enc_async
status = xpt_register_async(AC_FOUND_DEVICE, enc_async, NULL, NULL);
xpt_register_async(0, enc_async, periph, periph->path);
path, enc_async, AC_FOUND_DEVICE, cgd);
static void enc_async(void *, uint32_t, struct cam_path *, void *);
xpt_register_async(AC_LOST_DEVICE, enc_async, periph, periph->path);