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netfilter: postpone the checksum calculation

PATCH Applied Changli Gao 2 participants 2 messages Jul 2, 2010 – Jul 5, 2010

Subsystems (3)
Networking Network drivers netfilter
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Changli Gao

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#0 lore raw

PATCH 1/1 netfilter: postpone the checksum calculation

netfilter: postpone the checksum calculation.

postpone the checksum calculation, then if the output NIC supports checksum offloading, we can utlize it. And though the output NIC doesn't support checksum offloading, but we'll mangle this packet, this can free us from updating the checksum, as the checksum calculation occurs later.

Signed-off-by Changli Gao <[email protected]>

----

 net/ipv4/netfilter/ipt_REJECT.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)
net/ipv4/netfilter/ipt_REJECT.c +5 -5
index f5f4a88..3d0e064 100644
@@ -95,10 +95,11 @@ static void send_reset(struct sk_buff *oldskb, int hook)
 	}
 
 	tcph->rst	= 1;
-	tcph->check	= tcp_v4_check(sizeof(struct tcphdr),
-				       niph->saddr, niph->daddr,
-				       csum_partial(tcph,
-						    sizeof(struct tcphdr), 0));
+	tcph->check = ~tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
+				    niph->daddr, 0);
+	nskb->ip_summed = CHECKSUM_PARTIAL;
+	nskb->csum_start = (unsigned char *)tcph - nskb->head;
+	nskb->csum_offset = offsetof(struct tcphdr, check);
 
 	addr_type = RTN_UNSPEC;
 	if (hook != NF_INET_FORWARD

@@ -115,7 +116,6 @@ static void send_reset(struct sk_buff *oldskb, int hook)
 		goto free_nskb;
 
 	niph->ttl	= dst_metric(skb_dst(nskb), RTAX_HOPLIMIT);
-	nskb->ip_summed = CHECKSUM_NONE;
 
 	/* "Never happens" */
 	if (nskb->len > dst_mtu(skb_dst(nskb)))
Applied
#1 lore raw
Quoted 6 lines · Changli Gao

netfilter: postpone the checksum calculation.

postpone the checksum calculation, then if the output NIC supports checksum offloading, we can utlize it. And though the output NIC doesn't support checksum offloading, but we'll mangle this packet, this can free us from updating the checksum, as the checksum calculation occurs later.

Applied, thanks.