Re: [RFC 2/5] qmp: add QMP command virtio-status

[Eric Blake]

On 4/2/20 5:02 AM, Laurent Vivier wrote:
> This new command shows the status of a VirtIODevice
> (features, endianness and number of virtqueues)
>
> Signed-off-by: Laurent Vivier <address@hidden>
> ---

> +++ b/qapi/virtio.json
> @@ -52,3 +52,68 @@
>   ##
>   
>   { 'command': 'query-virtio', 'returns': ['VirtioInfo'] }
> +
> +##
> +# @VirtioStatus:
> +#
> +# @device_id: VirtIODevice status

As this is a new API, it should stick to our naming conventions:

device-id

> +#
> +# @device_endian: VirtIODevice device_endian

device-endian

> +#
> +# @guest_features: VirtIODevice guest_features

guest-features

> +#
> +# @host_features: VirtIODevice host_features

host-features

> +#
> +# @backend_features: VirtIODevice backend_features

backend-features

> +#
> +# @num_vqs: number of VirtIODevice queues

num-vqs

> +#
> +# Since: 5.1
> +#
> +##
> +
> +{ 'struct': 'VirtioStatus',
> +  'data': {
> +    'device_id': 'int',
> +    'device_endian': 'str',
> +    'guest_features': 'uint64',
> +    'host_features': 'uint64',
> +    'backend_features': 'uint64',

A bare int requires subsequent decoding.  Can this instead be an array 
of enum values, with enum values naming each enabled feature?

> +    'num_vqs': 'uint16'
> +  }
> +}
> +
> +##
> +# @virtio-status:
> +#
> +# Return the status of virtio device
> +#
> +# @path: QOBject path of the VirtIODevice
> +#
> +# Returns: status of the VirtIODevice
> +#
> +# Since: 5.1
> +#
> +# Example:
> +#
> +# -> { "execute": "virtio-status",
> +#      "arguments": {
> +#          "path": "/machine/peripheral-anon/device[3]/virtio-backend"
> +#      }
> +#   }
> +# <- { "return": {
> +#          "backend_features": 0,
> +#          "guest_features": 5111807911,

again, this means nothing to me.
  "guest-features": ["feature-a","feature-b"]
is vastly more usable if I'm inspecting the query output, compared to 
decoding the decimal number back into bits then doing a lookup into the 
documentation of which bits mean which features.

> +#          "num_vqs": 3,
> +#          "host_features": 6337593319,
> +#          "device_endian": "little",
> +#          "device_id": 1
> +#      }
> +#    }
> +#
> +##
> +
> +{ 'command': 'virtio-status',
> +  'data': { 'path': 'str' },
> +  'returns': 'VirtioStatus'
> +}

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org