Re: [PATCH v10 08/10] dyndbg: add print-to-tracefs, selftest with it - RFC

Jason Baron
2021-11-12T17:33:20Z

On 11/12/21 12:07 PM, Steven Rostedt wrote:
> On Fri, 12 Nov 2021 10:08:41 -0500
> Jason Baron <jbaron@akamai.com> wrote:
>
>>> A key difference between that patchset and this patch (besides that
>>> small fact that I used +x instead of +T) was that my patchset allowed
>>> the dyndbg trace to be emitted to the main buffer and did not force them
>>> to be in an instance-specific buffer.
>>
>> Yes, I agree I'd prefer that we print here to the 'main' buffer - it seems to keep things simpler and easier to combine the output from different
>> sources as you mentioned.
>
> I do not want anything to print to the "main buffer" that can not be
> filtered or turned off by the tracing infrastructure itself (aka tracefs
> file system).
>
> Once we allow that, then the trace file will become useless because
> everything will write to the main buffer and fill it with noise.
>
> Events that can be enabled and disabled from tracefs are fine, as they can
> be limited. This is why I added that nasty warning if people leave around
> trace_printk(), because it does exactly this (write to the main buffer).
> It's fine for debugging a custom kernel, but should never be enabled in
> something that is shipped, or part of mainline.
>
> -- Steve
>

Ok, it looks like Vincent's patch defines a dyndbg event and then uses
'trace_dyndbg()' to output to the 'main' log. So all dynamic output to
the 'main' ftrace buffer goes through that event if I understand it
correctly. Here's a pointer to it for reference:

https://lore.kernel.org/lkml/20200825153338.17061-3-vincent.whitchurch@axis.com/

Would you be ok with that approach?

Thanks,

-Jason