[dpdk-dev] [PATCH v3] net/virtio: fix wrong TX pkt length stats

[Zhiyong Yang <zhiyong.yang@intel.com>]

In the function virtqueue_enqueue_xmit(), when can_push is true,
vtnet_hdr_size is added to pkt_len by calling rte_pktmbuf_prepend.
which is wrong for pkt stats, virtio header length should be subtracted
before calling stats function.

Fixes: 58169a9c8153 ("net/virtio: support Tx checksum offload")

Cc: stable@dpdk.org
Cc: yliu@fridaylinux.org
Cc: maxime.coquelin@redhat.com
Signed-off-by: Zhiyong Yang <zhiyong.yang@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---

Changes in V3:
Move code inside "if (can_push)" clause and simplify comments.

Changes in V2:
Put code in the function virtqueue_enqueue_xmit() according to
yuanhan's comments.

 drivers/net/virtio/virtio_rxtx.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
index 2cf82fef4..ac4055d45 100644
--- a/drivers/net/virtio/virtio_rxtx.c
+++ b/drivers/net/virtio/virtio_rxtx.c
@@ -299,6 +299,10 @@ virtqueue_enqueue_xmit(struct virtnet_tx *txvq, struct rte_mbuf *cookie,
 		/* prepend cannot fail, checked by caller */
 		hdr = (struct virtio_net_hdr *)
 			rte_pktmbuf_prepend(cookie, head_size);
+		/* rte_pktmbuf_prepend() counts the hdr size to the pkt length,
+		 * which is wrong. Below subtract restores correct pkt size.
+		 */
+		cookie->pkt_len -= head_size;
 		/* if offload disabled, it is not zeroed below, do it now */
 		if (offload == 0) {
 			ASSIGN_UNLESS_EQUAL(hdr->csum_start, 0);
-- 
2.13.3