path: root/fs/btrfs/extent_map.c

// SPDX-License-Identifier: GPL-2.0

#include <linux/err.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include "ctree.h"
#include "volumes.h"
#include "extent_map.h"
#include "compression.h"
#include "btrfs_inode.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 __cold 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_CACHED;
	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->compress_type = BTRFS_COMPRESS_NONE;
	refcount_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;
	if (refcount_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_cached *root, struct extent_map *em)
{
	struct rb_node **p = &root->rb_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);
	bool leftmost = true;

	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;
			leftmost = false;
		} 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_cached(&em->rb_node, root, leftmost);
	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_or_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;

	ASSERT(prev_or_next_ret);

	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;
	}

	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);
	}

	/*
	 * Previous extent map found, return as in this case the caller does not
	 * care about the next one.
	 */
	if (prev) {
		*prev_or_next_ret = prev;
		return NULL;
	}

	prev = orig_prev;
	prev_entry = rb_entry(prev, struct extent_map, rb_node);
	while (prev && offset < prev_entry->start) {
		prev