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

1. staticvoidreadLogLines(log_device_t*devices)
2. {
3. log_device_t*dev;
4. intmax=0;
5. intret;
6. intqueued_lines=0;
7. boolsleep=true;
8. charbuffer[256]={0};//addby Jay Zhang
11. intresult;
12. fd_setreadset;
15. for(dev=devices;dev;dev=dev->next){
16. if(dev->fd>max){
17. max=dev->fd;
18. }
19. }
22. while(1){
23. do{
24. timevaltimeout={0,5000/*5ms*/};//Ifweoversleepit'sok,i.e.ignoreEINTR.
25. FD_ZERO(&readset);
26. for(dev=devices;dev;dev=dev->next){
27. FD_SET(dev->fd,&readset);
28. }
29. result=select(max+1,&readset,NULL,NULL,sleep?NULL:&timeout);
30. }while(result==-1&&errno==EINTR);
33. if(result>=0){
34. for(dev=devices;dev;dev=dev->next){
35. if(FD_ISSET(dev->fd,&readset)){
36. queued_entry_t*entry=newqueued_entry_t();
37. /*NOTE:driverguaranteeswereadexactlyonefullentry*/
38. ret=read(dev->fd,entry->buf,LOGGER_ENTRY_MAX_LEN);
39. if(ret<0){
40. if(errno==EINTR){
41. deleteentry;
42. gotonext;
43. }
44. if(errno==EAGAIN){
45. deleteentry;
46. break;
47. }
48. perror("logcatread");
49. exit(EXIT_FAILURE);
50. }
51. elseif(!ret){
52. fprintf(stderr,"read:UnexpectedEOF!\n");
53. exit(EXIT_FAILURE);
54. }
57. entry->entry.msg[entry->entry.len]='\0';
60. dev->enqueue(entry);
61. ++queued_lines;
64. #if1//readkernellog
65. if((ret=klogctl(9,buffer,sizeof(buffer)))>0){
66. if((ret=klogctl(2,buffer,sizeof(buffer)))>0){
67. entry->entry.tid=0;
68. entry->entry.pid=getpid();
69. /*priority*/
70. entry->entry.msg[0]=Android_LOG_INFO;
71. /*tag*/
72. strcpy(entry->entry.msg+1,KERNEL_TAG);
73. /*message*/
74. strncpy(entry->entry.msg+1+sizeof(KERNEL_TAG),buffer,ret);
75. entry->entry.len=1+sizeof(KERNEL_TAG)+ret+1;
76. entry->entry.msg[entry->entry.len]='/0';
77. /*
78. if(g_printBinary){
79. printBinary(dev,entry->entry);
80. }else{
81. (void)processBuffer(dev,entry->entry);
82. }
83. */
84. printNextEntry(dev);
85. }
86. }
87. #endif
88. }
89. }
92. if(result==0){
93. //wedidourshorttimeouttrickandthere'snothingnew
94. //printeverythingwehaveandwaitformoredata
95. sleep=true;
96. while(true){
97. chooseFirst(devices,&dev);
98. if(dev==NULL){
99. break;
100. }
101. if(g_tail_lines==0||queued_lines<=g_tail_lines){
102. printNextEntry(dev);
103. }else{
104. skipNextEntry(dev);
105. }
106. --queued_lines;
107. }
110. //thecallerrequestedtojustdumpthelogandexit
111. if(g_nonblock){
112. exit(0);
113. }
114. }else{
115. //printallthataren'tthelastintheirlist
116. sleep=false;
117. while(g_tail_lines==0||queued_lines>g_tail_lines){
118. chooseFirst(devices,&dev);
119. if(dev==NULL||dev->queue->next==NULL){
120. break;
121. }
122. if(g_tail_lines==0){
123. printNextEntry(dev);
124. }else{
125. skipNextEntry(dev);
126. }
127. --queued_lines;
128. }
129. }
130. }
131. next:
132. ;
133. }
134. }

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