[PATCH v3 2/2] selftests/damon/sysfs.py: validate memcg_path staging readback

[Cheng Nie]

Add a dedicated test at the end of main() that writes memcg_path to
sysfs and checks the readback path.  Configure the memcg filter before
start(), verify staging readback without commit(), and ignore start()
failures so the test does not depend on CONFIG_MEMCG or cgroup layout.

Signed-off-by: Cheng Nie <niecheng1@xxxxxxxxxxxxx>
---
 tools/testing/selftests/damon/sysfs.py | 34 ++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/tools/testing/selftests/damon/sysfs.py b/tools/testing/selftests/damon/sysfs.py
index aa03a1187489..7a17ab88361b 100755
--- a/tools/testing/selftests/damon/sysfs.py
+++ b/tools/testing/selftests/damon/sysfs.py
@@ -250,6 +250,38 @@ def assert_ctxs_committed(kdamonds):
             if ctx in ctxs_paused_for_dump:
                 ctx.pause = False
 
+def test_memcg_filter_memcg_path_staging():
+    global kdamonds
+    memcg_filter = _damon_sysfs.DamosFilter(
+            type_='memcg', matching=True, allow=True, memcg_path='/')
+    kdamonds = _damon_sysfs.Kdamonds(
+            [_damon_sysfs.Kdamond(
+                contexts=[_damon_sysfs.DamonCtx(
+                    targets=[_damon_sysfs.DamonTarget(pid=-1)],
+                    schemes=[_damon_sysfs.Damos(
+                        ops_filters=[memcg_filter])],
+                    )])])
+    kdamonds.start()
+
+    shown, rd_err = _damon_sysfs.read_file(
+            os.path.join(memcg_filter.sysfs_dir(), 'memcg_path'))
+    if rd_err is not None:
+        print('memcg_path staging: sysfs read (%s)' % rd_err)
+        kdamonds.stop()
+        exit(1)
+    if shown.rstrip('\n') != memcg_filter.memcg_path:
+        print('memcg_path staging: memcg_path readback '
+              '(shown=%s, expected=%s)' %
+              (shown.rstrip('\n'), memcg_filter.memcg_path))
+        kdamonds.stop()
+        exit(1)
+
+    err = kdamonds.stop()
+    if err is not None:
+        print('memcg_path staging: kdamond stop (%s)' % err)
+        exit(1)
+    kdamonds = None
+
 def main():
     global kdamonds
     kdamonds = _damon_sysfs.Kdamonds(
@@ -356,5 +388,7 @@ def main():
     assert_ctxs_committed(kdamonds)
     kdamonds.stop()
 
+    test_memcg_filter_memcg_path_staging()
+
 if __name__ == '__main__':
     main()
-- 
2.51.0