linux-kernel - Re: blk_classic tracing horribly broken

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Date:	Thu, 22 Sep 2011 14:32:29 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	jens.axboe@...ionio.com, linux-kernel@...r.kernel.org
Subject: Re: blk_classic tracing horribly broken

Christoph Hellwig <hch@...radead.org> writes:

> On Thu, Sep 22, 2011 at 01:57:11PM -0400, Jeff Moyer wrote:
>> Hi,
>> 
>> I've stared at the code for a while, and I've come up empty.  Would
>> anyone care to take a stab at fixing this?
>> 
>> To reproduce:
>> 
>> mount -t debugfs none /sys/kernel/debug
>> cd /sys/kernel/debug/tracing
>> echo blk > current_tracer
>> echo 1 > events/block/enable
>> echo 1 > options/blk_classic
>> echo 1 > tracing_on
>> 
>> dd if=/dev/<device> of=/dev/null bs=1M count=1 iflag=direct
>> cat trace
>
> Why are you using this interface anyway?  We actually had planned to
> drop it long time ago, but for some reason that never happened.

I was using it when testing the flush+fua reporting in blktrace, to be
sure we didn't break it.  Since it was already broken, I didn't have to
worry, but I put it on my todo list to investigate why.  Dropping broken
code is fine with me (given that there are two alternatives to use).

Cheers,
Jeff
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