Re: [Qemu-devel] [PATCH] virtio: set virtio-net/virtio-mmio host features

[Mario Smarduch <m.smarduch@samsung.com>]

On 02/20/2014 11:35 AM, Peter Maydell wrote:
> On 20 February 2014 19:09, Mario Smarduch <m.smarduch@samsung.com> wrote:
>> host features since you don't know what virtio device will be plugged
>> in later.
> 
> I think this function is the right place to set these properties,
> yes. What I'm saying is that I don't see why you're doing it
> this way rather than using the existing per-backend hook.
> Maybe there's a reason not to use that hook, but you don't say.
> 

Appears virtio-net beckend hooks are common to several transports, 
and would require virtio-mmio exception to set the host_features. 
If I'm missing something please recommend.

>> It's virtio_net_properties[] can only set virtio-net
>> properites when it's instantiated. I think the proper way would
>> be to refactor virtio-mmio to similar structure PCI version uses then
>> one virtio_net_properties[] can be used selecting PCI or virtio-mmio at
>> compile time. But right now it's unclear to me how pci and virtio-mmio
>> versions intend to co-exist.

> 
> This is the result of a refactoring last year to allow virtio-mmio.
> Basically the underlying structure now is:
> 
>  [some virtio transport device] <- virtio bus -> [virtio backend]
> 
> where the transport could be mmio, PCI, CCW, etc, and the
> backend is net, blk, balloon, etc. We also provide devices
> which are "virtio PCI transport plus a specific backend"
> for (a) user convenience and (b) backwards compatibility, since
> the pre-refactoring structure put the transport and backend
> all in one lump. The all-in-one-lump arrangement is legacy:
> we shouldn't break it, but it's not the model for virtio-mmio
> to follow either.
> 
> The transport shouldn't know anything specific about the
> backend it's plugged into (or vice-versa), but it's fine
> for there to be hook functions so the transport and backend
> can call each other at the appropriate times.
> 
> thanks
> -- PMM
>