net/tipc/discover.c - kernel/msm-4.9 - Gitiles

 /*
  * net/tipc/discover.c
  *
  * Copyright (c) 2003-2006, Ericsson AB
  * Copyright (c) 2005-2006, 2010-2011, 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 "link.h"
 #include "discover.h"

 #define TIPC_LINK_REQ_INIT	125	/* min delay during bearer start up */
 #define TIPC_LINK_REQ_FAST	1000	/* max delay if bearer has no links */
 #define TIPC_LINK_REQ_SLOW	60000	/* max delay if bearer has links */
 #define TIPC_LINK_REQ_INACTIVE	0xffffffff /* indicates no timer in use */


 /**
  * struct tipc_link_req - information about an ongoing link setup request
  * @bearer: bearer issuing requests
  * @dest: destination address for request messages
  * @domain: network domain to which links can be established
  * @num_nodes: number of nodes currently discovered (i.e. with an active link)
  * @buf: request message to be (repeatedly) sent
  * @timer: timer governing period between requests
  * @timer_intv: current interval between requests (in ms)
  */
 struct tipc_link_req {
 	struct tipc_bearer *bearer;
 	struct tipc_media_addr dest;
 	u32 domain;
 	int num_nodes;
 	struct sk_buff *buf;
 	struct timer_list timer;
 	unsigned int timer_intv;
 };

 /**
  * tipc_disc_init_msg - initialize a link setup message
  * @type: message type (request or response)
  * @dest_domain: network domain of node(s) which should respond to message
  * @b_ptr: ptr to bearer issuing message
  */
 static struct sk_buff *tipc_disc_init_msg(u32 type,
 					  u32 dest_domain,
 					  struct tipc_bearer *b_ptr)
 {
 	struct sk_buff *buf = tipc_buf_acquire(INT_H_SIZE);
 	struct tipc_msg *msg;

 	if (buf) {
 		msg = buf_msg(buf);
 		tipc_msg_init(msg, LINK_CONFIG, type, INT_H_SIZE, dest_domain);
 		msg_set_non_seq(msg, 1);
 		msg_set_node_sig(msg, tipc_random);
 		msg_set_dest_domain(msg, dest_domain);
 		msg_set_bc_netid(msg, tipc_net_id);
 		b_ptr->media->addr2msg(&b_ptr->addr, msg_media_addr(msg));
 	}
 	return buf;
 }

 /**
  * disc_dupl_alert - issue node address duplication alert
  * @b_ptr: pointer to bearer detecting duplication
  * @node_addr: duplicated node address
  * @media_addr: media address advertised by duplicated node
  */
 static void disc_dupl_alert(struct tipc_bearer *b_ptr, u32 node_addr,
 			    struct tipc_media_addr *media_addr)
 {
 	char node_addr_str[16];
 	char media_addr_str[64];

 	tipc_addr_string_fill(node_addr_str, node_addr);
 	tipc_media_addr_printf(media_addr_str, sizeof(media_addr_str),
 			       media_addr);
 	pr_warn("Duplicate %s using %s seen on <%s>\n", node_addr_str,
 		media_addr_str, b_ptr->name);
 }

 /**
  * tipc_disc_recv_msg - handle incoming link setup message (request or response)
  * @buf: buffer containing message
  * @b_ptr: bearer that message arrived on
  */
 void tipc_disc_recv_msg(struct sk_buff *buf, struct tipc_bearer *b_ptr)
 {
 	struct tipc_node *n_ptr;
 	struct tipc_link *link;
 	struct tipc_media_addr media_addr;
 	struct sk_buff *rbuf;
 	struct tipc_msg *msg = buf_msg(buf);
 	u32 dest = msg_dest_domain(msg);
 	u32 orig = msg_prevnode(msg);
 	u32 net_id = msg_bc_netid(msg);
 	u32 type = msg_type(msg);
 	u32 signature = msg_node_sig(msg);
 	int addr_mismatch;
 	int link_fully_up;

 	media_addr.broadcast = 1;
 	b_ptr->media->msg2addr(&media_addr, msg_media_addr(msg));
 	kfree_skb(buf);

 	/* Ensure message from node is valid and communication is permitted */
 	if (net_id != tipc_net_id)
 		return;
 	if (media_addr.broadcast)
 		return;
 	if (!tipc_addr_domain_valid(dest))
 		return;
 	if (!tipc_addr_node_valid(orig))
 		return;
 	if (orig == tipc_own_addr) {
 		if (memcmp(&media_addr, &b_ptr->addr, sizeof(media_addr)))
 			disc_dupl_alert(b_ptr, tipc_own_addr, &media_addr);
 		return;
 	}
 	if (!tipc_in_scope(dest, tipc_own_addr))
 		return;
 	if (!tipc_in_scope(b_ptr->link_req->domain, orig))
 		return;

 	/* Locate structure corresponding to requesting node */
 	n_ptr = tipc_node_find(orig);
 	if (!n_ptr) {
 		n_ptr = tipc_node_create(orig);
 		if (!n_ptr)
 			return;
 	}
 	tipc_node_lock(n_ptr);

 	/* Prepare to validate requesting node's signature and media address */
 	link = n_ptr->links[b_ptr->identity];
 	addr_mismatch = (link != NULL) &&
 		memcmp(&link->media_addr, &media_addr, sizeof(media_addr));

 	/*
 	 * Ensure discovery message's signature is correct
 	 *
 	 * If signature is incorrect and there is no working link to the node,
 	 * accept the new signature but invalidate all existing links to the
 	 * node so they won't re-activate without a new discovery message.
 	 *
 	 * If signature is incorrect and the requested link to the node is
 	 * working, accept the new signature. (This is an instance of delayed
 	 * rediscovery, where a link endpoint was able to re-establish contact
 	 * with its peer endpoint on a node that rebooted before receiving a
 	 * discovery message from that node.)
 	 *
 	 * If signature is incorrect and there is a working link to the node
 	 * that is not the requested link, reject the request (must be from
 	 * a duplicate node).
 	 */
 	if (signature != n_ptr->signature) {
 		if (n_ptr->working_links == 0) {
 			struct tipc_link *curr_link;
 			int i;

 			for (i = 0; i < MAX_BEARERS; i++) {
 				curr_link = n_ptr->links[i];
 				if (curr_link) {
 					memset(&curr_link->media_addr, 0,
 					       sizeof(media_addr));
 					tipc_link_reset(curr_link);
 				}
 			}
 			addr_mismatch = (link != NULL);
 		} else if (tipc_link_is_up(link) && !addr_mismatch) {
 			/* delayed rediscovery */
 		} else {
 			disc_dupl_alert(b_ptr, orig, &media_addr);
 			tipc_node_unlock(n_ptr);
 			return;
 		}
 		n_ptr->signature = signature;
 	}

 	/*
 	 * Ensure requesting node's media address is correct
 	 *
 	 * If media address doesn't match and the link is working, reject the
 	 * request (must be from a duplicate node).
 	 *
 	 * If media address doesn't match and the link is not working, accept
 	 * the new media address and reset the link to ensure it starts up
 	 * cleanly.
 	 */
 	if (addr_mismatch) {
 		if (tipc_link_is_up(link)) {
 			disc_dupl_alert(b_ptr, orig, &media_addr);
 			tipc_node_unlock(n_ptr);
 			return;
 		} else {
 			memcpy(&link->media_addr, &media_addr,
 			       sizeof(media_addr));
 			tipc_link_reset(link);
 		}
 	}

 	/* Create a link endpoint for this bearer, if necessary */
 	if (!link) {
 		link = tipc_link_create(n_ptr, b_ptr, &media_addr);
 		if (!link) {
 			tipc_node_unlock(n_ptr);
 			return;
 		}
 	}

 	/* Accept discovery message & send response, if necessary */
 	link_fully_up = link_working_working(link);

 	if ((type == DSC_REQ_MSG) && !link_fully_up && !b_ptr->blocked) {
 		rbuf = tipc_disc_init_msg(DSC_RESP_MSG, orig, b_ptr);
 		if (rbuf) {
 			b_ptr->media->send_msg(rbuf, b_ptr, &media_addr);
 			kfree_skb(rbuf);
 		}
 	}

 	tipc_node_unlock(n_ptr);
 }

 /**
  * disc_update - update frequency of periodic link setup requests
  * @req: ptr to link request structure
  *
  * Reinitiates discovery process if discovery object has no associated nodes
  * and is either not currently searching or is searching at a slow rate
  */
 static void disc_update(struct tipc_link_req *req)
 {
 	if (!req->num_nodes) {
 		if ((req->timer_intv == TIPC_LINK_REQ_INACTIVE) ||
 		    (req->timer_intv > TIPC_LINK_REQ_FAST)) {
 			req->timer_intv = TIPC_LINK_REQ_INIT;
 			k_start_timer(&req->timer, req->timer_intv);
 		}
 	}
 }

 /**
  * tipc_disc_add_dest - increment set of discovered nodes
  * @req: ptr to link request structure
  */
 void tipc_disc_add_dest(struct tipc_link_req *req)
 {
 	req->num_nodes++;
 }

 /**
  * tipc_disc_remove_dest - decrement set of discovered nodes
  * @req: ptr to link request structure
  */
 void tipc_disc_remove_dest(struct tipc_link_req *req)
 {
 	req->num_nodes--;
 	disc_update(req);
 }

 /**
  * disc_send_msg - send link setup request message
  * @req: ptr to link request structure
  */
 static void disc_send_msg(struct tipc_link_req *req)
 {
 	if (!req->bearer->blocked)
 		tipc_bearer_send(req->bearer, req->buf, &req->dest);
 }

 /**
  * disc_timeout - send a periodic link setup request
  * @req: ptr to link request structure
  *
  * Called whenever a link setup request timer associated with a bearer expires.
  */
 static void disc_timeout(struct tipc_link_req *req)
 {
 	int max_delay;

 	spin_lock_bh(&req->bearer->lock);

 	/* Stop searching if only desired node has been found */
 	if (tipc_node(req->domain) && req->num_nodes) {
 		req->timer_intv = TIPC_LINK_REQ_INACTIVE;
 		goto exit;
 	}

 	/*
 	 * Send discovery message, then update discovery timer
 	 *
 	 * Keep doubling time between requests until limit is reached;
 	 * hold at fast polling rate if don't have any associated nodes,
 	 * otherwise hold at slow polling rate
 	 */
 	disc_send_msg(req);

 	req->timer_intv *= 2;
 	if (req->num_nodes)
 		max_delay = TIPC_LINK_REQ_SLOW;
 	else
 		max_delay = TIPC_LINK_REQ_FAST;
 	if (req->timer_intv > max_delay)
 		req->timer_intv = max_delay;

 	k_start_timer(&req->timer, req->timer_intv);
 exit:
 	spin_unlock_bh(&req->bearer->lock);
 }

 /**
  * tipc_disc_create - create object to send periodic link setup requests
  * @b_ptr: ptr to bearer issuing requests
  * @dest: destination address for request messages
  * @dest_domain: network domain to which links can be established
  *
  * Returns 0 if successful, otherwise -errno.
  */
 int tipc_disc_create(struct tipc_bearer *b_ptr,
 		     struct tipc_media_addr *dest, u32 dest_domain)
 {
 	struct tipc_link_req *req;

 	req = kmalloc(sizeof(*req), GFP_ATOMIC);
 	if (!req)
 		return -ENOMEM;

 	req->buf = tipc_disc_init_msg(DSC_REQ_MSG, dest_domain, b_ptr);
 	if (!req->buf) {
 		kfree(req);
 		return -ENOMSG;
 	}

 	memcpy(&req->dest, dest, sizeof(*dest));
 	req->bearer = b_ptr;
 	req->domain = dest_domain;
 	req->num_nodes = 0;
 	req->timer_intv = TIPC_LINK_REQ_INIT;
 	k_init_timer(&req->timer, (Handler)disc_timeout, (unsigned long)req);
 	k_start_timer(&req->timer, req->timer_intv);
 	b_ptr->link_req = req;
 	disc_send_msg(req);
 	return 0;
 }

 /**
  * tipc_disc_delete - destroy object sending periodic link setup requests
  * @req: ptr to link request structure
  */
 void tipc_disc_delete(struct tipc_link_req *req)
 {
 	k_cancel_timer(&req->timer);
 	k_term_timer(&req->timer);
 	kfree_skb(req->buf);
 	kfree(req);
 }
	/*
	* net/tipc/discover.c
	*
	* Copyright (c) 2003-2006, Ericsson AB
	* Copyright (c) 2005-2006, 2010-2011, 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 "link.h"
	#include "discover.h"

	#define TIPC_LINK_REQ_INIT 125 /* min delay during bearer start up */
	#define TIPC_LINK_REQ_FAST 1000 /* max delay if bearer has no links */
	#define TIPC_LINK_REQ_SLOW 60000 /* max delay if bearer has links */
	#define TIPC_LINK_REQ_INACTIVE 0xffffffff /* indicates no timer in use */


	/**
	* struct tipc_link_req - information about an ongoing link setup request
	* @bearer: bearer issuing requests
	* @dest: destination address for request messages
	* @domain: network domain to which links can be established
	* @num_nodes: number of nodes currently discovered (i.e. with an active link)
	* @buf: request message to be (repeatedly) sent
	* @timer: timer governing period between requests
	* @timer_intv: current interval between requests (in ms)
	*/
	struct tipc_link_req {
	struct tipc_bearer *bearer;
	struct tipc_media_addr dest;
	u32 domain;
	int num_nodes;
	struct sk_buff *buf;
	struct timer_list timer;
	unsigned int timer_intv;
	};

	/**
	* tipc_disc_init_msg - initialize a link setup message
	* @type: message type (request or response)
	* @dest_domain: network domain of node(s) which should respond to message
	* @b_ptr: ptr to bearer issuing message
	*/
	static struct sk_buff *tipc_disc_init_msg(u32 type,
	u32 dest_domain,
	struct tipc_bearer *b_ptr)
	{
	struct sk_buff *buf = tipc_buf_acquire(INT_H_SIZE);
	struct tipc_msg *msg;

	if (buf) {
	msg = buf_msg(buf);
	tipc_msg_init(msg, LINK_CONFIG, type, INT_H_SIZE, dest_domain);
	msg_set_non_seq(msg, 1);
	msg_set_node_sig(msg, tipc_random);
	msg_set_dest_domain(msg, dest_domain);
	msg_set_bc_netid(msg, tipc_net_id);
	b_ptr->media->addr2msg(&b_ptr->addr, msg_media_addr(msg));
	}
	return buf;
	}

	/**
	* disc_dupl_alert - issue node address duplication alert
	* @b_ptr: pointer to bearer detecting duplication
	* @node_addr: duplicated node address
	* @media_addr: media address advertised by duplicated node
	*/
	static void disc_dupl_alert(struct tipc_bearer *b_ptr, u32 node_addr,
	struct tipc_media_addr *media_addr)
	{
	char node_addr_str[16];
	char media_addr_str[64];

	tipc_addr_string_fill(node_addr_str, node_addr);
	tipc_media_addr_printf(media_addr_str, sizeof(media_addr_str),
	media_addr);
	pr_warn("Duplicate %s using %s seen on <%s>\n", node_addr_str,
	media_addr_str, b_ptr->name);
	}

	/**
	* tipc_disc_recv_msg - handle incoming link setup message (request or response)
	* @buf: buffer containing message
	* @b_ptr: bearer that message arrived on
	*/
	void tipc_disc_recv_msg(struct sk_buff buf, struct tipc_bearer b_ptr)
	{
	struct tipc_node *n_ptr;
	struct tipc_link *link;
	struct tipc_media_addr media_addr;
	struct sk_buff *rbuf;
	struct tipc_msg *msg = buf_msg(buf);
	u32 dest = msg_dest_domain(msg);
	u32 orig = msg_prevnode(msg);
	u32 net_id = msg_bc_netid(msg);
	u32 type = msg_type(msg);
	u32 signature = msg_node_sig(msg);
	int addr_mismatch;
	int link_fully_up;

	media_addr.broadcast = 1;
	b_ptr->media->msg2addr(&media_addr, msg_media_addr(msg));
	kfree_skb(buf);

	/* Ensure message from node is valid and communication is permitted */
	if (net_id != tipc_net_id)
	return;
	if (media_addr.broadcast)
	return;
	if (!tipc_addr_domain_valid(dest))
	return;
	if (!tipc_addr_node_valid(orig))
	return;
	if (orig == tipc_own_addr) {
	if (memcmp(&media_addr, &b_ptr->addr, sizeof(media_addr)))
	disc_dupl_alert(b_ptr, tipc_own_addr, &media_addr);
	return;
	}
	if (!tipc_in_scope(dest, tipc_own_addr))
	return;
	if (!tipc_in_scope(b_ptr->link_req->domain, orig))
	return;

	/* Locate structure corresponding to requesting node */
	n_ptr = tipc_node_find(orig);
	if (!n_ptr) {
	n_ptr = tipc_node_create(orig);
	if (!n_ptr)
	return;
	}
	tipc_node_lock(n_ptr);

	/* Prepare to validate requesting node's signature and media address */
	link = n_ptr->links[b_ptr->identity];
	addr_mismatch = (link != NULL) &&
	memcmp(&link->media_addr, &media_addr, sizeof(media_addr));

	/*
	* Ensure discovery message's signature is correct
	*
	* If signature is incorrect and there is no working link to the node,
	* accept the new signature but invalidate all existing links to the
	* node so they won't re-activate without a new discovery message.
	*
	* If signature is incorrect and the requested link to the node is
	* working, accept the new signature. (This is an instance of delayed
	* rediscovery, where a link endpoint was able to re-establish contact
	* with its peer endpoint on a node that rebooted before receiving a
	* discovery message from that node.)
	*
	* If signature is incorrect and there is a working link to the node
	* that is not the requested link, reject the request (must be from
	* a duplicate node).
	*/
	if (signature != n_ptr->signature) {
	if (n_ptr->working_links == 0) {
	struct tipc_link *curr_link;
	int i;

	for (i = 0; i < MAX_BEARERS; i++) {
	curr_link = n_ptr->links[i];
	if (curr_link) {
	memset(&curr_link->media_addr, 0,
	sizeof(media_addr));
	tipc_link_reset(curr_link);
	}
	}
	addr_mismatch = (link != NULL);
	} else if (tipc_link_is_up(link) && !addr_mismatch) {
	/* delayed rediscovery */
	} else {
	disc_dupl_alert(b_ptr, orig, &media_addr);
	tipc_node_unlock(n_ptr);
	return;
	}
	n_ptr->signature = signature;
	}

	/*
	* Ensure requesting node's media address is correct
	*
	* If media address doesn't match and the link is working, reject the
	* request (must be from a duplicate node).
	*
	* If media address doesn't match and the link is not working, accept
	* the new media address and reset the link to ensure it starts up
	* cleanly.
	*/
	if (addr_mismatch) {
	if (tipc_link_is_up(link)) {
	disc_dupl_alert(b_ptr, orig, &media_addr);
	tipc_node_unlock(n_ptr);
	return;
	} else {
	memcpy(&link->media_addr, &media_addr,
	sizeof(media_addr));
	tipc_link_reset(link);
	}
	}

	/* Create a link endpoint for this bearer, if necessary */
	if (!link) {
	link = tipc_link_create(n_ptr, b_ptr, &media_addr);
	if (!link) {
	tipc_node_unlock(n_ptr);
	return;
	}
	}

	/* Accept discovery message & send response, if necessary */
	link_fully_up = link_working_working(link);

	if ((type == DSC_REQ_MSG) && !link_fully_up && !b_ptr->blocked) {
	rbuf = tipc_disc_init_msg(DSC_RESP_MSG, orig, b_ptr);
	if (rbuf) {
	b_ptr->media->send_msg(rbuf, b_ptr, &media_addr);
	kfree_skb(rbuf);
	}
	}

	tipc_node_unlock(n_ptr);
	}

	/**
	* disc_update - update frequency of periodic link setup requests
	* @req: ptr to link request structure
	*
	* Reinitiates discovery process if discovery object has no associated nodes
	* and is either not currently searching or is searching at a slow rate
	*/
	static void disc_update(struct tipc_link_req *req)
	{
	if (!req->num_nodes) {
	if ((req->timer_intv == TIPC_LINK_REQ_INACTIVE) \|\|
	(req->timer_intv > TIPC_LINK_REQ_FAST)) {
	req->timer_intv = TIPC_LINK_REQ_INIT;
	k_start_timer(&req->timer, req->timer_intv);
	}
	}
	}

	/**
	* tipc_disc_add_dest - increment set of discovered nodes
	* @req: ptr to link request structure
	*/
	void tipc_disc_add_dest(struct tipc_link_req *req)
	{
	req->num_nodes++;
	}

	/**
	* tipc_disc_remove_dest - decrement set of discovered nodes
	* @req: ptr to link request structure
	*/
	void tipc_disc_remove_dest(struct tipc_link_req *req)
	{
	req->num_nodes--;
	disc_update(req);
	}

	/**
	* disc_send_msg - send link setup request message
	* @req: ptr to link request structure
	*/
	static void disc_send_msg(struct tipc_link_req *req)
	{
	if (!req->bearer->blocked)
	tipc_bearer_send(req->bearer, req->buf, &req->dest);
	}

	/**
	* disc_timeout - send a periodic link setup request
	* @req: ptr to link request structure
	*
	* Called whenever a link setup request timer associated with a bearer expires.
	*/
	static void disc_timeout(struct tipc_link_req *req)
	{
	int max_delay;

	spin_lock_bh(&req->bearer->lock);

	/* Stop searching if only desired node has been found */
	if (tipc_node(req->domain) && req->num_nodes) {
	req->timer_intv = TIPC_LINK_REQ_INACTIVE;
	goto exit;
	}

	/*
	* Send discovery message, then update discovery timer
	*
	* Keep doubling time between requests until limit is reached;
	* hold at fast polling rate if don't have any associated nodes,
	* otherwise hold at slow polling rate
	*/
	disc_send_msg(req);

	req->timer_intv *= 2;
	if (req->num_nodes)
	max_delay = TIPC_LINK_REQ_SLOW;
	else
	max_delay = TIPC_LINK_REQ_FAST;
	if (req->timer_intv > max_delay)
	req->timer_intv = max_delay;

	k_start_timer(&req->timer, req->timer_intv);
	exit:
	spin_unlock_bh(&req->bearer->lock);
	}

	/**
	* tipc_disc_create - create object to send periodic link setup requests
	* @b_ptr: ptr to bearer issuing requests
	* @dest: destination address for request messages
	* @dest_domain: network domain to which links can be established
	*
	* Returns 0 if successful, otherwise -errno.
	*/
	int tipc_disc_create(struct tipc_bearer *b_ptr,
	struct tipc_media_addr *dest, u32 dest_domain)
	{
	struct tipc_link_req *req;

	req = kmalloc(sizeof(*req), GFP_ATOMIC);
	if (!req)
	return -ENOMEM;

	req->buf = tipc_disc_init_msg(DSC_REQ_MSG, dest_domain, b_ptr);
	if (!req->buf) {
	kfree(req);
	return -ENOMSG;
	}

	memcpy(&req->dest, dest, sizeof(*dest));
	req->bearer = b_ptr;
	req->domain = dest_domain;
	req->num_nodes = 0;
	req->timer_intv = TIPC_LINK_REQ_INIT;
	k_init_timer(&req->timer, (Handler)disc_timeout, (unsigned long)req);
	k_start_timer(&req->timer, req->timer_intv);
	b_ptr->link_req = req;
	disc_send_msg(req);
	return 0;
	}

	/**
	* tipc_disc_delete - destroy object sending periodic link setup requests
	* @req: ptr to link request structure
	*/
	void tipc_disc_delete(struct tipc_link_req *req)
	{
	k_cancel_timer(&req->timer);
	k_term_timer(&req->timer);
	kfree_skb(req->buf);
	kfree(req);
	}