Re: what should a virtio-mmio transport without a backend look like?

[Christopher Covington <cov@codeaurora.org>]

Hi Peter,

On 06/21/2013 11:23 AM, Peter Maydell wrote:
> On 20 June 2013 13:58, Christopher Covington <cov@codeaurora.org> wrote:
>>> On Thu, 2013-06-20 at 11:29 +0100, Peter Maydell wrote:
>>>> 1. One question I've run into is: what should a virtio-mmio transport
>>>> with no backend look like to the guest OS? The spec as written
>>>> seems to assume that there's always some backend present.
>>>> (The idea is that QEMU might just always instantiate say 8
>>>> mmio transports, and then whether they actually have a
>>>> blk/net/whatever backend depends on user options).
> 
>> Might it be reasonably easy to just not enumerate unused transports
>> in the device tree or kernel parameters?
> 
> At least for QEMU, the backend that plugs into the transport
> isn't created until after the machine model has created
> transports and put together the device tree blob. So we don't
> really have the information about what devices are going to
> appear at the point we're doing this.

Would using CONFIG_VIRTIO_MMIO_CMDLINE_DEVICES enumeration instead of device
tree be any easier?

How does the back end know which devices to create?

Thanks,
Christopher

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