extent_map.c

Go to the documentation of this file.

#include <linux/err.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/hardirq.h>
#include "ctree.h"
#include "extent_map.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_RECLAIM_ACCOUNT | SLAB_MEM_SPREAD, NULL);
    if (!extent_map_cache)
        return -ENOMEM;
    return 0;
}

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

void extent_map_tree_init(struct extent_map_tree *tree)
{
    tree->map = RB_ROOT;
    INIT_LIST_HEAD(&tree->modified_extents);
    rwlock_init(&tree->lock);
}

struct extent_map *alloc_extent_map(void)
{
    struct extent_map *em;
    em = kmem_cache_alloc(extent_map_cache, GFP_NOFS);
    if (!em)
        return NULL;
    em->in_tree = 0;
    em->flags = 0;
    em->compress_type = BTRFS_COMPRESS_NONE;
    em->generation = 0;
    atomic_set(&em->refs, 1);
    INIT_LIST_HEAD(&em->list);
    return em;
}

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(em->in_tree);
        WARN_ON(!list_empty(&em->list));
        kmem_cache_free(extent_map_cache, em);
    }
}

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;
    struct extent_map *entry;

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

        WARN_ON(!entry->in_tree);

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

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

/*
 * 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;

        WARN_ON(!entry->in_tree);

        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 (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->len += merge->len;
            em->block_len += merge->block_len;
            em->block_start = merge->block_start;
            merge->in_tree = 0;
            if (merge->generation > em->generation) {
                em->mod_start = em->start;
                em->mod_len = em->len;
                em->generation = merge->generation;
                list_move(&em->list, &tree->modified_extents);
            }

            list_del_init(&merge->list);
            rb_erase(&merge->rb_node, &tree->map);
            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->len;
        rb_erase(&merge->rb_node, &tree->map);
        merge->in_tree = 0;
        if (merge->generation > em->generation) {
            em->mod_len = em->len;
            em->generation = merge->generation;
            list_move(&em->list, &tree->modified_extents);
        }
        list_del_init(&merge->list);
        free_extent_map(merge);
    }
}

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;

    list_move(&em->list, &tree->modified_extents);
    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_PREALLOC, &em->flags)) {
        prealloc = true;
        clear_bit(EXTENT_FLAG_PREALLOC, &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;

}

int add_extent_mapping(struct extent_map_tree *tree,
               struct extent_map *em)
{
    int ret = 0;
    struct rb_node *rb;
    struct extent_map *exist;

    exist = lookup_extent_mapping(tree, em->start, em->len);
    if (exist) {
        free_extent_map(exist);
        ret = -EEXIST;
        goto out;
    }
    rb = tree_insert(&tree->map, em->start, &em->rb_node);
    if (rb) {
        ret = -EEXIST;
        goto out;
    }
    atomic_inc(&em->refs);

    em->mod_start = em->start;
    em->mod_len = em->len;

    try_merge_map(tree, em);
out:
    return ret;
}

/* 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;
}

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;
}

struct extent_map *lookup_extent_mapping(struct extent_map_tree *tree,
                     u64 start, u64 len)
{
    return __lookup_extent_mapping(tree, start, len, 1);
}

struct extent_map *search_extent_mapping(struct extent_map_tree *tree,
                     u64 start, u64 len)
{
    return __lookup_extent_mapping(tree, start, len, 0);
}

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);
    em->in_tree = 0;
    return ret;
}