vringh_iov_pull_user
EXPORT_SYMBOL(vringh_iov_pull_user);
ssize_t vringh_iov_pull_user(struct vringh_iov *riov, void *dst, size_t len);
rlen = vringh_iov_pull_user(&riov, rbuf,
err = vringh_iov_pull_user(&riov, buf, 5);
assert(vringh_iov_pull_user(&riov, buf, 5) == 0);
err = vringh_iov_pull_user(&riov, buf, 3);
err = vringh_iov_pull_user(&riov, buf, 29);