Re: [Qemu-devel] [PATCH] virtio-input: send rel-wheel events for wheel buttons

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> >          .select    = VIRTIO_INPUT_CFG_EV_BITS,
> >          .subsel    = EV_REL,
> > -        .size      = 1,
> > +        .size      = 2,
> >          .u.bitmap  = {
> > -            (1 << REL_X) | (1 << REL_Y),
> > +            (1 << REL_X) | (1 << REL_Y),  (1 << (REL_WHEEL - 8))
> 
> Works only when REL_WHEEL is between 8 and 15.
> Add BUILD_BUG_ON?

Not needed IMO, REL_WHEEL value is kernel/userspace abi and will never
change.

> 
> >          },
> >      },
> >      { /* end of list */ },
> 
> Is it problematic e.g. if you migrate from a host with REL_WHEEL
> to one without? Should we maintain a version without REL_WHEEL
> for old machine types?

Yes, we need a compat property.

Possibly it is easier to fix on the guest side, assuming it is actually
needed (see other reply).

cheers,
  Gerd