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Re: [Xen-devel] xen intro q

> On Mon, 2003-11-17 at 15:38, Bin Ren wrote:
> > 
> > It's relevant to say that Xen re-uses some Linux kernel source codes,
> > and chooses a similar directory structure, Xen authors gain much
> > knowledge and inspiration from Linux kernel.
> > 
> > The similarity ends here.
> Fair enough, I suppose a better question is how do you plan on
> maintaining support for all the new hardware (even ia32 only)over time? 
> If I had the goal of porting xen to amd64, I'd much rather port a xen
> patch onto the linux kernel than fork the kernel, stuff in the xen
> infrastructure and then maintain my fork for all eternity ;-)


As regards maintaining support for new hardware there are two
areas to consider: hardware device drivers and cpu variant

Our plan for the former is to provide source-level compatibility
with Linux device drivers. We're already pretty close to this for
network drivers, but we still have some work to do for SCSI and
other drivers. (this is on our todo list)

As regards CPU variants, these don't occur too frequently.
Looking at the Intel x86 line, the most frequent thing that needs
updating is IOAPIC support. Since Xen's start of day code is very
similar to Linux's, we're able to import these changes pretty
easily. Major changes to the CPU like PAE36 or x86_64 have a
significant impact on Xen, and there's not really much Linux code
we could borrow to help us here, as its rather different. [BTW:
We do have plans (and a design) for x86_64 support, but PAE36
isn't currently high on our agenda right now.]

Apart from the start of day code and device drivers, Xen really
doesn't have much in common with Linux. I think trying to merge
the two would get ugly very quickly.

Xen is really quite small compared to an OS, and I think it's
best to think of Xen as a 'next-generation BIOS replacement' ---
OS neutral, and an opportunity to sort out the current PC device
driver mess, to everyone's benefit. 


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