[PATCH] [28/106] Treat writes as new when holes span across page boundaries

[Andi Kleen]

2.6.35-longterm review patch.  If anyone has any objections, please let me 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>
Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>

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

Index: linux-2.6.35.y/fs/ocfs2/aops.c
===================================================================
--- linux-2.6.35.y.orig/fs/ocfs2/aops.c
+++ linux-2.6.35.y/fs/ocfs2/aops.c
@@ -1039,6 +1039,12 @@ 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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