/*
 * Copyright (C) 2008 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#include <linux/sched.h>
#include <linux/sort.h>
#include "ctree.h"
#include "ref-cache.h"
#include "transaction.h"

/*
 * leaf refs are used to cache the information about which extents
 * a given leaf has references on.  This allows us to process that leaf
 * in btrfs_drop_snapshot without needing to read it back from disk.
 */

/*
 * kmalloc a leaf reference struct and update the counters for the
 * total ref cache size
 */
struct btrfs_leaf_ref *btrfs_alloc_leaf_ref(struct btrfs_root *root,
                                            int nr_extents)
{
        struct btrfs_leaf_ref *ref;
        size_t size = btrfs_leaf_ref_size(nr_extents);

        ref = kmalloc(size, GFP_NOFS);
        if (ref) {
                spin_lock(&root->fs_info->ref_cache_lock);
                root->fs_info->total_ref_cache_size += size;
                spin_unlock(&root->fs_info->ref_cache_lock);

                memset(ref, 0, sizeof(*ref));
                atomic_set(&ref->usage, 1);
                INIT_LIST_HEAD(&ref->list);
        }
        return ref;
}

/*
 * free a leaf reference struct and update the counters for the
 * total ref cache size
 */
void btrfs_free_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref)
{
        if (!ref)
                return;
        WARN_ON(atomic_read(&ref->usage) == 0);
        if (atomic_dec_and_test(&ref->usage)) {
                size_t size = btrfs_leaf_ref_size(ref->nritems);

                BUG_ON(ref->in_tree);
                kfree(ref);

                spin_lock(&root->fs_info->ref_cache_lock);
                root->fs_info->total_ref_cache_size -= size;
                spin_unlock(&root->fs_info->ref_cache_lock);
        }
}

static struct rb_node *tree_insert(struct rb_root *root, u64 bytenr,
                                   struct rb_node *node)
{
        struct rb_node **p = &root->rb_node;
        struct rb_node *parent = NULL;
        struct btrfs_leaf_ref *entry;

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

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

        entry = rb_entry(node, struct btrfs_leaf_ref, rb_node);
        rb_link_node(node, parent, p);
        rb_insert_color(node, root);
        return NULL;
}

static struct rb_node *tree_search(struct rb_root *root, u64 bytenr)
{
        struct rb_node *n = root->rb_node;
        struct btrfs_leaf_ref *entry;

        while (n) {
                entry = rb_entry(n, struct btrfs_leaf_ref, rb_node);
                WARN_ON(!entry->in_tree);

                if (bytenr < entry->bytenr)
                        n = n->rb_left;
                else if (bytenr > entry->bytenr)
                        n = n->rb_right;
                else
                        return n;
        }
        return NULL;
}

int btrfs_remove_leaf_refs(struct btrfs_root *root, u64 max_root_gen,
                           int shared)
{
        struct btrfs_leaf_ref *ref = NULL;
        struct btrfs_leaf_ref_tree *tree = root->ref_tree;

        if (shared)
                tree = &root->fs_info->shared_ref_tree;
        if (!tree)
                return 0;

        spin_lock(&tree->lock);
        while (!list_empty(&tree->list)) {
                ref = list_entry(tree->list.next, struct btrfs_leaf_ref, list);
                BUG_ON(ref->tree != tree);
                if (ref->root_gen > max_root_gen)
                        break;
                if (!xchg(&ref->in_tree, 0)) {
                        cond_resched_lock(&tree->lock);
                        continue;
                }

                rb_erase(&ref->rb_node, &tree->root);
                list_del_init(&ref->list);

                spin_unlock(&tree->lock);
                btrfs_free_leaf_ref(root, ref);
                cond_resched();
                spin_lock(&tree->lock);
        }
        spin_unlock(&tree->lock);
        return 0;
}

/*
 * find the leaf ref for a given extent.  This returns the ref struct with
 * a usage reference incremented
 */
struct btrfs_leaf_ref *btrfs_lookup_leaf_ref(struct btrfs_root *root,
                                             u64 bytenr)
{
        struct rb_node *rb;
        struct btrfs_leaf_ref *ref = NULL;
        struct btrfs_leaf_ref_tree *tree = root->ref_tree;
again:
        if (tree) {
                spin_lock(&tree->lock);
                rb = tree_search(&tree->root, bytenr);
                if (rb)
                        ref = rb_entry(rb, struct btrfs_leaf_ref, rb_node);
                if (ref)
                        atomic_inc(&ref->usage);
                spin_unlock(&tree->lock);
                if (ref)
                        return ref;
        }
        if (tree != &root->fs_info->shared_ref_tree) {
                tree = &root->fs_info->shared_ref_tree;
                goto again;
        }
        return NULL;
}

/*
 * add a fully filled in leaf ref struct
 * remove all the refs older than a given root generation
 */
int btrfs_add_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref,
                       int shared)
{
        int ret = 0;
        struct rb_node *rb;
        struct btrfs_leaf_ref_tree *tree = root->ref_tree;

        if (shared)
                tree = &root->fs_info->shared_ref_tree;

        spin_lock(&tree->lock);
        rb = tree_insert(&tree->root, ref->bytenr, &ref->rb_node);
        if (rb) {
                ret = -EEXIST;
        } else {
                atomic_inc(&ref->usage);
                ref->tree = tree;
                ref->in_tree = 1;
                list_add_tail(&ref->list, &tree->list);
        }
        spin_unlock(&tree->lock);
        return ret;
}

/*
 * remove a single leaf ref from the tree.  This drops the ref held by the tree
 * only
 */
int btrfs_remove_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref)
{
        struct btrfs_leaf_ref_tree *tree;

        if (!xchg(&ref->in_tree, 0))
                return 0;

        tree = ref->tree;
        spin_lock(&tree->lock);

        rb_erase(&ref->rb_node, &tree->root);
        list_del_init(&ref->list);

        spin_unlock(&tree->lock);

        btrfs_free_leaf_ref(root, ref);
        return 0;
}