linux-kernel - [PATCH net-next v2 2/7] netpoll: factor out UDP checksum calculation into helper

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Message-Id: <20250702-netpoll_untagle_ip-v2-2-13cf3db24e2b@debian.org>
Date: Wed, 02 Jul 2025 03:06:34 -0700
From: Breno Leitao <leitao@...ian.org>
To: "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
 Andrew Lunn <andrew+netdev@...n.ch>, Shuah Khan <shuah@...nel.org>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-kselftest@...r.kernel.org, Breno Leitao <leitao@...ian.org>, 
 kernel-team@...a.com
Subject: [PATCH net-next v2 2/7] netpoll: factor out UDP checksum
 calculation into helper

Extract UDP checksum calculation logic from netpoll_send_udp()
into a new static helper function netpoll_udp_checksum(). This
reduces code duplication and improves readability for both IPv4
and IPv6 cases.

No functional change intended.

Signed-off-by: Breno Leitao <leitao@...ian.org>
---
 net/core/netpoll.c | 41 ++++++++++++++++++++++++++---------------
 1 file changed, 26 insertions(+), 15 deletions(-)

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index ac0ae9630654a..24e6ad2da8096 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -372,6 +372,31 @@ static netdev_tx_t __netpoll_send_skb(struct netpoll *np, struct sk_buff *skb)
 	return ret;
 }
 
+static void netpoll_udp_checksum(struct netpoll *np, struct sk_buff *skb,
+				 int len)
+{
+	struct udphdr *udph;
+	int udp_len;
+
+	udp_len = len + sizeof(struct udphdr);
+	udph = udp_hdr(skb);
+
+	/* check needs to be set, since it will be consumed in csum_partial */
+	udph->check = 0;
+	if (np->ipv6)
+		udph->check = csum_ipv6_magic(&np->local_ip.in6,
+					      &np->remote_ip.in6,
+					      udp_len, IPPROTO_UDP,
+					      csum_partial(udph, udp_len, 0));
+	else
+		udph->check = csum_tcpudp_magic(np->local_ip.ip,
+						np->remote_ip.ip,
+						udp_len, IPPROTO_UDP,
+						csum_partial(udph, udp_len, 0));
+	if (udph->check == 0)
+		udph->check = CSUM_MANGLED_0;
+}
+
 netdev_tx_t netpoll_send_skb(struct netpoll *np, struct sk_buff *skb)
 {
 	unsigned long flags;
@@ -425,15 +450,8 @@ int netpoll_send_udp(struct netpoll *np, const char *msg, int len)
 	udph->dest = htons(np->remote_port);
 	udph->len = htons(udp_len);
 
-	udph->check = 0;
+	netpoll_udp_checksum(np, skb, len);
 	if (np->ipv6) {
-		udph->check = csum_ipv6_magic(&np->local_ip.in6,
-					      &np->remote_ip.in6,
-					      udp_len, IPPROTO_UDP,
-					      csum_partial(udph, udp_len, 0));
-		if (udph->check == 0)
-			udph->check = CSUM_MANGLED_0;
-
 		skb_push(skb, sizeof(struct ipv6hdr));
 		skb_reset_network_header(skb);
 		ip6h = ipv6_hdr(skb);
@@ -454,13 +472,6 @@ int netpoll_send_udp(struct netpoll *np, const char *msg, int len)
 		skb_reset_mac_header(skb);
 		skb->protocol = eth->h_proto = htons(ETH_P_IPV6);
 	} else {
-		udph->check = csum_tcpudp_magic(np->local_ip.ip,
-						np->remote_ip.ip,
-						udp_len, IPPROTO_UDP,
-						csum_partial(udph, udp_len, 0));
-		if (udph->check == 0)
-			udph->check = CSUM_MANGLED_0;
-
 		skb_push(skb, sizeof(struct iphdr));
 		skb_reset_network_header(skb);
 		iph = ip_hdr(skb);

-- 
2.47.1