[libvirt] qemu: domain notification for serial channel changes

[Matt Broadstone]

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.

Regards,
Matt