linux-kernel - Re: [PATCH v2 3/3] tracing: make "string" the default type for [ku]probe event $comm

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Message-Id: <20160607170232.575878d689a656f53d357e22@kernel.org>
Date:	Tue, 7 Jun 2016 17:02:32 +0900
From:	Masami Hiramatsu <mhiramat@...nel.org>
To:	Omar Sandoval <osandov@...ndov.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Namhyung Kim <namhyung@...il.com>,
	linux-kernel@...r.kernel.org, kernel-team@...com,
	Omar Sandoval <osandov@...com>
Subject: Re: [PATCH v2 3/3] tracing: make "string" the default type for
 [ku]probe event $comm

On Thu,  2 Jun 2016 18:11:03 -0700
Omar Sandoval <osandov@...ndov.com> wrote:

> From: Omar Sandoval <osandov@...com>
> 
> You'd only ever want $comm as a string, but the default is still u64.
> Push the type parsing later so we can decide based on the actual
> fetcharg and make "string" the default for $comm.

Hmm, at this moment, I'd rather like a small hack in 
traceprobe_parse_probe_arg() as like below:

--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -522,6 +522,12 @@ int traceprobe_parse_probe_arg(char *arg, ssize_t *size,
                arg[t - parg->comm] = '\0';
                t++;
        }
+       /*
+        * The default type of "$comm" should be a string, and it must not
+        * be dereferred
+        */
+       if (!t && strcmp("$comm", arg))
+               t = "string";
        parg->type = find_fetch_type(t, ftbl);
        if (!parg->type) {
                pr_info("Unsupported type: %s\n", t);

This is not general, but easy to review :)

Thank you,

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