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&gt; 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?