Re: [PATCH v4 46/55] qapi: add query-targets

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

On 28/9/26 12:57, Daniel P. Berrangé wrote:
> On Mon, Sep 28, 2026 at 06:51:41PM +0800, Yonggang Luo wrote:
>> On Mon, Sep 28, 2026 at 6:39 PM Philippe Mathieu-Daudé <
>> philmd@oss.qualcomm.com> wrote:
>>>
>>> On 28/9/26 12:13, Daniel P. Berrangé wrote:
>>>> On Sat, Sep 26, 2026 at 03:00:45PM +0800, Yonggang Luo wrote:
>>>>> query-targets lists each linked target, including none, with its
>>>>> arch, endianness, and the machines that target accepts.
>>>>>
>>>>> Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
>>>>> ---
>>>>>    hw/core/machine-qmp-cmds.c | 30 ++++++++++++++++++++++++++++++
>>>>>    qapi/machine.json          | 35 +++++++++++++++++++++++++++++++++++
>>>>>    2 files changed, 65 insertions(+)
>>>>
>>>>
>>>>> diff --git a/qapi/machine.json b/qapi/machine.json
>>>>> index 6aaa2af709a..d8cdea6203e 100644
>>>>> --- a/qapi/machine.json
>>>>> +++ b/qapi/machine.json
>>>>> @@ -307,6 +307,41 @@
>>>>>    ##
>>>>>    { 'command': 'query-target', 'returns': 'QemuTargetInfo' }
>>>>>
>>>>> +##
>>>>> +# @TargetMachines:
>>>>> +#
>>>>> +# One registered system target and the machines that can run on it.
>>>>> +#
>>>>> +# @arch: the target architecture
>>>>> +#
>>>>> +# @endianness: the target endianness
>>>>> +#
>>>>> +# @machines: machine type names, not aliases
>>>>> +#
>>>>> +# Since: 11.2
>>>>> +##
>>>>> +{ 'struct': 'TargetMachines',
>>>>> +  'data': { 'arch': 'SysEmuTarget',
>>>>> +            'endianness': 'EndianMode',
>>>>> +            'machines': ['str'] } }
>>>>
>>>> We already have  'QemuTargetInfo' struct which is used
>>>> with 'query-target', that should also be used with the
>>>> new 'query-targets' command.
>>>>
>>>> We need to add the 'endianness' field to QemuTargetInfo.
>>>
>>> Why do we want to expose endianness, and what endianness to
>>> expose? Endianness is a runtime bit state of CPUs. Sometime
>>> this bit is hardwired but that is an implementation detail.
>>
>> For some targets it's, but for some targets it's not. for example
>>
>> mips-softmmu.mak
>> mipsel-softmmu.mak
>> mips64el-softmmu.mak
>> mips64-softmmu.mak
>>
>>
>> mips64el-softmmu.mak
>> mips64-softmmu.mak
>> only differ the endianless
> 
> "EndianMode" is a tri-state including 'unspecified' as a value,
> so we can cope with both scenarios - the targets where endianness
> is runtime switchable in the CPU can use 'unspecified' as the
> EndianMode. That behaviour should be documented in the QAPI
> docs for QemuTargetInfo

OK but still I don't understand the usefulness of exposing that
at the machine level, since this is a CPU property.

Machine != QEMU binary.

Are you trying to expose binary properties to management layer?
Can you explain the use case?