Re: Small O_SYNC writes are no longer NFS_DATA_SYNC

[NeilBrown <neilb@suse.de>]

On Mon, 21 Mar 2011 18:54:55 -0400 Trond Myklebust
<Trond.Myklebust@netapp.com> wrote:

> On Tue, 2011-03-22 at 09:17 +1100, NeilBrown wrote:
> > On Mon, 21 Mar 2011 17:02:00 -0400 Trond Myklebust
> > <Trond.Myklebust@netapp.com> wrote:
> > I must admit that I found the terminology a bit confusing for 
> > FLUSH_COND_STABLE.
> > What is means is "if this turns out to be part of a larger request, then clear
> > FLUSH_STABLE" - which sounds a bit more like "FLUSH_COND_UNSTABLE" - i.e. if
> > a condition is met, then make it unstable.
> > But I don't think that change would help at all.
> > 
> > How about changing the test in nfs_write_rpcsetup to
> > 	if (how & (FLUSH_STABLE|FLUSH_CONDSTABLE)) {
> > 		data->args.stable = NFS_DATA_SYNC;
> > 		if (!nfs_need_commit(NFS_I(inode)))
> > 			data->args.stable = NFS_FILE_SYNC;
> > 	}
> > 
> > and then just set either FLUSH_STABLE or FLUSH_COND_STABLE - never both -
> > and when you test FLUSH_COND_STABLE and then some other condition, just
> > clear FLUSH_COND_STABLE.
> > 
> > I would find that quite a bit more readable.
> 
> The reason why I opted not to go for that approach was because
> nfs_write_rpcsetup() doesn't really know about whether or not there are
> any more RPCs pending (and so having a 'conditional' flag being
> interpreted there didn't appear to make sense), but if you feel that is
> easier on the eyes then I'm happy to change my opinion.
> 

I do see your point - by the time we get to nfs_write_rpcsetup it isn't
really conditional any more - it is now mandatory.

Maybe one cannot get the names perfect.  However I find that having
interdependencies between different flag bits can easily become confusing.

So I have a slight preference for my version, but I concede that it isn't a
clear winner.

Thanks,
NeilBrown