title: kvm does not log output
body: <p>KVM tells me on <code>-help</code>:</p>
  
  <pre><code>-d item1,...    enable logging of specified items (use '-d help' for a list of log items)
  
  -D logfile      output log to logfile (default stderr)
  </code></pre>
  
  <p>I used it:
  <code>kvm -d in_asm,int -D mylog.log -boot d -cdrom myiso.iso -m 4069 -smp 4 -serial file:serial.log</code></p>
  
  <p>Using <code>qemu-system-x86_64</code> instead of <code>kvm</code>, everything is right, all output will be logged. But on enabling <code>kvm</code> (using <code>-enable-kvm</code> flag or command <code>kvm</code>), the file will be truncated but nothing logged.</p>