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《Android 5.0 如何正确启用isLoggable(一)__使用详解》

概要

        在上文《Android 5.0 如何正确启用isLoggable(一)__使用详解》中分析了isLoggable的使用方法，本文主要分析isLoggable实现原理以及user版系统root后永久enable isLoggable的原理，并使用脚本自动设置isLoggable相关属性。

本文来自http://blog.csdn.net/yihongyuelan 转载请务必注明出处

isLoggable工作原理

        isLoggable定义在frameworks/base/core/java/android/util/Log.java中：

    /**
     * Checks to see whether or not a log for the specified tag is loggable at the specified level.
     *
     *  The default level of any tag is set to INFO. This means that any level above and including
     *  INFO will be logged. Before you make any calls to a logging method you should check to see
     *  if your tag should be logged. You can change the default level by setting a system property:
     *      'setprop log.tag.<YOUR_LOG_TAG> <LEVEL>'
     *  Where level is either VERBOSE, DEBUG, INFO, WARN, ERROR, ASSERT, or SUPPRESS. SUPPRESS will
     *  turn off all logging for your tag. You can also create a local.prop file that with the
     *  following in it:
     *      'log.tag.<YOUR_LOG_TAG>=<LEVEL>'
     *  and place that in /data/local.prop.
     *
     * @param tag The tag to check.
     * @param level The level to check.
     * @return Whether or not that this is allowed to be logged.
     * @throws IllegalArgumentException is thrown if the tag.length() > 23.
     */
    public static native boolean isLoggable(String tag, int level);

static JNINativeMethod gMethods[] = {
    /* name, signature, funcPtr */
    { "isLoggable",      "(Ljava/lang/String;I)Z", (void*) android_util_Log_isLoggable },
    { "println_native",  "(IILjava/lang/String;Ljava/lang/String;)I", (void*) android_util_Log_println_native },
};

static jboolean android_util_Log_isLoggable(JNIEnv* env, jobject clazz, jstring tag, jint level)
{
    //... ...省略
    jboolean result = false;
    if ((strlen(chars)+sizeof(LOG_NAMESPACE)) > PROPERTY_KEY_MAX) {
        char buf2[200];
        snprintf(buf2, sizeof(buf2), "Log tag \"%s\" exceeds limit of %zu characters\n",
                chars, PROPERTY_KEY_MAX - sizeof(LOG_NAMESPACE));
        jniThrowException(env, "java/lang/IllegalArgumentException", buf2);
    } else {
        // 调用本地isLoggalbe方法
        result = isLoggable(chars, level);
    }
    env->ReleaseStringUTFChars(tag, chars);
    return result;
}

#define LOG_NAMESPACE "log.tag."
static jboolean isLoggable(const char* tag, jint level) {
    String8 key;
    key.append(LOG_NAMESPACE);
    key.append(tag);

    char buf[PROPERTY_VALUE_MAX];
	//获取属性log.tag.<Your_TAG>的值
    if (property_get(key.string(), buf, "") <= 0) {
        buf[0] = '\0';
    }
    int logLevel = toLevel(buf);
    return logLevel >= 0 && level >= logLevel;
}

static int toLevel(const char* value)
{
    switch (value[0]) {
        case 'V': return levels.verbose;
        case 'D': return levels.debug;
        case 'I': return levels.info;
        case 'W': return levels.warn;
        case 'E': return levels.error;
        case 'A': return levels.assert;
        case 'S': return -1; // SUPPRESS
    }
    return levels.info;
}

struct levels_t {
    jint verbose;
    jint debug;
    jint info;
    jint warn;
    jint error;
    jint assert;
};
static levels_t levels;

int register_android_util_Log(JNIEnv* env)
{
    jclass clazz = FindClassOrDie(env, "android/util/Log");
    //获取android.util.Log中VERBOSE/DEBUG/INFO/WARN/ERROR/ASSERT的值，并赋给levels
    levels.verbose = env->GetStaticIntField(clazz, GetStaticFieldIDOrDie(env, clazz, "VERBOSE", "I"));
    levels.debug = env->GetStaticIntField(clazz, GetStaticFieldIDOrDie(env, clazz, "DEBUG", "I"));
    levels.info = env->GetStaticIntField(clazz, GetStaticFieldIDOrDie(env, clazz, "INFO", "I"));
    levels.warn = env->GetStaticIntField(clazz, GetStaticFieldIDOrDie(env, clazz, "WARN", "I"));
    levels.error = env->GetStaticIntField(clazz, GetStaticFieldIDOrDie(env, clazz, "ERROR", "I"));
    levels.assert = env->GetStaticIntField(clazz, GetStaticFieldIDOrDie(env, clazz, "ASSERT", "I"));
    return RegisterMethodsOrDie(env, "android/util/Log", gMethods, NELEM(gMethods));
}

static jboolean isLoggable(const char* tag, jint level) {
    //... ...省略
    int logLevel = toLevel(buf);
    return logLevel >= 0 && level >= logLevel;
}

android.util.Log.isLoggable("InCall", android.util.Log.DEBUG);

        这里的level是DEBUG也就是3，相当于 level >= logLevel变为3 >= logLevel。如果没有设置属性值log.tag.InCall的值，则logLevel的默认返回为4 ( INFO)，因此 3 >= 4不成立返回false，因此logLevel >=0 && level >= logLevel返回false；如果设置log.tag.InCall的值为D或者V，则logLevel返回为 3或者2，因此level >= logLevel成立，从而使得isLoggable返回为true。

Android Property System简介

        在isLoggable的调用流程中涉及到属性值的读取，这里简单了解Android Property System的工作流程。如下图所示：

图 1 android property system (Pic  From @rxwen)

        蓝色表示独立进程，橙色表示共享内存，白色表示属性文件。属性值的获取通过property consumer完成，当系统启动时会将persistent file中的属性值加载到共享内存中，如果需要设置属性值，那么property setter会通过socket将需求提交给property service，由property service将属性值写入到共享内存中。

        因为设置属性如log.tag.InCall D后会写入到共享内存中，但设备重启后会重新申请共享内存并加载属性文件，而手动设置的属性并没有写入属性文件，所以重启设备后log.tag.InCall的属性会失效。

local .prop文件加载流程

        在前文《Android 5.0 如何正确启用isLoggable(一)__使用详解》中提到，如果想要重启后设置的log.tag.<Your_Tag>属性依然有效，那么需要将log.tag.InCall=D写入/data/local.prop文件中，重启设备后系统会加载该路径下的属性文件。那这一步是如何完成的呢？这就涉及到Android Property System的初始化流程。

        Android Property Service是在Init进程中被初始化的，而在初始化过程中会加载指定路径下的属性文件，加载流程如下图所示：

图 2 Property files init flow

图中涉及文件路径：

/system/core/init/init.cpp

/system/core/init/init_parser.cpp

/system/core/init/builtins.cpp

/system/core/init/property_service.cpp

/system/core/rootdir/init.rc

        init进程启动后首先执行main()方法，之后通过init_parse_config_file()加载init.rc文件，并对init.rc文件进行解析，最后将解析出来的service、action及其command存入链表中。在完成init.rc解析之后通过execute_one_command()方法，逐个取出链表中的command并执行。init.rc中的properties相关action如下：

# Load properties from /system/ + /factory after fs mount.
on load_all_props_action
    load_all_props
    start logd-reinit

#ifndef KEYWORD
//... ...
#define __MAKE_KEYWORD_ENUM__
#define KEYWORD(symbol, flags, nargs, func) K_##symbol,
enum {
    K_UNKNOWN,
#endif
    //... ...
    KEYWORD(load_persist_props,    COMMAND, 0, do_load_persist_props)
    KEYWORD(load_all_props,        COMMAND, 0, do_load_all_props)
    //... ...
#ifdef __MAKE_KEYWORD_ENUM__
    KEYWORD_COUNT,
};
#undef __MAKE_KEYWORD_ENUM__
#undef KEYWORD
#endif

void load_all_props() {
    load_properties_from_file(PROP_PATH_SYSTEM_BUILD, NULL);
    load_properties_from_file(PROP_PATH_VENDOR_BUILD, NULL);
    load_properties_from_file(PROP_PATH_BOOTIMAGE_BUILD, NULL);
    load_properties_from_file(PROP_PATH_FACTORY, "ro.*");

    load_override_properties();

    /* Read persistent properties after all default values have been loaded. */
    load_persistent_properties();
}

        展开load_override_properties()方法可以看到：

static void load_override_properties() {
    if (ALLOW_LOCAL_PROP_OVERRIDE) {
        char debuggable[PROP_VALUE_MAX];
        int ret = property_get("ro.debuggable", debuggable);
        if (ret && (strcmp(debuggable, "1") == 0)) {
            load_properties_from_file(PROP_PATH_LOCAL_OVERRIDE, NULL);
        }
    }
}

#define PROP_PATH_RAMDISK_DEFAULT  "/default.prop"
#define PROP_PATH_SYSTEM_BUILD     "/system/build.prop"
#define PROP_PATH_VENDOR_BUILD     "/vendor/build.prop"
#define PROP_PATH_LOCAL_OVERRIDE   "/data/local.prop"
#define PROP_PATH_FACTORY          "/factory/factory.prop"

user版系统永久开启isLoggable原理

        在前文《Android 5.0 如何正确启用isLoggable(一)__使用详解》中，已给出使能isLoggable的方法以及各种方法间的优劣对比。其中，如果当前设备是user版，但在获取root权限之后能够永久开启isLoggable。通过前面的分析可以知道，在user版系统中，/data/local.prop属性文件是不会被property service读取的，但/system/build.prop属性文件无论user还是userdebug/eng版本都会读取，因此直接将log.tag.<Your_Tag>追加到/system/build.prop文件中即可。

        也可以使用以下脚本(Windows)设置isLoggable的属性值( 需要adbd获取root权限即能够使用adb remount )：

@echo off
echo ============= Open Hidden Logs =============
echo =============   version 0.2  =============
echo =============     20150605   =============
echo =============      SEVEN     =============

REM Update:
REM 1. Rename the script to OpenHiddenLogs.bat.
REM 2. Adaptation of user mode device.
REM 3. Add the instructions and steps.

REM Instructions:
REM This script is used to enable some hide logs in Android Platforms.
REM Android property system provides an approach to enable isLoggable(String tag, int level).
REM You'll find some code in Android as below:
REM private static final String TAG = "Telecom";
REM public static final boolean DEBUG = android.util.Log.isLoggable(TAG, android.util.Log.DEBUG);
REM if (DEBUG) {
REM    android.util.Log.d(TAG, getPrefix(obj) + str1 + str2);
REM }
REM If you want to enable the Log.d(), you need to type "adb shell setprop log.tag.Telecom V"
REM in your console, and kill the process of com.android.server.telecom, then Log.d() is enabled.
REM But if you reboot your device, the Log.d() is disabled, so we write the TAG to property system
REM to enable Log.d() forever. If you have any questions, please feel free to let me know.
REM Email: yihongyuelan@gmail.com

REM Steps:
REM 1. Get your device root permission.
REM 2. Running the OpenHideLogs.bat;


echo.
set NOROOTSTR=adbd cannot run as root
set ROOTSTR=adbd is already running as root
set BUILDTYPE=user

for /f "delims=" %%a in ('adb shell getprop ro.build.type') do set "build_type=%%a"
echo Your device is %build_type% Mode
echo.

:ISENABLED
for /f "delims=" %%c in ('adb shell getprop log.tag.InCall') do set "check=%%c"
if "%check%" == "V" (
	echo Hidden Logs has been enabled!
	pause
	exit
) else (
	echo Hidden Logs hasn't been enabled! 
)

echo.
for /f "delims=" %%b in ('adb root') do set "str=%%b"
REM echo %str%
set EXISTS_FLAG=false
echo %str%|find "%ROOTSTR%">nul&&set EXISTS_FLAG=true
if "%EXISTS_FLAG%"=="true" (
	echo Checking ROOT permission PASS
	ping -n 5 127.0.0.1 >nul
	adb remount
	if "%build_type%" == "%BUILDTYPE%" (
		adb shell "echo log.tag.InCall=V 					>> /system/build.prop"
		adb shell "echo log.tag.Telephony=V 				>> /system/build.prop"
		adb shell "echo log.tag.Telecom=V 					>> /system/build.prop"
		adb shell "echo log.tag.TelecomFramework=V 			>> /system/build.prop"
		adb shell "echo log.tag.Mms=V 						>> /system/build.prop"
		adb shell "echo log.tag.MessageTemplateProvider=V 	>> /system/build.prop"
		adb shell "echo log.tag.CarrierText=V			 	>> /system/build.prop"
	) else (
		adb push local.prop /data/
		adb shell chmod 644 /data/local.prop
		adb shell chown system:system /data/local.prop
	)
	adb reboot
	adb wait-for-device
	goto :ISENABLED
) else (
	echo Checking ROOT permission FAIL
	echo Please get the root privileges for adbd and try again
	pause
	exit
)

log.tag.InCall=V
log.tag.Telephony=V
log.tag.Telecom=V
log.tag.TelecomFramework=V
log.tag.Mms=V
log.tag.MessageTemplateProvider=V
log.tag.CarrierText=V

小结

        起初，看到android.util.Log.isLoggable(TAG, android.util.Log.DEBUG)代码，想当然的认为如果在userdebug的版本中isLoggable会返回true，结果查看后发现相关log并没有打印，进一步的分析后发现isLoggable背后的实现原理，同时也体会到了使用isLoggable控制log输出的灵活性。对于开发者来说，可以很好的利用isLoggable开启user版系统中的隐藏log，从而为相关问题提供更详细的log。对于isLoggable的重要知识点，总结如下：

        1. isLoggable默认阈值是4 (INFO)

        如果log level小于4 (INFO)，即3 (DEBUG) 和2 (VERBOSE)，则isLoggable返回false；

        2. isLoggable可以通过设置属性值使其返回true

        通过设置如log.tag.InCall D的属性，可以使得对应的isLoggable返回true，但需要注意的是，在设置属性之后需要重启相关进程，也可以通过adb shell stop & adb shell start重启Zygote及其子进程，不过该方法在完全重启设备后失效；

        3. 设置属性文件可以永久使isLoggable返回true

        在userdebug/eng版本中，可以将属性值log.tag.InCall=D写入/data/local.prop文件，这样isLoggable返回为true，并且在设备重启之后依然有效。如果在user版的系统中已经获取到root权限，可以向/system/build.prop中追加属性值，也可以达到重启后永久使isLoggable返回true的目的；

参考：

深入讲解Android Property机制 ：本文详细分析了Android 4.4 Android Property的各个流程

Android的init过程（二）：初始化语言（init.rc）解析：本文详细分析init.rc的解析过程，注意nargs在解析是会先执行nargs++

Android SystemProperties设置/取得系统属性的用法总结：本文是Android Property系统的集合贴

相关资源免积分下载：戳这里

Android 5.0 如何正确启用isLoggable(二)__原理分析

标签：android   telephony   isloggable   property   

原文地址：http://blog.csdn.net/yihongyuelan/article/details/46413207