Re: [RFC 7/11] virtio_pci: new, capability-aware driver.

[Rusty Russell <rusty@xxxxxxxxxxxxxxx>]

On Sun, 18 Dec 2011 12:18:32 +0200, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:
> On Fri, Dec 16, 2011 at 12:20:08PM +1030, Rusty Russell wrote:
> > Perhaps a new feature VIRTIO_F_UNSTABLE?  Which (unlike other features)
> > appears and vanishes around config writes by either side?  Kind of a
> > hack though...
> 
> Not sure how this can work in such a setup: when would guest
> check this bit to avoid races?
> A separate registers also seems nicer than a flag.
> 
> Some other possible design choices:
> - a flag to signal config accesses in progress by guest
>   host would need to buffer changes and apply them in one go
>   when flag is cleared
> - a register to make host get/set config in guest memory
> - use a control vq for all devices

- seqlock-style generation count register(s)?  Has the advantage of
  being a noop if things never change.

- continue to ignore it ;)

And yes, it's a more general problem than virtio_pci...

Cheers,
Rusty.

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