[libvirt] qemu: domain notification for serial channel changes

[Daniel P. Berrange]

On Mon, Nov 07, 2016 at 03:05:24PM +0100, Peter Krempa wrote:
> On Mon, Nov 07, 2016 at 08:56:58 -0500, Matt Broadstone wrote:
> > On Mon, Nov 7, 2016 at 8:52 AM, Matt Broadstone <mbroadst at gmail.com> wrote:
> > > On Mon, Nov 7, 2016 at 8:35 AM, Peter Krempa <pkrempa at redhat.com> wrote:
> > >> On Mon, Nov 07, 2016 at 13:31:30 +0000, Daniel Berrange wrote:
> > >>> On Mon, Nov 07, 2016 at 08:22:59AM -0500, Matt Broadstone wrote:
> 
> [...]
> 
> > >>
> > >> That choice was deliberate. I planned to add a separate event for
> > >> channels but never got around to do it actually. The guest agent event
> > >> is separate since libvirt can have different handling regarding the
> > >> guest agent state and I did not want to mix them.
> > >>
> > >> Peter
> > >
> > > Daniel, Peter,
> > >
> > > Thanks for your quick responses. I have a few questions before implementation:
> > >
> > >   - I assume that you would prefer to keep the existing guest
> > > lifecycle events, for backwards compatibility?
> > >
> > >   - Do you have a preference wrt naming this event? I see some
> > > inconsistencies the events ids (design-wise) (e.g.
> > > VIR_DOMAIN_EVENT_ID_DEVICE_ADDED  / VIR_DOMAIN_EVENT_ID_DEVICE_REMOVED
> > > / VIR_DOMAIN_EVENT_ID_DEVICE_DEVICE_REMOVAL_FAILED, instead of a
> > > single event for all potential changes like
> > > VIR_DOMAIN_EVENT_ID_AGENT_LIFECYCLE).
> 
> A single event is preferred. Multiple names regarding the device
> lifecycle are a result of iterative adding of events over a long time.
> 
> > >
> > > Matt
> > 
> > Ah, sorry one followup question. Should the event generalize to serial
> > changes, or is the preference to keep it specific to channels?
> 
> Qemu currently implements this for virtio channels, thus it will work
> currently only for channels.
> 
> The design of the data returned by the event may allow to use other
> devices like 'serial'. The difference is that a serial device uses port
> number as the target, whereas channel uses channel name.

AFAIK, it is impossible to implement this event for anything other
than virtio-channels. With serial port emulation there's no way
for QEMU to know whether the guest OS has the port open or not - the
concept only exists in the virtio-serial device model.

Regards,
Daniel
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