linux/net/tipc/node.c

/*
 * net/tipc/node.c: TIPC node management routines
 *
 * Copyright (c) 2000-2006, Ericsson AB
 * Copyright (c) 2005-2006, Wind River Systems
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the names of the copyright holders nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * Alternatively, this software may be distributed under the terms of the
 * GNU General Public License ("GPL") version 2 as published by the Free
 * Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include "core.h"
#include "config.h"
#include "node.h"
#include "cluster.h"
#include "net.h"
#include "addr.h"
#include "node_subscr.h"
#include "link.h"
#include "port.h"
#include "bearer.h"
#include "name_distr.h"

void node_print(struct print_buf *buf, struct tipc_node *n_ptr, char *str);
static void node_lost_contact(struct tipc_node *n_ptr);
static void node_established_contact(struct tipc_node *n_ptr);

struct tipc_node *tipc_nodes = NULL;	/* sorted list of nodes within cluster */

static DEFINE_SPINLOCK(node_create_lock);

u32 tipc_own_tag = 0;

/**
 * tipc_node_create - create neighboring node
 *
 * Currently, this routine is called by neighbor discovery code, which holds
 * net_lock for reading only.  We must take node_create_lock to ensure a node
 * isn't created twice if two different bearers discover the node at the same
 * time.  (It would be preferable to switch to holding net_lock in write mode,
 * but this is a non-trivial change.)
 */

struct tipc_node *tipc_node_create(u32 addr)
{
	struct cluster *c_ptr;
	struct tipc_node *n_ptr;
	struct tipc_node **curr_node;

	spin_lock_bh(&node_create_lock);

	for (n_ptr = tipc_nodes; n_ptr; n_ptr = n_ptr->next) {
		if (addr < n_ptr->addr)
			break;
		if (addr == n_ptr->addr) {
			spin_unlock_bh(&node_create_lock);
			return n_ptr;
		}
	}

	n_ptr = kzalloc(sizeof(*n_ptr),GFP_ATOMIC);
	if (!n_ptr) {
		spin_unlock_bh(&node_create_lock);
		warn("Node creation failed, no memory\n");
		return NULL;
	}

	c_ptr = tipc_cltr_find(addr);
	if (!c_ptr) {
		c_ptr = tipc_cltr_create(addr);
	}
	if (!c_ptr) {
		spin_unlock_bh(&node_create_lock);
		kfree(n_ptr);
		return NULL;
	}

	n_ptr->addr = addr;
		spin_lock_init(&n_ptr->lock);
	INIT_LIST_HEAD(&n_ptr->nsub);
	n_ptr->owner = c_ptr;
	tipc_cltr_attach_node(c_ptr, n_ptr);
	n_ptr->last_router = -1;

	/* Insert node into ordered list */
	for (curr_node = &tipc_nodes; *curr_node;
	     curr_node = &(*curr_node)->next) {
		if (addr < (*curr_node)->addr) {
			n_ptr->next = *curr_node;
			break;
		}
	}
	(*curr_node) = n_ptr;
	spin_unlock_bh(&node_create_lock);
	return n_ptr;
}

void tipc_node_delete(struct tipc_node *n_ptr)
{
	if (!n_ptr)
		return;

#if 0
	/* Not needed because links are already deleted via tipc_bearer_stop() */

	u32 l_num;

	for (l_num = 0; l_num < MAX_BEARERS; l_num++) {
		link_delete(n_ptr->links[l_num]);
	}
#endif

	dbg("node %x deleted\n", n_ptr->addr);
	kfree(n_ptr);
}


/**
 * tipc_node_link_up - handle addition of link
 *
 * Link becomes active (alone or shared) or standby, depending on its priority.
 */

void tipc_node_link_up(struct tipc_node *n_ptr, struct link *l_ptr)
{
	struct link **active = &n_ptr->active_links[0];

	n_ptr->working_links++;

	info("Established link <%s> on network plane %c\n",
	     l_ptr->name, l_ptr->b_ptr->net_plane);

	if (!active[0]) {
		dbg(" link %x into %x/%x\n", l_ptr, &active[0], &active[1]);
		active[0] = active[1] = l_ptr;
		node_established_contact(n_ptr);
		return;
	}
	if (l_ptr->priority < active[0]->priority) {
		info("New link <%s> becomes standby\n", l_ptr->name);
		return;
	}
	tipc_link_send_duplicate(active[0], l_ptr);
	if (l_ptr->priority == active[0]->priority) {
		active[0] = l_ptr;
		return;
	}
	info("Old link <%s> becomes standby\n", active[0]->name);
	if (active[1] != active[0])
		info("Old link <%s> becomes standby\n", active[1]->name);
	active[0] = active[1] = l_ptr;
}

/**
 * node_select_active_links - select active link
 */

static void node_select_active_links(struct tipc_node *n_ptr)
{
	struct link **active = &n_ptr->active_links[0];
	u32 i;
	u32 highest_prio = 0;

	active[0] = active[1] = NULL;

	for (i = 0; i < MAX_BEARERS; i++) {
		struct link *l_ptr = n_ptr->links[i];

		if (!l_ptr || !tipc_link_is_up(l_ptr) ||
		    (l_ptr->priority < highest_prio))
			continue;

		if (l_ptr->priority > highest_prio) {
			highest_prio = l_ptr->priority;
			active[0] = active[1] = l_ptr;
		} else {
			active[1] = l_ptr;
		}
	}
}

/**
 * tipc_node_link_down - handle loss of link
 */

void tipc_node_link_down(struct tipc_node *n_ptr, struct link *l_ptr)
{
	struct link **active;

	n_ptr->working_links--;

	if (!tipc_link_is_active(l_ptr)) {
		info("Lost standby link <%s> on network plane %c\n",
		     l_ptr->name, l_ptr->b_ptr->net_plane);
		return;
	}
	info("Lost link <%s> on network plane %c\n",
		l_ptr->name, l_ptr->b_ptr->net_plane);

	active = &n_ptr->active_links[0];
	if (active[0] == l_ptr)
		active[0] = active[1];
	if (active[1] == l_ptr)
		active[1] = active[0];
	if (active[0] == l_ptr)
		node_select_active_links(n_ptr);
	if (tipc_node_is_up(n_ptr))
		tipc_link_changeover(l_ptr);
	else
		node_lost_contact(n_ptr);
}

int tipc_node_has_active_links(struct tipc_node *n_ptr)
{
	return n_ptr->active_links[0] != NULL;
}

int tipc_node_has_redundant_links(struct tipc_node *n_ptr)
{
	return (n_ptr->working_links > 1);
}

static int tipc_node_has_active_routes(struct tipc_node *n_ptr)
{
	return (n_ptr && (n_ptr->last_router >= 0));
}

int tipc_node_is_up(struct tipc_node *n_ptr)
{
	return (tipc_node_has_active_links(n_ptr) || tipc_node_has_active_routes(n_ptr));
}

struct tipc_node *tipc_node_attach_link(struct link *l_ptr)
{
	struct tipc_node *n_ptr = tipc_node_find(l_ptr->addr);

	if (!n_ptr)
		n_ptr = tipc_node_create(l_ptr->addr);
	if (n_ptr) {
		u32 bearer_id = l_ptr->b_ptr->identity;
		char addr_string[16];

		if (n_ptr->link_cnt >= 2) {
			err("Attempt to create third link to %s\n",
			    tipc_addr_string_fill(addr_string, n_ptr->addr));
			return NULL;
		}

		if (!n_ptr->links[bearer_id]) {
			n_ptr->links[bearer_id] = l_ptr;
			tipc_net.zones[tipc_zone(l_ptr->addr)]->links++;
			n_ptr->link_cnt++;
			return n_ptr;
		}
		err("Attempt to establish second link on <%s> to %s\n",
		    l_ptr->b_ptr->publ.name,
		    tipc_addr_string_fill(addr_string, l_ptr->addr));
	}
	return NULL;
}

void tipc_node_detach_link(struct tipc_node *n_ptr, struct link *l_ptr)
{
	n_ptr->links[l_ptr->b_ptr->identity] = NULL;
	tipc_net.zones[tipc_zone(l_ptr->addr)]->links--;
	n_ptr->link_cnt--;
}

/*
 * Routing table management - five cases to handle:
 *
 * 1: A link towards a zone/cluster external node comes up.
 *    => Send a multicast message updating routing tables of all
 *    system nodes within own cluster that the new destination
 *    can be reached via this node.
 *    (node.establishedContact()=>cluster.multicastNewRoute())
 *
 * 2: A link towards a slave node comes up.
 *    => Send a multicast message updating routing tables of all
 *    system nodes within own cluster that the new destination
 *    can be reached via this node.
 *    (node.establishedContact()=>cluster.multicastNewRoute())
 *    => Send a  message to the slave node about existence
 *    of all system nodes within cluster:
 *    (node.establishedContact()=>cluster.sendLocalRoutes())
 *
 * 3: A new cluster local system node becomes available.
 *    => Send message(s) to this particular node containing
 *    information about all cluster external and slave
 *     nodes which can be reached via this node.
 *    (node.establishedContact()==>network.sendExternalRoutes())
 *    (node.establishedContact()==>network.sendSlaveRoutes())
 *    => Send messages to all directly connected slave nodes
 *    containing information about the existence of the new node
 *    (node.establishedContact()=>cluster.multicastNewRoute())
 *
 * 4: The link towards a zone/cluster external node or slave
 *    node goes down.
 *    => Send a multcast message updating routing tables of all
 *    nodes within cluster that the new destination can not any
 *    longer be reached via this node.
 *    (node.lostAllLinks()=>cluster.bcastLostRoute())
 *
 * 5: A cluster local system node becomes unavailable.
 *    => Remove all references to this node from the local
 *    routing tables. Note: This is a completely node
 *    local operation.
 *    (node.lostAllLinks()=>network.removeAsRouter())
 *    => Send messages to all directly connected slave nodes
 *    containing information about loss of the node
 *    (node.establishedContact()=>cluster.multicastLostRoute())
 *
 */

static void node_established_contact(struct tipc_node *n_ptr)
{
	struct cluster *c_ptr;

	dbg("node_established_contact:-> %x\n", n_ptr->addr);
	if (!tipc_node_has_active_routes(n_ptr) && in_own_cluster(n_ptr->addr)) {
		tipc_k_signal((Handler)tipc_named_node_up, n_ptr->addr);
	}

	/* Syncronize broadcast acks */
	n_ptr->bclink.acked = tipc_bclink_get_last_sent();

	if (is_slave(tipc_own_addr))
		return;
	if (!in_own_cluster(n_ptr->addr)) {
		/* Usage case 1 (see above) */
		c_ptr = tipc_cltr_find(tipc_own_addr);
		if (!c_ptr)
			c_ptr = tipc_cltr_create(tipc_own_addr);
		if (c_ptr)
			tipc_cltr_bcast_new_route(c_ptr, n_ptr->addr, 1,
						  tipc_max_nodes);
		return;
	}

	c_ptr = n_ptr->owner;
	if (is_slave(n_ptr->addr)) {
		/* Usage case 2 (see above) */
		tipc_cltr_bcast_new_route(c_ptr, n_ptr->addr, 1, tipc_max_nodes);
		tipc_cltr_send_local_routes(c_ptr, n_ptr->addr);
		return;
	}

	if (n_ptr->bclink.supported) {
		tipc_nmap_add(&tipc_cltr_bcast_nodes, n_ptr->addr);
		if (n_ptr->addr < tipc_own_addr)
			tipc_own_tag++;
	}

	/* Case 3 (see above) */
	tipc_net_send_external_routes(n_ptr->addr);
	tipc_cltr_send_slave_routes(c_ptr, n_ptr->addr);
	tipc_cltr_bcast_new_route(c_ptr, n_ptr->addr, LOWEST_SLAVE,
				  tipc_highest_allowed_slave);
}

static void node_cleanup_finished(unsigned long node_addr)
{
	struct tipc_node *n_ptr;

	read_lock_bh(&tipc_net_lock);
	n_ptr = tipc_node_find(node_addr);
	if (n_ptr) {
		tipc_node_lock(n_ptr);
		n_ptr->cleanup_required = 0;
		tipc_node_unlock(n_ptr);
	}
	read_unlock_bh(&tipc_net_lock);
}

static void node_lost_contact(struct tipc_node *n_ptr)
{
	struct cluster *c_ptr;
	struct tipc_node_subscr *ns, *tns;
	char addr_string[16];
	u32 i;

	/* Clean up broadcast reception remains */
	n_ptr->bclink.gap_after = n_ptr->bclink.gap_to = 0;
	while (n_ptr->bclink.deferred_head) {
		struct sk_buff* buf = n_ptr->bclink.deferred_head;
		n_ptr->bclink.deferred_head = buf->next;
		buf_discard(buf);
	}
	if (n_ptr->bclink.defragm) {
		buf_discard(n_ptr->bclink.defragm);
		n_ptr->bclink.defragm = NULL;
	}
	if (in_own_cluster(n_ptr->addr) && n_ptr->bclink.supported) {
		tipc_bclink_acknowledge(n_ptr, mod(n_ptr->bclink.acked + 10000));
	}

	/* Update routing tables */
	if (is_slave(tipc_own_addr)) {
		tipc_net_remove_as_router(n_ptr->addr);
	} else {
		if (!in_own_cluster(n_ptr->addr)) {
			/* Case 4 (see above) */
			c_ptr = tipc_cltr_find(tipc_own_addr);
			tipc_cltr_bcast_lost_route(c_ptr, n_ptr->addr, 1,
						   tipc_max_nodes);
		} else {
			/* Case 5 (see above) */
			c_ptr = tipc_cltr_find(n_ptr->addr);
			if (is_slave(n_ptr->addr)) {
				tipc_cltr_bcast_lost_route(c_ptr, n_ptr->addr, 1,
							   tipc_max_nodes);
			} else {
				if (n_ptr->bclink.supported) {
					tipc_nmap_remove(&tipc_cltr_bcast_nodes,
							 n_ptr->addr);
					if (n_ptr->addr < tipc_own_addr)
						tipc_own_tag--;
				}
				tipc_net_remove_as_router(n_ptr->addr);
				tipc_cltr_bcast_lost_route(c_ptr, n_ptr->addr,
							   LOWEST_SLAVE,
							   tipc_highest_allowed_slave);
			}
		}
	}
	if (tipc_node_has_active_routes(n_ptr))
		return;

	info("Lost contact with %s\n",
	     tipc_addr_string_fill(addr_string, n_ptr->addr));

	/* Abort link changeover */
	for (i = 0; i < MAX_BEARERS; i++) {
		struct link *l_ptr = n_ptr->links[i];
		if (!l_ptr)
			continue;
		l_ptr->reset_checkpoint = l_ptr->next_in_no;
		l_ptr->exp_msg_count = 0;
		tipc_link_reset_fragments(l_ptr);
	}

	/* Notify subscribers */
	list_for_each_entry_safe(ns, tns, &n_ptr->nsub, nodesub_list) {
		ns->node = NULL;
		list_del_init(&ns->nodesub_list);
		tipc_k_signal((Handler)ns->handle_node_down,
			      (unsigned long)ns->usr_handle);
	}

	/* Prevent re-contact with node until all cleanup is done */

	n_ptr->cleanup_required = 1;
	tipc_k_signal((Handler)node_cleanup_finished, n_ptr->addr);
}

/**
 * tipc_node_select_next_hop - find the next-hop node for a message
 *
 * Called by when cluster local lookup has failed.
 */

struct tipc_node *tipc_node_select_next_hop(u32 addr, u32 selector)
{
	struct tipc_node *n_ptr;
	u32 router_addr;

	if (!tipc_addr_domain_valid(addr))
		return NULL;

	/* Look for direct link to destination processsor */
	n_ptr = tipc_node_find(addr);
	if (n_ptr && tipc_node_has_active_links(n_ptr))
		return n_ptr;

	/* Cluster local system nodes *must* have direct links */
	if (!is_slave(addr) && in_own_cluster(addr))
		return NULL;

	/* Look for cluster local router with direct link to node */
	router_addr = tipc_node_select_router(n_ptr, selector);
	if (router_addr)
		return tipc_node_select(router_addr, selector);

	/* Slave nodes can only be accessed within own cluster via a
	   known router with direct link -- if no router was found,give up */
	if (is_slave(addr))
		return NULL;

	/* Inter zone/cluster -- find any direct link to remote cluster */
	addr = tipc_addr(tipc_zone(addr), tipc_cluster(addr), 0);
	n_ptr = tipc_net_select_remote_node(addr, selector);
	if (n_ptr && tipc_node_has_active_links(n_ptr))
		return n_ptr;

	/* Last resort -- look for any router to anywhere in remote zone */
	router_addr =  tipc_net_select_router(addr, selector);
	if (router_addr)
		return tipc_node_select(router_addr, selector);

	return NULL;
}

/**
 * tipc_node_select_router - select router to reach specified node
 *
 * Uses a deterministic and fair algorithm for selecting router node.
 */

u32 tipc_node_select_router(struct tipc_node *n_ptr, u32 ref)
{
	u32 ulim;
	u32 mask;
	u32 start;
	u32 r;

	if (!n_ptr)
		return 0;

	if (n_ptr->last_router < 0)
		return 0;
	ulim = ((n_ptr->last_router + 1) * 32) - 1;

	/* Start entry must be random */
	mask = tipc_max_nodes;
	while (mask > ulim)
		mask >>= 1;
	start = ref & mask;
	r = start;

	/* Lookup upwards with wrap-around */
	do {
		if (((n_ptr->routers[r / 32]) >> (r % 32)) & 1)
			break;
	} while (++r <= ulim);
	if (r > ulim) {
		r = 1;
		do {
			if (((n_ptr->routers[r / 32]) >> (r % 32)) & 1)
				break;
		} while (++r < start);
		assert(r != start);
	}
	assert(r && (r <= ulim));
	return tipc_addr(own_zone(), own_cluster(), r);
}

void tipc_node_add_router(struct tipc_node *n_ptr, u32 router)
{
	u32 r_num = tipc_node(router);

	n_ptr->routers[r_num / 32] =
		((1 << (r_num % 32)) | n_ptr->routers[r_num / 32]);
	n_ptr->last_router = tipc_max_nodes / 32;
	while ((--n_ptr->last_router >= 0) &&
	       !n_ptr->routers[n_ptr->last_router]);
}

void tipc_node_remove_router(struct tipc_node *n_ptr, u32 router)
{
	u32 r_num = tipc_node(router);

	if (n_ptr->last_router < 0)
		return;		/* No routes */

	n_ptr->routers[r_num / 32] =
		((~(1 << (r_num % 32))) & (n_ptr->routers[r_num / 32]));
	n_ptr->last_router = tipc_max_nodes / 32;
	while ((--n_ptr->last_router >= 0) &&
	       !n_ptr->routers[n_ptr->last_router]);

	if (!tipc_node_is_up(n_ptr))
		node_lost_contact(n_ptr);
}

#if 0
void node_print(struct print_buf *buf, struct tipc_node *n_ptr, char *str)
{
	u32 i;

	tipc_printf(buf, "\n\n%s", str);
	for (i = 0; i < MAX_BEARERS; i++) {
		if (!n_ptr->links[i])
			continue;
		tipc_printf(buf, "Links[%u]: %x, ", i, n_ptr->links[i]);
	}
	tipc_printf(buf, "Active links: [%x,%x]\n",
		    n_ptr->active_links[0], n_ptr->active_links[1]);
}
#endif

u32 tipc_available_nodes(const u32 domain)
{
	struct tipc_node *n_ptr;
	u32 cnt = 0;

	read_lock_bh(&tipc_net_lock);
	for (n_ptr = tipc_nodes; n_ptr; n_ptr = n_ptr->next) {
		if (!tipc_in_scope(domain, n_ptr->addr))
			continue;
		if (tipc_node_is_up(n_ptr))
			cnt++;
	}
	read_unlock_bh(&tipc_net_lock);
	return cnt;
}

struct sk_buff *tipc_node_get_nodes(const void *req_tlv_area, int req_tlv_space)
{
	u32 domain;
	struct sk_buff *buf;
	struct tipc_node *n_ptr;
	struct tipc_node_info node_info;
	u32 payload_size;

	if (!TLV_CHECK(req_tlv_area, req_tlv_space, TIPC_TLV_NET_ADDR))
		return tipc_cfg_reply_error_string(TIPC_CFG_TLV_ERROR);

	domain = ntohl(*(__be32 *)TLV_DATA(req_tlv_area));
	if (!tipc_addr_domain_valid(domain))
		return tipc_cfg_reply_error_string(TIPC_CFG_INVALID_VALUE
						   " (network address)");

	read_lock_bh(&tipc_net_lock);
	if (!tipc_nodes) {
		read_unlock_bh(&tipc_net_lock);
		return tipc_cfg_reply_none();
	}

	/* For now, get space for all other nodes
	   (will need to modify this when slave nodes are supported */

	payload_size = TLV_SPACE(sizeof(node_info)) * (tipc_max_nodes - 1);
	if (payload_size > 32768u) {
		read_unlock_bh(&tipc_net_lock);
		return tipc_cfg_reply_error_string(TIPC_CFG_NOT_SUPPORTED
						   " (too many nodes)");
	}
	buf = tipc_cfg_reply_alloc(payload_size);
	if (!buf) {
		read_unlock_bh(&tipc_net_lock);
		return NULL;
	}

	/* Add TLVs for all nodes in scope */

	for (n_ptr = tipc_nodes; n_ptr; n_ptr = n_ptr->next) {
		if (!tipc_in_scope(domain, n_ptr->addr))
			continue;
		node_info.addr = htonl(n_ptr->addr);
		node_info.up = htonl(tipc_node_is_up(n_ptr));
		tipc_cfg_append_tlv(buf, TIPC_TLV_NODE_INFO,
				    &node_info, sizeof(node_info));
	}

	read_unlock_bh(&tipc_net_lock);
	return buf;
}

struct sk_buff *tipc_node_get_links(const void *req_tlv_area, int req_tlv_space)
{
	u32 domain;
	struct sk_buff *buf;
	struct tipc_node *n_ptr;
	struct tipc_link_info link_info;
	u32 payload_size;

	if (!TLV_CHECK(req_tlv_area, req_tlv_space, TIPC_TLV_NET_ADDR))
		return tipc_cfg_reply_error_string(TIPC_CFG_TLV_ERROR);

	domain = ntohl(*(__be32 *)TLV_DATA(req_tlv_area));
	if (!tipc_addr_domain_valid(domain))
		return tipc_cfg_reply_error_string(TIPC_CFG_INVALID_VALUE
						   " (network address)");

	if (tipc_mode != TIPC_NET_MODE)
		return tipc_cfg_reply_none();

	read_lock_bh(&tipc_net_lock);

	/* Get space for all unicast links + multicast link */

	payload_size = TLV_SPACE(sizeof(link_info)) *
		(tipc_net.zones[tipc_zone(tipc_own_addr)]->links + 1);
	if (payload_size > 32768u) {
		read_unlock_bh(&tipc_net_lock);
		return tipc_cfg_reply_error_string(TIPC_CFG_NOT_SUPPORTED
						   " (too many links)");
	}
	buf = tipc_cfg_reply_alloc(payload_size);
	if (!buf) {
		read_unlock_bh(&tipc_net_lock);
		return NULL;
	}

	/* Add TLV for broadcast link */

	link_info.dest = htonl(tipc_own_addr & 0xfffff00);
	link_info.up = htonl(1);
	strlcpy(link_info.str, tipc_bclink_name, TIPC_MAX_LINK_NAME);
	tipc_cfg_append_tlv(buf, TIPC_TLV_LINK_INFO, &link_info, sizeof(link_info));

	/* Add TLVs for any other links in scope */

	for (n_ptr = tipc_nodes; n_ptr; n_ptr = n_ptr->next) {
		u32 i;

		if (!tipc_in_scope(domain, n_ptr->addr))
			continue;
		tipc_node_lock(n_ptr);
		for (i = 0; i < MAX_BEARERS; i++) {
			if (!n_ptr->links[i])
				continue;
			link_info.dest = htonl(n_ptr->addr);
			link_info.up = htonl(tipc_link_is_up(n_ptr->links[i]));
			strcpy(link_info.str, n_ptr->links[i]->name);
			tipc_cfg_append_tlv(buf, TIPC_TLV_LINK_INFO,
					    &link_info, sizeof(link_info));
		}
		tipc_node_unlock(n_ptr);
	}

	read_unlock_bh(&tipc_net_lock);
	return buf;
}