linux-kernel - Re: [PATCH] tracing/probe: Test nr_args match in looking for same probe events

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Message-Id: <20190927175405.GA7088@linux.vnet.ibm.com>
Date:   Fri, 27 Sep 2019 23:24:05 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Naveen Rao <naveen.n.rao@...ux.vnet.ibm.com>,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: Re: [PATCH] tracing/probe: Test nr_args match in looking for same
 probe events

> > 
> > This has a side-effect where the newer probe has same argument commands, we
> > still end up appending the probe.
> 
> ??
> 
> How so?
> 
> If the two have the same number of arguments we do exactly what we did
> before this patch. Please explain to me how that side effect would happen?
> 
> It basically is doing, "if the two probes do not have the same number
> of arguments, don't bother comparing, because they are different."
> 

Lets take the first probe has 3 arguments passed to it and the second probe
has just 2 arguments. If the first two arguments are same type, name, and
comm, should we append to the first probe? I think No, I would believe we
should append only if the comm of either of the arguments was different.

Example:
echo p:test _do_fork arg1=%ax arg2=%bx arg3=%cx >> kprobe_events

echo p:test _do_fork arg1=%ax arg2=%bx >> kprobe_events