[libvirt] [PATCH 09/10] qemu: caps: Probe events from 'query-qmp-schema' rather than 'query-events'

[Eric Blake]

On 2/7/19 6:28 AM, Peter Krempa wrote:
> QEMU plans to deprecate 'query-events' as it's non-extensible. Events
> are also described by 'query-qmp-schema' so we can use that one instead.
> 
> This patch adds detection of events to
> virQEMUCapsProbeQMPSchemaCapabilities using the same structure declaring
> them for the old approach (virQEMUCapsEvents). This is possible as the
> name is the same in the QMP schema and our detector supports that
> trivially.
> 
> For any complex queries virQEMUCapsQMPSchemaQueries can be used in the
> future.
> 
> For now we still call 'query-events' and discard the result so that it's
> obvious that the tests pass. This will be cleaned up later.
> 
> Signed-off-by: Peter Krempa <pkrempa at redhat.com>
> ---
>  src/qemu/qemu_capabilities.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
> index 7f3f87c48d..9c79511b1d 100644
> --- a/src/qemu/qemu_capabilities.c
> +++ b/src/qemu/qemu_capabilities.c
> @@ -2123,6 +2123,12 @@ virQEMUCapsProbeQMPEvents(virQEMUCapsPtr qemuCaps,
>      if ((nevents = qemuMonitorGetEvents(mon, &events)) < 0)
>          return -1;
> 
> +    /* we can probe events also from the QMP schema so we can skip this here */
> +    if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_QUERY_QMP_SCHEMA)) {
> +        virStringListFreeCount(events, nevents);
> +        return 0;
> +    }

Slick. For this patch, we call query-events unconditionally (as before),
but when qemu is new enough to also have introspection, we throw away
the results without using them...

> +
>      virQEMUCapsProcessStringFlags(qemuCaps,
>                                    ARRAY_CARDINALITY(virQEMUCapsEvents),
>                                    virQEMUCapsEvents,
> @@ -4138,6 +4144,14 @@ virQEMUCapsProbeQMPSchemaCapabilities(virQEMUCapsPtr qemuCaps,
>              virQEMUCapsSet(qemuCaps, entry->flag);
>      }
> 
> +    /* probe also for basic event support */
> +    for (i = 0; i < ARRAY_CARDINALITY(virQEMUCapsEvents); i++) {
> +        entry = virQEMUCapsEvents + i;
> +
> +        if (virQEMUQAPISchemaPathExists(entry->value, schema))
> +            virQEMUCapsSet(qemuCaps, entry->flag);
> +    }
> +

...and rebuild the same results from the introspection. I like the
split, and am glad that it was fairly trivial to update to introspection
while still keeping the fallback to query-events on older qemu.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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