# Re: \[PATCH net-next v8 15/16\] selftests/net: Add env for container based tests

- From: David Wei \<hidden\>
- Date: 2026-02-01 22:53:39 
- List: netdev
- Page: https://ratatoskr.run/netdev/2026/02/7942317
- Thread: https://ratatoskr.run/netdev/2026/01/7942161/t.md

```text
On 2026-02-01 09:38, Jakub Kicinski wrote:
> On Thu, 29 Jan 2026 23:28:29 +0100 Daniel Borkmann wrote:
>> +class NetDrvContEnv(NetDrvEpEnv):
>> +    """
>> +    Class for an environment with a netkit pair setup for forwarding traffic
>> +    between the physical interface and a network namespace.
>
> A little diagram would be pretty awesome to have here, and perhaps copy
> it to the README file too?

Sounds good, I'll add one. I forget how much you like ASCII diagrams.

>
>> +    """
>> +
>> +    def __init__(self, src_path, rxqueues=1, **kwargs):
>> +        super().__init__(src_path, **kwargs)
>> +
>> +        self.require_ipver("6")
>> +        local_prefix = self.env.get("LOCAL_PREFIX_V6")
>> +        if not local_prefix:
>> +            raise KsftSkipEx("LOCAL_PREFIX_V6 required")
>> +
>> +        local_prefix = local_prefix.rstrip("/64").rstrip("::").rstrip(":")
>> +        self.ipv6_prefix = f"{local_prefix}::"
>> +        self.nk_host_ipv6 = f"{local_prefix}::2:1"
>> +        self.nk_guest_ipv6 = f"{local_prefix}::2:2"
>> +
>> +        self.netns = None
>> +        self._nk_host_ifname = None
>> +        self._nk_guest_ifname = None
>> +        self._tc_attached = False
>> +        self._bpf_prog_pref = None
>> +        self._bpf_prog_id = None
>> +        self._init_ns_attached = False
>
> I'm not a Python expert but the pre-init of variables that are set
> later on in __init__() (on all possible paths) seems like a waste of LoC

It's so that exceptions thrown -> __del__() don't complain about
undefined vars.

>
>> +
>> +        ip(f"link add type netkit mode l2 forward peer forward numrxqueues {rxqueues}")
>
> Would we be able to do this with YNL?
> no big deal but always nice to avoid the dependency on very latest CLI

Hmm, I tried looking into this already. My understanding is that this
can be done in C but not currently in YNL, not without adding a spec.

>
>> +        all_links = ip("-d link show", json=True)
>> +        netkit_links = [link for link in all_links
>> +                        if link.get('linkinfo', {}).get('info_kind') == 'netkit'
>> +                        and 'UP' not in link.get('flags', [])]
>
> And of course if you use YNL you can actually ask Netlink to
> echo back / return to you what interface it ended up creating.
> No need for the scanning..
>
>> +        if len(netkit_links) != 2:
>> +            raise KsftSkipEx("Failed to create netkit pair")
>> +
>> +        netkit_links.sort(key=lambda x: x['ifindex'])
>> +        self._nk_host_ifname = netkit_links[1]['ifname']
>> +        self._nk_guest_ifname = netkit_links[0]['ifname']
>> +        self.nk_host_ifindex = netkit_links[1]['ifindex']
>> +        self.nk_guest_ifindex = netkit_links[0]['ifindex']
>> +
>> +        self._setup_ns()
>> +        self._attach_bpf()
>
>> +    def _setup_ns(self):
>> +        self.netns = NetNS()
>> +        cmd("ip netns attach init 1")
>> +        self._init_ns_attached = True
>> +        ip("netns set init 0", ns=self.netns)
>
> Hm, refactor class NetNSEnter or just use its enter method?

I did consider this but I didn't feel like it fit the very specific
purpose of NetNSEnter. I needed the init ns to have a valid nsid from
within the test netns, which I didn't think many other tests would need.

>
>> +        ip(f"link set dev {self._nk_guest_ifname} netns {self.netns.name}")
>> +        ip(f"link set dev {self._nk_host_ifname} up")
>> +        ip(f"-6 addr add fe80::1/64 dev {self._nk_host_ifname} nodad")
>> +        ip(f"-6 route add {self.nk_guest_ipv6}/128 via fe80::2 dev {self._nk_host_ifname}")
>> +
>> +        ip("link set lo up", ns=self.netns)
>> +        ip(f"link set dev {self._nk_guest_ifname} up", ns=self.netns)
>> +        ip(f"-6 addr add fe80::2/64 dev {self._nk_guest_ifname}", ns=self.netns)
>> +        ip(f"-6 addr add {self.nk_guest_ipv6}/64 dev {self._nk_guest_ifname} nodad", ns=self.netns)
>> +        ip(f"-6 route add default via fe80::1 dev {self._nk_guest_ifname}", ns=self.netns)
>> +
>> +    def _attach_bpf(self):
>> +        bpf_obj = self.test_dir / "nk_forward.bpf.o"
>> +        if not bpf_obj.exists():
>> +            raise KsftSkipEx("BPF prog not found")
>> +
>> +        cmd(f"tc filter add dev {self.ifname} ingress bpf obj {bpf_obj} sec tc/ingress direct-action")
>> +        self._tc_attached = True
>> +
>> +        tc_info = cmd(f"tc filter show dev {self.ifname} ingress").stdout
>
> Don't we need to also add a qdisc if there isn't one already?

Sorry, why would qdisc be needed? The bpf prog attaches to tc. I don't
know anything about qdisc, though.

>
>> +        match = re.search(r'pref (\d+).*nk_forward\.bpf.*id (\d+)', tc_info)
>
> I haven't checked but TC doesn't support enough JSON and YNL doesn't
> support enough TC to avoid re hacks? :( :(

Yeah the old TC tool doesn't give me this info programmatically :(

Borkmann mentioned TC is outdated/unmaintained. I did use tcx via a C
loader before, but that was removed in an earlier iteration.

>
>
> As I mentioned to David in person, Wei Wang also needs to use this
> class for PSP tests so would be awesome to detach these from the large
> series. I promise to prioritize the "detached" bits of these series in
> case you're worried about the MW.

I'll move the env, basic ping test out. Then keep the queue lease tests,
adding the error paths you requested, in this series.
```