mptcp: introduce and use mptcp_try_coalesce()

Factor-out existing code, will be re-used by the
next patch.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/mptcp/protocol.c

@@ -112,6 +112,22 @@ static int __mptcp_socket_create(struct mptcp_sock *msk)
  return 0;
 }
 
+static bool mptcp_try_coalesce(struct sock *sk, struct sk_buff *to,
+ struct sk_buff *from)
+{
+ bool fragstolen;
+ int delta;
+
+ if (MPTCP_SKB_CB(from)->offset ||
+ !skb_try_coalesce(to, from, &fragstolen, &delta))
+ return false;
+
+ kfree_skb_partial(from, fragstolen);
+ atomic_add(delta, &sk->sk_rmem_alloc);
+ sk_mem_charge(sk, delta);
+ return true;
+}
+
 static void __mptcp_move_skb(struct mptcp_sock *msk, struct sock *ssk,
  struct sk_buff *skb,
  unsigned int offset, size_t copy_len)
@@ -123,24 +139,15 @@ static void __mptcp_move_skb(struct mptcp_sock *msk, struct sock *ssk,
 
  skb_ext_reset(skb);
  skb_orphan(skb);
+ MPTCP_SKB_CB(skb)->offset = offset;
  msk->ack_seq += copy_len;
 
  tail = skb_peek_tail(&sk->sk_receive_queue);
- if (offset == 0 && tail) {
- bool fragstolen;
- int delta;
-
- if (skb_try_coalesce(tail, skb, &fragstolen, &delta)) {
- kfree_skb_partial(skb, fragstolen);
- atomic_add(delta, &sk->sk_rmem_alloc);
- sk_mem_charge(sk, delta);
- return;
- }
- }
+ if (tail && mptcp_try_coalesce(sk, tail, skb))
+ return;
 
  skb_set_owner_r(skb, sk);
  __skb_queue_tail(&sk->sk_receive_queue, skb);
- MPTCP_SKB_CB(skb)->offset = offset;
 }
 
 static void mptcp_stop_timer(struct sock *sk)