Re: [PATCH net-next] net: dummy: add phony ndo_setup_tc stub

[Florian Westphal <fw@strlen.de>]

Jakub Kicinski <kuba@kernel.org> wrote:
> On Tue,  9 Jun 2026 16:28:09 +0200 Florian Westphal wrote:
> > Unlike netdevsim, dummy is a data sink so no capabilities (e.g.
> > u32-style matcher, vport device redirects, PPPoE header push/pop etc).
> > have to be implemented.
> 
> If no "peer" is configured netdevsim is also a data sink.

Yes, but you can configure peers.  And then this fake offload stub
is a liar.

I would expect that offloads for netdevsim actually work, i.e.
that a shaper shapes, that ets offload does delay packets and
in case of flowtable that it will move skbs from one vport to
another (if that was requested).

> We added netdevsim because dummy and veth started accumulating
> "features" which were clearly just for test harnesses. Would be
> great if we could stay the course and put whatever changes you
> need in netdevsim, even if it requires some hacks.

Is a lot more work.  I don't have time ATM to implement a u32-style
packet matcher or a fake software flowtable.

> Is there anything fundamentally blocking the use of netdevsim?
> Or is it just convenience (since netdevsim is a bit of a PITA
> to create and establish the name of)?

I played with netdevsim, aside from the above (i.e., I don't expect
netdevsim to say 'offloaded' and then ignore all the offloaded
commands...) the worst part is the naming and the behaviour when
creating new devices while in a network namespace.  Test is spawned via
'unshare -n' -- I did not find a way to really extract the new device name
reliably except via 'ip link'.

I think thats solveable, so yes, I could make netdevsim lie instead.

But I don't think its the right thing to do.

If you disagree and think that this is fine I can retarget this to
netdevsim, no problem.