Re: [Qemu-devel] Re: [PATCH 5/6] trace-state: [simple] add "-trace events" argument to control initial state

[Stefan Hajnoczi <stefanha@gmail.com>]

On Wed, Apr 6, 2011 at 3:15 PM, Lluís <xscript@gmx.net> wrote:
> Stefan Hajnoczi writes:
>
>>> +            if (len > 1) {              /* skip empty lines */
>>> +                line[len - 1] = '\0';
>>> +                if (!st_change_trace_event_state(line, true)) {
>
>> The build breaks when --enable-trace-backend != simple because this
>> code is outside an #ifdef CONFIG_SIMPLE_TRACE.  Please add this:
>
>> diff --git a/simpletrace.h b/simpletrace.h
>> index 8d893bd..5d9d2ec 100644
>> --- a/simpletrace.h
>> +++ b/simpletrace.h
>> @@ -43,6 +43,11 @@ static inline bool st_init(const char *file)
>>  {
>>      return true;
>>  }
>> +
>> +static bool st_change_trace_event_state(const char *tname, bool tstate)
>> +{
>> +    return true;
>> +}
>>  #endif /* !CONFIG_SIMPLE_TRACE */
>
>>  #endif /* SIMPLETRACE_H */
>
> Hmmm... why don't simply conditionally call st_init (put it into an
> #ifdef) and remove the "#else" in simpletrace.h.
>
> I've looked at it and it's not called from anywhere else.

The benefit to stubbing out these functions is that callers don't have
#ifdefs.  And caller code is always built (i.e. syntax checked by the
parser) so it helps avoid bitrot.  vl.c:main() is already a long and
ugly function so it would be nice to avoid #ifdefs there.

> This also reminds me that I didn't see any "-trace" option parsing in
> the OS-specific frontends (at least in linux-user).

User emulation does not have any way to control simpletrace today.

Stefan