Re: [Xen-devel] To use xcs or not?

[Anthony Liguori <anthony@xxxxxxxxxxxxx>]

Jacob Gorm Hansen wrote:

> OK, I actually got the impression that using XCS was the easiest way 
> around the problem, as you seem to need a lot of code for setting up 
> your own channel (which I can copy-paste from somewhere I am sure).
For just using notify, it's quite simply.  The control channels are 
complicated because of the ring queue stuff.  If you were implementing 
this as a virtual device in vm-tools (of course, I'm not bias ;-)), all 
you would do is open /dev/evtchn and add that to the set of listener fds 
(see the console device for an example of this).
You would also need to allocate a port for notifications (vmm_alloc_port 
in vm-tools or xc_evtchn_bind_interdomain otherwise).  The easiest thing 
to do would be to use a well known endpoint (anything above 10 should be 
relatively safe for now although you'll probably need to negotiate it in 
the future).
When you get a read event on /dev/evtchn, all you do is read a 2 byte 
value from it.  This will be the port the event happened on.  You'll 
also have to unmask the event by writing that same value back to the device.
> Can I setup my own event channel in the guest, and still access it 
> using /dev/evtchn in dom0?
Yup.

Regards,

> Thanks,
> Jacob
--
Anthony Liguori
anthony@xxxxxxxxxxxxx



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