[PATCH net] selftests/bpf: fix netdevsim trap_flow_action_cookie read

[Hangbin Liu]

When read netdevsim trap_flow_action_cookie, we need to init it first,
or we will get "Invalid argument" error.

Fixes: d3cbb907ae57 ("netdevsim: add ACL trap reporting cookie as a metadata")
Signed-off-by: Hangbin Liu <liuhang...@gmail.com>
---
 tools/testing/selftests/bpf/test_offload.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/testing/selftests/bpf/test_offload.py 
b/tools/testing/selftests/bpf/test_offload.py
index 8294ae3ffb3c..43c9cda199b8 100755
--- a/tools/testing/selftests/bpf/test_offload.py
+++ b/tools/testing/selftests/bpf/test_offload.py
@@ -318,6 +318,9 @@ class DebugfsDir:
                 continue
 
             if os.path.isfile(p):
+                # We need to init trap_flow_action_cookie before read it
+                if f == "trap_flow_action_cookie":
+                    cmd('echo deadbeef > %s/%s' % (path, f))
                 _, out = cmd('cat %s/%s' % (path, f))
                 dfs[f] = out.strip()
             elif os.path.isdir(p):
-- 
2.25.4