Re: [Xen-devel] Some general questions about Xen development

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> 1) With the experiment of the developers of Xen, is it possible to evaluate 
> the
> cost of porting an existing linux driver under Xen. I quickly look network
> driver like 3c59x and it seems that it is possible to use the main part of the
> original file. Is it nearly the same for other drivers or is it really 
> specific
> to each one?

Porting network drivers is pretty straightforward, particularly
for decent hardware that supports scatter gather DMA.

SCSI drivers can be more troublesome, depending on how much they
rely on using Linux process features (xen is entirely event driven).
 
> 2) I read that some other tools use a type II VMM which seems to be a
> "(micro|nano)kernel" with an hosted OS. The goal is to used some fonctions of
> the hosted OS like the drivers. It allows to run native linux drivers. 
> I saw in the TODO list that you would like to move the network and the block
> device drivers out of Xen. Do you already have an idea about the impact of
> porting a driver from Linux to Xen? In fact, a problem to use Xen (for me) is 
> if
> we must rewrite many drivers for Xen...

We have plans that will make importing device drivers much
easier, by providing a more complete Linux environment emulation.

> 3) You (Ian I think) told me that there is some people who are interested to
> port Xen on IA64.

A number of people have suggested various architecture ports, but
to date, i'm not aware of anyone actually having gotten
underway. It's bound to throw up issues where we need to do a
little bit of Xen refactoring, moving stuff to arch-dep
directories.

A good first start might be an x86_64 port, for which I believe
Keir has a design.

Ian


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