linux-kernel - Re: [PATCH v7 00/16] tracing: probeevent: Improve fetcharg features

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Date:   Tue, 8 May 2018 13:01:27 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-trace-users@...r.kernel.org, linux-kselftest@...r.kernel.org,
        shuah@...nel.org, Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Subject: Re: [PATCH v7 00/16] tracing: probeevent: Improve fetcharg features

On Mon, 7 May 2018 11:30:03 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Sun, 6 May 2018 00:51:43 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:
> 
> > OK, now I think it is a time to introduce new unified interface for dynamic events,
> > tracefs/dynamic_events and make uprobe_events and kprobe_events as symbolic-links
> > to the new interface file.
> 
> So basically make one file that does all the work?
> 
> I'm not sure we can keep the other files as symbolic links. Because we
> don't want the kprobe_events showing up in the uprobe_events file, and
> vice versa. We need to keep all this backward compatible.

Good catch!
Can't we check which file the user opened? If not, even though
we can setup a filter in ops->open().

> 
> But I do like the idea of one file to rule them all, approach.

Thanks!

> 
> -- Steve
> 
> 
> > 
> > Actually, there is no reason we split those 2 interfaces, since
> > both have similar, but very clear syntax differences.
> > 
> > o Uprobe event definition
> >   p[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a uprobe
> >   r[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a return uprobe (uretprobe)
> >   -:[GRP/]EVENT                           : Clear uprobe or uretprobe event
> > 
> > o Kprobe event definition
> >   p[:[GRP/]EVENT] [MOD:]SYM[+offs]|MEMADDR [FETCHARGS]  : Set a probe
> >   r[MAXACTIVE][:[GRP/]EVENT] [MOD:]SYM[+0] [FETCHARGS]  : Set a return probe
> >   -:[GRP/]EVENT                                         : Clear a probe
> > 
> > At first, it is clear that those can share the parser. 2nd, it is easy to
> > distinguish those, because Uprobe event must require the PATH which starts
> > with '/', on the other hand, Kprobe event must NOT start with '/'.
> > (both SYM and MOD will start with alphabet or '_', of course MEMADDR
> > will start with digits)
> > 
> > If we can merge those to unified dynamic_events interface, I think
> > 'f[:[GRP/]EVENT] SYM(CAST)' is also acceptable, since it is no more
> > only for kprobe/uprobe. We can directly add some other dynamic
> > events via dynamic_events interface. ;)
> > 
> > Thank you,
> > 
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>