From mboxrd@z Thu Jan  1 00:00:00 1970
From: Martin Peschke <mpeschke@linux.vnet.ibm.com>
Date: Wed, 19 Nov 2008 11:38:38 +0000
Subject: bad trace magic
Message-Id: <1227094718.10046.29.camel@kitka.ibm.com>
List-Id: <linux-btrace.vger.kernel.org>
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To: linux-btrace@vger.kernel.org

Hi,

I run across blktrace complaints about broken traces once in a while.
I have pimped up the debugging output in verify_trace():

  --- bad trace magic ---
  magic    0x00000000
  sequence 0x00000000
  time     0x0000000000000000
  sector   0x0000000000000000
  bytes	   0x65617407		<--- begin of trace (trace magic)
  action   0x000005b0
  pid      0x0000029c
  device   0x7c185ac0
  cpu      0x00000000
  error    0x0036
  pdu_len  0x18c0

  00000000 00000000 00000000 00000000 00000000 00000000
  65617407 000005b0 0000029c 7c185ac0 00000000 003618c0

  bad trace in /sys/kernel/debug/block/sdbm/trace1

Traces appear to get out of place by some bytes. The offset varies.


I have got a couple of questions:

Does blktrace stop processing of a trace stream in this case, doesn't
it?

Next I am going to dump the trace which precedes a broken trace.
Any better ideas how to debug this one?


Thanks,
Martin