selftests/damon/sysfs: test filters directory

Add simple test cases for scheme filters of DAMON sysfs interface.  The
test cases check if the files are populated as expected, receives some
valid inputs, and refuses some invalid inputs.

Link: https://lkml.kernel.org/r/20221205230830.144349-10-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/damon/sysfs.sh

@@ -96,6 +96,34 @@ test_stats()
 	done
 }
 
+test_filter()
+{
+	filter_dir=$1
+	ensure_file "$filter_dir/type" "exist" "600"
+	ensure_write_succ "$filter_dir/type" "anon" "valid input"
+	ensure_write_succ "$filter_dir/type" "memcg" "valid input"
+	ensure_write_fail "$filter_dir/type" "foo" "invalid input"
+	ensure_file "$filter_dir/matching" "exist" "600"
+	ensure_file "$filter_dir/memcg_path" "exist" "600"
+}
+
+test_filters()
+{
+	filters_dir=$1
+	ensure_dir "$filters_dir" "exist"
+	ensure_file "$filters_dir/nr_filters" "exist" "600"
+	ensure_write_succ  "$filters_dir/nr_filters" "1" "valid input"
+	test_filter "$filters_dir/0"
+
+	ensure_write_succ  "$filters_dir/nr_filters" "2" "valid input"
+	test_filter "$filters_dir/0"
+	test_filter "$filters_dir/1"
+
+	ensure_write_succ "$filters_dir/nr_filters" "0" "valid input"
+	ensure_dir "$filters_dir/0" "not_exist"
+	ensure_dir "$filters_dir/1" "not_exist"
+}
+
 test_watermarks()
 {
 	watermarks_dir=$1
@@ -143,6 +171,7 @@ test_scheme()
 	test_access_pattern "$scheme_dir/access_pattern"
 	test_quotas "$scheme_dir/quotas"
 	test_watermarks "$scheme_dir/watermarks"
+	test_filters "$scheme_dir/filters"
 	test_stats "$scheme_dir/stats"
 	test_tried_regions "$scheme_dir/tried_regions"
 }