Re: [Patch 3/6] statistics infrastructure - prerequisite: timestamp

[Martin Peschke <mp3@de.ibm.com>]

Tim Bird wrote:
> Martin Peschke wrote:
>> And I think that I have fixed a printed_len related miscalculation.
>> printed_len needs to be increased if no valid log level has been found
>> and a log level prefix has been added by printk(). Otherwise, printed_len
>> must not be increased. The old code did it the other way around (in the
>> timestamp case).
> 
> I'm not following your change here.  I can't find the problem you
> mention in the original code.  And your fix appears to mess up the
> printed_len.

I am sorry for not responding sooner ... and I am sorry for introducing
a bug here. I think you are right.

>> +		if (new_line) {
>> +			/* The log level token is first. */
>> +			int loglev_char;
>> +			if (p[0] == '<' && p[1] >='0' &&
>> +			    p[1] <= '7' && p[2] == '>') {
>> +				loglev_char = p[1];
>> +				p += 3;
>> +				printed_len -= 3;
> Here you subtract from the printed_len to account for skipping
> the submitted log level.
> 
>> +			} else	{
>> +				loglev_char = default_message_loglevel + '0';
>> +			}
>> +			emit_log_char('<');
>> +			emit_log_char(loglev_char);
>> +			emit_log_char('>');
> 
> But here you don't re-count the chars for the log-level
> you are adding back in.  There's a discrepancy here.

Correct. My print_len loses 3 in the 'got log level'-case due to a surplus
substraction. It also loses 3 in the other case due to adding a log level
substring that is not entered in the books.

This is how I would fix it:

         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);

         ...

         if (new_line) {
                 /* The log level token is first. */
                 int loglev_char;
                 if (p[0] == '<' && p[1] >='0' &&
                     p[1] <= '7' && p[2] == '>') {
                         loglev_char = p[1];
                         p += 3;
                 } else  {
                         loglev_char = default_message_loglevel + '0';
                         print_len += 3;
                 }
                 emit_log_char('<');
                 emit_log_char(loglev_char);
                 emit_log_char('>');


Could you confirm, please. I will send a patch to Andrew then.


Or, Andrew, do you prefer a replacement patch for my
statistics-infrastructure-prerequisite-timestamp.patch
that introduces this miscalculation. I could put
statistics-infrastructure-make-printk_clock-a-generic-kernel-wide-nsec-resolution.patch
into that one as well, so that all the timestamp related printk-changes are in
one place.