//xen/include/public/xen.h
struct mmuext_op{
  unsigned int cmd;
  union{
  xen_pfn_t mfn;
  unsigned long linear_addr;
  }  arg1;
  union{
    unsigned int nr_ents;
    Xen_GUEST_HANDLE_00030205(void) vcpumask;
  }  arg2;
};
typedef struct mmuext_op mmuext_op_t;
DEFINE_Xen_GUEST_HANDLE(mmuext_op_t);
Algorithm 1