QEMU tracing using systemtap-initscript
---------------------------------------

You can capture QEMU trace data all the time using systemtap-initscript.  This
uses SystemTap's flight recorder mode to trace all running guests to a
fixed-size buffer on the host.  Old trace entries are overwritten by new
entries when the buffer size wraps.

1. Install the systemtap-initscript package:
  # yum install systemtap-initscript

2. Install the systemtap scripts and the conf file:
  # cp /usr/share/qemu-kvm/systemtap/script.d/qemu_kvm.stp /etc/systemtap/script.d/
  # cp /usr/share/qemu-kvm/systemtap/conf.d/qemu_kvm.conf /etc/systemtap/conf.d/

The set of trace events to enable is given in qemu_kvm.stp.  This SystemTap
script can be customized to add or remove trace events provided in
/usr/share/systemtap/tapset/qemu-kvm-simpletrace.stp.

SystemTap customizations can be made to qemu_kvm.conf to control the flight
recorder buffer size and whether to store traces in memory only or disk too.
See stap(1) for option documentation.

3. Start the systemtap service.
　# service systemtap start qemu_kvm

4. Make the service start at boot time.
　# chkconfig systemtap on

5. Confirm that the service works.
  # service systemtap status qemu_kvm
  qemu_kvm is running...

When you want to inspect the trace buffer, perform the following steps:

1. Dump the trace buffer.
  # staprun -A qemu_kvm >/tmp/trace.log

2. Start the systemtap service because the preceding step stops the service.
  # service systemtap start qemu_kvm

3. Translate the trace record to readable format.
  # /usr/share/qemu-kvm/simpletrace.py --no-header /usr/share/qemu-kvm/trace-events /tmp/trace.log