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    Subject[PATCH] Teach do_mpage_readpage() about unwritten buffers
    Teach do_mpage_readpage() about unwritten extents so we can
    always map them in get_blocks rather than they are are holes on
    read. Allows setup_swap_extents() to use preallocated files on XFS
    filesystems for swap files without ever needing to convert them.

    Signed-Off-By: Dave Chinner <dgc@sgi.com>

    ---
    fs/mpage.c | 5 +++--
    fs/xfs/linux-2.6/xfs_aops.c | 13 +++----------
    2 files changed, 6 insertions(+), 12 deletions(-)

    Index: 2.6.x-xfs-new/fs/mpage.c
    ===================================================================
    --- 2.6.x-xfs-new.orig/fs/mpage.c 2007-05-29 16:17:59.000000000 +1000
    +++ 2.6.x-xfs-new/fs/mpage.c 2007-06-27 22:39:35.568852270 +1000
    @@ -207,7 +207,8 @@ do_mpage_readpage(struct bio *bio, struc
    * Map blocks using the result from the previous get_blocks call first.
    */
    nblocks = map_bh->b_size >> blkbits;
    - if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
    + if (buffer_mapped(map_bh) && !buffer_unwritten(map_bh) &&
    + block_in_file > *first_logical_block &&
    block_in_file < (*first_logical_block + nblocks)) {
    unsigned map_offset = block_in_file - *first_logical_block;
    unsigned last = nblocks - map_offset;
    @@ -242,7 +243,7 @@ do_mpage_readpage(struct bio *bio, struc
    *first_logical_block = block_in_file;
    }

    - if (!buffer_mapped(map_bh)) {
    + if (!buffer_mapped(map_bh) || buffer_unwritten(map_bh)) {
    fully_mapped = 0;
    if (first_hole == blocks_per_page)
    first_hole = page_block;
    Index: 2.6.x-xfs-new/fs/xfs/linux-2.6/xfs_aops.c
    ===================================================================
    --- 2.6.x-xfs-new.orig/fs/xfs/linux-2.6/xfs_aops.c 2007-06-05 22:14:39.000000000 +1000
    +++ 2.6.x-xfs-new/fs/xfs/linux-2.6/xfs_aops.c 2007-06-27 22:39:29.545636749 +1000
    @@ -1340,16 +1340,9 @@ __xfs_get_blocks(
    return 0;

    if (iomap.iomap_bn != IOMAP_DADDR_NULL) {
    - /*
    - * For unwritten extents do not report a disk address on
    - * the read case (treat as if we're reading into a hole).
    - */
    - if (create || !(iomap.iomap_flags & IOMAP_UNWRITTEN)) {
    - xfs_map_buffer(bh_result, &iomap, offset,
    - inode->i_blkbits);
    - }
    - if (create && (iomap.iomap_flags & IOMAP_UNWRITTEN)) {
    - if (direct)
    + xfs_map_buffer(bh_result, &iomap, offset, inode->i_blkbits);
    + if (iomap.iomap_flags & IOMAP_UNWRITTEN) {
    + if (create && direct)
    bh_result->b_private = inode;
    set_buffer_unwritten(bh_result);
    }
    -
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