adb logcat 打印内核消息

在默认情况下，adb logcat只能显示应用程序的调试信息，我把logcat.cpp修改了一下，让它同时可以打印内核调试信息：

修改的文件：system/core/logcat/logcat.cpp

1、首先先加入头文件
#include <sys/klog.h> //add by Jay

2、定义所使用的TAG
#define KERNEL_TAG "Kernel"

3、替换readLogLines函数

 staticvoidreadLogLines(log_device_t*devices)
 {
 log_device_t*dev;
 intmax=0;
 intret;
 intqueued_lines=0;
 boolsleep=true;
 charbuffer[256]={0};//addby Jay Zhang


 intresult;
 fd_setreadset;


 for(dev=devices;dev;dev=dev->next){
 if(dev->fd>max){
 max=dev->fd;
 }
 }


 while(1){
 do{
 timevaltimeout={0,5000/*5ms*/};//Ifweoversleepit'sok,i.e.ignoreEINTR.
 FD_ZERO(&readset);
 for(dev=devices;dev;dev=dev->next){
 FD_SET(dev->fd,&readset);
 }
 result=select(max+1,&readset,NULL,NULL,sleep?NULL:&timeout);
 }while(result==-1&&errno==EINTR);


 if(result>=0){
 for(dev=devices;dev;dev=dev->next){
 if(FD_ISSET(dev->fd,&readset)){
 queued_entry_t*entry=newqueued_entry_t();
 /*NOTE:driverguaranteeswereadexactlyonefullentry*/
 ret=read(dev->fd,entry->buf,LOGGER_ENTRY_MAX_LEN);
 if(ret<0){
 if(errno==EINTR){
 deleteentry;
 gotonext;
 }
 if(errno==EAGAIN){
 deleteentry;
 break;
 }
 perror("logcatread");
 exit(EXIT_FAILURE);
 }
 elseif(!ret){
 fprintf(stderr,"read:UnexpectedEOF!\n");
 exit(EXIT_FAILURE);
 }


 entry->entry.msg[entry->entry.len]='\0';


 dev->enqueue(entry);
 ++queued_lines;


 #if1//readkernellog
 if((ret=klogctl(9,buffer,sizeof(buffer)))>0){
 if((ret=klogctl(2,buffer,sizeof(buffer)))>0){
 entry->entry.tid=0;
 entry->entry.pid=getpid();
 /*priority*/
 entry->entry.msg[0]=Android_LOG_INFO;
 /*tag*/
 strcpy(entry->entry.msg+1,KERNEL_TAG);
 /*message*/
 strncpy(entry->entry.msg+1+sizeof(KERNEL_TAG),buffer,ret);
 entry->entry.len=1+sizeof(KERNEL_TAG)+ret+1;
 entry->entry.msg[entry->entry.len]='/0';
 /*
 if(g_printBinary){
 printBinary(dev,entry->entry);
 }else{
 (void)processBuffer(dev,entry->entry);
 }
 */
 printNextEntry(dev);
 }
 }
 #endif
 }
 }


 if(result==0){
 //wedidourshorttimeouttrickandthere'snothingnew
 //printeverythingwehaveandwaitformoredata
 sleep=true;
 while(true){
 chooseFirst(devices,&dev);
 if(dev==NULL){
 break;
 }
 if(g_tail_lines==0||queued_lines<=g_tail_lines){
 printNextEntry(dev);
 }else{
 skipNextEntry(dev);
 }
 --queued_lines;
 }


 //thecallerrequestedtojustdumpthelogandexit
 if(g_nonblock){
 exit(0);
 }
 }else{
 //printallthataren'tthelastintheirlist
 sleep=false;
 while(g_tail_lines==0||queued_lines>g_tail_lines){
 chooseFirst(devices,&dev);
 if(dev==NULL||dev->queue->next==NULL){
 break;
 }
 if(g_tail_lines==0){
 printNextEntry(dev);
 }else{
 skipNextEntry(dev);
 }
 --queued_lines;
 }
 }
 }
 next:
 ;
 }
 }

这里没有把内核调试信息的级别转换成Androind的LOG级别，entry->entry.msg[0] =Android_LOG_INFO;使用了ANDROID_LOG_INFO级别，进程ID用了当前的进程ID。

然后就可以使用logcat来抓取kernel的log了！

若只打印内核消息，使用：adb logcat -s Kernel:I
http://www.linuxidc.com/Linux/2011-09/43674.htm