Re: [virtio-dev] [PATCH v3] content: enhance device requirements for feature bits

[Cornelia Huck <cohuck@redhat.com>]

On Wed, 20 Jun 2018 00:30:59 +0800
Tiwei Bie <tiwei.bie@intel.com> wrote:

> On Tue, Jun 19, 2018 at 12:46:45PM +0200, Halil Pasic wrote:
> > On 06/19/2018 11:14 AM, Tiwei Bie wrote:  
> > > On Mon, Jun 18, 2018 at 07:28:33PM +0300, Michael S. Tsirkin wrote:  
> [...]
> > > 
> > > If it would be better to drop this patch,
> > > I'm fine with dropping it. Thanks!
> > >   
> > 
> > @Tiwei Bie
> > Thanks for your flexibility! What is your opinion (after considering the
> > arguments from my previous mail), is it better to include this patch in the spec or
> > is it better to drop it? Were you able to identify mistakes in my reasoning
> > (I mean points (1)-(12))?
> >   
> 
> Hi Halil,
> 
> I think maybe you thought too much about this proposal
> (or maybe I really missed something obvious). In my
> opinion, the device requirement proposed by this patch
> is quite simple and straightforward:
> 
> - It's just to make the spec explicitly require that
>   a certain virtio device shouldn't fail re-negotiation
>   of a feature set it has successfully accepted once.
> 
> - It covers the cases of virtio device reset and system
>   reset (which includes normal shutdown and start).
> 
> I think the requirement is reasonable because for a
> certain virtio device, there is no reason that the
> feature bits it offers will change (because it should
> always offer all the features it understands). And we
> are just to add a device normative to make the spec be
> more explicit about that (because if a device really
> changes the features it offers after a device or
> system reset, something will go wrong). If the configs
> of an emulated virtio device are changed, maybe we
> shouldn't treat it as the same device any more, and
> IMO this case is not related to this proposal.
> 
> Although we have 'Each virtio device offers all the
> features it understands', it's not an explicit device
> requirement. So I don't think it's a bad idea to
> have an explicit device requirement about this.

I think this reasoning is sane and we really should not overthink it.
The update as has been voted on looks fine to me.

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