[PATH bpf-next 2/2] selftests/bpf: Check that flow dissector can be re-attached

@@ -0,0 +1,93 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test that the flow_dissector program can be updated with a single
+ * syscall by attaching a new program that replaces the existing one.
+ *
+ * Corner case - the same program cannot be attached twice.
+ */
+#include <errno.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <unistd.h>
+
+#include <linux/bpf.h>
+#include <bpf/bpf.h>
+
+#include "test_progs.h"
+
+/* Not used here. For CHECK macro sake only. */
+static int duration;
+
+static bool is_attached(void)
+{
+	bool attached = true;
+	int err, net_fd = -1;
+	__u32 cnt;
+
+	net_fd = open("/proc/self/ns/net", O_RDONLY);
+	if (net_fd < 0)
+		goto out;
+
+	err = bpf_prog_query(net_fd, BPF_FLOW_DISSECTOR, 0, NULL, NULL, &cnt);
+	if (CHECK(err, "bpf_prog_query", "ret %d errno %d\n", err, errno))
+		goto out;
+
+	attached = (cnt > 0);
+out:
+	close(net_fd);
+	return attached;
+}
+
+static int load_prog(void)
+{
+	struct bpf_insn prog[] = {
+		BPF_MOV64_IMM(BPF_REG_0, BPF_OK),
+		BPF_EXIT_INSN(),
+	};
+	int fd;
+
+	fd = bpf_load_program(BPF_PROG_TYPE_FLOW_DISSECTOR, prog,
+			      ARRAY_SIZE(prog), "GPL", 0, NULL, 0);
+	CHECK(fd < 0, "bpf_load_program", "ret %d errno %d\n", fd, errno);
+
+	return fd;
+}
+
+void test_flow_dissector_reattach(void)
+{
+	int prog_fd[2] = { -1, -1 };
+	int err;
+
+	if (is_attached())
+		return;
+
+	prog_fd[0] = load_prog();
+	if (prog_fd[0] < 0)
+		return;
+
+	prog_fd[1] = load_prog();
+	if (prog_fd[1] < 0)
+		goto out_close;
+
+	err = bpf_prog_attach(prog_fd[0], 0, BPF_FLOW_DISSECTOR, 0);
+	if (CHECK(err, "bpf_prog_attach-0", "ret %d errno %d\n", err, errno))
+		goto out_close;
+
+	/* Expect success when attaching a different program */
+	err = bpf_prog_attach(prog_fd[1], 0, BPF_FLOW_DISSECTOR, 0);
+	if (CHECK(err, "bpf_prog_attach-1", "ret %d errno %d\n", err, errno))
+		goto out_detach;
+
+	/* Expect failure when attaching the same program twice */
+	err = bpf_prog_attach(prog_fd[1], 0, BPF_FLOW_DISSECTOR, 0);
+	CHECK(!err || errno != EINVAL, "bpf_prog_attach-2",
+	      "ret %d errno %d\n", err, errno);
+
+out_detach:
+	err = bpf_prog_detach(0, BPF_FLOW_DISSECTOR);
+	CHECK(err, "bpf_prog_detach", "ret %d errno %d\n", err, errno);
+
+out_close:
+	close(prog_fd[1]);
+	close(prog_fd[0]);
+}