file.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/pagemap.h>
#include <linux/highmem.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/backing-dev.h>
#include <linux/mpage.h>
#include <linux/falloc.h>
#include <linux/swap.h>
#include <linux/writeback.h>
#include <linux/statfs.h>
#include <linux/compat.h>
#include <linux/slab.h>
#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "btrfs_inode.h"
#include "ioctl.h"
#include "print-tree.h"
#include "tree-log.h"
#include "locking.h"
#include "compat.h"
#include "volumes.h"

/*
 * when auto defrag is enabled we
 * queue up these defrag structs to remember which
 * inodes need defragging passes
 */
struct inode_defrag {
    struct rb_node rb_node;
    /* objectid */
    u64 ino;
    /*
     * transid where the defrag was added, we search for
     * extents newer than this
     */
    u64 transid;

    /* root objectid */
    u64 root;

    /* last offset we were able to defrag */
    u64 last_offset;

    /* if we've wrapped around back to zero once already */
    int cycled;
};

static int __compare_inode_defrag(struct inode_defrag *defrag1,
                  struct inode_defrag *defrag2)
{
    if (defrag1->root > defrag2->root)
        return 1;
    else if (defrag1->root < defrag2->root)
        return -1;
    else if (defrag1->ino > defrag2->ino)
        return 1;
    else if (defrag1->ino < defrag2->ino)
        return -1;
    else
        return 0;
}

/* pop a record for an inode into the defrag tree.  The lock
 * must be held already
 *
 * If you're inserting a record for an older transid than an
 * existing record, the transid already in the tree is lowered
 *
 * If an existing record is found the defrag item you
 * pass in is freed
 */
static void __btrfs_add_inode_defrag(struct inode *inode,
                    struct inode_defrag *defrag)
{
    struct btrfs_root *root = BTRFS_I(inode)->root;
    struct inode_defrag *entry;
    struct rb_node **p;
    struct rb_node *parent = NULL;
    int ret;

    p = &root->fs_info->defrag_inodes.rb_node;
    while (*p) {
        parent = *p;
        entry = rb_entry(parent, struct inode_defrag, rb_node);

        ret = __compare_inode_defrag(defrag, entry);
        if (ret < 0)
            p = &parent->rb_left;
        else if (ret > 0)
            p = &parent->rb_right;
        else {
            /* if we're reinserting an entry for
             * an old defrag run, make sure to
             * lower the transid of our existing record
             */
            if (defrag->transid < entry->transid)
                entry->transid = defrag->transid;
            if (defrag->last_offset > entry->last_offset)
                entry->last_offset = defrag->last_offset;
            goto exists;
        }
    }
    set_bit(BTRFS_INODE_IN_DEFRAG, &BTRFS_I(inode)->runtime_flags);
    rb_link_node(&defrag->rb_node, parent, p);
    rb_insert_color(&defrag->rb_node, &root->fs_info->defrag_inodes);
    return;

exists:
    kfree(defrag);
    return;

}

/*
 * insert a defrag record for this inode if auto defrag is
 * enabled
 */
int btrfs_add_inode_defrag(struct btrfs_trans_handle *trans,
               struct inode *inode)
{
    struct btrfs_root *root = BTRFS_I(inode)->root;
    struct inode_defrag *defrag;
    u64 transid;

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

    if (btrfs_fs_closing(root->fs_info))
        return 0;

    if (test_bit(BTRFS_INODE_IN_DEFRAG, &BTRFS_I(inode)->runtime_flags))
        return 0;

    if (trans)
        transid = trans->transid;
    else
        transid = BTRFS_I(inode)->root->last_trans;

    defrag = kzalloc(sizeof(*defrag), GFP_NOFS);
    if (!defrag)
        return -ENOMEM;

    defrag->ino = btrfs_ino(inode);
    defrag->transid = transid;
    defrag->root = root->root_key.objectid;

    spin_lock(&root->fs_info->defrag_inodes_lock);
    if (!test_bit(BTRFS_INODE_IN_DEFRAG, &BTRFS_I(inode)->runtime_flags))
        __btrfs_add_inode_defrag(inode, defrag);
    else
        kfree(defrag);
    spin_unlock(&root->fs_info->defrag_inodes_lock);
    return 0;
}

/*
 * must be called with the defrag_inodes lock held
 */
struct inode_defrag *btrfs_find_defrag_inode(struct btrfs_fs_info *info,
                         u64 root, u64 ino,
                         struct rb_node **next)
{
    struct inode_defrag *entry = NULL;
    struct inode_defrag tmp;
    struct rb_node *p;
    struct rb_node *parent = NULL;
    int ret;

    tmp.ino = ino;
    tmp.root = root;

    p = info->defrag_inodes.rb_node;
    while (p) {
        parent = p;
        entry = rb_entry(parent, struct inode_defrag, rb_node);

        ret = __compare_inode_defrag(&tmp, entry);
        if (ret < 0)
            p = parent->rb_left;
        else if (ret > 0)
            p = parent->rb_right;
        else
            return entry;
    }

    if (next) {
        while (parent && __compare_inode_defrag(&tmp, entry) > 0) {
            parent = rb_next(parent);
            entry = rb_entry(parent, struct inode_defrag, rb_node);
        }
        *next = parent;
    }
    return NULL;
}

/*
 * run through the list of inodes in the FS that need
 * defragging
 */
int btrfs_run_defrag_inodes(struct btrfs_fs_info *fs_info)
{
    struct inode_defrag *defrag;
    struct btrfs_root *inode_root;
    struct inode *inode;
    struct rb_node *n;
    struct btrfs_key key;
    struct btrfs_ioctl_defrag_range_args range;
    u64 first_ino = 0;
    u64 root_objectid = 0;
    int num_defrag;
    int defrag_batch = 1024;

    memset(&range, 0, sizeof(range));
    range.len = (u64)-1;

    atomic_inc(&fs_info->defrag_running);
    spin_lock(&fs_info->defrag_inodes_lock);
    while(1) {
        n = NULL;

        /* find an inode to defrag */
        defrag = btrfs_find_defrag_inode(fs_info, root_objectid,
                         first_ino, &n);
        if (!defrag) {
            if (n) {
                defrag = rb_entry(n, struct inode_defrag,
                          rb_node);
            } else if (root_objectid || first_ino) {
                root_objectid = 0;
                first_ino = 0;
                continue;
            } else {
                break;
            }
        }

        /* remove it from the rbtree */
        first_ino = defrag->ino + 1;
        root_objectid = defrag->root;
        rb_erase(&defrag->rb_node, &fs_info->defrag_inodes);

        if (btrfs_fs_closing(fs_info))
            goto next_free;

        spin_unlock(&fs_info->defrag_inodes_lock);

        /* get the inode */
        key.objectid = defrag->root;
        btrfs_set_key_type(&key, BTRFS_ROOT_ITEM_KEY);
        key.offset = (u64)-1;
        inode_root = btrfs_read_fs_root_no_name(fs_info, &key);
        if (IS_ERR(inode_root))
            goto next;

        key.objectid = defrag->ino;
        btrfs_set_key_type(&key, BTRFS_INODE_ITEM_KEY);
        key.offset = 0;

        inode = btrfs_iget(fs_info->sb, &key, inode_root, NULL);
        if (IS_ERR(inode))
            goto next;

        /* do a chunk of defrag */
        clear_bit(BTRFS_INODE_IN_DEFRAG, &BTRFS_I(inode)->runtime_flags);
        range.start = defrag->last_offset;
        num_defrag = btrfs_defrag_file(inode, NULL, &range, defrag->transid,
                           defrag_batch);
        /*
         * if we filled the whole defrag batch, there
         * must be more work to do.  Queue this defrag
         * again
         */
        if (num_defrag == defrag_batch) {
            defrag->last_offset = range.start;
            __btrfs_add_inode_defrag(inode, defrag);
            /*
             * we don't want to kfree defrag, we added it back to
             * the rbtree
             */
            defrag = NULL;
        } else if (defrag->last_offset && !defrag->cycled) {
            /*
             * we didn't fill our defrag batch, but
             * we didn't start at zero.  Make sure we loop
             * around to the start of the file.
             */
            defrag->last_offset = 0;
            defrag->cycled = 1;
            __btrfs_add_inode_defrag(inode, defrag);
            defrag = NULL;
        }

        iput(inode);
next:
        spin_lock(&fs_info->defrag_inodes_lock);
next_free:
        kfree(defrag);
    }
    spin_unlock(&fs_info->defrag_inodes_lock);

    atomic_dec(&fs_info->defrag_running);

    /*
     * during unmount, we use the transaction_wait queue to
     * wait for the defragger to stop
     */
    wake_up(&fs_info->transaction_wait);
    return 0;
}

/* simple helper to fault in pages and copy.  This should go away
 * and be replaced with calls into generic code.
 */
static noinline int btrfs_copy_from_user(loff_t pos, int num_pages,
                     size_t write_bytes,
                     struct page **prepared_pages,
                     struct iov_iter *i)
{
    size_t copied = 0;
    size_t total_copied = 0;
    int pg = 0;
    int offset = pos & (PAGE_CACHE_SIZE - 1);

    while (write_bytes > 0) {
        size_t count = min_t(size_t,
                     PAGE_CACHE_SIZE - offset, write_bytes);
        struct page *page = prepared_pages[pg];
        /*
         * Copy data from userspace to the current page
         *
         * Disable pagefault to avoid recursive lock since
         * the pages are already locked
         */
        pagefault_disable();
        copied = iov_iter_copy_from_user_atomic(page, i, offset, count);
        pagefault_enable();

        /* Flush processor's dcache for this page */
        flush_dcache_page(page);

        /*
         * if we get a partial write, we can end up with
         * partially up to date pages.  These add
         * a lot of complexity, so make sure they don't
         * happen by forcing this copy to be retried.
         *
         * The rest of the btrfs_file_write code will fall
         * back to page at a time copies after we return 0.
         */
        if (!PageUptodate(page) && copied < count)
            copied = 0;

        iov_iter_advance(i, copied);
        write_bytes -= copied;
        total_copied += copied;

        /* Return to btrfs_file_aio_write to fault page */
        if (unlikely(copied == 0))
            break;

        if (unlikely(copied < PAGE_CACHE_SIZE - offset)) {
            offset += copied;
        } else {
            pg++;
            offset = 0;
        }
    }
    return total_copied;
}

/*
 * unlocks pages after btrfs_file_write is done with them
 */
void btrfs_drop_pages(struct page **pages, size_t num_pages)
{
    size_t i;
    for (i = 0; i < num_pages; i++) {
        /* page checked is some magic around finding pages that
         * have been modified without going through btrfs_set_page_dirty
         * clear it here
         */
        ClearPageChecked(pages[i]);
        unlock_page(pages[i]);
        mark_page_accessed(pages[i]);
        page_cache_release(pages[i]);
    }
}

/*
 * after copy_from_user, pages need to be dirtied and we need to make
 * sure holes are created between the current EOF and the start of
 * any next extents (if required).
 *
 * this also makes the decision about creating an inline extent vs
 * doing real data extents, marking pages dirty and delalloc as required.
 */
int btrfs_dirty_pages(struct btrfs_root *root, struct inode *inode,
              struct page **pages, size_t num_pages,
              loff_t pos, size_t write_bytes,
              struct extent_state **cached)
{
    int err = 0;
    int i;
    u64 num_bytes;
    u64 start_pos;
    u64 end_of_last_block;
    u64 end_pos = pos + write_bytes;
    loff_t isize = i_size_read(inode);

    start_pos = pos & ~((u64)root->sectorsize - 1);
    num_bytes = (write_bytes + pos - start_pos +
            root->sectorsize - 1) & ~((u64)root->sectorsize - 1);

    end_of_last_block = start_pos + num_bytes - 1;
    err = btrfs_set_extent_delalloc(inode, start_pos, end_of_last_block,
                    cached);
    if (err)
        return err;

    for (i = 0; i < num_pages; i++) {
        struct page *p = pages[i];
        SetPageUptodate(p);
        ClearPageChecked(p);
        set_page_dirty(p);
    }

    /*
     * we've only changed i_size in ram, and we haven't updated
     * the disk i_size.  There is no need to log the inode
     * at this time.
     */
    if (end_pos > isize)
        i_size_write(inode, end_pos);
    return 0;
}

/*
 * this drops all the extents in the cache that intersect the range
 * [start, end].  Existing extents are split as required.
 */
void btrfs_drop_extent_cache(struct inode *inode, u64 start, u64 end,
                 int skip_pinned)
{
    struct extent_map *em;
    struct extent_map *split = NULL;
    struct extent_map *split2 = NULL;
    struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
    u64 len = end - start + 1;
    u64 gen;
    int ret;
    int testend = 1;
    unsigned long flags;
    int compressed = 0;

    WARN_ON(end < start);
    if (end == (u64)-1) {
        len = (u64)-1;
        testend = 0;
    }
    while (1) {
        int no_splits = 0;

        if (!split)
            split = alloc_extent_map();
        if (!split2)
            split2 = alloc_extent_map();
        if (!split || !split2)
            no_splits = 1;

        write_lock(&em_tree->lock);
        em = lookup_extent_mapping(em_tree, start, len);
        if (!em) {
            write_unlock(&em_tree->lock);
            break;
        }
        flags = em->flags;
        gen = em->generation;
        if (skip_pinned && test_bit(EXTENT_FLAG_PINNED, &em->flags)) {
            if (testend && em->start + em->len >= start + len) {
                free_extent_map(em);
                write_unlock(&em_tree->lock);
                break;
            }
            start = em->start + em->len;
            if (testend)
                len = start + len - (em->start + em->len);
            free_extent_map(em);
            write_unlock(&em_tree->lock);
            continue;
        }
        compressed = test_bit(EXTENT_FLAG_COMPRESSED, &em->flags);
        clear_bit(EXTENT_FLAG_PINNED, &em->flags);
        remove_extent_mapping(em_tree, em);
        if (no_splits)
            goto next;

        if (em->block_start < EXTENT_MAP_LAST_BYTE &&
            em->start < start) {
            split->start = em->start;
            split->len = start - em->start;
            split->orig_start = em->orig_start;
            split->block_start = em->block_start;

            if (compressed)
                split->block_len = em->block_len;
            else
                split->block_len = split->len;
            split->generation = gen;
            split->bdev = em->bdev;
            split->flags = flags;
            split->compress_type = em->compress_type;
            ret = add_extent_mapping(em_tree, split);
            BUG_ON(ret); /* Logic error */
            list_move(&split->list, &em_tree->modified_extents);
            free_extent_map(split);
            split = split2;
            split2 = NULL;
        }
        if (em->block_start < EXTENT_MAP_LAST_BYTE &&
            testend && em->start + em->len > start + len) {
            u64 diff = start + len - em->start;

            split->start = start + len;
            split->len = em->start + em->len - (start + len);
            split->bdev = em->bdev;
            split->flags = flags;
            split->compress_type = em->compress_type;
            split->generation = gen;

            if (compressed) {
                split->block_len = em->block_len;
                split->block_start = em->block_start;
                split->orig_start = em->orig_start;
            } else {
                split->block_len = split->len;
                split->block_start = em->block_start + diff;
                split->orig_start = split->start;
            }

            ret = add_extent_mapping(em_tree, split);
            BUG_ON(ret); /* Logic error */
            list_move(&split->list, &em_tree->modified_extents);
            free_extent_map(split);
            split = NULL;
        }
next:
        write_unlock(&em_tree->lock);

        /* once for us */
        free_extent_map(em);
        /* once for the tree*/
        free_extent_map(em);
    }
    if (split)
        free_extent_map(split);
    if (split2)
        free_extent_map(split2);
}

/*
 * this is very complex, but the basic idea is to drop all extents
 * in the range start - end.  hint_block is filled in with a block number
 * that would be a good hint to the block allocator for this file.
 *
 * If an extent intersects the range but is not entirely inside the range
 * it is either truncated or split.  Anything entirely inside the range
 * is deleted from the tree.
 */
int __btrfs_drop_extents(struct btrfs_trans_handle *trans,
             struct btrfs_root *root, struct inode *inode,
             struct btrfs_path *path, u64 start, u64 end,
             u64 *drop_end, int drop_cache)
{
    struct extent_buffer *leaf;
    struct btrfs_file_extent_item *fi;
    struct btrfs_key key;
    struct btrfs_key new_key;
    u64 ino = btrfs_ino(inode);
    u64 search_start = start;
    u64 disk_bytenr = 0;
    u64 num_bytes = 0;
    u64 extent_offset = 0;
    u64 extent_end = 0;
    int del_nr = 0;
    int del_slot = 0;
    int extent_type;
    int recow;
    int ret;
    int modify_tree = -1;
    int update_refs = (root->ref_cows || root == root->fs_info->tree_root);
    int found = 0;

    if (drop_cache)
        btrfs_drop_extent_cache(inode, start, end - 1, 0);

    if (start >= BTRFS_I(inode)->disk_i_size)
        modify_tree = 0;

    while (1) {
        recow = 0;
        ret = btrfs_lookup_file_extent(trans, root, path, ino,
                           search_start, modify_tree);
        if (ret < 0)
            break;
        if (ret > 0 && path->slots[0] > 0 && search_start == start) {
            leaf = path->nodes[0];
            btrfs_item_key_to_cpu(leaf, &key, path->slots[0] - 1);
            if (key.objectid == ino &&
                key.type == BTRFS_EXTENT_DATA_KEY)
                path->slots[0]--;
        }
        ret = 0;
next_slot:
        leaf = path->nodes[0];
        if (path->slots[0] >= btrfs_header_nritems(leaf)) {
            BUG_ON(del_nr > 0);
            ret = btrfs_next_leaf(root, path);
            if (ret < 0)
                break;
            if (ret > 0) {
                ret = 0;
                break;
            }
            leaf = path->nodes[0];
            recow = 1;
        }

        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
        if (key.objectid > ino ||
            key.type > BTRFS_EXTENT_DATA_KEY || key.offset >= end)
            break;

        fi = btrfs_item_ptr(leaf, path->slots[0],
                    struct btrfs_file_extent_item);
        extent_type = btrfs_file_extent_type(leaf, fi);

        if (extent_type == BTRFS_FILE_EXTENT_REG ||
            extent_type == BTRFS_FILE_EXTENT_PREALLOC) {
            disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
            num_bytes = btrfs_file_extent_disk_num_bytes(leaf, fi);
            extent_offset = btrfs_file_extent_offset(leaf, fi);
            extent_end = key.offset +
                btrfs_file_extent_num_bytes(leaf, fi);
        } else if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
            extent_end = key.offset +
                btrfs_file_extent_inline_len(leaf, fi);
        } else {
            WARN_ON(1);
            extent_end = search_start;
        }

        if (extent_end <= search_start) {
            path->slots[0]++;
            goto next_slot;
        }

        found = 1;
        search_start = max(key.offset, start);
        if (recow || !modify_tree) {
            modify_tree = -1;
            btrfs_release_path(path);
            continue;
        }

        /*
         *     | - range to drop - |
         *  | -------- extent -------- |
         */
        if (start > key.offset && end < extent_end) {
            BUG_ON(del_nr > 0);
            BUG_ON(extent_type == BTRFS_FILE_EXTENT_INLINE);

            memcpy(&new_key, &key, sizeof(new_key));
            new_key.offset = start;
            ret = btrfs_duplicate_item(trans, root, path,
                           &new_key);
            if (ret == -EAGAIN) {
                btrfs_release_path(path);
                continue;
            }
            if (ret < 0)
                break;

            leaf = path->nodes[0];
            fi = btrfs_item_ptr(leaf, path->slots[0] - 1,
                        struct btrfs_file_extent_item);
            btrfs_set_file_extent_num_bytes(leaf, fi,
                            start - key.offset);

            fi = btrfs_item_ptr(leaf, path->slots[0],
                        struct btrfs_file_extent_item);

            extent_offset += start - key.offset;
            btrfs_set_file_extent_offset(leaf, fi, extent_offset);
            btrfs_set_file_extent_num_bytes(leaf, fi,
                            extent_end - start);
            btrfs_mark_buffer_dirty(leaf);

            if (update_refs && disk_bytenr > 0) {
                ret = btrfs_inc_extent_ref(trans, root,
                        disk_bytenr, num_bytes, 0,
                        root->root_key.objectid,
                        new_key.objectid,
                        start - extent_offset, 0);
                BUG_ON(ret); /* -ENOMEM */
            }
            key.offset = start;
        }
        /*
         *  | ---- range to drop ----- |
         *      | -------- extent -------- |
         */
        if (start <= key.offset && end < extent_end) {
            BUG_ON(extent_type == BTRFS_FILE_EXTENT_INLINE);

            memcpy(&new_key, &key, sizeof(new_key));
            new_key.offset = end;
            btrfs_set_item_key_safe(trans, root, path, &new_key);

            extent_offset += end - key.offset;
            btrfs_set_file_extent_offset(leaf, fi, extent_offset);
            btrfs_set_file_extent_num_bytes(leaf, fi,
                            extent_end - end);
            btrfs_mark_buffer_dirty(leaf);
            if (update_refs && disk_bytenr > 0)
                inode_sub_bytes(inode, end - key.offset);
            break;
        }

        search_start = extent_end;
        /*
         *       | ---- range to drop ----- |
         *  | -------- extent -------- |
         */
        if (start > key.offset && end >= extent_end) {
            BUG_ON(del_nr > 0);
            BUG_ON(extent_type == BTRFS_FILE_EXTENT_INLINE);

            btrfs_set_file_extent_num_bytes(leaf, fi,
                            start - key.offset);
            btrfs_mark_buffer_dirty(leaf);
            if (update_refs && disk_bytenr > 0)
                inode_sub_bytes(inode, extent_end - start);
            if (end == extent_end)
                break;

            path->slots[0]++;
            goto next_slot;
        }

        /*
         *  | ---- range to drop ----- |
         *    | ------ extent ------ |
         */
        if (start <= key.offset && end >= extent_end) {
            if (del_nr == 0) {
                del_slot = path->slots[0];
                del_nr = 1;
            } else {
                BUG_ON(del_slot + del_nr != path->slots[0]);
                del_nr++;
            }

            if (update_refs &&
                extent_type == BTRFS_FILE_EXTENT_INLINE) {
                inode_sub_bytes(inode,
                        extent_end - key.offset);
                extent_end = ALIGN(extent_end,
                           root->sectorsize);
            } else if (update_refs && disk_bytenr > 0) {
                ret = btrfs_free_extent(trans, root,
                        disk_bytenr, num_bytes, 0,
                        root->root_key.objectid,
                        key.objectid, key.offset -
                        extent_offset, 0);
                BUG_ON(ret); /* -ENOMEM */
                inode_sub_bytes(inode,
                        extent_end - key.offset);
            }

            if (end == extent_end)
                break;

            if (path->slots[0] + 1 < btrfs_header_nritems(leaf)) {
                path->slots[0]++;
                goto next_slot;
            }

            ret = btrfs_del_items(trans, root, path, del_slot,
                          del_nr);
            if (ret) {
                btrfs_abort_transaction(trans, root, ret);
                break;
            }

            del_nr = 0;
            del_slot = 0;

            btrfs_release_path(path);
            continue;
        }

        BUG_ON(1);
    }

    if (!ret && del_nr > 0) {
        ret = btrfs_del_items(trans, root, path, del_slot, del_nr);
        if (ret)
            btrfs_abort_transaction(trans, root, ret);
    }

    if (drop_end)
        *drop_end = found ? min(end, extent_end) : end;
    btrfs_release_path(path);
    return ret;
}

int btrfs_drop_extents(struct btrfs_trans_handle *trans,
               struct btrfs_root *root, struct inode *inode, u64 start,
               u64 end, int drop_cache)
{
    struct btrfs_path *path;
    int ret;

    path = btrfs_alloc_path();
    if (!path)
        return -ENOMEM;
    ret = __btrfs_drop_extents(trans, root, inode, path, start, end, NULL,
                   drop_cache);
    btrfs_free_path(path);
    return ret;
}

static int extent_mergeable(struct extent_buffer *leaf, int slot,
                u64 objectid, u64 bytenr, u64 orig_offset,
                u64 *start, u64 *end)
{
    struct btrfs_file_extent_item *fi;
    struct btrfs_key key;
    u64 extent_end;

    if (slot < 0 || slot >= btrfs_header_nritems(leaf))
        return 0;

    btrfs_item_key_to_cpu(leaf, &key, slot);
    if (key.objectid != objectid || key.type != BTRFS_EXTENT_DATA_KEY)
        return 0;

    fi = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item);
    if (btrfs_file_extent_type(leaf, fi) != BTRFS_FILE_EXTENT_REG ||
        btrfs_file_extent_disk_bytenr(leaf, fi) != bytenr ||
        btrfs_file_extent_offset(leaf, fi) != key.offset - orig_offset ||
        btrfs_file_extent_compression(leaf, fi) ||
        btrfs_file_extent_encryption(leaf, fi) ||
        btrfs_file_extent_other_encoding(leaf, fi))
        return 0;

    extent_end = key.offset + btrfs_file_extent_num_bytes(leaf, fi);
    if ((*start && *start != key.offset) || (*end && *end != extent_end))
        return 0;

    *start = key.offset;
    *end = extent_end;
    return 1;
}

/*
 * Mark extent in the range start - end as written.
 *
 * This changes extent type from 'pre-allocated' to 'regular'. If only
 * part of extent is marked as written, the extent will be split into
 * two or three.
 */
int btrfs_mark_extent_written(struct btrfs_trans_handle *trans,
                  struct inode *inode, u64 start, u64 end)
{
    struct btrfs_root *root = BTRFS_I(inode)->root;
    struct extent_buffer *leaf;
    struct btrfs_path *path;
    struct btrfs_file_extent_item *fi;
    struct btrfs_key key;
    struct btrfs_key new_key;
    u64 bytenr;
    u64 num_bytes;
    u64 extent_end;
    u64 orig_offset;
    u64 other_start;
    u64 other_end;
    u64 split;
    int del_nr = 0;
    int del_slot = 0;
    int recow;
    int ret;
    u64 ino = btrfs_ino(inode);

    path = btrfs_alloc_path();
    if (!path)
        return -ENOMEM;
again:
    recow = 0;
    split = start;
    key.objectid = ino;
    key.type = BTRFS_EXTENT_DATA_KEY;
    key.offset = split;

    ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
    if (ret < 0)
        goto out;
    if (ret > 0 && path->slots[0] > 0)
        path->slots[0]--;

    leaf = path->nodes[0];
    btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
    BUG_ON(key.objectid != ino || key.type != BTRFS_EXTENT_DATA_KEY);
    fi = btrfs_item_ptr(leaf, path->slots[0],
                struct btrfs_file_extent_item);
    BUG_ON(btrfs_file_extent_type(leaf, fi) !=
           BTRFS_FILE_EXTENT_PREALLOC);
    extent_end = key.offset + btrfs_file_extent_num_bytes(leaf, fi);
    BUG_ON(key.offset > start || extent_end < end);

    bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
    num_bytes = btrfs_file_extent_disk_num_bytes(leaf, fi);
    orig_offset = key.offset - btrfs_file_extent_offset(leaf, fi);
    memcpy(&new_key, &key, sizeof(new_key));

    if (start == key.offset && end < extent_end) {
        other_start = 0;
        other_end = start;
        if (extent_mergeable(leaf, path->slots[0] - 1,
                     ino, bytenr, orig_offset,
                     &other_start, &other_end)) {
            new_key.offset = end;
            btrfs_set_item_key_safe(trans, root, path, &new_key);
            fi = btrfs_item_ptr(leaf, path->slots[0],
                        struct btrfs_file_extent_item);
            btrfs_set_file_extent_generation(leaf, fi,
                             trans->transid);
            btrfs_set_file_extent_num_bytes(leaf, fi,
                            extent_end - end);
            btrfs_set_file_extent_offset(leaf, fi,
                             end - orig_offset);
            fi = btrfs_item_ptr(leaf, path->slots[0] - 1,
                        struct btrfs_file_extent_item);
            btrfs_set_file_extent_generation(leaf, fi,
                             trans->transid);
            btrfs_set_file_extent_num_bytes(leaf, fi,
                            end - other_start);
            btrfs_mark_buffer_dirty(leaf);
            goto out;
        }
    }

    if (start > key.offset && end == extent_end) {
        other_start = end;
        other_end = 0;
        if (extent_mergeable(leaf, path->slots[0] + 1,
                     ino, bytenr, orig_offset,
                     &other_start, &other_end)) {
            fi = btrfs_item_ptr(leaf, path->slots[0],
                        struct btrfs_file_extent_item);
            btrfs_set_file_extent_num_bytes(leaf, fi,
                            start - key.offset);
            btrfs_set_file_extent_generation(leaf, fi,
                             trans->transid);
            path->slots[0]++;
            new_key.offset = start;
            btrfs_set_item_key_safe(trans, root, path, &new_key);

            fi = btrfs_item_ptr(leaf, path->slots[0],
                        struct btrfs_file_extent_item);
            btrfs_set_file_extent_generation(leaf, fi,
                             trans->transid);
            btrfs_set_file_extent_num_bytes(leaf, fi,
                            other_end - start);
            btrfs_set_file_extent_offset(leaf, fi,
                             start - orig_offset);
            btrfs_mark_buffer_dirty(leaf);
            goto out;
        }
    }

    while (start > key.offset || end < extent_end) {
        if (key.offset == start)
            split = end;

        new_key.offset = split;
        ret = btrfs_duplicate_item(trans, root, path, &new_key);
        if (ret == -EAGAIN) {
            btrfs_release_path(path);
            goto again;
        }
        if (ret < 0) {
            btrfs_abort_transaction(trans, root, ret);
            goto out;
        }

        leaf = path->nodes[0];
        fi = btrfs_item_ptr(leaf, path->slots[0] - 1,
                    struct btrfs_file_extent_item);
        btrfs_set_file_extent_generation(leaf, fi, trans->transid);
        btrfs_set_file_extent_num_bytes(leaf, fi,
                        split - key.offset);

        fi = btrfs_item_ptr(leaf, path->slots[0],
                    struct btrfs_file_extent_item);

        btrfs_set_file_extent_generation(leaf, fi, trans->transid);
        btrfs_set_file_extent_offset(leaf, fi, split - orig_offset);
        btrfs_set_file_extent_num_bytes(leaf, fi,
                        extent_end - split);
        btrfs_mark_buffer_dirty(leaf);

        ret = btrfs_inc_extent_ref(trans, root, bytenr, num_bytes, 0,
                       root->root_key.objectid,
                       ino, orig_offset, 0);
        BUG_ON(ret); /* -ENOMEM */

        if (split == start) {
            key.offset = start;
        } else {
            BUG_ON(start != key.offset);
            path->slots[0]--;
            extent_end = end;
        }
        recow = 1;
    }

    other_start = end;
    other_end = 0;
    if (extent_mergeable(leaf, path->slots[0] + 1,
                 ino, bytenr, orig_offset,
                 &other_start, &other_end)) {
        if (recow) {
            btrfs_release_path(path);
            goto again;
        }
        extent_end = other_end;
        del_slot = path->slots[0] + 1;
        del_nr++;
        ret = btrfs_free_extent(trans, root, bytenr, num_bytes,
                    0, root->root_key.objectid,
                    ino, orig_offset, 0);
        BUG_ON(ret); /* -ENOMEM */
    }
    other_start = 0;
    other_end = start;
    if (extent_mergeable(leaf, path->slots[0] - 1,
                 ino, bytenr, orig_offset,
                 &other_start, &other_end)) {
        if (recow) {
            btrfs_release_path(path);
            goto again;
        }
        key.offset = other_start;
        del_slot = path->slots[0];
        del_nr++;
        ret = btrfs_free_extent(trans, root, bytenr, num_bytes,
                    0, root->root_key.objectid,
                    ino, orig_offset, 0);
        BUG_ON(ret); /* -ENOMEM */
    }
    if (del_nr == 0) {
        fi = btrfs_item_ptr(leaf, path->slots[0],
               struct btrfs_file_extent_item);
        btrfs_set_file_extent_type(leaf, fi,
                       BTRFS_FILE_EXTENT_REG);
        btrfs_set_file_extent_generation(leaf, fi, trans->transid);
        btrfs_mark_buffer_dirty(leaf);
    } else {
        fi = btrfs_item_ptr(leaf, del_slot - 1,
               struct btrfs_file_extent_item);
        btrfs_set_file_extent_type(leaf, fi,
                       BTRFS_FILE_EXTENT_REG);
        btrfs_set_file_extent_generation(leaf, fi, trans->transid);
        btrfs_set_file_extent_num_bytes(leaf, fi,
                        extent_end - key.offset);
        btrfs_mark_buffer_dirty(leaf);

        ret = btrfs_del_items(trans, root, path, del_slot, del_nr);
        if (ret < 0) {
            btrfs_abort_transaction(trans, root, ret);
            goto out;
        }
    }
out:
    btrfs_free_path(path);
    return 0;
}

/*
 * on error we return an unlocked page and the error value
 * on success we return a locked page and 0
 */
static int prepare_uptodate_page(struct page *page, u64 pos,
                 bool force_uptodate)
{
    int ret = 0;

    if (((pos & (PAGE_CACHE_SIZE - 1)) || force_uptodate) &&
        !PageUptodate(page)) {
        ret = btrfs_readpage(NULL, page);
        if (ret)
            return ret;
        lock_page(page);
        if (!PageUptodate(page)) {
            unlock_page(page);
            return -EIO;
        }
    }
    return 0;
}

/*
 * this gets pages into the page cache and locks them down, it also properly
 * waits for data=ordered extents to finish before allowing the pages to be
 * modified.
 */
static noinline int prepare_pages(struct btrfs_root *root, struct file *file,
             struct page **pages, size_t num_pages,
             loff_t pos, unsigned long first_index,
             size_t write_bytes, bool force_uptodate)
{
    struct extent_state *cached_state = NULL;
    int i;
    unsigned long index = pos >> PAGE_CACHE_SHIFT;
    struct inode *inode = fdentry(file)->d_inode;
    gfp_t mask = btrfs_alloc_write_mask(inode->i_mapping);
    int err = 0;
    int faili = 0;
    u64 start_pos;
    u64 last_pos;

    start_pos = pos & ~((u64)root->sectorsize - 1);
    last_pos = ((u64)index + num_pages) << PAGE_CACHE_SHIFT;

again:
    for (i = 0; i < num_pages; i++) {
        pages[i] = find_or_create_page(inode->i_mapping, index + i,
                           mask | __GFP_WRITE);
        if (!pages[i]) {
            faili = i - 1;
            err = -ENOMEM;
            goto fail;
        }

        if (i == 0)
            err = prepare_uptodate_page(pages[i], pos,
                            force_uptodate);
        if (i == num_pages - 1)
            err = prepare_uptodate_page(pages[i],
                            pos + write_bytes, false);
        if (err) {
            page_cache_release(pages[i]);
            faili = i - 1;
            goto fail;
        }
        wait_on_page_writeback(pages[i]);
    }
    err = 0;
    if (start_pos < inode->i_size) {
        struct btrfs_ordered_extent *ordered;
        lock_extent_bits(&BTRFS_I(inode)->io_tree,
                 start_pos, last_pos - 1, 0, &cached_state);
        ordered = btrfs_lookup_first_ordered_extent(inode,
                                last_pos - 1);
        if (ordered &&
            ordered->file_offset + ordered->len > start_pos &&
            ordered->file_offset < last_pos) {
            btrfs_put_ordered_extent(ordered);
            unlock_extent_cached(&BTRFS_I(inode)->io_tree,
                         start_pos, last_pos - 1,
                         &cached_state, GFP_NOFS);
            for (i = 0; i < num_pages; i++) {
                unlock_page(pages[i]);
                page_cache_release(pages[i]);
            }
            btrfs_wait_ordered_range(inode, start_pos,
                         last_pos - start_pos);
            goto again;
        }
        if (ordered)
            btrfs_put_ordered_extent(ordered);

        clear_extent_bit(&BTRFS_I(inode)->io_tree, start_pos,
                  last_pos - 1, EXTENT_DIRTY | EXTENT_DELALLOC |
                  EXTENT_DO_ACCOUNTING | EXTENT_DEFRAG,
                  0, 0, &cached_state, GFP_NOFS);
        unlock_extent_cached(&BTRFS_I(inode)->io_tree,
                     start_pos, last_pos - 1, &cached_state,
                     GFP_NOFS);
    }
    for (i = 0; i < num_pages; i++) {
        if (clear_page_dirty_for_io(pages[i]))
            account_page_redirty(pages[i]);
        set_page_extent_mapped(pages[i]);
        WARN_ON(!PageLocked(pages[i]));
    }
    return 0;
fail:
    while (faili >= 0) {
        unlock_page(pages[faili]);
        page_cache_release(pages[faili]);
        faili--;
    }
    return err;

}

static noinline ssize_t __btrfs_buffered_write(struct file *file,
                           struct iov_iter *i,
                           loff_t pos)
{
    struct inode *inode = fdentry(file)->d_inode;
    struct btrfs_root *root = BTRFS_I(inode)->root;
    struct page **pages = NULL;
    unsigned long first_index;
    size_t num_written = 0;
    int nrptrs;
    int ret = 0;
    bool force_page_uptodate = false;

    nrptrs = min((iov_iter_count(i) + PAGE_CACHE_SIZE - 1) /
             PAGE_CACHE_SIZE, PAGE_CACHE_SIZE /
             (sizeof(struct page *)));
    nrptrs = min(nrptrs, current->nr_dirtied_pause - current->nr_dirtied);
    nrptrs = max(nrptrs, 8);
    pages = kmalloc(nrptrs * sizeof(struct page *), GFP_KERNEL);
    if (!pages)
        return -ENOMEM;

    first_index = pos >> PAGE_CACHE_SHIFT;

    while (iov_iter_count(i) > 0) {
        size_t offset = pos & (PAGE_CACHE_SIZE - 1);
        size_t write_bytes = min(iov_iter_count(i),
                     nrptrs * (size_t)PAGE_CACHE_SIZE -
                     offset);
        size_t num_pages = (write_bytes + offset +
                    PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
        size_t dirty_pages;
        size_t copied;

        WARN_ON(num_pages > nrptrs);

        /*
         * Fault pages before locking them in prepare_pages
         * to avoid recursive lock
         */
        if (unlikely(iov_iter_fault_in_readable(i, write_bytes))) {
            ret = -EFAULT;
            break;
        }

        ret = btrfs_delalloc_reserve_space(inode,
                    num_pages << PAGE_CACHE_SHIFT);
        if (ret)
            break;

        /*
         * This is going to setup the pages array with the number of
         * pages we want, so we don't really need to worry about the
         * contents of pages from loop to loop
         */
        ret = prepare_pages(root, file, pages, num_pages,
                    pos, first_index, write_bytes,
                    force_page_uptodate);
        if (ret) {
            btrfs_delalloc_release_space(inode,
                    num_pages << PAGE_CACHE_SHIFT);
            break;
        }

        copied = btrfs_copy_from_user(pos, num_pages,
                       write_bytes, pages, i);

        /*
         * if we have trouble faulting in the pages, fall
         * back to one page at a time
         */
        if (copied < write_bytes)
            nrptrs = 1;

        if (copied == 0) {
            force_page_uptodate = true;
            dirty_pages = 0;
        } else {
            force_page_uptodate = false;
            dirty_pages = (copied + offset +
                       PAGE_CACHE_SIZE - 1) >>
                       PAGE_CACHE_SHIFT;
        }

        /*
         * If we had a short copy we need to release the excess delaloc
         * bytes we reserved.  We need to increment outstanding_extents
         * because btrfs_delalloc_release_space will decrement it, but
         * we still have an outstanding extent for the chunk we actually
         * managed to copy.
         */
        if (num_pages > dirty_pages) {
            if (copied > 0) {
                spin_lock(&BTRFS_I(inode)->lock);
                BTRFS_I(inode)->outstanding_extents++;
                spin_unlock(&BTRFS_I(inode)->lock);
            }
            btrfs_delalloc_release_space(inode,
                    (num_pages - dirty_pages) <<
                    PAGE_CACHE_SHIFT);
        }

        if (copied > 0) {
            ret = btrfs_dirty_pages(root, inode, pages,
                        dirty_pages, pos, copied,
                        NULL);
            if (ret) {
                btrfs_delalloc_release_space(inode,
                    dirty_pages << PAGE_CACHE_SHIFT);
                btrfs_drop_pages(pages, num_pages);
                break;
            }
        }

        btrfs_drop_pages(pages, num_pages);

        cond_resched();

        balance_dirty_pages_ratelimited_nr(inode->i_mapping,
                           dirty_pages);
        if (dirty_pages < (root->leafsize >> PAGE_CACHE_SHIFT) + 1)
            btrfs_btree_balance_dirty(root, 1);

        pos += copied;
        num_written += copied;
    }

    kfree(pages);

    return num_written ? num_written : ret;
}

static ssize_t __btrfs_direct_write(struct kiocb *iocb,
                    const struct iovec *iov,
                    unsigned long nr_segs, loff_t pos,
                    loff_t *ppos, size_t count, size_t ocount)
{
    struct file *file = iocb->ki_filp;
    struct iov_iter i;
    ssize_t written;
    ssize_t written_buffered;
    loff_t endbyte;
    int err;

    written = generic_file_direct_write(iocb, iov, &nr_segs, pos, ppos,
                        count, ocount);

    if (written < 0 || written == count)
        return written;

    pos += written;
    count -= written;
    iov_iter_init(&i, iov, nr_segs, count, written);
    written_buffered = __btrfs_buffered_write(file, &i, pos);
    if (written_buffered < 0) {
        err = written_buffered;
        goto out;
    }
    endbyte = pos + written_buffered - 1;
    err = filemap_write_and_wait_range(file->f_mapping, pos, endbyte);
    if (err)
        goto out;
    written += written_buffered;
    *ppos = pos + written_buffered;
    invalidate_mapping_pages(file->f_mapping, pos >> PAGE_CACHE_SHIFT,
                 endbyte >> PAGE_CACHE_SHIFT);
out:
    return written ? written : err;
}

static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
                    const struct iovec *iov,
                    unsigned long nr_segs, loff_t pos)
{
    struct file *file = iocb->ki_filp;
    struct inode *inode = fdentry(file)->d_inode;
    struct btrfs_root *root = BTRFS_I(inode)->root;
    loff_t *ppos = &iocb->ki_pos;
    u64 start_pos;
    ssize_t num_written = 0;
    ssize_t err = 0;
    size_t count, ocount;

    sb_start_write(inode->i_sb);

    mutex_lock(&inode->i_mutex);

    err = generic_segment_checks(iov, &nr_segs, &ocount, VERIFY_READ);
    if (err) {
        mutex_unlock(&inode->i_mutex);
        goto out;
    }
    count = ocount;

    current->backing_dev_info = inode->i_mapping->backing_dev_info;
    err = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode));
    if (err) {
        mutex_unlock(&inode->i_mutex);
        goto out;
    }

    if (count == 0) {
        mutex_unlock(&inode->i_mutex);
        goto out;
    }

    err = file_remove_suid(file);
    if (err) {
        mutex_unlock(&inode->i_mutex);
        goto out;
    }

    /*
     * If BTRFS flips readonly due to some impossible error
     * (fs_info->fs_state now has BTRFS_SUPER_FLAG_ERROR),
     * although we have opened a file as writable, we have
     * to stop this write operation to ensure FS consistency.
     */
    if (root->fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) {
        mutex_unlock(&inode->i_mutex);
        err = -EROFS;
        goto out;
    }

    err = file_update_time(file);
    if (err) {
        mutex_unlock(&inode->i_mutex);
        goto out;
    }

    start_pos = round_down(pos, root->sectorsize);
    if (start_pos > i_size_read(inode)) {
        err = btrfs_cont_expand(inode, i_size_read(inode), start_pos);
        if (err) {
            mutex_unlock(&inode->i_mutex);
            goto out;
        }
    }

    if (unlikely(file->f_flags & O_DIRECT)) {
        num_written = __btrfs_direct_write(iocb, iov, nr_segs,
                           pos, ppos, count, ocount);
    } else {
        struct iov_iter i;

        iov_iter_init(&i, iov, nr_segs, count, num_written);

        num_written = __btrfs_buffered_write(file, &i, pos);
        if (num_written > 0)
            *ppos = pos + num_written;
    }

    mutex_unlock(&inode->i_mutex);

    /*
     * we want to make sure fsync finds this change
     * but we haven't joined a transaction running right now.
     *
     * Later on, someone is sure to update the inode and get the
     * real transid recorded.
     *
     * We set last_trans now to the fs_info generation + 1,
     * this will either be one more than the running transaction
     * or the generation used for the next transaction if there isn't
     * one running right now.
     */
    BTRFS_I(inode)->last_trans = root->fs_info->generation + 1;
    if (num_written > 0 || num_written == -EIOCBQUEUED) {
        err = generic_write_sync(file, pos, num_written);
        if (err < 0 && num_written > 0)
            num_written = err;
    }
out:
    sb_end_write(inode->i_sb);
    current->backing_dev_info = NULL;
    return num_written ? num_written : err;
}

int btrfs_release_file(struct inode *inode, struct file *filp)
{
    /*
     * ordered_data_close is set by settattr when we are about to truncate
     * a file from a non-zero size to a zero size.  This tries to
     * flush down new bytes that may have been written if the
     * application were using truncate to replace a file in place.
     */
    if (test_and_clear_bit(BTRFS_INODE_ORDERED_DATA_CLOSE,
                   &BTRFS_I(inode)->runtime_flags)) {
        btrfs_add_ordered_operation(NULL, BTRFS_I(inode)->root, inode);
        if (inode->i_size > BTRFS_ORDERED_OPERATIONS_FLUSH_LIMIT)
            filemap_flush(inode->i_mapping);
    }
    if (filp->private_data)
        btrfs_ioctl_trans_end(filp);
    return 0;
}

/*
 * fsync call for both files and directories.  This logs the inode into
 * the tree log instead of forcing full commits whenever possible.
 *
 * It needs to call filemap_fdatawait so that all ordered extent updates are
 * in the metadata btree are up to date for copying to the log.
 *
 * It drops the inode mutex before doing the tree log commit.  This is an
 * important optimization for directories because holding the mutex prevents
 * new operations on the dir while we write to disk.
 */
int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
{
    struct dentry *dentry = file->f_path.dentry;
    struct inode *inode = dentry->d_inode;
    struct btrfs_root *root = BTRFS_I(inode)->root;
    int ret = 0;
    struct btrfs_trans_handle *trans;

    trace_btrfs_sync_file(file, datasync);

    /*
     * We write the dirty pages in the range and wait until they complete
     * out of the ->i_mutex. If so, we can flush the dirty pages by
     * multi-task, and make the performance up.
     */
    ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
    if (ret)
        return ret;

    mutex_lock(&inode->i_mutex);

    /*
     * We flush the dirty pages again to avoid some dirty pages in the
     * range being left.
     */
    atomic_inc(&root->log_batch);
    btrfs_wait_ordered_range(inode, start, end);
    atomic_inc(&root->log_batch);

    /*
     * check the transaction that last modified this inode
     * and see if its already been committed
     */
    if (!BTRFS_I(inode)->last_trans) {
        mutex_unlock(&inode->i_mutex);
        goto out;
    }

    /*
     * if the last transaction that changed this file was before
     * the current transaction, we can bail out now without any
     * syncing
     */
    smp_mb();
    if (btrfs_inode_in_log(inode, root->fs_info->generation) ||
        BTRFS_I(inode)->last_trans <=
        root->fs_info->last_trans_committed) {
        BTRFS_I(inode)->last_trans = 0;

        /*
         * We'v had everything committed since the last time we were
         * modified so clear this flag in case it was set for whatever
         * reason, it's no longer relevant.
         */
        clear_bit(BTRFS_INODE_NEEDS_FULL_SYNC,
              &BTRFS_I(inode)->runtime_flags);
        mutex_unlock(&inode->i_mutex);
        goto out;
    }

    /*
     * ok we haven't committed the transaction yet, lets do a commit
     */
    if (file->private_data)
        btrfs_ioctl_trans_end(file);

    trans = btrfs_start_transaction(root, 0);
    if (IS_ERR(trans)) {
        ret = PTR_ERR(trans);
        mutex_unlock(&inode->i_mutex);
        goto out;
    }

    ret = btrfs_log_dentry_safe(trans, root, dentry);
    if (ret < 0) {
        mutex_unlock(&inode->i_mutex);
        goto out;
    }

    /* we've logged all the items and now have a consistent
     * version of the file in the log.  It is possible that
     * someone will come in and modify the file, but that's
     * fine because the log is consistent on disk, and we
     * have references to all of the file's extents
     *
     * It is possible that someone will come in and log the
     * file again, but that will end up using the synchronization
     * inside btrfs_sync_log to keep things safe.
     */
    mutex_unlock(&inode->i_mutex);

    if (ret != BTRFS_NO_LOG_SYNC) {
        if (ret > 0) {
            ret = btrfs_commit_transaction(trans, root);
        } else {
            ret = btrfs_sync_log(trans, root);
            if (ret == 0)
                ret = btrfs_end_transaction(trans, root);
            else
                ret = btrfs_commit_transaction(trans, root);
        }
    } else {
        ret = btrfs_end_transaction(trans, root);
    }
out:
    return ret > 0 ? -EIO : ret;
}

static const struct vm_operations_struct btrfs_file_vm_ops = {
    .fault      = filemap_fault,
    .page_mkwrite   = btrfs_page_mkwrite,
    .remap_pages    = generic_file_remap_pages,
};

static int btrfs_file_mmap(struct file  *filp, struct vm_area_struct *vma)
{
    struct address_space *mapping = filp->f_mapping;

    if (!mapping->a_ops->readpage)
        return -ENOEXEC;

    file_accessed(filp);
    vma->vm_ops = &btrfs_file_vm_ops;

    return 0;
}

static int hole_mergeable(struct inode *inode, struct extent_buffer *leaf,
              int slot, u64 start, u64 end)
{
    struct btrfs_file_extent_item *fi;
    struct btrfs_key key;

    if (slot < 0 || slot >= btrfs_header_nritems(leaf))
        return 0;

    btrfs_item_key_to_cpu(leaf, &key, slot);
    if (key.objectid != btrfs_ino(inode) ||
        key.type != BTRFS_EXTENT_DATA_KEY)
        return 0;

    fi = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item);

    if (btrfs_file_extent_type(leaf, fi) != BTRFS_FILE_EXTENT_REG)
        return 0;

    if (btrfs_file_extent_disk_bytenr(leaf, fi))
        return 0;

    if (key.offset == end)
        return 1;
    if (key.offset + btrfs_file_extent_num_bytes(leaf, fi) == start)
        return 1;
    return 0;
}

static int fill_holes(struct btrfs_trans_handle *trans, struct inode *inode,
              struct btrfs_path *path, u64 offset, u64 end)
{
    struct btrfs_root *root = BTRFS_I(inode)->root;
    struct extent_buffer *leaf;
    struct btrfs_file_extent_item *fi;
    struct extent_map *hole_em;
    struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
    struct btrfs_key key;
    int ret;

    key.objectid = btrfs_ino(inode);
    key.type = BTRFS_EXTENT_DATA_KEY;
    key.offset = offset;


    ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
    if (ret < 0)
        return ret;
    BUG_ON(!ret);

    leaf = path->nodes[0];
    if (hole_mergeable(inode, leaf, path->slots[0]-1, offset, end)) {
        u64 num_bytes;

        path->slots[0]--;
        fi = btrfs_item_ptr(leaf, path->slots[0],
                    struct btrfs_file_extent_item);
        num_bytes = btrfs_file_extent_num_bytes(leaf, fi) +
            end - offset;
        btrfs_set_file_extent_num_bytes(leaf, fi, num_bytes);
        btrfs_set_file_extent_ram_bytes(leaf, fi, num_bytes);
        btrfs_set_file_extent_offset(leaf, fi, 0);
        btrfs_mark_buffer_dirty(leaf);
        goto out;
    }

    if (hole_mergeable(inode, leaf, path->slots[0]+1, offset, end)) {
        u64 num_bytes;

        path->slots[0]++;
        key.offset = offset;
        btrfs_set_item_key_safe(trans, root, path, &key);
        fi = btrfs_item_ptr(leaf, path->slots[0],
                    struct btrfs_file_extent_item);
        num_bytes = btrfs_file_extent_num_bytes(leaf, fi) + end -
            offset;
        btrfs_set_file_extent_num_bytes(leaf, fi, num_bytes);
        btrfs_set_file_extent_ram_bytes(leaf, fi, num_bytes);
        btrfs_set_file_extent_offset(leaf, fi, 0);
        btrfs_mark_buffer_dirty(leaf);
        goto out;
    }
    btrfs_release_path(path);

    ret = btrfs_insert_file_extent(trans, root, btrfs_ino(inode), offset,
                       0, 0, end - offset, 0, end - offset,
                       0, 0, 0);
    if (ret)
        return ret;

out:
    btrfs_release_path(path);

    hole_em = alloc_extent_map();
    if (!hole_em) {
        btrfs_drop_extent_cache(inode, offset, end - 1, 0);
        set_bit(BTRFS_INODE_NEEDS_FULL_SYNC,
            &BTRFS_I(inode)->runtime_flags);
    } else {
        hole_em->start = offset;
        hole_em->len = end - offset;
        hole_em->orig_start = offset;

        hole_em->block_start = EXTENT_MAP_HOLE;
        hole_em->block_len = 0;
        hole_em->bdev = root->fs_info->fs_devices->latest_bdev;
        hole_em->compress_type = BTRFS_COMPRESS_NONE;
        hole_em->generation = trans->transid;

        do {
            btrfs_drop_extent_cache(inode, offset, end - 1, 0);
            write_lock(&em_tree->lock);
            ret = add_extent_mapping(em_tree, hole_em);
            if (!ret)
                list_move(&hole_em->list,
                      &em_tree->modified_extents);
            write_unlock(&em_tree->lock);
        } while (ret == -EEXIST);
        free_extent_map(hole_em);
        if (ret)
            set_bit(BTRFS_INODE_NEEDS_FULL_SYNC,
                &BTRFS_I(inode)->runtime_flags);
    }

    return 0;
}

static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
{
    struct btrfs_root *root = BTRFS_I(inode)->root;
    struct extent_state *cached_state = NULL;
    struct btrfs_path *path;
    struct btrfs_block_rsv *rsv;
    struct btrfs_trans_handle *trans;
    u64 mask = BTRFS_I(inode)->root->sectorsize - 1;
    u64 lockstart = (offset + mask) & ~mask;
    u64 lockend = ((offset + len) & ~mask) - 1;
    u64 cur_offset = lockstart;
    u64 min_size = btrfs_calc_trunc_metadata_size(root, 1);
    u64 drop_end;
    unsigned long nr;
    int ret = 0;
    int err = 0;
    bool same_page = (offset >> PAGE_CACHE_SHIFT) ==
        ((offset + len) >> PAGE_CACHE_SHIFT);

    btrfs_wait_ordered_range(inode, offset, len);

    mutex_lock(&inode->i_mutex);
    if (offset >= inode->i_size) {
        mutex_unlock(&inode->i_mutex);
        return 0;
    }

    /*
     * Only do this if we are in the same page and we aren't doing the
     * entire page.
     */
    if (same_page && len < PAGE_CACHE_SIZE) {
        ret = btrfs_truncate_page(inode, offset, len, 0);
        mutex_unlock(&inode->i_mutex);
        return ret;
    }

    /* zero back part of the first page */
    ret = btrfs_truncate_page(inode, offset, 0, 0);
    if (ret) {
        mutex_unlock(&inode->i_mutex);
        return ret;
    }

    /* zero the front end of the last page */
    ret = btrfs_truncate_page(inode, offset + len, 0, 1);
    if (ret) {
        mutex_unlock(&inode->i_mutex);
        return ret;
    }

    if (lockend < lockstart) {
        mutex_unlock(&inode->i_mutex);
        return 0;
    }

    while (1) {
        struct btrfs_ordered_extent *ordered;

        truncate_pagecache_range(inode, lockstart, lockend);

        lock_extent_bits(&BTRFS_I(inode)->io_tree, lockstart, lockend,
                 0, &cached_state);
        ordered = btrfs_lookup_first_ordered_extent(inode, lockend);

        /*
         * We need to make sure we have no ordered extents in this range
         * and nobody raced in and read a page in this range, if we did
         * we need to try again.
         */
        if ((!ordered ||
            (ordered->file_offset + ordered->len < lockstart ||
             ordered->file_offset > lockend)) &&
             !test_range_bit(&BTRFS_I(inode)->io_tree, lockstart,
                     lockend, EXTENT_UPTODATE, 0,
                     cached_state)) {
            if (ordered)
                btrfs_put_ordered_extent(ordered);
            break;
        }
        if (ordered)
            btrfs_put_ordered_extent(ordered);
        unlock_extent_cached(&BTRFS_I(inode)->io_tree, lockstart,
                     lockend, &cached_state, GFP_NOFS);
        btrfs_wait_ordered_range(inode, lockstart,
                     lockend - lockstart + 1);
    }

    path = btrfs_alloc_path();
    if (!path) {
        ret = -ENOMEM;
        goto out;
    }

    rsv = btrfs_alloc_block_rsv(root, BTRFS_BLOCK_RSV_TEMP);
    if (!rsv) {
        ret = -ENOMEM;
        goto out_free;
    }
    rsv->size = btrfs_calc_trunc_metadata_size(root, 1);
    rsv->failfast = 1;

    /*
     * 1 - update the inode
     * 1 - removing the extents in the range
     * 1 - adding the hole extent
     */
    trans = btrfs_start_transaction(root, 3);
    if (IS_ERR(trans)) {
        err = PTR_ERR(trans);
        goto out_free;
    }

    ret = btrfs_block_rsv_migrate(&root->fs_info->trans_block_rsv, rsv,
                      min_size);
    BUG_ON(ret);
    trans->block_rsv = rsv;

    while (cur_offset < lockend) {
        ret = __btrfs_drop_extents(trans, root, inode, path,
                       cur_offset, lockend + 1,
                       &drop_end, 1);
        if (ret != -ENOSPC)
            break;

        trans->block_rsv = &root->fs_info->trans_block_rsv;

        ret = fill_holes(trans, inode, path, cur_offset, drop_end);
        if (ret) {
            err = ret;
            break;
        }

        cur_offset = drop_end;

        ret = btrfs_update_inode(trans, root, inode);
        if (ret) {
            err = ret;
            break;
        }

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

        trans = btrfs_start_transaction(root, 3);
        if (IS_ERR(trans)) {
            ret = PTR_ERR(trans);
            trans = NULL;
            break;
        }

        ret = btrfs_block_rsv_migrate(&root->fs_info->trans_block_rsv,
                          rsv, min_size);
        BUG_ON(ret);    /* shouldn't happen */
        trans->block_rsv = rsv;
    }

    if (ret) {
        err = ret;
        goto out_trans;
    }

    trans->block_rsv = &root->fs_info->trans_block_rsv;
    ret = fill_holes(trans, inode, path, cur_offset, drop_end);
    if (ret) {
        err = ret;
        goto out_trans;
    }

out_trans:
    if (!trans)
        goto out_free;

    trans->block_rsv = &root->fs_info->trans_block_rsv;
    ret = btrfs_update_inode(trans, root, inode);
    nr = trans->blocks_used;
    btrfs_end_transaction(trans, root);
    btrfs_btree_balance_dirty(root, nr);
out_free:
    btrfs_free_path(path);
    btrfs_free_block_rsv(root, rsv);
out:
    unlock_extent_cached(&BTRFS_I(inode)->io_tree, lockstart, lockend,
                 &cached_state, GFP_NOFS);
    mutex_unlock(&inode->i_mutex);
    if (ret && !err)
        err = ret;
    return err;
}

static long btrfs_fallocate(struct file *file, int mode,
                loff_t offset, loff_t len)
{
    struct inode *inode = file->f_path.dentry->d_inode;
    struct extent_state *cached_state = NULL;
    u64 cur_offset;
    u64 last_byte;
    u64 alloc_start;
    u64 alloc_end;
    u64 alloc_hint = 0;
    u64 locked_end;
    u64 mask = BTRFS_I(inode)->root->sectorsize - 1;
    struct extent_map *em;
    int ret;

    alloc_start = offset & ~mask;
    alloc_end =  (offset + len + mask) & ~mask;

    /* Make sure we aren't being give some crap mode */
    if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
        return -EOPNOTSUPP;

    if (mode & FALLOC_FL_PUNCH_HOLE)
        return btrfs_punch_hole(inode, offset, len);

    /*
     * Make sure we have enough space before we do the
     * allocation.
     */
    ret = btrfs_check_data_free_space(inode, alloc_end - alloc_start + 1);
    if (ret)
        return ret;

    /*
     * wait for ordered IO before we have any locks.  We'll loop again
     * below with the locks held.
     */
    btrfs_wait_ordered_range(inode, alloc_start, alloc_end - alloc_start);

    mutex_lock(&inode->i_mutex);
    ret = inode_newsize_ok(inode, alloc_end);
    if (ret)
        goto out;

    if (alloc_start > inode->i_size) {
        ret = btrfs_cont_expand(inode, i_size_read(inode),
                    alloc_start);
        if (ret)
            goto out;
    }

    locked_end = alloc_end - 1;
    while (1) {
        struct btrfs_ordered_extent *ordered;

        /* the extent lock is ordered inside the running
         * transaction
         */
        lock_extent_bits(&BTRFS_I(inode)->io_tree, alloc_start,
                 locked_end, 0, &cached_state);
        ordered = btrfs_lookup_first_ordered_extent(inode,
                                alloc_end - 1);
        if (ordered &&
            ordered->file_offset + ordered->len > alloc_start &&
            ordered->file_offset < alloc_end) {
            btrfs_put_ordered_extent(ordered);
            unlock_extent_cached(&BTRFS_I(inode)->io_tree,
                         alloc_start, locked_end,
                         &cached_state, GFP_NOFS);
            /*
             * we can't wait on the range with the transaction
             * running or with the extent lock held
             */
            btrfs_wait_ordered_range(inode, alloc_start,
                         alloc_end - alloc_start);
        } else {
            if (ordered)
                btrfs_put_ordered_extent(ordered);
            break;
        }
    }

    cur_offset = alloc_start;
    while (1) {
        u64 actual_end;

        em = btrfs_get_extent(inode, NULL, 0, cur_offset,
                      alloc_end - cur_offset, 0);
        if (IS_ERR_OR_NULL(em)) {
            if (!em)
                ret = -ENOMEM;
            else
                ret = PTR_ERR(em);
            break;
        }
        last_byte = min(extent_map_end(em), alloc_end);
        actual_end = min_t(u64, extent_map_end(em), offset + len);
        last_byte = (last_byte + mask) & ~mask;

        if (em->block_start == EXTENT_MAP_HOLE ||
            (cur_offset >= inode->i_size &&
             !test_bit(EXTENT_FLAG_PREALLOC, &em->flags))) {
            ret = btrfs_prealloc_file_range(inode, mode, cur_offset,
                            last_byte - cur_offset,
                            1 << inode->i_blkbits,
                            offset + len,
                            &alloc_hint);

            if (ret < 0) {
                free_extent_map(em);
                break;
            }
        } else if (actual_end > inode->i_size &&
               !(mode & FALLOC_FL_KEEP_SIZE)) {
            /*
             * We didn't need to allocate any more space, but we
             * still extended the size of the file so we need to
             * update i_size.
             */
            inode->i_ctime = CURRENT_TIME;
            i_size_write(inode, actual_end);
            btrfs_ordered_update_i_size(inode, actual_end, NULL);
        }
        free_extent_map(em);

        cur_offset = last_byte;
        if (cur_offset >= alloc_end) {
            ret = 0;
            break;
        }
    }
    unlock_extent_cached(&BTRFS_I(inode)->io_tree, alloc_start, locked_end,
                 &cached_state, GFP_NOFS);
out:
    mutex_unlock(&inode->i_mutex);
    /* Let go of our reservation. */
    btrfs_free_reserved_data_space(inode, alloc_end - alloc_start + 1);
    return ret;
}

static int find_desired_extent(struct inode *inode, loff_t *offset, int origin)
{
    struct btrfs_root *root = BTRFS_I(inode)->root;
    struct extent_map *em;
    struct extent_state *cached_state = NULL;
    u64 lockstart = *offset;
    u64 lockend = i_size_read(inode);
    u64 start = *offset;
    u64 orig_start = *offset;
    u64 len = i_size_read(inode);
    u64 last_end = 0;
    int ret = 0;

    lockend = max_t(u64, root->sectorsize, lockend);
    if (lockend <= lockstart)
        lockend = lockstart + root->sectorsize;

    len = lockend - lockstart + 1;

    len = max_t(u64, len, root->sectorsize);
    if (inode->i_size == 0)
        return -ENXIO;

    lock_extent_bits(&BTRFS_I(inode)->io_tree, lockstart, lockend, 0,
             &cached_state);

    /*
     * Delalloc is such a pain.  If we have a hole and we have pending
     * delalloc for a portion of the hole we will get back a hole that
     * exists for the entire range since it hasn't been actually written
     * yet.  So to take care of this case we need to look for an extent just
     * before the position we want in case there is outstanding delalloc
     * going on here.
     */
    if (origin == SEEK_HOLE && start != 0) {
        if (start <= root->sectorsize)
            em = btrfs_get_extent_fiemap(inode, NULL, 0, 0,
                             root->sectorsize, 0);
        else
            em = btrfs_get_extent_fiemap(inode, NULL, 0,
                             start - root->sectorsize,
                             root->sectorsize, 0);
        if (IS_ERR(em)) {
            ret = PTR_ERR(em);
            goto out;
        }
        last_end = em->start + em->len;
        if (em->block_start == EXTENT_MAP_DELALLOC)
            last_end = min_t(u64, last_end, inode->i_size);
        free_extent_map(em);
    }

    while (1) {
        em = btrfs_get_extent_fiemap(inode, NULL, 0, start, len, 0);
        if (IS_ERR(em)) {
            ret = PTR_ERR(em);
            break;
        }

        if (em->block_start == EXTENT_MAP_HOLE) {
            if (test_bit(EXTENT_FLAG_VACANCY, &em->flags)) {
                if (last_end <= orig_start) {
                    free_extent_map(em);
                    ret = -ENXIO;
                    break;
                }
            }

            if (origin == SEEK_HOLE) {
                *offset = start;
                free_extent_map(em);
                break;
            }
        } else {
            if (origin == SEEK_DATA) {
                if (em->block_start == EXTENT_MAP_DELALLOC) {
                    if (start >= inode->i_size) {
                        free_extent_map(em);
                        ret = -ENXIO;
                        break;
                    }
                }

                *offset = start;
                free_extent_map(em);
                break;
            }
        }

        start = em->start + em->len;
        last_end = em->start + em->len;

        if (em->block_start == EXTENT_MAP_DELALLOC)
            last_end = min_t(u64, last_end, inode->i_size);

        if (test_bit(EXTENT_FLAG_VACANCY, &em->flags)) {
            free_extent_map(em);
            ret = -ENXIO;
            break;
        }
        free_extent_map(em);
        cond_resched();
    }
    if (!ret)
        *offset = min(*offset, inode->i_size);
out:
    unlock_extent_cached(&BTRFS_I(inode)->io_tree, lockstart, lockend,
                 &cached_state, GFP_NOFS);
    return ret;
}

static loff_t btrfs_file_llseek(struct file *file, loff_t offset, int origin)
{
    struct inode *inode = file->f_mapping->host;
    int ret;

    mutex_lock(&inode->i_mutex);
    switch (origin) {
    case SEEK_END:
    case SEEK_CUR:
        offset = generic_file_llseek(file, offset, origin);
        goto out;
    case SEEK_DATA:
    case SEEK_HOLE:
        if (offset >= i_size_read(inode)) {
            mutex_unlock(&inode->i_mutex);
            return -ENXIO;
        }

        ret = find_desired_extent(inode, &offset, origin);
        if (ret) {
            mutex_unlock(&inode->i_mutex);
            return ret;
        }
    }

    if (offset < 0 && !(file->f_mode & FMODE_UNSIGNED_OFFSET)) {
        offset = -EINVAL;
        goto out;
    }
    if (offset > inode->i_sb->s_maxbytes) {
        offset = -EINVAL;
        goto out;
    }

    /* Special lock needed here? */
    if (offset != file->f_pos) {
        file->f_pos = offset;
        file->f_version = 0;
    }
out:
    mutex_unlock(&inode->i_mutex);
    return offset;
}

const struct file_operations btrfs_file_operations = {
    .llseek     = btrfs_file_llseek,
    .read       = do_sync_read,
    .write      = do_sync_write,
    .aio_read       = generic_file_aio_read,
    .splice_read    = generic_file_splice_read,
    .aio_write  = btrfs_file_aio_write,
    .mmap       = btrfs_file_mmap,
    .open       = generic_file_open,
    .release    = btrfs_release_file,
    .fsync      = btrfs_sync_file,
    .fallocate  = btrfs_fallocate,
    .unlocked_ioctl = btrfs_ioctl,
#ifdef CONFIG_COMPAT
    .compat_ioctl   = btrfs_ioctl,
#endif
};