[PATCH v4] selftests/landlock: skip overlayfs test when kernel not support it

[<jeffxu@google.com>]

From: Jeff Xu <jeffxu@google.com>

Overlayfs can be disabled in kernel config, causing related tests to fail.
Add check for overlayfs’s supportability at runtime, so we can call SKIP()
when needed.

Signed-off-by: Jeff Xu <jeffxu@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
---
 tools/testing/selftests/landlock/fs_test.c | 53 ++++++++++++++++++++--
 1 file changed, 50 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index 21a2ce8fa739..aaece185579d 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -11,6 +11,7 @@
 #include <fcntl.h>
 #include <linux/landlock.h>
 #include <sched.h>
+#include <stdio.h>
 #include <string.h>
 #include <sys/capability.h>
 #include <sys/mount.h>
@@ -62,6 +63,7 @@ static const char dir_s3d1[] = TMP_DIR "/s3d1";
 static const char dir_s3d2[] = TMP_DIR "/s3d1/s3d2";
 static const char dir_s3d3[] = TMP_DIR "/s3d1/s3d2/s3d3";
 
+static const char proc_filesystems[] = "/proc/filesystems";
 /*
  * layout1 hierarchy:
  *
@@ -169,6 +171,42 @@ static int remove_path(const char *const path)
 	return err;
 }
 
+static bool fgrep(FILE *inf, const char *str)
+{
+	char line[32];
+	int slen = strlen(str);
+
+	while (!feof(inf)) {
+		if (!fgets(line, sizeof(line), inf))
+			break;
+		if (strncmp(line, str, slen))
+			continue;
+
+		return true;
+	}
+
+	return false;
+}
+
+static bool supports_overlayfs(void)
+{
+	bool ret = false;
+	FILE *inf = fopen(proc_filesystems, "r");
+
+	/*
+	 * If fopen fails, return supported.
+	 * This helps to detect missing file (shall not
+	 * happen).
+	 */
+	if (!inf)
+		return true;
+
+	ret = fgrep(inf, "nodev\toverlay\n");
+	fclose(inf);
+
+	return ret;
+}
+
 static void prepare_layout(struct __test_metadata *const _metadata)
 {
 	disable_caps(_metadata);
@@ -3404,6 +3442,8 @@ FIXTURE(layout2_overlay) {};
 
 FIXTURE_SETUP(layout2_overlay)
 {
+	int rc;
+
 	prepare_layout(_metadata);
 
 	create_directory(_metadata, LOWER_BASE);
@@ -3431,11 +3471,18 @@ FIXTURE_SETUP(layout2_overlay)
 	create_directory(_metadata, MERGE_DATA);
 	set_cap(_metadata, CAP_SYS_ADMIN);
 	set_cap(_metadata, CAP_DAC_OVERRIDE);
-	ASSERT_EQ(0, mount("overlay", MERGE_DATA, "overlay", 0,
-			   "lowerdir=" LOWER_DATA ",upperdir=" UPPER_DATA
-			   ",workdir=" UPPER_WORK));
+
+	rc = mount("overlay", MERGE_DATA, "overlay", 0,
+		   "lowerdir=" LOWER_DATA ",upperdir=" UPPER_DATA
+		   ",workdir=" UPPER_WORK);
 	clear_cap(_metadata, CAP_DAC_OVERRIDE);
 	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	if (rc < 0) {
+		ASSERT_EQ(ENODEV, errno);
+		ASSERT_FALSE(supports_overlayfs());
+		SKIP(return, "overlayfs is not supported");
+	}
 }
 
 FIXTURE_TEARDOWN(layout2_overlay)

base-commit: 50cd95ac46548429e5bba7ca75cc97d11a697947
-- 
2.37.1.595.g718a3a8f04-goog