linux-kernel - Re: [PATCH 11/13] tracing/kprobes: Add priv argument to fetch functions

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Message-ID: <87r4av1tuw.fsf@sejong.aot.lge.com>
Date:	Tue, 05 Nov 2013 11:10:31 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Namhyung Kim <namhyung.kim@....com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hyeoncheol Lee <cheol.lee@....com>,
	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	"zhangwei\(Jovi\)" <jovi.zhangwei@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH 11/13] tracing/kprobes: Add priv argument to fetch functions

On Mon, 4 Nov 2013 17:09:14 +0100, Oleg Nesterov wrote:
> See my replies to 0/13. Lets assume that you agree that get_user_vaddr()
> doesn't need tu->inode.

Okay.

>
> On 10/29, Namhyung Kim wrote:
>>
>> This argument is for passing private data structure to each fetch
>> function and will be used by uprobes.
>
> In this case, why do we need this "void *priv"? It actually becomes
> "bool need_addr_translation".

Right.  I added it because the deref method is used for both of kprobes
and uprobes and it only needed for uprobes.  And I thought if we need
something for kprobes later, it can be reused so make it general.

>
> Can't we avoid it? Can't we just add FETCH_MTD_memory_notranslate ?
> kprobes should use the same methods for FETCH_MTD_memory*, uprobes
> should obviously adjust the addr in FETCH_MTD_memory.
>
> Then (afaics) we need a single change in parse_probe_arg(),
>
> 	-	dprm->fetch = t->fetch[FETCH_MTD_memory];
> 	+	dprm->fetch = t->fetch[FETCH_MTD_memory_notranslate];
>
> Yes, this will blow *probes_fetch_type_table[], but looks simpler.

Looks good to me too, thanks! :)

>
> And. This way it would be simple to teach parse_probe_arg('@') to use
> _notranslate, say, "@=addr" or whatever.

Yeah, it'll be useful at least for fetching data in anon pages.

Thanks,
Namhyung
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