net: mctp: usblib: Add initial kunit tx tests

Add tests for the transmit path, where MCTP packets are handed to
outgoing USB transfer data. Testing a spanning transfer that is expected
to succeed, the failure paths when sends fail, and large sequential
sends.

Signed-off-by: James Lee <james@codeconstruct.com.au>
Link: https://patch.msgid.link/20261014-dev-mctp-usb-lib-test-v3-6-ee5bc3ea1db1@codeconstruct.com.au
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/mctp/mctp-usblib-test.c

@@ -6,6 +6,7 @@
  * Copyright (C) 2026 Code Construct Pty Ltd
  */
 
+#include <linux/array_size.h>
 #include <uapi/linux/netdevice.h>
 #include <linux/netdevice.h>
 #include <kunit/test.h>
@@ -16,6 +17,13 @@
 
 #define HDR_LEN sizeof(struct mctp_usb_hdr)
 
+struct tx_buff {
+	struct list_head list;
+
+	size_t length;
+	u8 data[] __counted_by(length);
+};
+
 struct mctp_usblib_test_dev {
 	struct net_device *ndev;
 	struct mctp_dev *mdev;
@@ -24,9 +32,104 @@ struct mctp_usblib_test_dev {
 
 struct mctp_usblib_test_ctx {
 	struct mctp_usblib_test_dev *dev;
+	struct list_head tx_xfers;
 	struct mctp_route rt;
 };
 
+static int mctp_usblib_test_tx_send(struct mctp_usblib_tx_ctx *tx_ctx,
+				    void *data, size_t len)
+{
+	struct mctp_usblib_test_ctx *ctx;
+	struct tx_buff *new_node;
+	struct net_device *ndev;
+
+	ctx = mctp_usblib_tx_ctx_priv(tx_ctx);
+	ndev = ctx->dev->ndev;
+
+	new_node = kzalloc_flex(*new_node, data, len, GFP_KERNEL);
+	if (!new_node)
+		return -ENOMEM;
+
+	new_node->length = len;
+	memcpy(new_node->data, data, len);
+	list_add_tail(&new_node->list, &ctx->tx_xfers);
+
+	mctp_usblib_tx_send_complete(tx_ctx, ndev, true);
+	return 0;
+}
+
+static int mctp_usblib_test_tx_send_fail(struct mctp_usblib_tx_ctx *tx_ctx,
+					 void *data, size_t len)
+{
+	return -ENOMEM;
+}
+
+static u8 *mctp_usblib_test_flatten_tx_buff(struct kunit *test,
+					    struct list_head *in,
+					    size_t *length_out)
+{
+	struct tx_buff *pos;
+	size_t length;
+	u8 *buf, *tail;
+
+	KUNIT_ASSERT_TRUE(test, length_out);
+	KUNIT_ASSERT_TRUE(test, in);
+
+	length = 0;
+	list_for_each_entry(pos, in, list)
+		length = size_add(length, pos->length);
+
+	KUNIT_ASSERT_NE(test, length, 0);
+	KUNIT_ASSERT_NE(test, length, SIZE_MAX);
+
+	buf = kunit_kzalloc(test, length, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, buf);
+
+	tail = buf;
+	list_for_each_entry(pos, in, list) {
+		memcpy(tail, pos->data, pos->length);
+		tail += pos->length;
+	}
+
+	*length_out = length;
+	return buf;
+}
+
+static u8 *mctp_usblib_test_init_buf(struct kunit *test, size_t length)
+{
+	u8 *buffer;
+	size_t i;
+
+	buffer = kunit_kzalloc(test, length, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, buffer);
+
+	for (i = 0; i < length; i++)
+		buffer[i] = i % 256;
+
+	return buffer;
+}
+
+static void mctp_usblib_test_fill_head(struct mctp_usb_hdr *head, size_t len)
+{
+	len += HDR_LEN;
+	head->id = cpu_to_be16(MCTP_USB_DMTF_ID);
+	head->len = cpu_to_be16(len & MCTP_USB_1_1_PKTLEN_MAX);
+}
+
+static struct sk_buff *mctp_usblib_test_init_skb(struct kunit *test,
+						 unsigned int length,
+						 struct net_device *ndev,
+						 void *data)
+{
+	struct sk_buff *skb;
+
+	skb = __netdev_alloc_skb(ndev, length, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, skb);
+
+	skb_put_data(skb, data, length);
+	return skb;
+}
+
 static netdev_tx_t mctp_usblib_dev_tx(struct sk_buff *skb,
 				      struct net_device *ndev)
 {
@@ -119,6 +222,7 @@ static int mctp_usblib_test_dst_output(struct mctp_dst *dst,
 static void mctp_usblib_test_fini_action(void *data)
 {
 	struct mctp_usblib_test_ctx *ctx = data;
+	struct tx_buff *curr, *temp;
 
 	/* The device will have been destroyed, so ->rt will be unlinked.
 	 * Just ensure that the refcount is as expected.
@@ -126,6 +230,8 @@ static void mctp_usblib_test_fini_action(void *data)
 	KUNIT_EXPECT_TRUE(current->kunit_test,
 			  refcount_dec_and_test(&ctx->rt.refs));
 
+	list_for_each_entry_safe(curr, temp, &ctx->tx_xfers, list)
+		kfree(curr);
 	kfree(ctx);
 }
 
@@ -141,6 +247,7 @@ static struct mctp_usblib_test_ctx *mctp_usblib_test_init(struct kunit *test)
 	INIT_LIST_HEAD(&ctx->rt.list);
 	rt = &ctx->rt;
 	refcount_set(&rt->refs, 1);
+	INIT_LIST_HEAD(&ctx->tx_xfers);
 
 	rc = kunit_add_action_or_reset(test, mctp_usblib_test_fini_action, ctx);
 	KUNIT_ASSERT_EQ(test, rc, 0);
@@ -227,6 +334,32 @@ static int mctp_usblib_test_rx_complete(struct net_device *netdev,
 	return rc;
 }
 
+static void action_tx_fini(void *data)
+{
+	struct mctp_usblib_tx *tx = data;
+
+	mctp_usblib_tx_fini(tx);
+	kfree(tx);
+}
+
+static struct mctp_usblib_tx *
+mctp_usblib_test_tx_init(struct kunit *test,
+			 const struct mctp_usblib_tx_ops *ops,
+			 void *priv, bool span)
+{
+	struct mctp_usblib_tx *tx;
+	int rc;
+
+	tx = kzalloc_obj(*tx);
+	KUNIT_ASSERT_NOT_NULL(test, tx);
+	rc = kunit_add_action_or_reset(test, action_tx_fini, tx);
+	KUNIT_ASSERT_EQ(test, rc, 0);
+
+	mctp_usblib_tx_init(tx, ops, priv, span);
+
+	return tx;
+}
+
 /* Single packet, starting on a transfer boundary, contained entirely within
  * the transfer
  */
@@ -585,6 +718,156 @@ static void mctp_usblib_test_rx_nonspanning_partial(struct kunit *test)
 	KUNIT_EXPECT_EQ(test, dev->rx_pkts.qlen, 0);
 }
 
+static void mctp_usblib_test_tx_pkt_span(struct kunit *test)
+{
+	struct mctp_usblib_test_ctx *ctx;
+	struct mctp_usblib_tx_ops ops;
+	struct mctp_usblib_tx *tx;
+	struct mctp_usb_hdr head;
+	struct net_device *ndev;
+	struct sk_buff *skb;
+	size_t len, tx_len;
+	u8 *buf, *flat_tx;
+	int rc;
+
+	len = 1000;
+
+	ctx = mctp_usblib_test_init(test);
+	ndev = ctx->dev->ndev;
+
+	ops.send = mctp_usblib_test_tx_send;
+
+	tx = mctp_usblib_test_tx_init(test, &ops, ctx, true);
+
+	buf = mctp_usblib_test_init_buf(test, len);
+	mctp_usblib_test_fill_head(&head, len);
+
+	skb = mctp_usblib_test_init_skb(test, len, ndev, buf);
+
+	rc = mctp_usblib_tx_push(ndev, tx, skb, false);
+	KUNIT_ASSERT_EQ(test, rc, 0);
+	KUNIT_ASSERT_FALSE(test, list_empty(&ctx->tx_xfers));
+
+	flat_tx = mctp_usblib_test_flatten_tx_buff(test, &ctx->tx_xfers,
+						   &tx_len);
+	KUNIT_ASSERT_NOT_NULL(test, flat_tx);
+
+	KUNIT_EXPECT_EQ(test, tx_len, len + HDR_LEN);
+	KUNIT_EXPECT_MEMEQ(test, flat_tx, &head, HDR_LEN);
+	KUNIT_EXPECT_MEMEQ(test, flat_tx + HDR_LEN, buf, len);
+}
+
+static void mctp_usblib_test_tx_failing_send(struct kunit *test)
+{
+	struct mctp_usblib_test_ctx *ctx;
+	struct mctp_usblib_tx_ops ops;
+	struct mctp_usblib_tx *tx;
+	struct net_device *ndev;
+	struct sk_buff *skb;
+	size_t len;
+	u8 *buf;
+	int rc;
+
+	len = 100;
+
+	ctx = mctp_usblib_test_init(test);
+	ndev = ctx->dev->ndev;
+
+	ops.send = mctp_usblib_test_tx_send_fail;
+
+	tx = mctp_usblib_test_tx_init(test, &ops, ctx, false);
+	buf = mctp_usblib_test_init_buf(test, len);
+	skb = mctp_usblib_test_init_skb(test, len, ndev, buf);
+
+	/* Doesn't call ops.send as more packets are expected,
+	 * so the push shouldn't fail.
+	 */
+	rc = mctp_usblib_tx_push(ndev, tx, skb, true);
+	KUNIT_ASSERT_EQ(test, rc, 0);
+
+	skb = mctp_usblib_test_init_skb(test, len, ndev, buf);
+
+	/* Calls ops.send as no further packets are expected. */
+	rc = mctp_usblib_tx_push(ndev, tx, skb, false);
+	KUNIT_EXPECT_EQ(test, rc, 0);
+	KUNIT_EXPECT_NULL(test, tx->cur_ctx);
+	KUNIT_EXPECT_TRUE(test, list_empty(&ctx->tx_xfers));
+}
+
+/* Test sending multiple packets in the same transfer, followed by one that
+ * spans multiple subsequent transfers.
+ */
+static void mctp_usblib_test_tx_multi_push(struct kunit *test)
+{
+	struct mctp_usblib_test_ctx *ctx;
+	size_t i, max_length, tx_length;
+	struct mctp_usblib_tx_ops ops;
+	u8 *buf, *flat_tx, *index;
+	struct mctp_usblib_tx *tx;
+	struct net_device *ndev;
+	struct sk_buff *skb;
+	const struct {
+		size_t len;
+		bool more;
+	} sends[] = {
+		{ 1000, true  },
+		{  500, false },
+		{ 5000, false },
+	};
+	int rc;
+
+	static_assert(!sends[ARRAY_SIZE(sends) - 1].more,
+		      "The last push must claim there will be no more");
+
+	max_length = 0;
+	for (i = 0; i < ARRAY_SIZE(sends); i++) {
+		if (sends[i].len > max_length)
+			max_length = sends[i].len;
+	}
+
+	ctx = mctp_usblib_test_init(test);
+	ndev = ctx->dev->ndev;
+
+	ops.send = mctp_usblib_test_tx_send;
+
+	tx = mctp_usblib_test_tx_init(test, &ops, ctx, true);
+	buf = mctp_usblib_test_init_buf(test, max_length);
+
+	for (i = 0; i < ARRAY_SIZE(sends); i++) {
+		skb = mctp_usblib_test_init_skb(test, sends[i].len, ndev, buf);
+
+		rc = mctp_usblib_tx_push(ndev, tx, skb, sends[i].more);
+		KUNIT_ASSERT_EQ(test, rc, 0);
+	}
+	KUNIT_ASSERT_FALSE(test, list_empty(&ctx->tx_xfers));
+
+	flat_tx = mctp_usblib_test_flatten_tx_buff(test, &ctx->tx_xfers,
+						   &tx_length);
+
+	for (i = 0, index = flat_tx; i < ARRAY_SIZE(sends); i++) {
+		size_t length_to_check, remaining_bytes;
+		struct mctp_usb_hdr head;
+
+		if (index - flat_tx >= tx_length - HDR_LEN)
+			break;
+
+		mctp_usblib_test_fill_head(&head, sends[i].len);
+		KUNIT_EXPECT_MEMEQ(test, index, &head, HDR_LEN);
+		index += HDR_LEN;
+		remaining_bytes = tx_length - (index - flat_tx);
+
+		length_to_check = sends[i].len;
+		KUNIT_EXPECT_GE(test, remaining_bytes, length_to_check);
+		length_to_check = min(remaining_bytes, length_to_check);
+
+		KUNIT_EXPECT_MEMEQ(test, index,
+				   buf, length_to_check);
+
+		index += length_to_check;
+	}
+	KUNIT_EXPECT_EQ(test, i, ARRAY_SIZE(sends));
+}
+
 static struct kunit_case mctp_usblib_test_cases[] = {
 	KUNIT_CASE(mctp_usblib_test_rx_single),
 	KUNIT_CASE_PARAM(mctp_usblib_test_rx_pkt_span,
@@ -594,6 +877,9 @@ static struct kunit_case mctp_usblib_test_cases[] = {
 	KUNIT_CASE(mctp_usblib_test_rx_invalid_dmtf_id),
 	KUNIT_CASE(mctp_usblib_test_rx_nonspanning_tiny),
 	KUNIT_CASE(mctp_usblib_test_rx_nonspanning_partial),
+	KUNIT_CASE(mctp_usblib_test_tx_pkt_span),
+	KUNIT_CASE(mctp_usblib_test_tx_multi_push),
+	KUNIT_CASE(mctp_usblib_test_tx_failing_send),
 	{}
 };