承接上文一个例子了解通过Openharmony的HDF框架实现简易驱动的流程，实现到了test_hdf_newdevice1设备的驱动。应用或服务如何与此设备通过HDF的框架的驱动消息机制，进行通信？

依旧以Openharmony中的V3.1 版本为基座，编写测试代码来进行分析说明。

HDF框架提供统一的驱动消息机制，支持用户应用向内核态驱动发送消息，也支持内核态驱动向用户态应用发送消息。

一、用户态应用测试程序

可以通过创建一个应用程序或动态库.so或静态库.a来与内核的驱动程序进行通信。这里简单以一个应用程序为例进行演示。

创建用户态应用测试程序步骤如下：

创建项目:

新建源文件:

添加编译配置:

编译烧录:

1.1 新建源文件test.c

通过驱动对外发布服务的名称(test_hdf_newdevice1)获取驱动的服务对象。

// test.c
#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <unistd.h>
#include <string.h>
#include <core/hdf_io_service_if.h>
#include "hdf_sbuf.h"
#include "osal_time.h"
#include "hilog/log.h"
...
int main(int arg, char **argv)
{struct HdfIoService *serv = HdfIoServiceBind("test_hdf_newdevice1");if (serv == NULL) {printf("get service fail!\n");return -1;}return 0;
}

注册事件监听对象HdfDevEventlistener

// test.c
...
#define TEST_WRITE_DATA 1234
static int OnDevEventReceive(struct HdfDevEventlistener *listener,struct HdfIoService *service, uint32_t id, struct HdfSBuf *data)
{printf("enter %d, service address is %p, event cmdId is %d\n",__func__, service, id);return 0;
}static struct HdfDevEventlistener listener = {.onReceive = OnDevEventReceive
}int main(int arg, char **argv)
{
...if (HdfDeviceRegisterEventListener(serv, &listener) != 0) {printf("register event listener fail!\n");}
...
}

准备写入的数据与读出数据

// test.c
...
int main(int arg, char **argv)
{
...struct HdfSBuf *data = HdfSbufObtainDefaultSize();if (data == NULL) {printf("fail to obtain sbuf data!\n");return -1;}struct HdfSBuf *reply = HdfSbufObtainDefaultSize();if (reply == NULL) {printf("fail to obtain sbuf reply!\n");HdfSbufRecycle(data);return -1;}// 写入传入的数据if (!HdfSbufWriteString(data, "Send Msg to Driver Message!")) {printf("fail to write sbuf!\n");HdfSbufRecycle(data);HdfSbufRecycle(reply);HdfDeviceUnregisterEventListener(serv, &listener);HdfIoServiceRecycle(serv);return -1;}
...
}

分发消息

...
int main(int arg, char **argv)
{
...if (serv->dispatcher->Dispatch(&service->object, TEST_WRITE_DATA, data, reply) != 0) {printf("fail to send service call!\n");HdfSbufRecycle(data);HdfSbufRecycle(reply);HdfDeviceUnregisterEventListener(serv, &listener);HdfIoServiceRecycle(serv);return -1;}
...
}

读取驱动返回数据

...
int main(int arg, char **argv)
{const char *result = HdfSbufReadString(reply);if (result == NULL) {printf("fail to read result from reply!\n");HdfSbufRecycle(data);HdfSbufRecycle(reply);HdfDeviceUnregisterEventListener(serv, &listener);HdfIoServiceRecycle(serv);  return -1;}printf("read result from driver: %s\n", result);HdfSbufRecycle(data);HdfSbufRecycle(reply);HdfDeviceUnregisterEventListener(serv, &listener);HdfIoServiceRecycle(serv);return 0;
}
...

1.2 添加编译配置BUILD.gn

import("//build/ohos.gni")
import("//drivers/adapter/uhdf2/uhdf.gni")ohos_executable("test_hdf_msg") {sources = ["test.c"]include_dirs = ["//drivers/framework/include","//drivers/framework/include/utils","//drivers/adapter/uhdf2/osal/include","//drivers/framework/include/osal"]deps = ["$hdf_uhdf_path/utils:libhdf_utils",]external_deps = ["device_driver_framework:libhdf_utils","hiviewdfx_hilog_native:libhilog","utils_base:utils"]
}

1.3 编译烧录

./build.sh --product-name rk3568
# 将生成的执行文件test_hdf_msg通过hdc发送开发板执行
# 上一篇中HdfNewdeviceIoServiceDispatch中接收到信息打印如下
# HdfNewdeviceIoServiceDispatch read data is: Send Msg to Driver Message!
# 返回如下信息
# read result from driver: I am driver's reply string!