[Devel] [PATCH vz10 3/3] selftests: drv-net: read the channel count over netlink

[Eva Kurchatova <eva.kurchatova@virtuozzo.com>]

napi_threaded needs the number of combined channels of the device and
asks ethtool to print it as JSON. Not every ethtool prints that one:
ethtool 6.11 does it for -k, -a, -c, -g and -x, but not for -l, and
the test ends in the first case:

  CmdExitFailure: Command failed: ethtool --json -l eth4
  STDERR: b'ethtool: bad command line argument(s)
  JSON output not available for this subcommand

  not ok 1 napi_threaded.napi_init

Ask the kernel for the count over netlink, which is where ethtool reads
it too, so the test no longer depends on the ethtool version installed.
Changing the count stays with ethtool -L, which needs no JSON. No other
test in the group asks ethtool for something it cannot print, so this is
the only one that needs it.

https://virtuozzo.atlassian.net/browse/VSTOR-139651
Feature: fix selftests
Signed-off-by: Eva Kurchatova <eva.kurchatova@virtuozzo.com>
---
 tools/testing/selftests/drivers/net/napi_threaded.py | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/drivers/net/napi_threaded.py b/tools/testing/selftests/drivers/net/napi_threaded.py
index 20f1a12552da..6662aee3442b 100755
--- a/tools/testing/selftests/drivers/net/napi_threaded.py
+++ b/tools/testing/selftests/drivers/net/napi_threaded.py
@@ -7,7 +7,7 @@ Test napi threaded states.
 
 from lib.py import ksft_run, ksft_exit
 from lib.py import ksft_eq, ksft_ne, ksft_ge
-from lib.py import NetDrvEnv, NetdevFamily
+from lib.py import EthtoolFamily, NetDrvEnv, NetdevFamily
 from lib.py import cmd, defer, ethtool
 
 
@@ -28,7 +28,13 @@ def _set_threaded_state(cfg, threaded) -> None:
 
 
 def _setup_deferred_cleanup(cfg) -> None:
-    combined = ethtool(f"-l {cfg.ifname}", json=True)[0].get("combined", 0)
+    # Not every ethtool prints the channel counts as JSON, the one on
+    # the test machine here does not:
+    #   ethtool: bad command line argument(s)
+    #   JSON output not available for this subcommand
+    # Ask the kernel for them instead, it is the same number.
+    chan = EthtoolFamily().channels_get({'header': {'dev-index': cfg.ifindex}})
+    combined = chan.get('combined-count', 0)
     ksft_ge(combined, 2)
     defer(ethtool, f"-L {cfg.ifname} combined {combined}")
 
-- 
2.55.0

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