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Date: Thu, 22 Sep 2011 14:12:16 -0400
From: Christoph Hellwig <hch@infradead.org>
To: Jeff Moyer <jmoyer@redhat.com>
Cc: jens.axboe@fusionio.com, linux-kernel@vger.kernel.org
Subject: Re: blk_classic tracing horribly broken
Message-ID: <20110922181216.GA13772@infradead.org>
References: <x491uv8h348.fsf@segfault.boston.devel.redhat.com>
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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.