Re: [PULL 1/1] machine: Disallow specifying topology parameters as zero

["wangyanan (Y)" <wangyanan55@huawei.com>]

On 2021/8/17 20:22, Andrew Jones wrote:
> On Tue, Aug 17, 2021 at 01:06:19PM +0100, Peter Maydell wrote:
>> On Tue, 17 Aug 2021 at 13:02, Andrew Jones <drjones@redhat.com> wrote:
>>> On Mon, Aug 16, 2021 at 11:37:21PM +0200, Paolo Bonzini wrote:
>>>> How do we know that no one has ever used such configuration? The conversion
>>>> was meant to be bug-compatible.
>>> We don't. But we do know that a zero input value was never documented
>>> prior to 1e63fe68580, which has not yet been released. Can we claim
>>> that an undocumented input value has undefined behavior, giving us
>>> freedom to modify that behavior until it is documented?
>> Dunno; I definitely don't want a behaviour-change patch at this
>> point in the release-cycle, though...
>>
> Can we replace this patch with the following one for now? And then
> discuss this further before committing to supporting a zero input?
Yeah, I think at least the doc needs to be fixed in 6.1.

Then we may think about deprecating this behavior since 6.2,
I have implemented the deprecation locally and it can be post
with the smp parsing improvement series.

Thanks,
Yanan
.
> Thanks,
> drew
>
> Author: Andrew Jones <drjones@redhat.com>
> Date:   Tue Aug 17 14:17:29 2021 +0200
>
>      qapi/machine.json: Remove zero value reference from SMPConfiguration documentation
>      
>      Commit 1e63fe685804 ("machine: pass QAPI struct to mc->smp_parse")
>      introduced documentation stating that a zero input value for an SMP
>      parameter indicates that its value should be automatically configured.
>      This is indeed how things work today, but we'd like to change that.
>      Avoid documenting behaviors we want to leave undefined for the time
>      being, giving us freedom to change it later.
>      
>      Fixes: 1e63fe685804 ("machine: pass QAPI struct to mc->smp_parse")
>      Signed-off-by: Andrew Jones <drjones@redhat.com>
>
> diff --git a/qapi/machine.json b/qapi/machine.json
> index c3210ee1fb24..157712f00614 100644
> --- a/qapi/machine.json
> +++ b/qapi/machine.json
> @@ -1288,7 +1288,7 @@
>   ##
>   # @SMPConfiguration:
>   #
> -# Schema for CPU topology configuration.  "0" or a missing value lets
> +# Schema for CPU topology configuration.  A missing value lets
>   # QEMU figure out a suitable value based on the ones that are provided.
>   #
>   # @cpus: number of virtual CPUs in the virtual machine
>
> .