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.

Signed-off-by: Geliang Tang <geliang.tang@suse.com>
---
 net/mptcp/protocol.c |  3 ++-
 net/mptcp/protocol.h |  3 ++-
 net/mptcp/sched.c    | 38 ++++++++++++++++++++++++++++++++++++--
 3 files changed, 40 insertions(+), 4 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 27feabd92b3e..27407b48f3ff 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2284,7 +2284,7 @@ static void mptcp_timeout_timer(struct timer_list *t)
  *
  * A backup subflow is returned only if that is the only kind available.
  */
-struct sock *mptcp_subflow_get_retrans(struct mptcp_sock *msk)
+struct sock *mptcp_subflow_get_retrans(const struct mptcp_sock *msk)
 {
 	struct sock *backup = NULL, *pick = NULL;
 	struct mptcp_subflow_context *subflow;
@@ -4030,6 +4030,7 @@ 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)
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index a4db0f8f00f4..12c8c95abf52 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -659,6 +659,7 @@ 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,
 		     gfp_t gfp);
@@ -669,7 +670,7 @@ void mptcp_sched_data_set_contexts(const struct mptcp_sock *msk,
 				   struct mptcp_sched_data *data);
 struct sock *mptcp_subflow_get_send(const struct mptcp_sock *msk,
 				    struct mptcp_sched_data *data);
-struct sock *mptcp_subflow_get_retrans(struct mptcp_sock *msk);
+struct sock *mptcp_subflow_get_retrans(const struct mptcp_sock *msk);
 int mptcp_sched_get_send(struct mptcp_sock *msk);
 int mptcp_sched_get_retrans(struct mptcp_sock *msk);
 
diff --git a/net/mptcp/sched.c b/net/mptcp/sched.c
index a6210ec4ba5f..fdf2459a0fcc 100644
--- a/net/mptcp/sched.c
+++ b/net/mptcp/sched.c
@@ -16,6 +16,33 @@
 static DEFINE_SPINLOCK(mptcp_sched_list_lock);
 static LIST_HEAD(mptcp_sched_list);
 
+static void mptcp_sched_default_data_init(const struct mptcp_sock *msk,
+					  struct mptcp_sched_data *data)
+{
+	data->snd_burst = 0;
+}
+
+static int mptcp_sched_default_get_subflow(const 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, data);
+	if (!ssk)
+		return -EINVAL;
+
+	mptcp_subflow_set_scheduled(mptcp_subflow_ctx(ssk), true);
+	return 0;
+}
+
+static struct mptcp_sched_ops mptcp_sched_default = {
+	.data_init	= mptcp_sched_default_data_init,
+	.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)
 {
@@ -50,17 +77,25 @@ 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,
 		     gfp_t gfp)
 {
 	if (!sched)
-		goto out;
+		sched = &mptcp_sched_default;
 
 	if (!bpf_try_module_get(sched, sched->owner))
 		return -EBUSY;
@@ -77,7 +112,6 @@ int mptcp_init_sched(struct mptcp_sock *msk,
 
 	pr_debug("sched=%s", msk->sched->name);
 
-out:
 	return 0;
 }
 
-- 
2.35.3