Re: [Qemu-devel] [RFC for 2.7 0/2] virtio: show guest features in 'info qtree'

["Denis V. Lunev" <den@openvz.org>]

On 05/11/2016 03:02 PM, Cornelia Huck wrote:
> On Wed, 11 May 2016 14:06:57 +0300
> "Denis V. Lunev" <den@openvz.org> wrote:
>
>> On 05/11/2016 01:34 PM, Cornelia Huck wrote:
>>> On Wed, 11 May 2016 12:52:02 +0300
>>> "Denis V. Lunev" <den@openvz.org> wrote:
>>>
>>>> It is very convinient and useful for debug purpose to expose the set of
>>>> features negotiated with guest. The patch exports those features via
>>>> read-only bit properties.
>>> I agree that it would be very helpful to be able to access the
>>> negotiated features via the monitor, but I disagree with your approach,
>>> especially the need to expose every single feature bit via a property.
>>>
>>> What about a command like 'info virtio' instead? This would allow us to
>>> dump not only guest features, but the host features initially offered
>>> alongside them and things like the status byte (so you can actually
>>> check whether feature negotiation was successful). Maybe similar to
>>> 'info block'.
>>>
>> Hmmm. Do you propose to print bits as HEX?
> Just print a 1 if the bit is set. This would make it easy to see if
> e.g. the guest only negotiated a small subset of the offered features.
>
>> Because if we are going
>> have then splitted out we have to provide individual bit descriptions.
>> Thus the amount of code could be similar.
>>
>> Actually I can add generic dump code into VirtIODevice and will use
>> host_features/guest_features fields but we should have a callback
>> defined for each device which will provide bit names.
> What about the individual drivers providing an array of strings for the
> feature names? Then you could easily print a list of feature bit names.
>
> For the virtio status (which I would find as useful as the feature
> bits), it's even easier as the status bits are common.
>
OK. We could try this approach.

Do you know any reasonable way to enumerate all VirtIO devices?
There is no need for this in the older code. We will need to enumerate
all VirtIO devices within 'info virtio' command.

Den