Re: [Qemu-block] [Qemu-devel] [PATCH v4 1/2] virtio: introduce `query-virtio' QMP command

[Jan Dakinevich]

On 10/03/2017 05:02 PM, Eric Blake wrote:
> On 10/03/2017 07:47 AM, Jan Dakinevich wrote:
>> The command is intended for gathering virtio information such as status,
>> feature bits, negotiation status. It is convenient and useful for debug
>> purpose.
>>
>> The commands returns generic virtio information for virtio such as
>> common feature names and status bits names and information for all
>> attached to current machine devices.
>>
>> To retrieve names of device-specific features `get_feature_name'
>> callback in VirtioDeviceClass also was introduced.
>>
>> Cc: Denis V. Lunev <address@hidden>
>> Signed-off-by: Jan Dakinevich <address@hidden>
>> ---
>>  hw/block/virtio-blk.c       |  21 +++++++++
>>  hw/char/virtio-serial-bus.c |  15 +++++++
>>  hw/display/virtio-gpu.c     |  13 ++++++
>>  hw/net/virtio-net.c         |  35 +++++++++++++++
>>  hw/scsi/virtio-scsi.c       |  16 +++++++
>>  hw/virtio/Makefile.objs     |   2 +
>>  hw/virtio/virtio-balloon.c  |  15 +++++++
>>  hw/virtio/virtio-stub.c     |   9 ++++
>>  hw/virtio/virtio.c          | 101 
>> ++++++++++++++++++++++++++++++++++++++++++++
>>  include/hw/virtio/virtio.h  |   2 +
>>  qapi-schema.json            |   1 +
>>  qapi/virtio.json            |  94 +++++++++++++++++++++++++++++++++++++++++
>>  12 files changed, 324 insertions(+)
>>  create mode 100644 hw/virtio/virtio-stub.c
>>  create mode 100644 qapi/virtio.json
> 
> This creates a new .json file, but does not touch MAINTAINERS.  Our idea
> in splitting the .json files was to make it easier for each sub-file
> that needs a specific maintainer in addition to the overall *.json line
> for QAPI maintainers, so this may deserve a MAINTAINERS entry.
> 

Ok.

>> +++ b/qapi/virtio.json
>> @@ -0,0 +1,94 @@
>> +# -*- Mode: Python -*-
>> +#
>> +
>> +##
>> +# = Virtio devices
>> +##
>> +
>> +{ 'include': 'common.json' }
>> +
>> +##
>> +# @VirtioInfoBit:
>> +#
>> +# Named virtio bit
>> +#
>> +# @bit: bit number
>> +#
>> +# @name: bit name
>> +#
>> +# Since: 2.11.0
>> +#
>> +##
>> +{
>> +    'struct': 'VirtioInfoBit',
>> +    'data': {
>> +        'bit': 'uint64',
> 
> Why is this a 64-bit value? Are the values 0-63, or are they 1, 2, 4, 8,
> ...?  The documentation on 'bit number' is rather sparse.

I would prefer `uint' here, but I don't see generic unsigned type (may
be, I am mistaken). I could use uint8 here, though.

> 
>> +        'name': 'str'
> 
> Wouldn't an enum type be better than an open-ended string?
> 

Bit names are not known here, they are obtained from virtio device
implementations.

>> +    }
>> +}
>> +
>> +##
>> +# @VirtioInfoDevice:
>> +#
>> +# Information about specific virtio device
>> +#
>> +# @qom_path: QOM path of the device
> 
> Please make this 'qom-path' - new interfaces should prefer '-' over '_'.

Ok.

>> +#
>> +# @feature-names: names of device-specific features
>> +#
>> +# @host-features: bitmask of features, provided by devices
>> +#
>> +# @guest-features: bitmask of features, acknowledged by guest
>> +#
>> +# @status: virtio device status bitmask
>> +#
>> +# Since: 2.11.0
>> +#
>> +##
>> +{
>> +    'struct': 'VirtioInfoDevice',
>> +    'data': {
>> +        'qom_path': 'str',
>> +        'feature-names': ['VirtioInfoBit'],
>> +        'host-features': 'uint64',
>> +        'guest-features': 'uint64',
>> +        'status': 'uint64'
> 
> I'm wondering if this is the best representation (where the caller has
> to parse the integer and then lookup in feature-names what each bit of
> the integer represents).  But I'm not sure I have anything better off
> the top of my head.
> 

Consider it as way to tell caller about names of supported features.

>> +    }
>> +}
>> +
>> +##
>> +# @VirtioInfo:
>> +#
>> +# Information about virtio devices
>> +#
>> +# @feature-names: names of common virtio features
>> +#
>> +# @status-names: names of bits which represents virtio device status
>> +#
>> +# @devices: list of per-device virtio information
>> +#
>> +# Since: 2.11.0
>> +#
>> +##
>> +{
>> +    'struct': 'VirtioInfo',
>> +    'data': {
>> +        'feature-names': ['VirtioInfoBit'],
> 
> Why is feature-names listed at two different nestings of the return value?
> 

These are different feature names. First names are common and predefined
for all devices. Second names are device-specific.

>> +        'status-names': ['VirtioInfoBit'],
>> +        'devices': ['VirtioInfoDevice']
>> +    }
>> +}
>> +
>> +
>> +##
>> +# @query-virtio:
>> +#
>> +# Returns generic and per-device virtio information
>> +#
>> +# Since: 2.11.0
>> +#
>> +##
>> +{
>> +    'command': 'query-virtio',
>> +    'returns': 'VirtioInfo'
>> +}
>>
> 

-- 
Best regards
Jan Dakinevich