[Ocfs2-devel] [PATCH] ocfs2: Fix a bug in direct IO read.

[Tao Ma]

ocfs2 will become read-only if we try to read the bytes which pass
the end of i_size. This can be easily reproduced by following steps:
1. mkfs a ocfs2 volume with bs=4k cs=4k and nosparse.
2. create a small file(say less than 100 bytes) and we will create the file
   which is allocated 1 cluster.
3. read 8196 bytes from the kernel using O_DIRECT which exceeds the limit.
4. The ocfs2 volume becomes read-only and dmesg shows:
OCFS2: ERROR (device sda13): ocfs2_direct_IO_get_blocks:
Inode 66010 has a hole at block 1
File system is now read-only due to the potential of on-disk corruption.
Please run fsck.ocfs2 once the file system is unmounted.

I have checked the code of 1.2 and copy the read check there.
And actually I think even with sparse-enabled, this read check is ok.

Signed-off-by: Tao Ma <tao.ma at oracle.com>
---
 fs/ocfs2/aops.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
index 80fa3fc..f27c1cc 100644
--- a/fs/ocfs2/aops.c
+++ b/fs/ocfs2/aops.c
@@ -576,6 +576,14 @@ static int ocfs2_direct_IO_get_blocks(struct inode *inode, sector_t iblock,
 	inode_blocks = ocfs2_blocks_for_bytes(inode->i_sb, i_size_read(inode));
 
 	/*
+	 * For a read which begins past the end of file, we return a hole.
+	 */
+	if (!create && (iblock >= inode_blocks)) {
+		ret = 0;
+		goto bail;
+	}
+
+	/*
 	 * Any write past EOF is not allowed because we'd be extending.
 	 */
 	if (create && (iblock + max_blocks) > inode_blocks) {
-- 
1.5.4.GIT