selftests: drv-net: test empty queue and NAPI responses in netlink

Make sure kernel doesn't respond to GETs for queues and NAPIs when
link is down. Not with valid data, or with empty message, we want
a ENOENT.

Link: https://patch.msgid.link/20241219032833.1165433-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

tools/testing/selftests/drivers/net/queues.py

@@ -1,10 +1,12 @@
 #!/usr/bin/env python3
 # SPDX-License-Identifier: GPL-2.0
 
-from lib.py import ksft_run, ksft_exit, ksft_eq, KsftSkipEx
-from lib.py import EthtoolFamily, NetdevFamily
+from lib.py import ksft_disruptive, ksft_exit, ksft_run
+from lib.py import ksft_eq, ksft_raises, KsftSkipEx
+from lib.py import EthtoolFamily, NetdevFamily, NlError
 from lib.py import NetDrvEnv
-from lib.py import cmd
+from lib.py import cmd, defer, ip
+import errno
 import glob
 
 
@@ -59,9 +61,27 @@ def addremove_queues(cfg, nl) -> None:
     ksft_eq(queues, expected)
 
 
+@ksft_disruptive
+def check_down(cfg, nl) -> None:
+    # Check the NAPI IDs before interface goes down and hides them
+    napis = nl.napi_get({'ifindex': cfg.ifindex}, dump=True)
+
+    ip(f"link set dev {cfg.dev['ifname']} down")
+    defer(ip, f"link set dev {cfg.dev['ifname']} up")
+
+    with ksft_raises(NlError) as cm:
+        nl.queue_get({'ifindex': cfg.ifindex, 'id': 0, 'type': 'rx'})
+    ksft_eq(cm.exception.nl_msg.error, -errno.ENOENT)
+
+    if napis:
+        with ksft_raises(NlError) as cm:
+            nl.napi_get({'id': napis[0]['id']})
+        ksft_eq(cm.exception.nl_msg.error, -errno.ENOENT)
+
+
 def main() -> None:
     with NetDrvEnv(__file__, queue_count=100) as cfg:
-        ksft_run([get_queues, addremove_queues], args=(cfg, NetdevFamily()))
+        ksft_run([get_queues, addremove_queues, check_down], args=(cfg, NetdevFamily()))
     ksft_exit()