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Xen 3.0 Virtualization Interface Guide
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A.8 Inter-Domain Communication

Xen provides a simple asynchronous notification mechanism via event channels. Each domain has a set of end-points (or ports) which may be bound to an event source (e.g. a physical IRQ, a virtual IRQ, or an port in another domain). When a pair of end-points in two different domains are bound together, then a `send' operation on one will cause an event to be received by the destination domain.

The control and use of event channels involves the following hypercall:


event_channel_op(evtchn_op_t *op)

Inter-domain event-channel management; op is a discriminated union which allows the following 7 operations:

alloc_unbound:
allocate a free (unbound) local port and prepare for connection from a specified domain.
bind_virq:
bind a local port to a virtual IRQ; any particular VIRQ can be bound to at most one port per domain.
bind_pirq:
bind a local port to a physical IRQ; once more, a given pIRQ can be bound to at most one port per domain. Furthermore the calling domain must be sufficiently privileged.
bind_interdomain:
construct an interdomain event channel; in general, the target domain must have previously allocated an unbound port for this channel, although this can be bypassed by privileged domains during domain setup.
close:
close an interdomain event channel.
send:
send an event to the remote end of a interdomain event channel.
status:
determine the current status of a local port.

For more details see xen/include/public/event_channel.h.

Event channels are the fundamental communication primitive between Xen domains and seamlessly support SMP. However they provide little bandwidth for communication per se, and hence are typically married with a piece of shared memory to produce effective and high-performance inter-domain communication.

Safe sharing of memory pages between guest OSes is carried out by granting access on a per page basis to individual domains. This is achieved by using the grant_table_op() hypercall.


grant_table_op(unsigned int cmd, void *uop, unsigned int count)

Used to invoke operations on a grant reference, to setup the grant table and to dump the tables' contents for debugging.

Xen 3.0 Virtualization Interface Guide
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  Published under the terms of the GNU General Public License Design by Interspire