selftests: bpf: test_kmod.sh: check the module path before insmod

test_kmod.sh reported false failure when module not present.
Check test_bpf.ko is present in the path before loading it.

Two cases to be addressed here,
In the development process of test_bpf.c unit testing will be done by
developers by using "insmod $SRC_TREE/lib/test_bpf.ko"

On the other hand testers run full tests by installing modules on device
under test (DUT) and followed by modprobe to insert the modules accordingly.
Signed-off-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/testing/selftests/bpf/test_kmod.sh

@@ -10,9 +10,21 @@ test_run()
 
 	echo "[ JIT enabled:$1 hardened:$2 ]"
 	dmesg -C
-	insmod $SRC_TREE/lib/test_bpf.ko 2> /dev/null
-	if [ $? -ne 0 ]; then
-		rc=1
+	if [ -f ${SRC_TREE}/lib/test_bpf.ko ]; then
+		insmod ${SRC_TREE}/lib/test_bpf.ko 2> /dev/null
+		if [ $? -ne 0 ]; then
+			rc=1
+		fi
+	else
+		# Use modprobe dry run to check for missing test_bpf module
+		if ! /sbin/modprobe -q -n test_bpf; then
+			echo "test_bpf: [SKIP]"
+		elif /sbin/modprobe -q test_bpf; then
+			echo "test_bpf: ok"
+		else
+			echo "test_bpf: [FAIL]"
+			rc=1
+		fi
 	fi
 	rmmod  test_bpf 2> /dev/null
 	dmesg | grep FAIL