typedef ssize_t (rw_iter_op)(struct kiocb *, struct iov_iter *);
static int aio_setup_vectored_rw(int rw, char __user *buf, size_t len,
typedef ssize_t (rw_iter_op)(struct kiocb *, struct iov_iter *);
static int aio_setup_vectored_rw(int rw, char __user *buf, size_t len,