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

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?




Anthony Liguori

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