ib_uverbs_ioctl_hdr
struct ib_uverbs_ioctl_hdr *hdr,
struct ib_uverbs_ioctl_hdr __user *user_hdr =
(struct ib_uverbs_ioctl_hdr __user *)arg;
struct ib_uverbs_ioctl_hdr hdr;
_IOWR(RDMA_IOCTL_MAGIC, 1, struct ib_uverbs_ioctl_hdr)