Date: Mon, 13 Apr 2009 22:11:55 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Jens Axboe <jens.axboe@oracle.com>, Steven Rostedt <rostedt@goodmis.org>,
       Tom Zanussi <tzanussi@gmail.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>, "Theodore Ts'o" <tytso@mit.edu>,
       Arnaldo Carvalho de Melo <acme@redhat.com>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] blktrace: move trace/ dir to /sys/block/sda/
Message-ID: <20090413201155.GA17450@elte.hu>
References: <49E31931.5000506@cn.fujitsu.com> <20090413180054.GZ5178@kernel.dk>
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* Jens Axboe <jens.axboe@oracle.com> wrote:

> On Mon, Apr 13 2009, Li Zefan wrote:
> > Impact: allow ftrace-plugin blktrace to trace device-mapper devices
> > 
> > blktrace can't trace a single partition, so it makes no sense to
> > have one trace/ dir in each /sys/block/sda/sdaX. Move it to
> > /sys/block/sda/.
> > 
> > Thus we fix an issue reported by Ted, that ftrace-plugin 
> > blktrace can't be used to trace device-mapper devices.
> 
> Perhaps I never committed that patch, but it would be trivial to 
> do partition based blktrace tracing. It's also quite useful. So 
> please don't go changing things to make that harder to support, it 
> would be nicer to just add the (small) bits to support 
> per-partition tracing. It's basically just a start/stop sector 
> range, while some events are per-device and should just be 
> included always.

btw., per tracepoint filters could be used for that. That would 
allow multiple partitions to be traced at once.

blktrace user-space could make use of sector range filters straight 
away [ hm, Tom - do we have the <= comparison operator already, or 
is that still WIP? ] - but i think it's better to do this in a more 
integrated way: via the sysfs API, via /sys/block/sda/sda2/trace/.

So when a partition's trace entry is activated, it would 
auto-install a specific filter expression for sda, with the sector 
range of that partition. Or something like that. How does this 
sound?

	Ingo
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