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

[Li Dongyang]

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.

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:
>