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Re: [Xen-devel] console hypercalls (was "How to invoke hypercalls")

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] console hypercalls (was "How to invoke hypercalls")
From: Hollis Blanchard <hollisb@xxxxxxxxxx>
Date: Mon, 14 Aug 2006 11:55:15 -0500
Cc: antoinet <xen@xxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, xen-ppc-devel <xen-ppc-devel@xxxxxxxxxxxxxxxxxxx>
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On Sun, 2006-08-13 at 18:51 +0100, Keir Fraser wrote:
> The usual domU console method is to pick up a console shared page from
> start_info structure and write console data to a ring buffer embedded in
> that shared page. See Linux's driver for an example, or mini-os's.
> Possibly Xen should be able to provide a serial-like interface on top of the
> console shared page, which would make initial OS porting a little easier. It
> would be something of a layer violation in the system (Xen talking up to
> dom0) but we do that already for HVM guests so there's a precedent (albeit
> one we'd like to get rid of).

This would be useful for PowerPC as well. The IBM Power Hypervisor (i.e.
the thing shipping on IBM's "System p" servers) defines the guest
console API as read/write hypercalls. It would be nice to emulate those
hypercalls so that legacy guests can run on Xen unmodified. However,
since the Xen hypervisor currently has no knowledge whatsoever of the
format of the console page, we can't.

Hollis Blanchard
IBM Linux Technology Center

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