Re: [Xen-devel] Xen as a kernel module

[Mark Williamson <Mark.Williamson@xxxxxxxxxxxx>]

On Wednesday 26 January 2005 08:41, Steven Hand wrote:
> >with Xen increasingly depending on Linux for bootstrap, drivers, packet
> >filtering etc., would it make sense to have the option of compiling Xen
> >as a Linux kernel module, like in VMWare or coLinux?
>
> Huh? Which kind of vmware? Afaik the hosted (type II) versions of
> vmware when running on a linux host have some modules which get installed
> but the VMM itself is not a module. And coLinux is basically a windows
> device driver which does task switching - a very clever and useful piece
> of software but not really a Linux kernel module.

IIRC, the coLinux device driver is available both for Windows and as a Linux 
kernel module.  The same Linux kernel can then run in either environment.

> Maybe - I guess it depends on what you mean. If you have:
>
>      [ VM1 ]   [ VM2 ] ....   [ VMN ]
>
>       [ new type II version of Xen ]
>
>             [ linux kernel ]
>
>               [ hardware ]
>
> then you require a way for VMx to communicate the new Xen thing,
> which then needs to syscall into the linux kernel. I'm not sure
> what VMx<->Xen comms would look like, or how it would perform. If
> you retain safety it seems like you might end up with the performance
> of UML, which if you go for 'high performance' then you may need to
> turn off the safety catch.

Couldn't we have the "Xen module" hijack the interrupt-handling of the host 
kernel (like the VMWare and coLinux modules themselves do AFAIK) in order to 
handle hypercalls directly?

Device communications could be handled by backend / frontend drivers 
essentially the same as the ones we use for vanilla Xen.

Cheers,
Mark


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