[PATCH net 1/2] selftests: drv-net: ring_reconfig: handle devices without channel config

["Bilal Yazıcıoğlu" <ahmetbilalyazicioglu@gmail.com>]

Drivers which don't implement the ethtool get_channels op (e.g.
e1000e) make ETHTOOL_MSG_CHANNELS_GET fail with -EOPNOTSUPP. YNL
raises that as an NlError, so ring_reconfig reports two failures on
such devices:

 - channels() fails on its first channels_get call, although there
   is nothing to test;
 - ringparam() fails in _configure_min_ring_cnt() before any ring
   size is tested. The helper only reduces the channel count to
   speed up the reconfiguration, ringparam() does not depend on it.

Skip channels() and return early from _configure_min_ring_cnt() when
the channel query is not supported, logging that the channel count
was left unchanged. Other netlink errors are still reported as
failures.

The issue was found through AI-assisted source code analysis
(OpenAI Codex) and confirmed on a ThinkPad T480 with an Intel I219-V
(e1000e, 8086:15d8): "ethtool -l" fails with "Operation not
supported" while "ethtool -g" works, and running the test functions
with the in-tree YNL library against the device fails with NlError
95 (EOPNOTSUPP).

No remote endpoint was available, so the full test was not run. On
the same machine the test functions were run under ksft_run with a
stub environment and all ethtool set requests blocked: channels() is
now skipped and _configure_min_ring_cnt() returns after the channel
query. Behaviour on devices which support channels was only checked
against an emulated ethtool family.

Fixes: ecca75ae5ae6 ("selftests: drv-net: replace the nsim ring test with a drv-net one")
Signed-off-by: Bilal Yazıcıoğlu <ahmetbilalyazicioglu@gmail.com>
---

Notes:
    Note, not part of this fix: with this patch ringparam() gets past
    _configure_min_ring_cnt() on e1000e and reaches the ring size loop.
    e1000e clamps ring sizes below 64 instead of rejecting them, so the
    check that the requested minimum was applied is expected to fail on
    that driver. I could not run that part (it needs a remote endpoint),
    and whether the test or the driver should change is a separate
    question.

 .../selftests/drivers/net/ring_reconfig.py    | 22 +++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/drivers/net/ring_reconfig.py b/tools/testing/selftests/drivers/net/ring_reconfig.py
index 6682d4badfb..baac20e8d3e 100755
--- a/tools/testing/selftests/drivers/net/ring_reconfig.py
+++ b/tools/testing/selftests/drivers/net/ring_reconfig.py
@@ -5,6 +5,7 @@
 Test channel and ring size configuration via ethtool (-L / -G).
 """
 
+import errno
 import socket
 import struct
 import time
@@ -26,6 +27,16 @@ MIN_TX_RING = 32
 MAX_TX_RING = 1024
 
 
+def _channels_get_or_skip(cfg, ehdr):
+    """ Get the channel config, skip the test if the device has none. """
+    try:
+        return cfg.eth.channels_get(ehdr)
+    except NlError as e:
+        if e.error == errno.EOPNOTSUPP:
+            raise KsftSkipEx("device does not support channel config") from e
+        raise
+
+
 def channels(cfg) -> None:
     """
     Twiddle channel counts in various combinations of parameters.
@@ -33,7 +44,7 @@ def channels(cfg) -> None:
     if the config is accepted and crashes.
     """
     ehdr = {'header':{'dev-index': cfg.ifindex}}
-    chans = cfg.eth.channels_get(ehdr)
+    chans = _channels_get_or_skip(cfg, ehdr)
 
     all_keys = ["rx", "tx", "combined"]
     mixes = [{"combined"}, {"rx", "tx"}, {"rx", "combined"}, {"tx", "combined"},
@@ -88,7 +99,14 @@ def channels(cfg) -> None:
 def _configure_min_ring_cnt(cfg) -> None:
     """ Try to configure a single Rx/Tx ring. """
     ehdr = {'header':{'dev-index': cfg.ifindex}}
-    chans = cfg.eth.channels_get(ehdr)
+    try:
+        chans = cfg.eth.channels_get(ehdr)
+    except NlError as e:
+        # Reducing the channel count is only an optimization
+        if e.error == errno.EOPNOTSUPP:
+            ksft_pr("Channel configuration unsupported; continuing ring test")
+            return
+        raise
 
     all_keys = ["rx-count", "tx-count", "combined-count"]
     restore = {}
-- 
2.56.0