[Qemu-devel] Re: [PATCH 2/3] Monitor command 'info trace'

[Stefan Hajnoczi <stefanha@gmail.com>]

On Fri, Jun 18, 2010 at 12:58 PM, Prerna Saxena
<prerna@linux.vnet.ibm.com> wrote:
> Hi Stefan, Jan,
> Thanks for taking a look.
>
> On 06/17/2010 08:38 PM, Stefan Hajnoczi wrote:
>>
>> On Wed, Jun 16, 2010 at 06:12:06PM +0530, Prerna Saxena wrote:
>>>
>>> diff --git a/simpletrace.c b/simpletrace.c
>>> index 2fec4d3..239ae3f 100644
>>> --- a/simpletrace.c
>>> +++ b/simpletrace.c
>>> @@ -62,3 +62,16 @@ void trace4(TraceEvent event, unsigned long x1,
>>> unsigned long x2, unsigned long
>>>  void trace5(TraceEvent event, unsigned long x1, unsigned long x2,
>>> unsigned long x3, unsigned long x4, unsigned long x5) {
>>>      trace(event, x1, x2, x3, x4, x5);
>>>  }
>>> +
>>> +void do_info_trace(Monitor *mon)
>>> +{
>>> +    unsigned int i, max_idx;
>>> +
>>> +    max_idx = trace_idx ? trace_idx : TRACE_BUF_LEN;
>>
>> trace_idx is always in the range [0, TRACE_BUF_LEN).  There is no need
>> to perform this test.
>
> I only display the logged contents in the trace buffer (till trace_idx) ,
> and not the entire trace buffer. Only when the index is full that the entire
> buffer is displayed.

Thanks for explaining, I understand what you are doing now.  Due to
this special case, the code will dump out the empty trace buffer if
used before anything has been traced (trace_idx=0).

>>> +        monitor_printf(mon, "Event %ld : %ld %ld %ld %ld %ld\n",
>>> +                          trace_buf[i].event, trace_buf[i].x1,
>>> trace_buf[i].x2,
>>> +                            trace_buf[i].x3, trace_buf[i].x4,
>>> trace_buf[i].x5);
>>
>> Getting only numeric output is the limitation of a binary trace.  It
>> would probably be possible to pretty-print without much additional code
>> by using the format strings from the trace-events file.
>>
>> I think the numeric dump is good for now though.  Hex is more compact
>> than decimal and would make pointers easier to spot.  Want to change
>> this?
>>
>
> I agree, but we can let this be a todo till after the first prototype goes
> upstream ?

I still vote for hex instead of decimal :).  Since you're already
spinning a new patch it would be nice to put that change in, but no
worries.

> I'll post patches by Monday that addresses your suggestions, and try to get
> it integrated with QMP.

Excellent, thanks.  I'd like to put your patches onto my tracing
branch soon and test out the overall workflow of tracing QEMU.

Stefan