Re: [libvirt] [Qemu-devel] [PATCH v7 1/3] qmp: adding 'wakeup-suspend-support' in query-target
On Wed, May 23, 2018 at 11:17:55AM +0200, Markus Armbruster wrote:
Eduardo Habkost <ehabkost(a)redhat.com> writes:
> On Mon, May 21, 2018 at 04:46:36PM -0300, Daniel Henrique Barboza wrote:
[...]
>> Since no objection was made back then, this logic was put
into query-target
>> starting
>> in v2. Still, I don't have any favorites though: query-target looks ok,
>> query-machine
>> looks ok and a new API looks ok too. It's all about what makes (more) sense
>> in the
>> management level, I think.
>
> I understand the original objection from Eric: having to add a
> new command for every runtime flag we want to expose to the user
> looks wrong to me.
Agreed.
> However, extending query-machines and query-target looks wrong
> too, however. query-target looks wrong because this not a
> property of the target. query-machines is wrong because this is
> not a static property of the machine-type, but of the running
> machine instance.
Of the two, query-machines looks less wrong.
Arguably, -no-acpi should not exist. It's an ad hoc flag that sneakily
splits a few machine types into two variants, with and without ACPI.
It's silently ignored for other machine types, even APCI-capable ones.
If the machine type variants with and without ACPI were separate types,
wakeup-suspend-support would be a static property of the machine type.
However, "separate types" probably doesn't scale: I'm afraid we'd
end up
with an undesirable number of machine types. Avoiding that is exactly
why we have machine types with configurable options. I suspect that's
how ACPI should be configured (if at all).
So, should we make -no-acpi sugar for a machine type parameter? And
then deprecate -no-acpi for good measure?
I think we should.
> Can we have a new query command that could be an obvious
> container for simple machine capabilities that are not static? A
> name like "query-machine" would be generic enough for that, I
> guess.
Having command names differ only in a single letter is awkward, but
let's focus on things other than naming now, and use
query-current-machine like a working title.
query-machines is wrong because wakeup-suspend-support isn't static for
some machine types.
query-current-machine is also kind of wrong because
wakeup-suspend-support *is* static for most machine types.
The most appropriate solution depends a lot on how/when
management software needs to query this.
If they only need to query it at runtime for a running VM,
there's no reason for us to go of our way and add complexity just
to make it look like static data in query-machines.
On the other hand, if they really need to query it before
configuring/starting a VM, it won't be useful at all to make it
available only at runtime.
Daniel, when/how exactly software would need to query the new
flag?
Worse, a machine type property that is static for all machine types
now
could conceivably become dynamic when we add a machine type
configuration knob.
This isn't the first time a machine capability that seems static
actually depends on other configuration arguments. We will
probably need to address this eventually.
Would a way to tie the property to the configuration knob help?
Something like wakeup-suspend-support taking values true (supported),
false (not supported), and "acpi" (supported if machine type
configuration knob "acpi" is switched on).
I would prefer a more generic mechanism. Maybe make
'query-machines' accept a 'machine-options' argument?
--
Eduardo