/*
 * Copyright (c) 2008,2009 NEC Software Tohoku, Ltd.
 * Written by Takashi Sato <t-sato@yk.jp.nec.com>
 *            Akira Fujita <a-fujita@rs.jp.nec.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of version 2.1 of the GNU Lesser General Public License
 * 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.
 */

#include <linux/fs.h>
#include <linux/quotaops.h>
#include <linux/slab.h>
#include "ext4_jbd2.h"
#include "ext4.h"

/**
 * get_ext_path - Find an extent path for designated logical block number.
 *
 * @inode:      an inode which is searched
 * @lblock:     logical block number to find an extent path
 * @path:       pointer to an extent path pointer (for output)
 *
 * ext4_ext_find_extent wrapper. Return 0 on success, or a negative error value
 * on failure.
 */
static inline int
get_ext_path(struct inode *inode, ext4_lblk_t lblock,
                struct ext4_ext_path **path)
{
        int ret = 0;

        *path = ext4_ext_find_extent(inode, lblock, *path);
        if (IS_ERR(*path)) {
                ret = PTR_ERR(*path);
                *path = NULL;
        } else if ((*path)[ext_depth(inode)].p_ext == NULL)
                ret = -ENODATA;

        return ret;
}

/**
 * copy_extent_status - Copy the extent's initialization status
 *
 * @src:        an extent for getting initialize status
 * @dest:       an extent to be set the status
 */
static void
copy_extent_status(struct ext4_extent *src, struct ext4_extent *dest)
{
        if (ext4_ext_is_uninitialized(src))
                ext4_ext_mark_uninitialized(dest);
        else
                dest->ee_len = cpu_to_le16(ext4_ext_get_actual_len(dest));
}

/**
 * mext_next_extent - Search for the next extent and set it to "extent"
 *
 * @inode:      inode which is searched
 * @path:       this will obtain data for the next extent
 * @extent:     pointer to the next extent we have just gotten
 *
 * Search the next extent in the array of ext4_ext_path structure (@path)
 * and set it to ext4_extent structure (@extent). In addition, the member of
 * @path (->p_ext) also points the next extent. Return 0 on success, 1 if
 * ext4_ext_path structure refers to the last extent, or a negative error
 * value on failure.
 */
static int
mext_next_extent(struct inode *inode, struct ext4_ext_path *path,
                      struct ext4_extent **extent)
{
        struct ext4_extent_header *eh;
        int ppos, leaf_ppos = path->p_depth;

        ppos = leaf_ppos;
        if (EXT_LAST_EXTENT(path[ppos].p_hdr) > path[ppos].p_ext) {
                /* leaf block */
                *extent = ++path[ppos].p_ext;
                path[ppos].p_block = ext4_ext_pblock(path[ppos].p_ext);
                return 0;
        }

        while (--ppos >= 0) {
                if (EXT_LAST_INDEX(path[ppos].p_hdr) >
                    path[ppos].p_idx) {
                        int cur_ppos = ppos;

                        /* index block */
                        path[ppos].p_idx++;
                        path[ppos].p_block = ext4_idx_pblock(path[ppos].p_idx);
                        if (path[ppos+1].p_bh)
                                brelse(path[ppos+1].p_bh);
                        path[ppos+1].p_bh =
                                sb_bread(inode->i_sb, path[ppos].p_block);
                        if (!path[ppos+1].p_bh)
                                return -EIO;
                        path[ppos+1].p_hdr =
                                ext_block_hdr(path[ppos+1].p_bh);

                        /* Halfway index block */
                        while (++cur_ppos < leaf_ppos) {
                                path[cur_ppos].p_idx =
                                        EXT_FIRST_INDEX(path[cur_ppos].p_hdr);
                                path[cur_ppos].p_block =
                                        ext4_idx_pblock(path[cur_ppos].p_idx);
                                if (path[cur_ppos+1].p_bh)
                                        brelse(path[cur_ppos+1].p_bh);
                                path[cur_ppos+1].p_bh = sb_bread(inode->i_sb,
                                        path[cur_ppos].p_block);
                                if (!path[cur_ppos+1].p_bh)
                                        return -EIO;
                                path[cur_ppos+1].p_hdr =
                                        ext_block_hdr(path[cur_ppos+1].p_bh);
                        }

                        path[leaf_ppos].p_ext = *extent = NULL;

                        eh = path[leaf_ppos].p_hdr;
                        if (le16_to_cpu(eh->eh_entries) == 0)
                                /* empty leaf is found */
                                return -ENODATA;

                        /* leaf block */
                        path[leaf_ppos].p_ext = *extent =
                                EXT_FIRST_EXTENT(path[leaf_ppos].p_hdr);
                        path[leaf_ppos].p_block =
                                        ext4_ext_pblock(path[leaf_ppos].p_ext);
                        return 0;
                }
        }
        /* We found the last extent */
        return 1;
}

/**
 * double_down_write_data_sem - Acquire two inodes' write lock of i_data_sem
 *
 * Acquire write lock of i_data_sem of the two inodes
 */
static void
double_down_write_data_sem(struct inode *first, struct inode *second)
{
        if (first < second) {
                down_write(&EXT4_I(first)->i_data_sem);
                down_write_nested(&EXT4_I(second)->i_data_sem, SINGLE_DEPTH_NESTING);
        } else {
                down_write(&EXT4_I(second)->i_data_sem);
                down_write_nested(&EXT4_I(first)->i_data_sem, SINGLE_DEPTH_NESTING);

        }
}

/**
 * double_up_write_data_sem - Release two inodes' write lock of i_data_sem
 *
 * @orig_inode:         original inode structure to be released its lock first
 * @donor_inode:        donor inode structure to be released its lock second
 * Release write lock of i_data_sem of two inodes (orig and donor).
 */
static void
double_up_write_data_sem(struct inode *orig_inode, struct inode *donor_inode)
{
        up_write(&EXT4_I(orig_inode)->i_data_sem);
        up_write(&EXT4_I(donor_inode)->i_data_sem);
}

/**
 * mext_insert_across_blocks - Insert extents across leaf block
 *
 * @handle:             journal handle
 * @orig_inode:         original inode
 * @o_start:            first original extent to be changed
 * @o_end:              last original extent to be changed
 * @start_ext:          first new extent to be inserted
 * @new_ext:            middle of new extent to be inserted
 * @end_ext:            last new extent to be inserted
 *
 * Allocate a new leaf block and insert extents into it. Return 0 on success,
 * or a negative error value on failure.
 */
static int
mext_insert_across_blocks(handle_t *handle, struct inode *orig_inode,
                struct ext4_extent *o_start, struct ext4_extent *o_end,
                struct ext4_extent *start_ext, struct ext4_extent *new_ext,
                struct ext4_extent *end_ext)
{
        struct ext4_ext_path *orig_path = NULL;
        ext4_lblk_t eblock = 0;
        int new_flag = 0;
        int end_flag = 0;
        int err = 0;

        if (start_ext->ee_len && new_ext->ee_len && end_ext->ee_len) {
                if (o_start == o_end) {

                        /*       start_ext   new_ext    end_ext
                         * donor |---------|-----------|--------|
                         * orig  |------------------------------|
                         */
                        end_flag = 1;
                } else {

                        /*       start_ext   new_ext   end_ext
                         * donor |---------|----------|---------|
                         * orig  |---------------|--------------|
                         */
                        o_end->ee_block = end_ext->ee_block;
                        o_end->ee_len = end_ext->ee_len;
                        ext4_ext_store_pblock(o_end, ext4_ext_pblock(end_ext));
                }

                o_start->ee_len = start_ext->ee_len;
                eblock = le32_to_cpu(start_ext->ee_block);
                new_flag = 1;

        } else if (start_ext->ee_len && new_ext->ee_len &&
                   !end_ext->ee_len && o_start == o_end) {

                /*       start_ext      new_ext
                 * donor |--------------|---------------|
                 * orig  |------------------------------|
                 */
                o_start->ee_len = start_ext->ee_len;
                eblock = le32_to_cpu(start_ext->ee_block);
                new_flag = 1;

        } else if (!start_ext->ee_len && new_ext->ee_len &&
                   end_ext->ee_len && o_start == o_end) {

                /*        new_ext       end_ext
                 * donor |--------------|---------------|
                 * orig  |------------------------------|
                 */
                o_end->ee_block = end_ext->ee_block;
                o_end->ee_len = end_ext->ee_len;
                ext4_ext_store_pblock(o_end, ext4_ext_pblock(end_ext));

                /*
                 * Set 0 to the extent block if new_ext was
                 * the first block.
                 */
                if (new_ext->ee_block)
                        eblock = le32_to_cpu(new_ext->ee_block);

                new_flag = 1;
        } else {
                ext4_debug("ext4 move extent: Unexpected insert case\n");
                return -EIO;
        }

        if (new_flag) {
                err = get_ext_path(orig_inode, eblock, &orig_path);
                if (err)
                        goto out;

                if (ext4_ext_insert_extent(handle, orig_inode,
                                        orig_path, new_ext, 0))
                        goto out;
        }

        if (end_flag) {
                err = get_ext_path(orig_inode,
                                le32_to_cpu(end_ext->ee_block) - 1, &orig_path);
                if (err)
                        goto out;

                if (ext4_ext_insert_extent(handle, orig_inode,
                                           orig_path, end_ext, 0))
                        goto out;
        }
out:
        if (orig_path) {
                ext4_ext_drop_refs(orig_path);
                kfree(orig_path);
        }

        return err;

}

/**
 * mext_insert_inside_block - Insert new extent to the extent block
 *
 * @o_start:            first original extent to be moved
 * @o_end:              last original extent to be moved
 * @start_ext:          first new extent to be inserted
 * @new_ext:            middle of new extent to be inserted
 * @end_ext:            last new extent to be inserted
 * @eh:                 extent header of target leaf block
 * @range_to_move:      used to decide how to insert extent
 *
 * Insert extents into the leaf block. The extent (@o_start) is overwritten
 * by inserted extents.
 */
static void
mext_insert_inside_block(struct ext4_extent *o_start,
                              struct ext4_extent *o_end,
                              struct ext4_extent *start_ext,
                              struct ext4_extent *new_ext,
                              struct ext4_extent *end_ext,
                              struct ext4_extent_header *eh,
                              int range_to_move)
{
        int i = 0;
        unsigned long len;

        /* Move the existing extents */
        if (range_to_move && o_end < EXT_LAST_EXTENT(eh)) {
                len = (unsigned long)(EXT_LAST_EXTENT(eh) + 1) -
                        (unsigned long)(o_end + 1);
                memmove(o_end + 1 + range_to_move, o_end + 1, len);
        }

        /* Insert start entry */
        if (start_ext->ee_len)
                o_start[i++].ee_len = start_ext->ee_len;

        /* Insert new entry */
        if (new_ext->ee_len) {
                o_start[i] = *new_ext;
                ext4_ext_store_pblock(&o_start[i++], ext4_ext_pblock(new_ext));
        }

        /* Insert end entry */
        if (end_ext->ee_len)
                o_start[i] = *end_ext;

        /* Increment the total entries counter on the extent block */
        le16_add_cpu(&eh->eh_entries, range_to_move);
}

/**
 * mext_insert_extents - Insert new extent
 *
 * @handle:     journal handle
 * @orig_inode: original inode
 * @orig_path:  path indicates first extent to be changed
 * @o_start:    first original extent to be changed
 * @o_end:      last original extent to be changed
 * @start_ext:  first new extent to be inserted
 * @new_ext:    middle of new extent to be inserted
 * @end_ext:    last new extent to be inserted
 *
 * Call the function to insert extents. If we cannot add more extents into
 * the leaf block, we call mext_insert_across_blocks() to create a
 * new leaf block. Otherwise call mext_insert_inside_block(). Return 0
 * on success, or a negative error value on failure.
 */
static int
mext_insert_extents(handle_t *handle, struct inode *orig_inode,
                         struct ext4_ext_path *orig_path,
                         struct ext4_extent *o_start,
                         struct ext4_extent *o_end,
                         struct ext4_extent *start_ext,
                         struct ext4_extent *new_ext,
                         struct ext4_extent *end_ext)
{
        struct  ext4_extent_header *eh;
        unsigned long need_slots, slots_range;
        int     range_to_move, depth, ret;

        /*
         * The extents need to be inserted
         * start_extent + new_extent + end_extent.
         */
        need_slots = (start_ext->ee_len ? 1 : 0) + (end_ext->ee_len ? 1 : 0) +
                (new_ext->ee_len ? 1 : 0);

        /* The number of slots between start and end */
        slots_range = ((unsigned long)(o_end + 1) - (unsigned long)o_start + 1)
                / sizeof(struct ext4_extent);

        /* Range to move the end of extent */
        range_to_move = need_slots - slots_range;
        depth = orig_path->p_depth;
        orig_path += depth;
        eh = orig_path->p_hdr;

        if (depth) {
                /* Register to journal */
                ret = ext4_journal_get_write_access(handle, orig_path->p_bh);
                if (ret)
                        return ret;
        }

        /* Expansion */
        if (range_to_move > 0 &&
                (range_to_move > le16_to_cpu(eh->eh_max)
                        - le16_to_cpu(eh->eh_entries))) {

                ret = mext_insert_across_blocks(handle, orig_inode, o_start,
                                        o_end, start_ext, new_ext, end_ext);
                if (ret < 0)
                        return ret;
        } else
                mext_insert_inside_block(o_start, o_end, start_ext, new_ext,
                                                end_ext, eh, range_to_move);

        if (depth) {
                ret = ext4_handle_dirty_metadata(handle, orig_inode,
                                                 orig_path->p_bh);
                if (ret)
                        return ret;
        } else {
                ret = ext4_mark_inode_dirty(handle, orig_inode);
                if (ret < 0)
                        return ret;
        }

        return 0;
}

/**
 * mext_leaf_block - Move one leaf extent block into the inode.
 *
 * @handle:             journal handle
 * @orig_inode:         original inode
 * @orig_path:          path indicates first extent to be changed
 * @dext:               donor extent
 * @from:               start offset on the target file
 *
 * In order to insert extents into the leaf block, we must divide the extent
 * in the leaf block into three extents. The one is located to be inserted
 * extents, and the others are located around it.
 *
 * Therefore, this function creates structures to save extents of the leaf
 * block, and inserts extents by calling mext_insert_extents() with
 * created extents. Return 0 on success, or a negative error value on failure.
 */
static int
mext_leaf_block(handle_t *handle, struct inode *orig_inode,
                     struct ext4_ext_path *orig_path, struct ext4_extent *dext,
                     ext4_lblk_t *from)
{
        struct ext4_extent *oext, *o_start, *o_end, *prev_ext;
        struct ext4_extent new_ext, start_ext, end_ext;
        ext4_lblk_t new_ext_end;
        int oext_alen, new_ext_alen, end_ext_alen;
        int depth = ext_depth(orig_inode);
        int ret;

        start_ext.ee_block = end_ext.ee_block = 0;
        o_start = o_end = oext = orig_path[depth].p_ext;
        oext_alen = ext4_ext_get_actual_len(oext);
        start_ext.ee_len = end_ext.ee_len = 0;

        new_ext.ee_block = cpu_to_le32(*from);
        ext4_ext_store_pblock(&new_ext, ext4_ext_pblock(dext));
        new_ext.ee_len = dext->ee_len;
        new_ext_alen = ext4_ext_get_actual_len(&new_ext);
        new_ext_end = le32_to_cpu(new_ext.ee_block) + new_ext_alen - 1;

        /*
         * Case: original extent is first
         * oext      |--------|
         * new_ext      |--|
         * start_ext |--|
         */
        if (le32_to_cpu(oext->ee_block) < le32_to_cpu(new_ext.ee_block) &&
                le32_to_cpu(new_ext.ee_block) <
                le32_to_cpu(oext->ee_block) + oext_alen) {
                start_ext.ee_len = cpu_to_le16(le32_to_cpu(new_ext.ee_block) -
                                               le32_to_cpu(oext->ee_block));
                start_ext.ee_block = oext->ee_block;
                copy_extent_status(oext, &start_ext);
        } else if (oext > EXT_FIRST_EXTENT(orig_path[depth].p_hdr)) {
                prev_ext = oext - 1;
                /*
                 * We can merge new_ext into previous extent,
                 * if these are contiguous and same extent type.
                 */
                if (ext4_can_extents_be_merged(orig_inode, prev_ext,
                                               &new_ext)) {
                        o_start = prev_ext;
                        start_ext.ee_len = cpu_to_le16(
                                ext4_ext_get_actual_len(prev_ext) +
                                new_ext_alen);
                        start_ext.ee_block = oext->ee_block;
                        copy_extent_status(prev_ext, &start_ext);
                        new_ext.ee_len = 0;
                }
        }

        /*
         * Case: new_ext_end must be less than oext
         * oext      |-----------|
         * new_ext       |-------|
         */
        if (le32_to_cpu(oext->ee_block) + oext_alen - 1 < new_ext_end) {
                EXT4_ERROR_INODE(orig_inode,
                        "new_ext_end(%u) should be less than or equal to "
                        "oext->ee_block(%u) + oext_alen(%d) - 1",
                        new_ext_end, le32_to_cpu(oext->ee_block),
                        oext_alen);
                ret = -EIO;
                goto out;
        }

        /*
         * Case: new_ext is smaller than original extent
         * oext    |---------------|
         * new_ext |-----------|
         * end_ext             |---|
         */
        if (le32_to_cpu(oext->ee_block) <= new_ext_end &&
                new_ext_end < le32_to_cpu(oext->ee_block) + oext_alen - 1) {
                end_ext.ee_len =
                        cpu_to_le16(le32_to_cpu(oext->ee_block) +
                        oext_alen - 1 - new_ext_end);
                copy_extent_status(oext, &end_ext);
                end_ext_alen = ext4_ext_get_actual_len(&end_ext);
                ext4_ext_store_pblock(&end_ext,
                        (ext4_ext_pblock(o_end) + oext_alen - end_ext_alen));
                end_ext.ee_block =
                        cpu_to_le32(le32_to_cpu(o_end->ee_block) +
                        oext_alen - end_ext_alen);
        }

        ret = mext_insert_extents(handle, orig_inode, orig_path, o_start,
                                o_end, &start_ext, &new_ext, &end_ext);
out:
        return ret;
}

/**
 * mext_calc_swap_extents - Calculate extents for extent swapping.
 *
 * @tmp_dext:           the extent that will belong to the original inode
 * @tmp_oext:           the extent that will belong to the donor inode
 * @orig_off:           block offset of original inode
 * @donor_off:          block offset of donor inode
 * @max_count:          the maximum length of extents
 *
 * Return 0 on success, or a negative error value on failure.
 */
static int
mext_calc_swap_extents(struct ext4_extent *tmp_dext,
                              struct ext4_extent *tmp_oext,
                              ext4_lblk_t orig_off, ext4_lblk_t donor_off,
                              ext4_lblk_t max_count)
{
        ext4_lblk_t diff, orig_diff;
        struct ext4_extent dext_old, oext_old;

        BUG_ON(orig_off != donor_off);

        /* original and donor extents have to cover the same block offset */
        if (orig_off < le32_to_cpu(tmp_oext->ee_block) ||
            le32_to_cpu(tmp_oext->ee_block) +
                        ext4_ext_get_actual_len(tmp_oext) - 1 < orig_off)
                return -ENODATA;

        if (orig_off < le32_to_cpu(tmp_dext->ee_block) ||
            le32_to_cpu(tmp_dext->ee_block) +
                        ext4_ext_get_actual_len(tmp_dext) - 1 < orig_off)
                return -ENODATA;

        dext_old = *tmp_dext;
        oext_old = *tmp_oext;

        /* When tmp_dext is too large, pick up the target range. */
        diff = donor_off - le32_to_cpu(tmp_dext->ee_block);

        ext4_ext_store_pblock(tmp_dext, ext4_ext_pblock(tmp_dext) + diff);
        tmp_dext->ee_block =
                        cpu_to_le32(le32_to_cpu(tmp_dext->ee_block) + diff);
        tmp_dext->ee_len = cpu_to_le16(le16_to_cpu(tmp_dext->ee_len) - diff);

        if (max_count < ext4_ext_get_actual_len(tmp_dext))
                tmp_dext->ee_len = cpu_to_le16(max_count);

        orig_diff = orig_off - le32_to_cpu(tmp_oext->ee_block);
        ext4_ext_store_pblock(tmp_oext, ext4_ext_pblock(tmp_oext) + orig_diff);

        /* Adjust extent length if donor extent is larger than orig */
        if (ext4_ext_get_actual_len(tmp_dext) >
            ext4_ext_get_actual_len(tmp_oext) - orig_diff)
                tmp_dext->ee_len = cpu_to_le16(le16_to_cpu(tmp_oext->ee_len) -
                                                orig_diff);

        tmp_oext->ee_len = cpu_to_le16(ext4_ext_get_actual_len(tmp_dext));

        copy_extent_status(&oext_old, tmp_dext);
        copy_extent_status(&dext_old, tmp_oext);

        return 0;
}

/**
 * mext_replace_branches - Replace original extents with new extents
 *
 * @handle:             journal handle
 * @orig_inode:         original inode
 * @donor_inode:        donor inode
 * @from:               block offset of orig_inode
 * @count:              block count to be replaced
 * @err:                pointer to save return value
 *
 * Replace original inode extents and donor inode extents page by page.
 * We implement this replacement in the following three steps:
 * 1. Save the block information of original and donor inodes into
 *    dummy extents.
 * 2. Change the block information of original inode to point at the
 *    donor inode blocks.
 * 3. Change the block information of donor inode to point at the saved
 *    original inode blocks in the dummy extents.
 *
 * Return replaced block count.
 */
static int
mext_replace_branches(handle_t *handle, struct inode *orig_inode,
                           struct inode *donor_inode, ext4_lblk_t from,
                           ext4_lblk_t count, int *err)
{
        struct ext4_ext_path *orig_path = NULL;
        struct ext4_ext_path *donor_path = NULL;
        struct ext4_extent *oext, *dext;
        struct ext4_extent tmp_dext, tmp_oext;
        ext4_lblk_t orig_off = from, donor_off = from;
        int depth;
        int replaced_count = 0;
        int dext_alen;

        /* Protect extent trees against block allocations via delalloc */
        double_down_write_data_sem(orig_inode, donor_inode);

        /* Get the original extent for the block "orig_off" */
        *err = get_ext_path(orig_inode, orig_off, &orig_path);
        if (*err)
                goto out;

        /* Get the donor extent for the head */
        *err = get_ext_path(donor_inode, donor_off, &donor_path);
        if (*err)
                goto out;
        depth = ext_depth(orig_inode);
        oext = orig_path[depth].p_ext;
        tmp_oext = *oext;

        depth = ext_depth(donor_inode);
        dext = donor_path[depth].p_ext;
        tmp_dext = *dext;

        *err = mext_calc_swap_extents(&tmp_dext, &tmp_oext, orig_off,
                                      donor_off, count);
        if (*err)
                goto out;

        /* Loop for the donor extents */
        while (1) {
                /* The extent for donor must be found. */
                if (!dext) {
                        EXT4_ERROR_INODE(donor_inode,
                                   "The extent for donor must be found");
                        *err = -EIO;
                        goto out;
                } else if (donor_off != le32_to_cpu(tmp_dext.ee_block)) {
                        EXT4_ERROR_INODE(donor_inode,
                                "Donor offset(%u) and the first block of donor "
                                "extent(%u) should be equal",
                                donor_off,
                                le32_to_cpu(tmp_dext.ee_block));
                        *err = -EIO;
                        goto out;
                }

                /* Set donor extent to orig extent */
                *err = mext_leaf_block(handle, orig_inode,
                                           orig_path, &tmp_dext, &orig_off);
                if (*err)
                        goto out;

                /* Set orig extent to donor extent */
                *err = mext_leaf_block(handle, donor_inode,
                                           donor_path, &tmp_oext, &donor_off);
                if (*err)
                        goto out;

                dext_alen = ext4_ext_get_actual_len(&tmp_dext);
                replaced_count += dext_alen;
                donor_off += dext_alen;
                orig_off += dext_alen;

                /* Already moved the expected blocks */
                if (replaced_count >= count)
                        break;

                if (orig_path)
                        ext4_ext_drop_refs(orig_path);
                *err = get_ext_path(orig_inode, orig_off, &orig_path);
                if (*err)
                        goto out;
                depth = ext_depth(orig_inode);
                oext = orig_path[depth].p_ext;
                tmp_oext = *oext;

                if (donor_path)
                        ext4_ext_drop_refs(donor_path);
                *err = get_ext_path(donor_inode, donor_off, &donor_path);
                if (*err)
                        goto out;
                depth = ext_depth(donor_inode);
                dext = donor_path[depth].p_ext;
                tmp_dext = *dext;

                *err = mext_calc_swap_extents(&tmp_dext, &tmp_oext, orig_off,
                                           donor_off, count - replaced_count);
                if (*err)
                        goto out;
        }

out:
        if (orig_path) {
                ext4_ext_drop_refs(orig_path);
                kfree(orig_path);
        }
        if (donor_path) {
                ext4_ext_drop_refs(donor_path);
                kfree(donor_path);
        }

        ext4_ext_invalidate_cache(orig_inode);
        ext4_ext_invalidate_cache(donor_inode);

        double_up_write_data_sem(orig_inode, donor_inode);

        return replaced_count;
}

/**
 * move_extent_per_page - Move extent data per page
 *
 * @o_filp:                     file structure of original file
 * @donor_inode:                donor inode
 * @orig_page_offset:           page index on original file
 * @data_offset_in_page:        block index where data swapping starts
 * @block_len_in_page:          the number of blocks to be swapped
 * @uninit:                     orig extent is uninitialized or not
 * @err:                        pointer to save return value
 *
 * Save the data in original inode blocks and replace original inode extents
 * with donor inode extents by calling mext_replace_branches().
 * Finally, write out the saved data in new original inode blocks. Return
 * replaced block count.
 */
static int
move_extent_per_page(struct file *o_filp, struct inode *donor_inode,
                  pgoff_t orig_page_offset, int data_offset_in_page,
                  int block_len_in_page, int uninit, int *err)
{
        struct inode *orig_inode = o_filp->f_dentry->d_inode;
        struct address_space *mapping = orig_inode->i_mapping;
        struct buffer_head *bh;
        struct page *page = NULL;
        const struct address_space_operations *a_ops = mapping->a_ops;
        handle_t *handle;
        ext4_lblk_t orig_blk_offset;
        long long offs = orig_page_offset << PAGE_CACHE_SHIFT;
        unsigned long blocksize = orig_inode->i_sb->s_blocksize;
        unsigned int w_flags = 0;
        unsigned int tmp_data_size, data_size, replaced_size;
        void *fsdata;
        int i, jblocks;
        int err2 = 0;
        int replaced_count = 0;
        int blocks_per_page = PAGE_CACHE_SIZE >> orig_inode->i_blkbits;

        /*
         * It needs twice the amount of ordinary journal buffers because
         * inode and donor_inode may change each different metadata blocks.
         */
        jblocks = ext4_writepage_trans_blocks(orig_inode) * 2;
        handle = ext4_journal_start(orig_inode, jblocks);
        if (IS_ERR(handle)) {
                *err = PTR_ERR(handle);
                return 0;
        }

        if (segment_eq(get_fs(), KERNEL_DS))
                w_flags |= AOP_FLAG_UNINTERRUPTIBLE;

        orig_blk_offset = orig_page_offset * blocks_per_page +
                data_offset_in_page;

        /*
         * If orig extent is uninitialized one,
         * it's not necessary force the page into memory
         * and then force it to be written out again.
         * Just swap data blocks between orig and donor.
         */
        if (uninit) {
                replaced_count = mext_replace_branches(handle, orig_inode,
                                                donor_inode, orig_blk_offset,
                                                block_len_in_page, err);
                goto out2;
        }

        offs = (long long)orig_blk_offset << orig_inode->i_blkbits;

        /* Calculate data_size */
        if ((orig_blk_offset + block_len_in_page - 1) ==
            ((orig_inode->i_size - 1) >> orig_inode->i_blkbits)) {
                /* Replace the last block */
                tmp_data_size = orig_inode->i_size & (blocksize - 1);
                /*
                 * If data_size equal zero, it shows data_size is multiples of
                 * blocksize. So we set appropriate value.
                 */
                if (tmp_data_size == 0)
                        tmp_data_size = blocksize;

                data_size = tmp_data_size +
                        ((block_len_in_page - 1) << orig_inode->i_blkbits);
        } else
                data_size = block_len_in_page << orig_inode->i_blkbits;

        replaced_size = data_size;

        *err = a_ops->write_begin(o_filp, mapping, offs, data_size, w_flags,
                                 &page, &fsdata);
        if (unlikely(*err < 0))
                goto out;

        if (!PageUptodate(page)) {
                mapping->a_ops->readpage(o_filp, page);
                lock_page(page);
        }

        /*
         * try_to_release_page() doesn't call releasepage in writeback mode.
         * We should care about the order of writing to the same file
         * by multiple move extent processes.
         * It needs to call wait_on_page_writeback() to wait for the
         * writeback of the page.
         */
        wait_on_page_writeback(page);

        /* Release old bh and drop refs */
        try_to_release_page(page, 0);

        replaced_count = mext_replace_branches(handle, orig_inode, donor_inode,
                                        orig_blk_offset, block_len_in_page,
                                        &err2);
        if (err2) {
                if (replaced_count) {
                        block_len_in_page = replaced_count;
                        replaced_size =
                                block_len_in_page << orig_inode->i_blkbits;
                } else
                        goto out;
        }

        if (!page_has_buffers(page))
                create_empty_buffers(page, 1 << orig_inode->i_blkbits, 0);

        bh = page_buffers(page);
        for (i = 0; i < data_offset_in_page; i++)
                bh = bh->b_this_page;

        for (i = 0; i < block_len_in_page; i++) {
                *err = ext4_get_block(orig_inode,
                                (sector_t)(orig_blk_offset + i), bh, 0);
                if (*err < 0)
                        goto out;

                if (bh->b_this_page != NULL)
                        bh = bh->b_this_page;
        }

        *err = a_ops->write_end(o_filp, mapping, offs, data_size, replaced_size,
                               page, fsdata);
        page = NULL;

out:
        if (unlikely(page)) {
                if (PageLocked(page))
                        unlock_page(page);
                page_cache_release(page);
                ext4_journal_stop(handle);
        }
out2:
        ext4_journal_stop(handle);

        if (err2)
                *err = err2;

        return replaced_count;
}

/**
 * mext_check_arguments - Check whether move extent can be done
 *
 * @orig_inode:         original inode
 * @donor_inode:        donor inode
 * @orig_start:         logical start offset in block for orig
 * @donor_start:        logical start offset in block for donor
 * @len:                the number of blocks to be moved
 *
 * Check the arguments of ext4_move_extents() whether the files can be
 * exchanged with each other.
 * Return 0 on success, or a negative error value on failure.
 */
static int
mext_check_arguments(struct inode *orig_inode,
                     struct inode *donor_inode, __u64 orig_start,
                     __u64 donor_start, __u64 *len)
{
        ext4_lblk_t orig_blocks, donor_blocks;
        unsigned int blkbits = orig_inode->i_blkbits;
        unsigned int blocksize = 1 << blkbits;

        if (donor_inode->i_mode & (S_ISUID|S_ISGID)) {
                ext4_debug("ext4 move extent: suid or sgid is set"
                           " to donor file [ino:orig %lu, donor %lu]\n",
                           orig_inode->i_ino, donor_inode->i_ino);
                return -EINVAL;
        }

        if (IS_IMMUTABLE(donor_inode) || IS_APPEND(donor_inode))
                return -EPERM;

        /* Ext4 move extent does not support swapfile */
        if (IS_SWAPFILE(orig_inode) || IS_SWAPFILE(donor_inode)) {
                ext4_debug("ext4 move extent: The argument files should "
                        "not be swapfile [ino:orig %lu, donor %lu]\n",
                        orig_inode->i_ino, donor_inode->i_ino);
                return -EINVAL;
        }

        /* Ext4 move extent supports only extent based file */
        if (!(ext4_test_inode_flag(orig_inode, EXT4_INODE_EXTENTS))) {
                ext4_debug("ext4 move extent: orig file is not extents "
                        "based file [ino:orig %lu]\n", orig_inode->i_ino);
                return -EOPNOTSUPP;
        } else if (!(ext4_test_inode_flag(donor_inode, EXT4_INODE_EXTENTS))) {
                ext4_debug("ext4 move extent: donor file is not extents "
                        "based file [ino:donor %lu]\n", donor_inode->i_ino);
                return -EOPNOTSUPP;
        }

        if ((!orig_inode->i_size) || (!donor_inode->i_size)) {
                ext4_debug("ext4 move extent: File size is 0 byte\n");
                return -EINVAL;
        }

        /* Start offset should be same */
        if (orig_start != donor_start) {
                ext4_debug("ext4 move extent: orig and donor's start "
                        "offset are not same [ino:orig %lu, donor %lu]\n",
                        orig_inode->i_ino, donor_inode->i_ino);
                return -EINVAL;
        }

        if ((orig_start >= EXT_MAX_BLOCKS) ||
            (donor_start >= EXT_MAX_BLOCKS) ||
            (*len > EXT_MAX_BLOCKS) ||
            (orig_start + *len >= EXT_MAX_BLOCKS))  {
                ext4_debug("ext4 move extent: Can't handle over [%u] blocks "
                        "[ino:orig %lu, donor %lu]\n", EXT_MAX_BLOCKS,
                        orig_inode->i_ino, donor_inode->i_ino);
                return -EINVAL;
        }

        if (orig_inode->i_size > donor_inode->i_size) {
                donor_blocks = (donor_inode->i_size + blocksize - 1) >> blkbits;
                /* TODO: eliminate this artificial restriction */
                if (orig_start >= donor_blocks) {
                        ext4_debug("ext4 move extent: orig start offset "
                        "[%llu] should be less than donor file blocks "
                        "[%u] [ino:orig %lu, donor %lu]\n",
                        orig_start, donor_blocks,
                        orig_inode->i_ino, donor_inode->i_ino);
                        return -EINVAL;
                }

                /* TODO: eliminate this artificial restriction */
                if (orig_start + *len > donor_blocks) {
                        ext4_debug("ext4 move extent: End offset [%llu] should "
                                "be less than donor file blocks [%u]."
                                "So adjust length from %llu to %llu "
                                "[ino:orig %lu, donor %lu]\n",
                                orig_start + *len, donor_blocks,
                                *len, donor_blocks - orig_start,
                                orig_inode->i_ino, donor_inode->i_ino);
                        *len = donor_blocks - orig_start;
                }
        } else {
                orig_blocks = (orig_inode->i_size + blocksize - 1) >> blkbits;
                if (orig_start >= orig_blocks) {
                        ext4_debug("ext4 move extent: start offset [%llu] "
                                "should be less than original file blocks "
                                "[%u] [ino:orig %lu, donor %lu]\n",

                                 orig_start, orig_blocks,
                                orig_inode->i_ino, donor_inode->i_ino);
                        return -EINVAL;
                }

                if (orig_start + *len > orig_blocks) {
                        ext4_debug("ext4 move extent: Adjust length "
                                "from %llu to %llu. Because it should be "
                                "less than original file blocks "
                                "[ino:orig %lu, donor %lu]\n",
                                *len, orig_blocks - orig_start,
                                orig_inode->i_ino, donor_inode->i_ino);
                        *len = orig_blocks - orig_start;
                }
        }

        if (!*len) {
                ext4_debug("ext4 move extent: len should not be 0 "
                        "[ino:orig %lu, donor %lu]\n", orig_inode->i_ino,
                        donor_inode->i_ino);
                return -EINVAL;
        }

        return 0;
}

/**
 * mext_inode_double_lock - Lock i_mutex on both @inode1 and @inode2
 *
 * @inode1:     the inode structure
 * @inode2:     the inode structure
 *
 * Lock two inodes' i_mutex
 */
static void
mext_inode_double_lock(struct inode *inode1, struct inode *inode2)
{
        BUG_ON(inode1 == inode2);
        if (inode1 < inode2) {
                mutex_lock_nested(&inode1->i_mutex, I_MUTEX_PARENT);
                mutex_lock_nested(&inode2->i_mutex, I_MUTEX_CHILD);
        } else {
                mutex_lock_nested(&inode2->i_mutex, I_MUTEX_PARENT);
                mutex_lock_nested(&inode1->i_mutex, I_MUTEX_CHILD);
        }
}

/**
 * mext_inode_double_unlock - Release i_mutex on both @inode1 and @inode2
 *
 * @inode1:     the inode that is released first
 * @inode2:     the inode that is released second
 *
 */

static void
mext_inode_double_unlock(struct inode *inode1, struct inode *inode2)
{
        mutex_unlock(&inode1->i_mutex);
        mutex_unlock(&inode2->i_mutex);
}

/**
 * ext4_move_extents - Exchange the specified range of a file
 *
 * @o_filp:             file structure of the original file
 * @d_filp:             file structure of the donor file
 * @orig_start:         start offset in block for orig
 * @donor_start:        start offset in block for donor
 * @len:                the number of blocks to be moved
 * @moved_len:          moved block length
 *
 * This function returns 0 and moved block length is set in moved_len
 * if succeed, otherwise returns error value.
 *
 * Note: ext4_move_extents() proceeds the following order.
 * 1:ext4_move_extents() calculates the last block number of moving extent
 *   function by the start block number (orig_start) and the number of blocks
 *   to be moved (len) specified as arguments.
 *   If the {orig, donor}_start points a hole, the extent's start offset
 *   pointed by ext_cur (current extent), holecheck_path, orig_path are set
 *   after hole behind.
 * 2:Continue step 3 to step 5, until the holecheck_path points to last_extent
 *   or the ext_cur exceeds the block_end which is last logical block number.
 * 3:To get the length of continues area, call mext_next_extent()
 *   specified with the ext_cur (initial value is holecheck_path) re-cursive,
 *   until find un-continuous extent, the start logical block number exceeds
 *   the block_end or the extent points to the last extent.
 * 4:Exchange the original inode data with donor inode data
 *   from orig_page_offset to seq_end_page.
 *   The start indexes of data are specified as arguments.
 *   That of the original inode is orig_page_offset,
 *   and the donor inode is also orig_page_offset
 *   (To easily handle blocksize != pagesize case, the offset for the
 *   donor inode is block unit).
 * 5:Update holecheck_path and orig_path to points a next proceeding extent,
 *   then returns to step 2.
 * 6:Release holecheck_path, orig_path and set the len to moved_len
 *   which shows the number of moved blocks.
 *   The moved_len is useful for the command to calculate the file offset
 *   for starting next move extent ioctl.
 * 7:Return 0 on success, or a negative error value on failure.
 */
int
ext4_move_extents(struct file *o_filp, struct file *d_filp,
                 __u64 orig_start, __u64 donor_start, __u64 len,
                 __u64 *moved_len)
{
        struct inode *orig_inode = o_filp->f_dentry->d_inode;
        struct inode *donor_inode = d_filp->f_dentry->d_inode;
        struct ext4_ext_path *orig_path = NULL, *holecheck_path = NULL;
        struct ext4_extent *ext_prev, *ext_cur, *ext_dummy;
        ext4_lblk_t block_start = orig_start;
        ext4_lblk_t block_end, seq_start, add_blocks, file_end, seq_blocks = 0;
        ext4_lblk_t rest_blocks;
        pgoff_t orig_page_offset = 0, seq_end_page;
        int ret, depth, last_extent = 0;
        int blocks_per_page = PAGE_CACHE_SIZE >> orig_inode->i_blkbits;
        int data_offset_in_page;
        int block_len_in_page;
        int uninit;

        if (orig_inode->i_sb != donor_inode->i_sb) {
                ext4_debug("ext4 move extent: The argument files "
                        "should be in same FS [ino:orig %lu, donor %lu]\n",
                        orig_inode->i_ino, donor_inode->i_ino);
                return -EINVAL;
        }

        /* orig and donor should be different inodes */
        if (orig_inode == donor_inode) {
                ext4_debug("ext4 move extent: The argument files should not "
                        "be same inode [ino:orig %lu, donor %lu]\n",
                        orig_inode->i_ino, donor_inode->i_ino);
                return -EINVAL;
        }

        /* Regular file check */
        if (!S_ISREG(orig_inode->i_mode) || !S_ISREG(donor_inode->i_mode)) {
                ext4_debug("ext4 move extent: The argument files should be "
                        "regular file [ino:orig %lu, donor %lu]\n",
                        orig_inode->i_ino, donor_inode->i_ino);
                return -EINVAL;
        }
        /* TODO: This is non obvious task to swap blocks for inodes with full
           jornaling enabled */
        if (ext4_should_journal_data(orig_inode) ||
            ext4_should_journal_data(donor_inode)) {
                return -EINVAL;
        }
        /* Protect orig and donor inodes against a truncate */
        mext_inode_double_lock(orig_inode, donor_inode);

        /* Protect extent tree against block allocations via delalloc */
        double_down_write_data_sem(orig_inode, donor_inode);
        /* Check the filesystem environment whether move_extent can be done */
        ret = mext_check_arguments(orig_inode, donor_inode, orig_start,
                                    donor_start, &len);
        if (ret)
                goto out;

        file_end = (i_size_read(orig_inode) - 1) >> orig_inode->i_blkbits;
        block_end = block_start + len - 1;
        if (file_end < block_end)
                len -= block_end - file_end;

        ret = get_ext_path(orig_inode, block_start, &orig_path);
        if (ret)
                goto out;

        /* Get path structure to check the hole */
        ret = get_ext_path(orig_inode, block_start, &holecheck_path);
        if (ret)
                goto out;

        depth = ext_depth(orig_inode);
        ext_cur = holecheck_path[depth].p_ext;

        /*
         * Get proper starting location of block replacement if block_start was
         * within the hole.
         */
        if (le32_to_cpu(ext_cur->ee_block) +
                ext4_ext_get_actual_len(ext_cur) - 1 < block_start) {
                /*
                 * The hole exists between extents or the tail of
                 * original file.
                 */
                last_extent = mext_next_extent(orig_inode,
                                        holecheck_path, &ext_cur);
                if (last_extent < 0) {
                        ret = last_extent;
                        goto out;
                }
                last_extent = mext_next_extent(orig_inode, orig_path,
                                                        &ext_dummy);
                if (last_extent < 0) {
                        ret = last_extent;
                        goto out;
                }
                seq_start = le32_to_cpu(ext_cur->ee_block);
        } else if (le32_to_cpu(ext_cur->ee_block) > block_start)
                /* The hole exists at the beginning of original file. */
                seq_start = le32_to_cpu(ext_cur->ee_block);
        else
                seq_start = block_start;

        /* No blocks within the specified range. */
        if (le32_to_cpu(ext_cur->ee_block) > block_end) {
                ext4_debug("ext4 move extent: The specified range of file "
                                                        "may be the hole\n");
                ret = -EINVAL;
                goto out;
        }

        /* Adjust start blocks */
        add_blocks = min(le32_to_cpu(ext_cur->ee_block) +
                         ext4_ext_get_actual_len(ext_cur), block_end + 1) -
                     max(le32_to_cpu(ext_cur->ee_block), block_start);

        while (!last_extent && le32_to_cpu(ext_cur->ee_block) <= block_end) {
                seq_blocks += add_blocks;

                /* Adjust tail blocks */
                if (seq_start + seq_blocks - 1 > block_end)
                        seq_blocks = block_end - seq_start + 1;

                ext_prev = ext_cur;
                last_extent = mext_next_extent(orig_inode, holecheck_path,
                                                &ext_cur);
                if (last_extent < 0) {
                        ret = last_extent;
                        break;
                }
                add_blocks = ext4_ext_get_actual_len(ext_cur);

                /*
                 * Extend the length of contiguous block (seq_blocks)
                 * if extents are contiguous.
                 */
                if (ext4_can_extents_be_merged(orig_inode,
                                               ext_prev, ext_cur) &&
                    block_end >= le32_to_cpu(ext_cur->ee_block) &&
                    !last_extent)
                        continue;

                /* Is original extent is uninitialized */
                uninit = ext4_ext_is_uninitialized(ext_prev);

                data_offset_in_page = seq_start % blocks_per_page;

                /*
                 * Calculate data blocks count that should be swapped
                 * at the first page.
                 */
                if (data_offset_in_page + seq_blocks > blocks_per_page) {
                        /* Swapped blocks are across pages */
                        block_len_in_page =
                                        blocks_per_page - data_offset_in_page;
                } else {
                        /* Swapped blocks are in a page */
                        block_len_in_page = seq_blocks;
                }

                orig_page_offset = seq_start >>
                                (PAGE_CACHE_SHIFT - orig_inode->i_blkbits);
                seq_end_page = (seq_start + seq_blocks - 1) >>
                                (PAGE_CACHE_SHIFT - orig_inode->i_blkbits);
                seq_start = le32_to_cpu(ext_cur->ee_block);
                rest_blocks = seq_blocks;

                /*
                 * Up semaphore to avoid following problems:
                 * a. transaction deadlock among ext4_journal_start,
                 *    ->write_begin via pagefault, and jbd2_journal_commit
                 * b. racing with ->readpage, ->write_begin, and ext4_get_block
                 *    in move_extent_per_page
                 */
                double_up_write_data_sem(orig_inode, donor_inode);

                while (orig_page_offset <= seq_end_page) {

                        /* Swap original branches with new branches */
                        block_len_in_page = move_extent_per_page(
                                                o_filp, donor_inode,
                                                orig_page_offset,
                                                data_offset_in_page,
                                                block_len_in_page, uninit,
                                                &ret);

                        /* Count how many blocks we have exchanged */
                        *moved_len += block_len_in_page;
                        if (ret < 0)
                                break;
                        if (*moved_len > len) {
                                EXT4_ERROR_INODE(orig_inode,
                                        "We replaced blocks too much! "
                                        "sum of replaced: %llu requested: %llu",
                                        *moved_len, len);
                                ret = -EIO;
                                break;
                        }

                        orig_page_offset++;
                        data_offset_in_page = 0;
                        rest_blocks -= block_len_in_page;
                        if (rest_blocks > blocks_per_page)
                                block_len_in_page = blocks_per_page;
                        else
                                block_len_in_page = rest_blocks;
                }

                double_down_write_data_sem(orig_inode, donor_inode);
                if (ret < 0)
                        break;

                /* Decrease buffer counter */
                if (holecheck_path)
                        ext4_ext_drop_refs(holecheck_path);
                ret = get_ext_path(orig_inode, seq_start, &holecheck_path);
                if (ret)
                        break;
                depth = holecheck_path->p_depth;

                /* Decrease buffer counter */
                if (orig_path)
                        ext4_ext_drop_refs(orig_path);
                ret = get_ext_path(orig_inode, seq_start, &orig_path);
                if (ret)
                        break;

                ext_cur = holecheck_path[depth].p_ext;
                add_blocks = ext4_ext_get_actual_len(ext_cur);
                seq_blocks = 0;

        }
out:
        if (*moved_len) {
                ext4_discard_preallocations(orig_inode);
                ext4_discard_preallocations(donor_inode);
        }

        if (orig_path) {
                ext4_ext_drop_refs(orig_path);
                kfree(orig_path);
        }
        if (holecheck_path) {
                ext4_ext_drop_refs(holecheck_path);
                kfree(holecheck_path);
        }
        double_up_write_data_sem(orig_inode, donor_inode);
        mext_inode_double_unlock(orig_inode, donor_inode);

        return ret;
}