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

[Andrew Jones]

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?

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