[dpdk-dev] [PATCH] net: fix unneeded replacement of 0 by ffff for TCP checksum

[Hongzhi Guo]

Per RFC768:
If the computed checksum is zero, it is transmitted as all ones.
An all zero transmitted checksum value means that the transmitter
generated no checksum.

RFC793 for TCP has no such special treatment for the checksum of zero.

Fixes: 6006818cfb26 ("net: new checksum functions")
Cc: stable at dpdk.org

Signed-off-by: Hongzhi Guo <guohongzhi1 at huawei.com>
---
v2:
* Fixed commit tile
* Fixed the API comment
---
---
 lib/librte_net/rte_ip.h | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/lib/librte_net/rte_ip.h b/lib/librte_net/rte_ip.h
index 292f63fd7..d03c77120 100644
--- a/lib/librte_net/rte_ip.h
+++ b/lib/librte_net/rte_ip.h
@@ -325,7 +325,7 @@ rte_ipv4_phdr_cksum(const struct rte_ipv4_hdr *ipv4_hdr, uint64_t ol_flags)
  *   The pointer to the beginning of the L4 header.
  * @return
  *   The complemented checksum to set in the IP packet
- *   or 0 on error
+ *   or 0 if the IP length is invalid in the header.
  */
 static inline uint16_t
 rte_ipv4_udptcp_cksum(const struct rte_ipv4_hdr *ipv4_hdr, const void *l4_hdr)
@@ -344,7 +344,13 @@ rte_ipv4_udptcp_cksum(const struct rte_ipv4_hdr *ipv4_hdr, const void *l4_hdr)
 
 	cksum = ((cksum & 0xffff0000) >> 16) + (cksum & 0xffff);
 	cksum = (~cksum) & 0xffff;
-	if (cksum == 0)
+	/*
+	 *Per RFC768:
+	 *If the computed checksum is zero for udp,
+	 *it is transmitted as all ones.
+	 *(the equivalent in one's complement arithmetic).
+	 */
+	if (cksum == 0 && ipv4_hdr->next_proto_id == IPPROTO_UDP)
 		cksum = 0xffff;
 
 	return (uint16_t)cksum;
@@ -438,7 +444,13 @@ rte_ipv6_udptcp_cksum(const struct rte_ipv6_hdr *ipv6_hdr, const void *l4_hdr)
 
 	cksum = ((cksum & 0xffff0000) >> 16) + (cksum & 0xffff);
 	cksum = (~cksum) & 0xffff;
-	if (cksum == 0)
+	/*
+	 *Per RFC768:
+	 *If the computed checksum is zero for udp,
+	 *it is transmitted as all ones.
+	 *(the equivalent in one's complement arithmetic).
+	 */
+	if (cksum == 0 && ipv6_hdr->proto == IPPROTO_UDP)
 		cksum = 0xffff;
 
 	return (uint16_t)cksum;
-- 
2.21.0.windows.1