4:17 a.m.
Eduardo Habkost <ehabkost(a)redhat.com> writes:
On Mon, May 21, 2018 at 04:46:36PM -0300, Daniel Henrique Barboza
wrote:
>
>
> On 05/21/2018 03:14 PM, Eduardo Habkost wrote:
> > > Issue#2: the flag isn't a property of the target. Due to -no-acpi,
it's
> > > not even a property of the machine type. If it was, query-machines
> > > would be the natural owner of the flag.
> > >
> > > Perhaps query-machines is still the proper owner. The value of
> > > wakeup-suspend-support would have to depend on -no-acpi for the machine
> > > types that honor it. Not ideal; I'd prefer MachineInfo to be static.
> > > Tolerable? I guess that's also a libvirt question.
> > It depends when libvirt is going to query it. Is it OK to only
> > query it after the VM is already up and running? If it is, then
> > we can simply expose it as a read-only property of the machine
> > object.
> >
> > Or, if we don't want to rely on qom-get as a stable API, we can
> > add a new query command (query-machine? query-power-management?)
> >
> In the first version this logic was included in a new query command called
> "query-wakeup-from-suspend-support":
>
> https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg00889.html
>
> In that review it was suggested that this logic could be a flag in either
> query-target
> or query-machines API. Before sending the v2 I sent the following comment:
>
> "After investigating, I think that it's simpler to hook the wakeup support
> info into
> TargetInfo than MachineInfo, given that the detection I'm using for this new
> property
> is based on the current runtime state. Hooking into MachineInfo would
> require to
> change the MachineClass to add a new property, then setting it up for the
> machines
> that have the wakeup support (only x86 so far). Definitely doable, but if we
> don't
> have any favorites between MachineInfo and TargetInfo I'd rather pick the
> simpler
> route.
>
> So, if no one objects, I'll rework this series by putting the logic inside
> query-target
> instead of a new API."
Apologies for not noticing this series months ago. :(
Seconded. Daniel, this (minor) mess is absolutely not your fault.
> 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?
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.
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.
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).
Markus, Eric, what do you think?
Haven't made up my mind, yet :)