fix(uavcan): warn while the dynamic node ID allocation table is full (#28243)

centralized::Storage never evicts, so a node ID spent on a board that is
gone stays spent. Once all of them are, every board the table has not
seen before is refused a node ID through a UAVCAN_TRACE that compiles to
nothing here - silent on the bus and on the console, so a full table
reads as a dead node.

Boards already in the table still get their cached ID and join fine, so
the bus looks healthy. A test station cycling boards through one flight
controller fills the table and stops allocating for good.

PX4_ERR every 5 s while full: the table does not empty itself, so this
is a fault someone has to clear, not a one-time notice.

src/drivers/uavcan/uavcan_main.cpp

@@ -759,6 +759,10 @@ UavcanNode::Run()
 		_servers->setArmed(actuator_armed.armed || actuator_armed.prearmed);
 	}
 
+	if (_servers != nullptr) {
+		_servers->warn_if_node_id_allocation_table_full();
+	}
+
 #ifdef CONFIG_MODULES_NFS_MOUNT
 
 	if (_servers != nullptr) {

src/drivers/uavcan/uavcan_servers.cpp

@@ -154,6 +154,30 @@ int UavcanServers::init()
 	return 0;
 }
 
+void UavcanServers::warn_if_node_id_allocation_table_full()
+{
+	/*
+	The table never evicts an entry, so a node ID spent on a board that is no longer present stays spent. Once
+	all of them are, every board the table has not seen before is refused a node ID, and the refusal is silent
+	on the bus and here - the node just never appears, which reads as a dead node rather than a full table.
+	Keep saying so: the table does not empty itself, so this is a fault someone has to clear.
+	*/
+	if (_server_instance.getNumAllocations() < uavcan::NodeID::MaxRecommendedForRegularNodes) {
+		return;
+	}
+
+	const hrt_abstime now = hrt_absolute_time();
+
+	if (_node_id_table_full_warned != 0 && now - _node_id_table_full_warned < NODE_ID_TABLE_FULL_WARN_INTERVAL) {
+		return;
+	}
+
+	_node_id_table_full_warned = now;
+	PX4_ERR("dynamic node ID table is full (%u/%u): no new node can join, delete %s and reboot",
+		static_cast<unsigned>(_server_instance.getNumAllocations()),
+		static_cast<unsigned>(uavcan::NodeID::MaxRecommendedForRegularNodes), UAVCAN_NODE_DB_PATH);
+}
+
 #ifdef CONFIG_MODULES_NFS_MOUNT
 void UavcanServers::check_nfs()
 {

src/drivers/uavcan/uavcan_servers.hpp

@@ -71,6 +71,8 @@ public:
 
 	int init();
 
+	void warn_if_node_id_allocation_table_full();
+
 #ifdef CONFIG_MODULES_NFS_MOUNT
 	void check_nfs();
 #endif
@@ -86,6 +88,8 @@ public:
 
 private:
 
+	static constexpr hrt_abstime NODE_ID_TABLE_FULL_WARN_INTERVAL{5_s};
+
 	void unpackFwFromROMFS(const char *sd_path, const char *romfs_path);
 	void migrateFWFromRoot(const char *sd_path, const char *sd_root_path);
 	int copyFw(const char *dst, const char *src);
@@ -100,5 +104,7 @@ private:
 
 	uavcan::NodeInfoRetriever &_node_info_retriever;
 
+	hrt_abstime _node_id_table_full_warned{0};
+
 	uORB::Subscription _nfs_up_sub{ORB_ID(nfs_up)};
 };