[PATCH] selftests/landlock: Skip scoped_signal subtest with MSG_OOB if not available

[Thomas Huth <thuth@redhat.com>]

From: Thomas Huth <thuth@redhat.com>

MSG_OOB might be disabled in the kernel for unix sockets (by not
selecting CONFIG_AF_UNIX_OOB), and in this case the related tests
of the scoped_signal_test are currently failing.  Add a runtime
probe using socketpair() to detect MSG_OOB support and skip the
test gracefully if it is unavailable.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 .../selftests/landlock/scoped_signal_test.c   | 21 +++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/tools/testing/selftests/landlock/scoped_signal_test.c b/tools/testing/selftests/landlock/scoped_signal_test.c
index 58d25157fe781..3cf20d769f2bc 100644
--- a/tools/testing/selftests/landlock/scoped_signal_test.c
+++ b/tools/testing/selftests/landlock/scoped_signal_test.c
@@ -398,6 +398,24 @@ static int setup_signal_handler(int signal)
 	return sigaction(SIGURG, &sa, NULL);
 }
 
+/*
+ * MSG_OOB might be disabled in the kernel via the CONFIG_AF_UNIX_OOB
+ * switch, so this function can be used for probing for its availability.
+ */
+static bool has_af_unix_oob(void)
+{
+	bool available = false;
+	int sp[2];
+
+	if (socketpair(AF_UNIX, SOCK_STREAM, 0, sp) == 0) {
+		available = (send(sp[0], ".", 1, MSG_OOB) == 1);
+		close(sp[0]);
+		close(sp[1]);
+	}
+
+	return available;
+}
+
 /* clang-format off */
 FIXTURE(fown) {};
 /* clang-format on */
@@ -460,6 +478,9 @@ TEST_F(fown, sigurg_socket)
 	int pipe_parent[2], pipe_child[2];
 	pid_t child;
 
+	if (!has_af_unix_oob())
+		SKIP(return, "CONFIG_AF_UNIX_OOB / MSG_OOB not available");
+
 	memset(&server_address, 0, sizeof(server_address));
 	set_unix_address(&server_address, 0);
 
-- 
2.55.0