Re: [RFC net 0/1] Fix netdevim to correctly mark NAPI IDs

[Joe Damato <jdamato@fastly.com>]

On Tue, Apr 15, 2025 at 05:11:54PM -0700, Jakub Kicinski wrote:
> On Tue, 15 Apr 2025 12:39:11 -0700 Joe Damato wrote:
> > On Mon, Mar 31, 2025 at 04:39:17PM -0700, Jakub Kicinski wrote:
> > > Up to you. The patch make me wonder how many other corner cases / bugs
> > > we may be missing in drivers. And therefore if we shouldn't flesh out
> > > more device-related tests. But exercising the core code makes sense
> > > in itself so no strong feelings.  
> > 
> > Sorry to revive this old thread, but I have a bit of time to get
> > this fixed now. I have a patch for netdevsim but am trying to figure
> > out what the best way to write a test for this is.
> > 
> > Locally, I've hacked up a tools/testing/selftests/drivers/net/napi_id.py
> > 
> > I'm using NetDrvEpEnv, but am not sure: is there an easy way in
> > Python to run stuff in a network namespace? Is there an example I
> > can look at?
> > 
> > In my Python code, I was thinking that I'd call fork and have each
> > python process (client and server) set their network namespace
> > according to the NetDrvEpEnv cfg... but wasn't sure if there was a
> > better/easier way ?
> > 
> > It looks like tools/testing/selftests/net/rds/test.py uses
> > LoadLibrary to call setns before creating a socket.
> > 
> > Should I go in that direction too?
> 
> Why do you need a netns? The NetDrvEpEnv will create one for you
> automatically and put one side of the netdevsim into it.
> Do you mean that you need to adjust that other endpoint?
> It's done the same way as if it was a remote machine:
> 
> 	cmd(..., host=cfg.remote)

Maybe I'm just thinking about it wrong and/or describing it poorly.

The idea was that napi_id.py test forks. One process does a
listen()/accept() and the other does a connect(). The accept side
checks that the napi ID is non-zero. For that to work, both
processes need their netdevsims to be able to talk to each other.

> If you really need a netnes check out
> tools/testing/selftests/net/lib/py/netns.py

I'll take a look, but I'm probably just missing something about how
to properly use NetDrvEpEnv.