mptcp: set data_ready status bit in subflow_check_data_avail()

This simplify mptcp_subflow_data_available() and will
made follow-up patches simpler.

Additionally remove the unneeded checks on subflow copied_seq:
we always whole skbs out of subflows.

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

net/mptcp/subflow.c

@@ -825,6 +825,8 @@ static bool subflow_check_data_avail(struct sock *ssk)
 
  pr_debug("msk=%p ssk=%p data_avail=%d skb=%p", subflow->conn, ssk,
  subflow->data_avail, skb_peek(&ssk->sk_receive_queue));
+ if (!skb_peek(&ssk->sk_receive_queue))
+ subflow->data_avail = 0;
  if (subflow->data_avail)
  return true;
 
@@ -849,6 +851,7 @@ static bool subflow_check_data_avail(struct sock *ssk)
  subflow->map_data_len = skb->len;
  subflow->map_subflow_seq = tcp_sk(ssk)->copied_seq -
  subflow->ssn_offset;
+ subflow->data_avail = 1;
  return true;
  }
 
@@ -876,8 +879,10 @@ static bool subflow_check_data_avail(struct sock *ssk)
  ack_seq = mptcp_subflow_get_mapped_dsn(subflow);
  pr_debug("msk ack_seq=%llx subflow ack_seq=%llx", old_ack,
  ack_seq);
- if (ack_seq == old_ack)
+ if (ack_seq == old_ack) {
+ subflow->data_avail = 1;
  break;
+ }
 
  /* only accept in-sequence mapping. Old values are spurious
  * retransmission; we can hit "future" values on active backup
@@ -922,13 +927,13 @@ static bool subflow_check_data_avail(struct sock *ssk)
  ssk->sk_error_report(ssk);
  tcp_set_state(ssk, TCP_CLOSE);
  tcp_send_active_reset(ssk, GFP_ATOMIC);
+ subflow->data_avail = 0;
  return false;
 }
 
 bool mptcp_subflow_data_available(struct sock *sk)
 {
  struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
- struct sk_buff *skb;
 
  /* check if current mapping is still valid */
  if (subflow->map_valid &&
@@ -941,15 +946,7 @@ bool mptcp_subflow_data_available(struct sock *sk)
  subflow->map_data_len);
  }
 
- if (!subflow_check_data_avail(sk)) {
- subflow->data_avail = 0;
- return false;
- }
-
- skb = skb_peek(&sk->sk_receive_queue);
- subflow->data_avail = skb &&
- before(tcp_sk(sk)->copied_seq, TCP_SKB_CB(skb)->end_seq);
- return subflow->data_avail;
+ return subflow_check_data_avail(sk);
 }
 
 /* If ssk has an mptcp parent socket, use the mptcp rcvbuf occupancy,