12.4 异步事件

　　如果建立了异步事件回调，则应当定义回调函数。

static void
ahc_async(void *callback_arg, u_int32_t code, struct cam_path *path, void *arg)

• callback_arg - 注册回调时提供的值

• code - 标识事件类型

• path - 标识事件作用于其上的设备

• arg - 事件特定的参量

　　单一类型事件的实现，AC_LOST_DEVICE，看起来如下：

    struct xxx_softc *softc;
    struct cam_sim *sim;
    int targ;
    struct ccb_trans_settings neg;

    sim = (struct cam_sim *)callback_arg;
    softc = (struct xxx_softc *)cam_sim_softc(sim);
    switch (code) {
    case AC_LOST_DEVICE:
        targ = xpt_path_target_id(path);
        if(targ <= OUR_MAX_SUPPORTED_TARGET) {
            clean_negotiations(softc, targ);
            /* send indication to CAM */
            neg.bus_width = 8;
            neg.sync_period = neg.sync_offset = 0;
            neg.valid = (CCB_TRANS_BUS_WIDTH_VALID
                | CCB_TRANS_SYNC_RATE_VALID | CCB_TRANS_SYNC_OFFSET_VALID);
            xpt_async(AC_TRANSFER_NEG, path, &neg);
        }
        break;
    default:
        break;
    }