fs/btrfs/extent_map.c - kernel/msm-4.9 - Gitiles

 #include <linux/err.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/hardirq.h>
 #include "ctree.h"
 #include "extent_map.h"
 #include "compression.h"


 static struct kmem_cache *extent_map_cache;

 int __init extent_map_init(void)
 {
 	extent_map_cache = kmem_cache_create("btrfs_extent_map",
 			sizeof(struct extent_map), 0,
 			SLAB_MEM_SPREAD, NULL);
 	if (!extent_map_cache)
 		return -ENOMEM;
 	return 0;
 }

 void extent_map_exit(void)
 {
 	kmem_cache_destroy(extent_map_cache);
 }

 /**
  * extent_map_tree_init - initialize extent map tree
  * @tree:		tree to initialize
  *
  * Initialize the extent tree @tree.  Should be called for each new inode
  * or other user of the extent_map interface.
  */
 void extent_map_tree_init(struct extent_map_tree *tree)
 {
 	tree->map = RB_ROOT;
 	INIT_LIST_HEAD(&tree->modified_extents);
 	rwlock_init(&tree->lock);
 }

 /**
  * alloc_extent_map - allocate new extent map structure
  *
  * Allocate a new extent_map structure.  The new structure is
  * returned with a reference count of one and needs to be
  * freed using free_extent_map()
  */
 struct extent_map *alloc_extent_map(void)
 {
 	struct extent_map *em;
 	em = kmem_cache_zalloc(extent_map_cache, GFP_NOFS);
 	if (!em)
 		return NULL;
 	RB_CLEAR_NODE(&em->rb_node);
 	em->flags = 0;
 	em->compress_type = BTRFS_COMPRESS_NONE;
 	em->generation = 0;
 	atomic_set(&em->refs, 1);
 	INIT_LIST_HEAD(&em->list);
 	return em;
 }

 /**
  * free_extent_map - drop reference count of an extent_map
  * @em:		extent map being released
  *
  * Drops the reference out on @em by one and free the structure
  * if the reference count hits zero.
  */
 void free_extent_map(struct extent_map *em)
 {
 	if (!em)
 		return;
 	WARN_ON(atomic_read(&em->refs) == 0);
 	if (atomic_dec_and_test(&em->refs)) {
 		WARN_ON(extent_map_in_tree(em));
 		WARN_ON(!list_empty(&em->list));
 		if (test_bit(EXTENT_FLAG_FS_MAPPING, &em->flags))
 			kfree(em->map_lookup);
 		kmem_cache_free(extent_map_cache, em);
 	}
 }

 /* simple helper to do math around the end of an extent, handling wrap */
 static u64 range_end(u64 start, u64 len)
 {
 	if (start + len < start)
 		return (u64)-1;
 	return start + len;
 }

 static int tree_insert(struct rb_root *root, struct extent_map *em)
 {
 	struct rb_node **p = &root->rb_node;
 	struct rb_node *parent = NULL;
 	struct extent_map *entry = NULL;
 	struct rb_node *orig_parent = NULL;
 	u64 end = range_end(em->start, em->len);

 	while (*p) {
 		parent = *p;
 		entry = rb_entry(parent, struct extent_map, rb_node);

 		if (em->start < entry->start)
 			p = &(*p)->rb_left;
 		else if (em->start >= extent_map_end(entry))
 			p = &(*p)->rb_right;
 		else
 			return -EEXIST;
 	}

 	orig_parent = parent;
 	while (parent && em->start >= extent_map_end(entry)) {
 		parent = rb_next(parent);
 		entry = rb_entry(parent, struct extent_map, rb_node);
 	}
 	if (parent)
 		if (end > entry->start && em->start < extent_map_end(entry))
 			return -EEXIST;

 	parent = orig_parent;
 	entry = rb_entry(parent, struct extent_map, rb_node);
 	while (parent && em->start < entry->start) {
 		parent = rb_prev(parent);
 		entry = rb_entry(parent, struct extent_map, rb_node);
 	}
 	if (parent)
 		if (end > entry->start && em->start < extent_map_end(entry))
 			return -EEXIST;

 	rb_link_node(&em->rb_node, orig_parent, p);
 	rb_insert_color(&em->rb_node, root);
 	return 0;
 }

 /*
  * search through the tree for an extent_map with a given offset.  If
  * it can't be found, try to find some neighboring extents
  */
 static struct rb_node *__tree_search(struct rb_root *root, u64 offset,
 				     struct rb_node **prev_ret,
 				     struct rb_node **next_ret)
 {
 	struct rb_node *n = root->rb_node;
 	struct rb_node *prev = NULL;
 	struct rb_node *orig_prev = NULL;
 	struct extent_map *entry;
 	struct extent_map *prev_entry = NULL;

 	while (n) {
 		entry = rb_entry(n, struct extent_map, rb_node);
 		prev = n;
 		prev_entry = entry;

 		if (offset < entry->start)
 			n = n->rb_left;
 		else if (offset >= extent_map_end(entry))
 			n = n->rb_right;
 		else
 			return n;
 	}

 	if (prev_ret) {
 		orig_prev = prev;
 		while (prev && offset >= extent_map_end(prev_entry)) {
 			prev = rb_next(prev);
 			prev_entry = rb_entry(prev, struct extent_map, rb_node);
 		}
 		*prev_ret = prev;
 		prev = orig_prev;
 	}

 	if (next_ret) {
 		prev_entry = rb_entry(prev, struct extent_map, rb_node);
 		while (prev && offset < prev_entry->start) {
 			prev = rb_prev(prev);
 			prev_entry = rb_entry(prev, struct extent_map, rb_node);
 		}
 		*next_ret = prev;
 	}
 	return NULL;
 }

 /* check to see if two extent_map structs are adjacent and safe to merge */
 static int mergable_maps(struct extent_map *prev, struct extent_map *next)
 {
 	if (test_bit(EXTENT_FLAG_PINNED, &prev->flags))
 		return 0;

 	/*
 	 * don't merge compressed extents, we need to know their
 	 * actual size
 	 */
 	if (test_bit(EXTENT_FLAG_COMPRESSED, &prev->flags))
 		return 0;

 	if (test_bit(EXTENT_FLAG_LOGGING, &prev->flags) ||
 	    test_bit(EXTENT_FLAG_LOGGING, &next->flags))
 		return 0;

 	/*
 	 * We don't want to merge stuff that hasn't been written to the log yet
 	 * since it may not reflect exactly what is on disk, and that would be
 	 * bad.
 	 */
 	if (!list_empty(&prev->list) || !list_empty(&next->list))
 		return 0;

 	if (extent_map_end(prev) == next->start &&
 	    prev->flags == next->flags &&
 	    prev->bdev == next->bdev &&
 	    ((next->block_start == EXTENT_MAP_HOLE &&
 	      prev->block_start == EXTENT_MAP_HOLE) ||
 	     (next->block_start == EXTENT_MAP_INLINE &&
 	      prev->block_start == EXTENT_MAP_INLINE) ||
 	     (next->block_start == EXTENT_MAP_DELALLOC &&
 	      prev->block_start == EXTENT_MAP_DELALLOC) ||
 	     (next->block_start < EXTENT_MAP_LAST_BYTE - 1 &&
 	      next->block_start == extent_map_block_end(prev)))) {
 		return 1;
 	}
 	return 0;
 }

 static void try_merge_map(struct extent_map_tree *tree, struct extent_map *em)
 {
 	struct extent_map *merge = NULL;
 	struct rb_node *rb;

 	if (em->start != 0) {
 		rb = rb_prev(&em->rb_node);
 		if (rb)
 			merge = rb_entry(rb, struct extent_map, rb_node);
 		if (rb && mergable_maps(merge, em)) {
 			em->start = merge->start;
 			em->orig_start = merge->orig_start;
 			em->len += merge->len;
 			em->block_len += merge->block_len;
 			em->block_start = merge->block_start;
 			em->mod_len = (em->mod_len + em->mod_start) - merge->mod_start;
 			em->mod_start = merge->mod_start;
 			em->generation = max(em->generation, merge->generation);

 			rb_erase(&merge->rb_node, &tree->map);
 			RB_CLEAR_NODE(&merge->rb_node);
 			free_extent_map(merge);
 		}
 	}

 	rb = rb_next(&em->rb_node);
 	if (rb)
 		merge = rb_entry(rb, struct extent_map, rb_node);
 	if (rb && mergable_maps(em, merge)) {
 		em->len += merge->len;
 		em->block_len += merge->block_len;
 		rb_erase(&merge->rb_node, &tree->map);
 		RB_CLEAR_NODE(&merge->rb_node);
 		em->mod_len = (merge->mod_start + merge->mod_len) - em->mod_start;
 		em->generation = max(em->generation, merge->generation);
 		free_extent_map(merge);
 	}
 }

 /**
  * unpin_extent_cache - unpin an extent from the cache
  * @tree:	tree to unpin the extent in
  * @start:	logical offset in the file
  * @len:	length of the extent
  * @gen:	generation that this extent has been modified in
  *
  * Called after an extent has been written to disk properly.  Set the generation
  * to the generation that actually added the file item to the inode so we know
  * we need to sync this extent when we call fsync().
  */
 int unpin_extent_cache(struct extent_map_tree *tree, u64 start, u64 len,
 		       u64 gen)
 {
 	int ret = 0;
 	struct extent_map *em;
 	bool prealloc = false;

 	write_lock(&tree->lock);
 	em = lookup_extent_mapping(tree, start, len);

 	WARN_ON(!em || em->start != start);

 	if (!em)
 		goto out;

 	em->generation = gen;
 	clear_bit(EXTENT_FLAG_PINNED, &em->flags);
 	em->mod_start = em->start;
 	em->mod_len = em->len;

 	if (test_bit(EXTENT_FLAG_FILLING, &em->flags)) {
 		prealloc = true;
 		clear_bit(EXTENT_FLAG_FILLING, &em->flags);
 	}

 	try_merge_map(tree, em);

 	if (prealloc) {
 		em->mod_start = em->start;
 		em->mod_len = em->len;
 	}

 	free_extent_map(em);
 out:
 	write_unlock(&tree->lock);
 	return ret;

 }

 void clear_em_logging(struct extent_map_tree *tree, struct extent_map *em)
 {
 	clear_bit(EXTENT_FLAG_LOGGING, &em->flags);
 	if (extent_map_in_tree(em))
 		try_merge_map(tree, em);
 }

 static inline void setup_extent_mapping(struct extent_map_tree *tree,
 					struct extent_map *em,
 					int modified)
 {
 	atomic_inc(&em->refs);
 	em->mod_start = em->start;
 	em->mod_len = em->len;

 	if (modified)
 		list_move(&em->list, &tree->modified_extents);
 	else
 		try_merge_map(tree, em);
 }

 /**
  * add_extent_mapping - add new extent map to the extent tree
  * @tree:	tree to insert new map in
  * @em:		map to insert
  *
  * Insert @em into @tree or perform a simple forward/backward merge with
  * existing mappings.  The extent_map struct passed in will be inserted
  * into the tree directly, with an additional reference taken, or a
  * reference dropped if the merge attempt was successful.
  */
 int add_extent_mapping(struct extent_map_tree *tree,
 		       struct extent_map *em, int modified)
 {
 	int ret = 0;

 	ret = tree_insert(&tree->map, em);
 	if (ret)
 		goto out;

 	setup_extent_mapping(tree, em, modified);
 out:
 	return ret;
 }

 static struct extent_map *
 __lookup_extent_mapping(struct extent_map_tree *tree,
 			u64 start, u64 len, int strict)
 {
 	struct extent_map *em;
 	struct rb_node *rb_node;
 	struct rb_node *prev = NULL;
 	struct rb_node *next = NULL;
 	u64 end = range_end(start, len);

 	rb_node = __tree_search(&tree->map, start, &prev, &next);
 	if (!rb_node) {
 		if (prev)
 			rb_node = prev;
 		else if (next)
 			rb_node = next;
 		else
 			return NULL;
 	}

 	em = rb_entry(rb_node, struct extent_map, rb_node);

 	if (strict && !(end > em->start && start < extent_map_end(em)))
 		return NULL;

 	atomic_inc(&em->refs);
 	return em;
 }

 /**
  * lookup_extent_mapping - lookup extent_map
  * @tree:	tree to lookup in
  * @start:	byte offset to start the search
  * @len:	length of the lookup range
  *
  * Find and return the first extent_map struct in @tree that intersects the
  * [start, len] range.  There may be additional objects in the tree that
  * intersect, so check the object returned carefully to make sure that no
  * additional lookups are needed.
  */
 struct extent_map *lookup_extent_mapping(struct extent_map_tree *tree,
 					 u64 start, u64 len)
 {
 	return __lookup_extent_mapping(tree, start, len, 1);
 }

 /**
  * search_extent_mapping - find a nearby extent map
  * @tree:	tree to lookup in
  * @start:	byte offset to start the search
  * @len:	length of the lookup range
  *
  * Find and return the first extent_map struct in @tree that intersects the
  * [start, len] range.
  *
  * If one can't be found, any nearby extent may be returned
  */
 struct extent_map *search_extent_mapping(struct extent_map_tree *tree,
 					 u64 start, u64 len)
 {
 	return __lookup_extent_mapping(tree, start, len, 0);
 }

 /**
  * remove_extent_mapping - removes an extent_map from the extent tree
  * @tree:	extent tree to remove from
  * @em:		extent map being removed
  *
  * Removes @em from @tree.  No reference counts are dropped, and no checks
  * are done to see if the range is in use
  */
 int remove_extent_mapping(struct extent_map_tree *tree, struct extent_map *em)
 {
 	int ret = 0;

 	WARN_ON(test_bit(EXTENT_FLAG_PINNED, &em->flags));
 	rb_erase(&em->rb_node, &tree->map);
 	if (!test_bit(EXTENT_FLAG_LOGGING, &em->flags))
 		list_del_init(&em->list);
 	RB_CLEAR_NODE(&em->rb_node);
 	return ret;
 }

 void replace_extent_mapping(struct extent_map_tree *tree,
 			    struct extent_map *cur,
 			    struct extent_map *new,
 			    int modified)
 {
 	WARN_ON(test_bit(EXTENT_FLAG_PINNED, &cur->flags));
 	ASSERT(extent_map_in_tree(cur));
 	if (!test_bit(EXTENT_FLAG_LOGGING, &cur->flags))
 		list_del_init(&cur->list);
 	rb_replace_node(&cur->rb_node, &new->rb_node, &tree->map);
 	RB_CLEAR_NODE(&cur->rb_node);

 	setup_extent_mapping(tree, new, modified);
 }
	#include <linux/err.h>
	#include <linux/slab.h>
	#include <linux/spinlock.h>
	#include <linux/hardirq.h>
	#include "ctree.h"
	#include "extent_map.h"
	#include "compression.h"


	static struct kmem_cache *extent_map_cache;

	int __init extent_map_init(void)
	{
	extent_map_cache = kmem_cache_create("btrfs_extent_map",
	sizeof(struct extent_map), 0,
	SLAB_MEM_SPREAD, NULL);
	if (!extent_map_cache)
	return -ENOMEM;
	return 0;
	}

	void extent_map_exit(void)
	{
	kmem_cache_destroy(extent_map_cache);
	}

	/**
	* extent_map_tree_init - initialize extent map tree
	* @tree: tree to initialize
	*
	* Initialize the extent tree @tree. Should be called for each new inode
	* or other user of the extent_map interface.
	*/
	void extent_map_tree_init(struct extent_map_tree *tree)
	{
	tree->map = RB_ROOT;
	INIT_LIST_HEAD(&tree->modified_extents);
	rwlock_init(&tree->lock);
	}

	/**
	* alloc_extent_map - allocate new extent map structure
	*
	* Allocate a new extent_map structure. The new structure is
	* returned with a reference count of one and needs to be
	* freed using free_extent_map()
	*/
	struct extent_map *alloc_extent_map(void)
	{
	struct extent_map *em;
	em = kmem_cache_zalloc(extent_map_cache, GFP_NOFS);
	if (!em)
	return NULL;
	RB_CLEAR_NODE(&em->rb_node);
	em->flags = 0;
	em->compress_type = BTRFS_COMPRESS_NONE;
	em->generation = 0;
	atomic_set(&em->refs, 1);
	INIT_LIST_HEAD(&em->list);
	return em;
	}

	/**
	* free_extent_map - drop reference count of an extent_map
	* @em: extent map being released
	*
	* Drops the reference out on @em by one and free the structure
	* if the reference count hits zero.
	*/
	void free_extent_map(struct extent_map *em)
	{
	if (!em)
	return;
	WARN_ON(atomic_read(&em->refs) == 0);
	if (atomic_dec_and_test(&em->refs)) {
	WARN_ON(extent_map_in_tree(em));
	WARN_ON(!list_empty(&em->list));
	if (test_bit(EXTENT_FLAG_FS_MAPPING, &em->flags))
	kfree(em->map_lookup);
	kmem_cache_free(extent_map_cache, em);
	}
	}

	/* simple helper to do math around the end of an extent, handling wrap */
	static u64 range_end(u64 start, u64 len)
	{
	if (start + len < start)
	return (u64)-1;
	return start + len;
	}

	static int tree_insert(struct rb_root root, struct extent_map em)
	{
	struct rb_node **p = &root->rb_node;
	struct rb_node *parent = NULL;
	struct extent_map *entry = NULL;
	struct rb_node *orig_parent = NULL;
	u64 end = range_end(em->start, em->len);

	while (*p) {
	parent = *p;
	entry = rb_entry(parent, struct extent_map, rb_node);

	if (em->start < entry->start)
	p = &(*p)->rb_left;
	else if (em->start >= extent_map_end(entry))
	p = &(*p)->rb_right;
	else
	return -EEXIST;
	}

	orig_parent = parent;
	while (parent && em->start >= extent_map_end(entry)) {
	parent = rb_next(parent);
	entry = rb_entry(parent, struct extent_map, rb_node);
	}
	if (parent)
	if (end > entry->start && em->start < extent_map_end(entry))
	return -EEXIST;

	parent = orig_parent;
	entry = rb_entry(parent, struct extent_map, rb_node);
	while (parent && em->start < entry->start) {
	parent = rb_prev(parent);
	entry = rb_entry(parent, struct extent_map, rb_node);
	}
	if (parent)
	if (end > entry->start && em->start < extent_map_end(entry))
	return -EEXIST;

	rb_link_node(&em->rb_node, orig_parent, p);
	rb_insert_color(&em->rb_node, root);
	return 0;
	}

	/*
	* search through the tree for an extent_map with a given offset. If
	* it can't be found, try to find some neighboring extents
	*/
	static struct rb_node __tree_search(struct rb_root root, u64 offset,
	struct rb_node **prev_ret,
	struct rb_node **next_ret)
	{
	struct rb_node *n = root->rb_node;
	struct rb_node *prev = NULL;
	struct rb_node *orig_prev = NULL;
	struct extent_map *entry;
	struct extent_map *prev_entry = NULL;

	while (n) {
	entry = rb_entry(n, struct extent_map, rb_node);
	prev = n;
	prev_entry = entry;

	if (offset < entry->start)
	n = n->rb_left;
	else if (offset >= extent_map_end(entry))
	n = n->rb_right;
	else
	return n;
	}

	if (prev_ret) {
	orig_prev = prev;
	while (prev && offset >= extent_map_end(prev_entry)) {
	prev = rb_next(prev);
	prev_entry = rb_entry(prev, struct extent_map, rb_node);
	}
	*prev_ret = prev;
	prev = orig_prev;
	}

	if (next_ret) {
	prev_entry = rb_entry(prev, struct extent_map, rb_node);
	while (prev && offset < prev_entry->start) {
	prev = rb_prev(prev);
	prev_entry = rb_entry(prev, struct extent_map, rb_node);
	}
	*next_ret = prev;
	}
	return NULL;
	}

	/* check to see if two extent_map structs are adjacent and safe to merge */
	static int mergable_maps(struct extent_map prev, struct extent_map next)
	{
	if (test_bit(EXTENT_FLAG_PINNED, &prev->flags))
	return 0;

	/*
	* don't merge compressed extents, we need to know their
	* actual size
	*/
	if (test_bit(EXTENT_FLAG_COMPRESSED, &prev->flags))
	return 0;

	if (test_bit(EXTENT_FLAG_LOGGING, &prev->flags) \|\|
	test_bit(EXTENT_FLAG_LOGGING, &next->flags))
	return 0;

	/*
	* We don't want to merge stuff that hasn't been written to the log yet
	* since it may not reflect exactly what is on disk, and that would be
	* bad.
	*/
	if (!list_empty(&prev->list) \|\| !list_empty(&next->list))
	return 0;

	if (extent_map_end(prev) == next->start &&
	prev->flags == next->flags &&
	prev->bdev == next->bdev &&
	((next->block_start == EXTENT_MAP_HOLE &&
	prev->block_start == EXTENT_MAP_HOLE) \|\|
	(next->block_start == EXTENT_MAP_INLINE &&
	prev->block_start == EXTENT_MAP_INLINE) \|\|
	(next->block_start == EXTENT_MAP_DELALLOC &&
	prev->block_start == EXTENT_MAP_DELALLOC) \|\|
	(next->block_start < EXTENT_MAP_LAST_BYTE - 1 &&
	next->block_start == extent_map_block_end(prev)))) {
	return 1;
	}
	return 0;
	}

	static void try_merge_map(struct extent_map_tree tree, struct extent_map em)
	{
	struct extent_map *merge = NULL;
	struct rb_node *rb;

	if (em->start != 0) {
	rb = rb_prev(&em->rb_node);
	if (rb)
	merge = rb_entry(rb, struct extent_map, rb_node);
	if (rb && mergable_maps(merge, em)) {
	em->start = merge->start;
	em->orig_start = merge->orig_start;
	em->len += merge->len;
	em->block_len += merge->block_len;
	em->block_start = merge->block_start;
	em->mod_len = (em->mod_len + em->mod_start) - merge->mod_start;
	em->mod_start = merge->mod_start;
	em->generation = max(em->generation, merge->generation);

	rb_erase(&merge->rb_node, &tree->map);
	RB_CLEAR_NODE(&merge->rb_node);
	free_extent_map(merge);
	}
	}

	rb = rb_next(&em->rb_node);
	if (rb)
	merge = rb_entry(rb, struct extent_map, rb_node);
	if (rb && mergable_maps(em, merge)) {
	em->len += merge->len;
	em->block_len += merge->block_len;
	rb_erase(&merge->rb_node, &tree->map);
	RB_CLEAR_NODE(&merge->rb_node);
	em->mod_len = (merge->mod_start + merge->mod_len) - em->mod_start;
	em->generation = max(em->generation, merge->generation);
	free_extent_map(merge);
	}
	}

	/**
	* unpin_extent_cache - unpin an extent from the cache
	* @tree: tree to unpin the extent in
	* @start: logical offset in the file
	* @len: length of the extent
	* @gen: generation that this extent has been modified in
	*
	* Called after an extent has been written to disk properly. Set the generation
	* to the generation that actually added the file item to the inode so we know
	* we need to sync this extent when we call fsync().
	*/
	int unpin_extent_cache(struct extent_map_tree *tree, u64 start, u64 len,
	u64 gen)
	{
	int ret = 0;
	struct extent_map *em;
	bool prealloc = false;

	write_lock(&tree->lock);
	em = lookup_extent_mapping(tree, start, len);

	WARN_ON(!em \|\| em->start != start);

	if (!em)
	goto out;

	em->generation = gen;
	clear_bit(EXTENT_FLAG_PINNED, &em->flags);
	em->mod_start = em->start;
	em->mod_len = em->len;

	if (test_bit(EXTENT_FLAG_FILLING, &em->flags)) {
	prealloc = true;
	clear_bit(EXTENT_FLAG_FILLING, &em->flags);
	}

	try_merge_map(tree, em);

	if (prealloc) {
	em->mod_start = em->start;
	em->mod_len = em->len;
	}

	free_extent_map(em);
	out:
	write_unlock(&tree->lock);
	return ret;

	}

	void clear_em_logging(struct extent_map_tree tree, struct extent_map em)
	{
	clear_bit(EXTENT_FLAG_LOGGING, &em->flags);
	if (extent_map_in_tree(em))
	try_merge_map(tree, em);
	}

	static inline void setup_extent_mapping(struct extent_map_tree *tree,
	struct extent_map *em,
	int modified)
	{
	atomic_inc(&em->refs);
	em->mod_start = em->start;
	em->mod_len = em->len;

	if (modified)
	list_move(&em->list, &tree->modified_extents);
	else
	try_merge_map(tree, em);
	}

	/**
	* add_extent_mapping - add new extent map to the extent tree
	* @tree: tree to insert new map in
	* @em: map to insert
	*
	* Insert @em into @tree or perform a simple forward/backward merge with
	* existing mappings. The extent_map struct passed in will be inserted
	* into the tree directly, with an additional reference taken, or a
	* reference dropped if the merge attempt was successful.
	*/
	int add_extent_mapping(struct extent_map_tree *tree,
	struct extent_map *em, int modified)
	{
	int ret = 0;

	ret = tree_insert(&tree->map, em);
	if (ret)
	goto out;

	setup_extent_mapping(tree, em, modified);
	out:
	return ret;
	}

	static struct extent_map *
	__lookup_extent_mapping(struct extent_map_tree *tree,
	u64 start, u64 len, int strict)
	{
	struct extent_map *em;
	struct rb_node *rb_node;
	struct rb_node *prev = NULL;
	struct rb_node *next = NULL;
	u64 end = range_end(start, len);

	rb_node = __tree_search(&tree->map, start, &prev, &next);
	if (!rb_node) {
	if (prev)
	rb_node = prev;
	else if (next)
	rb_node = next;
	else
	return NULL;
	}

	em = rb_entry(rb_node, struct extent_map, rb_node);

	if (strict && !(end > em->start && start < extent_map_end(em)))
	return NULL;

	atomic_inc(&em->refs);
	return em;
	}

	/**
	* lookup_extent_mapping - lookup extent_map
	* @tree: tree to lookup in
	* @start: byte offset to start the search
	* @len: length of the lookup range
	*
	* Find and return the first extent_map struct in @tree that intersects the
	* [start, len] range. There may be additional objects in the tree that
	* intersect, so check the object returned carefully to make sure that no
	* additional lookups are needed.
	*/
	struct extent_map lookup_extent_mapping(struct extent_map_tree tree,
	u64 start, u64 len)
	{
	return __lookup_extent_mapping(tree, start, len, 1);
	}

	/**
	* search_extent_mapping - find a nearby extent map
	* @tree: tree to lookup in
	* @start: byte offset to start the search
	* @len: length of the lookup range
	*
	* Find and return the first extent_map struct in @tree that intersects the
	* [start, len] range.
	*
	* If one can't be found, any nearby extent may be returned
	*/
	struct extent_map search_extent_mapping(struct extent_map_tree tree,
	u64 start, u64 len)
	{
	return __lookup_extent_mapping(tree, start, len, 0);
	}

	/**
	* remove_extent_mapping - removes an extent_map from the extent tree
	* @tree: extent tree to remove from
	* @em: extent map being removed
	*
	* Removes @em from @tree. No reference counts are dropped, and no checks
	* are done to see if the range is in use
	*/
	int remove_extent_mapping(struct extent_map_tree tree, struct extent_map em)
	{
	int ret = 0;

	WARN_ON(test_bit(EXTENT_FLAG_PINNED, &em->flags));
	rb_erase(&em->rb_node, &tree->map);
	if (!test_bit(EXTENT_FLAG_LOGGING, &em->flags))
	list_del_init(&em->list);
	RB_CLEAR_NODE(&em->rb_node);
	return ret;
	}

	void replace_extent_mapping(struct extent_map_tree *tree,
	struct extent_map *cur,
	struct extent_map *new,
	int modified)
	{
	WARN_ON(test_bit(EXTENT_FLAG_PINNED, &cur->flags));
	ASSERT(extent_map_in_tree(cur));
	if (!test_bit(EXTENT_FLAG_LOGGING, &cur->flags))
	list_del_init(&cur->list);
	rb_replace_node(&cur->rb_node, &new->rb_node, &tree->map);
	RB_CLEAR_NODE(&cur->rb_node);

	setup_extent_mapping(tree, new, modified);
	}