[libvirt] qemu: domain notification for serial channel changes

[Daniel P. Berrange]

On Mon, Nov 07, 2016 at 08:22:59AM -0500, Matt Broadstone wrote:
> Hi,
> 
> I was in the process of implementing a custom qemu agent which
> communicates over virtio-serial channels, when I noticed that the only
> way to receive channel state change notifications was to poll the
> domstatus XML file. There does seem to be code in libvirt to monitor
> for serial change events
> (https://libvirt.org/git/?p=libvirt.git;a=blob;f=src/qemu/qemu_driver.c;h=38c841420e325b6227b3bcd67a26a9b9560b487f;hb=HEAD#l4402),
> however it's hardcoded/specific to the qemu-ga (explicitly checking
> for ports named "org.qemu.guest_agent.0").
> 
> It occurs to me that while there was a class of events added for guest
> lifecycle changes, it might be a more generic solution to provide
> events for character device changes. Am I missing some existing
> functionality here?  I'm a first-time poster here so I was hoping to
> both signal my intent to implement something more generic, as well as
> ping the community to see if there would be interest in this work or
> reasons why I shouldn't be doing this.

Yes, having that previous event tied to just the QEMU guest agent looks
like a mistake to me. We should have a general lifecycle evnt for
channel devices. It would basically be the same as the guest agent
lifecycle event, but would include the port name, so you can distinguish
events from different channels.

Regards,
Daniel
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