[libvirt] [PATCHv3 09/10] threshold: add threshold event handling in qemu

[Peter Krempa]

On Mon, Jun 22, 2015 at 17:06:45 -0600, Eric Blake wrote:
> With this patch, block write threshold events delivered by qemu
> are converted into libvirt events.
> 
> This patch takes the easy road, and only reports events if
> the node name is still cached by libvirtd (true in the common
> case when libvirtd is not restarted, since you can't get an
> event if you didn't register a threshold).  A followup patch
> will be needed to properly handle grabbing the job lock and
> getting the node name when the cache lookup fails, using code
> similar to how we update domain XML after a block job
> completes.  But for getting the initial API in place, I
> figured this was a good enough start.
> 
> * src/qemu/qemu_monitor_json.c
> (qemuMonitorJSONHandleBlockWriteThreshold): New function.
> * src/qemu/qemu_monitor.c (qemuMonitorEmitBlockThreshold):
> Likewise.
> * src/qemu/qemu_monitor.h (qemuMonitorEmitBlockThreshold):
> Likewise.
> * src/qemu/qemu_process.c (qemuProcessHandleBlockThreshold):
> Likewise.
> 
> Signed-off-by: Eric Blake <eblake at redhat.com>
> ---
>  src/qemu/qemu_monitor.c      | 14 ++++++++++++++
>  src/qemu/qemu_monitor.h      | 11 +++++++++++
>  src/qemu/qemu_monitor_json.c | 31 +++++++++++++++++++++++++++++++
>  src/qemu/qemu_process.c      | 44 ++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 100 insertions(+)

...

> 
> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> index ba84182..5f582e5 100644
> --- a/src/qemu/qemu_process.c
> +++ b/src/qemu/qemu_process.c
> @@ -1037,6 +1037,49 @@ qemuProcessHandleBlockJob(qemuMonitorPtr mon ATTRIBUTE_UNUSED,
> 
> 
>  static int
> +qemuProcessHandleBlockThreshold(qemuMonitorPtr mon ATTRIBUTE_UNUSED,
> +                                virDomainObjPtr vm,
> +                                const char *node,
> +                                unsigned long long threshold,
> +                                unsigned long long length,
> +                                void *opaque)
> +{
> +    virQEMUDriverPtr driver = opaque;
> +    virDomainDiskDefPtr disk;
> +    virObjectEventPtr event = NULL;
> +    const char *path = NULL;
> +
> +    virObjectLock(vm);
> +
> +    VIR_DEBUG("Block threshold for node %s (domain: %p,%s) threshold %llu "
> +              "length %llu", node, vm, vm->def->name, threshold, length);
> +
> +    /* TODO: If the node name is not found in the current domain XML,
> +     * we need to grab a job lock and query the monitor to repopulate
> +     * the node name cache.  For now, if that happens, we just discard
> +     * the event.  */

This duality of operations is why we should cache the node names
upfront.

> +    if (!(disk = qemuDomainDiskResolveAllocationNode(driver, vm, node,
> +                                                     false))) {
> +        VIR_WARN("failed to locate disk matching node '%s'", node);
> +        goto cleanup;
> +    }
> +    if (virStorageSourceIsLocalStorage(disk->src))
> +        path = disk->src->path;
> +
> +    /* TODO: Once we support node names for more than just the active
> +     * layer, we will need to map this into 'vda[1]' notation. */
> +    event = virDomainEventWriteThresholdNewFromObj(vm, disk->dst, path,
> +                                                   threshold, length);
> +

Peter
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