In general we want to avoid adding compatibility bits to generic code and confine it to platform-compat.[ch] wherever possible. You have added code in xencomm.[ch] and hypercall.h which I think we can avoid.

I also try to avoid checking version numbers if I can, preferring to check for the presence of absence of specific definitions instead. This is useful when dealing with kernels with backported bits. Unfortunately it doesn't help with the gfp_t typedef :-( but we'll come to that later.

I've attached my current patch including the ptrace fix from above and the comments from below. Can you give it a go?