selftests: net: devlink_port_split.py: skip test if no suitable device available

The `devlink -j port show` command output may not contain the "flavour"
key, an example from Ubuntu 22.10 s390x LPAR(5.19.0-37-generic), with
mlx4 driver and iproute2-5.15.0:
  {"port":{"pci/0001:00:00.0/1":{"type":"eth","netdev":"ens301"},
           "pci/0001:00:00.0/2":{"type":"eth","netdev":"ens301d1"},
           "pci/0002:00:00.0/1":{"type":"eth","netdev":"ens317"},
           "pci/0002:00:00.0/2":{"type":"eth","netdev":"ens317d1"}}}

This will cause a KeyError exception.

Create a validate_devlink_output() to check for this "flavour" from
devlink command output to avoid this KeyError exception. Also let
it handle the check for `devlink -j dev show` output in main().

Apart from this, if the test was not started because the max lanes of
the designated device is 0. The script will still return 0 and thus
causing a false-negative test result.

Use a found_max_lanes flag to determine if these tests were skipped
due to this reason and return KSFT_SKIP to make it more clear.

Link: https://bugs.launchpad.net/bugs/1937133
Fixes: f3348a8 ("selftests: net: Add port split test")
Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Link: https://lore.kernel.org/r/20230315165353.229590-1-po-hsu.lin@canonical.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Cypresslin

tools/testing/selftests/net/devlink_port_split.py

@@ -59,6 +59,8 @@ def get_if_names(dev):
         assert stderr == ""
         ports = json.loads(stdout)['port']
 
+        validate_devlink_output(ports, 'flavour')
+
         for port in ports:
             if dev in port:
                 if ports[port]['flavour'] == 'physical':
@@ -220,6 +222,27 @@ def split_splittable_port(port, k, lanes, dev):
     unsplit(port.bus_info)
 
 
+def validate_devlink_output(devlink_data, target_property=None):
+    """
+    Determine if test should be skipped by checking:
+      1. devlink_data contains values
+      2. The target_property exist in devlink_data
+    """
+    skip_reason = None
+    if any(devlink_data.values()):
+        if target_property:
+            skip_reason = "{} not found in devlink output, test skipped".format(target_property)
+            for key in devlink_data:
+                if target_property in devlink_data[key]:
+                    skip_reason = None
+    else:
+        skip_reason = 'devlink output is empty, test skipped'
+
+    if skip_reason:
+        print(skip_reason)
+        sys.exit(KSFT_SKIP)
+
+
 def make_parser():
     parser = argparse.ArgumentParser(description='A test for port splitting.')
     parser.add_argument('--dev',
@@ -240,12 +263,9 @@ def main(cmdline=None):
         stdout, stderr = run_command(cmd)
         assert stderr == ""
 
+        validate_devlink_output(json.loads(stdout))
         devs = json.loads(stdout)['dev']
-        if devs:
-            dev = list(devs.keys())[0]
-        else:
-            print("no devlink device was found, test skipped")
-            sys.exit(KSFT_SKIP)
+        dev = list(devs.keys())[0]
 
     cmd = "devlink dev show %s" % dev
     stdout, stderr = run_command(cmd)
@@ -255,6 +275,7 @@ def main(cmdline=None):
 
     ports = devlink_ports(dev)
 
+    found_max_lanes = False
     for port in ports.if_names:
         max_lanes = get_max_lanes(port.name)
 
@@ -277,6 +298,11 @@ def main(cmdline=None):
                 split_splittable_port(port, lane, max_lanes, dev)
 
                 lane //= 2
+        found_max_lanes = True
+
+    if not found_max_lanes:
+        print(f"Test not started, no port of device {dev} reports max_lanes")
+        sys.exit(KSFT_SKIP)
 
 
 if __name__ == "__main__":