selftests: bpf: Skip write only files in debugfs

DebugFS for netdevsim now contains some "action trigger" files
which are write only. Don't try to capture the contents of those.

Note that we can't use os.access() because the script requires
root.

Fixes: 4418f862d6 ("netdevsim: implement support for devlink region and snapshots")
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/bpf/test_offload.py

@@ -22,6 +22,7 @@ import os
 import pprint
 import random
 import re
+import stat
 import string
 import struct
 import subprocess
@@ -311,7 +312,11 @@ class DebugfsDir:
         for f in out.split():
             if f == "ports":
                 continue
+
             p = os.path.join(path, f)
+            if not os.stat(p).st_mode & stat.S_IRUSR:
+                continue
+
             if os.path.isfile(p):
                 _, out = cmd('cat %s/%s' % (path, f))
                 dfs[f] = out.strip()