[dpdk-dev] [PATCH v1 1/2] net/tap: calculate checksums of multi segs packets

[Ophir Munk <ophirmu@mellanox.com>]

Prior to this commit IP/UDP/TCP checksum offload calculations
were skipped in case of a multi segments packet.
This commit enables TAP checksum calculations for multi segments
packets.
The only restriction is that the first segment must contain all
headers of layers 2, 3 and 4 (where layer 4 header size equals
TCP header size).

Signed-off-by: Ophir Munk <ophirmu@mellanox.com>
---
 drivers/net/tap/rte_eth_tap.c | 54 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 40 insertions(+), 14 deletions(-)

diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
index 61d6465..df23c4d 100644
--- a/drivers/net/tap/rte_eth_tap.c
+++ b/drivers/net/tap/rte_eth_tap.c
@@ -509,6 +509,10 @@ pmd_tx_burst(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 		char m_copy[mbuf->data_len];
 		int n;
 		int j;
+		int k; /* first index in iovecs for copying segments */
+		uint16_t l234_len; /* length of layers 2,3,4 headers */
+		uint16_t seg_len; /* length of first segment */
+		uint16_t nb_segs;
 
 		/* stats.errs will be incremented */
 		if (rte_pktmbuf_pkt_len(mbuf) > max_size)
@@ -529,30 +533,52 @@ pmd_tx_burst(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 		if (j & (0x40 | 0x60))
 			pi.proto = (j == 0x40) ? 0x0008 : 0xdd86;
 
-		iovecs[0].iov_base = &pi;
-		iovecs[0].iov_len = sizeof(pi);
-		for (j = 1; j <= mbuf->nb_segs; j++) {
-			iovecs[j].iov_len = rte_pktmbuf_data_len(seg);
-			iovecs[j].iov_base =
-				rte_pktmbuf_mtod(seg, void *);
-			seg = seg->next;
-		}
+		k = 0;
+		iovecs[k].iov_base = &pi;
+		iovecs[k].iov_len = sizeof(pi);
+		k++;
+		nb_segs = mbuf->nb_segs;
 		if (txq->csum &&
 		    ((mbuf->ol_flags & (PKT_TX_IP_CKSUM | PKT_TX_IPV4) ||
 		     (mbuf->ol_flags & PKT_TX_L4_MASK) == PKT_TX_UDP_CKSUM ||
 		     (mbuf->ol_flags & PKT_TX_L4_MASK) == PKT_TX_TCP_CKSUM))) {
-			/* Support only packets with all data in the same seg */
-			if (mbuf->nb_segs > 1)
+			/* Support only packets with at least layer 4
+			 * header included in the first segment
+			 */
+			seg_len = rte_pktmbuf_data_len(mbuf);
+			l234_len = mbuf->l2_len + mbuf->l3_len +
+				sizeof(struct tcp_hdr);
+			if (seg_len < l234_len)
 				break;
-			/* To change checksums, work on a copy of data. */
+
+			/* To change checksums, work on a
+			 * copy of l2, l3 l4 headers.
+			 */
 			rte_memcpy(m_copy, rte_pktmbuf_mtod(mbuf, void *),
-				   rte_pktmbuf_data_len(mbuf));
+					l234_len);
 			tap_tx_offload(m_copy, mbuf->ol_flags,
 				       mbuf->l2_len, mbuf->l3_len);
-			iovecs[1].iov_base = m_copy;
+			iovecs[k].iov_base = m_copy;
+			iovecs[k].iov_len = l234_len;
+			k++;
+			/* Update next iovecs[] beyond l2, l3, l4 headers */
+			if (seg_len > l234_len) {
+				iovecs[k].iov_len = seg_len - l234_len;
+				iovecs[k].iov_base =
+					rte_pktmbuf_mtod(seg, char *) +
+						l234_len;
+				k++;
+			}
+			nb_segs--;
+			seg = seg->next;
+		}
+		for (j = k; j <= nb_segs; j++) {
+			iovecs[j].iov_len = rte_pktmbuf_data_len(seg);
+			iovecs[j].iov_base = rte_pktmbuf_mtod(seg, void *);
+			seg = seg->next;
 		}
 		/* copy the tx frame data */
-		n = writev(txq->fd, iovecs, mbuf->nb_segs + 1);
+		n = writev(txq->fd, iovecs, j);
 		if (n <= 0)
 			break;
 
-- 
2.7.4