Re: [PATCH] test: Wait for network before starting passt in two_guests setup

[Stefano Brivio <sbrivio@redhat.com>]

On Mon, 7 Nov 2022 14:21:30 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Fri, Nov 04, 2022 at 02:53:36AM +0100, Stefano Brivio wrote:
> > As pasta now configures that target network namespace with
> > --config-net, we need to wait for addresses and routes to be actually
> > present. Just sending netlink messages doesn't mean this is done
> > synchronously.
> > 
> > A more elegant alternative, which probably makes sense regardless of
> > this test setup, would be to query, from pasta, addresses and routes
> > we added, and wait until they're there, before proceeding.
> > 
> > Signed-off-by: Stefano Brivio <sbrivio@redhat.com>  
> 
> Ugly, but I see the point.
> 
> As you say in future I hope we can actually detect the completion of
> interface configuration which would be useful both here and other
> places.

Yes... the outcome of "pasta --config-net ip address show" (compared to
"pasta --config-net -- sh -c 'sleep 0.05; ip address show'") is a bit
bothering.

> One other thing to consider - in the case where pasta is spawing a new
> process, rather than attaching to an existing one, it's possibly
> counterintuitive that the process starts before pasta has completed
> setup.  We possibly should get the spawned thread to wait until the
> main pasta thread is entering its main loop before exec()ing the
> shell.  Obviously requires some sync mechanism, which is a bit clunky.

Right, that might be a problem if somebody spawns a script that relies
on the tap interface to be working right away (even though the delay is
probably small enough for all practical cases).

I'll file a ticket covering both topics.

-- 
Stefano