[Xen-devel] console driver - How domain0 processes console messages ?

[Andrew Warfield <andrew.warfield@xxxxxxxxx>]

> Andrew, as I understand, xcs provides xend's functionalities, and to
> some extent (I expect that xcs is still under development) we can use
> xcs instead of xend to manage domainUs. Is that correct?

Not exactly. ;)  As the control rings are shared memory, and indexed
using shared pointers, it isn't really possible to have multiple
clients in dom0 using them concurrently.  With xend connecting
directly to these rings, it was impossible to add new control messages
(for instance if you were working on a new driver) without having to
get waist-deep in xend itself.

xcs (xen control switch) just acts as a mux/demux for the control
channels.  In the unstable tree, xend has been modified to bind to
only the control messages that it is actively handling.  This means
that other control messages may be handled by completely separate
daemons in dom0.  It hopefully will also allow us to start to move
away from the current monolithic xend code, to a new set of control
tools in the very near future.

If all you are trying to do is add a relatively simple service between
dom0 and your domains, then xcs should help.  One example here would
be to build a rough load-balancer that received cpu load announcements
from a set of VMs and then periodically repinned them to alternate
CPUs or migrated them to other physical hosts.  (Just in case anybody
is looking for a little project. ;) )

Several people are working on new control tools at the moment.
Anthony Liguori has posted some first-round c-based tools to the list
in the past week or so.  Mike Wray is also in the process of
redesigning xend itself.  If you are looking for something in the
short term, Anthony's stuff may be helpful, and I'm sure he'd
appreciate any feedback.

cheers,
a.


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