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



> > 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.

> 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?  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.

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

Thanks for the help,
Mark


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