驱动消息机制管理

使用场景

当用户态应用和内核态驱动需要交互时，可以使用HDF框架的消息机制来实现。

接口说明

消息机制的功能主要有以下两种：

1. 用户态应用发送消息到驱动。
2. 用户态应用接收驱动主动上报事件。

表 1 消息机制接口

开发步骤

1. 将驱动配置信息中服务策略policy字段设置为2（SERVICE_POLICY_CAPACITY，参考policy定义）。

   device_sample :: Device {
       policy = 2;
       ...
   }

2. 配置驱动信息中的服务设备节点权限（permission字段）是框架给驱动创建设备节点的权限，默认是0666，驱动开发者根据驱动的实际使用场景配置驱动设备节点的权限。

3. 在服务实现过程中，实现服务基类成员IDeviceIoService中的Dispatch方法。

   // Dispatch是用来处理用户态发下来的消息
   int32_t SampleDriverDispatch(struct HdfDeviceObject *device, int cmdCode, struct HdfSBuf *data, struct HdfSBuf *reply)
   {
       HDF_LOGE("sample driver lite A dispatch");
       return 0;
   }
   int32_t SampleDriverBind(struct HdfDeviceObject *device)
   {
       HDF_LOGE("test for lite os sample driver A Open!");
       if (device == NULL) {
           HDF_LOGE("test for lite os sample driver A Open failed!");
           return -1;
       }
       static struct ISampleDriverService sampleDriverA = {
           .ioService.Dispatch = SampleDriverDispatch,
           .ServiceA = SampleDriverServiceA,
           .ServiceB = SampleDriverServiceB,
       };
       device->service = (struct IDeviceIoService *)(&sampleDriverA);
       return 0;
   }

4. 驱动定义消息处理函数中的cmd类型。

   #define SAMPLE_WRITE_READ 1    // 读写操作码1

5. 用户态获取服务接口并发送消息到驱动。

   int SendMsg(const char *testMsg)
   {
       if (testMsg == NULL) {
           HDF_LOGE("test msg is null");
           return -1;
       }
       struct HdfIoService *serv = HdfIoServiceBind("sample_driver", 0);
       if (serv == NULL) {
           HDF_LOGE("fail to get service");
           return -1;
       }
       struct HdfSBuf *data = HdfSBufObtainDefaultSize();
       if (data == NULL) {
           HDF_LOGE("fail to obtain sbuf data");
           return -1;
       }
       struct HdfSBuf *reply = HdfSBufObtainDefaultSize();
       if (reply == NULL) {
           HDF_LOGE("fail to obtain sbuf reply");
           ret = HDF_DEV_ERR_NO_MEMORY;
           goto out;
       }
       if (!HdfSbufWriteString(data, testMsg)) {
           HDF_LOGE("fail to write sbuf");
           ret = HDF_FAILURE;
           goto out;
       }
       int ret = serv->dispatcher->Dispatch(&serv->object, SAMPLE_WRITE_READ, data, reply);
       if (ret != HDF_SUCCESS) {
           HDF_LOGE("fail to send service call");
           goto out;
       }
   out:
       HdfSBufRecycle(data);
       HdfSBufRecycle(reply);
       HdfIoServiceRecycle(serv);
       return ret;
   }

6. 用户态接收该驱动上报的消息。

   1. 用户态编写驱动上报消息的处理函数。

      static int OnDevEventReceived(void *priv,  uint32_t id, struct HdfSBuf *data)
      {
          OsalTimespec time;
          OsalGetTime(&time);
          HDF_LOGE("%s received event at %llu.%llu", (char *)priv, time.sec, time.usec);
      
          const char *string = HdfSbufReadString(data);
          if (string == NULL) {
              HDF_LOGE("fail to read string in event data");
              return -1;
          }
          HDF_LOGE("%s: dev event received: %d %s",  (char *)priv, id, string);
          return 0;
      }

   2. 用户态注册接收驱动上报消息的操作方法。

      int RegisterListen()
      {
          struct HdfIoService *serv = HdfIoServiceBind("sample_driver", 0);
          if (serv == NULL) {
              HDF_LOGE("fail to get service");
              return -1;
          }
          static struct HdfDevEventlistener listener = {
              .callBack = OnDevEventReceived,
              .priv ="Service0"
          };
          if (HdfDeviceRegisterEventListener(serv, &listener) != 0) {
              HDF_LOGE("fail to register event listener");
              return -1;
          }
          ......
          HdfDeviceUnregisterEventListener(serv, &listener);
          HdfIoServiceRecycle(serv);
          return 0;
      }

   3. 驱动上报事件。

      int32_t SampleDriverDispatch(struct HdfDeviceObject *device, int cmdCode, struct HdfSBuf *data, struct HdfSBuf *reply)
      {
          ... // process api call here
          return HdfDeviceSendEvent(deviceObject, cmdCode, data);
      }