android 利用superuser编写使用root权限的app及修改CPU governor

        在默认情况下，Android的java层apk是没有root权限的，如果apk需要root权限进行一些操作，如system目录下的文件读写、cpu频率的改变等，需要获取root权限。

        非常幸运的是，国外的牛人写了获取root权限的工具，就是superuser，他主要由两部分组成：su和superuser.apk。su是真正起作用的命令，其他的程序通过它获取root权限，而superuser.apk是一个权限跟踪应用程序，主要记录那些apk程序需要获取root权限及root权限的授权。

1) su的源代码在github站点的仓库里，https://github.com/ChainsDD/su-binary.git 

2) superuser.apk的源代码在 https://github.com/ChainsDD/Superuser.git

大家可以下载下来仔细研究一下。

接下来具体讲解如何利用这两个工具来编写使用root权限的apk，通过设置cpu的governor，可以改变cpu的动态调频模式，但是 /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor 这个sys接口的权限是：

-rw-rw-r--    1 0        1000          4096 Apr 13 15:41 scaling_governor

其他的用户只有只读权限，所以要访问该接口，我们需要在程序里获取root权限。

下面是我写的一个例子：

01.package com.feng.setcpu;  
02.  
03.import java.io.DataInputStream;  
04.import java.io.DataOutputStream;  
05.import java.io.IOException;  
06.import java.util.ArrayList;  
07.import java.util.List;  
08.  
09.import android.app.Activity;  
10.import android.os.Bundle;  
11.import android.util.Log;  
12.import android.view.View;  
13.import android.widget.AdapterView;  
14.import android.widget.AdapterView.OnItemSelectedListener;  
15.import android.widget.ArrayAdapter;  
16.import android.widget.Spinner;  
17.import android.widget.TextView;  
18.import android.widget.Toast;  
19.  
20.public class SetCPU extends Activity {  
21.      
22.    private final String TAG = "SetCPU";  
23.    private List<String> governors;  
24.      
25.    private Spinner spinner;  
26.    private ArrayAdapter<String> adapter;  
27.    private TextView tv;  
28.      
29.    private int curCpuGovernor;  
30.    private final String cpuFreqPath = "/sys/devices/system/cpu/cpu0/cpufreq";  
31.    /** Called when the activity is first created. */  
32.    @Override  
33.    public void onCreate(Bundle savedInstanceState) {  
34.        super.onCreate(savedInstanceState);  
35.        setContentView(R.layout.main);  
36.          
37.        governors = readCpuGovernors();  
38.        curCpuGovernor = governors.indexOf(readCurCpuGovernor());  
39.        spinner = (Spinner) findViewById(R.id.governors);  
40.        tv = (TextView) findViewById(R.id.tv);  
41.          
42.        adapter=new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, governors);  
43.        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);  
44.        spinner.setAdapter(adapter);  
45.        spinner.setPrompt("CPU Governors");  
46.        spinner.setOnItemSelectedListener(new OnItemSelectedListener() {  
47.  
48.            @Override  
49.            public void onItemSelected(AdapterView<?> parent, View view,  
50.                    int position, long id) {  
51.                Log.i(TAG, "set CPU Governor " + readCurCpuGovernor() + "-> " + governors.get(position));  
52.                  
53.                writeCpuGovernor(governors.get(position));  
54.                if(governors.get(position).equals(readCurCpuGovernor())){  
55.                    Toast.makeText(SetCPU.this, "write CPU Governor success!", Toast.LENGTH_LONG).show();  
56.                    curCpuGovernor = governors.indexOf(readCurCpuGovernor());  
57.                }  
58.                else{  
59.                    Toast.makeText(SetCPU.this, "write CPU Governor failed!", Toast.LENGTH_LONG).show();  
60.                    spinner.setSelection(curCpuGovernor);  
61.                }  
62.            }  
63.  
64.            @Override  
65.            public void onNothingSelected(AdapterView<?> parent) {  
66.                  
67.            }  
68.        });  
69.          
70.          
71.    }  
72.      
73.    private boolean writeCpuGovernor(String governor)  
74.    {  
75.        DataOutputStream os = null;  
76.        byte[] buffer = new byte[256];  
77.        String command = "echo " + governor  + " > " + cpuFreqPath + "/scaling_governor";  
78.        Log.i(TAG, "command: " + command);  
79.        try {  
80.            Process process = Runtime.getRuntime().exec("su");  
81.            os = new DataOutputStream(process.getOutputStream());  
82.            os.writeBytes(command + "\n");  
83.            os.writeBytes("exit\n");  
84.            os.flush();  
85.            process.waitFor();  
86.            Log.i(TAG, "exit value = " + process.exitValue());  
87.        } catch (IOException e) {  
88.            Log.i(TAG, "writeCpuGovernor: write CPU Governor(" + governor + ") failed!");  
89.            return false;  
90.        } catch (InterruptedException e) {  
91.            e.printStackTrace();  
92.        }  
93.        return true;  
94.    }  
95.      
96.    private String readCurCpuGovernor()  
97.    {  
98.        String governor = null;  
99.        DataInputStream is = null;  
100.        try {  
101.            Process process = Runtime.getRuntime().exec("cat " + cpuFreqPath + "/scaling_governor");  
102.            is = new DataInputStream(process.getInputStream());  
103.            governor = is.readLine();  
104.        } catch (IOException e) {  
105.            Log.i(TAG, "readCurCpuGovernor: read CPU Governor failed!");  
106.            return null;  
107.        }  
108.        return governor;  
109.    }  
110.      
111.    private List<String> readCpuGovernors()  
112.    {  
113.        List<String> governors = new ArrayList<String>();  
114.        DataInputStream is = null;  
115.        try {  
116.            Process process = Runtime.getRuntime().exec("cat " + cpuFreqPath + "/scaling_available_governors");  
117.            is = new DataInputStream(process.getInputStream());  
118.            String line = is.readLine();  
119.      
120.            String[] strs = line.split(" ");  
121.            for(int i = 0; i < strs.length; i++)  
122.                governors.add(strs[i]);  
123.        } catch (IOException e) {  
124.            Log.i(TAG, "readCpuGovernors: read CPU Governors failed!");  
125.        }  
126.        return governors;  
127.    }  
128.}  

转自： http://blog.csdn.net/fengyanhui/article/details/7459639