DAMON debugfs interface selftests use test_write_result() to check if
valid or invalid writes to files of the interface success or fail as
expected.  File write error messages from expected failures are only
making the output noisy.  Hide such expected error messages.

Fixes: b348eb7abd09 ("mm/damon: add user space selftests")
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 tools/testing/selftests/damon/_debugfs_common.sh | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/damon/_debugfs_common.sh b/tools/testing/selftests/damon/_debugfs_common.sh
index aa995516870b..54d45791b0d9 100644
--- a/tools/testing/selftests/damon/_debugfs_common.sh
+++ b/tools/testing/selftests/damon/_debugfs_common.sh
@@ -8,7 +8,12 @@ test_write_result() {
 	expect_reason=$4
 	expected=$5
 
-	echo "$content" > "$file"
+	if [ "$expected" = "0" ]
+	then
+		echo "$content" > "$file"
+	else
+		echo "$content" > "$file" 2> /dev/null
+	fi
 	if [ $? -ne "$expected" ]
 	then
 		echo "writing $content to $file doesn't return $expected"
-- 
2.39.5