app访问文件

app访问文件，写内容到文件，驱动 DEVICE_ATTR 处理内容

FileOutputStream

package com.example.administrator.otgselect;

import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.Button;
import android.view.View;

import java.io.File;
import java.io.FileOutputStream;

public class MainActivity extends AppCompatActivity {

    private static final boolean DEBUG = true;
    private static final String TAG = "OTG_GPIO";

    private static final String FL_CLASS_PATH = "sys/devices/soc.0/msmgpio_ctrl.70/";
    private FileOutputStream fos;
   // public native void OtgDisable();//ioctl
   // public native void OtgEnable();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        Log.d(TAG, "lmy onCreate");
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button on = (Button) findViewById(R.id.otg_on);
        on.setOnClickListener(mOnClickListener);
        Button off = (Button) findViewById(R.id.otg_off);
        off.setOnClickListener(mOnClickListener);
        if (DEBUG) Log.e(TAG, "start listen");
    }



    private final View.OnClickListener mOnClickListener = new View.OnClickListener() {
        @Override
        public void onClick(final View v) {
            switch (v.getId()) {
                case R.id.otg_on:
                    try {
                        if (DEBUG) Log.e(TAG, "otg_on");
                        fos = new FileOutputStream(new File(FL_CLASS_PATH,"otg_gpio_ctrl"));
                        fos.write("enable".getBytes());
                    } catch(Exception e){
                        if (DEBUG) Log.e(TAG, "on exception!!!");
                        e.printStackTrace();
                    }finally{
                        try{
                            fos.close();
                        }catch(Exception e){
                            e.printStackTrace();
                        }
                    }
                    break;
                case R.id.otg_off:
                    try {
                        if (DEBUG) Log.e(TAG, "otg off");
                        fos = new FileOutputStream(new File(FL_CLASS_PATH,"otg_gpio_ctrl"));
                        fos.write("disable".getBytes());
                    } catch(Exception e){
                        if (DEBUG) Log.e(TAG, "off exception!!!");
                        e.printStackTrace();
                    }finally{
                        try{
                            fos.close();
                        }catch(Exception e){
                            e.printStackTrace();
                        }
                    }
                    break;
            }
        }
    };
}

运行起来肯定是没权限的，会Exception， 打log， permission Error。

1、被访问的文件在sys，权限是rwx-r-r,  非root写不了，所以，chmod 766

2、avc denied, (1) setenforce 0 (2) 添加policy

3、相对于ioctl 访问文件，直接读写限制太多，最好用jni ioctl

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.administrator.otgselect.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!" />
    <Button
        android:id="@+id/otg_on"
        android:layout_width="wrap_content"
        android:layout_height="80dp"
        android:layout_marginTop="80dp"
        android:layout_centerHorizontal="true"
        android:text="OTG ON"/>
    <Button
        android:id="@+id/otg_off"
        android:layout_width="wrap_content"
        android:layout_height="80dp"
        android:layout_marginTop="200dp"
        android:layout_centerHorizontal="true"
        android:text="OTG OFF"/>
</RelativeLayout>