[virtio-dev] RE: [PATCH 08/11] transport-pci: Introduce virtio extended capability

Parav Pandit
2023-05-19T21:03:13Z

> From: Michael S. Tsirkin <mst@redhat.com>
> Sent: Friday, May 19, 2023 2:10 AM
>
> So looking at this in isolation, it probably warrants an extra github issue. So I
> would like to find out whether we should introduce this capability and switch to
> it for new devices.
>
> My main question is whether e.g. seabios will be able to use it.
> Could you take a look at the source and let us all know?
>
Existing unmodified seabios cannot use it because it is not looking at the new offset and cap_id.
But that is the case with any existing software, not just seabios.

New capability is in addition to the existing one.
And code already exists to refer to the old one, so I am not seeing any gain to create them now.
Any new capability that one creates in the future can be in the extended area.

You mentioned a perf angle that it takes half the time, but I don't see how as the only change between legacy and ext is: offset.