[libvirt] Using virtEvents

[D. Herrendoerfer]

Daniel, Eric

On Jan 5, 2012, at 6:35 PM, Daniel P. Berrange wrote:

Thank you very much for the introduction, I've spent the
week digging through the code and have a way better
understanding of the difference in the handling of events
now.

>
> Any event loop callback must be sure to complete in very
> fast time, since all I/O processsing is blocked while an
> event callback is running. So typically callbacks would
> restrict themselvs to reading/writing I/O on the triggering
> file descriptor, or some other small non-blocking piece of
> worker.
>
> If your event loop callback intends to invoke complex
> APis, which may in turn need to do I/O, then you must
> spawn a new thread so that you don't block the whole
> event loop.

I agree. I want to add a netlink socket interface to libvirtd
through the event handler interface.
The callback itself then receives the netlink message
and passes it to its own registered netlink event callbacks.
Since most netlink messages to libvirt do little more than trigger
a log entry or cause a lldpad message they return almost immediately.
More complex functions will receive the message fully, and can
then detach themselves as threads.

For a start I'll add a callback into the macvlan setup function, if
a 802.1qbg link goes down it receives a message and adds a
log entry. When the link goes back up it re-sends the associate
netlink message to lldpad. It does not wait for confirmation but
exits right away.

I have most of the code ready and working - but I still need to get
the lldpad message decoding done because this is not finalized in
lldpad yet.

... but I'd like to know if you see any showstoppers in here.

Regards,

D.Herrendoerfer <herrend at de dot ibm dot com > <d.herrendoerfer at  
herrendoerfer dot name>
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