libvirt users - May 2017 - Re: Callback re-registration after libvirtd restart

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?

Thanks.

BR
Daniel Kucera.

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
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|

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@redhat.com>:
> 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
> --
> |: https://berrange.com      -o-    https://www.flickr.com/photos/
> dberrange :|
> |: https://libvirt.org         -o-
> https://fstop138.berrange.com :|
> |: https://entangle-photo.org    -o-    https://www.instagram.com/
> dberrange :|
>