* Re: [virtio-dev] Re: [PATCH] Update virtio input device specification
[not found] ` <1491484886.12607.57.camel@redhat.com>
@ 2018-06-20 3:13 ` Michael S. Tsirkin
2018-08-28 12:05 ` Michael S. Tsirkin
0 siblings, 1 reply; 2+ messages in thread
From: Michael S. Tsirkin @ 2018-06-20 3:13 UTC (permalink / raw)
To: Gerd Hoffmann; +Cc: Ladi Prosek, virtio-dev, Stefan Hajnoczi
On Thu, Apr 06, 2017 at 03:21:26PM +0200, Gerd Hoffmann wrote:
> Hi,
>
> > The downside is that this is hard to specify formally, the same way we
> > do other devices. Say we do that and point to a fixed version of the
> > relevant Linux headers and the headers evolve and add or change
> > something. Then we would either go change the spec to be in sync with
> > the headers or build a compatibility layer in the implementation.
>
> Highly unlikely that the structs and ioctls in linux header change.
> It's userspace <=> kernel abi. And even if they change some days it
> would have to happen in a backward compatible way. So I think
> documenting the ioctl structs we have today is reasonable. If new
> ioctls for new device types show up we probably need a virtio feature
> flag anyway to properly support them.
>
> Events (new key codes for example) are added now and then. So for them
> we might continue referencing the include file with the codes instead of
> copying them into the spec.
>
> > because evdev
> > needs to maintain some reasonable backwards compatibility by itself so
> > it's very unlikely that things would break.
>
> Yep. Unknown events can simply be ignored. And you can query the
> device to figure which events (aka keys / axis / ...) are supported
> (ioctl in evdev, config space in virtio). So that level of
> compatibility is already taken care of, in both evdev and virtio.
>
> > > Let's assume linux gains ability to generate new events on top of old
> > > ones.
> > > Do you want to send both in all cases?
> > > If you only send multitouch how do you handle old guests?
> > > If you send both how does new guest know it should
> > > ignore old events?
> >
> > I think that these are valid concerns but they need to be addressed at
> > the evdev layer, not in virtio.
>
> Indeed. And I think multitouch is addressed by simply sending both.
> Apps without multitouch support simply ignore the multitouch events.
> Apps with multitouch support can figure this is a multitouch-capable
> device and ignore the old events on those.
>
> cheers,
> Gerd
Gerd is there a chance you could try and address whatever
you think needs to be addressed and repost?
Would be nice to have this in 1.1 and I think it's better
to have an incomplete description than none.
>
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^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [virtio-dev] Re: [PATCH] Update virtio input device specification
2018-06-20 3:13 ` [virtio-dev] Re: [PATCH] Update virtio input device specification Michael S. Tsirkin
@ 2018-08-28 12:05 ` Michael S. Tsirkin
0 siblings, 0 replies; 2+ messages in thread
From: Michael S. Tsirkin @ 2018-08-28 12:05 UTC (permalink / raw)
To: Gerd Hoffmann; +Cc: Ladi Prosek, virtio-dev, Stefan Hajnoczi
On Wed, Jun 20, 2018 at 06:13:35AM +0300, Michael S. Tsirkin wrote:
> On Thu, Apr 06, 2017 at 03:21:26PM +0200, Gerd Hoffmann wrote:
> > Hi,
> >
> > > The downside is that this is hard to specify formally, the same way we
> > > do other devices. Say we do that and point to a fixed version of the
> > > relevant Linux headers and the headers evolve and add or change
> > > something. Then we would either go change the spec to be in sync with
> > > the headers or build a compatibility layer in the implementation.
> >
> > Highly unlikely that the structs and ioctls in linux header change.
> > It's userspace <=> kernel abi. And even if they change some days it
> > would have to happen in a backward compatible way. So I think
> > documenting the ioctl structs we have today is reasonable. If new
> > ioctls for new device types show up we probably need a virtio feature
> > flag anyway to properly support them.
> >
> > Events (new key codes for example) are added now and then. So for them
> > we might continue referencing the include file with the codes instead of
> > copying them into the spec.
> >
> > > because evdev
> > > needs to maintain some reasonable backwards compatibility by itself so
> > > it's very unlikely that things would break.
> >
> > Yep. Unknown events can simply be ignored. And you can query the
> > device to figure which events (aka keys / axis / ...) are supported
> > (ioctl in evdev, config space in virtio). So that level of
> > compatibility is already taken care of, in both evdev and virtio.
> >
> > > > Let's assume linux gains ability to generate new events on top of old
> > > > ones.
> > > > Do you want to send both in all cases?
> > > > If you only send multitouch how do you handle old guests?
> > > > If you send both how does new guest know it should
> > > > ignore old events?
> > >
> > > I think that these are valid concerns but they need to be addressed at
> > > the evdev layer, not in virtio.
> >
> > Indeed. And I think multitouch is addressed by simply sending both.
> > Apps without multitouch support simply ignore the multitouch events.
> > Apps with multitouch support can figure this is a multitouch-capable
> > device and ignore the old events on those.
> >
> > cheers,
> > Gerd
>
>
> Gerd is there a chance you could try and address whatever
> you think needs to be addressed and repost?
>
> Would be nice to have this in 1.1 and I think it's better
> to have an incomplete description than none.
Ping.
>
> >
> > ---------------------------------------------------------------------
> > To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org
> > For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org
> For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org
---------------------------------------------------------------------
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2018-06-20 3:13 ` [virtio-dev] Re: [PATCH] Update virtio input device specification Michael S. Tsirkin
2018-08-28 12:05 ` Michael S. Tsirkin
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