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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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