Re: [RFC PATCH] KVM: Specify byte order for KVM_EXIT_MMIO

[Paolo Bonzini <pbonzini@redhat.com>]

Il 24/01/2014 01:01, Peter Maydell ha scritto:
>> >
>> > +The 'data' member byte order is host kernel native endianness, regardless of
>> > +the endianness of the guest, and represents the the value as it would go on the
>> > +bus in real hardware.  The host kernel should always be able to do:
>> > +<type> val = *((<type> *)mmio.data).
> I think this would be better phrased as "The host userspace should always",
> since this documentation is supposed to be telling userspace what the
> kernel's contract with it is, not the kernel keeping notes for itself on
> its own implementation. (It also clarifies what the intention is for the
> obscure and maybe-we'll-never-implement-this case of an LE host
> kernel using a compatibility interface to run the host userspace (QEMU)
> as a BE process which sees the same ABI a BE kernel provides,
> without actually dragging that red herring explicitly into the documentation.)

I agree, and also the first line should mention userspace.

In PPC I think it's possible or even common to have BE host kernel and 
LE host userspace (or perhaps vice versa is the common one).

Paolo