[PATCH v3] net/af_packet: add multi-segment mbuf support for jumbo frames

[Sriram Yagnaraman]

Enable jumbo frame reception with default mbuf data room size by
chaining multiple mbufs when packet exceeds single mbuf tailroom.

Scatter Rx is only enabled when RTE_ETH_RX_OFFLOAD_SCATTER is
requested. Packets are dropped if they exceed single mbuf size
and scatter is not enabled, or if mbuf allocation fails during
chaining. Error counter rx_dropped_pkts tracks all drops.

This allows receiving 9KB jumbo frames using standard 2KB mbufs,
chaining ~5 segments per jumbo packet.
---
 doc/guides/rel_notes/release_26_03.rst    |  5 ++
 drivers/net/af_packet/rte_eth_af_packet.c | 76 +++++++++++++++++++----
 2 files changed, 68 insertions(+), 13 deletions(-)

diff --git a/doc/guides/rel_notes/release_26_03.rst b/doc/guides/rel_notes/release_26_03.rst
index fdc880687b..ec627e76c9 100644
--- a/doc/guides/rel_notes/release_26_03.rst
+++ b/doc/guides/rel_notes/release_26_03.rst
@@ -65,6 +65,11 @@ New Features
 
   * Added support for V4000 Krackan2e.
 
+* **Updated AF_PACKET ethernet driver.**
+
+  * Added support for multi-segment mbuf reception to handle jumbo frames
+    with standard mbuf sizes when scatter Rx offload is enabled.
+
 * **Updated CESNET nfb ethernet driver.**
 
   * The timestamp value has been updated to make it usable.
diff --git a/drivers/net/af_packet/rte_eth_af_packet.c b/drivers/net/af_packet/rte_eth_af_packet.c
index e132dc387b..5d43306c09 100644
--- a/drivers/net/af_packet/rte_eth_af_packet.c
+++ b/drivers/net/af_packet/rte_eth_af_packet.c
@@ -56,6 +56,7 @@ struct __rte_cache_aligned pkt_rx_queue {
 	uint16_t in_port;
 	uint8_t vlan_strip;
 	uint8_t timestamp_offloading;
+	uint8_t scatter_enabled;
 
 	volatile unsigned long rx_pkts;
 	volatile unsigned long rx_bytes;
@@ -125,12 +126,13 @@ eth_af_packet_rx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 {
 	unsigned i;
 	struct tpacket2_hdr *ppd;
-	struct rte_mbuf *mbuf;
+	struct rte_mbuf *mbuf, *seg, *prev;
 	uint8_t *pbuf;
 	struct pkt_rx_queue *pkt_q = queue;
 	uint16_t num_rx = 0;
 	unsigned long num_rx_bytes = 0;
 	unsigned int framecount, framenum;
+	uint16_t pkt_len, data_len, remaining;
 
 	if (unlikely(nb_pkts == 0))
 		return 0;
@@ -154,8 +156,11 @@ eth_af_packet_rx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 			break;
 		}
 
-		/* drop packets that won't fit in the mbuf */
-		if (ppd->tp_snaplen > rte_pktmbuf_tailroom(mbuf)) {
+		pkt_len = ppd->tp_snaplen;
+		pbuf = (uint8_t *) ppd + ppd->tp_mac;
+
+		/* drop packets that won't fit in single mbuf if scatter not enabled */
+		if (!pkt_q->scatter_enabled && pkt_len > rte_pktmbuf_tailroom(mbuf)) {
 			rte_pktmbuf_free(mbuf);
 			ppd->tp_status = TP_STATUS_KERNEL;
 			if (++framenum >= framecount)
@@ -164,10 +169,57 @@ eth_af_packet_rx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 			continue;
 		}
 
-		/* packet will fit in the mbuf, go ahead and receive it */
-		rte_pktmbuf_pkt_len(mbuf) = rte_pktmbuf_data_len(mbuf) = ppd->tp_snaplen;
-		pbuf = (uint8_t *) ppd + ppd->tp_mac;
-		memcpy(rte_pktmbuf_mtod(mbuf, void *), pbuf, rte_pktmbuf_data_len(mbuf));
+		/* copy first segment */
+		data_len = RTE_MIN(pkt_len, rte_pktmbuf_tailroom(mbuf));
+		memcpy(rte_pktmbuf_mtod(mbuf, void *), pbuf, data_len);
+		rte_pktmbuf_data_len(mbuf) = data_len;
+		mbuf->nb_segs = 1;
+		remaining = pkt_len - data_len;
+		pbuf += data_len;
+		prev = mbuf;
+
+		/* chain additional segments if needed */
+		while (remaining > 0) {
+			seg = rte_pktmbuf_alloc(pkt_q->mb_pool);
+			if (unlikely(seg == NULL)) {
+				rte_pktmbuf_free(mbuf);
+				ppd->tp_status = TP_STATUS_KERNEL;
+				if (++framenum >= framecount)
+					framenum = 0;
+				pkt_q->rx_dropped_pkts++;
+				continue;
+			}
+
+			/* Remove headroom to maximize data space in chained segments */
+			rte_pktmbuf_prepend(seg, rte_pktmbuf_headroom(seg));
+
+			data_len = RTE_MIN(remaining, rte_pktmbuf_tailroom(seg));
+			if (unlikely(data_len == 0)) {
+				rte_pktmbuf_free(seg);
+				rte_pktmbuf_free(mbuf);
+				ppd->tp_status = TP_STATUS_KERNEL;
+				if (++framenum >= framecount)
+					framenum = 0;
+				pkt_q->rx_dropped_pkts++;
+				continue;
+			}
+
+			memcpy(rte_pktmbuf_mtod(seg, void *), pbuf, data_len);
+			rte_pktmbuf_data_len(seg) = data_len;
+			pbuf += data_len;
+			remaining -= data_len;
+
+			prev->next = seg;
+			prev = seg;
+			mbuf->nb_segs++;
+		}
+
+		/* release incoming frame and advance ring buffer */
+		ppd->tp_status = TP_STATUS_KERNEL;
+		if (++framenum >= framecount)
+			framenum = 0;
+
+		rte_pktmbuf_pkt_len(mbuf) = pkt_len;
 
 		/* check for vlan info */
 		if (ppd->tp_status & TP_STATUS_VLAN_VALID) {
@@ -188,14 +240,10 @@ eth_af_packet_rx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 			mbuf->ol_flags |= timestamp_dynflag;
 		}
 
-		/* release incoming frame and advance ring buffer */
-		ppd->tp_status = TP_STATUS_KERNEL;
-		if (++framenum >= framecount)
-			framenum = 0;
 		mbuf->port = pkt_q->in_port;
 
 		/* account for the receive frame */
-		bufs[i] = mbuf;
+		bufs[num_rx] = mbuf;
 		num_rx++;
 		num_rx_bytes += mbuf->pkt_len;
 	}
@@ -412,7 +460,8 @@ eth_dev_info(struct rte_eth_dev *dev, struct rte_eth_dev_info *dev_info)
 	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;
 }
@@ -599,6 +648,7 @@ eth_rx_queue_setup(struct rte_eth_dev *dev,
 	pkt_q->in_port = dev->data->port_id;
 	pkt_q->vlan_strip = internals->vlan_strip;
 	pkt_q->timestamp_offloading = internals->timestamp_offloading;
+	pkt_q->scatter_enabled = !!(dev->data->dev_conf.rxmode.offloads & RTE_ETH_RX_OFFLOAD_SCATTER);
 
 	return 0;
 }
-- 
2.43.7