selftets/damon/sysfs: test existence and permission of avail_operations

This commit adds a selftest test case for ensuring the existence and the
permission (read-only) of the 'avail_oprations' DAMON sysfs file.

Link: https://lkml.kernel.org/r/20220426203843.45238-4-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/damon/sysfs.sh

@@ -231,6 +231,7 @@ test_context()
 {
 	context_dir=$1
 	ensure_dir "$context_dir" "exist"
+	ensure_file "$context_dir/avail_operations" "exit" 400
 	ensure_file "$context_dir/operations" "exist" 600
 	test_monitoring_attrs "$context_dir/monitoring_attrs"
 	test_targets "$context_dir/targets"