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

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Message-Id: <20110413155147.139187670@clark.kroah.org>
Date:	Wed, 13 Apr 2011 08:51:03 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Goldwyn Rodrigues <rgoldwyn@...e.de>,
	jlbec <jlbec@...lplan.org>
Subject: [39/74] Treat writes as new when holes span across page boundaries

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

------------------

From: Goldwyn Rodrigues <rgoldwyn@...il.com>

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@...e.de>
Signed-off-by: jlbec <jlbec@...lplan.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 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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