Eduardo Habkost <ehabkost@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 :)