[Xen-devel] Re: [Qemu-devel] [PATCH 03/15] xen: Add a new target to qemu: target-xen

[Ian Jackson <Ian.Jackson@eu.citrix.com>]

Blue Swirl writes ("[Xen-devel] Re: [Qemu-devel] [PATCH 03/15] xen: Add a new target to qemu: target-xen"):
> I don't understand why it would be a target, QEMU calls CPU
> architectures targets. Isn't it possible to have Xen for Sparc, PPC or
> ARM? It should really be just a machine, not copy&paste from x86
> target.

Qemu's targets include much more of Qemu's system emulation than is
appropriate for Xen, because the hypervisor is doing more of the
work.  For example, there is no representation of the guest CPU state
outside the hypervisor so Qemu doesn't see that at all.

So it makes sense to do Xen emulation in Qemu as a new target than
just as a machine.

Yes, in principle Xen for Sparc, PPC and ARM are possible; some of
these have existed in the past although targets other than i386,
itanium and amd64 aren't currently supported by xen-unstable.  So
perhaps the currently-introduced xen target should be called
target-i386-xen.  However, in practice since in a Xen system Qemu
doesn't deal with CPU instructions these other targets will be much
more like each other than (say) i386 is close to m68k.

Or to put it all another way: from the point of view of Qemu, Xen is
a weird kind of cpu architecture whose instruction emulation is done
"by magic" and Qemu doesn't need to care vary much about that.

Ian.