cam_open_btl
device = cam_open_btl(mybus, mytarget, mylun, O_RDWR, NULL);
cam_open_btl(bus, target, lun, O_RDWR, NULL) :
sess->camdev = cam_open_btl(sess->cam.path_id, sess->cam.target_id,
struct cam_device * cam_open_btl(path_id_t path_id, target_id_t target_id,