无法使用Android应用程序通过JNI写入sys / class / uwb / scan文件

Question

定义SCAN_FILE / sys / class / uwb_rc / uwb0 / scan

我的目标是在

中写入android中的SCAN_FILE

  " echo 9 0 >  /sys/class/uwb_rc/uwb0/scan "

我想使用Android应用程序和JNI集成的文件操作来实现它

我的代码如下所示： -

package com.samsung.w;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.OutputStream;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.TextView;


public class write extends Activity {

    private static final String TAG = "test";

    TextView tv_status;
    /** Called when the activity is first created. */

    private Object myClickHandler;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Log.e(TAG, "entered after main and waiting ...");
       getAccessPerm("/sys/class/uwb_rc/uwb0/scan");        
    } 



    private void getAccessPerm(String path)
    {

        try {

            String command = String.format("echo \"chmod 777 %s\" | su\nexit\n", path);
            Process sh_process = Runtime.getRuntime().exec("sh");               

            OutputStream writer = sh_process.getOutputStream();
            writer.write(command.getBytes("ASCII")); 
            BufferedReader stdError = new BufferedReader(new InputStreamReader(
                                                    sh_process.getErrorStream()));

            String err_line = null;
            if((err_line = stdError.readLine()) != null) {

                Log.e(TAG, "getAccessPerm: chmod cmd failed");
                System.out.println(err_line);
                while ((err_line = stdError.readLine()) != null) {
                    System.out.println(err_line);
                } 
            }   
        }
        catch (Exception e) {

            Log.e(TAG, "getAccessPerm: exception");
            e.printStackTrace();   
        }      
    }



    public void myClickHandler(View view) {
        switch (view.getId()) {
        case R.id.scan_button: 
        TextView textview = (TextView)findViewById(R.id.tv_title);
            textview.setText(scaninit());
            break;   
        }
    }   
public native String  scaninit(); 



    static {
       System.loadLibrary("write");
    }
}

相应的JNI文件是

    jstring Java_com_samsung_w_write_scaninit(JNIEnv* env, jobject thiz) {
    FILE* file = fopen("/sys/class/uwb_rc/uwb0/scan", "rw");
    char *mystring[20];
    if (file != NULL) {
        fputs("9 0", file);
        fgets(mystring, 4, file);
        fclose(file);

        return (*env)->NewStringUTF(env, mystring);
    }

    return (*env)->NewStringUTF(env, "file opening failed!");
}

Android Manifest文件就像这样

    <?xml version="1.0" encoding="utf-8"?>
<manifest
 xmlns:android="http://schemas.android.com/apk/res/android"
 package="com.samsung.w"
 android:versionCode="1"
 android:versionName="1.0">
 <uses-sdk android:minSdkVersion="7" />
 <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> **
 <uses-permission android:name="android.permission.FACTORY_TEST" /> **
 <application
  android:icon="@drawable/icon"
  android:label="@string/app_name">
  <activity
   android:name=".write"
   android:label="@string/app_name">
   <intent-filter>
    <action android:name="android.intent.action.MAIN" />
    <category android:name="android.intent.category.LAUNCHER" />
   </intent-filter>
  </activity>

 </application>
</manifest> 

** - 试过这两个想法是与权限问题有关但没有用

cat上的SCAN_FILE中的默认值： -

   #cat /sys/class/uwb_rc/uwb0/scan

   3 0 

adb shell中的typin结果

 #echo 9 0 > | cat sys/class/uwb_rc/uwb0/scan
      9 0

但是当我使用Android应用程序时，我无法看到此更改

  #cat /sys/class/uwb_rc/uwb0/scan
     3 0   (default value on booting)

有人请帮助我

Answer 1

感谢Bhushan帮助我解决这个问题

问题出在内核源代码DEVICE属性中，必须将权限写入

as

  

DEVICE_ATTR（scan，0777，uwb_rc_scan_show，uwb_rc_scan_store）;

而不是

DEVICE_ATTR（扫描，S_IRUGO | S_IWUSR，uwb_rc_scan_show，uwb_rc_scan_store）;

然后在C代码中fopen shoudl处于r +模式，如

  

FILE * file = fopen（“/ sys / class / uwb_rc / uwb0 / scan”，“r +”）;

这个论坛真棒：）