Re: [Xen-devel] [XTF PATCH] xtf-runner: fix two synchronisation issues

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Jul 29, 2016 at 03:35:06PM +0100, Ian Jackson wrote:
> Wei Liu writes ("Re: [XTF PATCH] xtf-runner: fix two synchronisation issues"):
> > On Fri, Jul 29, 2016 at 03:21:52PM +0100, Ian Jackson wrote:
> > > Wei Liu writes ("[XTF PATCH] xtf-runner: fix two synchronisation issues"):
> > > > There were two synchronisation issues for the old code:
> > > > 
> > > > 1. There was no guarantee that guest console was ready before "xl
> > > >    console" invocation.
> > > 
> > > Is this not a bug in xl console ?
> > 
> > I don't think so. It gives up when it can't get tty from xenstore. I
> > think that's reasonable.
> 
> If you say
>   xl create /etc/xen/foo.cfg
>   xl console foo
> then surely you shouldn't find that xl console fails because of some
> race.
> 

What if the guest just doesn't have / want a console? In that case there
will never be a tty node in xenstore, so xl console should wait forever
for one? What is the expectation for this case?

> > > > 2. Poll xenstore guest console node to make sure console is available
> > > >    before "xl console" invocation.
> > > 
> > > Users of things like xl shouldn't need to prat about in xenstore too.
> > 
> > What does this mean?
> 
> I mean that xenstore is part of the implementation of libxl, not part
> of its public interface.  In this sense it is a bit like libxc.
> libxl callers should (in general) not look at xenstore - and of
> course they should therefore;2~ not need to do so.
> 

In this particular case, all nodes that xtf-runner code reles on are
documented, so I already consider them public interfaces.

> If the xtf runner needs to look in xenstore (other than perhaps if
> it's doing strange things there as part of its test cases) then that
> means there is some interface or capability missing in libxl.
> 

I don't disagree.

But the missing capability won't be backported to older version of Xen.
I don't want to eliminate the possibility for running xtf on older
versions of Xen.

> OTOH I'm slightly confused because I was under the impression that
> there was a polling loop in xl console (xenconsole) already.
> 
> Maybe I don't understand your problem.
> 

The issue is that when it tries to get tty from xenstore and there isn't
one, it gives up. Your polling loop is something else.

http://osstest.xs.citrite.net/~osstest/testlogs/logs/66855/test-xtf-amd64-amd64-1/10.ts-xtf-fep.log

Wei.

> Ian.

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