mptcp: cleanup mptcp_subflow_discard_data()

There is no need to use the tcp_read_sock(), we can
simply drop the skb. Additionally try to look at next
buffer for in order data.

This both simplify the code and avoid unneeded indirect
calls.

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

net/mptcp/protocol.h

@@ -359,7 +359,6 @@ int mptcp_is_enabled(struct net *net);
 void mptcp_subflow_fully_established(struct mptcp_subflow_context *subflow,
  struct mptcp_options_received *mp_opt);
 bool mptcp_subflow_data_available(struct sock *sk);
-int mptcp_subflow_discard_data(struct sock *sk, unsigned limit);
 void __init mptcp_subflow_init(void);
 void mptcp_subflow_shutdown(struct sock *sk, struct sock *ssk, int how);
 void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,

net/mptcp/subflow.c

@@ -805,50 +805,22 @@ static enum mapping_status get_mapping_status(struct sock *ssk,
  return MAPPING_OK;
 }
 
-static int subflow_read_actor(read_descriptor_t *desc,
- struct sk_buff *skb,
- unsigned int offset, size_t len)
+static void mptcp_subflow_discard_data(struct sock *ssk, struct sk_buff *skb,
+ unsigned limit)
 {
- size_t copy_len = min(desc->count, len);
-
- desc->count -= copy_len;
+ struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+ bool fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
+ u32 incr;
 
- pr_debug("flushed %zu bytes, %zu left", copy_len, desc->count);
- return copy_len;
-}
+ incr = limit >= skb->len ? skb->len + fin : limit;
 
-int mptcp_subflow_discard_data(struct sock *ssk, unsigned limit)
-{
- struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
- u32 map_remaining;
- size_t delta;
-
- map_remaining = subflow->map_data_len -
- mptcp_subflow_get_map_offset(subflow);
- delta = min_t(size_t, limit, map_remaining);
-
- /* discard mapped data */
- pr_debug("discarding %zu bytes, current map len=%d", delta,
- map_remaining);
- if (delta) {
- read_descriptor_t desc = {
- .count = delta,
- };
- int ret;
-
- ret = tcp_read_sock(ssk, &desc, subflow_read_actor);
- if (ret < 0) {
- ssk->sk_err = -ret;
- return ret;
- }
- if (ret < delta)
- return 0;
- if (delta == map_remaining) {
- subflow->data_avail = 0;
- subflow->map_valid = 0;
- }
- }
- return 0;
+ pr_debug("discarding=%d len=%d seq=%d", incr, skb->len,
+ subflow->map_subflow_seq);
+ tcp_sk(ssk)->copied_seq += incr;
+ if (!before(tcp_sk(ssk)->copied_seq, TCP_SKB_CB(skb)->end_seq))
+ sk_eat_skb(ssk, skb);
+ if (mptcp_subflow_get_map_offset(subflow) >= subflow->map_data_len)
+ subflow->map_valid = 0;
 }
 
 static bool subflow_check_data_avail(struct sock *ssk)
@@ -923,9 +895,7 @@ static bool subflow_check_data_avail(struct sock *ssk)
  /* only accept in-sequence mapping. Old values are spurious
  * retransmission
  */
- if (mptcp_subflow_discard_data(ssk, old_ack - ack_seq))
- goto fatal;
- return false;
+ mptcp_subflow_discard_data(ssk, skb, old_ack - ack_seq);
  }
  return true;