Re: Callback re-registration after libvirtd restart

[Daniel Kučera <libvirt@xxxxxxxxx>]

Hi Daniel,

I tried that but it doesn't work:

func libvirt_close_callback(conn *libvirt.Connect, reason libvirt.ConnectCloseReason){
    log.Printf("close callback: %+v", reason)
}

func event_listen() {
    log.Printf("event_listen %s", conf.Libvirt.LocalUrl)
    hv, err := libvirt.NewConnect(conf.Libvirt.LocalUrl)

    err = hv.RegisterCloseCallback(libvirt_close_callback)
    if err != nil {
        log.Printf("unable to register close callback")
        return
    }
...

The callback fires only when I kill my app,

^CGot signal:%!(EXTRA syscall.Signal=interrupt)
close callback: 0

but not when I restart libvirtd. I tried using both local and remote connect URIs: qemu+ssh://10.130.16.101/system, qemu+ssh://localhost/system, qemu+ssh:///system

Thanks.

D.

2017-05-17 15:24 GMT+02:00 Daniel P. Berrange <berrange@xxxxxxxxxx>:

On Wed, May 17, 2017 at 03:08:23PM +0200, Daniel Kučera wrote:
> Hi all,
>
> I'm using libvirt-go and I following code to listen for lifecycle events:
>
> func event_listen() {
>     log.Printf("event_listen %s", conf.Libvirt.LocalUrl)
>     hv, err := libvirt.NewConnect(conf.Libvirt.LocalUrl)
>
>     lifecycleCallback := func(c *libvirt.Connect, d *libvirt.Domain, event
> *libvirt.DomainEventLifecycle) {
>         event_message(c, d, "lifecycle", event)
>     }
>
>     _, err = hv.DomainEventLifecycleRegister(nil, lifecycleCallback)
>     if err != nil {
>         log.Printf("unable to register event callback")
>         return
>     }
>
>     log.Printf("Libvirt event listener started")
>
>     go func() {
>         for err == nil {
>             err = libvirt.EventRunDefaultImpl()
>             log.Printf("EventRunDefaultImpl err: %+v", err)
>         }
>         time.Sleep(time.Second)
>         event_listen()
>     }()
>
> }
>
> It works ok until I restart libvirtd (service libvirtd restart). After
> that, the inner go func waits some time and continues without error. But
> the callback is not working anymore.
>
> My question is, how can I detect hv reconnect (I guess it's happening in
> background) so I know when to reinitialize callbacks?

There is a separate event you can listen to that notifies when the connection
is closed. See the RegisterCloseCallback() method on the Connect object.

Basically register a callback there, and when it fires, unregister your
existing domain event callbacks, and close your existing Connect object
handle. Then fire a goroutine that loops once every few seconds trying
to open a new Connect object, and when that succeeds register new
domain event callbacks.

Regards,
Daniel
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