Ocfs2 devel - Nov 2018 - [PATCH] ocfs2: clear zero in unaligned direct IO

Unused portion of a part-written fs-block-sized block is not set to
zero in unaligned append direct write.This can lead to serious data
inconsistencies.

Ocfs2 manage disk with cluster size(for example, 1M), part-written in
one cluster will change the cluster state from UN-WRITTEN to WRITTEN,
VFS(function dio_zero_block) doesn't do the cleaning because bh's state
is not set to NEW in function ocfs2_dio_wr_get_block when we write a
WRITTEN cluster. For example, the cluster size is 1M, file size is 8k
and we direct write from 14k to 15k, then 12k~14k and 15k~16k will
contain dirty data.

We have to deal with two cases:
1.The starting position of direct write is outside the file.
2.The starting position of direct write is located in the file.

We need set bh's state to NEW in the first case. In the second case,
we need mapped twice because bh's state of area out file should be set
to NEW while area in file not.

Signed-off-by: Jia Guo <guojia12 at huawei.com>
Reviewed-by: Yiwen Jiang <jiangyiwen at huawei.com>
---
 fs/ocfs2/aops.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
index eb1ce30..6e1f902 100644
--- a/fs/ocfs2/aops.c
+++ b/fs/ocfs2/aops.c
@@ -2152,13 +2152,30 @@ static int ocfs2_dio_wr_get_block(struct inode *inode,
sector_t iblock,
 	struct ocfs2_dio_write_ctxt *dwc = NULL;
 	struct buffer_head *di_bh = NULL;
 	u64 p_blkno;
-	loff_t pos = iblock << inode->i_sb->s_blocksize_bits;
+	unsigned i_blkbits = inode->i_sb->s_blocksize_bits;
+	loff_t pos = iblock << i_blkbits;
+	sector_t endblk = (i_size_read(inode) - 1) >> i_blkbits;
 	unsigned len, total_len = bh_result->b_size;
 	int ret = 0, first_get_block = 0;

 	len = osb->s_clustersize - (pos & (osb->s_clustersize - 1));
 	len = min(total_len, len);

+	/*
+	 * bh_result->b_size is count in get_more_blocks according to write
+ 	 * "pos" and "end", we need map twice to return different
buffer state:
+ 	 * 1. area in file size, not set NEW;
+ 	 * 2. area out file size, set  NEW.
+ 	 *
+ 	 *		   iblock    endblk
+ 	 * |--------|---------|---------|---------
+ 	 * |<-------area in file------->|
+ 	 */
+
+	if ((iblock <= endblk) &&
+	    ((iblock + ((len - 1) >> i_blkbits)) > endblk))
+		len = (endblk - iblock + 1) << i_blkbits;
+
 	mlog(0, "get block of %lu at %llu:%u req %u\n",
 			inode->i_ino, pos, len, total_len);

@@ -2242,6 +2259,9 @@ static int ocfs2_dio_wr_get_block(struct inode *inode,
sector_t iblock,
 	if (desc->c_needs_zero)
 		set_buffer_new(bh_result);

+	if (iblock > endblk)
+		set_buffer_new(bh_result);
+
 	/* May sleep in end_io. It should not happen in a irq context. So defer
 	 * it to dio work queue. */
 	set_buffer_defer_completion(bh_result);
--