ib_user_mad_reg_req
struct ib_user_mad_reg_req ureq;
(u32 __user *) (arg + offsetof(struct ib_user_mad_reg_req, id)))) {
#define IB_USER_MAD_REGISTER_AGENT _IOWR(RDMA_IOCTL_MAGIC, 0x01, struct ib_user_mad_reg_req)