在開(kāi)發(fā)Android應(yīng)用程序時(shí),少不了使用Log來(lái)監(jiān)控和調(diào)試程序的執(zhí)行。在上一篇文章Android日志系統(tǒng)驅(qū)動(dòng)程序Logger源代碼分析中,我們分析了驅(qū)動(dòng)程序Logger的源代碼,在前面的文章淺談Android系統(tǒng)開(kāi)發(fā)中Log的使用一文,我們也簡(jiǎn)單介紹在應(yīng)用程序中使Log的方法,在這篇文章中,我們將詳細(xì)介紹Android應(yīng)用程序框架層和系統(tǒng)運(yùn)行庫(kù)存層日志系統(tǒng)的源代碼,使得我們可以更好地理解Android的日志系統(tǒng)的實(shí)現(xiàn)。
我們?cè)贏ndroid應(yīng)用程序,一般是調(diào)用應(yīng)用程序框架層的Java接口(android.util.Log)來(lái)使用日志系統(tǒng),這個(gè)Java接口通過(guò)JNI方法和系統(tǒng)運(yùn)行庫(kù)最終調(diào)用內(nèi)核驅(qū)動(dòng)程序Logger把Log寫(xiě)到內(nèi)核空間中。按照這個(gè)調(diào)用過(guò)程,我們一步步介紹Android應(yīng)用程序框架層日志系統(tǒng)的源代碼。學(xué)習(xí)完這個(gè)過(guò)程之后,我們可以很好地理解Android系統(tǒng)的架構(gòu),即應(yīng)用程序?qū)樱ˋpplication)的接口是如何一步一步地調(diào)用到內(nèi)核空間的。
一. 應(yīng)用程序框架層日志系統(tǒng)Java接口的實(shí)現(xiàn)。
在淺談Android系統(tǒng)開(kāi)發(fā)中Log的使用一文中,我們?cè)?jīng)介紹過(guò)Android應(yīng)用程序框架層日志系統(tǒng)的源代碼接口。這里,為了描述方便和文章的完整性,我們重新貼一下這部份的代碼,在frameworks/base/core/java/android/util/Log.java文件中,實(shí)現(xiàn)日志系統(tǒng)的Java接口: - ................................................
public final class Log {
................................................
/**
* Priority constant for the println method; use Log.v.
*/
public static final int VERBOSE = 2;
/**
* Priority constant for the println method; use Log.d.
*/
public static final int DEBUG = 3;
/**
* Priority constant for the println method; use Log.i.
*/
public static final int INFO = 4;
/**
* Priority constant for the println method; use Log.w.
*/
public static final int WARN = 5;
/**
* Priority constant for the println method; use Log.e.
*/
public static final int ERROR = 6;
/**
* Priority constant for the println method.
*/
public static final int ASSERT = 7;
.....................................................
public static int v(String tag, String msg) {
return println_native(LOG_ID_MAIN, VERBOSE, tag, msg);
}
public static int v(String tag, String msg, Throwable tr) {
return println_native(LOG_ID_MAIN, VERBOSE, tag, msg + - + getStackTraceString(tr));
}
public static int d(String tag, String msg) {
return println_native(LOG_ID_MAIN, DEBUG, tag, msg);
}
public static int d(String tag, String msg, Throwable tr) {
return println_native(LOG_ID_MAIN, DEBUG, tag, msg + - + getStackTraceString(tr));
}
public static int i(String tag, String msg) {
return println_native(LOG_ID_MAIN, INFO, tag, msg);
}
public static int i(String tag, String msg, Throwable tr) {
return println_native(LOG_ID_MAIN, INFO, tag, msg + - + getStackTraceString(tr));
}
public static int w(String tag, String msg) {
return println_native(LOG_ID_MAIN, WARN, tag, msg);
}
public static int w(String tag, String msg, Throwable tr) {
return println_native(LOG_ID_MAIN, WARN, tag, msg + - + getStackTraceString(tr));
}
public static int w(String tag, Throwable tr) {
return println_native(LOG_ID_MAIN, WARN, tag, getStackTraceString(tr));
}
public static int e(String tag, String msg) {
return println_native(LOG_ID_MAIN, ERROR, tag, msg);
}
public static int e(String tag, String msg, Throwable tr) {
return println_native(LOG_ID_MAIN, ERROR, tag, msg + - + getStackTraceString(tr));
}
..................................................................
/** @hide */ public static native int LOG_ID_MAIN = 0;
/** @hide */ public static native int LOG_ID_RADIO = 1;
/** @hide */ public static native int LOG_ID_EVENTS = 2;
/** @hide */ public static native int LOG_ID_SYSTEM = 3;
/** @hide */ public static native int println_native(int bufID,
int priority, String tag, String msg);
}
復(fù)制代碼 定義了2~7一共6個(gè)日志優(yōu)先級(jí)別ID和4個(gè)日志緩沖區(qū)ID。回憶一下Android日志系統(tǒng)驅(qū)動(dòng)程序Logger源代碼分析一文,在Logger驅(qū)動(dòng)程序模塊中,定義了log_main、log_events和log_radio三個(gè)日志緩沖區(qū),分別對(duì)應(yīng)三個(gè)設(shè)備文件/dev/log/main、/dev/log/events和/dev/log/radio。這里的4個(gè)日志緩沖區(qū)的前面3個(gè)ID就是對(duì)應(yīng)這三個(gè)設(shè)備文件的文件描述符了,在下面的章節(jié)中,我們將看到這三個(gè)文件描述符是如何創(chuàng)建的。在下載下來(lái)的Android內(nèi)核源代碼中,第4個(gè)日志緩沖區(qū)LOG_ID_SYSTEM并沒(méi)有對(duì)應(yīng)的設(shè)備文件,在這種情況下,它和LOG_ID_MAIN對(duì)應(yīng)同一個(gè)緩沖區(qū)ID,在下面的章節(jié)中,我們同樣可以看到這兩個(gè)ID是如何對(duì)應(yīng)到同一個(gè)設(shè)備文件的。
在整個(gè)Log接口中,最關(guān)鍵的地方聲明了println_native本地方法,所有的Log接口都是通過(guò)調(diào)用這個(gè)本地方法來(lái)實(shí)現(xiàn)Log的定入。下面我們就繼續(xù)分析這個(gè)本地方法println_native。
二. 應(yīng)用程序框架層日志系統(tǒng)JNI方法的實(shí)現(xiàn)。
在frameworks/base/core/jni/android_util_Log.cpp文件中,實(shí)現(xiàn)JNI方法println_native: - /* //device/libs/android_runtime/android_util_Log.cpp
**
** Copyright 2006, The Android Open Source Project
**
** Licensed under the Apache License, Version 2.0 (the "License");
** you may not use this file except in compliance with the License.
** You may obtain a copy of the License at
**
** http://www.apache.org/licenses/LICENSE-2.0
**
** Unless required by applicable law or agreed to in writing, software
** distributed under the License is distributed on an "AS IS" BASIS,
** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
** See the License for the specific language governing permissions and
** limitations under the License.
*/
#define LOG_NAMESPACE "log.tag."
#define LOG_TAG "Log_println"
#include <assert.h>
#include <cutils/properties.h>
#include <utils/Log.h>
#include <utils/String8.h>
#include "jni.h"
#include "utils/misc.h"
#include "android_runtime/AndroidRuntime.h"
#define MIN(a,b) ((a<b)?a:b)
namespace android {
struct levels_t {
jint verbose;
jint debug;
jint info;
jint warn;
jint error;
jint assert;
};
static levels_t levels;
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;
}
static jboolean android_util_Log_isLoggable(JNIEnv* env, jobject clazz, jstring tag, jint level)
{
#ifndef HAVE_ANDROID_OS
return false;
#else /* HAVE_ANDROID_OS */
int len;
char key[PROPERTY_KEY_MAX];
char buf[PROPERTY_VALUE_MAX];
if (tag == NULL) {
return false;
}
jboolean result = false;
const char* chars = env->GetStringUTFChars(tag, NULL);
if ((strlen(chars)+sizeof(LOG_NAMESPACE)) > PROPERTY_KEY_MAX) {
jclass clazz = env->FindClass("java/lang/IllegalArgumentException");
char buf2[200];
snprintf(buf2, sizeof(buf2), "Log tag "%s" exceeds limit of %d characters - ",
chars, PROPERTY_KEY_MAX - sizeof(LOG_NAMESPACE));
// release the chars!
env->ReleaseStringUTFChars(tag, chars);
env->ThrowNew(clazz, buf2);
return false;
} else {
strncpy(key, LOG_NAMESPACE, sizeof(LOG_NAMESPACE)-1);
strcpy(key + sizeof(LOG_NAMESPACE) - 1, chars);
}
env->ReleaseStringUTFChars(tag, chars);
len = property_get(key, buf, "");
int logLevel = toLevel(buf);
return (logLevel >= 0 && level >= logLevel) ? true : false;
#endif /* HAVE_ANDROID_OS */
}
/*
* In class android.util.Log:
* public static native int println_native(int buffer, int priority, String tag, String msg)
*/
static jint android_util_Log_println_native(JNIEnv* env, jobject clazz,
jint bufID, jint priority, jstring tagObj, jstring msgObj)
{
const char* tag = NULL;
const char* msg = NULL;
if (msgObj == NULL) {
jclass npeClazz;
npeClazz = env->FindClass("java/lang/NullPointerException");
assert(npeClazz != NULL);
env->ThrowNew(npeClazz, "println needs a message");
return -1;
}
if (bufID < 0 || bufID >= LOG_ID_MAX) {
jclass npeClazz;
npeClazz = env->FindClass("java/lang/NullPointerException");
assert(npeClazz != NULL);
env->ThrowNew(npeClazz, "bad bufID");
return -1;
}
if (tagObj != NULL)
tag = env->GetStringUTFChars(tagObj, NULL);
msg = env->GetStringUTFChars(msgObj, NULL);
int res = __android_log_buf_write(bufID, (android_LogPriority)priority, tag, msg);
if (tag != NULL)
env->ReleaseStringUTFChars(tagObj, tag);
env->ReleaseStringUTFChars(msgObj, msg);
return res;
}
/*
* JNI registration.
*/
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 },
};
int register_android_util_Log(JNIEnv* env)
{
jclass clazz = env->FindClass("android/util/Log");
if (clazz == NULL) {
LOGE("Cant find android/util/Log");
return -1;
}
levels.verbose = env->GetStaticIntField(clazz, env->GetStaticFieldID(clazz, "VERBOSE", "I"));
levels.debug = env->GetStaticIntField(clazz, env->GetStaticFieldID(clazz, "DEBUG", "I"));
levels.info = env->GetStaticIntField(clazz, env->GetStaticFieldID(clazz, "INFO", "I"));
levels.warn = env->GetStaticIntField(clazz, env->GetStaticFieldID(clazz, "WARN", "I"));
levels.error = env->GetStaticIntField(clazz, env->GetStaticFieldID(clazz, "ERROR", "I"));
levels.assert = env->GetStaticIntField(clazz, env->GetStaticFieldID(clazz, "ASSERT", "I"));
return AndroidRuntime::registerNativeMethods(env, "android/util/Log", gMethods, NELEM(gMethods));
}
}; // namespace android
復(fù)制代碼 在gMethods變量中,定義了println_native本地方法對(duì)應(yīng)的函數(shù)調(diào)用是android_util_Log_println_native。在android_util_Log_println_native函數(shù)中,通過(guò)了各項(xiàng)參數(shù)驗(yàn)證正確后,就調(diào)用運(yùn)行時(shí)庫(kù)函數(shù)__android_log_buf_write來(lái)實(shí)現(xiàn)Log的寫(xiě)入操作。__android_log_buf_write函實(shí)實(shí)現(xiàn)在liblog庫(kù)中,它有4個(gè)參數(shù),分別緩沖區(qū)ID、優(yōu)先級(jí)別ID、Tag字符串和Msg字符串。下面運(yùn)行時(shí)庫(kù)liblog中的__android_log_buf_write的實(shí)現(xiàn)。
三. 系統(tǒng)運(yùn)行庫(kù)層日志系統(tǒng)的實(shí)現(xiàn)。
在系統(tǒng)運(yùn)行庫(kù)層liblog庫(kù)的實(shí)現(xiàn)中,內(nèi)容比較多,這里,我們只關(guān)注日志寫(xiě)入操作__android_log_buf_write的相關(guān)實(shí)現(xiàn): - int __android_log_buf_write(int bufID, int prio, const char *tag, const char *msg)
{
struct iovec vec[3];
if (!tag)
tag = "";
/* XXX: This needs to go! */
if (!strcmp(tag, "HTC_RIL") ||
!strncmp(tag, "RIL", 3) || /* Any log tag with "RIL" as the prefix */
!strcmp(tag, "AT") ||
!strcmp(tag, "GSM") ||
!strcmp(tag, "STK") ||
!strcmp(tag, "CDMA") ||
!strcmp(tag, "PHONE") ||
!strcmp(tag, "SMS"))
bufID = LOG_ID_RADIO;
vec[0].iov_base = (unsigned char *) &prio;
vec[0].iov_len = 1;
vec[1].iov_base = (void *) tag;
vec[1].iov_len = strlen(tag) + 1;
vec[2].iov_base = (void *) msg;
vec[2].iov_len = strlen(msg) + 1;
return write_to_log(bufID, vec, 3);
}
復(fù)制代碼 函數(shù)首先是檢查傳進(jìn)來(lái)的tag參數(shù)是否是為HTC_RIL、RIL、AT、GSM、STK、CDMA、PHONE和SMS中的一個(gè),如果是,就無(wú)條件地使用ID為L(zhǎng)OG_ID_RADIO的日志緩沖區(qū)作為寫(xiě)入緩沖區(qū),接著,把傳進(jìn)來(lái)的參數(shù)prio、tag和msg分別存放在一個(gè)向量數(shù)組中,調(diào)用write_to_log函數(shù)來(lái)進(jìn)入下一步操作。write_to_log是一個(gè)函數(shù)指針,定義在文件開(kāi)始的位置上: - static int __write_to_log_init(log_id_t, struct iovec *vec, size_t nr);
static int (*write_to_log)(log_id_t, struct iovec *vec, size_t nr) = __write_to_log_init;
復(fù)制代碼 并且初始化為_(kāi)_write_to_log_init函數(shù): - static int __write_to_log_init(log_id_t log_id, struct iovec *vec, size_t nr)
{
#ifdef HAVE_PTHREADS
pthread_mutex_lock(&log_init_lock);
#endif
if (write_to_log == __write_to_log_init) {
log_fds[LOG_ID_MAIN] = log_open("/dev/"LOGGER_LOG_MAIN, O_WRONLY);
log_fds[LOG_ID_RADIO] = log_open("/dev/"LOGGER_LOG_RADIO, O_WRONLY);
log_fds[LOG_ID_EVENTS] = log_open("/dev/"LOGGER_LOG_EVENTS, O_WRONLY);
log_fds[LOG_ID_SYSTEM] = log_open("/dev/"LOGGER_LOG_SYSTEM, O_WRONLY);
write_to_log = __write_to_log_kernel;
if (log_fds[LOG_ID_MAIN] < 0 || log_fds[LOG_ID_RADIO] < 0 ||
log_fds[LOG_ID_EVENTS] < 0) {
log_close(log_fds[LOG_ID_MAIN]);
log_close(log_fds[LOG_ID_RADIO]);
log_close(log_fds[LOG_ID_EVENTS]);
log_fds[LOG_ID_MAIN] = -1;
log_fds[LOG_ID_RADIO] = -1;
log_fds[LOG_ID_EVENTS] = -1;
write_to_log = __write_to_log_null;
}
if (log_fds[LOG_ID_SYSTEM] < 0) {
log_fds[LOG_ID_SYSTEM] = log_fds[LOG_ID_MAIN];
}
}
#ifdef HAVE_PTHREADS
pthread_mutex_unlock(&log_init_lock);
#endif
return write_to_log(log_id, vec, nr);
}
復(fù)制代碼 這里我們可以看到,如果是第一次調(diào)write_to_log函數(shù),write_to_log == __write_to_log_init判斷語(yǔ)句就會(huì)true,于是執(zhí)行l(wèi)og_open函數(shù)打開(kāi)設(shè)備文件,并把文件描述符保存在log_fds數(shù)組中。如果打開(kāi)/dev/LOGGER_LOG_SYSTEM文件失敗,即log_fds[LOG_ID_SYSTEM] < 0,就把log_fds[LOG_ID_SYSTEM]設(shè)置為log_fds[LOG_ID_MAIN],這就是我們上面描述的如果不存在ID為L(zhǎng)OG_ID_SYSTEM的日志緩沖區(qū),就把LOG_ID_SYSTEM設(shè)置為和LOG_ID_MAIN對(duì)應(yīng)的日志緩沖區(qū)了。LOGGER_LOG_MAIN、LOGGER_LOG_RADIO、LOGGER_LOG_EVENTS和LOGGER_LOG_SYSTEM四個(gè)宏定義在system/core/include/cutils/logger.h文件中: - #define LOGGER_LOG_MAIN "log/main"
#define LOGGER_LOG_RADIO "log/radio"
#define LOGGER_LOG_EVENTS "log/events"
#define LOGGER_LOG_SYSTEM "log/system"
復(fù)制代碼 接著,把write_to_log函數(shù)指針指向__write_to_log_kernel函數(shù): - static int __write_to_log_kernel(log_id_t log_id, struct iovec *vec, size_t nr)
{
ssize_t ret;
int log_fd;
if (/*(int)log_id >= 0 &&*/ (int)log_id < (int)LOG_ID_MAX) {
log_fd = log_fds[(int)log_id];
} else {
return EBADF;
}
do {
ret = log_writev(log_fd, vec, nr);
} while (ret < 0 && errno == EINTR);
return ret;
}
復(fù)制代碼 函數(shù)調(diào)用log_writev來(lái)實(shí)現(xiàn)Log的寫(xiě)入,注意,這里通過(guò)一個(gè)循環(huán)來(lái)寫(xiě)入Log,直到寫(xiě)入成功為止。這里log_writev是一個(gè)宏,在文件開(kāi)始的地方定義為: - #if FAKE_LOG_DEVICE
// This will be defined when building for the host.
#define log_open(pathname, flags) fakeLogOpen(pathname, flags)
#define log_writev(filedes, vector, count) fakeLogWritev(filedes, vector, count)
#define log_close(filedes) fakeLogClose(filedes)
#else
#define log_open(pathname, flags) open(pathname, flags)
#define log_writev(filedes, vector, count) writev(filedes, vector, count)
#define log_close(filedes) close(filedes)
#endif
復(fù)制代碼 這里,我們看到,一般情況下,log_writev就是writev了,這是個(gè)常見(jiàn)的批量文件寫(xiě)入函數(shù),就不多說(shuō)了。
至些,整個(gè)調(diào)用過(guò)程就結(jié)束了??偨Y(jié)一下,首先是從應(yīng)用程序?qū)诱{(diào)用應(yīng)用程序框架層的Java接口,應(yīng)用程序框架層的Java接口通過(guò)調(diào)用本層的JNI方法進(jìn)入到系統(tǒng)運(yùn)行庫(kù)層的C接口,系統(tǒng)運(yùn)行庫(kù)層的C接口通過(guò)設(shè)備文件來(lái)訪問(wèn)內(nèi)核空間層的Logger驅(qū)動(dòng)程序。這是一個(gè)典型的調(diào)用過(guò)程,很好地詮釋Android的系統(tǒng)架構(gòu),希望讀者好好領(lǐng)會(huì) |