Qemu (host) <-> host userspace signaling?

[pav <pav@aster.pl>]

Hello,

I am looking for a simple way to get a bidirectional event notification 
interface between qemu/kvm and host userspace processes. Just a "kick", 
messages/data not required.


What I basically need is a way to have an interested host process 
informed by a custom qemu device that something happened (i.e. after a 
MMIO write) and the other way around - to allow similar notifications 
from the process to the qemu device. Of course I do not want qemu to 
sleep.
Instant reaction to such events is not required.


I understand I could use a unix socket and qemu_chr_open() and friends 
for this, but isn't a full-blown socket a bit of an overkill for a simple 
"kick" interface?
>From what I understand qemu would then act as a server and sleep just 
after starting (or later?), waiting for connections? Or maybe there is a 
way to reverse it, have qemu be the client, although that could still 
make qemu sleep?.
I guess it could use some kind of poll/select, but I am not sure where in 
qemu should such code be put in though...


Or maybe there is something else for this in qemu already? I had thought 
iosignalfd or eventfd were made for that, but if I understand correctly, 
they communicate with the guest and are for something different?

I would be very greatful for your help.

Best regards,
Pav