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    Subject[34-longterm 038/196] Treat writes as new when holes span across page boundaries
    Date
    From: Goldwyn Rodrigues <rgoldwyn@gmail.com>

    -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    If you see a problem with using this for longterm, please comment.
    -------------------

    commit 272b62c1f0f6f742046e45b50b6fec98860208a0 upstream.

    When a hole spans across page boundaries, the next write forces
    a read of the block. This could end up reading existing garbage
    data from the disk in ocfs2_map_page_blocks. This leads to
    non-zero holes. In order to avoid this, mark the writes as new
    when the holes span across page boundaries.

    Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.de>
    Signed-off-by: jlbec <jlbec@evilplan.org>
    Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
    ---
    fs/ocfs2/aops.c | 6 ++++++
    1 file changed, 6 insertions(+)

    diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
    index e504ab7..3de08db 100644
    --- a/fs/ocfs2/aops.c
    +++ b/fs/ocfs2/aops.c
    @@ -1035,6 +1035,12 @@ static int ocfs2_prepare_page_for_write(struct inode *inode, u64 *p_blkno,
    ocfs2_figure_cluster_boundaries(OCFS2_SB(inode->i_sb), cpos,
    &cluster_start, &cluster_end);

    + /* treat the write as new if the a hole/lseek spanned across
    + * the page boundary.
    + */
    + new = new | ((i_size_read(inode) <= page_offset(page)) &&
    + (page_offset(page) <= user_pos));
    +
    if (page == wc->w_target_page) {
    map_from = user_pos & (PAGE_CACHE_SIZE - 1);
    map_to = map_from + user_len;
    --
    1.7.9.3


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