Adb logcat prints kernel messages

By default, adb logcat can only display the debugging information of the application. I modified logcat. cpp so that it can print the kernel debugging information at the same time:

Modified file: system/core/logcat. cpp

1. First add the header file
# Include <sys/klog. h> // add

2. Define the TAG used
# Define KERNEL_TAG "Kernel"

3. Replace the readLogLines Function

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-> next ){
If (dev-> fd> max ){
Max = dev-> fd;
}
}
 
 
While (1 ){
Do {
Timeval timeout = {0, 5000/* 5 ms */}; // If we oversleep it's OK, I. e. ignore EINTR.
FD_ZERO (& readset );
For (dev = devices; 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-> 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:
;
}
}
The kernel debugging information level is not converted to the LOG level of Androind, entry-> entry. msg [0] = Android_LOG_INFO; The ANDROID_LOG_INFO level is used, and the process ID uses the current process ID.

Then you can use logcat to capture the log of the kernel!

To print only Kernel messages, use: adb logcat-s Kernel: I

From the column zhangjie201412