mptcp: add net.mptcp.available_schedulers

The sysctl lists the available schedulers that can be set using
net.mptcp.scheduler similarly to net.ipv4.tcp_available_congestion_control.

Signed-off-by: Gregory Detal <gregory.detal@gmail.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Tested-by: Geliang Tang <geliang@kernel.org>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Mat Martineau <martineau@kernel.org>
Link: https://lore.kernel.org/r/20240514011335.176158-5-martineau@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/mptcp.h

@@ -97,6 +97,9 @@ struct mptcp_out_options {
 };
 
 #define MPTCP_SCHED_NAME_MAX	16
+#define MPTCP_SCHED_MAX		128
+#define MPTCP_SCHED_BUF_MAX	(MPTCP_SCHED_NAME_MAX * MPTCP_SCHED_MAX)
+
 #define MPTCP_SUBFLOWS_MAX	8
 
 struct mptcp_sched_data {

net/mptcp/ctrl.c

@@ -133,6 +133,24 @@ static int proc_scheduler(struct ctl_table *ctl, int write,
 	return ret;
 }
 
+static int proc_available_schedulers(struct ctl_table *ctl,
+				     int write, void *buffer,
+				     size_t *lenp, loff_t *ppos)
+{
+	struct ctl_table tbl = { .maxlen = MPTCP_SCHED_BUF_MAX, };
+	int ret;
+
+	tbl.data = kmalloc(tbl.maxlen, GFP_USER);
+	if (!tbl.data)
+		return -ENOMEM;
+
+	mptcp_get_available_schedulers(tbl.data, MPTCP_SCHED_BUF_MAX);
+	ret = proc_dostring(&tbl, write, buffer, lenp, ppos);
+	kfree(tbl.data);
+
+	return ret;
+}
+
 static struct ctl_table mptcp_sysctl_table[] = {
 	{
 		.procname = "enabled",
@@ -187,6 +205,12 @@ static struct ctl_table mptcp_sysctl_table[] = {
 		.mode = 0644,
 		.proc_handler = proc_scheduler,
 	},
+	{
+		.procname = "available_schedulers",
+		.maxlen	= MPTCP_SCHED_BUF_MAX,
+		.mode = 0644,
+		.proc_handler = proc_available_schedulers,
+	},
 	{
 		.procname = "close_timeout",
 		.maxlen = sizeof(unsigned int),
@@ -214,7 +238,8 @@ static int mptcp_pernet_new_table(struct net *net, struct mptcp_pernet *pernet)
 	table[4].data = &pernet->stale_loss_cnt;
 	table[5].data = &pernet->pm_type;
 	table[6].data = &pernet->scheduler;
-	table[7].data = &pernet->close_timeout;
+	/* table[7] is for available_schedulers which is read-only info */
+	table[8].data = &pernet->close_timeout;
 
 	hdr = register_net_sysctl_sz(net, MPTCP_SYSCTL_PATH, table,
 				     ARRAY_SIZE(mptcp_sysctl_table));

net/mptcp/protocol.h

@@ -686,6 +686,7 @@ unsigned int mptcp_stale_loss_cnt(const struct net *net);
 unsigned int mptcp_close_timeout(const struct sock *sk);
 int mptcp_get_pm_type(const struct net *net);
 const char *mptcp_get_scheduler(const struct net *net);
+void mptcp_get_available_schedulers(char *buf, size_t maxlen);
 void __mptcp_subflow_fully_established(struct mptcp_sock *msk,
 				       struct mptcp_subflow_context *subflow,
 				       const struct mptcp_options_received *mp_opt);

net/mptcp/sched.c

@@ -51,6 +51,28 @@ struct mptcp_sched_ops *mptcp_sched_find(const char *name)
 	return ret;
 }
 
+/* Build string with list of available scheduler values.
+ * Similar to tcp_get_available_congestion_control()
+ */
+void mptcp_get_available_schedulers(char *buf, size_t maxlen)
+{
+	struct mptcp_sched_ops *sched;
+	size_t offs = 0;
+
+	rcu_read_lock();
+	spin_lock(&mptcp_sched_list_lock);
+	list_for_each_entry_rcu(sched, &mptcp_sched_list, list) {
+		offs += snprintf(buf + offs, maxlen - offs,
+				 "%s%s",
+				 offs == 0 ? "" : " ", sched->name);
+
+		if (WARN_ON_ONCE(offs >= maxlen))
+			break;
+	}
+	spin_unlock(&mptcp_sched_list_lock);
+	rcu_read_unlock();
+}
+
 int mptcp_register_scheduler(struct mptcp_sched_ops *sched)
 {
 	if (!sched->get_subflow)