Merge branch 'work.namespace' into for-linus

[mirror_ubuntu-artful-kernel.git] / fs / btrfs / ordered-data.c

/*
 * 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/slab.h>
#include <linux/blkdev.h>
#include <linux/writeback.h>
#include <linux/pagevec.h>
#include "ctree.h"
#include "transaction.h"
#include "btrfs_inode.h"
#include "extent_io.h"
#include "disk-io.h"
#include "compression.h"

static struct kmem_cache *btrfs_ordered_extent_cache;

static u64 entry_end(struct btrfs_ordered_extent *entry)
{
        if (entry->file_offset + entry->len < entry->file_offset)
                return (u64)-1;
        return entry->file_offset + entry->len;
}

/* returns NULL if the insertion worked, or it returns the node it did find
 * in the tree
 */
static struct rb_node *tree_insert(struct rb_root *root, u64 file_offset,
                                   struct rb_node *node)
{
        struct rb_node **p = &root->rb_node;
        struct rb_node *parent = NULL;
        struct btrfs_ordered_extent *entry;

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

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

        rb_link_node(node, parent, p);
        rb_insert_color(node, root);
        return NULL;
}

static void ordered_data_tree_panic(struct inode *inode, int errno,
                                               u64 offset)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        btrfs_panic(fs_info, errno,
                    "Inconsistency in ordered tree at offset %llu", offset);
}

/*
 * look for a given offset in the tree, and if it can't be found return the
 * first lesser offset
 */
static struct rb_node *__tree_search(struct rb_root *root, u64 file_offset,
                                     struct rb_node **prev_ret)
{
        struct rb_node *n = root->rb_node;
        struct rb_node *prev = NULL;
        struct rb_node *test;
        struct btrfs_ordered_extent *entry;
        struct btrfs_ordered_extent *prev_entry = NULL;

        while (n) {
                entry = rb_entry(n, struct btrfs_ordered_extent, rb_node);
                prev = n;
                prev_entry = entry;

                if (file_offset < entry->file_offset)
                        n = n->rb_left;
                else if (file_offset >= entry_end(entry))
                        n = n->rb_right;
                else
                        return n;
        }
        if (!prev_ret)
                return NULL;

        while (prev && file_offset >= entry_end(prev_entry)) {
                test = rb_next(prev);
                if (!test)
                        break;
                prev_entry = rb_entry(test, struct btrfs_ordered_extent,
                                      rb_node);
                if (file_offset < entry_end(prev_entry))
                        break;

                prev = test;
        }
        if (prev)
                prev_entry = rb_entry(prev, struct btrfs_ordered_extent,
                                      rb_node);
        while (prev && file_offset < entry_end(prev_entry)) {
                test = rb_prev(prev);
                if (!test)
                        break;
                prev_entry = rb_entry(test, struct btrfs_ordered_extent,
                                      rb_node);
                prev = test;
        }
        *prev_ret = prev;
        return NULL;
}

/*
 * helper to check if a given offset is inside a given entry
 */
static int offset_in_entry(struct btrfs_ordered_extent *entry, u64 file_offset)
{
        if (file_offset < entry->file_offset ||
            entry->file_offset + entry->len <= file_offset)
                return 0;
        return 1;
}

static int range_overlaps(struct btrfs_ordered_extent *entry, u64 file_offset,
                          u64 len)
{
        if (file_offset + len <= entry->file_offset ||
            entry->file_offset + entry->len <= file_offset)
                return 0;
        return 1;
}

/*
 * look find the first ordered struct that has this offset, otherwise
 * the first one less than this offset
 */
static inline struct rb_node *tree_search(struct btrfs_ordered_inode_tree *tree,
                                          u64 file_offset)
{
        struct rb_root *root = &tree->tree;
        struct rb_node *prev = NULL;
        struct rb_node *ret;
        struct btrfs_ordered_extent *entry;

        if (tree->last) {
                entry = rb_entry(tree->last, struct btrfs_ordered_extent,
                                 rb_node);
                if (offset_in_entry(entry, file_offset))
                        return tree->last;
        }
        ret = __tree_search(root, file_offset, &prev);
        if (!ret)
                ret = prev;
        if (ret)
                tree->last = ret;
        return ret;
}

/* allocate and add a new ordered_extent into the per-inode tree.
 * file_offset is the logical offset in the file
 *
 * start is the disk block number of an extent already reserved in the
 * extent allocation tree
 *
 * len is the length of the extent
 *
 * The tree is given a single reference on the ordered extent that was
 * inserted.
 */
static int __btrfs_add_ordered_extent(struct inode *inode, u64 file_offset,
                                      u64 start, u64 len, u64 disk_len,
                                      int type, int dio, int compress_type)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct btrfs_ordered_inode_tree *tree;
        struct rb_node *node;
        struct btrfs_ordered_extent *entry;

        tree = &BTRFS_I(inode)->ordered_tree;
        entry = kmem_cache_zalloc(btrfs_ordered_extent_cache, GFP_NOFS);
        if (!entry)
                return -ENOMEM;

        entry->file_offset = file_offset;
        entry->start = start;
        entry->len = len;
        entry->disk_len = disk_len;
        entry->bytes_left = len;
        entry->inode = igrab(inode);
        entry->compress_type = compress_type;
        entry->truncated_len = (u64)-1;
        if (type != BTRFS_ORDERED_IO_DONE && type != BTRFS_ORDERED_COMPLETE)
                set_bit(type, &entry->flags);

        if (dio)
                set_bit(BTRFS_ORDERED_DIRECT, &entry->flags);

        /* one ref for the tree */
        atomic_set(&entry->refs, 1);
        init_waitqueue_head(&entry->wait);
        INIT_LIST_HEAD(&entry->list);
        INIT_LIST_HEAD(&entry->root_extent_list);
        INIT_LIST_HEAD(&entry->work_list);
        init_completion(&entry->completion);
        INIT_LIST_HEAD(&entry->log_list);
        INIT_LIST_HEAD(&entry->trans_list);

        trace_btrfs_ordered_extent_add(inode, entry);

        spin_lock_irq(&tree->lock);
        node = tree_insert(&tree->tree, file_offset,
                           &entry->rb_node);
        if (node)
                ordered_data_tree_panic(inode, -EEXIST, file_offset);
        spin_unlock_irq(&tree->lock);

        spin_lock(&root->ordered_extent_lock);
        list_add_tail(&entry->root_extent_list,
                      &root->ordered_extents);
        root->nr_ordered_extents++;
        if (root->nr_ordered_extents == 1) {
                spin_lock(&fs_info->ordered_root_lock);
                BUG_ON(!list_empty(&root->ordered_root));
                list_add_tail(&root->ordered_root, &fs_info->ordered_roots);
                spin_unlock(&fs_info->ordered_root_lock);
        }
        spin_unlock(&root->ordered_extent_lock);

        return 0;
}

int btrfs_add_ordered_extent(struct inode *inode, u64 file_offset,
                             u64 start, u64 len, u64 disk_len, int type)
{
        return __btrfs_add_ordered_extent(inode, file_offset, start, len,
                                          disk_len, type, 0,
                                          BTRFS_COMPRESS_NONE);
}

int btrfs_add_ordered_extent_dio(struct inode *inode, u64 file_offset,
                                 u64 start, u64 len, u64 disk_len, int type)
{
        return __btrfs_add_ordered_extent(inode, file_offset, start, len,
                                          disk_len, type, 1,
                                          BTRFS_COMPRESS_NONE);
}

int btrfs_add_ordered_extent_compress(struct inode *inode, u64 file_offset,
                                      u64 start, u64 len, u64 disk_len,
                                      int type, int compress_type)
{
        return __btrfs_add_ordered_extent(inode, file_offset, start, len,
                                          disk_len, type, 0,
                                          compress_type);
}

/*
 * Add a struct btrfs_ordered_sum into the list of checksums to be inserted
 * when an ordered extent is finished.  If the list covers more than one
 * ordered extent, it is split across multiples.
 */
void btrfs_add_ordered_sum(struct inode *inode,
                           struct btrfs_ordered_extent *entry,
                           struct btrfs_ordered_sum *sum)
{
        struct btrfs_ordered_inode_tree *tree;

        tree = &BTRFS_I(inode)->ordered_tree;
        spin_lock_irq(&tree->lock);
        list_add_tail(&sum->list, &entry->list);
        spin_unlock_irq(&tree->lock);
}

/*
 * this is used to account for finished IO across a given range
 * of the file.  The IO may span ordered extents.  If
 * a given ordered_extent is completely done, 1 is returned, otherwise
 * 0.
 *
 * test_and_set_bit on a flag in the struct btrfs_ordered_extent is used
 * to make sure this function only returns 1 once for a given ordered extent.
 *
 * file_offset is updated to one byte past the range that is recorded as
 * complete.  This allows you to walk forward in the file.
 */
int btrfs_dec_test_first_ordered_pending(struct inode *inode,
                                   struct btrfs_ordered_extent **cached,
                                   u64 *file_offset, u64 io_size, int uptodate)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct btrfs_ordered_inode_tree *tree;
        struct rb_node *node;
        struct btrfs_ordered_extent *entry = NULL;
        int ret;
        unsigned long flags;
        u64 dec_end;
        u64 dec_start;
        u64 to_dec;

        tree = &BTRFS_I(inode)->ordered_tree;
        spin_lock_irqsave(&tree->lock, flags);
        node = tree_search(tree, *file_offset);
        if (!node) {
                ret = 1;
                goto out;
        }

        entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
        if (!offset_in_entry(entry, *file_offset)) {
                ret = 1;
                goto out;
        }

        dec_start = max(*file_offset, entry->file_offset);
        dec_end = min(*file_offset + io_size, entry->file_offset +
                      entry->len);
        *file_offset = dec_end;
        if (dec_start > dec_end) {
                btrfs_crit(fs_info, "bad ordering dec_start %llu end %llu",
                           dec_start, dec_end);
        }
        to_dec = dec_end - dec_start;
        if (to_dec > entry->bytes_left) {
                btrfs_crit(fs_info,
                           "bad ordered accounting left %llu size %llu",
                           entry->bytes_left, to_dec);
        }
        entry->bytes_left -= to_dec;
        if (!uptodate)
                set_bit(BTRFS_ORDERED_IOERR, &entry->flags);

        if (entry->bytes_left == 0) {
                ret = test_and_set_bit(BTRFS_ORDERED_IO_DONE, &entry->flags);
                /*
                 * Implicit memory barrier after test_and_set_bit
                 */
                if (waitqueue_active(&entry->wait))
                        wake_up(&entry->wait);
        } else {
                ret = 1;
        }
out:
        if (!ret && cached && entry) {
                *cached = entry;
                atomic_inc(&entry->refs);
        }
        spin_unlock_irqrestore(&tree->lock, flags);
        return ret == 0;
}

/*
 * this is used to account for finished IO across a given range
 * of the file.  The IO should not span ordered extents.  If
 * a given ordered_extent is completely done, 1 is returned, otherwise
 * 0.
 *
 * test_and_set_bit on a flag in the struct btrfs_ordered_extent is used
 * to make sure this function only returns 1 once for a given ordered extent.
 */
int btrfs_dec_test_ordered_pending(struct inode *inode,
                                   struct btrfs_ordered_extent **cached,
                                   u64 file_offset, u64 io_size, int uptodate)
{
        struct btrfs_ordered_inode_tree *tree;
        struct rb_node *node;
        struct btrfs_ordered_extent *entry = NULL;
        unsigned long flags;
        int ret;

        tree = &BTRFS_I(inode)->ordered_tree;
        spin_lock_irqsave(&tree->lock, flags);
        if (cached && *cached) {
                entry = *cached;
                goto have_entry;
        }

        node = tree_search(tree, file_offset);
        if (!node) {
                ret = 1;
                goto out;
        }

        entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
have_entry:
        if (!offset_in_entry(entry, file_offset)) {
                ret = 1;
                goto out;
        }

        if (io_size > entry->bytes_left) {
                btrfs_crit(BTRFS_I(inode)->root->fs_info,
                           "bad ordered accounting left %llu size %llu",
                       entry->bytes_left, io_size);
        }
        entry->bytes_left -= io_size;
        if (!uptodate)
                set_bit(BTRFS_ORDERED_IOERR, &entry->flags);

        if (entry->bytes_left == 0) {
                ret = test_and_set_bit(BTRFS_ORDERED_IO_DONE, &entry->flags);
                /*
                 * Implicit memory barrier after test_and_set_bit
                 */
                if (waitqueue_active(&entry->wait))
                        wake_up(&entry->wait);
        } else {
                ret = 1;
        }
out:
        if (!ret && cached && entry) {
                *cached = entry;
                atomic_inc(&entry->refs);
        }
        spin_unlock_irqrestore(&tree->lock, flags);
        return ret == 0;
}

/* Needs to either be called under a log transaction or the log_mutex */
void btrfs_get_logged_extents(struct inode *inode,
                              struct list_head *logged_list,
                              const loff_t start,
                              const loff_t end)
{
        struct btrfs_ordered_inode_tree *tree;
        struct btrfs_ordered_extent *ordered;
        struct rb_node *n;
        struct rb_node *prev;

        tree = &BTRFS_I(inode)->ordered_tree;
        spin_lock_irq(&tree->lock);
        n = __tree_search(&tree->tree, end, &prev);
        if (!n)
                n = prev;
        for (; n; n = rb_prev(n)) {
                ordered = rb_entry(n, struct btrfs_ordered_extent, rb_node);
                if (ordered->file_offset > end)
                        continue;
                if (entry_end(ordered) <= start)
                        break;
                if (test_and_set_bit(BTRFS_ORDERED_LOGGED, &ordered->flags))
                        continue;
                list_add(&ordered->log_list, logged_list);
                atomic_inc(&ordered->refs);
        }
        spin_unlock_irq(&tree->lock);
}

void btrfs_put_logged_extents(struct list_head *logged_list)
{
        struct btrfs_ordered_extent *ordered;

        while (!list_empty(logged_list)) {
                ordered = list_first_entry(logged_list,
                                           struct btrfs_ordered_extent,
                                           log_list);
                list_del_init(&ordered->log_list);
                btrfs_put_ordered_extent(ordered);
        }
}

void btrfs_submit_logged_extents(struct list_head *logged_list,
                                 struct btrfs_root *log)
{
        int index = log->log_transid % 2;

        spin_lock_irq(&log->log_extents_lock[index]);
        list_splice_tail(logged_list, &log->logged_list[index]);
        spin_unlock_irq(&log->log_extents_lock[index]);
}

void btrfs_wait_logged_extents(struct btrfs_trans_handle *trans,
                               struct btrfs_root *log, u64 transid)
{
        struct btrfs_ordered_extent *ordered;
        int index = transid % 2;

        spin_lock_irq(&log->log_extents_lock[index]);
        while (!list_empty(&log->logged_list[index])) {
                struct inode *inode;
                ordered = list_first_entry(&log->logged_list[index],
                                           struct btrfs_ordered_extent,
                                           log_list);
                list_del_init(&ordered->log_list);
                inode = ordered->inode;
                spin_unlock_irq(&log->log_extents_lock[index]);

                if (!test_bit(BTRFS_ORDERED_IO_DONE, &ordered->flags) &&
                    !test_bit(BTRFS_ORDERED_DIRECT, &ordered->flags)) {
                        u64 start = ordered->file_offset;
                        u64 end = ordered->file_offset + ordered->len - 1;

                        WARN_ON(!inode);
                        filemap_fdatawrite_range(inode->i_mapping, start, end);
                }
                wait_event(ordered->wait, test_bit(BTRFS_ORDERED_IO_DONE,
                                                   &ordered->flags));

                /*
                 * In order to keep us from losing our ordered extent
                 * information when committing the transaction we have to make
                 * sure that any logged extents are completed when we go to
                 * commit the transaction.  To do this we simply increase the
                 * current transactions pending_ordered counter and decrement it
                 * when the ordered extent completes.
                 */
                if (!test_bit(BTRFS_ORDERED_COMPLETE, &ordered->flags)) {
                        struct btrfs_ordered_inode_tree *tree;

                        tree = &BTRFS_I(inode)->ordered_tree;
                        spin_lock_irq(&tree->lock);
                        if (!test_bit(BTRFS_ORDERED_COMPLETE, &ordered->flags)) {
                                set_bit(BTRFS_ORDERED_PENDING, &ordered->flags);
                                atomic_inc(&trans->transaction->pending_ordered);
                        }
                        spin_unlock_irq(&tree->lock);
                }
                btrfs_put_ordered_extent(ordered);
                spin_lock_irq(&log->log_extents_lock[index]);
        }
        spin_unlock_irq(&log->log_extents_lock[index]);
}

void btrfs_free_logged_extents(struct btrfs_root *log, u64 transid)
{
        struct btrfs_ordered_extent *ordered;
        int index = transid % 2;

        spin_lock_irq(&log->log_extents_lock[index]);
        while (!list_empty(&log->logged_list[index])) {
                ordered = list_first_entry(&log->logged_list[index],
                                           struct btrfs_ordered_extent,
                                           log_list);
                list_del_init(&ordered->log_list);
                spin_unlock_irq(&log->log_extents_lock[index]);
                btrfs_put_ordered_extent(ordered);
                spin_lock_irq(&log->log_extents_lock[index]);
        }
        spin_unlock_irq(&log->log_extents_lock[index]);
}

/*
 * used to drop a reference on an ordered extent.  This will free
 * the extent if the last reference is dropped
 */
void btrfs_put_ordered_extent(struct btrfs_ordered_extent *entry)
{
        struct list_head *cur;
        struct btrfs_ordered_sum *sum;

        trace_btrfs_ordered_extent_put(entry->inode, entry);

        if (atomic_dec_and_test(&entry->refs)) {
                ASSERT(list_empty(&entry->log_list));
                ASSERT(list_empty(&entry->trans_list));
                ASSERT(list_empty(&entry->root_extent_list));
                ASSERT(RB_EMPTY_NODE(&entry->rb_node));
                if (entry->inode)
                        btrfs_add_delayed_iput(entry->inode);
                while (!list_empty(&entry->list)) {
                        cur = entry->list.next;
                        sum = list_entry(cur, struct btrfs_ordered_sum, list);
                        list_del(&sum->list);
                        kfree(sum);
                }
                kmem_cache_free(btrfs_ordered_extent_cache, entry);
        }
}

/*
 * remove an ordered extent from the tree.  No references are dropped
 * and waiters are woken up.
 */
void btrfs_remove_ordered_extent(struct inode *inode,
                                 struct btrfs_ordered_extent *entry)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct btrfs_ordered_inode_tree *tree;
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct rb_node *node;
        bool dec_pending_ordered = false;

        tree = &BTRFS_I(inode)->ordered_tree;
        spin_lock_irq(&tree->lock);
        node = &entry->rb_node;
        rb_erase(node, &tree->tree);
        RB_CLEAR_NODE(node);
        if (tree->last == node)
                tree->last = NULL;
        set_bit(BTRFS_ORDERED_COMPLETE, &entry->flags);
        if (test_and_clear_bit(BTRFS_ORDERED_PENDING, &entry->flags))
                dec_pending_ordered = true;
        spin_unlock_irq(&tree->lock);

        /*
         * The current running transaction is waiting on us, we need to let it
         * know that we're complete and wake it up.
         */
        if (dec_pending_ordered) {
                struct btrfs_transaction *trans;

                /*
                 * The checks for trans are just a formality, it should be set,
                 * but if it isn't we don't want to deref/assert under the spin
                 * lock, so be nice and check if trans is set, but ASSERT() so
                 * if it isn't set a developer will notice.
                 */
                spin_lock(&fs_info->trans_lock);
                trans = fs_info->running_transaction;
                if (trans)
                        atomic_inc(&trans->use_count);
                spin_unlock(&fs_info->trans_lock);

                ASSERT(trans);
                if (trans) {
                        if (atomic_dec_and_test(&trans->pending_ordered))
                                wake_up(&trans->pending_wait);
                        btrfs_put_transaction(trans);
                }
        }

        spin_lock(&root->ordered_extent_lock);
        list_del_init(&entry->root_extent_list);
        root->nr_ordered_extents--;

        trace_btrfs_ordered_extent_remove(inode, entry);

        if (!root->nr_ordered_extents) {
                spin_lock(&fs_info->ordered_root_lock);
                BUG_ON(list_empty(&root->ordered_root));
                list_del_init(&root->ordered_root);
                spin_unlock(&fs_info->ordered_root_lock);
        }
        spin_unlock(&root->ordered_extent_lock);
        wake_up(&entry->wait);
}

static void btrfs_run_ordered_extent_work(struct btrfs_work *work)
{
        struct btrfs_ordered_extent *ordered;

        ordered = container_of(work, struct btrfs_ordered_extent, flush_work);
        btrfs_start_ordered_extent(ordered->inode, ordered, 1);
        complete(&ordered->completion);
}

/*
 * wait for all the ordered extents in a root.  This is done when balancing
 * space between drives.
 */
int btrfs_wait_ordered_extents(struct btrfs_root *root, int nr,
                               const u64 range_start, const u64 range_len)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        LIST_HEAD(splice);
        LIST_HEAD(skipped);
        LIST_HEAD(works);
        struct btrfs_ordered_extent *ordered, *next;
        int count = 0;
        const u64 range_end = range_start + range_len;

        mutex_lock(&root->ordered_extent_mutex);
        spin_lock(&root->ordered_extent_lock);
        list_splice_init(&root->ordered_extents, &splice);
        while (!list_empty(&splice) && nr) {
                ordered = list_first_entry(&splice, struct btrfs_ordered_extent,
                                           root_extent_list);

                if (range_end <= ordered->start ||
                    ordered->start + ordered->disk_len <= range_start) {
                        list_move_tail(&ordered->root_extent_list, &skipped);
                        cond_resched_lock(&root->ordered_extent_lock);
                        continue;
                }

                list_move_tail(&ordered->root_extent_list,
                               &root->ordered_extents);
                atomic_inc(&ordered->refs);
                spin_unlock(&root->ordered_extent_lock);

                btrfs_init_work(&ordered->flush_work,
                                btrfs_flush_delalloc_helper,
                                btrfs_run_ordered_extent_work, NULL, NULL);
                list_add_tail(&ordered->work_list, &works);
                btrfs_queue_work(fs_info->flush_workers, &ordered->flush_work);

                cond_resched();
                spin_lock(&root->ordered_extent_lock);
                if (nr != -1)
                        nr--;
                count++;
        }
        list_splice_tail(&skipped, &root->ordered_extents);
        list_splice_tail(&splice, &root->ordered_extents);
        spin_unlock(&root->ordered_extent_lock);

        list_for_each_entry_safe(ordered, next, &works, work_list) {
                list_del_init(&ordered->work_list);
                wait_for_completion(&ordered->completion);
                btrfs_put_ordered_extent(ordered);
                cond_resched();
        }
        mutex_unlock(&root->ordered_extent_mutex);

        return count;
}

int btrfs_wait_ordered_roots(struct btrfs_fs_info *fs_info, int nr,
                              const u64 range_start, const u64 range_len)
{
        struct btrfs_root *root;
        struct list_head splice;
        int done;
        int total_done = 0;

        INIT_LIST_HEAD(&splice);

        mutex_lock(&fs_info->ordered_operations_mutex);
        spin_lock(&fs_info->ordered_root_lock);
        list_splice_init(&fs_info->ordered_roots, &splice);
        while (!list_empty(&splice) && nr) {
                root = list_first_entry(&splice, struct btrfs_root,
                                        ordered_root);
                root = btrfs_grab_fs_root(root);
                BUG_ON(!root);
                list_move_tail(&root->ordered_root,
                               &fs_info->ordered_roots);
                spin_unlock(&fs_info->ordered_root_lock);

                done = btrfs_wait_ordered_extents(root, nr,
                                                  range_start, range_len);
                btrfs_put_fs_root(root);
                total_done += done;

                spin_lock(&fs_info->ordered_root_lock);
                if (nr != -1) {
                        nr -= done;
                        WARN_ON(nr < 0);
                }
        }
        list_splice_tail(&splice, &fs_info->ordered_roots);
        spin_unlock(&fs_info->ordered_root_lock);
        mutex_unlock(&fs_info->ordered_operations_mutex);

        return total_done;
}

/*
 * Used to start IO or wait for a given ordered extent to finish.
 *
 * If wait is one, this effectively waits on page writeback for all the pages
 * in the extent, and it waits on the io completion code to insert
 * metadata into the btree corresponding to the extent
 */
void btrfs_start_ordered_extent(struct inode *inode,
                                       struct btrfs_ordered_extent *entry,
                                       int wait)
{
        u64 start = entry->file_offset;
        u64 end = start + entry->len - 1;

        trace_btrfs_ordered_extent_start(inode, entry);

        /*
         * pages in the range can be dirty, clean or writeback.  We
         * start IO on any dirty ones so the wait doesn't stall waiting
         * for the flusher thread to find them
         */
        if (!test_bit(BTRFS_ORDERED_DIRECT, &entry->flags))
                filemap_fdatawrite_range(inode->i_mapping, start, end);
        if (wait) {
                wait_event(entry->wait, test_bit(BTRFS_ORDERED_COMPLETE,
                                                 &entry->flags));
        }
}

/*
 * Used to wait on ordered extents across a large range of bytes.
 */
int btrfs_wait_ordered_range(struct inode *inode, u64 start, u64 len)
{
        int ret = 0;
        int ret_wb = 0;
        u64 end;
        u64 orig_end;
        struct btrfs_ordered_extent *ordered;

        if (start + len < start) {
                orig_end = INT_LIMIT(loff_t);
        } else {
                orig_end = start + len - 1;
                if (orig_end > INT_LIMIT(loff_t))
                        orig_end = INT_LIMIT(loff_t);
        }

        /* start IO across the range first to instantiate any delalloc
         * extents
         */
        ret = btrfs_fdatawrite_range(inode, start, orig_end);
        if (ret)
                return ret;

        /*
         * If we have a writeback error don't return immediately. Wait first
         * for any ordered extents that haven't completed yet. This is to make
         * sure no one can dirty the same page ranges and call writepages()
         * before the ordered extents complete - to avoid failures (-EEXIST)
         * when adding the new ordered extents to the ordered tree.
         */
        ret_wb = filemap_fdatawait_range(inode->i_mapping, start, orig_end);

        end = orig_end;
        while (1) {
                ordered = btrfs_lookup_first_ordered_extent(inode, end);
                if (!ordered)
                        break;
                if (ordered->file_offset > orig_end) {
                        btrfs_put_ordered_extent(ordered);
                        break;
                }
                if (ordered->file_offset + ordered->len <= start) {
                        btrfs_put_ordered_extent(ordered);
                        break;
                }
                btrfs_start_ordered_extent(inode, ordered, 1);
                end = ordered->file_offset;
                if (test_bit(BTRFS_ORDERED_IOERR, &ordered->flags))
                        ret = -EIO;
                btrfs_put_ordered_extent(ordered);
                if (ret || end == 0 || end == start)
                        break;
                end--;
        }
        return ret_wb ? ret_wb : ret;
}

/*
 * find an ordered extent corresponding to file_offset.  return NULL if
 * nothing is found, otherwise take a reference on the extent and return it
 */
struct btrfs_ordered_extent *btrfs_lookup_ordered_extent(struct inode *inode,
                                                         u64 file_offset)
{
        struct btrfs_ordered_inode_tree *tree;
        struct rb_node *node;
        struct btrfs_ordered_extent *entry = NULL;

        tree = &BTRFS_I(inode)->ordered_tree;
        spin_lock_irq(&tree->lock);
        node = tree_search(tree, file_offset);
        if (!node)
                goto out;

        entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
        if (!offset_in_entry(entry, file_offset))
                entry = NULL;
        if (entry)
                atomic_inc(&entry->refs);
out:
        spin_unlock_irq(&tree->lock);
        return entry;
}

/* Since the DIO code tries to lock a wide area we need to look for any ordered
 * extents that exist in the range, rather than just the start of the range.
 */
struct btrfs_ordered_extent *btrfs_lookup_ordered_range(struct inode *inode,
                                                        u64 file_offset,
                                                        u64 len)
{
        struct btrfs_ordered_inode_tree *tree;
        struct rb_node *node;
        struct btrfs_ordered_extent *entry = NULL;

        tree = &BTRFS_I(inode)->ordered_tree;
        spin_lock_irq(&tree->lock);
        node = tree_search(tree, file_offset);
        if (!node) {
                node = tree_search(tree, file_offset + len);
                if (!node)
                        goto out;
        }

        while (1) {
                entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
                if (range_overlaps(entry, file_offset, len))
                        break;

                if (entry->file_offset >= file_offset + len) {
                        entry = NULL;
                        break;
                }
                entry = NULL;
                node = rb_next(node);
                if (!node)
                        break;
        }
out:
        if (entry)
                atomic_inc(&entry->refs);
        spin_unlock_irq(&tree->lock);
        return entry;
}

bool btrfs_have_ordered_extents_in_range(struct inode *inode,
                                         u64 file_offset,
                                         u64 len)
{
        struct btrfs_ordered_extent *oe;

        oe = btrfs_lookup_ordered_range(inode, file_offset, len);
        if (oe) {
                btrfs_put_ordered_extent(oe);
                return true;
        }
        return false;
}

/*
 * lookup and return any extent before 'file_offset'.  NULL is returned
 * if none is found
 */
struct btrfs_ordered_extent *
btrfs_lookup_first_ordered_extent(struct inode *inode, u64 file_offset)
{
        struct btrfs_ordered_inode_tree *tree;
        struct rb_node *node;
        struct btrfs_ordered_extent *entry = NULL;

        tree = &BTRFS_I(inode)->ordered_tree;
        spin_lock_irq(&tree->lock);
        node = tree_search(tree, file_offset);
        if (!node)
                goto out;

        entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
        atomic_inc(&entry->refs);
out:
        spin_unlock_irq(&tree->lock);
        return entry;
}

/*
 * After an extent is done, call this to conditionally update the on disk
 * i_size.  i_size is updated to cover any fully written part of the file.
 */
int btrfs_ordered_update_i_size(struct inode *inode, u64 offset,
                                struct btrfs_ordered_extent *ordered)
{
        struct btrfs_ordered_inode_tree *tree = &BTRFS_I(inode)->ordered_tree;
        u64 disk_i_size;
        u64 new_i_size;
        u64 i_size = i_size_read(inode);
        struct rb_node *node;
        struct rb_node *prev = NULL;
        struct btrfs_ordered_extent *test;
        int ret = 1;
        u64 orig_offset = offset;

        spin_lock_irq(&tree->lock);
        if (ordered) {
                offset = entry_end(ordered);
                if (test_bit(BTRFS_ORDERED_TRUNCATED, &ordered->flags))
                        offset = min(offset,
                                     ordered->file_offset +
                                     ordered->truncated_len);
        } else {
                offset = ALIGN(offset, btrfs_inode_sectorsize(inode));
        }
        disk_i_size = BTRFS_I(inode)->disk_i_size;

        /* truncate file */
        if (disk_i_size > i_size) {
                BTRFS_I(inode)->disk_i_size = orig_offset;
                ret = 0;
                goto out;
        }

        /*
         * if the disk i_size is already at the inode->i_size, or
         * this ordered extent is inside the disk i_size, we're done
         */
        if (disk_i_size == i_size)
                goto out;

        /*
         * We still need to update disk_i_size if outstanding_isize is greater
         * than disk_i_size.
         */
        if (offset <= disk_i_size &&
            (!ordered || ordered->outstanding_isize <= disk_i_size))
                goto out;

        /*
         * walk backward from this ordered extent to disk_i_size.
         * if we find an ordered extent then we can't update disk i_size
         * yet
         */
        if (ordered) {
                node = rb_prev(&ordered->rb_node);
        } else {
                prev = tree_search(tree, offset);
                /*
                 * we insert file extents without involving ordered struct,
                 * so there should be no ordered struct cover this offset
                 */
                if (prev) {
                        test = rb_entry(prev, struct btrfs_ordered_extent,
                                        rb_node);
                        BUG_ON(offset_in_entry(test, offset));
                }
                node = prev;
        }
        for (; node; node = rb_prev(node)) {
                test = rb_entry(node, struct btrfs_ordered_extent, rb_node);

                /* We treat this entry as if it doesn't exist */
                if (test_bit(BTRFS_ORDERED_UPDATED_ISIZE, &test->flags))
                        continue;
                if (test->file_offset + test->len <= disk_i_size)
                        break;
                if (test->file_offset >= i_size)
                        break;
                if (entry_end(test) > disk_i_size) {
                        /*
                         * we don't update disk_i_size now, so record this
                         * undealt i_size. Or we will not know the real
                         * i_size.
                         */
                        if (test->outstanding_isize < offset)
                                test->outstanding_isize = offset;
                        if (ordered &&
                            ordered->outstanding_isize >
                            test->outstanding_isize)
                                test->outstanding_isize =
                                                ordered->outstanding_isize;
                        goto out;
                }
        }
        new_i_size = min_t(u64, offset, i_size);

        /*
         * Some ordered extents may completed before the current one, and
         * we hold the real i_size in ->outstanding_isize.
         */
        if (ordered && ordered->outstanding_isize > new_i_size)
                new_i_size = min_t(u64, ordered->outstanding_isize, i_size);
        BTRFS_I(inode)->disk_i_size = new_i_size;
        ret = 0;
out:
        /*
         * We need to do this because we can't remove ordered extents until
         * after the i_disk_size has been updated and then the inode has been
         * updated to reflect the change, so we need to tell anybody who finds
         * this ordered extent that we've already done all the real work, we
         * just haven't completed all the other work.
         */
        if (ordered)
                set_bit(BTRFS_ORDERED_UPDATED_ISIZE, &ordered->flags);
        spin_unlock_irq(&tree->lock);
        return ret;
}

/*
 * search the ordered extents for one corresponding to 'offset' and
 * try to find a checksum.  This is used because we allow pages to
 * be reclaimed before their checksum is actually put into the btree
 */
int btrfs_find_ordered_sum(struct inode *inode, u64 offset, u64 disk_bytenr,
                           u32 *sum, int len)
{
        struct btrfs_ordered_sum *ordered_sum;
        struct btrfs_ordered_extent *ordered;
        struct btrfs_ordered_inode_tree *tree = &BTRFS_I(inode)->ordered_tree;
        unsigned long num_sectors;
        unsigned long i;
        u32 sectorsize = btrfs_inode_sectorsize(inode);
        int index = 0;

        ordered = btrfs_lookup_ordered_extent(inode, offset);
        if (!ordered)
                return 0;

        spin_lock_irq(&tree->lock);
        list_for_each_entry_reverse(ordered_sum, &ordered->list, list) {
                if (disk_bytenr >= ordered_sum->bytenr &&
                    disk_bytenr < ordered_sum->bytenr + ordered_sum->len) {
                        i = (disk_bytenr - ordered_sum->bytenr) >>
                            inode->i_sb->s_blocksize_bits;
                        num_sectors = ordered_sum->len >>
                                      inode->i_sb->s_blocksize_bits;
                        num_sectors = min_t(int, len - index, num_sectors - i);
                        memcpy(sum + index, ordered_sum->sums + i,
                               num_sectors);

                        index += (int)num_sectors;
                        if (index == len)
                                goto out;
                        disk_bytenr += num_sectors * sectorsize;
                }
        }
out:
        spin_unlock_irq(&tree->lock);
        btrfs_put_ordered_extent(ordered);
        return index;
}

int __init ordered_data_init(void)
{
        btrfs_ordered_extent_cache = kmem_cache_create("btrfs_ordered_extent",
                                     sizeof(struct btrfs_ordered_extent), 0,
                                     SLAB_MEM_SPREAD,
                                     NULL);
        if (!btrfs_ordered_extent_cache)
                return -ENOMEM;

        return 0;
}

void ordered_data_exit(void)
{
        kmem_cache_destroy(btrfs_ordered_extent_cache);
}