Re: [Qemu-devel] [PATCH 0/4] qtest: fix "device_del" out-of-order events

[Peter Xu]

On Wed, Sep 13, 2017 at 11:53:16AM +0200, Thomas Huth wrote:
> On 13.09.2017 11:36, Peter Xu wrote:
> > It starts from a "make check" failure on one of my private tree. The
> > problem is that when we do "device_del" we normally looking for two
> > things: one response (which is mostly empty), and a REMOVE event.  The
> > tricky point is the event can either be there before/after the empty
> > response.  So I added qmp_device_del() to make sure the order does not
> > matter, then use it where proper.
> > 
> > Since I'm at it, I also added the sister helper qmp_device_add(), it
> > helps to remove LOCs.
> 
> I've had a similar idea a couple of weeks ago, see here:
> 
> http://patchwork.ozlabs.org/patch/801487/

Good to know!

> 
> > I still don't 100% sure why my private tree can trigger this error,
> > while the master cannot. Anyway, I think this is something we should
> > have, no matter what.
> 
> Did you maybe touch the USB tests in your private tree?

No.  But I changed some internals of QMP there, I guess that's the
reason that caused the misorder to happen more easily.

> As far as I know, some test currently use QMP in a bad way, for example
> usb_test_hotplug() only checks for the DEVICE_DELETED at the end, but
> forgets to read back the final return value. That return value is then
> presented to the next part of the code that uses QMP instead ... it
> currently only works more or less by accident, but as soon as you try to
> add new code inbetween, it certainly will fail.
> ==> We really got to clean this up (either with my patch or your patch
> series).

Agree.

I think your patch is nicer on the interface (as you have mentioned in
the other reply), I can try to review it later.

However it seems that your patch didn't really solve the problem I
encountered (mis-ordered message arrivals).  It would be good if you
want to solve it together, or I can draft patch upon yours.

Thanks,

-- 
Peter Xu