esp4: add gso_segment for esp4 beet mode

Similar to xfrm4_tunnel/transport_gso_segment(), _gso_segment()
is added to do gso_segment for esp4 beet mode. Before calling
inet_offloads[proto]->callbacks.gso_segment, it needs to do:

  - Get the upper proto from ph header to get its gso_segment
    when xo->proto is IPPROTO_BEETPH.

  - Add SKB_GSO_TCPV4 to gso_type if x->sel.family == AF_INET6
    and the proto == IPPROTO_TCP, so that the current tcp ipv4
    packet can be segmented.

  - Calculate a right value for skb->transport_header and move
    skb->data to the transport header position.
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/ipv4/esp4_offload.c

@@ -132,6 +132,36 @@ static struct sk_buff *xfrm4_transport_gso_segment(struct xfrm_state *x,
 	return segs;
 }
 
+static struct sk_buff *xfrm4_beet_gso_segment(struct xfrm_state *x,
+					      struct sk_buff *skb,
+					      netdev_features_t features)
+{
+	struct xfrm_offload *xo = xfrm_offload(skb);
+	struct sk_buff *segs = ERR_PTR(-EINVAL);
+	const struct net_offload *ops;
+	int proto = xo->proto;
+
+	skb->transport_header += x->props.header_len;
+
+	if (proto == IPPROTO_BEETPH) {
+		struct ip_beet_phdr *ph = (struct ip_beet_phdr *)skb->data;
+
+		skb->transport_header += ph->hdrlen * 8;
+		proto = ph->nexthdr;
+	} else if (x->sel.family != AF_INET6) {
+		skb->transport_header -= IPV4_BEET_PHMAXLEN;
+	} else if (proto == IPPROTO_TCP) {
+		skb_shinfo(skb)->gso_type |= SKB_GSO_TCPV4;
+	}
+
+	__skb_pull(skb, skb_transport_offset(skb));
+	ops = rcu_dereference(inet_offloads[proto]);
+	if (likely(ops && ops->callbacks.gso_segment))
+		segs = ops->callbacks.gso_segment(skb, features);
+
+	return segs;
+}
+
 static struct sk_buff *xfrm4_outer_mode_gso_segment(struct xfrm_state *x,
 						    struct sk_buff *skb,
 						    netdev_features_t features)
@@ -141,6 +171,8 @@ static struct sk_buff *xfrm4_outer_mode_gso_segment(struct xfrm_state *x,
 		return xfrm4_tunnel_gso_segment(x, skb, features);
 	case XFRM_MODE_TRANSPORT:
 		return xfrm4_transport_gso_segment(x, skb, features);
+	case XFRM_MODE_BEET:
+		return xfrm4_beet_gso_segment(x, skb, features);
 	}
 
 	return ERR_PTR(-EOPNOTSUPP);