[PATCH net v2] selftests: rtnetlink: add 'ethtool' as a dependency

[Ales Nezbeda <anezbeda@redhat.com>]

Introduction of `kci_test_macsec_offload()` in `rtnetlink.sh` created
a new dependency `ethtool` for the test suite. This dependency is not
reflected in checks that run before all the tests, so if the `ethtool`
is not present, all tests will start, but `macsec_offload` test will
fail with a misleading message. Message would say that MACsec offload is
not supported, yet it never actually managed to check this, since it
needs the `ethtool` to do so.

Use `require_command` in `rtnetlink.sh` to allow single check command
for all the dependencies. This also requires adding the `require_command`
to the `lib.sh` used by the test.

Fixes: 3b5222e2ac57 ("selftests: rtnetlink: add MACsec offload tests")
Signed-off-by: Ales Nezbeda <anezbeda@redhat.com>
---
v2
  - Add `require_command` to the `lib.sh` and use that instead
  - v1 ref: https://lore.kernel.org/netdev/20240903151524.586614-1-anezbeda@redhat.com
---
 tools/testing/selftests/net/lib.sh       | 13 +++++++++++++
 tools/testing/selftests/net/rtnetlink.sh |  9 +++------
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/net/lib.sh b/tools/testing/selftests/net/lib.sh
index 8ee4489238ca..890c579674be 100644
--- a/tools/testing/selftests/net/lib.sh
+++ b/tools/testing/selftests/net/lib.sh
@@ -218,3 +218,16 @@ tc_rule_handle_stats_get()
 	    | jq ".[] | select(.options.handle == $handle) | \
 		  .options.actions[0].stats$selector"
 }
+
+##############################################################################
+# Sanity checks
+
+require_command()
+{
+	local cmd=$1; shift
+
+	if [[ ! -x "$(command -v "$cmd")" ]]; then
+		echo "SKIP: $cmd not installed"
+		exit $ksft_skip
+	fi
+}
\ No newline at end of file
diff --git a/tools/testing/selftests/net/rtnetlink.sh b/tools/testing/selftests/net/rtnetlink.sh
index bdf6f10d0558..4a9ffd06990b 100755
--- a/tools/testing/selftests/net/rtnetlink.sh
+++ b/tools/testing/selftests/net/rtnetlink.sh
@@ -1306,12 +1306,9 @@ if [ "$(id -u)" -ne 0 ];then
 	exit $ksft_skip
 fi
 
-for x in ip tc;do
-	$x -Version 2>/dev/null >/dev/null
-	if [ $? -ne 0 ];then
-		end_test "SKIP: Could not run test without the $x tool"
-		exit $ksft_skip
-	fi
+#check for dependencies
+for x in ip tc ethtool;do
+	require_command $x
 done
 
 while getopts t:hvpP o; do
-- 
2.46.0