Re: [Xen-devel] [XTF PATCH v2] xtf-runner: support two modes for getting output

[Ian Jackson <ian.jackson@xxxxxxxxxxxxx>]

Andrew Cooper writes ("Re: [XTF PATCH v2] xtf-runner: support two modes for 
getting output"):
> On 11/08/16 18:51, Wei Liu wrote:
> > I'm pretty out of idea here.
> 
> Because of XTF's behaviour (waiting for xenconsoled to catch up), you
> know for certain that once `xl create` has finished, nothing more will
> write into the log.

You're missing the problem, I think.  It's this possible race:

   VM prints last output to ring
                                        xenconsoled wakes up from poll
   VM calls shutdown
             xenstored sends domain death event
             xl receives domain death event
             xl tears down guest, destroying
                 all relevant xenstore nodes
             xl exits
                     xtf-runner opens logfile
                     xtf-runner reads logfile
                     xtf-runner gets eof on logfile

                                       xenconsoled reads data from
                                       ring (which page is now only
                                       owned by xenconsoled)

                                       xenconsoled writes final data
                                       to logfile

Wei: Maybe you could rely on `xl console' not exiting until xenconsole
has written the last data to the logfile ?  You say:

> It is sure that xenconsoled will close the tty before closing the file,
> so stat'ing the actual device node won't work either.

We don't care when xenconsoled closes the logfile.  We care about when
it last calls write() (with a nonempty buffer).

Ian.

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