transaction.c

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/*
 * 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/fs.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/writeback.h>
#include <linux/pagemap.h>
#include <linux/blkdev.h>
#include <linux/uuid.h>
#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "locking.h"
#include "tree-log.h"
#include "inode-map.h"
#include "volumes.h"

#define BTRFS_ROOT_TRANS_TAG 0

void put_transaction(struct btrfs_transaction *transaction)
{
    WARN_ON(atomic_read(&transaction->use_count) == 0);
    if (atomic_dec_and_test(&transaction->use_count)) {
        BUG_ON(!list_empty(&transaction->list));
        WARN_ON(transaction->delayed_refs.root.rb_node);
        memset(transaction, 0, sizeof(*transaction));
        kmem_cache_free(btrfs_transaction_cachep, transaction);
    }
}

static noinline void switch_commit_root(struct btrfs_root *root)
{
    free_extent_buffer(root->commit_root);
    root->commit_root = btrfs_root_node(root);
}

/*
 * either allocate a new transaction or hop into the existing one
 */
static noinline int join_transaction(struct btrfs_root *root, int type)
{
    struct btrfs_transaction *cur_trans;
    struct btrfs_fs_info *fs_info = root->fs_info;

    spin_lock(&fs_info->trans_lock);
loop:
    /* The file system has been taken offline. No new transactions. */
    if (fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) {
        spin_unlock(&fs_info->trans_lock);
        return -EROFS;
    }

    if (fs_info->trans_no_join) {
        /* 
         * If we are JOIN_NOLOCK we're already committing a current
         * transaction, we just need a handle to deal with something
         * when committing the transaction, such as inode cache and
         * space cache. It is a special case.
         */
        if (type != TRANS_JOIN_NOLOCK) {
            spin_unlock(&fs_info->trans_lock);
            return -EBUSY;
        }
    }

    cur_trans = fs_info->running_transaction;
    if (cur_trans) {
        if (cur_trans->aborted) {
            spin_unlock(&fs_info->trans_lock);
            return cur_trans->aborted;
        }
        atomic_inc(&cur_trans->use_count);
        atomic_inc(&cur_trans->num_writers);
        cur_trans->num_joined++;
        spin_unlock(&fs_info->trans_lock);
        return 0;
    }
    spin_unlock(&fs_info->trans_lock);

    /*
     * If we are ATTACH, we just want to catch the current transaction,
     * and commit it. If there is no transaction, just return ENOENT.
     */
    if (type == TRANS_ATTACH)
        return -ENOENT;

    cur_trans = kmem_cache_alloc(btrfs_transaction_cachep, GFP_NOFS);
    if (!cur_trans)
        return -ENOMEM;

    spin_lock(&fs_info->trans_lock);
    if (fs_info->running_transaction) {
        /*
         * someone started a transaction after we unlocked.  Make sure
         * to redo the trans_no_join checks above
         */
        kmem_cache_free(btrfs_transaction_cachep, cur_trans);
        cur_trans = fs_info->running_transaction;
        goto loop;
    } else if (fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) {
        spin_unlock(&fs_info->trans_lock);
        kmem_cache_free(btrfs_transaction_cachep, cur_trans);
        return -EROFS;
    }

    atomic_set(&cur_trans->num_writers, 1);
    cur_trans->num_joined = 0;
    init_waitqueue_head(&cur_trans->writer_wait);
    init_waitqueue_head(&cur_trans->commit_wait);
    cur_trans->in_commit = 0;
    cur_trans->blocked = 0;
    /*
     * One for this trans handle, one so it will live on until we
     * commit the transaction.
     */
    atomic_set(&cur_trans->use_count, 2);
    cur_trans->commit_done = 0;
    cur_trans->start_time = get_seconds();

    cur_trans->delayed_refs.root = RB_ROOT;
    cur_trans->delayed_refs.num_entries = 0;
    cur_trans->delayed_refs.num_heads_ready = 0;
    cur_trans->delayed_refs.num_heads = 0;
    cur_trans->delayed_refs.flushing = 0;
    cur_trans->delayed_refs.run_delayed_start = 0;

    /*
     * although the tree mod log is per file system and not per transaction,
     * the log must never go across transaction boundaries.
     */
    smp_mb();
    if (!list_empty(&fs_info->tree_mod_seq_list)) {
        printk(KERN_ERR "btrfs: tree_mod_seq_list not empty when "
            "creating a fresh transaction\n");
        WARN_ON(1);
    }
    if (!RB_EMPTY_ROOT(&fs_info->tree_mod_log)) {
        printk(KERN_ERR "btrfs: tree_mod_log rb tree not empty when "
            "creating a fresh transaction\n");
        WARN_ON(1);
    }
    atomic_set(&fs_info->tree_mod_seq, 0);

    spin_lock_init(&cur_trans->commit_lock);
    spin_lock_init(&cur_trans->delayed_refs.lock);

    INIT_LIST_HEAD(&cur_trans->pending_snapshots);
    list_add_tail(&cur_trans->list, &fs_info->trans_list);
    extent_io_tree_init(&cur_trans->dirty_pages,
                 fs_info->btree_inode->i_mapping);
    fs_info->generation++;
    cur_trans->transid = fs_info->generation;
    fs_info->running_transaction = cur_trans;
    cur_trans->aborted = 0;
    spin_unlock(&fs_info->trans_lock);

    return 0;
}

/*
 * this does all the record keeping required to make sure that a reference
 * counted root is properly recorded in a given transaction.  This is required
 * to make sure the old root from before we joined the transaction is deleted
 * when the transaction commits
 */
static int record_root_in_trans(struct btrfs_trans_handle *trans,
                   struct btrfs_root *root)
{
    if (root->ref_cows && root->last_trans < trans->transid) {
        WARN_ON(root == root->fs_info->extent_root);
        WARN_ON(root->commit_root != root->node);

        /*
         * see below for in_trans_setup usage rules
         * we have the reloc mutex held now, so there
         * is only one writer in this function
         */
        root->in_trans_setup = 1;

        /* make sure readers find in_trans_setup before
         * they find our root->last_trans update
         */
        smp_wmb();

        spin_lock(&root->fs_info->fs_roots_radix_lock);
        if (root->last_trans == trans->transid) {
            spin_unlock(&root->fs_info->fs_roots_radix_lock);
            return 0;
        }
        radix_tree_tag_set(&root->fs_info->fs_roots_radix,
               (unsigned long)root->root_key.objectid,
               BTRFS_ROOT_TRANS_TAG);
        spin_unlock(&root->fs_info->fs_roots_radix_lock);
        root->last_trans = trans->transid;

        /* this is pretty tricky.  We don't want to
         * take the relocation lock in btrfs_record_root_in_trans
         * unless we're really doing the first setup for this root in
         * this transaction.
         *
         * Normally we'd use root->last_trans as a flag to decide
         * if we want to take the expensive mutex.
         *
         * But, we have to set root->last_trans before we
         * init the relocation root, otherwise, we trip over warnings
         * in ctree.c.  The solution used here is to flag ourselves
         * with root->in_trans_setup.  When this is 1, we're still
         * fixing up the reloc trees and everyone must wait.
         *
         * When this is zero, they can trust root->last_trans and fly
         * through btrfs_record_root_in_trans without having to take the
         * lock.  smp_wmb() makes sure that all the writes above are
         * done before we pop in the zero below
         */
        btrfs_init_reloc_root(trans, root);
        smp_wmb();
        root->in_trans_setup = 0;
    }
    return 0;
}


int btrfs_record_root_in_trans(struct btrfs_trans_handle *trans,
                   struct btrfs_root *root)
{
    if (!root->ref_cows)
        return 0;

    /*
     * see record_root_in_trans for comments about in_trans_setup usage
     * and barriers
     */
    smp_rmb();
    if (root->last_trans == trans->transid &&
        !root->in_trans_setup)
        return 0;

    mutex_lock(&root->fs_info->reloc_mutex);
    record_root_in_trans(trans, root);
    mutex_unlock(&root->fs_info->reloc_mutex);

    return 0;
}

/* wait for commit against the current transaction to become unblocked
 * when this is done, it is safe to start a new transaction, but the current
 * transaction might not be fully on disk.
 */
static void wait_current_trans(struct btrfs_root *root)
{
    struct btrfs_transaction *cur_trans;

    spin_lock(&root->fs_info->trans_lock);
    cur_trans = root->fs_info->running_transaction;
    if (cur_trans && cur_trans->blocked) {
        atomic_inc(&cur_trans->use_count);
        spin_unlock(&root->fs_info->trans_lock);

        wait_event(root->fs_info->transaction_wait,
               !cur_trans->blocked);
        put_transaction(cur_trans);
    } else {
        spin_unlock(&root->fs_info->trans_lock);
    }
}

static int may_wait_transaction(struct btrfs_root *root, int type)
{
    if (root->fs_info->log_root_recovering)
        return 0;

    if (type == TRANS_USERSPACE)
        return 1;

    if (type == TRANS_START &&
        !atomic_read(&root->fs_info->open_ioctl_trans))
        return 1;

    return 0;
}

static struct btrfs_trans_handle *start_transaction(struct btrfs_root *root,
                            u64 num_items, int type,
                            int noflush)
{
    struct btrfs_trans_handle *h;
    struct btrfs_transaction *cur_trans;
    u64 num_bytes = 0;
    int ret;
    u64 qgroup_reserved = 0;

    if (root->fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR)
        return ERR_PTR(-EROFS);

    if (current->journal_info) {
        WARN_ON(type != TRANS_JOIN && type != TRANS_JOIN_NOLOCK);
        h = current->journal_info;
        h->use_count++;
        h->orig_rsv = h->block_rsv;
        h->block_rsv = NULL;
        goto got_it;
    }

    /*
     * Do the reservation before we join the transaction so we can do all
     * the appropriate flushing if need be.
     */
    if (num_items > 0 && root != root->fs_info->chunk_root) {
        if (root->fs_info->quota_enabled &&
            is_fstree(root->root_key.objectid)) {
            qgroup_reserved = num_items * root->leafsize;
            ret = btrfs_qgroup_reserve(root, qgroup_reserved);
            if (ret)
                return ERR_PTR(ret);
        }

        num_bytes = btrfs_calc_trans_metadata_size(root, num_items);
        if (noflush)
            ret = btrfs_block_rsv_add_noflush(root,
                        &root->fs_info->trans_block_rsv,
                        num_bytes);
        else
            ret = btrfs_block_rsv_add(root,
                        &root->fs_info->trans_block_rsv,
                        num_bytes);
        if (ret)
            return ERR_PTR(ret);
    }
again:
    h = kmem_cache_alloc(btrfs_trans_handle_cachep, GFP_NOFS);
    if (!h)
        return ERR_PTR(-ENOMEM);

    /*
     * If we are JOIN_NOLOCK we're already committing a transaction and
     * waiting on this guy, so we don't need to do the sb_start_intwrite
     * because we're already holding a ref.  We need this because we could
     * have raced in and did an fsync() on a file which can kick a commit
     * and then we deadlock with somebody doing a freeze.
     *
     * If we are ATTACH, it means we just want to catch the current
     * transaction and commit it, so we needn't do sb_start_intwrite(). 
     */
    if (type < TRANS_JOIN_NOLOCK)
        sb_start_intwrite(root->fs_info->sb);

    if (may_wait_transaction(root, type))
        wait_current_trans(root);

    do {
        ret = join_transaction(root, type);
        if (ret == -EBUSY)
            wait_current_trans(root);
    } while (ret == -EBUSY);

    if (ret < 0) {
        /* We must get the transaction if we are JOIN_NOLOCK. */
        BUG_ON(type == TRANS_JOIN_NOLOCK);

        if (type < TRANS_JOIN_NOLOCK)
            sb_end_intwrite(root->fs_info->sb);
        kmem_cache_free(btrfs_trans_handle_cachep, h);
        return ERR_PTR(ret);
    }

    cur_trans = root->fs_info->running_transaction;

    h->transid = cur_trans->transid;
    h->transaction = cur_trans;
    h->blocks_used = 0;
    h->bytes_reserved = 0;
    h->root = root;
    h->delayed_ref_updates = 0;
    h->use_count = 1;
    h->adding_csums = 0;
    h->block_rsv = NULL;
    h->orig_rsv = NULL;
    h->aborted = 0;
    h->qgroup_reserved = qgroup_reserved;
    h->delayed_ref_elem.seq = 0;
    h->type = type;
    INIT_LIST_HEAD(&h->qgroup_ref_list);
    INIT_LIST_HEAD(&h->new_bgs);

    smp_mb();
    if (cur_trans->blocked && may_wait_transaction(root, type)) {
        btrfs_commit_transaction(h, root);
        goto again;
    }

    if (num_bytes) {
        trace_btrfs_space_reservation(root->fs_info, "transaction",
                          h->transid, num_bytes, 1);
        h->block_rsv = &root->fs_info->trans_block_rsv;
        h->bytes_reserved = num_bytes;
    }

got_it:
    btrfs_record_root_in_trans(h, root);

    if (!current->journal_info && type != TRANS_USERSPACE)
        current->journal_info = h;
    return h;
}

struct btrfs_trans_handle *btrfs_start_transaction(struct btrfs_root *root,
                           int num_items)
{
    return start_transaction(root, num_items, TRANS_START, 0);
}

struct btrfs_trans_handle *btrfs_start_transaction_noflush(
                    struct btrfs_root *root, int num_items)
{
    return start_transaction(root, num_items, TRANS_START, 1);
}

struct btrfs_trans_handle *btrfs_join_transaction(struct btrfs_root *root)
{
    return start_transaction(root, 0, TRANS_JOIN, 0);
}

struct btrfs_trans_handle *btrfs_join_transaction_nolock(struct btrfs_root *root)
{
    return start_transaction(root, 0, TRANS_JOIN_NOLOCK, 0);
}

struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *root)
{
    return start_transaction(root, 0, TRANS_USERSPACE, 0);
}

struct btrfs_trans_handle *btrfs_attach_transaction(struct btrfs_root *root)
{
    return start_transaction(root, 0, TRANS_ATTACH, 0);
}

/* wait for a transaction commit to be fully complete */
static noinline void wait_for_commit(struct btrfs_root *root,
                    struct btrfs_transaction *commit)
{
    wait_event(commit->commit_wait, commit->commit_done);
}

int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid)
{
    struct btrfs_transaction *cur_trans = NULL, *t;
    int ret;

    ret = 0;
    if (transid) {
        if (transid <= root->fs_info->last_trans_committed)
            goto out;

        /* find specified transaction */
        spin_lock(&root->fs_info->trans_lock);
        list_for_each_entry(t, &root->fs_info->trans_list, list) {
            if (t->transid == transid) {
                cur_trans = t;
                atomic_inc(&cur_trans->use_count);
                break;
            }
            if (t->transid > transid)
                break;
        }
        spin_unlock(&root->fs_info->trans_lock);
        ret = -EINVAL;
        if (!cur_trans)
            goto out;  /* bad transid */
    } else {
        /* find newest transaction that is committing | committed */
        spin_lock(&root->fs_info->trans_lock);
        list_for_each_entry_reverse(t, &root->fs_info->trans_list,
                        list) {
            if (t->in_commit) {
                if (t->commit_done)
                    break;
                cur_trans = t;
                atomic_inc(&cur_trans->use_count);
                break;
            }
        }
        spin_unlock(&root->fs_info->trans_lock);
        if (!cur_trans)
            goto out;  /* nothing committing|committed */
    }

    wait_for_commit(root, cur_trans);

    put_transaction(cur_trans);
    ret = 0;
out:
    return ret;
}

void btrfs_throttle(struct btrfs_root *root)
{
    if (!atomic_read(&root->fs_info->open_ioctl_trans))
        wait_current_trans(root);
}

static int should_end_transaction(struct btrfs_trans_handle *trans,
                  struct btrfs_root *root)
{
    int ret;

    ret = btrfs_block_rsv_check(root, &root->fs_info->global_block_rsv, 5);
    return ret ? 1 : 0;
}

int btrfs_should_end_transaction(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root)
{
    struct btrfs_transaction *cur_trans = trans->transaction;
    int updates;
    int err;

    smp_mb();
    if (cur_trans->blocked || cur_trans->delayed_refs.flushing)
        return 1;

    updates = trans->delayed_ref_updates;
    trans->delayed_ref_updates = 0;
    if (updates) {
        err = btrfs_run_delayed_refs(trans, root, updates);
        if (err) /* Error code will also eval true */
            return err;
    }

    return should_end_transaction(trans, root);
}

static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
              struct btrfs_root *root, int throttle)
{
    struct btrfs_transaction *cur_trans = trans->transaction;
    struct btrfs_fs_info *info = root->fs_info;
    int count = 0;
    int lock = (trans->type != TRANS_JOIN_NOLOCK);
    int err = 0;

    if (--trans->use_count) {
        trans->block_rsv = trans->orig_rsv;
        return 0;
    }

    /*
     * do the qgroup accounting as early as possible
     */
    err = btrfs_delayed_refs_qgroup_accounting(trans, info);

    btrfs_trans_release_metadata(trans, root);
    trans->block_rsv = NULL;
    /*
     * the same root has to be passed to start_transaction and
     * end_transaction. Subvolume quota depends on this.
     */
    WARN_ON(trans->root != root);

    if (trans->qgroup_reserved) {
        btrfs_qgroup_free(root, trans->qgroup_reserved);
        trans->qgroup_reserved = 0;
    }

    if (!list_empty(&trans->new_bgs))
        btrfs_create_pending_block_groups(trans, root);

    while (count < 2) {
        unsigned long cur = trans->delayed_ref_updates;
        trans->delayed_ref_updates = 0;
        if (cur &&
            trans->transaction->delayed_refs.num_heads_ready > 64) {
            trans->delayed_ref_updates = 0;
            btrfs_run_delayed_refs(trans, root, cur);
        } else {
            break;
        }
        count++;
    }
    btrfs_trans_release_metadata(trans, root);
    trans->block_rsv = NULL;

    if (!list_empty(&trans->new_bgs))
        btrfs_create_pending_block_groups(trans, root);

    if (lock && !atomic_read(&root->fs_info->open_ioctl_trans) &&
        should_end_transaction(trans, root)) {
        trans->transaction->blocked = 1;
        smp_wmb();
    }

    if (lock && cur_trans->blocked && !cur_trans->in_commit) {
        if (throttle) {
            /*
             * We may race with somebody else here so end up having
             * to call end_transaction on ourselves again, so inc
             * our use_count.
             */
            trans->use_count++;
            return btrfs_commit_transaction(trans, root);
        } else {
            wake_up_process(info->transaction_kthread);
        }
    }

    if (trans->type < TRANS_JOIN_NOLOCK)
        sb_end_intwrite(root->fs_info->sb);

    WARN_ON(cur_trans != info->running_transaction);
    WARN_ON(atomic_read(&cur_trans->num_writers) < 1);
    atomic_dec(&cur_trans->num_writers);

    smp_mb();
    if (waitqueue_active(&cur_trans->writer_wait))
        wake_up(&cur_trans->writer_wait);
    put_transaction(cur_trans);

    if (current->journal_info == trans)
        current->journal_info = NULL;

    if (throttle)
        btrfs_run_delayed_iputs(root);

    if (trans->aborted ||
        root->fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) {
        err = -EIO;
    }
    assert_qgroups_uptodate(trans);

    memset(trans, 0, sizeof(*trans));
    kmem_cache_free(btrfs_trans_handle_cachep, trans);
    return err;
}

int btrfs_end_transaction(struct btrfs_trans_handle *trans,
              struct btrfs_root *root)
{
    int ret;

    ret = __btrfs_end_transaction(trans, root, 0);
    if (ret)
        return ret;
    return 0;
}

int btrfs_end_transaction_throttle(struct btrfs_trans_handle *trans,
                   struct btrfs_root *root)
{
    int ret;

    ret = __btrfs_end_transaction(trans, root, 1);
    if (ret)
        return ret;
    return 0;
}

int btrfs_end_transaction_dmeta(struct btrfs_trans_handle *trans,
                struct btrfs_root *root)
{
    return __btrfs_end_transaction(trans, root, 1);
}

/*
 * when btree blocks are allocated, they have some corresponding bits set for
 * them in one of two extent_io trees.  This is used to make sure all of
 * those extents are sent to disk but does not wait on them
 */
int btrfs_write_marked_extents(struct btrfs_root *root,
                   struct extent_io_tree *dirty_pages, int mark)
{
    int err = 0;
    int werr = 0;
    struct address_space *mapping = root->fs_info->btree_inode->i_mapping;
    struct extent_state *cached_state = NULL;
    u64 start = 0;
    u64 end;

    while (!find_first_extent_bit(dirty_pages, start, &start, &end,
                      mark, &cached_state)) {
        convert_extent_bit(dirty_pages, start, end, EXTENT_NEED_WAIT,
                   mark, &cached_state, GFP_NOFS);
        cached_state = NULL;
        err = filemap_fdatawrite_range(mapping, start, end);
        if (err)
            werr = err;
        cond_resched();
        start = end + 1;
    }
    if (err)
        werr = err;
    return werr;
}

/*
 * when btree blocks are allocated, they have some corresponding bits set for
 * them in one of two extent_io trees.  This is used to make sure all of
 * those extents are on disk for transaction or log commit.  We wait
 * on all the pages and clear them from the dirty pages state tree
 */
int btrfs_wait_marked_extents(struct btrfs_root *root,
                  struct extent_io_tree *dirty_pages, int mark)
{
    int err = 0;
    int werr = 0;
    struct address_space *mapping = root->fs_info->btree_inode->i_mapping;
    struct extent_state *cached_state = NULL;
    u64 start = 0;
    u64 end;

    while (!find_first_extent_bit(dirty_pages, start, &start, &end,
                      EXTENT_NEED_WAIT, &cached_state)) {
        clear_extent_bit(dirty_pages, start, end, EXTENT_NEED_WAIT,
                 0, 0, &cached_state, GFP_NOFS);
        err = filemap_fdatawait_range(mapping, start, end);
        if (err)
            werr = err;
        cond_resched();
        start = end + 1;
    }
    if (err)
        werr = err;
    return werr;
}

/*
 * when btree blocks are allocated, they have some corresponding bits set for
 * them in one of two extent_io trees.  This is used to make sure all of
 * those extents are on disk for transaction or log commit
 */
int btrfs_write_and_wait_marked_extents(struct btrfs_root *root,
                struct extent_io_tree *dirty_pages, int mark)
{
    int ret;
    int ret2;

    ret = btrfs_write_marked_extents(root, dirty_pages, mark);
    ret2 = btrfs_wait_marked_extents(root, dirty_pages, mark);

    if (ret)
        return ret;
    if (ret2)
        return ret2;
    return 0;
}

int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans,
                     struct btrfs_root *root)
{
    if (!trans || !trans->transaction) {
        struct inode *btree_inode;
        btree_inode = root->fs_info->btree_inode;
        return filemap_write_and_wait(btree_inode->i_mapping);
    }
    return btrfs_write_and_wait_marked_extents(root,
                       &trans->transaction->dirty_pages,
                       EXTENT_DIRTY);
}

/*
 * this is used to update the root pointer in the tree of tree roots.
 *
 * But, in the case of the extent allocation tree, updating the root
 * pointer may allocate blocks which may change the root of the extent
 * allocation tree.
 *
 * So, this loops and repeats and makes sure the cowonly root didn't
 * change while the root pointer was being updated in the metadata.
 */
static int update_cowonly_root(struct btrfs_trans_handle *trans,
                   struct btrfs_root *root)
{
    int ret;
    u64 old_root_bytenr;
    u64 old_root_used;
    struct btrfs_root *tree_root = root->fs_info->tree_root;

    old_root_used = btrfs_root_used(&root->root_item);
    btrfs_write_dirty_block_groups(trans, root);

    while (1) {
        old_root_bytenr = btrfs_root_bytenr(&root->root_item);
        if (old_root_bytenr == root->node->start &&
            old_root_used == btrfs_root_used(&root->root_item))
            break;

        btrfs_set_root_node(&root->root_item, root->node);
        ret = btrfs_update_root(trans, tree_root,
                    &root->root_key,
                    &root->root_item);
        if (ret)
            return ret;

        old_root_used = btrfs_root_used(&root->root_item);
        ret = btrfs_write_dirty_block_groups(trans, root);
        if (ret)
            return ret;
    }

    if (root != root->fs_info->extent_root)
        switch_commit_root(root);

    return 0;
}

/*
 * update all the cowonly tree roots on disk
 *
 * The error handling in this function may not be obvious. Any of the
 * failures will cause the file system to go offline. We still need
 * to clean up the delayed refs.
 */
static noinline int commit_cowonly_roots(struct btrfs_trans_handle *trans,
                     struct btrfs_root *root)
{
    struct btrfs_fs_info *fs_info = root->fs_info;
    struct list_head *next;
    struct extent_buffer *eb;
    int ret;

    ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
    if (ret)
        return ret;

    eb = btrfs_lock_root_node(fs_info->tree_root);
    ret = btrfs_cow_block(trans, fs_info->tree_root, eb, NULL,
                  0, &eb);
    btrfs_tree_unlock(eb);
    free_extent_buffer(eb);

    if (ret)
        return ret;

    ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
    if (ret)
        return ret;

    ret = btrfs_run_dev_stats(trans, root->fs_info);
    BUG_ON(ret);

    ret = btrfs_run_qgroups(trans, root->fs_info);
    BUG_ON(ret);

    /* run_qgroups might have added some more refs */
    ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
    BUG_ON(ret);

    while (!list_empty(&fs_info->dirty_cowonly_roots)) {
        next = fs_info->dirty_cowonly_roots.next;
        list_del_init(next);
        root = list_entry(next, struct btrfs_root, dirty_list);

        ret = update_cowonly_root(trans, root);
        if (ret)
            return ret;
    }

    down_write(&fs_info->extent_commit_sem);
    switch_commit_root(fs_info->extent_root);
    up_write(&fs_info->extent_commit_sem);

    return 0;
}

/*
 * dead roots are old snapshots that need to be deleted.  This allocates
 * a dirty root struct and adds it into the list of dead roots that need to
 * be deleted
 */
int btrfs_add_dead_root(struct btrfs_root *root)
{
    spin_lock(&root->fs_info->trans_lock);
    list_add(&root->root_list, &root->fs_info->dead_roots);
    spin_unlock(&root->fs_info->trans_lock);
    return 0;
}

/*
 * update all the cowonly tree roots on disk
 */
static noinline int commit_fs_roots(struct btrfs_trans_handle *trans,
                    struct btrfs_root *root)
{
    struct btrfs_root *gang[8];
    struct btrfs_fs_info *fs_info = root->fs_info;
    int i;
    int ret;
    int err = 0;

    spin_lock(&fs_info->fs_roots_radix_lock);
    while (1) {
        ret = radix_tree_gang_lookup_tag(&fs_info->fs_roots_radix,
                         (void **)gang, 0,
                         ARRAY_SIZE(gang),
                         BTRFS_ROOT_TRANS_TAG);
        if (ret == 0)
            break;
        for (i = 0; i < ret; i++) {
            root = gang[i];
            radix_tree_tag_clear(&fs_info->fs_roots_radix,
                    (unsigned long)root->root_key.objectid,
                    BTRFS_ROOT_TRANS_TAG);
            spin_unlock(&fs_info->fs_roots_radix_lock);

            btrfs_free_log(trans, root);
            btrfs_update_reloc_root(trans, root);
            btrfs_orphan_commit_root(trans, root);

            btrfs_save_ino_cache(root, trans);

            /* see comments in should_cow_block() */
            root->force_cow = 0;
            smp_wmb();

            if (root->commit_root != root->node) {
                mutex_lock(&root->fs_commit_mutex);
                switch_commit_root(root);
                btrfs_unpin_free_ino(root);
                mutex_unlock(&root->fs_commit_mutex);

                btrfs_set_root_node(&root->root_item,
                            root->node);
            }

            err = btrfs_update_root(trans, fs_info->tree_root,
                        &root->root_key,
                        &root->root_item);
            spin_lock(&fs_info->fs_roots_radix_lock);
            if (err)
                break;
        }
    }
    spin_unlock(&fs_info->fs_roots_radix_lock);
    return err;
}

/*
 * defrag a given btree.  If cacheonly == 1, this won't read from the disk,
 * otherwise every leaf in the btree is read and defragged.
 */
int btrfs_defrag_root(struct btrfs_root *root, int cacheonly)
{
    struct btrfs_fs_info *info = root->fs_info;
    struct btrfs_trans_handle *trans;
    int ret;
    unsigned long nr;

    if (xchg(&root->defrag_running, 1))
        return 0;

    while (1) {
        trans = btrfs_start_transaction(root, 0);
        if (IS_ERR(trans))
            return PTR_ERR(trans);

        ret = btrfs_defrag_leaves(trans, root, cacheonly);

        nr = trans->blocks_used;
        btrfs_end_transaction(trans, root);
        btrfs_btree_balance_dirty(info->tree_root, nr);
        cond_resched();

        if (btrfs_fs_closing(root->fs_info) || ret != -EAGAIN)
            break;
    }
    root->defrag_running = 0;
    return ret;
}

/*
 * new snapshots need to be created at a very specific time in the
 * transaction commit.  This does the actual creation
 */
static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
                   struct btrfs_fs_info *fs_info,
                   struct btrfs_pending_snapshot *pending)
{
    struct btrfs_key key;
    struct btrfs_root_item *new_root_item;
    struct btrfs_root *tree_root = fs_info->tree_root;
    struct btrfs_root *root = pending->root;
    struct btrfs_root *parent_root;
    struct btrfs_block_rsv *rsv;
    struct inode *parent_inode;
    struct btrfs_path *path;
    struct btrfs_dir_item *dir_item;
    struct dentry *parent;
    struct dentry *dentry;
    struct extent_buffer *tmp;
    struct extent_buffer *old;
    struct timespec cur_time = CURRENT_TIME;
    int ret;
    u64 to_reserve = 0;
    u64 index = 0;
    u64 objectid;
    u64 root_flags;
    uuid_le new_uuid;

    path = btrfs_alloc_path();
    if (!path) {
        ret = pending->error = -ENOMEM;
        goto path_alloc_fail;
    }

    new_root_item = kmalloc(sizeof(*new_root_item), GFP_NOFS);
    if (!new_root_item) {
        ret = pending->error = -ENOMEM;
        goto root_item_alloc_fail;
    }

    ret = btrfs_find_free_objectid(tree_root, &objectid);
    if (ret) {
        pending->error = ret;
        goto no_free_objectid;
    }

    btrfs_reloc_pre_snapshot(trans, pending, &to_reserve);

    if (to_reserve > 0) {
        ret = btrfs_block_rsv_add_noflush(root, &pending->block_rsv,
                          to_reserve);
        if (ret) {
            pending->error = ret;
            goto no_free_objectid;
        }
    }

    ret = btrfs_qgroup_inherit(trans, fs_info, root->root_key.objectid,
                   objectid, pending->inherit);
    if (ret) {
        pending->error = ret;
        goto no_free_objectid;
    }

    key.objectid = objectid;
    key.offset = (u64)-1;
    key.type = BTRFS_ROOT_ITEM_KEY;

    rsv = trans->block_rsv;
    trans->block_rsv = &pending->block_rsv;

    dentry = pending->dentry;
    parent = dget_parent(dentry);
    parent_inode = parent->d_inode;
    parent_root = BTRFS_I(parent_inode)->root;
    record_root_in_trans(trans, parent_root);

    /*
     * insert the directory item
     */
    ret = btrfs_set_inode_index(parent_inode, &index);
    BUG_ON(ret); /* -ENOMEM */

    /* check if there is a file/dir which has the same name. */
    dir_item = btrfs_lookup_dir_item(NULL, parent_root, path,
                     btrfs_ino(parent_inode),
                     dentry->d_name.name,
                     dentry->d_name.len, 0);
    if (dir_item != NULL && !IS_ERR(dir_item)) {
        pending->error = -EEXIST;
        goto fail;
    } else if (IS_ERR(dir_item)) {
        ret = PTR_ERR(dir_item);
        btrfs_abort_transaction(trans, root, ret);
        goto fail;
    }
    btrfs_release_path(path);

    /*
     * pull in the delayed directory update
     * and the delayed inode item
     * otherwise we corrupt the FS during
     * snapshot
     */
    ret = btrfs_run_delayed_items(trans, root);
    if (ret) {  /* Transaction aborted */
        btrfs_abort_transaction(trans, root, ret);
        goto fail;
    }

    record_root_in_trans(trans, root);
    btrfs_set_root_last_snapshot(&root->root_item, trans->transid);
    memcpy(new_root_item, &root->root_item, sizeof(*new_root_item));
    btrfs_check_and_init_root_item(new_root_item);

    root_flags = btrfs_root_flags(new_root_item);
    if (pending->readonly)
        root_flags |= BTRFS_ROOT_SUBVOL_RDONLY;
    else
        root_flags &= ~BTRFS_ROOT_SUBVOL_RDONLY;
    btrfs_set_root_flags(new_root_item, root_flags);

    btrfs_set_root_generation_v2(new_root_item,
            trans->transid);
    uuid_le_gen(&new_uuid);
    memcpy(new_root_item->uuid, new_uuid.b, BTRFS_UUID_SIZE);
    memcpy(new_root_item->parent_uuid, root->root_item.uuid,
            BTRFS_UUID_SIZE);
    new_root_item->otime.sec = cpu_to_le64(cur_time.tv_sec);
    new_root_item->otime.nsec = cpu_to_le32(cur_time.tv_nsec);
    btrfs_set_root_otransid(new_root_item, trans->transid);
    memset(&new_root_item->stime, 0, sizeof(new_root_item->stime));
    memset(&new_root_item->rtime, 0, sizeof(new_root_item->rtime));
    btrfs_set_root_stransid(new_root_item, 0);
    btrfs_set_root_rtransid(new_root_item, 0);

    old = btrfs_lock_root_node(root);
    ret = btrfs_cow_block(trans, root, old, NULL, 0, &old);
    if (ret) {
        btrfs_tree_unlock(old);
        free_extent_buffer(old);
        btrfs_abort_transaction(trans, root, ret);
        goto fail;
    }

    btrfs_set_lock_blocking(old);

    ret = btrfs_copy_root(trans, root, old, &tmp, objectid);
    /* clean up in any case */
    btrfs_tree_unlock(old);
    free_extent_buffer(old);
    if (ret) {
        btrfs_abort_transaction(trans, root, ret);
        goto fail;
    }

    /* see comments in should_cow_block() */
    root->force_cow = 1;
    smp_wmb();

    btrfs_set_root_node(new_root_item, tmp);
    /* record when the snapshot was created in key.offset */
    key.offset = trans->transid;
    ret = btrfs_insert_root(trans, tree_root, &key, new_root_item);
    btrfs_tree_unlock(tmp);
    free_extent_buffer(tmp);
    if (ret) {
        btrfs_abort_transaction(trans, root, ret);
        goto fail;
    }

    /*
     * insert root back/forward references
     */
    ret = btrfs_add_root_ref(trans, tree_root, objectid,
                 parent_root->root_key.objectid,
                 btrfs_ino(parent_inode), index,
                 dentry->d_name.name, dentry->d_name.len);
    if (ret) {
        btrfs_abort_transaction(trans, root, ret);
        goto fail;
    }

    key.offset = (u64)-1;
    pending->snap = btrfs_read_fs_root_no_name(root->fs_info, &key);
    if (IS_ERR(pending->snap)) {
        ret = PTR_ERR(pending->snap);
        btrfs_abort_transaction(trans, root, ret);
        goto fail;
    }

    ret = btrfs_reloc_post_snapshot(trans, pending);
    if (ret) {
        btrfs_abort_transaction(trans, root, ret);
        goto fail;
    }

    ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
    if (ret) {
        btrfs_abort_transaction(trans, root, ret);
        goto fail;
    }

    ret = btrfs_insert_dir_item(trans, parent_root,
                    dentry->d_name.name, dentry->d_name.len,
                    parent_inode, &key,
                    BTRFS_FT_DIR, index);
    /* We have check then name at the beginning, so it is impossible. */
    BUG_ON(ret == -EEXIST);
    if (ret) {
        btrfs_abort_transaction(trans, root, ret);
        goto fail;
    }

    btrfs_i_size_write(parent_inode, parent_inode->i_size +
                     dentry->d_name.len * 2);
    parent_inode->i_mtime = parent_inode->i_ctime = CURRENT_TIME;
    ret = btrfs_update_inode_fallback(trans, parent_root, parent_inode);
    if (ret)
        btrfs_abort_transaction(trans, root, ret);
fail:
    dput(parent);
    trans->block_rsv = rsv;
no_free_objectid:
    kfree(new_root_item);
root_item_alloc_fail:
    btrfs_free_path(path);
path_alloc_fail:
    btrfs_block_rsv_release(root, &pending->block_rsv, (u64)-1);
    return ret;
}

/*
 * create all the snapshots we've scheduled for creation
 */
static noinline int create_pending_snapshots(struct btrfs_trans_handle *trans,
                         struct btrfs_fs_info *fs_info)
{
    struct btrfs_pending_snapshot *pending;
    struct list_head *head = &trans->transaction->pending_snapshots;

    list_for_each_entry(pending, head, list)
        create_pending_snapshot(trans, fs_info, pending);
    return 0;
}

static void update_super_roots(struct btrfs_root *root)
{
    struct btrfs_root_item *root_item;
    struct btrfs_super_block *super;

    super = root->fs_info->super_copy;

    root_item = &root->fs_info->chunk_root->root_item;
    super->chunk_root = root_item->bytenr;
    super->chunk_root_generation = root_item->generation;
    super->chunk_root_level = root_item->level;

    root_item = &root->fs_info->tree_root->root_item;
    super->root = root_item->bytenr;
    super->generation = root_item->generation;
    super->root_level = root_item->level;
    if (btrfs_test_opt(root, SPACE_CACHE))
        super->cache_generation = root_item->generation;
}

int btrfs_transaction_in_commit(struct btrfs_fs_info *info)
{
    int ret = 0;
    spin_lock(&info->trans_lock);
    if (info->running_transaction)
        ret = info->running_transaction->in_commit;
    spin_unlock(&info->trans_lock);
    return ret;
}

int btrfs_transaction_blocked(struct btrfs_fs_info *info)
{
    int ret = 0;
    spin_lock(&info->trans_lock);
    if (info->running_transaction)
        ret = info->running_transaction->blocked;
    spin_unlock(&info->trans_lock);
    return ret;
}

/*
 * wait for the current transaction commit to start and block subsequent
 * transaction joins
 */
static void wait_current_trans_commit_start(struct btrfs_root *root,
                        struct btrfs_transaction *trans)
{
    wait_event(root->fs_info->transaction_blocked_wait, trans->in_commit);
}

/*
 * wait for the current transaction to start and then become unblocked.
 * caller holds ref.
 */
static void wait_current_trans_commit_start_and_unblock(struct btrfs_root *root,
                     struct btrfs_transaction *trans)
{
    wait_event(root->fs_info->transaction_wait,
           trans->commit_done || (trans->in_commit && !trans->blocked));
}

/*
 * commit transactions asynchronously. once btrfs_commit_transaction_async
 * returns, any subsequent transaction will not be allowed to join.
 */
struct btrfs_async_commit {
    struct btrfs_trans_handle *newtrans;
    struct btrfs_root *root;
    struct delayed_work work;
};

static void do_async_commit(struct work_struct *work)
{
    struct btrfs_async_commit *ac =
        container_of(work, struct btrfs_async_commit, work.work);

    /*
     * We've got freeze protection passed with the transaction.
     * Tell lockdep about it.
     */
    rwsem_acquire_read(
        &ac->root->fs_info->sb->s_writers.lock_map[SB_FREEZE_FS-1],
        0, 1, _THIS_IP_);

    current->journal_info = ac->newtrans;

    btrfs_commit_transaction(ac->newtrans, ac->root);
    kfree(ac);
}

int btrfs_commit_transaction_async(struct btrfs_trans_handle *trans,
                   struct btrfs_root *root,
                   int wait_for_unblock)
{
    struct btrfs_async_commit *ac;
    struct btrfs_transaction *cur_trans;

    ac = kmalloc(sizeof(*ac), GFP_NOFS);
    if (!ac)
        return -ENOMEM;

    INIT_DELAYED_WORK(&ac->work, do_async_commit);
    ac->root = root;
    ac->newtrans = btrfs_join_transaction(root);
    if (IS_ERR(ac->newtrans)) {
        int err = PTR_ERR(ac->newtrans);
        kfree(ac);
        return err;
    }

    /* take transaction reference */
    cur_trans = trans->transaction;
    atomic_inc(&cur_trans->use_count);

    btrfs_end_transaction(trans, root);

    /*
     * Tell lockdep we've released the freeze rwsem, since the
     * async commit thread will be the one to unlock it.
     */
    rwsem_release(&root->fs_info->sb->s_writers.lock_map[SB_FREEZE_FS-1],
              1, _THIS_IP_);

    schedule_delayed_work(&ac->work, 0);

    /* wait for transaction to start and unblock */
    if (wait_for_unblock)
        wait_current_trans_commit_start_and_unblock(root, cur_trans);
    else
        wait_current_trans_commit_start(root, cur_trans);

    if (current->journal_info == trans)
        current->journal_info = NULL;

    put_transaction(cur_trans);
    return 0;
}


static void cleanup_transaction(struct btrfs_trans_handle *trans,
                struct btrfs_root *root, int err)
{
    struct btrfs_transaction *cur_trans = trans->transaction;

    WARN_ON(trans->use_count > 1);

    btrfs_abort_transaction(trans, root, err);

    spin_lock(&root->fs_info->trans_lock);
    list_del_init(&cur_trans->list);
    if (cur_trans == root->fs_info->running_transaction) {
        root->fs_info->running_transaction = NULL;
        root->fs_info->trans_no_join = 0;
    }
    spin_unlock(&root->fs_info->trans_lock);

    btrfs_cleanup_one_transaction(trans->transaction, root);

    put_transaction(cur_trans);
    put_transaction(cur_trans);

    trace_btrfs_transaction_commit(root);

    btrfs_scrub_continue(root);

    if (current->journal_info == trans)
        current->journal_info = NULL;

    kmem_cache_free(btrfs_trans_handle_cachep, trans);
}

/*
 * btrfs_transaction state sequence:
 *    in_commit = 0, blocked = 0  (initial)
 *    in_commit = 1, blocked = 1
 *    blocked = 0
 *    commit_done = 1
 */
int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root)
{
    unsigned long joined = 0;
    struct btrfs_transaction *cur_trans = trans->transaction;
    struct btrfs_transaction *prev_trans = NULL;
    DEFINE_WAIT(wait);
    int ret = -EIO;
    int should_grow = 0;
    unsigned long now = get_seconds();
    int flush_on_commit = btrfs_test_opt(root, FLUSHONCOMMIT);

    btrfs_run_ordered_operations(root, 0);

    if (cur_trans->aborted)
        goto cleanup_transaction;

    /* make a pass through all the delayed refs we have so far
     * any runnings procs may add more while we are here
     */
    ret = btrfs_run_delayed_refs(trans, root, 0);
    if (ret)
        goto cleanup_transaction;

    btrfs_trans_release_metadata(trans, root);
    trans->block_rsv = NULL;

    cur_trans = trans->transaction;

    /*
     * set the flushing flag so procs in this transaction have to
     * start sending their work down.
     */
    cur_trans->delayed_refs.flushing = 1;

    if (!list_empty(&trans->new_bgs))
        btrfs_create_pending_block_groups(trans, root);

    ret = btrfs_run_delayed_refs(trans, root, 0);
    if (ret)
        goto cleanup_transaction;

    spin_lock(&cur_trans->commit_lock);
    if (cur_trans->in_commit) {
        spin_unlock(&cur_trans->commit_lock);
        atomic_inc(&cur_trans->use_count);
        ret = btrfs_end_transaction(trans, root);

        wait_for_commit(root, cur_trans);

        put_transaction(cur_trans);

        return ret;
    }

    trans->transaction->in_commit = 1;
    trans->transaction->blocked = 1;
    spin_unlock(&cur_trans->commit_lock);
    wake_up(&root->fs_info->transaction_blocked_wait);

    spin_lock(&root->fs_info->trans_lock);
    if (cur_trans->list.prev != &root->fs_info->trans_list) {
        prev_trans = list_entry(cur_trans->list.prev,
                    struct btrfs_transaction, list);
        if (!prev_trans->commit_done) {
            atomic_inc(&prev_trans->use_count);
            spin_unlock(&root->fs_info->trans_lock);

            wait_for_commit(root, prev_trans);

            put_transaction(prev_trans);
        } else {
            spin_unlock(&root->fs_info->trans_lock);
        }
    } else {
        spin_unlock(&root->fs_info->trans_lock);
    }

    if (!btrfs_test_opt(root, SSD) &&
        (now < cur_trans->start_time || now - cur_trans->start_time < 1))
        should_grow = 1;

    do {
        int snap_pending = 0;

        joined = cur_trans->num_joined;
        if (!list_empty(&trans->transaction->pending_snapshots))
            snap_pending = 1;

        WARN_ON(cur_trans != trans->transaction);

        if (flush_on_commit || snap_pending) {
            btrfs_start_delalloc_inodes(root, 1);
            btrfs_wait_ordered_extents(root, 1);
        }

        ret = btrfs_run_delayed_items(trans, root);
        if (ret)
            goto cleanup_transaction;

        /*
         * running the delayed items may have added new refs. account
         * them now so that they hinder processing of more delayed refs
         * as little as possible.
         */
        btrfs_delayed_refs_qgroup_accounting(trans, root->fs_info);

        /*
         * rename don't use btrfs_join_transaction, so, once we
         * set the transaction to blocked above, we aren't going
         * to get any new ordered operations.  We can safely run
         * it here and no for sure that nothing new will be added
         * to the list
         */
        btrfs_run_ordered_operations(root, 1);

        prepare_to_wait(&cur_trans->writer_wait, &wait,
                TASK_UNINTERRUPTIBLE);

        if (atomic_read(&cur_trans->num_writers) > 1)
            schedule_timeout(MAX_SCHEDULE_TIMEOUT);
        else if (should_grow)
            schedule_timeout(1);

        finish_wait(&cur_trans->writer_wait, &wait);
    } while (atomic_read(&cur_trans->num_writers) > 1 ||
         (should_grow && cur_trans->num_joined != joined));

    /*
     * Ok now we need to make sure to block out any other joins while we
     * commit the transaction.  We could have started a join before setting
     * no_join so make sure to wait for num_writers to == 1 again.
     */
    spin_lock(&root->fs_info->trans_lock);
    root->fs_info->trans_no_join = 1;
    spin_unlock(&root->fs_info->trans_lock);
    wait_event(cur_trans->writer_wait,
           atomic_read(&cur_trans->num_writers) == 1);

    /*
     * the reloc mutex makes sure that we stop
     * the balancing code from coming in and moving
     * extents around in the middle of the commit
     */
    mutex_lock(&root->fs_info->reloc_mutex);

    /*
     * We needn't worry about the delayed items because we will
     * deal with them in create_pending_snapshot(), which is the
     * core function of the snapshot creation.
     */
    ret = create_pending_snapshots(trans, root->fs_info);
    if (ret) {
        mutex_unlock(&root->fs_info->reloc_mutex);
        goto cleanup_transaction;
    }

    /*
     * We insert the dir indexes of the snapshots and update the inode
     * of the snapshots' parents after the snapshot creation, so there
     * are some delayed items which are not dealt with. Now deal with
     * them.
     *
     * We needn't worry that this operation will corrupt the snapshots,
     * because all the tree which are snapshoted will be forced to COW
     * the nodes and leaves.
     */
    ret = btrfs_run_delayed_items(trans, root);
    if (ret) {
        mutex_unlock(&root->fs_info->reloc_mutex);
        goto cleanup_transaction;
    }

    ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
    if (ret) {
        mutex_unlock(&root->fs_info->reloc_mutex);
        goto cleanup_transaction;
    }

    /*
     * make sure none of the code above managed to slip in a
     * delayed item
     */
    btrfs_assert_delayed_root_empty(root);

    WARN_ON(cur_trans != trans->transaction);

    btrfs_scrub_pause(root);
    /* btrfs_commit_tree_roots is responsible for getting the
     * various roots consistent with each other.  Every pointer
     * in the tree of tree roots has to point to the most up to date
     * root for every subvolume and other tree.  So, we have to keep
     * the tree logging code from jumping in and changing any
     * of the trees.
     *
     * At this point in the commit, there can't be any tree-log
     * writers, but a little lower down we drop the trans mutex
     * and let new people in.  By holding the tree_log_mutex
     * from now until after the super is written, we avoid races
     * with the tree-log code.
     */
    mutex_lock(&root->fs_info->tree_log_mutex);

    ret = commit_fs_roots(trans, root);
    if (ret) {
        mutex_unlock(&root->fs_info->tree_log_mutex);
        mutex_unlock(&root->fs_info->reloc_mutex);
        goto cleanup_transaction;
    }

    /* commit_fs_roots gets rid of all the tree log roots, it is now
     * safe to free the root of tree log roots
     */
    btrfs_free_log_root_tree(trans, root->fs_info);

    ret = commit_cowonly_roots(trans, root);
    if (ret) {
        mutex_unlock(&root->fs_info->tree_log_mutex);
        mutex_unlock(&root->fs_info->reloc_mutex);
        goto cleanup_transaction;
    }

    btrfs_prepare_extent_commit(trans, root);

    cur_trans = root->fs_info->running_transaction;

    btrfs_set_root_node(&root->fs_info->tree_root->root_item,
                root->fs_info->tree_root->node);
    switch_commit_root(root->fs_info->tree_root);

    btrfs_set_root_node(&root->fs_info->chunk_root->root_item,
                root->fs_info->chunk_root->node);
    switch_commit_root(root->fs_info->chunk_root);

    assert_qgroups_uptodate(trans);
    update_super_roots(root);

    if (!root->fs_info->log_root_recovering) {
        btrfs_set_super_log_root(root->fs_info->super_copy, 0);
        btrfs_set_super_log_root_level(root->fs_info->super_copy, 0);
    }

    memcpy(root->fs_info->super_for_commit, root->fs_info->super_copy,
           sizeof(*root->fs_info->super_copy));

    trans->transaction->blocked = 0;
    spin_lock(&root->fs_info->trans_lock);
    root->fs_info->running_transaction = NULL;
    root->fs_info->trans_no_join = 0;
    spin_unlock(&root->fs_info->trans_lock);
    mutex_unlock(&root->fs_info->reloc_mutex);

    wake_up(&root->fs_info->transaction_wait);

    ret = btrfs_write_and_wait_transaction(trans, root);
    if (ret) {
        btrfs_error(root->fs_info, ret,
                "Error while writing out transaction.");
        mutex_unlock(&root->fs_info->tree_log_mutex);
        goto cleanup_transaction;
    }

    ret = write_ctree_super(trans, root, 0);
    if (ret) {
        mutex_unlock(&root->fs_info->tree_log_mutex);
        goto cleanup_transaction;
    }

    /*
     * the super is written, we can safely allow the tree-loggers
     * to go about their business
     */
    mutex_unlock(&root->fs_info->tree_log_mutex);

    btrfs_finish_extent_commit(trans, root);

    cur_trans->commit_done = 1;

    root->fs_info->last_trans_committed = cur_trans->transid;

    wake_up(&cur_trans->commit_wait);

    spin_lock(&root->fs_info->trans_lock);
    list_del_init(&cur_trans->list);
    spin_unlock(&root->fs_info->trans_lock);

    put_transaction(cur_trans);
    put_transaction(cur_trans);

    if (trans->type < TRANS_JOIN_NOLOCK)
        sb_end_intwrite(root->fs_info->sb);

    trace_btrfs_transaction_commit(root);

    btrfs_scrub_continue(root);

    if (current->journal_info == trans)
        current->journal_info = NULL;

    kmem_cache_free(btrfs_trans_handle_cachep, trans);

    if (current != root->fs_info->transaction_kthread)
        btrfs_run_delayed_iputs(root);

    return ret;

cleanup_transaction:
    btrfs_trans_release_metadata(trans, root);
    trans->block_rsv = NULL;
    btrfs_printk(root->fs_info, "Skipping commit of aborted transaction.\n");
//  WARN_ON(1);
    if (current->journal_info == trans)
        current->journal_info = NULL;
    cleanup_transaction(trans, root, ret);

    return ret;
}

/*
 * interface function to delete all the snapshots we have scheduled for deletion
 */
int btrfs_clean_old_snapshots(struct btrfs_root *root)
{
    LIST_HEAD(list);
    struct btrfs_fs_info *fs_info = root->fs_info;

    spin_lock(&fs_info->trans_lock);
    list_splice_init(&fs_info->dead_roots, &list);
    spin_unlock(&fs_info->trans_lock);

    while (!list_empty(&list)) {
        int ret;

        root = list_entry(list.next, struct btrfs_root, root_list);
        list_del(&root->root_list);

        btrfs_kill_all_delayed_nodes(root);

        if (btrfs_header_backref_rev(root->node) <
            BTRFS_MIXED_BACKREF_REV)
            ret = btrfs_drop_snapshot(root, NULL, 0, 0);
        else
            ret =btrfs_drop_snapshot(root, NULL, 1, 0);
        BUG_ON(ret < 0);
    }
    return 0;
}