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：

用户态应用发送消息到驱动。
用户态应用接收驱动主动上报事件。

表1 消息机制接口

方法	描述
struct HdfIoService HdfIoServiceBind(const char serviceName);	用户态获取驱动的服务，获取该服务之后通过服务中的Dispatch方法向驱动发送消息。
void HdfIoServiceRecycle(struct HdfIoService *service);	释放驱动服务。
int HdfDeviceRegisterEventListener(struct HdfIoService target, struct HdfDevEventlistener listener);	用户态程序注册接收驱动上报事件的操作方法。
int HdfDeviceSendEvent(struct HdfDeviceObject deviceObject, uint32_t id, struct HdfSBuf data);	驱动主动上报事件接口。

开发步骤

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;
    ...
}
```
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。

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 HdfDeviceIoClient *device, int cmdCode, struct HdfSBuf *data, struct HdfSBuf *reply)
{
    HDF_LOGI("sample driver lite A dispatch");
    return HDF_SUCCESS;
}
int32_t SampleDriverBind(struct HdfDeviceObject *device)
{
    HDF_LOGI("test for lite os sample driver A Open!");
    if (device == NULL) {
        HDF_LOGE("test for lite os sample driver A Open failed!");
        return HDF_FAILURE;
    }
    static struct ISampleDriverService sampleDriverA = {
        .ioService.Dispatch = SampleDriverDispatch,
        .ServiceA = SampleDriverServiceA,
        .ServiceB = SampleDriverServiceB,
    };
    device->service = (struct IDeviceIoService *)(&sampleDriverA);
    return HDF_SUCCESS;
}

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

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 HDF_FAILURE;
    }
    struct HdfIoService *serv = HdfIoServiceBind("sample_driver");
    if (serv == NULL) {
        HDF_LOGE("fail to get service");
        return HDF_FAILURE;
    }
    struct HdfSBuf *data = HdfSbufObtainDefaultSize();
    if (data == NULL) {
        HDF_LOGE("fail to obtain sbuf data");
        return HDF_FAILURE;
    }
    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);
    HdfSbbufRecycle(reply);
    HdfIoServiceRecycle(serv);
    return ret;
}

用户态接收该驱动上报的消息。

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_LOGI("%{public}s received event at %{public}llu.%{public}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 HDF_FAILURE;
    }
    HDF_LOGI("%{public}s: dev event received: %{public}d %{public}s",  (char *)priv, id, string);
    return HDF_SUCCESS;
}

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");
    if (serv == NULL) {
        HDF_LOGE("fail to get service");
        return HDF_FAILURE;
    }
    static struct HdfDevEventlistener listener = {
        .callBack = OnDevEventReceived,
        .priv ="Service0"
    };
    if (HdfDeviceRegisterEventListener(serv, &listener) != 0) {
        HDF_LOGE("fail to register event listener");
        return HDF_FAILURE;
    }
    ......
    HdfDeviceUnregisterEventListener(serv, &listener);
    HdfIoServiceRecycle(serv);
    return HDF_SUCCESS;
}

驱动上报事件。

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