extent_map.c 8.6 KB
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#include <linux/err.h>
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#include <linux/gfp.h>
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#include <linux/slab.h>
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#include <linux/module.h>
#include <linux/spinlock.h>
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#include <linux/version.h>
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#include <linux/hardirq.h>
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#include "extent_map.h"

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/* temporary define until extent_map moves out of btrfs */
struct kmem_cache *btrfs_cache_create(const char *name, size_t size,
				       unsigned long extra_flags,
				       void (*ctor)(void *, struct kmem_cache *,
						    unsigned long));

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static struct kmem_cache *extent_map_cache;
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int __init extent_map_init(void)
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{
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	extent_map_cache = btrfs_cache_create("extent_map",
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					    sizeof(struct extent_map), 0,
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					    NULL);
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	if (!extent_map_cache)
		return -ENOMEM;
	return 0;
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}

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

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/**
 * extent_map_tree_init - initialize extent map tree
 * @tree:		tree to initialize
 * @mask:		flags for memory allocations during tree operations
 *
 * Initialize the extent tree @tree.  Should be called for each new inode
 * or other user of the extent_map interface.
 */
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void extent_map_tree_init(struct extent_map_tree *tree, gfp_t mask)
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{
	tree->map.rb_node = NULL;
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	spin_lock_init(&tree->lock);
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}
EXPORT_SYMBOL(extent_map_tree_init);

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/**
 * alloc_extent_map - allocate new extent map structure
 * @mask:	memory allocation flags
 *
 * 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()
 */
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struct extent_map *alloc_extent_map(gfp_t mask)
{
	struct extent_map *em;
	em = kmem_cache_alloc(extent_map_cache, mask);
	if (!em || IS_ERR(em))
		return em;
	em->in_tree = 0;
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	em->flags = 0;
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	atomic_set(&em->refs, 1);
	return em;
}
EXPORT_SYMBOL(alloc_extent_map);

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/**
 * free_extent_map - drop reference count of an extent_map
 * @em:		extent map beeing releasead
 *
 * Drops the reference out on @em by one and free the structure
 * if the reference count hits zero.
 */
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void free_extent_map(struct extent_map *em)
{
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Chris Mason 已提交
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	if (!em)
		return;
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	WARN_ON(atomic_read(&em->refs) == 0);
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	if (atomic_dec_and_test(&em->refs)) {
		WARN_ON(em->in_tree);
		kmem_cache_free(extent_map_cache, em);
	}
}
EXPORT_SYMBOL(free_extent_map);

static struct rb_node *tree_insert(struct rb_root *root, u64 offset,
				   struct rb_node *node)
{
	struct rb_node ** p = &root->rb_node;
	struct rb_node * parent = NULL;
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	struct extent_map *entry;
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	while(*p) {
		parent = *p;
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		entry = rb_entry(parent, struct extent_map, rb_node);

		WARN_ON(!entry->in_tree);
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		if (offset < entry->start)
			p = &(*p)->rb_left;
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		else if (offset >= extent_map_end(entry))
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			p = &(*p)->rb_right;
		else
			return parent;
	}

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	entry = rb_entry(node, struct extent_map, rb_node);
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	entry->in_tree = 1;
	rb_link_node(node, parent, p);
	rb_insert_color(node, root);
	return NULL;
}

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

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		WARN_ON(!entry->in_tree);

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		if (offset < entry->start)
			n = n->rb_left;
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		else if (offset >= extent_map_end(entry))
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			n = n->rb_right;
		else
			return n;
	}
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	if (prev_ret) {
		orig_prev = prev;
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		while(prev && offset >= extent_map_end(prev_entry)) {
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			prev = rb_next(prev);
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			prev_entry = rb_entry(prev, struct extent_map, rb_node);
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		}
		*prev_ret = prev;
		prev = orig_prev;
	}

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

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/*
 * look for an offset in the tree, and if it can't be found, return
 * the first offset we can find smaller than 'offset'.
 */
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static inline struct rb_node *tree_search(struct rb_root *root, u64 offset)
{
	struct rb_node *prev;
	struct rb_node *ret;
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	ret = __tree_search(root, offset, &prev, NULL);
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	if (!ret)
		return prev;
	return ret;
}

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

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	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;
	}
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	return 0;
}

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/**
 * 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 sucessfull.
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 */
int add_extent_mapping(struct extent_map_tree *tree,
		       struct extent_map *em)
{
	int ret = 0;
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	struct extent_map *merge = NULL;
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	struct rb_node *rb;
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	struct extent_map *exist;
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	exist = lookup_extent_mapping(tree, em->start, em->len);
	if (exist) {
		free_extent_map(exist);
		ret = -EEXIST;
		goto out;
	}
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	assert_spin_locked(&tree->lock);
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	rb = tree_insert(&tree->map, em->start, &em->rb_node);
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	if (rb) {
		ret = -EEXIST;
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		free_extent_map(merge);
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		goto out;
	}
	atomic_inc(&em->refs);
	if (em->start != 0) {
		rb = rb_prev(&em->rb_node);
		if (rb)
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			merge = rb_entry(rb, struct extent_map, rb_node);
		if (rb && mergable_maps(merge, em)) {
			em->start = merge->start;
			em->len += merge->len;
			em->block_start = merge->block_start;
			merge->in_tree = 0;
			rb_erase(&merge->rb_node, &tree->map);
			free_extent_map(merge);
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		}
	 }
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	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;
		rb_erase(&merge->rb_node, &tree->map);
		merge->in_tree = 0;
		free_extent_map(merge);
	}
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out:
	return ret;
}
EXPORT_SYMBOL(add_extent_mapping);

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

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/**
 * 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.
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 */
struct extent_map *lookup_extent_mapping(struct extent_map_tree *tree,
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					 u64 start, u64 len)
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{
	struct extent_map *em;
	struct rb_node *rb_node;
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	struct rb_node *prev = NULL;
	struct rb_node *next = NULL;
	u64 end = range_end(start, len);

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	assert_spin_locked(&tree->lock);
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	rb_node = __tree_search(&tree->map, start, &prev, &next);
	if (!rb_node && prev) {
		em = rb_entry(prev, struct extent_map, rb_node);
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		if (end > em->start && start < extent_map_end(em))
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			goto found;
	}
	if (!rb_node && next) {
		em = rb_entry(next, struct extent_map, rb_node);
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		if (end > em->start && start < extent_map_end(em))
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			goto found;
	}
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	if (!rb_node) {
		em = NULL;
		goto out;
	}
	if (IS_ERR(rb_node)) {
		em = ERR_PTR(PTR_ERR(rb_node));
		goto out;
	}
	em = rb_entry(rb_node, struct extent_map, rb_node);
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	if (end > em->start && start < extent_map_end(em))
		goto found;

	em = NULL;
	goto out;

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found:
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	atomic_inc(&em->refs);
out:
	return em;
}
EXPORT_SYMBOL(lookup_extent_mapping);

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/**
 * remove_extent_mapping - removes an extent_map from the extent tree
 * @tree:	extent tree to remove from
 * @em:		extent map beeing removed
 *
 * Removes @em from @tree.  No reference counts are dropped, and no checks
 * are done to see if the range is in use
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 */
int remove_extent_mapping(struct extent_map_tree *tree, struct extent_map *em)
{
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	int ret = 0;
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	WARN_ON(test_bit(EXTENT_FLAG_PINNED, &em->flags));
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	assert_spin_locked(&tree->lock);
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	rb_erase(&em->rb_node, &tree->map);
	em->in_tree = 0;
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	return ret;
}
EXPORT_SYMBOL(remove_extent_mapping);
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