Re: [PATCH v3 1/4] qapi: net: Add query-netdevs command

[Markus Armbruster]

Alexey Kirillov <lekiravi@yandex-team.ru> writes:

> 07.09.2020, 15:40, "Markus Armbruster" <armbru@redhat.com>:
>> Alexey Kirillov <lekiravi@yandex-team.ru> writes:
>>
>>>  Hi!
>>>
>>>  02.09.2020, 14:23, "Markus Armbruster" <armbru@redhat.com>:
>>>>  Alexey Kirillov <lekiravi@yandex-team.ru> writes:
>>>>
>>>>>   Add a qmp command that provides information about currently attached
>>>>>   backend network devices and their configuration.
>>>>>
>>>>>   Signed-off-by: Alexey Kirillov <lekiravi@yandex-team.ru>
>>>>
>>>>  [...]
>>>>>   diff --git a/qapi/net.json b/qapi/net.json
>>>>>   index ddb113e5e5..c09322bb42 100644
>>>>>   --- a/qapi/net.json
>>>>>   +++ b/qapi/net.json
>>>>>   @@ -714,3 +714,71 @@
>>>>>    ##
>>>>>    { 'event': 'FAILOVER_NEGOTIATED',
>>>>>      'data': {'device-id': 'str'} }
>>>>>   +
>>>>>   +##
>>>>>   +# @NetdevInfo:
>>>>>   +#
>>>>>   +# Configuration of a network backend device (netdev).
>>>>>   +#
>>>>>   +# @id: Device identifier.
>>>>>   +#
>>>>>   +# @type: Specify the driver used for interpreting remaining arguments.
>>>>>   +#
>>>>>   +# @peer-id: Connected frontend network device identifier.
>>>>>   +#
>>>>>   +# Since: 5.2
>>>>>   +##
>>>>>   +{ 'union': 'NetdevInfo',
>>>>>   + 'base': { 'id': 'str',
>>>>>   + 'type': 'NetClientDriver',
>>>>>   + '*peer-id': 'str' },
>>>>>   + 'discriminator': 'type',
>>>>>   + 'data': {
>>>>>   + 'user': 'NetdevUserOptions',
>>>>>   + 'tap': 'NetdevTapOptions',
>>>>>   + 'l2tpv3': 'NetdevL2TPv3Options',
>>>>>   + 'socket': 'NetdevSocketOptions',
>>>>>   + 'vde': 'NetdevVdeOptions',
>>>>>   + 'bridge': 'NetdevBridgeOptions',
>>>>>   + 'netmap': 'NetdevNetmapOptions',
>>>>>   + 'vhost-user': 'NetdevVhostUserOptions',
>>>>>   + 'vhost-vdpa': 'NetdevVhostVDPAOptions' } }
>>>>
>>>>  This is union Netdev plus a common member @peer-id, less the variant
>>>>  members for NetClientDriver values 'nic' and 'hubport'.
>>>>
>>>>  Can 'type: 'nic' and 'type': 'hubport' occur?
>>>
>>>  No, it can't. We don't support NIC/hubport in query-netdevs, so we neither 
>>> create this
>>>  structure for them, nor store config.
>>
>> Same for 'none', I guess.
>>
>> As defined, NetdevInfo allows types 'none', 'nic', and 'hubport', it
>> just has no variant members for them. The fact that they can't occur is
>> not coded into the type, and therefore not visible in introspection.
>>
>> To make introspection more precise, we'd have to define a new enum type.
>> How much that would complicate the C code is unclear.
>>
>> Do we need it to be more precise? Eric, got an opinion?
>>
>> Existing type Netdev has the same issue for 'none' and 'nic'. I guess
>> this is so we can reuse the type for -net. Not sure that's a good idea,
>> but not this patch's problem.
>>
>>>>  What's the use case for @peer-id?
>>>
>>>  Main reason is to provide information "is this backend connected to 
>>> frontend device".
>>>  User also may want to know which backend used for frontend device.
>>>
>>>>  Assuming we want @peer-id: its documentation is too vague. Cases:
>>>>
>>>>  * Not connected to a frontend: I guess @peer-id is absent then.
>>>
>>>  Absolutely correct.
>>>
>>>>  * Connected to a frontend
>>>>
>>>>    - that has a qdev ID (the thing you set with -device id=...): I guess
>>>>      it's the qdev ID then.
>>>
>>>  Correct.
>>>
>>>>    - that doesn't have a qdev ID: anyone's guess.
>>>
>>>  We use field "name" of structure NetClientState, so if there is no direct 
>>> ID setting,
>>>  there must be generated name (in format "model.id").
>>
>> Perhaps:
>>
>>       # @peer-id: the connected network backend's name (absent if no
>>       # backend is connected)
>
> Maybe you mean:
>
> # @peer-id: The connected frontend network device name (absent if no frontend
> # is connected).

Yes, I wrote backend, but meant frontend.

Aside: our naming is undisciplined: we use both "id" and "name" in QMP
for NetClientState member name.  Unfortunate.

> In any case, thanks for pointing. I'll add this in the next patch version.
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