Re: [PATCH net v4 3/4] netdevsim: support devmem RX and TX bindings

[Mina Almasry]

On Wed, Oct 21, 2026 at 1:23 PM Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
>
> On Tue, 20 Oct 2026 23:17:34 -0700 Mina Almasry wrote:
> > But on the other hand the test coverage is nice, and maybe one day if
> > we add enough devmem support in netdevsim we'll be able to fuzz the
> > data path or something. Is there a way to get the best of both worlds?
> > Like put a comment on top of netdevsim that this is test simulator
> > device and any missing functionality and/or bugs in it should be
> > medium criticality max or something? Or is it too much trouble and I
> > should drop the netdevsim support and tests?
>
> I already strip Fixes tags and apply the patches to net-next.
> But it's still a burden. If you're signing up to fix the issues /
> review the slop we can try.

Hi Jakub,

So I started looking into whether we can improve test and fuzz
coverage with an improved netdevsim. My LLM prototyped full datapath
(with devmem) and offload support in netdevsim so the hardware
selftests and packetdrill run and pass in a plain VM without physical
NICs. I posted the branch at:

https://github.com/mina/linux/tree/nsim-devmem-rx-tx

The main problem is the total LLM generated diff to netdevsim: 62
files changed with 5,525 additions and 672 deletions :( So it's a big
change.

But with this, we can do pretty cool things:

- All 36/36 drivers/net/hw/ tests, 18/18 drivers/net/ tests, and
164/164 net/packetdrill/ tests now pass on a linked netdevsim pair,
without needing real hardware. This is significant because a lot of
these 'driver' tests also actually tested unique code paths in core
like devmem.

- NIPA can now (I think) run all these netdev driver tests and
packetdrills without real hardware:
https://github.com/mina/patches/tree/nipa-nsim-hw-and-packetdrill

- Packetdrill can now run on netdevsim:
https://github.com/mina/patches/tree/packetdrill-nsim-default

-(best part) Syzkaller can now fuzz live devmem/zcrx datapath &
offload netlink APIs:
https://github.com/mina/patches/tree/syzkaller-nsim-full-net-coverage

You asked me to do add syzkaller devmem support before, but adding
devmem support to netdevsim was too hard. With LLMs, it's almost
trivial, but it involves a lot of generated code.

Do you think this (or a subset) is valuable to post upstream to add to
netdevsim?

-- 
Thanks,
Mina