[PATCH net 5/5] selftests: net: add a test case for nsid in all nsid notifications

[Ilya Maximets]

The test makes subscribes to link events from all namespaces and
makes sure that local events do not carry NSID in their ancillary
data (even if there is a self-referential NSID allocated for the
local namespace), and remote events do.

Assisted-by: OpenCode:claude-opus-4.6
Signed-off-by: Ilya Maximets <i.maximets@xxxxxxx>
---
 tools/testing/selftests/net/link_netns.py | 52 +++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/tools/testing/selftests/net/link_netns.py b/tools/testing/selftests/net/link_netns.py
index 2aae422d3f8a6..1e766154cb573 100755
--- a/tools/testing/selftests/net/link_netns.py
+++ b/tools/testing/selftests/net/link_netns.py
@@ -33,6 +33,57 @@ def test_event() -> None:
                   "Received unexpected link notification")
 
 
+def test_event_all_nsid() -> None:
+    """NETLINK_LISTEN_ALL_NSID notifications: local events must not
+    carry nsid even with a self-referential mapping.  Remote events
+    must carry the correct nsid."""
+
+    with NetNS() as ns1, NetNS() as ns2:
+        net1, net2 = str(ns1), str(ns2)
+
+        with NetNSEnter(net1):
+            rtnl = RtnlFamily()
+        rtnl.ntf_listen_all_nsid()
+        rtnl.ntf_subscribe("rtnlgrp-link")
+
+        # Case 1: no nsid assigned, local event, no nsid expected.
+        ip("link add dummy-lo type dummy", ns=net1)
+
+        # Case 2: self-referential nsid, local event, still no nsid.
+        ip(f"netns set {net1} {LINK_NETNSID}", ns=net1)
+        ip("link add dummy-sr type dummy", ns=net1)
+
+        # Case 3: remote event, nsid present.
+        ip(f"netns set {net2} {LINK_NETNSID2}", ns=net1)
+        ip("link add dummy-re type dummy", ns=net2)
+
+        # Collect the three newlink events, ignoring unrelated noise.
+        events = {}
+        for msg in rtnl.poll_ntf(duration=1):
+            if msg['name'] == 'getlink':
+                ifname = msg['msg'].get('ifname')
+                if ifname in ('dummy-lo', 'dummy-sr', 'dummy-re'):
+                    events[ifname] = msg
+            if len(events) == 3:
+                break
+
+        ksft_true('dummy-lo' in events, "missing local event")
+        ksft_true(events['dummy-lo'].get('nsid') is None,
+                  "local event without nsid should not carry nsid")
+
+        ksft_true('dummy-sr' in events, "missing self-ref event")
+        ksft_true(events['dummy-sr'].get('nsid') is None,
+                  "local event with self-ref nsid should not carry nsid")
+
+        ksft_true('dummy-re' in events, "missing remote event")
+        ksft_eq(events['dummy-re'].get('nsid'), LINK_NETNSID2,
+                "remote event should carry nsid")
+
+        ip("link del dummy-lo", ns=net1)
+        ip("link del dummy-sr", ns=net1)
+        ip("link del dummy-re", ns=net2)
+
+
 def validate_link_netns(netns, ifname, link_netnsid) -> bool:
     link_info = ip(f"-d link show dev {ifname}", ns=netns, json=True)
     if not link_info:
@@ -175,6 +226,7 @@ def test_peer_net_cross_ns() -> None:
 def main() -> None:
     ksft_run([
         test_event,
+        test_event_all_nsid,
         test_link_net,
         test_peer_net,
         test_peer_net_cross_ns,
-- 
2.53.0