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

[Li Dongyang]

Hi, Tao,
On Friday 09 April 2010 10:38:33 Tao Ma wrote:
> Hi Dongyang,
> 
> Li Dongyang wrote:
> > This is because ocfs2_file_aio_write calls ocfs2_prepare_inode_for_write
> > which sets direct_io to 0 if it finds out that direct IO would extend the
> > file. But later we call __generic_file_aio_write which end's up calling
> > generic_file_direct_write because the file has O_DIRECT flag.So every
> > time we do a direct write extending the file, the inode->i_size gets
> > inconsistent with the i_size on disk because we call
> > generic_file_direct_write, and if we do a truncate after this, we will
> > meet a bug in ocfs2_truncate_file.
> 
> yes we have O_DIRECT flag set and in __generic_file_aio_write it will
> call generic_file_direct_write first and then trigger to
> ocfs2_direct_IO. In this function we will check again and return 0. And
> _generic_file_aio_write will fall back to buffered write if the directIO
> can't write. Am I wrong somehow?
> 
yes ocfs2_direct_IO has some check, but it just check if we are appending(the 
i_size <= offset), if the offset < i_size and offset + count > i_size, it will 
do direct io anyway. seems we also can fix this by adding a check to 
ocfs2_direct_IO.
Br,
Li Dongyang
> Regards,
> Tao
> 
> > On Friday 09 April 2010 02:41:26 Sunil Mushran wrote:
> >> I cannot read the bugzilla. Now it maybe that that bz
> >> cannot be made public. That's ok. But if that's the case,
> >> can you explain the problem encountered. I am not qs
> >> the fix... rather trying to understand why this has not
> >> been reported before.
> >>
> >> Li Dongyang wrote:
> >>> 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
> >>>
> >>>
> >>> Signed-off-by: Li Dongyang <lidongyang at novell.com>
> >>> ---
> >>>  fs/ocfs2/file.c |   27 +++++++++++++++++----------
> >>>  1 files changed, 17 insertions(+), 10 deletions(-)
> >>>
> >>> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
> >>> index de059f4..707f2a2 100644
> >>> --- a/fs/ocfs2/file.c
> >>> +++ b/fs/ocfs2/file.c
> >>> @@ -1973,18 +1973,24 @@ 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,
> >>> +	count = ocount;
> >>> +	ret = generic_write_checks(file, ppos, &count,
> >>>  					   S_ISBLK(inode->i_mode));
> >>> -		if (ret)
> >>> -			goto out_dio;
> >>> +	if (ret)
> >>> +		goto out_dio;
> >>> +
> >>> +	ret = file_remove_suid(file);
> >>> +	if (ret)
> >>> +		goto out_dio;
> >>>
> >>> +	file_update_time(file);
> >>> +
> >>> +	if (direct_io) {
> >>>  		written = generic_file_direct_write(iocb, iov, &nr_segs, *ppos,
> >>>  						    ppos, count, ocount);
> >>>  		if (written < 0) {
> >>> @@ -1999,7 +2005,8 @@ 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:
> >
> > _______________________________________________
> > Ocfs2-devel mailing list
> > Ocfs2-devel at oss.oracle.com
> > http://oss.oracle.com/mailman/listinfo/ocfs2-devel
>