Re: [libvirt] [PATCH v3 3/4] qemu_capabilities: Introduce QEMU_CAPS_PM_WAKEUP_SUPPORT
On 4/11/19 10:39 AM, Peter Krempa wrote:
On Thu, Apr 11, 2019 at 10:25:11 +0200, Michal Privoznik wrote:
> This capability tells whether qemu is capable of waking up the
> guest from PM suspend.
>
> Based-on-work-of: Daniel Henrique Barboza <danielhb413(a)gmail.com>
> Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com>
> ---
> src/qemu/qemu_capabilities.c | 24 +++++++++++++++++++
> src/qemu/qemu_capabilities.h | 3 +++
> .../caps_4.0.0.riscv32.replies | 11 +++++++++
> .../caps_4.0.0.riscv32.xml | 1 +
> .../caps_4.0.0.riscv64.replies | 11 +++++++++
> .../caps_4.0.0.riscv64.xml | 1 +
> .../caps_4.0.0.x86_64.replies | 11 +++++++++
> .../caps_4.0.0.x86_64.xml | 1 +
> 8 files changed, 63 insertions(+)
>
[...]
> bool
> virQEMUCapsCPUFilterFeatures(const char *name,
> void *opaque)
> @@ -4373,6 +4395,8 @@ virQEMUCapsInitQMPMonitor(virQEMUCapsPtr qemuCaps,
> return -1;
> if (virQEMUCapsProbeQMPSEVCapabilities(qemuCaps, mon) < 0)
> return -1;
> + if (virQEMUCapsProbeQMPCurrentMachine(qemuCaps, mon) < 0)
> + return -1;
This seems wrong by definition. The function is supposed to query
current machine, but the capability lookup code uses 'none' machine
type. IIUC the support for wakeup in some cases depends on the presence
of ACPI in the guest and thus really can't be cached this way.
Yep, I was just about to write this but then got sidetracked.
So I see two options here:
1) Query if guest is capable of PM suspend at runtime. However, this has
to be done in a clever way. It would need to be done not only in
qemuProcessLaunch() (or some subordinate functions), it would need to be
done in qemuProcessReconnect() too (to cover case when user is upgrading
libvirt). For this, qemuMonitorConnect() looks like the best place -
it's called from both locations and it also already contains some
'runtime capabilities' querying. Except not really - the migration
capabilities queried there are stored in @priv->migrationCaps rather
than priv->qemuCaps.
Problem with storing runtime capabilities in priv->qemuCaps is that they
would get formatted into status XML. And this opens whole different can
of worms. For instance, this feature relies on 'query-commands' to see
if 'query-current-machine' command is available. Well, we can't re-run
'query-commands' in runtime because that might change the set of
qemuCaps used when constructing cmd line.
Way around this is to have 'runtime only' capabilities, that would not
be stored in status XML. At some point we will need those, but writing
that infrastructure is not easy and a bit too much to ask for this small
fix. Especially, when we have another option:
2) Issue 'query-current-machine' from qemuDomainPMSuspendForDuration().
In every run. This is a bit suboptimal, but how frequently do we expect
this API to be called? Caching qemu capabilities is there to speed up
decission process which makes sense if we'd be making the decission 1000
times a second (e.g. building cmd line). With this approach the slowdown
would be negligible. Of course, we would need to run the command in
'silent' mode, i.e. not report any error if qemu doesn't know it.
Michal