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[Xen-users] Re: Xen is a feature

To: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Subject: [Xen-users] Re: Xen is a feature
From: Avi Kivity <avi@xxxxxxxxxx>
Date: Tue, 02 Jun 2009 21:59:19 +0300
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Linus Torvalds wrote:
The point? Xen really is horribly badly separated out. It gets way more incestuous with other systems than it should. It's entirely possible that this is very fundamental to both paravirtualization and to hypervisor behavior, but it doesn't matter - it just measn that I can well see that Xen is a f*cking pain to merge.

So please, Xen people, look at your track record, and look at the issues from the standpoint of somebody merging your code, rather than just from the standpoint of somebody who whines "I want my code to be merged".

IOW, if you have trouble getting your code merged, ask yourself what _you_ are doing wrong.

There is in fact a way to get dom0 support with nearly no changes to Linux, but it involves massive changes to Xen itself and requires hardware support: run dom0 as a fully virtualized guest, and assign it all the resources dom0 can access. It's probably a massive effort though.

I've considered it for kvm when faced with the "I want a thin hypervisor" question: compile the hypervisor kernel with PCI support but nothing else (no CONFIG_BLOCK or CONFIG_NET, no device drivers), load userspace from initramfs, and assign host devices to one or more privileged guests. You could probably run the host with a heavily stripped configuration, and enjoy the slimness while every interrupt invokes the scheduler, a context switch, and maybe an IPI for good measure.

--
Do not meddle in the internals of kernels, for they are subtle and quick to 
panic.


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