Add test ensuring that network device stats are updated appropriately
when a previously pushed packet fails to send during a subsequent push.

Signed-off-by: James Lee <[email protected]>

---
v2:
- Fix preemption management
v3:
- Rename mctp_usblib_test_tx_overflow()
- Correct stats collection
- Remove magic numbers from mctp_usblib_test_append_failure()
---
 drivers/net/mctp/mctp-usblib-test.c | 42 +++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/drivers/net/mctp/mctp-usblib-test.c 
b/drivers/net/mctp/mctp-usblib-test.c
index 
16c2c9963d2d4493268687764a1e9209f8c9a901..b7e8743c561f948a9528fccfaa5a50cd78b3320e
 100644
--- a/drivers/net/mctp/mctp-usblib-test.c
+++ b/drivers/net/mctp/mctp-usblib-test.c
@@ -868,6 +868,47 @@ static void mctp_usblib_test_tx_multi_push(struct kunit 
*test)
        KUNIT_EXPECT_EQ(test, i, ARRAY_SIZE(sends));
 }
 
+static void mctp_usblib_test_append_failure(struct kunit *test)
+{
+       struct mctp_usblib_test_ctx *ctx;
+       struct rtnl_link_stats64 stats;
+       struct mctp_usblib_tx_ops ops;
+       struct mctp_usblib_tx *tx;
+       struct net_device *ndev;
+       struct sk_buff *skb;
+       u64 tx_dropped;
+       size_t i;
+       u8 *buf;
+       int rc;
+
+       const size_t packet_count = 3;
+       const size_t len = (MCTP_USB_1_0_XFER_SIZE / packet_count) + 1
+                          - sizeof(struct mctp_usb_hdr);
+       static_assert(len >= MCTP_USB_BTU);
+
+       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);
+
+       for (i = 0; i < packet_count; i++) {
+               tx_dropped = dev_get_stats(ndev, &stats)->tx_dropped;
+               KUNIT_EXPECT_EQ(test, tx_dropped, 0);
+               skb = mctp_usblib_test_init_skb(test, len, ndev, buf);
+
+               rc = mctp_usblib_tx_push(ndev, tx, skb, i != packet_count - 1);
+               KUNIT_EXPECT_EQ(test, rc, 0);
+               KUNIT_EXPECT_TRUE(test, list_empty(&ctx->tx_xfers));
+       }
+
+       tx_dropped = dev_get_stats(ndev, &stats)->tx_dropped;
+       KUNIT_EXPECT_EQ(test, tx_dropped, packet_count);
+       KUNIT_EXPECT_NULL(test, tx->cur_ctx);
+}
+
 static struct kunit_case mctp_usblib_test_cases[] = {
        KUNIT_CASE(mctp_usblib_test_rx_single),
        KUNIT_CASE_PARAM(mctp_usblib_test_rx_pkt_span,
@@ -880,6 +921,7 @@ static struct kunit_case mctp_usblib_test_cases[] = {
        KUNIT_CASE(mctp_usblib_test_tx_pkt_span),
        KUNIT_CASE(mctp_usblib_test_tx_multi_push),
        KUNIT_CASE(mctp_usblib_test_tx_failing_send),
+       KUNIT_CASE(mctp_usblib_test_append_failure),
        {}
 };
 

-- 
2.47.3


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