Re: [Xen-devel] single kernel for xen0 & xenU

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> I'm sure someone asked in this list if they can run the same kernel in
> xen0 and xenU and that the answer was yes, but now I can't find it - did
> I imagine it?
> 
> Presumably all I need to do is compile the kernel with frontend and
> backend drivers and xen will sort the rest out itself right? What
> disadvantages are there to this approach apart from kernel bloat? Are
> there any optimisations made in the kernel compile if it is front- or
> back-end?

There's no downside to using a xen0 kernel in other domains,
apart from a bit of extra bloat and a slightly longer boot time.

> Which brings up another point, how often these days is xen changing such
> that a xenU domain won't migrate between domains if one is todays build
> and another is yesterdays build?

There haven't been any API changes for some time.
 
> Finally, is anyone working on a shared memory filesystem that can be
> exported by xen0 and read by xenU, and would be available very early on
> in the boot cycle? I ask because updating modules is one of the hard
> things to do in xenU on boot when the xenU filesystem isn't readily
> mountable by xen0.

We've reasonably well thought out plans for something like this,
but its a way down the todo list. NFS isn't ideal, but it works
well enough.

> My workaround is to put all the xenU modules in the initrd and copy them
> out of that on boot into the live filesystem before they are required.
> Or at least it will be once I get it going. Is anyone interested in a
> quick howto on that assuming it works well?

That's not a bad solution, though I tend to avoid initrd's as too
much hassle. Even when I'm using iscsi/gnbd I tend to do the
setup in dom0 then export the device to the other domain as its
rootfs. This works fine for migration, providing both dom0's have
the devices imported.

Ian


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