[PATCH bpf-next 2/7] net: Update an existing TCP congestion control algorithm.

[Kui-Feng Lee <kuifeng@meta.com>]

This feature lets you immediately transition to another congestion
control algorithm or implementation with the same name.  Once a name
is updated, new connections will apply this new algorithm.

Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
---
 include/linux/bpf.h            |  1 +
 include/net/tcp.h              |  2 ++
 net/bpf/bpf_dummy_struct_ops.c |  6 ++++++
 net/ipv4/bpf_tcp_ca.c          |  6 ++++++
 net/ipv4/tcp_cong.c            | 39 ++++++++++++++++++++++++++++++++++
 5 files changed, 54 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 13683584b071..5fe39f56a760 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1450,6 +1450,7 @@ struct bpf_struct_ops {
 			   void *kdata, const void *udata);
 	int (*reg)(void *kdata);
 	void (*unreg)(void *kdata);
+	int (*update)(void *kdata, void *old_kdata);
 	const struct btf_type *type;
 	const struct btf_type *value_type;
 	const char *name;
diff --git a/include/net/tcp.h b/include/net/tcp.h
index db9f828e9d1e..239cc0e2639c 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1117,6 +1117,8 @@ struct tcp_congestion_ops {
 
 int tcp_register_congestion_control(struct tcp_congestion_ops *type);
 void tcp_unregister_congestion_control(struct tcp_congestion_ops *type);
+int tcp_update_congestion_control(struct tcp_congestion_ops *type,
+				  struct tcp_congestion_ops *old_type);
 
 void tcp_assign_congestion_control(struct sock *sk);
 void tcp_init_congestion_control(struct sock *sk);
diff --git a/net/bpf/bpf_dummy_struct_ops.c b/net/bpf/bpf_dummy_struct_ops.c
index ff4f89a2b02a..158f14e240d0 100644
--- a/net/bpf/bpf_dummy_struct_ops.c
+++ b/net/bpf/bpf_dummy_struct_ops.c
@@ -222,12 +222,18 @@ static void bpf_dummy_unreg(void *kdata)
 {
 }
 
+static int bpf_dummy_update(void *kdata, void *old_kdata)
+{
+	return -EOPNOTSUPP;
+}
+
 struct bpf_struct_ops bpf_bpf_dummy_ops = {
 	.verifier_ops = &bpf_dummy_verifier_ops,
 	.init = bpf_dummy_init,
 	.check_member = bpf_dummy_ops_check_member,
 	.init_member = bpf_dummy_init_member,
 	.reg = bpf_dummy_reg,
+	.update = bpf_dummy_update,
 	.unreg = bpf_dummy_unreg,
 	.name = "bpf_dummy_ops",
 };
diff --git a/net/ipv4/bpf_tcp_ca.c b/net/ipv4/bpf_tcp_ca.c
index 13fc0c185cd9..66ce5fadfe42 100644
--- a/net/ipv4/bpf_tcp_ca.c
+++ b/net/ipv4/bpf_tcp_ca.c
@@ -266,10 +266,16 @@ static void bpf_tcp_ca_unreg(void *kdata)
 	tcp_unregister_congestion_control(kdata);
 }
 
+static int bpf_tcp_ca_update(void *kdata, void *old_kdata)
+{
+	return tcp_update_congestion_control(kdata, old_kdata);
+}
+
 struct bpf_struct_ops bpf_tcp_congestion_ops = {
 	.verifier_ops = &bpf_tcp_ca_verifier_ops,
 	.reg = bpf_tcp_ca_reg,
 	.unreg = bpf_tcp_ca_unreg,
+	.update = bpf_tcp_ca_update,
 	.check_member = bpf_tcp_ca_check_member,
 	.init_member = bpf_tcp_ca_init_member,
 	.init = bpf_tcp_ca_init,
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index db8b4b488c31..22fd7c12360e 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -130,6 +130,45 @@ void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
 }
 EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
 
+/* Replace a registered old ca with a new one.
+ *
+ * The new ca must have the same name as the old one, that has been
+ * registered.
+ */
+int tcp_update_congestion_control(struct tcp_congestion_ops *ca, struct tcp_congestion_ops *old_ca)
+{
+	struct tcp_congestion_ops *existing;
+	int ret = 0;
+
+	/* all algorithms must implement these */
+	if (!ca->ssthresh || !ca->undo_cwnd ||
+	    !(ca->cong_avoid || ca->cong_control)) {
+		pr_err("%s does not implement required ops\n", old_ca->name);
+		return -EINVAL;
+	}
+
+	ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
+
+	spin_lock(&tcp_cong_list_lock);
+	existing = tcp_ca_find_key(ca->key);
+	if (ca->key == TCP_CA_UNSPEC || !existing || strcmp(existing->name, ca->name)) {
+		pr_notice("%s not registered or non-unique key\n",
+			  ca->name);
+		ret = -EINVAL;
+	} else if (existing != old_ca) {
+		pr_notice("invalid old congestion control algorithm to replace\n");
+		ret = -EINVAL;
+	} else {
+		list_del_rcu(&existing->list);
+		list_add_tail_rcu(&ca->list, &tcp_cong_list);
+		pr_debug("%s updated\n", ca->name);
+	}
+	spin_unlock(&tcp_cong_list_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(tcp_update_congestion_control);
+
 u32 tcp_ca_get_key_by_name(struct net *net, const char *name, bool *ecn_ca)
 {
 	const struct tcp_congestion_ops *ca;
-- 
2.30.2