linux-kernel - Re: [PATCH v2 11/11] Uprobes traceevents patch.

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Message-ID: <4BB41E38.8080406@redhat.com>
Date:	Thu, 01 Apr 2010 00:16:56 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	rostedt@...dmis.org
CC:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Randy Dunlap <rdunlap@...otime.net>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 11/11] Uprobes traceevents patch.

Hi Steven,

Steven Rostedt wrote:
> On Wed, 2010-03-31 at 21:23 +0530, Srikar Dronamraju wrote:
> 
>>  libftrace-y := ftrace.o
>> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
>> index 2825ef2..9fe02ab 100644
>> --- a/kernel/trace/trace.h
>> +++ b/kernel/trace/trace.h
>> @@ -126,6 +126,18 @@ struct kretprobe_trace_entry {
>>  	(offsetof(struct kretprobe_trace_entry, args) +	\
>>  	(sizeof(unsigned long) * (n)))
>>  
>> +struct uprobe_trace_entry {
>> +	struct trace_entry	ent;
>> +	pid_t			pid;
> 
> Unless pid is not the current pid, ent already records it.

Indeed.

>> +	unsigned long		ip;
>> +	int			nargs;
>> +	unsigned long		args[];
>> +};
> 
> Note, you want to really add this to trace_entries.h instead:
> 
> FTRACE_ENTRY(uprobe, uprobe_trace_entry,
> 
> 	TRACE_GRAPH_ENT,
> 
> 	F_STRUCT(
> 		__field(	unsigned long,	ip	)
> 		__field(	int,		nargs	)
> 		__dynamic_array(unsigned long,	args	)
> 	),
> 
> 	F_printk("%lx nrargs:%u", __entry->ip, __entry->nargs)
> );
> 
> 
> This will put this event into the events/ftrace directory. Don't worry
> about the printk format, we can write a plugin for it to override it if
> need be.

Hmm, interesting idea. But this dynamic event definition allows us
to filter events based on each argument value.

As you can see this code, 

>> +struct probe_arg {
>> +	struct fetch_func	fetch;
>> +	const char		*name;
>> +};

each argument can have unique name. Therefore user can write a filter
by using these names.

Moreover, dynamic events (at least kprobe-tracer) are going to support
'types' for each argument. this means that the arg[] in *probe_trace_entry
will be no longer an unsigned long array.

Thank you,

-- 
Masami Hiramatsu
e-mail: mhiramat@...hat.com
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