From mboxrd@z Thu Jan  1 00:00:00 1970
From: Akira Hayakawa <ruby.wktk@gmail.com>
Date: Thu, 05 Dec 2013 12:12:49 +0000
Subject: [Question] btt -B doesn't output anything with DM device
Message-Id: <52A06DC1.4070402@gmail.com>
List-Id: <linux-btrace.vger.kernel.org>
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To: linux-btrace@vger.kernel.org
Cc: dm-devel@redhat.com, devel@etsukata.com

Hi, Guys,

I am trying to visualize io pattern by bno_plot.
bno_plot requires an output from btt -B but
btt -B doesn't output anything for DM devices (e.g. /dev/mapper/mydev) while
it does for real block devices (e.g. /dev/sdc).


For narrowing down the problem
I reproduced this problem with simple linear device.

# Setup
root@Freedom:/home/akira# dmsetup create mydev --table "0 100000 linear /dev/sdc 0"
root@Freedom:/home/akira# dmsetup ls
pdc_fgaahfadb   (254:0)
mydev   (254:1) <- this

# Trace
root@Freedom:/home/akira# cat devlist
/dev/mapper/mydev
/dev/sdc
root@Freedom:/home/akira# blktrace -w 30 -I devlist -D mytrace
== dm-1 =  CPU  0:                    0 events,        0 KiB data
  CPU  1:                  378 events,       18 KiB data
  Total:                   378 events (dropped 0),       18 KiB data
== sdc =  CPU  0:                    0 events,        0 KiB data
  CPU  1:                  781 events,       37 KiB data
  Total:                   781 events (dropped 0),       37 KiB data
root@Freedom:/home/akira# ls mytrace/
dm-1.blktrace.0  dm-1.blktrace.1  sdc.blktrace.0  sdc.blktrace.1

# btt
root@Freedom:/home/akira# btt -i mytrace/sdc.blktrace.* -B sdc
root@Freedom:/home/akira# btt -i mytrace/dm-1.blktrace.* -B dm-1  
root@Freedom:/home/akira# ls *.dat
sdc_008,032_c.dat  sdc_008,032_r.dat


btt doesn't output anything with dm-1.blktrace.* .
Is this intentionally designed or just a (known/unknown) bug?
Or, do I forget something?


Thanks,
Akira