Re: [PATCH v3 1/6] accel: Introduce 'query-accels' QMP command

From: Markus Armbruster <armbru@redhat.com>
To: "Philippe Mathieu-Daudé" <philmd@redhat.com>
Cc: "Laurent Vivier" <lvivier@redhat.com>,
	"Thomas Huth" <thuth@redhat.com>,
	"Daniel P . Berrangé" <berrange@redhat.com>,
	"Eduardo Habkost" <ehabkost@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	"Richard Henderson" <richard.henderson@linaro.org>,
	qemu-devel@nongnu.org, "Andrew Jones" <drjones@redhat.com>,
	qemu-arm@nongnu.org, "Claudio Fontana" <cfontana@suse.de>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Igor Mammedov" <imammedo@redhat.com>
Subject: Re: [PATCH v3 1/6] accel: Introduce 'query-accels' QMP command
Date: Thu, 15 Apr 2021 17:06:57 +0200	[thread overview]
Message-ID: <87im4nbn8u.fsf@dusky.pond.sub.org> (raw)
In-Reply-To: <20210415122633.4054644-2-philmd@redhat.com> ("Philippe =?utf-8?Q?Mathieu-Daud=C3=A9=22's?= message of "Thu, 15 Apr 2021 14:26:28 +0200")

Philippe Mathieu-Daudé <philmd@redhat.com> writes:

> Introduce the 'query-accels' QMP command which returns a list
> of built-in accelerator names.
>
> - Accelerator is a QAPI enum of all existing accelerators,
>
> - AcceleratorInfo is a QAPI structure providing accelerator
>   specific information. Currently the common structure base
>   provides the name of the accelerator, while the specific
>   part is empty, but each accelerator can expand it.
>
> - 'query-accels' QMP command returns a list of @AcceleratorInfo
>
> For example on a KVM-only build we get:
>
>     { "execute": "query-accels" }
>     {
>         "return": [
>             {
>                 "name": "qtest"
>             },
>             {
>                 "name": "kvm"
>             }
>         ]
>     }
>
> Note that we can't make the enum values or union branches conditional
> because of target-specific poisoning of accelerator definitions.
>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
> Since v2: @since 6.0 -> 6.1, added note (Eric)
> Since v1: 'type' -> 'name' in comments
> ---
>  qapi/machine.json | 49 +++++++++++++++++++++++++++++++++++++++++++++++
>  accel/accel-qmp.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++
>  accel/meson.build |  2 +-
>  3 files changed, 99 insertions(+), 1 deletion(-)
>  create mode 100644 accel/accel-qmp.c
>
> diff --git a/qapi/machine.json b/qapi/machine.json
> index 6e90d463fc9..4babc06f8b0 100644
> --- a/qapi/machine.json
> +++ b/qapi/machine.json
> @@ -1274,3 +1274,52 @@
>  ##
>  { 'event': 'MEM_UNPLUG_ERROR',
>    'data': { 'device': 'str', 'msg': 'str' } }
> +
> +##
> +# @Accelerator:
> +#
> +# An enumeration of accelerator names.
> +#
> +# Since: 6.1
> +##
> +{ 'enum': 'Accelerator',
> +  'data': [ 'qtest', 'tcg', 'kvm', 'hax', 'hvf', 'whpx', 'xen' ] }
> +
> +##
> +# @AcceleratorInfo:
> +#
> +# Accelerator information.
> +#
> +# @name: The accelerator name.
> +#
> +# Since: 6.1
> +##
> +{ 'union': 'AcceleratorInfo',
> +  'base': {'name': 'Accelerator'},
> +  'discriminator': 'name',
> +  'data': { } }

Not wrong, but feels overengineered unless you have concrete plans to
add variant members in the near future.  Simpler:

   { 'struct': 'AcceleratorInfo',
     'data': { 'name': 'Accelerator' } }

Changing this to flat union when we actually need it won't break
compatibility.

> +
> +##
> +# @query-accels:
> +#
> +# Get a list of AcceleratorInfo for all built-in accelerators.
> +#
> +# Returns: a list of @AcceleratorInfo describing each accelerator.
> +#
> +# Since: 6.1
> +#
> +# Example:
> +#
> +# -> { "execute": "query-accels" }
> +# <- { "return": [
> +#        {
> +#            "name": "qtest"
> +#        },
> +#        {
> +#            "name": "kvm"
> +#        }
> +#    ] }
> +#
> +##
> +{ 'command': 'query-accels',
> +  'returns': ['AcceleratorInfo'] }
[...]