Re: [Xen-devel] questions regarding interdomain communication and xen-guest communication

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> Aastha Mehta <aasthakm@xxxxxxxxx> 10/23/13 7:44 PM >>>
>If there is an interdomain event channel set up between two guests, do
>they communicate directly with each other, bypassing the hypervisor
>completely?

No, event channel delivery works via the hypervisor.

> In case of an asynchronous I/O does one guest have to
>register its callbacks with the other guest directly?
>Or does one guest hypercall into xen, which then upcalls into the
>other guest and then transfer reply in the reverse using another pair
>of hypercall and upcall?

Again, the latter.

> Can event channels be set up ad hoc between
>two, for example, dom0 and a guest domain? Or can they only be used by
>drivers, e.g. between network frontend and backend drivers?

The former.

>Regarding xen -- domain communication: how can xen send some request
>to dom0 for some operation that needs to be performed in the dom0 and
>get back results from the dom0?

Look at the MCE polling Dom0 performs for example, or the memory pressure
threshold handling: One model would be for Dom0 to set up a (dedicated)
vIRQ for that purpose, and Xen trigger that vIRQ when it needs Dom0's help.

> Does such a communication have to be synchronous?

I would say no, unless your use case has such a requirement.

Jan


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