mptcp: add accounting for pending data

Preparation patch to track the data pending in the msk
write queue. No functional change introduced here

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

net/mptcp/protocol.c

@@ -1849,6 +1849,7 @@ static int __mptcp_init_sock(struct sock *sk)
 	__set_bit(MPTCP_SEND_SPACE, &msk->flags);
 	INIT_WORK(&msk->work, mptcp_worker);
 	msk->out_of_order_queue = RB_ROOT;
+	msk->first_pending = NULL;
 
 	msk->first = NULL;
 	inet_csk(sk)->icsk_sync_mss = mptcp_sync_mss;

net/mptcp/protocol.h

@@ -187,9 +187,10 @@ struct mptcp_pm_data {
 struct mptcp_data_frag {
 	struct list_head list;
 	u64 data_seq;
-	int data_len;
-	int offset;
-	int overhead;
+	u16 data_len;
+	u16 offset;
+	u16 overhead;
+	u16 already_sent;
 	struct page *page;
 };
 
@@ -219,6 +220,7 @@ struct mptcp_sock {
 	struct rb_root  out_of_order_queue;
 	struct list_head conn_list;
 	struct list_head rtx_queue;
+	struct mptcp_data_frag *first_pending;
 	struct list_head join_list;
 	struct skb_ext	*cached_ext;	/* for the next sendmsg */
 	struct socket	*subflow; /* outgoing connect/listener/!mp_capable */
@@ -240,6 +242,36 @@ static inline struct mptcp_sock *mptcp_sk(const struct sock *sk)
 	return (struct mptcp_sock *)sk;
 }
 
+static inline struct mptcp_data_frag *mptcp_send_head(const struct sock *sk)
+{
+	const struct mptcp_sock *msk = mptcp_sk(sk);
+
+	return READ_ONCE(msk->first_pending);
+}
+
+static inline struct mptcp_data_frag *mptcp_send_next(struct sock *sk)
+{
+	struct mptcp_sock *msk = mptcp_sk(sk);
+	struct mptcp_data_frag *cur;
+
+	cur = msk->first_pending;
+	return list_is_last(&cur->list, &msk->rtx_queue) ? NULL :
+						     list_next_entry(cur, list);
+}
+
+static inline struct mptcp_data_frag *mptcp_pending_tail(const struct sock *sk)
+{
+	struct mptcp_sock *msk = mptcp_sk(sk);
+
+	if (!msk->first_pending)
+		return NULL;
+
+	if (WARN_ON_ONCE(list_empty(&msk->rtx_queue)))
+		return NULL;
+
+	return list_last_entry(&msk->rtx_queue, struct mptcp_data_frag, list);
+}
+
 static inline struct mptcp_data_frag *mptcp_rtx_tail(const struct sock *sk)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);