selftests: hid: attach/detach 2 bpf programs, not just one

Add a second BPF program to attach to the device, as the development of
this feature showed that we also need to ensure we can detach multiple
programs to a device (hid_bpf_link->hid_table_index was actually not set
initially, and this lead to any BPF program not being released except for
the first one).

Signed-off-by: Benjamin Tissoires <[e-mail]>
Signed-off-by: Jiri Kosina <[e-mail]>

tools/testing/selftests/hid/hid_bpf.c

···
 {
 	const struct test_program progs[] = {
 		{ .name = "hid_first_event" },
+		{ .name = "hid_second_event" },
 	};
 	__u8 buf[10] = {0};
 	int err;
···
 	ASSERT_EQ(buf[0], 1);
 	ASSERT_EQ(buf[2], 47);
 
-	/* pin the program and immediately unpin it */
+	/* make sure both programs are run */
+	ASSERT_EQ(buf[3], 52);
+
+	/* pin the first program and immediately unpin it */
 #define PIN_PATH "/sys/fs/bpf/hid_first_event"
 	bpf_program__pin(self->skel->progs.hid_first_event, PIN_PATH);
 	remove(PIN_PATH);
···
 	ASSERT_EQ(buf[0], 1);
 	ASSERT_EQ(buf[1], 47);
 	ASSERT_EQ(buf[2], 0);
+	ASSERT_EQ(buf[3], 0);
 
 	/* re-attach our program */
 
···
 	ASSERT_EQ(err, 6) TH_LOG("read_hidraw");
 	ASSERT_EQ(buf[0], 1);
 	ASSERT_EQ(buf[2], 47);
+	ASSERT_EQ(buf[3], 52);
 }
 
 /*

tools/testing/selftests/hid/progs/hid.c

···
 }
 
 SEC("?fmod_ret/hid_bpf_device_event")
+int BPF_PROG(hid_second_event, struct hid_bpf_ctx *hid_ctx)
+{
+	__u8 *rw_data = hid_bpf_get_data(hid_ctx, 0 /* offset */, 4 /* size */);
+
+	if (!rw_data)
+		return 0; /* EPERM check */
+
+	rw_data[3] = rw_data[2] + 5;
+
+	return hid_ctx->size;
+}
+
+SEC("?fmod_ret/hid_bpf_device_event")
 int BPF_PROG(hid_change_report_id, struct hid_bpf_ctx *hid_ctx)
 {
 	__u8 *rw_data = hid_bpf_get_data(hid_ctx, 0 /* offset */, 3 /* size */);