Re: [libvirt] Re: [PATCH 2/3] Introduce monitor 'wait' command
On 04/08/09 16:33, Daniel P. Berrange wrote:
On Wed, Apr 08, 2009 at 09:16:43AM -0500, Anthony Liguori wrote:
> The wait command will pause the monitor the command was issued in until a new
> event becomes available. Events are queued if there isn't a waiter present.
> The wait command completes after a single event is available.
>
> Today, we queue events indefinitely but in the future, I suspect we'll drop
> events that are older than a certain amount of time to avoid infinitely
> allocating memory for long running VMs.
>
> To make use of the new notification mechanism, this patch introduces a
> qemu_notify_event() API. This API takes three parameters: a class which is
> meant to classify the type of event being generated, a name which is meant to
> distinguish which event in the class that has been generated, and a details
> parameters which is meant to allow events to send arbitrary data with a given
> event.
Perhaps we should have the ability to turn on/off events, via a 'notify EVENT'
command, and a way turn off the prompt on the channel used for receiving
events.
That would nicely solve the "queue events indefinitely" issue. By
default no events are generated. Apps which want receive them (and thus
receive them) can enable them as needed.
And then in the 2nd monitor channel, a single 'wait' command
would turn
off the monitor prompt and make the channel dedicated for just events,
one per line
(qemu) wait
rtc-change UTC+0100
vnc-client connect 192.46.12.4:9353
vnc-client disconnect 192.46.12.4:9353
vnc-client connect 192.46.12.2:9353
vnc-client disconnect 192.46.12.2:9353
IMHO this is more useful than having "wait" just get one event. You'll
need a dedicated monitor channel for events anyway, so with
one-event-per-wait the management app would have to issue wait in a loop.
BTW: "wait" is quite generic. Maybe we should name the commands
notify-*, i.e. have
notify-enable $class
notify-disable $class
notify-getevents
cheers,
Gerd