Re: [PATCH v8 02/12] accel: Introduce 'query-accels' QMP command

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 6/8/21 3:27 PM, Thomas Huth wrote:
> On 26/05/2021 19.04, Philippe Mathieu-Daudé wrote:
>> 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"
>>              }
>>          ]
>>      }
>>
>> Reviewed-by: Eric Blake <eblake@redhat.com>
>> Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
>> Tested-by: Alex Bennée <alex.bennee@linaro.org>
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>> ---
>> v8:
>> - Include code snippet from Markus adding to machine-target.json
>>    to be able to use enum values or union branches conditional.
>> - Use accel_find() on enum to be sure the accelerator is enabled
>>    at runtime (chat with jsnow / eblake).
>>
>> Cc: Eric Blake <eblake@redhat.com>
>> Cc: John Snow <jsnow@redhat.com>
>> Cc: Markus Armbruster <armbru@redhat.com>
>> ---
>>   qapi/machine-target.json | 54 ++++++++++++++++++++++++++++++++++++++++
>>   accel/accel-qmp.c        | 32 ++++++++++++++++++++++++
>>   accel/meson.build        |  2 +-
>>   3 files changed, 87 insertions(+), 1 deletion(-)
>>   create mode 100644 accel/accel-qmp.c
>>
>> diff --git a/qapi/machine-target.json b/qapi/machine-target.json
>> index e7811654b72..586a61b5d99 100644
>> --- a/qapi/machine-target.json
>> +++ b/qapi/machine-target.json
>> @@ -329,3 +329,57 @@
>>   ##
>>   { 'command': 'query-cpu-definitions', 'returns': ['CpuDefinitionInfo'],
>>     'if': 'defined(TARGET_PPC) || defined(TARGET_ARM) ||
>> defined(TARGET_I386) || defined(TARGET_S390X) || defined(TARGET_MIPS)' }
>> +
>> +##
>> +# @Accelerator:
>> +#
>> +# An enumeration of accelerator names.
>> +#
>> +# Since: 6.1
>> +##
>> +{ 'enum': 'Accelerator',
>> +  'data': [
>> +      { 'name': 'hax', 'if': 'defined(CONFIG_HAX)' },
>> +      { 'name': 'hvf', 'if': 'defined(CONFIG_HVF)' },
>> +      { 'name': 'kvm', 'if': 'defined(CONFIG_KVM)' },
>> +      { 'name': 'qtest' },
>> +      { 'name': 'tcg', 'if': 'defined(CONFIG_TCG)' },
>> +      { 'name': 'whpx', 'if': 'defined(CONFIG_WHPX)' },
>> +      { 'name': 'xen', 'if': 'defined(CONFIG_XEN_BACKEND)' } ] }
>> +
>> +##
>> +# @AcceleratorInfo:
>> +#
>> +# Accelerator information.
>> +#
>> +# @name: The accelerator name.
>> +#
>> +# Since: 6.1
>> +##
>> +{ 'struct': 'AcceleratorInfo',
>> +  'data': { 'name': 'Accelerator' } }
>> +
>> +##
>> +# @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'] }
> 
> What about Markus' comment here:
> 
>  https://lore.kernel.org/qemu-devel/87mtsoieyz.fsf@dusky.pond.sub.org/
> 
> ?
> 
> If I've got him right, you don't need the command at all, the Accelerator
> enum should be sufficient?

Yes, this is the part jsnow said "we are waiting for Markus to comment"
on the other thread ;) We'd like to only have enums, but QAPI doesn't
seem to allow a "leaf without branch", we need a command or struct to
use the enum else it is elided. Or maybe we didn't understood Markus
idea.