[39/74] Treat writes as new when holes span across page boundaries

From: Greg KH
Date: Wed Apr 13 2011 - 12:04:33 EST

2.6.32-longterm review patch. If anyone has any objections, please let us know.


From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxxx>

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@xxxxxxx>
Signed-off-by: jlbec <jlbec@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

fs/ocfs2/aops.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/fs/ocfs2/aops.c
+++ b/fs/ocfs2/aops.c
@@ -1091,6 +1091,12 @@ static int ocfs2_prepare_page_for_write(
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;

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