debug：am、cmd命令源码分析

debug：am、cmd命令源码分析

目录

• debug：am、cmd命令源码分析
  • am命令的实现
    • 手机里的am
    • am.jar
  • cmd命令的实现
    • 手机里的cmd
    • cmd activity
      • cmd.cpp#cmdMain
      • Binder.cpp#shellCommand
      • Binder.java#onTransact
      • ActivityManagerService.java#onShellCommand
      • ActivityManagerShellCommand#onCommand
  • 总结

am命令的实现

手机里的am

:/ # which am
/system/bin/am
:/ # file /system/bin/am
/system/bin/am: /system/bin/sh script
:/ # cat am 
#!/system/bin/sh

if [ "$1" != "instrument" ] ; then
    cmd activity "$@"
else
    base=/system
    export CLASSPATH=$base/framework/am.jar
    exec app_process $base/bin com.android.commands.am.Am "$@"
fi

aosp里的am代码位置

frameworks/base/cmds/am$

am命令是个shell脚本，非instrument时调用cmd命令。am.jar也在手机里，/system/framework/am.jar

am.jar

只有俩文件

frameworks/base/cmds/am/src/com/android/commands/am$ ls
Am.java  Instrument.java

frameworks/base/cmds/am/src/com/android/commands/am/Am.java

 39 public class Am extends BaseCommand {
 49     public static void main(String[] args) {
 50         (new Am()).run(args);
 51     }     
------------------------------------------------------------------
 62     @Override
 63     public void onRun() throws Exception {
 64 
 65         mAm = ActivityManager.getService();
 71         mPm = IPackageManager.Stub.asInterface(ServiceManager.getService("package"));
 77         String op = nextArgRequired();
 78 
 79         if (op.equals("instrument")) {
 80             runInstrument();
 81         } else {
 82             runAmCmd(getRawArgs());
------------------------------------------------------------------
138     void runAmCmd(String[] args) throws AndroidException {
139         final MyShellCallback cb = new MyShellCallback();
140         try {
141             mAm.asBinder().shellCommand(FileDescriptor.in, FileDescriptor.out, FileDescriptor.err,                                  
142                     args, cb, new ResultReceiver(null) { });
143         } catch (RemoteException e) {

50行的run是在父类BaseCommand里，然后又分发到子类onRun方法

如果是通过am命令来启动的话，这里只会走到80行，但是，am.jar也是可以完全支持cmd activity相同的效果。

直接运行am.jar时就走到82行了，在141行binder沟通ams。

cmd命令的实现

手机里的cmd

:/ # which cmd
/system/bin/cmd
:/ # file /system/bin/cmd
/system/bin/cmd: ELF shared object, 64-bit LSB arm64, dynamic (/system/bin/linker64), for Android 30, BuildID=ab0acb6f2e4ab587eb5166cd5c29e254, stripped

cmd是个二进制可执行程序

aosp里的cmd代码位置

frameworks/native/cmds/cmd

cmd activity

cmd activity发生了什么

frameworks/native/cmds/cmd/main.cpp

21 int main(int argc, char* const argv[]) {
 22     signal(SIGPIPE, SIG_IGN);
 23 
 24     std::vector<std::string_view> arguments;
 25     arguments.reserve(argc - 1);
 26     // 0th argument is a program name, skipping.
 27     for (int i = 1; i < argc; ++i) {
 28         arguments.emplace_back(argv[i]);
 29     }
 30 
 31     return cmdMain(arguments, android::aout, android::aerr, STDIN_FILENO, STDOUT_FILENO,
 32                    STDERR_FILENO, RunMode::kStandalone);
 33 }

cmd.cpp#cmdMain

啥都没干，跳到cmd.cpp#cmdMain

frameworks/native/cmds/cmd/cmd.cpp

167 int cmdMain(const std::vector<std::string_view>& argv, TextOutput& outputLog, TextOutput& errorLog,
168             int in, int out, int err, RunMode runMode) {
169     sp<ProcessState> proc = ProcessState::self();
170     proc->startThreadPool();
175     sp<IServiceManager> sm = defaultServiceManager();
215     sp<IBinder> service;
216     if(waitForService) {
217         service = sm->waitForService(serviceName);
218     } else {
219         service = sm->checkService(serviceName);
220     }
239     status_t error = IBinder::shellCommand(service, in, out, err, args, cb, result);

169、170、171行老三样，沟通binder驱动，拿到ServiceManager的代理

217、219行拿到传入参数的binder代理。我们传的是activity，所以这就是ams的代理。

239行，通过代理发起ipc调用。

Binder.cpp#shellCommand

frameworks/native/libs/binder/Binder.cpp

 66 status_t IBinder::shellCommand(const sp<IBinder>& target, int in, int out, int err,
 67     Vector<String16>& args, const sp<IShellCallback>& callback,
 68     const sp<IResultReceiver>& resultReceiver)
 69 {
 70     Parcel send;
 71     Parcel reply;
 72     send.writeFileDescriptor(in);
 73     send.writeFileDescriptor(out);
 74     send.writeFileDescriptor(err);
 75     const size_t numArgs = args.size();
 76     send.writeInt32(numArgs);
 77     for (size_t i = 0; i < numArgs; i++) {
 78         send.writeString16(args[i]);
 79     }
 80     send.writeStrongBinder(callback != nullptr ? IInterface::asBinder(callback) : nullptr);
 81     send.writeStrongBinder(resultReceiver != nullptr ? IInterface::asBinder(resultReceiver) : nullptr);
 82     return target->transact(SHELL_COMMAND_TRANSACTION, send, &reply);                   
 83 }

binder的流转细节就不说了，直接跳到服务端，看针对这个命令的处理SHELL_COMMAND_TRANSACTION。

Binder.java#onTransact

frameworks/base/core/java/android/os/Binder.java

 782     protected boolean onTransact(int code, @NonNull Parcel data, @Nullable Parcel reply,
 783             int flags) throws RemoteException {
 804         } else if (code == SHELL_COMMAND_TRANSACTION) {
 805             ParcelFileDescriptor in = data.readFileDescriptor();
 806             ParcelFileDescriptor out = data.readFileDescriptor();
 807             ParcelFileDescriptor err = data.readFileDescriptor();
 808             String[] args = data.readStringArray();
 812                 if (out != null) {
 813                     shellCommand(in != null ? in.getFileDescriptor() : null,
 814                             out.getFileDescriptor(),
 815                             err != null ? err.getFileDescriptor() : out.getFileDescriptor(),
 816                             args, shellCallback, resultReceiver);       
------------------------------------------------------------
 925     public void shellCommand(@Nullable FileDescriptor in, @Nullable FileDescriptor out,
 926             @Nullable FileDescriptor err,
 927             @NonNull String[] args, @Nullable ShellCallback callback,
 928             @NonNull ResultReceiver resultReceiver) throws RemoteException {
 929         onShellCommand(in, out, err, args, callback, resultReceiver);                   

929行的实现在AMS里

ActivityManagerService.java#onShellCommand

frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

10501     @Override
10502     public void onShellCommand(FileDescriptor in, FileDescriptor out,                 
10503             FileDescriptor err, String[] args, ShellCallback callback,
10504             ResultReceiver resultReceiver) {
10505         (new ActivityManagerShellCommand(this, false)).exec(
10506                 this, in, out, err, args, callback, resultReceiver);
10507     }

继续跟10505

public abstract class ShellCommand extends BasicShellCommandHandler {
final class ActivityManagerShellCommand extends ShellCommand {  

看一下继承关系，这里需要注意的是，10505的exec是调用到父类的父类，然后又返回返回到ActivityManagerShellCommand的onCommand

ActivityManagerShellCommand#onCommand

frameworks/base/services/core/java/com/android/server/am/ActivityManagerShellCommand

 176     @Override
 177     public int onCommand(String cmd) {      
 183             switch (cmd) {
 184                 case "start":
 185                 case "start-activity":
 186                     return runStartActivity(pw);
......
 203                 case "trace-ipc":
 204                     return runTraceIpc(pw);
......

总结

总体流程比较简单，需要关注的点有

• am和cmd的binder客户端实现，也就是怎么写一个binder客户端(java、native)。

• binder的流转，对端在哪

• 最后是shellcommand的命令分发。

以此做参考，可以添加一些自己的命令与实现，做一些调试小工具。