ext4: allow a NULL argument to ext4_ext_drop_refs()

[deliverable/linux.git] / fs / ext4 / move_extent.c

/*
 * 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"
#include "ext4_extents.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 **orig_path)
{
        int ret = 0;
        struct ext4_ext_path *path;

        path = ext4_ext_find_extent(inode, lblock, orig_path, EXT4_EX_NOCACHE);
        if (IS_ERR(path))
                ret = PTR_ERR(path);
        else if (path[ext_depth(inode)].p_ext == NULL)
                ret = -ENODATA;
        else
                *orig_path = path;

        return ret;
}

/**
 * ext4_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
 */
void
ext4_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);

        }
}

/**
 * ext4_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).
 */
void
ext4_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_check_coverage - Check that all extents in range has the same type
 *
 * @inode:              inode in question
 * @from:               block offset of inode
 * @count:              block count to be checked
 * @unwritten:          extents expected to be unwritten
 * @err:                pointer to save error value
 *
 * Return 1 if all extents in range has expected type, and zero otherwise.
 */
static int
mext_check_coverage(struct inode *inode, ext4_lblk_t from, ext4_lblk_t count,
                    int unwritten, int *err)
{
        struct ext4_ext_path *path = NULL;
        struct ext4_extent *ext;
        int ret = 0;
        ext4_lblk_t last = from + count;
        while (from < last) {
                *err = get_ext_path(inode, from, &path);
                if (*err)
                        goto out;
                ext = path[ext_depth(inode)].p_ext;
                if (unwritten != ext4_ext_is_unwritten(ext))
                        goto out;
                from += ext4_ext_get_actual_len(ext);
                ext4_ext_drop_refs(path);
        }
        ret = 1;
out:
        ext4_ext_drop_refs(path);
        kfree(path);
        return ret;
}

/**
 * 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.
 */

/**
 * mext_page_double_lock - Grab and lock pages on both @inode1 and @inode2
 *
 * @inode1:     the inode structure
 * @inode2:     the inode structure
 * @index:      page index
 * @page:       result page vector
 *
 * Grab two locked pages for inode's by inode order
 */
static int
mext_page_double_lock(struct inode *inode1, struct inode *inode2,
                      pgoff_t index1, pgoff_t index2, struct page *page[2])
{
        struct address_space *mapping[2];
        unsigned fl = AOP_FLAG_NOFS;

        BUG_ON(!inode1 || !inode2);
        if (inode1 < inode2) {
                mapping[0] = inode1->i_mapping;
                mapping[1] = inode2->i_mapping;
        } else {
                pgoff_t tmp = index1;
                index1 = index2;
                index2 = tmp;
                mapping[0] = inode2->i_mapping;
                mapping[1] = inode1->i_mapping;
        }

        page[0] = grab_cache_page_write_begin(mapping[0], index1, fl);
        if (!page[0])
                return -ENOMEM;

        page[1] = grab_cache_page_write_begin(mapping[1], index2, fl);
        if (!page[1]) {
                unlock_page(page[0]);
                page_cache_release(page[0]);
                return -ENOMEM;
        }
        /*
         * grab_cache_page_write_begin() may not wait on page's writeback if
         * BDI not demand that. But it is reasonable to be very conservative
         * here and explicitly wait on page's writeback
         */
        wait_on_page_writeback(page[0]);
        wait_on_page_writeback(page[1]);
        if (inode1 > inode2) {
                struct page *tmp;
                tmp = page[0];
                page[0] = page[1];
                page[1] = tmp;
        }
        return 0;
}

/* Force page buffers uptodate w/o dropping page's lock */
static int
mext_page_mkuptodate(struct page *page, unsigned from, unsigned to)
{
        struct inode *inode = page->mapping->host;
        sector_t block;
        struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
        unsigned int blocksize, block_start, block_end;
        int i, err,  nr = 0, partial = 0;
        BUG_ON(!PageLocked(page));
        BUG_ON(PageWriteback(page));

        if (PageUptodate(page))
                return 0;

        blocksize = 1 << inode->i_blkbits;
        if (!page_has_buffers(page))
                create_empty_buffers(page, blocksize, 0);

        head = page_buffers(page);
        block = (sector_t)page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
        for (bh = head, block_start = 0; bh != head || !block_start;
             block++, block_start = block_end, bh = bh->b_this_page) {
                block_end = block_start + blocksize;
                if (block_end <= from || block_start >= to) {
                        if (!buffer_uptodate(bh))
                                partial = 1;
                        continue;
                }
                if (buffer_uptodate(bh))
                        continue;
                if (!buffer_mapped(bh)) {
                        err = ext4_get_block(inode, block, bh, 0);
                        if (err) {
                                SetPageError(page);
                                return err;
                        }
                        if (!buffer_mapped(bh)) {
                                zero_user(page, block_start, blocksize);
                                set_buffer_uptodate(bh);
                                continue;
                        }
                }
                BUG_ON(nr >= MAX_BUF_PER_PAGE);
                arr[nr++] = bh;
        }
        /* No io required */
        if (!nr)
                goto out;

        for (i = 0; i < nr; i++) {
                bh = arr[i];
                if (!bh_uptodate_or_lock(bh)) {
                        err = bh_submit_read(bh);
                        if (err)
                                return err;
                }
        }
out:
        if (!partial)
                SetPageUptodate(page);
        return 0;
}

/**
 * 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
 * @unwritten:                  orig extent is unwritten 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, pgoff_t donor_page_offset,
                     int data_offset_in_page,
                     int block_len_in_page, int unwritten, int *err)
{
        struct inode *orig_inode = file_inode(o_filp);
        struct page *pagep[2] = {NULL, NULL};
        handle_t *handle;
        ext4_lblk_t orig_blk_offset, donor_blk_offset;
        unsigned long blocksize = orig_inode->i_sb->s_blocksize;
        unsigned int w_flags = 0;
        unsigned int tmp_data_size, data_size, replaced_size;
        int err2, jblocks, retries = 0;
        int replaced_count = 0;
        int from = data_offset_in_page << orig_inode->i_blkbits;
        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.
         */
again:
        *err = 0;
        jblocks = ext4_writepage_trans_blocks(orig_inode) * 2;
        handle = ext4_journal_start(orig_inode, EXT4_HT_MOVE_EXTENTS, 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;

        donor_blk_offset = donor_page_offset * blocks_per_page +
                data_offset_in_page;

        /* 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 = mext_page_double_lock(orig_inode, donor_inode, orig_page_offset,
                                     donor_page_offset, pagep);
        if (unlikely(*err < 0))
                goto stop_journal;
        /*
         * If orig extent was unwritten it can become initialized
         * at any time after i_data_sem was dropped, in order to
         * serialize with delalloc we have recheck extent while we
         * hold page's lock, if it is still the case data copy is not
         * necessary, just swap data blocks between orig and donor.
         */
        if (unwritten) {
                ext4_double_down_write_data_sem(orig_inode, donor_inode);
                /* If any of extents in range became initialized we have to
                 * fallback to data copying */
                unwritten = mext_check_coverage(orig_inode, orig_blk_offset,
                                                block_len_in_page, 1, err);
                if (*err)
                        goto drop_data_sem;

                unwritten &= mext_check_coverage(donor_inode, donor_blk_offset,
                                                 block_len_in_page, 1, err);
                if (*err)
                        goto drop_data_sem;

                if (!unwritten) {
                        ext4_double_up_write_data_sem(orig_inode, donor_inode);
                        goto data_copy;
                }
                if ((page_has_private(pagep[0]) &&
                     !try_to_release_page(pagep[0], 0)) ||
                    (page_has_private(pagep[1]) &&
                     !try_to_release_page(pagep[1], 0))) {
                        *err = -EBUSY;
                        goto drop_data_sem;
                }
                replaced_count = ext4_swap_extents(handle, orig_inode,
                                                   donor_inode, orig_blk_offset,
                                                   donor_blk_offset,
                                                   block_len_in_page, 1, err);
        drop_data_sem:
                ext4_double_up_write_data_sem(orig_inode, donor_inode);
                goto unlock_pages;
        }
data_copy:
        *err = mext_page_mkuptodate(pagep[0], from, from + replaced_size);
        if (*err)
                goto unlock_pages;

        /* At this point all buffers in range are uptodate, old mapping layout
         * is no longer required, try to drop it now. */
        if ((page_has_private(pagep[0]) && !try_to_release_page(pagep[0], 0)) ||
            (page_has_private(pagep[1]) && !try_to_release_page(pagep[1], 0))) {
                *err = -EBUSY;
                goto unlock_pages;
        }
        ext4_double_down_write_data_sem(orig_inode, donor_inode);
        replaced_count = ext4_swap_extents(handle, orig_inode, donor_inode,
                                               orig_blk_offset, donor_blk_offset,
                                           block_len_in_page, 1, err);
        ext4_double_up_write_data_sem(orig_inode, donor_inode);
        if (*err) {
                if (replaced_count) {
                        block_len_in_page = replaced_count;
                        replaced_size =
                                block_len_in_page << orig_inode->i_blkbits;
                } else
                        goto unlock_pages;
        }
        /* Perform all necessary steps similar write_begin()/write_end()
         * but keeping in mind that i_size will not change */
        *err = __block_write_begin(pagep[0], from, replaced_size,
                                   ext4_get_block);
        if (!*err)
                *err = block_commit_write(pagep[0], from, from + replaced_size);

        if (unlikely(*err < 0))
                goto repair_branches;

        /* Even in case of data=writeback it is reasonable to pin
         * inode to transaction, to prevent unexpected data loss */
        *err = ext4_jbd2_file_inode(handle, orig_inode);

unlock_pages:
        unlock_page(pagep[0]);
        page_cache_release(pagep[0]);
        unlock_page(pagep[1]);
        page_cache_release(pagep[1]);
stop_journal:
        ext4_journal_stop(handle);
        /* Buffer was busy because probably is pinned to journal transaction,
         * force transaction commit may help to free it. */
        if (*err == -EBUSY && ext4_should_retry_alloc(orig_inode->i_sb,
                                                      &retries))
                goto again;
        return replaced_count;

repair_branches:
        /*
         * This should never ever happen!
         * Extents are swapped already, but we are not able to copy data.
         * Try to swap extents to it's original places
         */
        ext4_double_down_write_data_sem(orig_inode, donor_inode);
        replaced_count = ext4_swap_extents(handle, donor_inode, orig_inode,
                                               orig_blk_offset, donor_blk_offset,
                                           block_len_in_page, 0, &err2);
        ext4_double_up_write_data_sem(orig_inode, donor_inode);
        if (replaced_count != block_len_in_page) {
                EXT4_ERROR_INODE_BLOCK(orig_inode, (sector_t)(orig_blk_offset),
                                       "Unable to copy data block,"
                                       " data will be lost.");
                *err = -EIO;
        }
        replaced_count = 0;
        goto unlock_pages;
}

/**
 * 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)
{
        __u64 orig_eof, donor_eof;
        unsigned int blkbits = orig_inode->i_blkbits;
        unsigned int blocksize = 1 << blkbits;

        orig_eof = (i_size_read(orig_inode) + blocksize - 1) >> blkbits;
        donor_eof = (i_size_read(donor_inode) + 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 -EBUSY;
        }

        /* 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 & ~(PAGE_MASK >> orig_inode->i_blkbits)) !=
            (donor_start & ~(PAGE_MASK >> orig_inode->i_blkbits))) {
                ext4_debug("ext4 move extent: orig and donor's start "
                        "offset are not alligned [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) ||
            (donor_start + *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_eof < orig_start + *len - 1)
                *len = orig_eof - orig_start;
        if (donor_eof < donor_start + *len - 1)
                *len = donor_eof - donor_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;
}

/**
 * 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_blk,
                  __u64 donor_blk, __u64 len, __u64 *moved_len)
{
        struct inode *orig_inode = file_inode(o_filp);
        struct inode *donor_inode = file_inode(d_filp);
        struct ext4_ext_path *path = NULL;
        int blocks_per_page = PAGE_CACHE_SIZE >> orig_inode->i_blkbits;
        ext4_lblk_t o_end, o_start = orig_blk;
        ext4_lblk_t d_start = donor_blk;
        int ret;

        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 */
        lock_two_nondirectories(orig_inode, donor_inode);

        /* Wait for all existing dio workers */
        ext4_inode_block_unlocked_dio(orig_inode);
        ext4_inode_block_unlocked_dio(donor_inode);
        inode_dio_wait(orig_inode);
        inode_dio_wait(donor_inode);

        /* Protect extent tree against block allocations via delalloc */
        ext4_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_blk,
                                    donor_blk, &len);
        if (ret)
                goto out;
        o_end = o_start + len;

        while (o_start < o_end) {
                struct ext4_extent *ex;
                ext4_lblk_t cur_blk, next_blk;
                pgoff_t orig_page_index, donor_page_index;
                int offset_in_page;
                int unwritten, cur_len;

                ret = get_ext_path(orig_inode, o_start, &path);
                if (ret)
                        goto out;
                ex = path[path->p_depth].p_ext;
                next_blk = ext4_ext_next_allocated_block(path);
                cur_blk = le32_to_cpu(ex->ee_block);
                cur_len = ext4_ext_get_actual_len(ex);
                /* Check hole before the start pos */
                if (cur_blk + cur_len - 1 < o_start) {
                        if (next_blk == EXT_MAX_BLOCKS) {
                                o_start = o_end;
                                ret = -ENODATA;
                                goto out;
                        }
                        d_start += next_blk - o_start;
                        o_start = next_blk;
                        goto repeat;
                /* Check hole after the start pos */
                } else if (cur_blk > o_start) {
                        /* Skip hole */
                        d_start += cur_blk - o_start;
                        o_start = cur_blk;
                        /* Extent inside requested range ?*/
                        if (cur_blk >= o_end)
                                goto out;
                } else { /* in_range(o_start, o_blk, o_len) */
                        cur_len += cur_blk - o_start;
                }
                unwritten = ext4_ext_is_unwritten(ex);
                if (o_end - o_start < cur_len)
                        cur_len = o_end - o_start;

                orig_page_index = o_start >> (PAGE_CACHE_SHIFT -
                                               orig_inode->i_blkbits);
                donor_page_index = d_start >> (PAGE_CACHE_SHIFT -
                                               donor_inode->i_blkbits);
                offset_in_page = o_start % blocks_per_page;
                if (cur_len > blocks_per_page- offset_in_page)
                        cur_len = blocks_per_page - offset_in_page;
                /*
                 * 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
                 */
                ext4_double_up_write_data_sem(orig_inode, donor_inode);
                /* Swap original branches with new branches */
                move_extent_per_page(o_filp, donor_inode,
                                     orig_page_index, donor_page_index,
                                     offset_in_page, cur_len,
                                     unwritten, &ret);
                ext4_double_down_write_data_sem(orig_inode, donor_inode);
                if (ret < 0)
                        break;
                o_start += cur_len;
                d_start += cur_len;
        repeat:
                ext4_ext_drop_refs(path);
                kfree(path);
                path = NULL;
        }
        *moved_len = o_start - orig_blk;
        if (*moved_len > len)
                *moved_len = len;

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

        ext4_ext_drop_refs(path);
        kfree(path);
        ext4_double_up_write_data_sem(orig_inode, donor_inode);
        ext4_inode_resume_unlocked_dio(orig_inode);
        ext4_inode_resume_unlocked_dio(donor_inode);
        unlock_two_nondirectories(orig_inode, donor_inode);

        return ret;
}