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Re: [PATCH tracing/kprobes 0/7] tracing/kprobes: kprobe-based event tracer update and perf support
- From: Frederic Weisbecker <fweisbec at gmail dot com>
- To: Masami Hiramatsu <mhiramat at redhat dot com>
- Cc: Steven Rostedt <rostedt at goodmis dot org>, Ingo Molnar <mingo at elte dot hu>, lkml <linux-kernel at vger dot kernel dot org>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Andi Kleen <ak at linux dot intel dot com>, Christoph Hellwig <hch at infradead dot org>, "Frank Ch. Eigler" <fche at redhat dot com>, "H. Peter Anvin" <hpa at zytor dot com>, Jason Baron <jbaron at redhat dot com>, Jim Keniston <jkenisto at us dot ibm dot com>, "K.Prasad" <prasad at linux dot vnet dot ibm dot com>, Lai Jiangshan <laijs at cn dot fujitsu dot com>, Li Zefan <lizf at cn dot fujitsu dot com>, Peter Zijlstra <peterz at infradead dot org>, Srikar Dronamraju <srikar at linux dot vnet dot ibm dot com>, Tom Zanussi <tzanussi at gmail dot com>, systemtap <systemtap at sources dot redhat dot com>, DLE <dle-develop at lists dot sourceforge dot net>
- Date: Mon, 14 Sep 2009 22:52:51 +0200
- Subject: Re: [PATCH tracing/kprobes 0/7] tracing/kprobes: kprobe-based event tracer update and perf support
- References: <20090910235258.22412.29317.stgit@dhcp-100-2-132.bos.redhat.com> <20090911013332.GB16396@nowhere> <4AAA74D2.9060203@redhat.com> <20090914025949.GB14306@nowhere> <4AAE7A5D.8010503@redhat.com>
On Mon, Sep 14, 2009 at 01:16:13PM -0400, Masami Hiramatsu wrote:
> Frederic Weisbecker wrote:
>> On Fri, Sep 11, 2009 at 12:03:30PM -0400, Masami Hiramatsu wrote:
>>> Frederic Weisbecker wrote:
>>>> May be another step in the todo-list that would be nice: define the format
>>>> for a type. Like it's done from ftrace events.
>>>
>>> Thanks!
>>>
>>> BTW, I'm not sure what the type means. Each event already has its own
>>> event ID and event_call. Could you tell me which part of ftrace I should
>>> refer to ?
>>>
>>
>>
>> Actually I meant the format for a field.
>> Say you define filename=arg1, it would be nice to have
>>
>> print "%s", filename
>>
>> in the format file.
>
> Ah, indeed. It is better to support 'type' casting for each argument.
> I think type casting can be done as below syntax.
>
> NAME=ARG:TYPE
> e.g.
> jiffies64=@jiffies64:u64
> message=%ax:str
>
Yeah looks good!
>> Hmm, now that I think about it, we can't dereference an array...for now :-)
>
> :-)
> BTW, currently, an entry of the array can be shown, e.g. +10(sa).
> Hmm, for more complex dereference(e.g. accessing a->b[a->c]), it might need
> another dereferencing syntax(e.g. "sa[16][sa[8]]"), or
> just allow to use braces(e.g. "+(+8(sa))(+16(sa))").
Well, that may be too much complexity.
I guess if we want multi level dereference, say you want a->b->c
it should be sufficient to probe the point where b->c gets it's
value (if any).
But it would be nice to fetch a range: sa[begin:end]
Or at least just giving the length of the range.