[lttng-dev] Use LTTng in legacy codebase/variable arguments

[Sudhagar Chinnaswamy]

Would appreciate any input/suggestion on this. Thanks a lot.

Regards,
Sudhagar

Visit my blog at: http://sudhagarc.blogspot.com

On Tue, Dec 23, 2014 at 3:16 AM, Sudhagar Chinnaswamy <sudhagar at gmail.com>
wrote:

> Hi:
>
> I have the same need as discussed in the below mentioned thread. I want to
> use LTTng, but most of the cases we need to log different parameters under
> the same provider and event.
>
> http://lists.lttng.org/pipermail/lttng-dev/2013-December/022134.html
>
> When I tried a simple program to log the variable arguments under same
> provider/event as suggested in the above thread using the macro below, I
> found that the function "my_snprintf" is called "twice" when the logging
> for the event is enabled for each tracepoint call. It seems inefficient to
> call the same function twice. Is there something that could be done to make
> it efficient or am I missing something?
>
> — 8< —
>
> #define tracepoint_for_format_string(provider, name, …) \
>
>       do { \
>
>             char msg_buf[MAX_BUFFER_SIZE]; \
>
>             tracepoint(provider, name, my_snprintf(msg_buf, MAX_BUFFER_SIZE, __VA_ARGS__)); \
>
>       } while (0)
>
> — 8< —
>
> Alternatively, is there any other approach to achieve my requirement: Need
> to use same provider & event name to log variable arguments?
>
> For e.g.,
> my_tracepoint(hello_world, test, "argc=%d, argv=%p", argc, argv);
> my_tracepoint(hello_world, test, "argv[%u] :: %s", x, argv[x]);
> my_tracepoint(hello_world, test, "Quitting now!");
>
> Thanks in advance.
>
> Regards,
> Sudhagar
>
>
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