[PATCH v19 21/25] net/pcap: add Rx scatter offload

[Stephen Hemminger]

Add RTE_ETH_RX_OFFLOAD_SCATTER to the advertised receive offload
capabilities. Validate in rx_queue_setup that the mbuf pool data
room is large enough when scatter is not enabled, following the
same pattern as the virtio driver.

Gate the multi-segment receive path on the scatter offload flag
and drop oversized packets when scatter is disabled.
Reject scatter with infinite_rx mode since the ring-based replay
path does not support multi-segment mbufs.

Signed-off-by: Stephen Hemminger <stephen at networkplumber.org>
---
 drivers/net/pcap/pcap_ethdev.c | 47 +++++++++++++++++++++++++++++++---
 1 file changed, 44 insertions(+), 3 deletions(-)

diff --git a/drivers/net/pcap/pcap_ethdev.c b/drivers/net/pcap/pcap_ethdev.c
index 8a2b5c1b4b..d8a924b0cd 100644
--- a/drivers/net/pcap/pcap_ethdev.c
+++ b/drivers/net/pcap/pcap_ethdev.c
@@ -79,6 +79,7 @@ struct pcap_rx_queue {
 	uint16_t port_id;
 	uint16_t queue_id;
 	bool vlan_strip;
+	bool rx_scatter;
 	bool timestamp_offloading;
 	struct rte_mempool *mb_pool;
 	struct queue_stat rx_stat;
@@ -112,6 +113,7 @@ struct pmd_internals {
 	bool phy_mac;
 	bool infinite_rx;
 	bool vlan_strip;
+	bool rx_scatter;
 	bool timestamp_offloading;
 };
 
@@ -342,14 +344,19 @@ eth_pcap_rx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 			/* pcap packet will fit in the mbuf, can copy it */
 			rte_memcpy(rte_pktmbuf_mtod(mbuf, void *), packet, len);
 			mbuf->data_len = len;
-		} else {
-			/* Try read jumbo frame into multi mbufs. */
+		} else if (pcap_q->rx_scatter) {
+			/* Scatter into multi-segment mbufs. */
 			if (unlikely(eth_pcap_rx_jumbo(pcap_q->mb_pool,
 						       mbuf, packet, len) == -1)) {
 				pcap_q->rx_stat.err_pkts++;
 				rte_pktmbuf_free(mbuf);
 				break;
 			}
+		} else {
+			/* Packet too large and scatter not enabled, drop it. */
+			pcap_q->rx_stat.err_pkts++;
+			rte_pktmbuf_free(mbuf);
+			continue;
 		}
 
 		mbuf->pkt_len = len;
@@ -907,6 +914,7 @@ eth_dev_configure(struct rte_eth_dev *dev)
 	const struct rte_eth_rxmode *rxmode = &dev_conf->rxmode;
 
 	internals->vlan_strip = !!(rxmode->offloads & RTE_ETH_RX_OFFLOAD_VLAN_STRIP);
+	internals->rx_scatter = !!(rxmode->offloads & RTE_ETH_RX_OFFLOAD_SCATTER);
 	internals->timestamp_offloading = !!(rxmode->offloads & RTE_ETH_RX_OFFLOAD_TIMESTAMP);
 	return 0;
 }
@@ -927,7 +935,8 @@ eth_dev_info(struct rte_eth_dev *dev,
 	dev_info->tx_offload_capa = RTE_ETH_TX_OFFLOAD_MULTI_SEGS |
 		RTE_ETH_TX_OFFLOAD_VLAN_INSERT;
 	dev_info->rx_offload_capa = RTE_ETH_RX_OFFLOAD_VLAN_STRIP |
-		RTE_ETH_RX_OFFLOAD_TIMESTAMP;
+		RTE_ETH_RX_OFFLOAD_TIMESTAMP |
+		RTE_ETH_RX_OFFLOAD_SCATTER;
 
 	return 0;
 }
@@ -1088,11 +1097,37 @@ eth_rx_queue_setup(struct rte_eth_dev *dev,
 {
 	struct pmd_internals *internals = dev->data->dev_private;
 	struct pcap_rx_queue *pcap_q = &internals->rx_queue[rx_queue_id];
+	uint16_t buf_size;
+	bool rx_scatter;
+
+	buf_size = rte_pktmbuf_data_room_size(mb_pool) - RTE_PKTMBUF_HEADROOM;
+	rx_scatter = !!(dev->data->dev_conf.rxmode.offloads &
+			RTE_ETH_RX_OFFLOAD_SCATTER);
+
+	/*
+	 * If Rx scatter is not enabled, verify that the mbuf data room
+	 * can hold the largest received packet in a single segment.
+	 * Use the MTU-derived frame size as the expected maximum, not
+	 * snapshot_len which is a capture truncation limit rather than
+	 * an expected packet size.
+	 */
+	if (!rx_scatter) {
+		uint32_t max_rx_pktlen = dev->data->mtu + RTE_ETHER_HDR_LEN;
+
+		if (max_rx_pktlen > buf_size) {
+			PMD_LOG(ERR,
+				"Rx scatter is disabled and RxQ mbuf pool object size is too small "
+				"(buf_size=%u, max_rx_pkt_len=%u)",
+				buf_size, max_rx_pktlen);
+			return -EINVAL;
+		}
+	}
 
 	pcap_q->mb_pool = mb_pool;
 	pcap_q->port_id = dev->data->port_id;
 	pcap_q->queue_id = rx_queue_id;
 	pcap_q->vlan_strip = internals->vlan_strip;
+	pcap_q->rx_scatter = rx_scatter;
 	dev->data->rx_queues[rx_queue_id] = pcap_q;
 	pcap_q->timestamp_offloading = internals->timestamp_offloading;
 
@@ -1105,6 +1140,12 @@ eth_rx_queue_setup(struct rte_eth_dev *dev,
 		pcap_t **pcap;
 		bool save_vlan_strip;
 
+		if (rx_scatter) {
+			PMD_LOG(ERR,
+				"Rx scatter is not supported with infinite_rx mode");
+			return -EINVAL;
+		}
+
 		pp = rte_eth_devices[pcap_q->port_id].process_private;
 		pcap = &pp->rx_pcap[pcap_q->queue_id];
 
-- 
2.51.0