Ocfs2 devel - Apr 2010 - [PATCH] ocfs2: avoid direct write if we fall back to buffered v2

when we fall back to buffered write from direct write, we call
__generic_file_aio_write but that will end up doing direct write
even we are only prepared to do buffered write because the file
has O_DIRECT flag set. This is a fix for
https://bugzilla.novell.com/show_bug.cgi?id=591039
revised with Joel's comments.

---
 fs/ocfs2/file.c |   23 ++++++++++++-----------
 1 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
index de059f4..0240de7 100644
--- a/fs/ocfs2/file.c
+++ b/fs/ocfs2/file.c
@@ -1973,18 +1973,18 @@ relock:
 	/* communicate with ocfs2_dio_end_io */
 	ocfs2_iocb_set_rw_locked(iocb, rw_level);
 
-	if (direct_io) {
-		ret = generic_segment_checks(iov, &nr_segs, &ocount,
-					     VERIFY_READ);
-		if (ret)
-			goto out_dio;
+	ret = generic_segment_checks(iov, &nr_segs, &ocount,
+				     VERIFY_READ);
+	if (ret)
+		goto out_dio;
 
-		count = ocount;
-		ret = generic_write_checks(file, ppos, &count,
-					   S_ISBLK(inode->i_mode));
-		if (ret)
-			goto out_dio;
+	count = ocount;
+	ret = generic_write_checks(file, ppos, &count,
+				   S_ISBLK(inode->i_mode));
+	if (ret)
+		goto out_dio;
 
+	if (direct_io) {
 		written = generic_file_direct_write(iocb, iov, &nr_segs, *ppos,
 						    ppos, count, ocount);
 		if (written < 0) {
@@ -1999,7 +1999,8 @@ relock:
 			goto out_dio;
 		}
 	} else {
-		written = __generic_file_aio_write(iocb, iov, nr_segs, ppos);
+		written = generic_file_buffered_write(iocb, iov, nr_segs, *ppos,
+						      ppos, count, 0);
 	}
 
 out_dio:
-- 
1.6.4.2

On Thu, Apr 15, 2010 at 09:01:56PM +0800, Li Dongyang
wrote:
> -	if (direct_io) {
> -		ret = generic_segment_checks(iov, &nr_segs, &ocount,
> -					     VERIFY_READ);
> -		if (ret)
> -			goto out_dio;
> +	ret = generic_segment_checks(iov, &nr_segs, &ocount,
> +				     VERIFY_READ);
> +	if (ret)
> +		goto out_dio;
>  
> -		count = ocount;
> -		ret = generic_write_checks(file, ppos, &count,
> -					   S_ISBLK(inode->i_mode));
> -		if (ret)
> -			goto out_dio;
> +	count = ocount;
> +	ret = generic_write_checks(file, ppos, &count,
> +				   S_ISBLK(inode->i_mode));
> +	if (ret)
> +		goto out_dio;
	Make sure you add the management of current->backing_dev_info
just like __generic_file_aio_write() does.  We want to ensure that page
writeback works OK.

Joel

-- 

"If the human brain were so simple we could understand it, we would
 be so simple that we could not."
	- W. A. Clouston

Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker at oracle.com
Phone: (650) 506-8127