Re: blk_classic tracing horribly broken

[Jeff Moyer <jmoyer@redhat.com>]

Christoph Hellwig <hch@infradead.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