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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 11/08/16 18:51, Wei Liu wrote:
> On Thu, Aug 11, 2016 at 06:17:31PM +0100, Ian Jackson wrote:
>> Wei Liu writes ("Re: [XTF PATCH v2] xtf-runner: support two modes for 
>> getting output"):
>>> On Thu, Aug 11, 2016 at 05:27:56PM +0100, Ian Jackson wrote:
>>>> This is perverse.  Why not just open it O_CREAT|O_RDONLY ?  If Python
>>>> can't do that then unconditionally opening it O_CREAT|O_RDWR would do.
>>> The open call doesn't accept O_CREAT|O_RDONLY.
>> open("t", O_RDONLY|O_CREAT, 0666)       = 3
>>
>> But maybe you mean Python's open doesn't.
>>
>>> Andy my experiment showed that "rb" doesn't create the file.
>> Yes, it wouldn't.  If you want a fopen mode, "a+" may be of some use.
>>
>>>>> +    logfile.seek(0, 2) # Go to end of file
>>>> Does Python not have SEEK_END somewhere ?
>>> There is one, but that's in os module.
>>> Python official document is using numeric values directly.
>> Seriously?  Fine, whatever.
>>
>>>>> +    lines = logfile.readlines()
>>>>> +    logfile.close()
>>>>> +
>>>>> +    if len(lines) == 0:
>>>>> +        raise RunnerError("Test output empty")
>>>> I think you are racing with xenconsoled here.  How do you know that
>>>> all the output has arrived ?
>>> Unfortunately there doesn't seem to be a direct way to synchronise
>>> between the two.
>>>
>>> Maybe the best bet is to watch the tty node for it to go away?
>> Does xenconsole write the remaining output to the logfile before
>> deleting the tty node from xenstore ?
>>
> Unfortunately no, watching tty node in xenstore won't work.  In fact,
> xenconsoled doesn't delete the tty node at all. It's libxl that deletes
> it AFAICT.
>
> It is sure that xenconsoled will close the tty before closing the file,
> so stat'ing the actual device node won't work either.
>
> 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.

This is a catch 22 situation though, as I specifically want to avoid
that behaviour.  Perhaps it is acceptable in logfile mode, if we can get
`xl console` mode working without the synchronous delay.

~Andrew

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