Android 让adb logcat打印内核调试信息

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 

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

3、替换readLogLines函数

static void readLogLines(log_device_t* devices)   {       log_device_t* dev;       int max = 0;       int ret;       int queued_lines = 0;       bool sleep = true;       char buffer[256] = {0}; //add by zhaofei              int result;       fd_set readset;             for (dev=devices; dev; dev = dev->next) {           if (dev->fd > max) {               max = dev->fd;           }       }             while (1) {           do {               timeval timeout = { 0, 5000 /* 5ms */ }; // If we oversleep it's ok, i.e. ignore EINTR.                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 = new queued_entry_t();                       /* NOTE: driver guarantees we read exactly one full entry */                       ret = read(dev->fd, entry->buf, LOGGER_ENTRY_MAX_LEN);                       if (ret < 0) {                           if (errno == EINTR) {                               delete entry;                               goto next;                           }                           if (errno == EAGAIN) {                               delete entry;                               break;                           }                           perror("logcat read");                           exit(EXIT_FAILURE);                       }                       else if (!ret) {                           fprintf(stderr, "read: Unexpected EOF!\n");                           exit(EXIT_FAILURE);                       }                             entry->entry.msg[entry->entry.len] = '\0';                             dev->enqueue(entry);                       ++queued_lines;         #if 1 //read kernel log                        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) {                   // we did our short timeout trick and there's nothing new                    // print everything we have and wait for more data                    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;                   }                         // the caller requested to just dump the log and exit                    if (g_nonblock) {                       exit(0);                   }               } else {                   // print all that aren't the last in their list                    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！