Messages in this thread | | | Date | Wed, 03 Jun 2009 13:41:58 +0200 | From | Gerd Hoffmann <> | Subject | Re: Merge Xen (the hypervisor) into Linux |
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On 06/03/09 13:15, Theodore Tso wrote: > On Wed, Jun 03, 2009 at 11:09:39AM +0200, Gerd Hoffmann wrote: >> It wasn't my intention to imply that. The interface can be extended >> when needed. PAT support will probably be such a case. Changing it in >> incompatible ways isn't going to work though. > > But that means that if there is some fundamentally broken piece of > dom0 design, that the Linux kernel will be stuck with it ***forever*** > and it will contaminate code paths and make the code harder to > maintain ***forever*** if we consent to the Xen merge?
No. Xen is stuck with it forever (or at least for a few releases). Even when adding new & better dom0/xen interfaces in the merge process Xen has to keep the old ones to handle the other dom0 guests (NetBSD, Solaris, old 2.6.18 out-of-tree linux kernel). Pretty much like the linux kernel has to keep old syscalls to not break the ABI for the applications, xen has to maintain old hypercalls[1].
Other way around: Apps can use new system calls only when running one recent kernels, and they have to deal with -ENOSYS. Likewise it might be that the pv_ops-based dom0 kernel can provide some features only when running on a recent hypervisor. That will likely be the case for PAT.
cheers, Gerd
[1] and other interfaces like trap'n'emulate certain instructions.
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