[dpdk-dev] [PATCH v2] net/tap: Allow all-zero checksum for UDP over IPv4

[Michael Pfeiffer]

Unlike TCP, UDP checksums are optional and may be zero to indicate "not
set" [RFC 768] (except for IPv6, where this prohibited [RFC 8200]). Add
this special case to the checksum offload emulation in net/tap.

Signed-off-by: Michael Pfeiffer <michael.pfeiffer at tu-ilmenau.de>
---

v2:
* Added comment.

 drivers/net/tap/rte_eth_tap.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
index 2f8abb12c..2542de306 100644
--- a/drivers/net/tap/rte_eth_tap.c
+++ b/drivers/net/tap/rte_eth_tap.c
@@ -303,6 +303,7 @@ tap_verify_csum(struct rte_mbuf *mbuf)
 	uint16_t cksum = 0;
 	void *l3_hdr;
 	void *l4_hdr;
+	struct rte_udp_hdr *udp_hdr;
 
 	if (l2 == RTE_PTYPE_L2_ETHER_VLAN)
 		l2_len += 4;
@@ -349,10 +350,23 @@ tap_verify_csum(struct rte_mbuf *mbuf)
 		/* Don't verify checksum for multi-segment packets. */
 		if (mbuf->nb_segs > 1)
 			return;
-		if (l3 == RTE_PTYPE_L3_IPV4)
+		if (l3 == RTE_PTYPE_L3_IPV4) {
+			if (l4 == RTE_PTYPE_L4_UDP) {
+				udp_hdr = (struct rte_udp_hdr *)l4_hdr;
+				if (udp_hdr->dgram_cksum == 0) {
+					/*
+					 * For IPv4, a zero UDP checksum
+					 * indicates that the sender did not
+					 * generate one [RFC 768].
+					 */
+					mbuf->ol_flags |= PKT_RX_L4_CKSUM_NONE;
+					return;
+				}
+			}
 			cksum = ~rte_ipv4_udptcp_cksum(l3_hdr, l4_hdr);
-		else if (l3 == RTE_PTYPE_L3_IPV6)
+		} else if (l3 == RTE_PTYPE_L3_IPV6) {
 			cksum = ~rte_ipv6_udptcp_cksum(l3_hdr, l4_hdr);
+		}
 		mbuf->ol_flags |= cksum ?
 			PKT_RX_L4_CKSUM_BAD :
 			PKT_RX_L4_CKSUM_GOOD;
-- 
2.20.1