Return-Path: <linux-kernel-owner+w=401wt.eu-S1758815AbZFKPsR@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1758815AbZFKPsR (ORCPT <rfc822;w@1wt.eu>);
	Thu, 11 Jun 2009 11:48:17 -0400
Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754196AbZFKPsD
	(ORCPT <rfc822;linux-kernel-outgoing>);
	Thu, 11 Jun 2009 11:48:03 -0400
Received: from thunk.org ([69.25.196.29]:43745 "EHLO thunker.thunk.org"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1755098AbZFKPsB (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Thu, 11 Jun 2009 11:48:01 -0400
Date: Thu, 11 Jun 2009 11:47:51 -0400
From: Theodore Tso <tytso@mit.edu>
To: Christoph Hellwig <hch@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
       Fr?d?ric Weisbecker <fweisbec@gmail.com>, Ingo Molnar <mingo@elte.hu>,
       linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
       Minchan Kim <minchan.kim@gmail.com>, Mel Gorman <mel@csn.ul.ie>,
       Rik van Riel <riel@redhat.com>, Pekka Enberg <penberg@cs.helsinki.fi>,
       Peter Zijlstra <peterz@infradead.org>,
       Mathieu Desnoyers <compudj@krystal.dyndns.org>,
       Lai Jiangshan <laijs@cn.fujitsu.com>, Zhaolei <zhaolei@cn.fujitsu.com>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Jason Baron <jbaron@redhat.com>, Jiaying Zhang <jiayingz@google.com>,
       Tom Zanussi <tzanussi@gmail.com>,
       Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Subject: Re: [PATCH 00/11] [GIT PULL] more updates for the tag format
Message-ID: <20090611154751.GD9275@mit.edu>
Mail-Followup-To: Theodore Tso <tytso@mit.edu>,
	Christoph Hellwig <hch@infradead.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Fr?d?ric Weisbecker <fweisbec@gmail.com>,
	Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Minchan Kim <minchan.kim@gmail.com>, Mel Gorman <mel@csn.ul.ie>,
	Rik van Riel <riel@redhat.com>,
	Pekka Enberg <penberg@cs.helsinki.fi>,
	Peter Zijlstra <peterz@infradead.org>,
	Mathieu Desnoyers <compudj@krystal.dyndns.org>,
	Lai Jiangshan <laijs@cn.fujitsu.com>,
	Zhaolei <zhaolei@cn.fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
	Jason Baron <jbaron@redhat.com>,
	Jiaying Zhang <jiayingz@google.com>,
	Tom Zanussi <tzanussi@gmail.com>,
	Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
References: <20090610054206.510574695@goodmis.org> <20090610092644.GA20889@elte.hu> <c62985530906100411o5a178352n53f7d247f6e9dba9@mail.gmail.com> <20090610130127.GA6647@mit.edu> <alpine.DEB.2.00.0906100911190.30552@gandalf.stny.rr.com> <20090610160303.GA10240@mit.edu> <20090611130318.GB14220@infradead.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20090611130318.GB14220@infradead.org>
User-Agent: Mutt/1.5.18 (2008-05-17)
X-SA-Exim-Connect-IP: <locally generated>
X-SA-Exim-Mail-From: tytso@mit.edu
X-SA-Exim-Scanned: No (on thunker.thunk.org); SAEximRunCond expanded to false
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 2016
Lines: 37

On Thu, Jun 11, 2009 at 09:03:18AM -0400, Christoph Hellwig wrote:
> On Wed, Jun 10, 2009 at 12:03:03PM -0400, Theodore Tso wrote:
> > Yes, another approach for handling this case would be to take my
> > "jbd2_dev_to_name" function and support it as a first-class tagged
> > type; after all, I'm sure ext4 won't be the only place that would like
> > to take a dev_t and print the device name.  So this could certainly be
> > fixed by adding some kind of "<dev:xxx>" sort of tagged name.
> 
> We should absolutely agree on one way to represent block device for
> tracers.  At this point xfs, gfs2 and the block tracer all use
> major/minor.  I agree that having a name would be nicer for text output,
> but I really want to keep the dev_t for the binary output.  We should
> also make sure we agree on a field name so that filtering will work
> the same for all block-related tracers (especially important if we want
> to trace something from the filesystem down to the block layer).

And I want to keep the dev_t as what stored in the ring buffer for
space reasons; but the text name is far more convient in terms of
being human-readable, *especially* given there are some crazy people
out there wanting to make major/minor numbers be completely random.
The problem with that is that a log trace file might not be useful
after a reboot, unless someone had enough foresight to save the device
mappings which were in effect at the that the trace was taken.

So if we store the dev_t in the ring buffer, and have a way of
translating the dev_t into a human-friendly name at printk happen, I
think that meets both of our goals.  That would imply that filtering
would be using a device number, which would certainly be more
efficient than doing a string compare.

					- Ted

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/