[RFC PATCH v2 40/45] mptcp: implement and use MPTCP-level retransmission

[Mat Martineau]

From: Paolo Abeni <pab...@redhat.com>

On timeout event, schedule a work queue to do the retransmission.
Retransmission code resemple closely sendmsg() implementation and
re-uses mptcp_sendmsg_frag, providing a dummy msghdr - for flags'
sake - and peeking the relevant dfrag from the rtx head.

Signed-off-by: Paolo Abeni <pab...@redhat.com>
---
 net/mptcp/protocol.c | 81 ++++++++++++++++++++++++++++++++++++++++++--
 net/mptcp/protocol.h | 11 ++++++
 2 files changed, 89 insertions(+), 3 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 6366dfd65aa8..b54fecf528b9 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -759,10 +759,12 @@ static void mptcp_retransmit_handler(struct sock *sk)
 {
        struct mptcp_sock *msk = mptcp_sk(sk);
 
-       if (atomic64_read(&msk->snd_una) == msk->write_seq)
+       if (atomic64_read(&msk->snd_una) == msk->write_seq) {
                mptcp_stop_timer(sk);
-       else
-               mptcp_reset_timer(sk);
+       } else {
+               if (schedule_work(&msk->rtx_work))
+                       sock_hold(sk);
+       }
 }
 
 static void mptcp_retransmit_timer(struct timer_list *t)
@@ -784,6 +786,66 @@ static void mptcp_retransmit_timer(struct timer_list *t)
        sock_put(sk);
 }
 
+static void mptcp_retransmit(struct work_struct *work)
+{
+       int orig_len, orig_offset, ret, mss_now = 0, size_goal = 0;
+       struct mptcp_data_frag *dfrag;
+       struct sock *ssk, *sk;
+       struct mptcp_sock *msk;
+       u64 orig_write_seq;
+       size_t copied = 0;
+       struct msghdr msg;
+       long timeo = 0;
+
+       msk = container_of(work, struct mptcp_sock, rtx_work);
+       sk = &msk->sk.icsk_inet.sk;
+
+       lock_sock(sk);
+       mptcp_clean_una(sk);
+       dfrag = mptcp_rtx_head(sk);
+       if (!dfrag)
+               goto unlock;
+
+       ssk = mptcp_subflow_get_ref(msk);
+       if (!ssk)
+               goto reset_unlock;
+
+       lock_sock(ssk);
+
+       msg.msg_flags = MSG_DONTWAIT;
+       orig_len = dfrag->data_len;
+       orig_offset = dfrag->offset;
+       orig_write_seq = dfrag->data_seq;
+       while (dfrag->data_len > 0) {
+               ret = mptcp_sendmsg_frag(sk, ssk, &msg, dfrag, &timeo, &mss_now,
+                                        &size_goal);
+               if (ret < 0)
+                       break;
+
+               copied += ret;
+               dfrag->data_len -= ret;
+       }
+       if (copied)
+               tcp_push(ssk, msg.msg_flags, mss_now, tcp_sk(ssk)->nonagle,
+                        size_goal);
+
+       dfrag->data_seq = orig_write_seq;
+       dfrag->offset = orig_offset;
+       dfrag->data_len = orig_len;
+
+       mptcp_set_timeout(sk, ssk);
+       release_sock(ssk);
+       sock_put(ssk);
+
+reset_unlock:
+       if (!mptcp_timer_pending(sk))
+               mptcp_reset_timer(sk);
+
+unlock:
+       release_sock(sk);
+       sock_put(sk);
+}
+
 static int __mptcp_init_sock(struct sock *sk)
 {
        struct mptcp_sock *msk = mptcp_sk(sk);
@@ -791,6 +853,8 @@ static int __mptcp_init_sock(struct sock *sk)
        INIT_LIST_HEAD(&msk->conn_list);
        INIT_LIST_HEAD(&msk->rtx_queue);
 
+       INIT_WORK(&msk->rtx_work, mptcp_retransmit);
+
        /* re-use the csk retrans timer for MPTCP-level retrans */
        timer_setup(&msk->sk.icsk_retransmit_timer, mptcp_retransmit_timer, 0);
 
@@ -823,6 +887,14 @@ static void __mptcp_clear_xmit(struct sock *sk)
                dfrag_clear(sk, dfrag);
 }
 
+static void mptcp_cancel_rtx_work(struct sock *sk)
+{
+       struct mptcp_sock *msk = mptcp_sk(sk);
+
+       if (cancel_work_sync(&msk->rtx_work))
+               sock_put(sk);
+}
+
 static void mptcp_close(struct sock *sk, long timeout)
 {
        struct mptcp_subflow_context *subflow, *tmp;
@@ -852,6 +924,8 @@ static void mptcp_close(struct sock *sk, long timeout)
        __mptcp_clear_xmit(sk);
        release_sock(sk);
 
+       mptcp_cancel_rtx_work(sk);
+
        sk_common_release(sk);
 }
 
@@ -860,6 +934,7 @@ static int mptcp_disconnect(struct sock *sk, int flags)
        lock_sock(sk);
        __mptcp_clear_xmit(sk);
        release_sock(sk);
+       mptcp_cancel_rtx_work(sk);
        return tcp_disconnect(sk, flags);
 }
 
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index ef35d0aa8eb7..0c6bc8617cf4 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -133,6 +133,7 @@ struct mptcp_sock {
        u32             token;
        unsigned long   flags;
        u16             dport;
+       struct work_struct rtx_work;
        struct list_head conn_list;
        struct list_head rtx_queue;
        struct socket   *subflow; /* outgoing connect/listener/!mp_capable */
@@ -158,6 +159,16 @@ static inline struct mptcp_data_frag *mptcp_rtx_tail(const 
struct sock *sk)
        return list_last_entry(&msk->rtx_queue, struct mptcp_data_frag, list);
 }
 
+static inline struct mptcp_data_frag *mptcp_rtx_head(const struct sock *sk)
+{
+       struct mptcp_sock *msk = mptcp_sk(sk);
+
+       if (list_empty(&msk->rtx_queue))
+               return NULL;
+
+       return list_first_entry(&msk->rtx_queue, struct mptcp_data_frag, list);
+}
+
 struct mptcp_subflow_request_sock {
        struct  tcp_request_sock sk;
        u8      mp_capable : 1,
-- 
2.23.0