mptcp: register default scheduler

This patch defines the default packet scheduler mptcp_sched_default.
Register it in mptcp_sched_init(), which is invoked in mptcp_proto_init().
Skip deleting this default scheduler in mptcp_unregister_scheduler().

Set msk->sched to the default scheduler when the input parameter of
mptcp_init_sched() is NULL.

Invoke mptcp_sched_default_get_subflow in get_send() and get_retrans()
if the defaut scheduler is set or msk->sched is NULL.

Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Geliang Tang <geliang.tang@suse.com>
Signed-off-by: Mat Martineau <martineau@kernel.org>
Link: https://lore.kernel.org/r/20230821-upstream-net-next-20230818-v1-10-0c860fb256a8@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/mptcp/protocol.c

@@ -3965,6 +3965,7 @@ void __init mptcp_proto_init(void)
 
 	mptcp_subflow_init();
 	mptcp_pm_init();
+	mptcp_sched_init();
 	mptcp_token_init();
 
 	if (proto_register(&mptcp_prot, 1) != 0)

net/mptcp/protocol.h

@@ -661,6 +661,7 @@ void mptcp_info2sockaddr(const struct mptcp_addr_info *info,
 struct mptcp_sched_ops *mptcp_sched_find(const char *name);
 int mptcp_register_scheduler(struct mptcp_sched_ops *sched);
 void mptcp_unregister_scheduler(struct mptcp_sched_ops *sched);
+void mptcp_sched_init(void);
 int mptcp_init_sched(struct mptcp_sock *msk,
 		     struct mptcp_sched_ops *sched);
 void mptcp_release_sched(struct mptcp_sock *msk);

net/mptcp/sched.c

@@ -16,6 +16,26 @@
 static DEFINE_SPINLOCK(mptcp_sched_list_lock);
 static LIST_HEAD(mptcp_sched_list);
 
+static int mptcp_sched_default_get_subflow(struct mptcp_sock *msk,
+					   struct mptcp_sched_data *data)
+{
+	struct sock *ssk;
+
+	ssk = data->reinject ? mptcp_subflow_get_retrans(msk) :
+			       mptcp_subflow_get_send(msk);
+	if (!ssk)
+		return -EINVAL;
+
+	mptcp_subflow_set_scheduled(mptcp_subflow_ctx(ssk), true);
+	return 0;
+}
+
+static struct mptcp_sched_ops mptcp_sched_default = {
+	.get_subflow	= mptcp_sched_default_get_subflow,
+	.name		= "default",
+	.owner		= THIS_MODULE,
+};
+
 /* Must be called with rcu read lock held */
 struct mptcp_sched_ops *mptcp_sched_find(const char *name)
 {
@@ -50,16 +70,24 @@ int mptcp_register_scheduler(struct mptcp_sched_ops *sched)
 
 void mptcp_unregister_scheduler(struct mptcp_sched_ops *sched)
 {
+	if (sched == &mptcp_sched_default)
+		return;
+
 	spin_lock(&mptcp_sched_list_lock);
 	list_del_rcu(&sched->list);
 	spin_unlock(&mptcp_sched_list_lock);
 }
 
+void mptcp_sched_init(void)
+{
+	mptcp_register_scheduler(&mptcp_sched_default);
+}
+
 int mptcp_init_sched(struct mptcp_sock *msk,
 		     struct mptcp_sched_ops *sched)
 {
 	if (!sched)
-		goto out;
+		sched = &mptcp_sched_default;
 
 	if (!bpf_try_module_get(sched, sched->owner))
 		return -EBUSY;
@@ -70,7 +98,6 @@ int mptcp_init_sched(struct mptcp_sock *msk,
 
 	pr_debug("sched=%s", msk->sched->name);
 
-out:
 	return 0;
 }
 
@@ -117,17 +144,9 @@ int mptcp_sched_get_send(struct mptcp_sock *msk)
 			return 0;
 	}
 
-	if (!msk->sched) {
-		struct sock *ssk;
-
-		ssk = mptcp_subflow_get_send(msk);
-		if (!ssk)
-			return -EINVAL;
-		mptcp_subflow_set_scheduled(mptcp_subflow_ctx(ssk), true);
-		return 0;
-	}
-
 	data.reinject = false;
+	if (msk->sched == &mptcp_sched_default || !msk->sched)
+		return mptcp_sched_default_get_subflow(msk, &data);
 	return msk->sched->get_subflow(msk, &data);
 }
 
@@ -147,16 +166,8 @@ int mptcp_sched_get_retrans(struct mptcp_sock *msk)
 			return 0;
 	}
 
-	if (!msk->sched) {
-		struct sock *ssk;
-
-		ssk = mptcp_subflow_get_retrans(msk);
-		if (!ssk)
-			return -EINVAL;
-		mptcp_subflow_set_scheduled(mptcp_subflow_ctx(ssk), true);
-		return 0;
-	}
-
 	data.reinject = true;
+	if (msk->sched == &mptcp_sched_default || !msk->sched)
+		return mptcp_sched_default_get_subflow(msk, &data);
 	return msk->sched->get_subflow(msk, &data);
 }