mptcp: pm: in-kernel: record fullmesh endp nb

Instead of iterating over all endpoints, under RCU read lock, just to
check if one of them as the fullmesh flag, we can keep a counter of
fullmesh endpoint, similar to what is done with the other flags.

This counter is now checked, before iterating over all endpoints.

Similar to the other counters, this new one is also exposed. A userspace
app can then know when it is being used in a fullmesh mode, with
potentially (too) many subflows.

Reviewed-by: Geliang Tang <[e-mail]>
Signed-off-by: Matthieu Baerts (NGI0) <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

include/uapi/linux/mptcp.h

···
 	__u64	mptcpi_bytes_acked;
 	__u8	mptcpi_subflows_total;
 	__u8	mptcpi_endp_laminar_max;
-	__u8	reserved[2];
+	__u8	mptcpi_endp_fullmesh_max;
+	__u8	reserved;
 	__u32	mptcpi_last_data_sent;
 	__u32	mptcpi_last_data_recv;
 	__u32	mptcpi_last_ack_recv;

net/mptcp/pm_kernel.c

···
 	u8			endp_signal_max;
 	u8			endp_subflow_max;
 	u8			endp_laminar_max;
+	u8			endp_fullmesh_max;
 	u8			limit_add_addr_accepted;
 	u8			limit_extra_subflows;
 	u8			next_id;
···
 	return READ_ONCE(pernet->endp_laminar_max);
 }
 EXPORT_SYMBOL_GPL(mptcp_pm_get_endp_laminar_max);
+
+u8 mptcp_pm_get_endp_fullmesh_max(const struct mptcp_sock *msk)
+{
+	struct pm_nl_pernet *pernet = pm_nl_get_pernet_from_msk(msk);
+
+	return READ_ONCE(pernet->endp_fullmesh_max);
+}
+EXPORT_SYMBOL_GPL(mptcp_pm_get_endp_fullmesh_max);
 
 u8 mptcp_pm_get_limit_add_addr_accepted(const struct mptcp_sock *msk)
 {
···
 	int i;
 
 	/* If there is at least one MPTCP endpoint with a fullmesh flag */
-	i = fill_local_addresses_vec_fullmesh(msk, remote, locals, c_flag_case);
-	if (i)
-		return i;
+	if (mptcp_pm_get_endp_fullmesh_max(msk)) {
+		i = fill_local_addresses_vec_fullmesh(msk, remote, locals,
+						      c_flag_case);
+		if (i)
+			return i;
+	}
 
 	/* If there is at least one MPTCP endpoint with a laminar flag */
 	if (mptcp_pm_get_endp_laminar_max(msk))
···
 	if (entry->flags & MPTCP_PM_ADDR_FLAG_LAMINAR) {
 		addr_max = pernet->endp_laminar_max;
 		WRITE_ONCE(pernet->endp_laminar_max, addr_max + 1);
+	}
+	if (entry->flags & MPTCP_PM_ADDR_FLAG_FULLMESH) {
+		addr_max = pernet->endp_fullmesh_max;
+		WRITE_ONCE(pernet->endp_fullmesh_max, addr_max + 1);
 	}
 
 	pernet->endpoints++;
···
 		addr_max = pernet->endp_laminar_max;
 		WRITE_ONCE(pernet->endp_laminar_max, addr_max - 1);
 	}
+	if (entry->flags & MPTCP_PM_ADDR_FLAG_FULLMESH) {
+		addr_max = pernet->endp_fullmesh_max;
+		WRITE_ONCE(pernet->endp_fullmesh_max, addr_max - 1);
+	}
 
 	pernet->endpoints--;
 	list_del_rcu(&entry->list);
···
 	changed = (local->flags ^ entry->flags) & mask;
 	entry->flags = (entry->flags & ~mask) | (local->flags & mask);
 	*local = *entry;
+
+	if (changed & MPTCP_PM_ADDR_FLAG_FULLMESH) {
+		u8 addr_max = pernet->endp_fullmesh_max;
+
+		if (entry->flags & MPTCP_PM_ADDR_FLAG_FULLMESH)
+			addr_max++;
+		else
+			addr_max--;
+
+		WRITE_ONCE(pernet->endp_fullmesh_max, addr_max);
+	}
+
 	spin_unlock_bh(&pernet->lock);
 
 	mptcp_pm_nl_set_flags_all(net, local, changed);

net/mptcp/protocol.h

···
 u8 mptcp_pm_get_endp_signal_max(const struct mptcp_sock *msk);
 u8 mptcp_pm_get_endp_subflow_max(const struct mptcp_sock *msk);
 u8 mptcp_pm_get_endp_laminar_max(const struct mptcp_sock *msk);
+u8 mptcp_pm_get_endp_fullmesh_max(const struct mptcp_sock *msk);
 u8 mptcp_pm_get_limit_add_addr_accepted(const struct mptcp_sock *msk);
 u8 mptcp_pm_get_limit_extra_subflows(const struct mptcp_sock *msk);
 

net/mptcp/sockopt.c

···
 			mptcp_pm_get_endp_subflow_max(msk);
 		info->mptcpi_endp_laminar_max =
 			mptcp_pm_get_endp_laminar_max(msk);
+		info->mptcpi_endp_fullmesh_max =
+			mptcp_pm_get_endp_fullmesh_max(msk);
 	}
 
 	if (__mptcp_check_fallback(msk))