict ordering. Hence we don't want to reclaim inodes
   * with this flag set because they are the inodes that are out of order.

   */

  static enum lru_status inode_lru_isolate(struct list_head *item,
  		struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)

  {

  	struct list_head *freeable = arg;
  	struct inode	*inode = container_of(item, struct inode, i_lru);

  	/*
  	 * we are inverting the lru lock/inode->i_lock here, so use a trylock.
  	 * If we fail to get the lock, just skip it.
  	 */
  	if (!spin_trylock(&inode->i_lock))
  		return LRU_SKIP;

  	/*
  	 * Referenced or dirty inodes are still in use. Give them another pass
  	 * through the LRU as we canot reclaim them now.
  	 */
  	if (atomic_read(&inode->i_count) ||
  	    (inode->i_state & ~I_REFERENCED)) {

  		list_lru_isolate(lru, &inode->i_lru);

  		spin_unlock(&inode->i_lock);
  		this_cpu_dec(nr_unused);
  		return LRU_REMOVED;
  	}

  	/* recently referenced inodes get one more pass */
  	if (inode->i_state & I_REFERENCED) {

  		inode->i_state &= ~I_REFERENCED;
  		spin_unlock(&inode->i_lock);
  		return LRU_ROTATE;
  	}

  	if (inode_has_buffers(inode) || inode->i_data.nrpages) {
  		__iget(inode);
  		spin_unlock(&inode->i_lock);
  		spin_unlock(lru_lock);
  		if (remove_inode_buffers(inode)) {
  			unsigned long reap;
  			reap = invalidate_mapping_pages(&inode->i_data, 0, -1);
  			if (current_is_kswapd())
  				__count_vm_events(KSWAPD_INODESTEAL, reap);
  			else
  				__count_vm_events(PGINODESTEAL, reap);
  			if (current->reclaim_state)
  				current->reclaim_state->reclaimed_slab += reap;

  		}

  		iput(inode);
  		spin_lock(lru_lock);
  		return LRU_RETRY;
  	}

  	WARN_ON(inode->i_state & I_NEW);
  	inode->i_state |= I_FREEING;

  	list_lru_isolate_move(lru, &inode->i_lru, freeable);

  	spin_unlock(&inode->i_lock);

  	this_cpu_dec(nr_unused);
  	return LRU_REMOVED;
  }

  /*
   * Walk the superblock inode LRU for freeable inodes and attempt to free them.
   * This is called from the superblock shrinker function with a number of inodes
   * to trim from the LRU. Inodes to be freed are moved to a temporary list and
   * then are freed outside inode_lock by dispose_list().
   */

  long prune_icache_sb(struct super_block *sb, struct shrink_control *sc)

  {
  	LIST_HEAD(freeable);
  	long freed;

  	freed = list_lru_shrink_walk(&sb->s_inode_lru, sc,
  				     inode_lru_isolate, &freeable);

  	dispose_list(&freeable);

  	return freed;

  }

  static void __wait_on_freeing_inode(struct inode *inode);
  /*
   * Called with the inode lock held.

   */

  static struct inode *find_inode(struct super_block *sb,
  				struct hlist_head *head,
  				int (*test)(struct inode *, void *),
  				void *data)

  {

  	struct inode *inode = NULL;

  
  repeat:

  	hlist_for_each_entry(inode, head, i_hash) {

  		if (inode->i_sb != sb)

  			continue;

  		if (!test(inode, data))

  			continue;

  		spin_lock(&inode->i_lock);

  		if (inode->i_state & (I_FREEING|I_WILL_FREE)) {

  			__wait_on_freeing_inode(inode);
  			goto repeat;
  		}

  		if (unlikely(inode->i_state & I_CREATING)) {
  			spin_unlock(&inode->i_lock);
  			return ERR_PTR(-ESTALE);
  		}

  		__iget(inode);

  		spin_unlock(&inode->i_lock);

  		return inode;

  	}

  	return NULL;

  }
  
  /*
   * find_inode_fast is the fast path version of find_inode, see the comment at
   * iget_locked for details.
   */

  static struct inode *find_inode_fast(struct super_block *sb,
  				struct hlist_head *head, unsigned long ino)

  {

  	struct inode *inode = NULL;

  
  repeat:

  	hlist_for_each_entry(inode, head, i_hash) {

  		if (inode->i_ino != ino)

  			continue;

  		if (inode->i_sb != sb)

  			continue;

  		spin_lock(&inode->i_lock);

  		if (inode->i_state & (I_FREEING|I_WILL_FREE)) {

  			__wait_on_freeing_inode(inode);
  			goto repeat;
  		}

  		if (unlikely(inode->i_state & I_CREATING)) {
  			spin_unlock(&inode->i_lock);
  			return ERR_PTR(-ESTALE);
  		}

  		__iget(inode);

  		spin_unlock(&inode->i_lock);

  		return inode;

  	}

  	return NULL;

  }

  /*
   * Each cpu owns a range of LAST_INO_BATCH numbers.
   * 'shared_last_ino' is dirtied only once out of LAST_INO_BATCH allocations,
   * to renew the exhausted range.

   *

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

   */

  #define LAST_INO_BATCH 1024
  static DEFINE_PER_CPU(unsigned int, last_ino);

  unsigned int get_next_ino(void)

  {

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

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

  	res++;
  	/* get_next_ino should not provide a 0 inode number */
  	if (unlikely(!res))
  		res++;
  	*p = res;

  	put_cpu_var(last_ino);
  	return res;

  }

  EXPORT_SYMBOL(get_next_ino);

  /**

   *	new_inode_pseudo 	- obtain an inode
   *	@sb: superblock
   *
   *	Allocates a new inode for given superblock.
   *	Inode wont be chained in superblock s_inodes list
   *	This means :
   *	- fs can't be unmount
   *	- quotas, fsnotify, writeback can't work
   */
  struct inode *new_inode_pseudo(struct super_block *sb)
  {
  	struct inode *inode = alloc_inode(sb);
  
  	if (inode) {
  		spin_lock(&inode->i_lock);
  		inode->i_state = 0;
  		spin_unlock(&inode->i_lock);
  		INIT_LIST_HEAD(&inode->i_sb_list);
  	}
  	return inode;
  }
  
  /**

   *	new_inode 	- obtain an inode
   *	@sb: superblock
   *

   *	Allocates a new inode for given superblock. The default gfp_mask

   *	for allocations related to inode->i_mapping is GFP_HIGHUSER_MOVABLE.

   *	If HIGHMEM pages are unsuitable or it is known that pages allocated
   *	for the page cache are not reclaimable or migratable,
   *	mapping_set_gfp_mask() must be called with suitable flags on the
   *	newly created inode's mapping
   *

   */
  struct inode *new_inode(struct super_block *sb)
  {

  	struct inode *inode;

  	spin_lock_prefetch(&sb->s_inode_list_lock);

  	inode = new_inode_pseudo(sb);
  	if (inode)

  		inode_sb_list_add(inode);

  	return inode;
  }

  EXPORT_SYMBOL(new_inode);

  #ifdef CONFIG_DEBUG_LOCK_ALLOC

  void lockdep_annotate_inode_mutex_key(struct inode *inode)
  {

  	if (S_ISDIR(inode->i_mode)) {

  		struct file_system_type *type = inode->i_sb->s_type;

  		/* Set new key only if filesystem hasn't already changed it */

  		if (lockdep_match_class(&inode->i_rwsem, &type->i_mutex_key)) {

  			/*
  			 * ensure nobody is actually holding i_mutex
  			 */

  			// mutex_destroy(&inode->i_mutex);
  			init_rwsem(&inode->i_rwsem);
  			lockdep_set_class(&inode->i_rwsem,

  					  &type->i_mutex_dir_key);
  		}

  	}

  }
  EXPORT_SYMBOL(lockdep_annotate_inode_mutex_key);

  #endif

  
  /**
   * unlock_new_inode - clear the I_NEW state and wake up any waiters
   * @inode:	new inode to unlock
   *
   * Called when the inode is fully initialised to clear the new state of the
   * inode and wake up anyone waiting for the inode to finish initialisation.
   */
  void unlock_new_inode(struct inode *inode)
  {
  	lockdep_annotate_inode_mutex_key(inode);

  	spin_lock(&inode->i_lock);

  	WARN_ON(!(inode->i_state & I_NEW));

  	inode->i_state &= ~I_NEW & ~I_CREATING;

  	smp_mb();

  	wake_up_bit(&inode->i_state, __I_NEW);
  	spin_unlock(&inode->i_lock);

  }

  EXPORT_SYMBOL(unlock_new_inode);

  void discard_new_inode(struct inode *inode)
  {
  	lockdep_annotate_inode_mutex_key(inode);
  	spin_lock(&inode->i_lock);
  	WARN_ON(!(inode->i_state & I_NEW));
  	inode->i_state &= ~I_NEW;
  	smp_mb();
  	wake_up_bit(&inode->i_state, __I_NEW);
  	spin_unlock(&inode->i_lock);
  	iput(inode);
  }
  EXPORT_SYMBOL(discard_new_inode);

  /**

   * lock_two_nondirectories - take two i_mutexes on non-directory objects

   *
   * Lock any non-NULL argument that is not a directory.
   * Zero, one or two objects may be locked by this function.
   *

   * @inode1: first inode to lock
   * @inode2: second inode to lock
   */
  void lock_two_nondirectories(struct inode *inode1, struct inode *inode2)
  {

  	if (inode1 > inode2)
  		swap(inode1, inode2);
  
  	if (inode1 && !S_ISDIR(inode1->i_mode))

  		inode_lock(inode1);

  	if (inode2 && !S_ISDIR(inode2->i_mode) && inode2 != inode1)

  		inode_lock_nested(inode2, I_MUTEX_NONDIR2);

  }
  EXPORT_SYMBOL(lock_two_nondirectories);
  
  /**
   * unlock_two_nondirectories - release locks from lock_two_nondirectories()
   * @inode1: first inode to unlock
   * @inode2: second inode to unlock
   */
  void unlock_two_nondirectories(struct inode *inode1, struct inode *inode2)
  {

  	if (inode1 && !S_ISDIR(inode1->i_mode))

  		inode_unlock(inode1);

  	if (inode2 && !S_ISDIR(inode2->i_mode) && inode2 != inode1)

  		inode_unlock(inode2);

  }
  EXPORT_SYMBOL(unlock_two_nondirectories);
  
  /**

   * inode_insert5 - obtain an inode from a mounted file system
   * @inode:	pre-allocated inode to use for insert to cache
   * @hashval:	hash value (usually inode number) to get
   * @test:	callback used for comparisons between inodes
   * @set:	callback used to initialize a new struct inode
   * @data:	opaque data pointer to pass to @test and @set
   *
   * Search for the inode specified by @hashval and @data in the inode cache,
   * and if present it is return it with an increased reference count. This is
   * a variant of iget5_locked() for callers that don't want to fail on memory
   * allocation of inode.
   *
   * If the inode is not in cache, insert the pre-allocated inode to cache and
   * return it locked, hashed, and with the I_NEW flag set. The file system gets
   * to fill it in before unlocking it via unlock_new_inode().
   *
   * Note both @test and @set are called with the inode_hash_lock held, so can't
   * sleep.
   */
  struct inode *inode_insert5(struct inode *inode, unsigned long hashval,
  			    int (*test)(struct inode *, void *),
  			    int (*set)(struct inode *, void *), void *data)
  {
  	struct hlist_head *head = inode_hashtable + hash(inode->i_sb, hashval);
  	struct inode *old;

  	bool creating = inode->i_state & I_CREATING;

  
  again:
  	spin_lock(&inode_hash_lock);
  	old = find_inode(inode->i_sb, head, test, data);
  	if (unlikely(old)) {
  		/*
  		 * Uhhuh, somebody else created the same inode under us.
  		 * Use the old inode instead of the preallocated one.
  		 */
  		spin_unlock(&inode_hash_lock);

  		if (IS_ERR(old))
  			return NULL;

  		wait_on_inode(old);
  		if (unlikely(inode_unhashed(old))) {
  			iput(old);
  			goto again;
  		}
  		return old;
  	}
  
  	if (set && unlikely(set(inode, data))) {
  		inode = NULL;
  		goto unlock;
  	}
  
  	/*
  	 * Return the locked inode with I_NEW set, the
  	 * caller is responsible for filling in the contents
  	 */
  	spin_lock(&inode->i_lock);
  	inode->i_state |= I_NEW;

  	hlist_add_head_rcu(&inode->i_hash, head);

  	spin_unlock(&inode->i_lock);

  	if (!creating)
  		inode_sb_list_add(inode);

  unlock:
  	spin_unlock(&inode_hash_lock);
  
  	return inode;
  }
  EXPORT_SYMBOL(inode_insert5);
  
  /**

   * iget5_locked - obtain an inode from a mounted file system
   * @sb:		super block of file system
   * @hashval:	hash value (usually inode number) to get
   * @test:	callback used for comparisons between inodes
   * @set:	callback used to initialize a new struct inode
   * @data:	opaque data pointer to pass to @test and @set
   *
   * Search for the inode specified by @hashval and @data in the inode cache,
   * and if present it is return it with an increased reference count. This is
   * a generalized version of iget_locked() for file systems where the inode
   * number is not sufficient for unique identification of an inode.
   *
   * If the inode is not in cache, allocate a new inode and return it locked,
   * hashed, and with the I_NEW flag set. The file system gets to fill it in
   * before unlocking it via unlock_new_inode().

   *

   * Note both @test and @set are called with the inode_hash_lock held, so can't
   * sleep.

   */

  struct inode *iget5_locked(struct super_block *sb, unsigned long hashval,
  		int (*test)(struct inode *, void *),
  		int (*set)(struct inode *, void *), void *data)

  {

  	struct inode *inode = ilookup5(sb, hashval, test, data);

  	if (!inode) {

  		struct inode *new = alloc_inode(sb);

  		if (new) {

  			new->i_state = 0;

  			inode = inode_insert5(new, hashval, test, set, data);
  			if (unlikely(inode != new))

  				destroy_inode(new);

  		}

  	}
  	return inode;

  }

  EXPORT_SYMBOL(iget5_locked);

  /**
   * iget_locked - obtain an inode from a mounted file system
   * @sb:		super block of file system
   * @ino:	inode number to get
   *
   * Search for the inode specified by @ino in the inode cache and if present
   * return it with an increased reference count. This is for file systems
   * where the inode number is sufficient for unique identification of an inode.
   *
   * If the inode is not in cache, allocate a new inode and return it locked,
   * hashed, and with the I_NEW flag set.  The file system gets to fill it in
   * before unlocking it via unlock_new_inode().

   */

  struct inode *iget_locked(struct super_block *sb, unsigned long ino)

  {

  	struct hlist_head *head = inode_hashtable + hash(sb, ino);

  	struct inode *inode;

  again:

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

  		if (IS_ERR(inode))
  			return NULL;

  		wait_on_inode(inode);

  		if (unlikely(inode_unhashed(inode))) {
  			iput(inode);
  			goto again;
  		}

  		return inode;
  	}

  	inode = alloc_inode(sb);
  	if (inode) {

  		struct inode *old;

  		spin_lock(&inode_hash_lock);

  		/* We released the lock, so.. */
  		old = find_inode_fast(sb, head, ino);
  		if (!old) {
  			inode->i_ino = ino;

  			spin_lock(&inode->i_lock);
  			inode->i_state = I_NEW;

  			hlist_add_head_rcu(&inode->i_hash, head);

  			spin_unlock(&inode->i_lock);

  			inode_sb_list_add(inode);

  			spin_unlock(&inode_hash_lock);

  
  			/* Return the locked inode with I_NEW set, the
  			 * caller is responsible for filling in the contents
  			 */
  			return inode;
  		}
  
  		/*
  		 * Uhhuh, somebody else created the same inode under
  		 * us. Use the old inode instead of the one we just
  		 * allocated.
  		 */

  		spin_unlock(&inode_hash_lock);

  		destroy_inode(inode);

  		if (IS_ERR(old))
  			return NULL;

  		inode = old;
  		wait_on_inode(inode);

  		if (unlikely(inode_unhashed(inode))) {
  			iput(inode);
  			goto again;
  		}

  	}
  	return inode;
  }

  EXPORT_SYMBOL(iget_locked);

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

  	struct inode *inode;

  	hlist_for_each_entry_rcu(inode, b, i_hash) {
  		if (inode->i_ino == ino && inode->i_sb == sb)

  			return 0;
  	}

  	return 1;
  }

  /**
   *	iunique - get a unique inode number
   *	@sb: superblock
   *	@max_reserved: highest reserved inode number
   *
   *	Obtain an inode number that is unique on the system for a given
   *	superblock. This is used by file systems that have no natural
   *	permanent inode numbering system. An inode number is returned that
   *	is higher than the reserved limit but unique.
   *
   *	BUGS:
   *	With a large number of inodes live on the file system this function
   *	currently becomes quite slow.
   */
  ino_t iunique(struct super_block *sb, ino_t max_reserved)
  {

  	/*
  	 * On a 32bit, non LFS stat() call, glibc will generate an EOVERFLOW
  	 * error if st_ino won't fit in target struct field. Use 32bit counter
  	 * here to attempt to avoid that.
  	 */

  	static DEFINE_SPINLOCK(iunique_lock);

  	static unsigned int counter;

  	ino_t res;

  	rcu_read_lock();

  	spin_lock(&iunique_lock);

  	do {
  		if (counter <= max_reserved)
  			counter = max_reserved + 1;

  		res = counter++;

  	} while (!test_inode_iunique(sb, res));
  	spin_unlock(&iunique_lock);

  	rcu_read_unlock();

  	return res;
  }

  EXPORT_SYMBOL(iunique);
  
  struct inode *igrab(struct inode *inode)
  {

  	spin_lock(&inode->i_lock);
  	if (!(inode->i_state & (I_FREEING|I_WILL_FREE))) {

  		__iget(inode);

  		spin_unlock(&inode->i_lock);
  	} else {
  		spin_unlock(&inode->i_lock);

  		/*
  		 * Handle the case where s_op->clear_inode is not been
  		 * called yet, and somebody is calling igrab
  		 * while the inode is getting freed.
  		 */
  		inode = NULL;

  	}

  	return inode;
  }

  EXPORT_SYMBOL(igrab);
  
  /**

   * ilookup5_nowait - search for an inode in the inode cache

   * @sb:		super block of file system to search

   * @hashval:	hash value (usually inode number) to search for

   * @test:	callback used for comparisons between inodes
   * @data:	opaque data pointer to pass to @test

   *

   * Search for the inode specified by @hashval and @data in the inode cache.

   * If the inode is in the cache, the inode is returned with an incremented
   * reference count.
   *

   * Note: I_NEW is not waited upon so you have to be very careful what you do
   * with the returned inode.  You probably should be using ilookup5() instead.

   *

   * Note2: @test is called with the inode_hash_lock held, so can't sleep.

   */

  struct inode *ilookup5_nowait(struct super_block *sb, unsigned long hashval,
  		int (*test)(struct inode *, void *), void *data)

  {

  	struct hlist_head *head = inode_hashtable + hash(sb, hashval);

  	struct inode *inode;

  	spin_lock(&inode_hash_lock);

  	inode = find_inode(sb, head, test, data);

  	spin_unlock(&inode_hash_lock);

  	return IS_ERR(inode) ? NULL : inode;

  }

  EXPORT_SYMBOL(ilookup5_nowait);
  
  /**
   * ilookup5 - search for an inode in the inode cache
   * @sb:		super block of file system to search
   * @hashval:	hash value (usually inode number) to search for
   * @test:	callback used for comparisons between inodes
   * @data:	opaque data pointer to pass to @test
   *

   * Search for the inode specified by @hashval and @data in the inode cache,
   * and if the inode is in the cache, return the inode with an incremented
   * reference count.  Waits on I_NEW before returning the inode.

   * returned with an incremented reference count.

   *

   * This is a generalized version of ilookup() for file systems where the
   * inode number is not sufficient for unique identification of an inode.

   *

   * Note: @test is called with the inode_hash_lock held, so can't sleep.

   */
  struct inode *ilookup5(struct super_block *sb, unsigned long hashval,
  		int (*test)(struct inode *, void *), void *data)
  {

  	struct inode *inode;
  again:
  	inode = ilookup5_nowait(sb, hashval, test, data);
  	if (inode) {

  		wait_on_inode(inode);

  		if (unlikely(inode_unhashed(inode))) {
  			iput(inode);
  			goto again;
  		}
  	}

  	return inode;

  }

  EXPORT_SYMBOL(ilookup5);
  
  /**
   * ilookup - search for an inode in the inode cache
   * @sb:		super block of file system to search
   * @ino:	inode number to search for
   *

   * Search for the inode @ino in the inode cache, and if the inode is in the
   * cache, the inode is returned with an incremented reference count.

   */
  struct inode *ilookup(struct super_block *sb, unsigned long ino)
  {
  	struct hlist_head *head = inode_hashtable + hash(sb, ino);

  	struct inode *inode;

  again:

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

  	if (inode) {

  		if (IS_ERR(inode))
  			return NULL;

  		wait_on_inode(inode);

  		if (unlikely(inode_unhashed(inode))) {
  			iput(inode);
  			goto again;
  		}
  	}

  	return inode;

  }

  EXPORT_SYMBOL(ilookup);

  /**
   * find_inode_nowait - find an inode in the inode cache
   * @sb:		super block of file system to search
   * @hashval:	hash value (usually inode number) to search for
   * @match:	callback used for comparisons between inodes
   * @data:	opaque data pointer to pass to @match
   *
   * Search for the inode specified by @hashval and @data in the inode
   * cache, where the helper function @match will return 0 if the inode
   * does not match, 1 if the inode does match, and -1 if the search
   * should be stopped.  The @match function must be responsible for
   * taking the i_lock spin_lock and checking i_state for an inode being
   * freed or being initialized, and incrementing the reference count
   * before returning 1.  It also must not sleep, since it is called with
   * the inode_hash_lock spinlock held.
   *
   * This is a even more generalized version of ilookup5() when the
   * function must never block --- find_inode() can block in
   * __wait_on_freeing_inode() --- or when the caller can not increment
   * the reference count because the resulting iput() might cause an
   * inode eviction.  The tradeoff is that the @match funtion must be
   * very carefully implemented.
   */
  struct inode *find_inode_nowait(struct super_block *sb,
  				unsigned long hashval,
  				int (*match)(struct inode *, unsigned long,
  					     void *),
  				void *data)
  {
  	struct hlist_head *head = inode_hashtable + hash(sb, hashval);
  	struct inode *inode, *ret_inode = NULL;
  	int mval;
  
  	spin_lock(&inode_hash_lock);
  	hlist_for_each_entry(inode, head, i_hash) {
  		if (inode->i_sb != sb)
  			continue;
  		mval = match(inode, hashval, data);
  		if (mval == 0)
  			continue;
  		if (mval == 1)
  			ret_inode = inode;
  		goto out;
  	}
  out:
  	spin_unlock(&inode_hash_lock);
  	return ret_inode;
  }
  EXPORT_SYMBOL(find_inode_nowait);

  /**
   * find_inode_rcu - find an inode in the inode cache
   * @sb:		Super block of file system to search
   * @hashval:	Key to hash
   * @test:	Function to test match on an inode
   * @data:	Data for test function
   *
   * Search for the inode specified by @hashval and @data in the inode cache,
   * where the helper function @test will return 0 if the inode does not match
   * and 1 if it does.  The @test function must be responsible for taking the
   * i_lock spin_lock and checking i_state for an inode being freed or being
   * initialized.
   *
   * If successful, this will return the inode for which the @test function
   * returned 1 and NULL otherwise.
   *
   * The @test function is not permitted to take a ref on any inode presented.
   * It is also not permitted to sleep.
   *
   * The caller must hold the RCU read lock.
   */
  struct inode *find_inode_rcu(struct super_block *sb, unsigned long hashval,
  			     int (*test)(struct inode *, void *), void *data)
  {
  	struct hlist_head *head = inode_hashtable + hash(sb, hashval);
  	struct inode *inode;
  
  	RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
  			 "suspicious find_inode_rcu() usage");
  
  	hlist_for_each_entry_rcu(inode, head, i_hash) {
  		if (inode->i_sb == sb &&
  		    !(READ_ONCE(inode->i_state) & (I_FREEING | I_WILL_FREE)) &&
  		    test(inode, data))
  			return inode;
  	}
  	return NULL;
  }
  EXPORT_SYMBOL(find_inode_rcu);
  
  /**
   * find_inode_by_rcu - Find an inode in the inode cache
   * @sb:		Super block of file system to search
   * @ino:	The inode number to match
   *
   * Search for the inode specified by @hashval and @data in the inode cache,
   * where the helper function @test will return 0 if the inode does not match
   * and 1 if it does.  The @test function must be responsible for taking the
   * i_lock spin_lock and checking i_state for an inode being freed or being
   * initialized.
   *
   * If successful, this will return the inode for which the @test function
   * returned 1 and NULL otherwise.
   *
   * The @test function is not permitted to take a ref on any inode presented.
   * It is also not permitted to sleep.
   *
   * The caller must hold the RCU read lock.
   */
  struct inode *find_inode_by_ino_rcu(struct super_block *sb,
  				    unsigned long ino)
  {
  	struct hlist_head *head = inode_hashtable + hash(sb, ino);
  	struct inode *inode;
  
  	RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
  			 "suspicious find_inode_by_ino_rcu() usage");
  
  	hlist_for_each_entry_rcu(inode, head, i_hash) {
  		if (inode->i_ino == ino &&
  		    inode->i_sb == sb &&
  		    !(READ_ONCE(inode->i_state) & (I_FREEING | I_WILL_FREE)))
  		    return inode;
  	}
  	return NULL;
  }
  EXPORT_SYMBOL(find_inode_by_ino_rcu);

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

  	while (1) {

  		struct inode *old = NULL;

  		spin_lock(&inode_hash_lock);

  		hlist_for_each_entry(old, head, i_hash) {

  			if (old->i_ino != ino)
  				continue;
  			if (old->i_sb != sb)
  				continue;

  			spin_lock(&old->i_lock);
  			if (old->i_state & (I_FREEING|I_WILL_FREE)) {
  				spin_unlock(&old->i_lock);

  				continue;

  			}

  			break;
  		}

  		if (likely(!old)) {

  			spin_lock(&inode->i_lock);

  			inode->i_state |= I_NEW | I_CREATING;

  			hlist_add_head_rcu(&inode->i_hash, head);

  			spin_unlock(&inode->i_lock);

  			spin_unlock(&inode_hash_lock);

  			return 0;
  		}

  		if (unlikely(old->i_state & I_CREATING)) {
  			spin_unlock(&old->i_lock);
  			spin_unlock(&inode_hash_lock);
  			return -EBUSY;
  		}

  		__iget(old);

  		spin_unlock(&old->i_lock);

  		spin_unlock(&inode_hash_lock);

  		wait_on_inode(old);

  		if (unlikely(!inode_unhashed(old))) {

  			iput(old);
  			return -EBUSY;
  		}
  		iput(old);
  	}
  }

  EXPORT_SYMBOL(insert_inode_locked);
  
  int insert_inode_locked4(struct inode *inode, unsigned long hashval,
  		int (*test)(struct inode *, void *), void *data)
  {

  	struct inode *old;
  
  	inode->i_state |= I_CREATING;
  	old = inode_insert5(inode, hashval, test, NULL, data);