cdev_read
error = cdev_read(dev, uio, flag);
error = cdev_read(vp->v_rdev, ap->a_uio, ap->a_ioflag);
error = cdev_read(devctty, ap->a_uio, ap->a_ioflag);
error = cdev_read(dev, uio, ap->a_ioflag);
dev_type_read(cdev_read);