udp: Add support for software checksum and GSO_PARTIAL with GSO offload

This patch adds support for a software provided checksum and GSO_PARTIAL
segmentation support. With this we can offload UDP segmentation on devices
that only have partial support for tunnels.

Since we are no longer needing the hardware checksum we can drop the checks
in the segmentation code that were verifying if it was present.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/udp_offload.c

@@ -214,6 +214,13 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
 		return segs;
 	}
 
+	/* GSO partial and frag_list segmentation only requires splitting
+	 * the frame into an MSS multiple and possibly a remainder, both
+	 * cases return a GSO skb. So update the mss now.
+	 */
+	if (skb_is_gso(segs))
+		mss *= skb_shinfo(segs)->gso_segs;
+
 	seg = segs;
 	uh = udp_hdr(seg);
 
@@ -232,6 +239,12 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
 		uh->len = newlen;
 		uh->check = check;
 
+		if (seg->ip_summed == CHECKSUM_PARTIAL)
+			gso_reset_checksum(seg, ~check);
+		else
+			uh->check = gso_make_checksum(seg, ~check) ? :
+				    CSUM_MANGLED_0;
+
 		seg = seg->next;
 		uh = udp_hdr(seg);
 	}
@@ -244,6 +257,11 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
 	uh->len = newlen;
 	uh->check = check;
 
+	if (seg->ip_summed == CHECKSUM_PARTIAL)
+		gso_reset_checksum(seg, ~check);
+	else
+		uh->check = gso_make_checksum(seg, ~check) ? : CSUM_MANGLED_0;
+
 	/* update refcount for the packet */
 	refcount_add(sum_truesize - gso_skb->truesize, &sk->sk_wmem_alloc);
 
@@ -251,15 +269,6 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
 }
 EXPORT_SYMBOL_GPL(__udp_gso_segment);
 
-static struct sk_buff *__udp4_gso_segment(struct sk_buff *gso_skb,
-					  netdev_features_t features)
-{
-	if (!can_checksum_protocol(features, htons(ETH_P_IP)))
-		return ERR_PTR(-EIO);
-
-	return __udp_gso_segment(gso_skb, features);
-}
-
 static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
 					 netdev_features_t features)
 {
@@ -283,7 +292,7 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
 		goto out;
 
 	if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4)
-		return __udp4_gso_segment(skb, features);
+		return __udp_gso_segment(skb, features);
 
 	mss = skb_shinfo(skb)->gso_size;
 	if (unlikely(skb->len <= mss))

net/ipv6/udp_offload.c

@@ -17,15 +17,6 @@
 #include <net/ip6_checksum.h>
 #include "ip6_offload.h"
 
-static struct sk_buff *__udp6_gso_segment(struct sk_buff *gso_skb,
-					  netdev_features_t features)
-{
-	if (!can_checksum_protocol(features, htons(ETH_P_IPV6)))
-		return ERR_PTR(-EIO);
-
-	return __udp_gso_segment(gso_skb, features);
-}
-
 static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb,
 					 netdev_features_t features)
 {
@@ -58,7 +49,7 @@ static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb,
 			goto out;
 
 		if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4)
-			return __udp6_gso_segment(skb, features);
+			return __udp_gso_segment(skb, features);
 
 		/* Do software UFO. Complete and fill in the UDP checksum as HW cannot
 		 * do checksum of UDP packets sent as multiple IP fragments.