Re: [RFC PATCH 03/35] Add Xen interface header files

Hollis Blanchard
2006-05-09T19:34:19Z

On Tue, 2006-05-09 at 16:15 +0100, Christoph Hellwig wrote:
>
> > +#ifdef __XEN__
> > +#define __DEFINE_GUEST_HANDLE(name, type) \
> > + typedef struct { type *p; } __guest_handle_ ## name
> > +#else
> > +#define __DEFINE_GUEST_HANDLE(name, type) \
> > + typedef type * __guest_handle_ ## name
> > +#endif
>
> please get rid of all these stupid typedefs

These typedefs are a new hack to work around a basic interface problem:
instead of explicitly-sized types, Xen uses longs and pointers in its
interface. On PowerPC in particular, where we need a 32-bit userland
communicating with a 64-bit hypervisor, those types don't work.

However, the maintainers are reluctant to switch the interface to use
explicitly-sized types because it would break binary compatibility.
These ugly "HANDLE" macros allow PowerPC to do what we need without
affecting binary compatibility on x86.

--
Hollis Blanchard
IBM Linux Technology Center