/*
 * Copyright (C) 2007 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/delay.h>
#include <linux/kthread.h>
#include <linux/pagemap.h>

#include "ctree.h"
#include "disk-io.h"
#include "free-space-cache.h"
#include "inode-map.h"
#include "transaction.h"

static int caching_kthread(void *data)
{
        struct btrfs_root *root = data;
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_free_space_ctl *ctl = root->free_ino_ctl;
        struct btrfs_key key;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        u64 last = (u64)-1;
        int slot;
        int ret;

        if (!btrfs_test_opt(root, INODE_MAP_CACHE))
                return 0;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        /* Since the commit root is read-only, we can safely skip locking. */
        path->skip_locking = 1;
        path->search_commit_root = 1;
        path->reada = 2;

        key.objectid = BTRFS_FIRST_FREE_OBJECTID;
        key.offset = 0;
        key.type = BTRFS_INODE_ITEM_KEY;
again:
        /* need to make sure the commit_root doesn't disappear */
        mutex_lock(&root->fs_commit_mutex);

        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                goto out;

        while (1) {
                if (btrfs_fs_closing(fs_info))
                        goto out;

                leaf = path->nodes[0];
                slot = path->slots[0];
                if (slot >= btrfs_header_nritems(leaf)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0)
                                goto out;
                        else if (ret > 0)
                                break;

                        if (need_resched() ||
                            btrfs_transaction_in_commit(fs_info)) {
                                leaf = path->nodes[0];

                                if (btrfs_header_nritems(leaf) == 0) {
                                        WARN_ON(1);
                                        break;
                                }

                                /*
                                 * Save the key so we can advances forward
                                 * in the next search.
                                 */
                                btrfs_item_key_to_cpu(leaf, &key, 0);
                                btrfs_release_path(path);
                                root->cache_progress = last;
                                mutex_unlock(&root->fs_commit_mutex);
                                schedule_timeout(1);
                                goto again;
                        } else
                                continue;
                }

                btrfs_item_key_to_cpu(leaf, &key, slot);

                if (key.type != BTRFS_INODE_ITEM_KEY)
                        goto next;

                if (key.objectid >= root->highest_objectid)
                        break;

                if (last != (u64)-1 && last + 1 != key.objectid) {
                        __btrfs_add_free_space(ctl, last + 1,
                                               key.objectid - last - 1);
                        wake_up(&root->cache_wait);
                }

                last = key.objectid;
next:
                path->slots[0]++;
        }

        if (last < root->highest_objectid - 1) {
                __btrfs_add_free_space(ctl, last + 1,
                                       root->highest_objectid - last - 1);
        }

        spin_lock(&root->cache_lock);
        root->cached = BTRFS_CACHE_FINISHED;
        spin_unlock(&root->cache_lock);

        root->cache_progress = (u64)-1;
        btrfs_unpin_free_ino(root);
out:
        wake_up(&root->cache_wait);
        mutex_unlock(&root->fs_commit_mutex);

        btrfs_free_path(path);

        return ret;
}

static void start_caching(struct btrfs_root *root)
{
        struct btrfs_free_space_ctl *ctl = root->free_ino_ctl;
        struct task_struct *tsk;
        int ret;
        u64 objectid;

        if (!btrfs_test_opt(root, INODE_MAP_CACHE))
                return;

        spin_lock(&root->cache_lock);
        if (root->cached != BTRFS_CACHE_NO) {
                spin_unlock(&root->cache_lock);
                return;
        }

        root->cached = BTRFS_CACHE_STARTED;
        spin_unlock(&root->cache_lock);

        ret = load_free_ino_cache(root->fs_info, root);
        if (ret == 1) {
                spin_lock(&root->cache_lock);
                root->cached = BTRFS_CACHE_FINISHED;
                spin_unlock(&root->cache_lock);
                return;
        }

        /*
         * It can be quite time-consuming to fill the cache by searching
         * through the extent tree, and this can keep ino allocation path
         * waiting. Therefore at start we quickly find out the highest
         * inode number and we know we can use inode numbers which fall in
         * [highest_ino + 1, BTRFS_LAST_FREE_OBJECTID].
         */
        ret = btrfs_find_free_objectid(root, &objectid);
        if (!ret && objectid <= BTRFS_LAST_FREE_OBJECTID) {
                __btrfs_add_free_space(ctl, objectid,
                                       BTRFS_LAST_FREE_OBJECTID - objectid + 1);
        }

        tsk = kthread_run(caching_kthread, root, "btrfs-ino-cache-%llu\n",
                          root->root_key.objectid);
        BUG_ON(IS_ERR(tsk));
}

int btrfs_find_free_ino(struct btrfs_root *root, u64 *objectid)
{
        if (!btrfs_test_opt(root, INODE_MAP_CACHE))
                return btrfs_find_free_objectid(root, objectid);

again:
        *objectid = btrfs_find_ino_for_alloc(root);

        if (*objectid != 0)
                return 0;

        start_caching(root);

        wait_event(root->cache_wait,
                   root->cached == BTRFS_CACHE_FINISHED ||
                   root->free_ino_ctl->free_space > 0);

        if (root->cached == BTRFS_CACHE_FINISHED &&
            root->free_ino_ctl->free_space == 0)
                return -ENOSPC;
        else
                goto again;
}

void btrfs_return_ino(struct btrfs_root *root, u64 objectid)
{
        struct btrfs_free_space_ctl *ctl = root->free_ino_ctl;
        struct btrfs_free_space_ctl *pinned = root->free_ino_pinned;

        if (!btrfs_test_opt(root, INODE_MAP_CACHE))
                return;

again:
        if (root->cached == BTRFS_CACHE_FINISHED) {
                __btrfs_add_free_space(ctl, objectid, 1);
        } else {
                /*
                 * If we are in the process of caching free ino chunks,
                 * to avoid adding the same inode number to the free_ino
                 * tree twice due to cross transaction, we'll leave it
                 * in the pinned tree until a transaction is committed
                 * or the caching work is done.
                 */

                mutex_lock(&root->fs_commit_mutex);
                spin_lock(&root->cache_lock);
                if (root->cached == BTRFS_CACHE_FINISHED) {
                        spin_unlock(&root->cache_lock);
                        mutex_unlock(&root->fs_commit_mutex);
                        goto again;
                }
                spin_unlock(&root->cache_lock);

                start_caching(root);

                if (objectid <= root->cache_progress ||
                    objectid > root->highest_objectid)
                        __btrfs_add_free_space(ctl, objectid, 1);
                else
                        __btrfs_add_free_space(pinned, objectid, 1);

                mutex_unlock(&root->fs_commit_mutex);
        }
}

/*
 * When a transaction is committed, we'll move those inode numbers which
 * are smaller than root->cache_progress from pinned tree to free_ino tree,
 * and others will just be dropped, because the commit root we were
 * searching has changed.
 *
 * Must be called with root->fs_commit_mutex held
 */
void btrfs_unpin_free_ino(struct btrfs_root *root)
{
        struct btrfs_free_space_ctl *ctl = root->free_ino_ctl;
        struct rb_root *rbroot = &root->free_ino_pinned->free_space_offset;
        struct btrfs_free_space *info;
        struct rb_node *n;
        u64 count;

        if (!btrfs_test_opt(root, INODE_MAP_CACHE))
                return;

        while (1) {
                n = rb_first(rbroot);
                if (!n)
                        break;

                info = rb_entry(n, struct btrfs_free_space, offset_index);
                BUG_ON(info->bitmap);

                if (info->offset > root->cache_progress)
                        goto free;
                else if (info->offset + info->bytes > root->cache_progress)
                        count = root->cache_progress - info->offset + 1;
                else
                        count = info->bytes;

                __btrfs_add_free_space(ctl, info->offset, count);
free:
                rb_erase(&info->offset_index, rbroot);
                kfree(info);
        }
}

#define INIT_THRESHOLD  (((1024 * 32) / 2) / sizeof(struct btrfs_free_space))
#define INODES_PER_BITMAP (PAGE_CACHE_SIZE * 8)

/*
 * The goal is to keep the memory used by the free_ino tree won't
 * exceed the memory if we use bitmaps only.
 */
static void recalculate_thresholds(struct btrfs_free_space_ctl *ctl)
{
        struct btrfs_free_space *info;
        struct rb_node *n;
        int max_ino;
        int max_bitmaps;

        n = rb_last(&ctl->free_space_offset);
        if (!n) {
                ctl->extents_thresh = INIT_THRESHOLD;
                return;
        }
        info = rb_entry(n, struct btrfs_free_space, offset_index);

        /*
         * Find the maximum inode number in the filesystem. Note we
         * ignore the fact that this can be a bitmap, because we are
         * not doing precise calculation.
         */
        max_ino = info->bytes - 1;

        max_bitmaps = ALIGN(max_ino, INODES_PER_BITMAP) / INODES_PER_BITMAP;
        if (max_bitmaps <= ctl->total_bitmaps) {
                ctl->extents_thresh = 0;
                return;
        }

        ctl->extents_thresh = (max_bitmaps - ctl->total_bitmaps) *
                                PAGE_CACHE_SIZE / sizeof(*info);
}

/*
 * We don't fall back to bitmap, if we are below the extents threshold
 * or this chunk of inode numbers is a big one.
 */
static bool use_bitmap(struct btrfs_free_space_ctl *ctl,
                       struct btrfs_free_space *info)
{
        if (ctl->free_extents < ctl->extents_thresh ||
            info->bytes > INODES_PER_BITMAP / 10)
                return false;

        return true;
}

static struct btrfs_free_space_op free_ino_op = {
        .recalc_thresholds      = recalculate_thresholds,
        .use_bitmap             = use_bitmap,
};

static void pinned_recalc_thresholds(struct btrfs_free_space_ctl *ctl)
{
}

static bool pinned_use_bitmap(struct btrfs_free_space_ctl *ctl,
                              struct btrfs_free_space *info)
{
        /*
         * We always use extents for two reasons:
         *
         * - The pinned tree is only used during the process of caching
         *   work.
         * - Make code simpler. See btrfs_unpin_free_ino().
         */
        return false;
}

static struct btrfs_free_space_op pinned_free_ino_op = {
        .recalc_thresholds      = pinned_recalc_thresholds,
        .use_bitmap             = pinned_use_bitmap,
};

void btrfs_init_free_ino_ctl(struct btrfs_root *root)
{
        struct btrfs_free_space_ctl *ctl = root->free_ino_ctl;
        struct btrfs_free_space_ctl *pinned = root->free_ino_pinned;

        spin_lock_init(&ctl->tree_lock);
        ctl->unit = 1;
        ctl->start = 0;
        ctl->private = NULL;
        ctl->op = &free_ino_op;

        /*
         * Initially we allow to use 16K of ram to cache chunks of
         * inode numbers before we resort to bitmaps. This is somewhat
         * arbitrary, but it will be adjusted in runtime.
         */
        ctl->extents_thresh = INIT_THRESHOLD;

        spin_lock_init(&pinned->tree_lock);
        pinned->unit = 1;
        pinned->start = 0;
        pinned->private = NULL;
        pinned->extents_thresh = 0;
        pinned->op = &pinned_free_ino_op;
}

int btrfs_save_ino_cache(struct btrfs_root *root,
                         struct btrfs_trans_handle *trans)
{
        struct btrfs_free_space_ctl *ctl = root->free_ino_ctl;
        struct btrfs_path *path;
        struct inode *inode;
        u64 alloc_hint = 0;
        int ret;
        int prealloc;
        bool retry = false;

        /* only fs tree and subvol/snap needs ino cache */
        if (root->root_key.objectid != BTRFS_FS_TREE_OBJECTID &&
            (root->root_key.objectid < BTRFS_FIRST_FREE_OBJECTID ||
             root->root_key.objectid > BTRFS_LAST_FREE_OBJECTID))
                return 0;

        /* Don't save inode cache if we are deleting this root */
        if (btrfs_root_refs(&root->root_item) == 0 &&
            root != root->fs_info->tree_root)
                return 0;

        if (!btrfs_test_opt(root, INODE_MAP_CACHE))
                return 0;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

again:
        inode = lookup_free_ino_inode(root, path);
        if (IS_ERR(inode) && PTR_ERR(inode) != -ENOENT) {
                ret = PTR_ERR(inode);
                goto out;
        }

        if (IS_ERR(inode)) {
                BUG_ON(retry);
                retry = true;

                ret = create_free_ino_inode(root, trans, path);
                if (ret)
                        goto out;
                goto again;
        }

        BTRFS_I(inode)->generation = 0;
        ret = btrfs_update_inode(trans, root, inode);
        WARN_ON(ret);

        if (i_size_read(inode) > 0) {
                ret = btrfs_truncate_free_space_cache(root, trans, path, inode);
                if (ret)
                        goto out_put;
        }

        spin_lock(&root->cache_lock);
        if (root->cached != BTRFS_CACHE_FINISHED) {
                ret = -1;
                spin_unlock(&root->cache_lock);
                goto out_put;
        }
        spin_unlock(&root->cache_lock);

        spin_lock(&ctl->tree_lock);
        prealloc = sizeof(struct btrfs_free_space) * ctl->free_extents;
        prealloc = ALIGN(prealloc, PAGE_CACHE_SIZE);
        prealloc += ctl->total_bitmaps * PAGE_CACHE_SIZE;
        spin_unlock(&ctl->tree_lock);

        /* Just to make sure we have enough space */
        prealloc += 8 * PAGE_CACHE_SIZE;

        ret = btrfs_check_data_free_space(inode, prealloc);
        if (ret)
                goto out_put;

        ret = btrfs_prealloc_file_range_trans(inode, trans, 0, 0, prealloc,
                                              prealloc, prealloc, &alloc_hint);
        if (ret)
                goto out_put;
        btrfs_free_reserved_data_space(inode, prealloc);

out_put:
        iput(inode);
out:
        if (ret == 0)
                ret = btrfs_write_out_ino_cache(root, trans, path);

        btrfs_free_path(path);
        return ret;
}

static int btrfs_find_highest_objectid(struct btrfs_root *root, u64 *objectid)
{
        struct btrfs_path *path;
        int ret;
        struct extent_buffer *l;
        struct btrfs_key search_key;
        struct btrfs_key found_key;
        int slot;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        search_key.objectid = BTRFS_LAST_FREE_OBJECTID;
        search_key.type = -1;
        search_key.offset = (u64)-1;
        ret = btrfs_search_slot(NULL, root, &search_key, path, 0, 0);
        if (ret < 0)
                goto error;
        BUG_ON(ret == 0);
        if (path->slots[0] > 0) {
                slot = path->slots[0] - 1;
                l = path->nodes[0];
                btrfs_item_key_to_cpu(l, &found_key, slot);
                *objectid = max_t(u64, found_key.objectid,
                                  BTRFS_FIRST_FREE_OBJECTID - 1);
        } else {
                *objectid = BTRFS_FIRST_FREE_OBJECTID - 1;
        }
        ret = 0;
error:
        btrfs_free_path(path);
        return ret;
}

int btrfs_find_free_objectid(struct btrfs_root *root, u64 *objectid)
{
        int ret;
        mutex_lock(&root->objectid_mutex);

        if (unlikely(root->highest_objectid < BTRFS_FIRST_FREE_OBJECTID)) {
                ret = btrfs_find_highest_objectid(root,
                                                  &root->highest_objectid);
                if (ret)
                        goto out;
        }

        if (unlikely(root->highest_objectid >= BTRFS_LAST_FREE_OBJECTID)) {
                ret = -ENOSPC;
                goto out;
        }

        *objectid = ++root->highest_objectid;
        ret = 0;
out:
        mutex_unlock(&root->objectid_mutex);
        return ret;
}