Re: [Libvir] Asynchronous notifications of domain start/stop
On Wed, Jul 18, 2007 at 10:56:42AM +0100, Richard W.M. Jones wrote:
I had some private discussions with a developer who wants to start
using
libvirt, but requires asynch notifications of domain start/stop (and
other stuff, but this will do for the moment). Right now he's using
XenStore watches. The alternative of polling didn't look very appealing
for him.
A rough API for this might look like this:
typedef int virEventHandle;
/* Register a callback to catch domain start events. */
virEventHandle virEventDomainStart
(virConnectPtr,
void (*f) (virConnectPtr, int domid));
/* Register a callback to catch domain stop events. */
virEventHandle virEventDomainStop
(virConnectPtr,
void (*f) (virConnectPtr, int domid));
/* Unregister any type of callback. */
int virEventCancel (virConnectPtr, virEventHandle handle);
Yuk - this is going to give an ever growing number of callbacks - there
are many interesting states besides Start & Start. Pause, resume, save,
restore. Probably want something that takes
void (*virDomainStateNotify)(virDomainPtr dom, int state);
The 'state' value could be any virDomainState constant - though we should
not notify for changes betweeen 'nostate', 'running' and
'blocked' because
they all effectively just mean 'running' and Xen domains ossicilate between
them many times a second. Or maybe define a different set of 'state'
transitions to represent the actiohn triggered, rather than the resulting
state ?
Any you could register with:
virDomainRegisterStateNotify(virDomainPtr, virDomainStateNotify);
virDomainRegisterStateNotify(virDomainPtr);
A pre-requisite of using these notifications would be that the application
had registered an event loop implementation, as per
http://www.redhat.com/archives/libvir-list/2007-May/msg00083.html
See src/event.c and srv/event.h for actual impls we already have.
Dan.
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