This patch adds per request hardware debugging data to the trace
record which is written per request. It's a replacement for some sad
kernel message based debugging code. Considering the amount of trace
data, printk() is not suitable for this stuff. Writing binary traces
is more efficient. In addition we got all information in one place.

The QTCB trace data is only dumped for requests other than SCSI
requests.  Otherwise we would flood the trace ring buffer. We are
mostly interested in non-SCSI, recovery related requests here anyway.

This patch also works around a known hardware bug. It truncates QTCB
traces so that we do not save unused areas of the hardware trace.
Signed-off-by: Martin Peschke <mp3@de.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>