mptcp: implement .read_sock

Current in-kernel TCP sockets -- i.e. from nvme_tcp_try_recv() -- need
to call .read_sock interface of struct proto_ops, but it's not
implemented in MPTCP.

This patch implements it with reference to __tcp_read_sock() and
__mptcp_recvmsg_mskq().

Corresponding to tcp_recv_skb(), a new helper for MPTCP named
mptcp_recv_skb() is added to peek a skb from sk->sk_receive_queue.

Compared with __mptcp_recvmsg_mskq(), mptcp_read_sock() uses
sk->sk_rcvbuf as the max read length. The LISTEN status is checked
before the while loop, and mptcp_recv_skb() and mptcp_cleanup_rbuf()
are invoked after the loop. In the loop, all flags checks for
__mptcp_recvmsg_mskq() are removed.

Reviewed-by: Hannes Reinecke <hare@kernel.org>
Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260130-net-next-mptcp-splice-v2-2-31332ba70d7f@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 5eb2a6182d4bcf7689d06fb1074e4cb4bc76d50b..2071f984da1284b0f1c3bb0f2b5bb9f200e1936a 100644 (file)
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -4317,6 +4317,86 @@ static __poll_t mptcp_poll(struct file *file, struct socket *sock,
        return mask;
 }
 
+static struct sk_buff *mptcp_recv_skb(struct sock *sk, u32 *off)
+{
+       struct mptcp_sock *msk = mptcp_sk(sk);
+       struct sk_buff *skb;
+       u32 offset;
+
+       if (!list_empty(&msk->backlog_list))
+               mptcp_move_skbs(sk);
+
+       while ((skb = skb_peek(&sk->sk_receive_queue)) != NULL) {
+               offset = MPTCP_SKB_CB(skb)->offset;
+               if (offset < skb->len) {
+                       *off = offset;
+                       return skb;
+               }
+               mptcp_eat_recv_skb(sk, skb);
+       }
+       return NULL;
+}
+
+/*
+ * Note:
+ *     - It is assumed that the socket was locked by the caller.
+ */
+static int __mptcp_read_sock(struct sock *sk, read_descriptor_t *desc,
+                            sk_read_actor_t recv_actor, bool noack)
+{
+       struct mptcp_sock *msk = mptcp_sk(sk);
+       struct sk_buff *skb;
+       int copied = 0;
+       u32 offset;
+
+       msk_owned_by_me(msk);
+
+       if (sk->sk_state == TCP_LISTEN)
+               return -ENOTCONN;
+       while ((skb = mptcp_recv_skb(sk, &offset)) != NULL) {
+               u32 data_len = skb->len - offset;
+               int count;
+               u32 size;
+
+               size = min_t(size_t, data_len, INT_MAX);
+               count = recv_actor(desc, skb, offset, size);
+               if (count <= 0) {
+                       if (!copied)
+                               copied = count;
+                       break;
+               }
+
+               copied += count;
+
+               msk->bytes_consumed += count;
+               if (count < data_len) {
+                       MPTCP_SKB_CB(skb)->offset += count;
+                       MPTCP_SKB_CB(skb)->map_seq += count;
+                       break;
+               }
+
+               mptcp_eat_recv_skb(sk, skb);
+       }
+
+       if (noack)
+               goto out;
+
+       mptcp_rcv_space_adjust(msk, copied);
+
+       if (copied > 0) {
+               mptcp_recv_skb(sk, &offset);
+               mptcp_cleanup_rbuf(msk, copied);
+       }
+out:
+       return copied;
+}
+
+static int mptcp_read_sock(struct sock *sk, read_descriptor_t *desc,
+                          sk_read_actor_t recv_actor)
+{
+       return __mptcp_read_sock(sk, desc, recv_actor, false);
+}
+
 static const struct proto_ops mptcp_stream_ops = {
        .family            = PF_INET,
        .owner             = THIS_MODULE,
@@ -4337,6 +4417,7 @@ static const struct proto_ops mptcp_stream_ops = {
        .recvmsg           = inet_recvmsg,
        .mmap              = sock_no_mmap,
        .set_rcvlowat      = mptcp_set_rcvlowat,
+       .read_sock         = mptcp_read_sock,
 };
 
 static struct inet_protosw mptcp_protosw = {
@@ -4441,6 +4522,7 @@ static const struct proto_ops mptcp_v6_stream_ops = {
        .compat_ioctl      = inet6_compat_ioctl,
 #endif
        .set_rcvlowat      = mptcp_set_rcvlowat,
+       .read_sock         = mptcp_read_sock,
 };
 
 static struct proto mptcp_v6_prot;