[PATCH 3/7] net/gve: don't write zero-length descriptors

[Joshua Washington <joshwash@google.com>]

Writing zero-length descriptors to the hardware can cause the hardware
to reject that packet and stop transmitting altogether.

Fixes: 4022f9999f56 ("net/gve: support basic Tx data path for DQO")
Cc: junfeng.guo@intel.com
Cc: stable@dpdk.org

Signed-off-by: Joshua Washington <joshwash@google.com>
Reviewed-by: Ankit Garg <nktgrg@google.com>
---
 drivers/net/gve/gve_tx_dqo.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/net/gve/gve_tx_dqo.c b/drivers/net/gve/gve_tx_dqo.c
index 652a0e5175..b2e5aae634 100644
--- a/drivers/net/gve/gve_tx_dqo.c
+++ b/drivers/net/gve/gve_tx_dqo.c
@@ -168,6 +168,11 @@ gve_tx_burst_dqo(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
 			if (sw_ring[sw_id] != NULL)
 				PMD_DRV_LOG(DEBUG, "Overwriting an entry in sw_ring");
 
+			/* Skip writing descriptor if mbuf has no data. */
+			if (!tx_pkt->data_len)
+				goto finish_mbuf;
+
+			txd = &txr[tx_id];
 			sw_ring[sw_id] = tx_pkt;
 
 			/* fill Tx descriptors */
@@ -189,12 +194,14 @@ gve_tx_burst_dqo(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
 				tx_id = (tx_id + 1) & mask;
 			}
 
+finish_mbuf:
 			sw_id = (sw_id + 1) & sw_mask;
 			bytes += tx_pkt->data_len;
 			tx_pkt = tx_pkt->next;
 		} while (tx_pkt);
 
-		/* fill the last descriptor with End of Packet (EOP) bit */
+		/* fill the last written descriptor with End of Packet (EOP) bit */
+		txd = &txr[(tx_id - 1) & mask];
 		txd->pkt.end_of_packet = 1;
 
 		txq->nb_free -= nb_descs;
-- 
2.50.0.727.gbf7dc18ff4-goog