linux-kernel - Re: [PATCH v6 01/12] tools lib traceevent: Convert remaining %p[fF] users to %p[sS]

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Date:   Mon, 16 Sep 2019 14:41:59 +0300
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Joe Perches <joe@...ches.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>, linux-kernel@...r.kernel.org,
        rafael@...nel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-acpi@...r.kernel.org, devicetree@...r.kernel.org,
        Rob Herring <robh@...nel.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Tzvetomir Stoyanov <tstoyanov@...are.com>,
        linux-trace-devel@...r.kernel.org, Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH v6 01/12] tools lib traceevent: Convert remaining %p[fF]
 users to %p[sS]

Hi Joe, Steven,

On Tue, Sep 10, 2019 at 12:44:03PM -0700, Joe Perches wrote:
> On Tue, 2019-09-10 at 15:03 -0400, Steven Rostedt wrote:
> > On Tue, 10 Sep 2019 11:42:06 -0700
> []
> > > btw:
> > > 
> > > Is there kernel version information available in
> > > trace output files?
> > 
> > Not really. This is just a library that parses the trace event formats,
> > there's not kernel versions passed in, but we do use variations in
> > formats and such to determine what is supported.
> > 
> > > If so, it might be reasonable to change the tooling
> > > there instead.
> > > 
> > 
> > Actually, I think we could just look to see if "%pfw" is used and fall
> > to that, otherwise consider it an older kernel and do it the original
> > way.
> 
> Well, if you think that works, OK great.
> 
> But could that work?
> How would an individual trace record know if
> another trace record used %pfw?
> 
> Perhaps not reusing %pf, marking it reserved
> for a period of years, and using another unused
> prefix %p<type> like %pnfw may be simpler.

%p[Ff]w does not exist (I grepped for it) in older kernels since v3.0. So
kernel support for %p[fF] and %pfw are mutually exclusive. If you're ok
with that, I could change the patch to check %pf isn't followed by 'w',
in order to support %pf on older kernels.

Although that still does not address using older tooling on newer kernels
with support for %pfw.

If you think that's an issue, I'll opt for another extension than %pfw,
which I chose originally since it's memorable --- fw for fwnode (names,
paths, and probably more in the future).

-- 
Regards,

Sakari Ailus
sakari.ailus@...ux.intel.com