Re: [Xen-devel] win4lin-like porting of win98 to xen?

[Avery Pennarun <apenwarr@xxxxxx>]

On Mon, Oct 11, 2004 at 01:38:10AM +0100, Mark A. Williamson wrote:

> > > That suggests using some kind of Xen-compatible kernel that can provide
> > > the DOS syscalls Win 9x needs to run.
> >
> > This certainly won't work. Despite their reliance on DOS for some
> > drivers, Win9x are not strictly layered on DOS; they are 32-bit
> > protected-mode OSes that also rely heavily on direct hardware access.
> 
> Hmmm.  Some tweaks to shadow page tables could be used to trap attempts to
> load the page table base register, so the memory management code would
> work.  Of course IO port accesses would be prevented by Xen completely but
> this could be worked round.

Clearly something must work, because win4lin runs fine (and very fast!)
under Linux, and I'm v*ery* sure it's not allowed to randomly probe I/O
ports there.

> > Duplicating the approach used by Win4Lin is also not a feasible amount of
> > work; it's almost a rewrite of the lower layers of Win9x.
> 
> What bits of Win 9x does Win4Lin actually replace?

At least: video driver, input drivers, sound drivers, network drivers,
parallel/serial port drivers, filesystem.  It doesn't emulate a block device
because it replaces the filesystem entirely.

> From what I've read, the kernel patch adds a DOS syscall interface that
> somehow helps Windows (apps) to run.  Presumably they don't reimplement
> all functionality of the win9x kernel-layer (the thought makes me
> shiver!).  I've never looked at the Win4Lin patch but it would be
> interesting to know exactly where it hooks into Windows Land.

The kernel patch, while mildly interesting, is definitely not the hardest
part of win4lin.

> For win9x under Xen I think that getting Win4Lin running under XenLinux
> would be the most straightforward way of doing things.

Yes.

> Is the kernel patch GPL?  If so, the commercial bit must be the userland
> software and the device drivers, right?  Given that, the quickest way to a
> free Win4Lin would be to reuse their kernel patch and rewrite the tools /
> drivers...  Still a nontrivial piece of work.

A free win4lin (ie. rewriting all those drivers) would be a *massive* amount
of work.  Fun, but a lot of work.  And it gets more and more obsolete each
day.  Lots of stuff still runs under win98, but it's certainly not a target
platform for modern developers.

Have fun,

Avery


-------------------------------------------------------
This SF.net email is sponsored by: IT Product Guide on ITManagersJournal
Use IT products in your business? Tell us what you think of them. Give us
Your Opinions, Get Free ThinkGeek Gift Certificates! Click to find out more
http://productguide.itmanagersjournal.com/guidepromo.tmpl
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.sourceforge.net/lists/listinfo/xen-devel