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?

+    """
+
+    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

+
+        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

+        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?

+        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?

+        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? :( :(


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.