linux-kernel - Re: [PATCH v3 1/5] docs: tracing: fprobe: document list filters and :entry/:exit

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Message-ID: <aOu91W3GegRiK8Pg@gmail.com>
Date: Sun, 12 Oct 2025 23:40:21 +0900
From: Ryan Chung <seokwoo.chung130@...il.com>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: rostedt@...dmis.org, mathieu.desnoyers@...icios.com, shuah@...nel.org,
	hca@...ux.ibm.com, corbet@....net,
	linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 1/5] docs: tracing: fprobe: document list filters and
 :entry/:exit

On Wed, Oct 08, 2025 at 10:06:11AM +0900, Masami Hiramatsu wrote:
> On Sun,  5 Oct 2025 08:46:55 +0900
> Ryan Chung <seokwoo.chung130@...il.com> wrote:
> 
> > Signed-off-by: Ryan Chung <seokwoo.chung130@...il.com>
> > ---
> >  Documentation/trace/fprobetrace.rst | 27 +++++++++++++++++++++------
> >  1 file changed, 21 insertions(+), 6 deletions(-)
> > 
> > diff --git a/Documentation/trace/fprobetrace.rst b/Documentation/trace/fprobetrace.rst
> > index b4c2ca3d02c1..629e2d7402bd 100644
> > --- a/Documentation/trace/fprobetrace.rst
> > +++ b/Documentation/trace/fprobetrace.rst
> > @@ -25,21 +25,36 @@ Synopsis of fprobe-events
> >  -------------------------
> >  ::
> >  
> > -  f[:[GRP1/][EVENT1]] SYM [FETCHARGS]                       : Probe on function entry
> > -  f[MAXACTIVE][:[GRP1/][EVENT1]] SYM%return [FETCHARGS]     : Probe on function exit
> > -  t[:[GRP2/][EVENT2]] TRACEPOINT [FETCHARGS]                : Probe on tracepoint
> > +  # fprobe (function entry/exit)
> > +  f[:[GRP1/][EVENT1]] SYM_OR_LIST[:entry|:exit] [FETCHARGS]
> > +
> > +  # legacy single-symbol exit
> > +  f[MAXACTIVE][:[GRP1/][EVENT1]] SYM%return [FETCHARGS]
> > +
> > +  # Probe on tracepoint
> > +  t[:[GRP2/][EVENT2]] TRACEPOINT [FETCHARGS]
> >  
> >   GRP1           : Group name for fprobe. If omitted, use "fprobes" for it.
> >   GRP2           : Group name for tprobe. If omitted, use "tracepoints" for it.
> > - EVENT1         : Event name for fprobe. If omitted, the event name is
> > -                  "SYM__entry" or "SYM__exit".
> > + EVENT1         : Event name for fprobe. If omitted,
> > +                  - For a single literal symbol, the event name is
> > +                    "SYM__entry" or "SYM__exit".
> > +                  - For a *list or any wildcard*, an explicit [GRP1/][EVENT1]
> > +                    is required; otherwise the parser rejects it.
> >   EVENT2         : Event name for tprobe. If omitted, the event name is
> >                    the same as "TRACEPOINT", but if the "TRACEPOINT" starts
> >                    with a digit character, "_TRACEPOINT" is used.
> >   MAXACTIVE      : Maximum number of instances of the specified function that
> >                    can be probed simultaneously, or 0 for the default value
> >                    as defined in Documentation/trace/fprobe.rst
> > -
> > + SYM_OR_LIST    : Either a single symbol, or a comma-separated list of
> > +                  include/exclude patterns:
> > +                  - Tokens are matched as symbols; wildcards may be used.
> > +                  - Tokens prefixed with '!' are exclusions.
> > +                  - Examples:
> > +                        foo             # single literal (entry)
> > +                        foo:exit        # single literal exit
> > +                        foo%return      # legacy single-symbol exit
> 
> So you can explain it in syntax formats:
> 
> Single function (including wildcard):
> 
>   f[:[GRP1/][EVENT1]] SYM[%return] [FETCHARGS]
> 
> Multiple functions:
> 
>   f[:[GRP1/]EVENT3 SYM[,[!]SYM[,...]][:entry|:exit] [FETCHARGS]
> 
> Where,
>  - SYM prefixed with '!' are exclusions.
>  - ":entry" suffix means it probes entry of given symbols. (default)
>  - ":exit" suffix means it probes exit of given symbols.
>  - "%return" suffix means it probes exit of SYM (single symbol).
> 
> Thank you,
> 
> 
> >   FETCHARGS      : Arguments. Each probe can have up to 128 args.
> >    ARG           : Fetch "ARG" function argument using BTF (only for function
> >                    entry or tracepoint.) (\*1)
> > -- 
> > 2.43.0
> > 
> 
> 
> -- 
> Masami Hiramatsu (Google) <mhiramat@...nel.org>o

Hi Masami. Thank you for your coments. I will fold this into v4 and make
sure examples and naming rules match the behavior. Thanks for the
guidance.

Best regards,
Ryan Chung