Re: [PATCH] tests/avocado: Cancel BootLinux tests in case there is no free port

[Thomas Huth]

On 07/03/2022 13.50, Daniel P. Berrangé wrote:
> On Mon, Feb 28, 2022 at 12:43:25PM +0100, Thomas Huth wrote:
> > The BootLinux tests are currently failing with an ugly python
> > stack trace on my RHEL8 system since they cannot get a free port
> > (likely due to the firewall settings on my system). Let's properly
> > check the return value of find_free_port() instead and cancel the
> > test gracefully if it cannot get a free port.
> >
> > Signed-off-by: Thomas Huth <thuth@redhat.com>
> > ---
> >   Unfortunately, it still takes > 70 seconds for each and every
> >   tests from tests/avocado/boot_linux.py to get canceled, so
> >   tests/avocado/boot_linux.py still renders "make check-avocado"
> >   for me pretty unusable... looking at the implementation of
> >   find_free_port() in Avocado, I wonder whether there isn't a
> >   better way to get a free port number in Python? Brute-forcing
> >   all ports between 1024 and 65536 seems just quite cumbersome
> >   to me...
>
> Even in the worst case of testing every single port,
> for INET and INET6 and for STREAM and DGRAM sockets,
> that find_free_port port completes in a couple of
> seconds.

Weird, on my system, the test runs for 70 seconds, just to finally 
discovered that there was no free port available.

> This code is all inherantly racy though, because as
> designed it is checking for a port that's available
> and then later calls wait_for_phone_home which spins
> up a HTTP server listening on the port. The port can
> be used in between the check and use. This can be
> the case if running many things in parallel on the
> host.
>
> It would be better to spin up that server using
> kernel port auto-selection at the start eliminating
> the race entirely.  Then just record the port that
> was allocated and use that when building thue
> cloudinit config for the guest.

That sounds much better, indeed... now we just need a volunteer to fix it ;-)

 Thomas