[PATCH v5] selftests/landlock: Skip overlayfs tests not supported

[jeffxu@chromium.org]

From: Jeff Xu <jeffxu@chromium.org>

overlayfs can be disabled in the kernel configuration (which is the case
for chromeOS), causing related tests to fail.  Skip such tests when an
overlayfs mount operation failed because the running kernel doesn't
support this file system.

Signed-off-by: Jeff Xu <jeffxu@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
---
 tools/testing/selftests/landlock/fs_test.c | 54 ++++++++++++++++++++--
 1 file changed, 51 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index 21a2ce8fa739..645304d9fe98 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>
@@ -169,6 +170,42 @@ static int remove_path(const char *const path)
 	return err;
 }
 
+static bool fgrep(FILE *file, const char *str)
+{
+	char line[32];
+	int str_len = strlen(str);
+
+	while (!feof(file)) {
+		if (!fgets(line, sizeof(line), file))
+			break;
+		if (strncmp(line, str, str_len))
+			continue;
+
+		return true;
+	}
+
+	return false;
+}
+
+static bool supports_overlayfs(void)
+{
+	bool ret;
+	FILE *file = fopen("/proc/filesystems", "r");
+
+	/*
+	 * A failed attempt to open /proc/filesystems
+	 * implies that the file system is supported (default
+	 * behavior). This can help detect such unattended issue
+	 * (which should not happen)."
+	 */
+	if (!file)
+		return true;
+
+	ret = fgrep(file, "nodev\toverlay\n");
+	fclose(file);
+	return ret;
+}
+
 static void prepare_layout(struct __test_metadata *const _metadata)
 {
 	disable_caps(_metadata);
@@ -3404,6 +3441,8 @@ FIXTURE(layout2_overlay) {};
 
 FIXTURE_SETUP(layout2_overlay)
 {
+	int ret, err;
+
 	prepare_layout(_metadata);
 
 	create_directory(_metadata, LOWER_BASE);
@@ -3431,11 +3470,20 @@ 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));
+
+	ret = mount("overlay", MERGE_DATA, "overlay", 0,
+		   "lowerdir=" LOWER_DATA ",upperdir=" UPPER_DATA
+		   ",workdir=" UPPER_WORK);
+	err = errno;
 	clear_cap(_metadata, CAP_DAC_OVERRIDE);
 	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	if (ret == -1) {
+		ASSERT_EQ(ENODEV, err);
+		ASSERT_FALSE(supports_overlayfs());
+		SKIP(return, "overlayfs is not supported");
+	}
+	ASSERT_EQ(0, ret);
 }
 
 FIXTURE_TEARDOWN(layout2_overlay)

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