br_stp.c

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/*
 *  Spanning tree protocol; generic parts
 *  Linux ethernet bridge
 *
 *  Authors:
 *  Lennert Buytenhek       <[email protected]>
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 */
#include <linux/kernel.h>
#include <linux/rculist.h>

#include "br_private.h"
#include "br_private_stp.h"

/* since time values in bpdu are in jiffies and then scaled (1/256)
 * before sending, make sure that is at least one STP tick.
 */
#define MESSAGE_AGE_INCR    ((HZ / 256) + 1)

static const char *const br_port_state_names[] = {
    [BR_STATE_DISABLED] = "disabled",
    [BR_STATE_LISTENING] = "listening",
    [BR_STATE_LEARNING] = "learning",
    [BR_STATE_FORWARDING] = "forwarding",
    [BR_STATE_BLOCKING] = "blocking",
};

void br_log_state(const struct net_bridge_port *p)
{
    br_info(p->br, "port %u(%s) entered %s state\n",
        (unsigned int) p->port_no, p->dev->name,
        br_port_state_names[p->state]);
}

/* called under bridge lock */
struct net_bridge_port *br_get_port(struct net_bridge *br, u16 port_no)
{
    struct net_bridge_port *p;

    list_for_each_entry_rcu(p, &br->port_list, list) {
        if (p->port_no == port_no)
            return p;
    }

    return NULL;
}

/* called under bridge lock */
static int br_should_become_root_port(const struct net_bridge_port *p,
                      u16 root_port)
{
    struct net_bridge *br;
    struct net_bridge_port *rp;
    int t;

    br = p->br;
    if (p->state == BR_STATE_DISABLED ||
        br_is_designated_port(p))
        return 0;

    if (memcmp(&br->bridge_id, &p->designated_root, 8) <= 0)
        return 0;

    if (!root_port)
        return 1;

    rp = br_get_port(br, root_port);

    t = memcmp(&p->designated_root, &rp->designated_root, 8);
    if (t < 0)
        return 1;
    else if (t > 0)
        return 0;

    if (p->designated_cost + p->path_cost <
        rp->designated_cost + rp->path_cost)
        return 1;
    else if (p->designated_cost + p->path_cost >
         rp->designated_cost + rp->path_cost)
        return 0;

    t = memcmp(&p->designated_bridge, &rp->designated_bridge, 8);
    if (t < 0)
        return 1;
    else if (t > 0)
        return 0;

    if (p->designated_port < rp->designated_port)
        return 1;
    else if (p->designated_port > rp->designated_port)
        return 0;

    if (p->port_id < rp->port_id)
        return 1;

    return 0;
}

/* called under bridge lock */
static void br_root_selection(struct net_bridge *br)
{
    struct net_bridge_port *p;
    u16 root_port = 0;

    list_for_each_entry(p, &br->port_list, list) {
        if (br_should_become_root_port(p, root_port))
            root_port = p->port_no;
    }

    br->root_port = root_port;

    if (!root_port) {
        br->designated_root = br->bridge_id;
        br->root_path_cost = 0;
    } else {
        p = br_get_port(br, root_port);
        br->designated_root = p->designated_root;
        br->root_path_cost = p->designated_cost + p->path_cost;
    }
}

/* called under bridge lock */
void br_become_root_bridge(struct net_bridge *br)
{
    br->max_age = br->bridge_max_age;
    br->hello_time = br->bridge_hello_time;
    br->forward_delay = br->bridge_forward_delay;
    br_topology_change_detection(br);
    del_timer(&br->tcn_timer);

    if (br->dev->flags & IFF_UP) {
        br_config_bpdu_generation(br);
        mod_timer(&br->hello_timer, jiffies + br->hello_time);
    }
}

/* called under bridge lock */
void br_transmit_config(struct net_bridge_port *p)
{
    struct br_config_bpdu bpdu;
    struct net_bridge *br;

    if (timer_pending(&p->hold_timer)) {
        p->config_pending = 1;
        return;
    }

    br = p->br;

    bpdu.topology_change = br->topology_change;
    bpdu.topology_change_ack = p->topology_change_ack;
    bpdu.root = br->designated_root;
    bpdu.root_path_cost = br->root_path_cost;
    bpdu.bridge_id = br->bridge_id;
    bpdu.port_id = p->port_id;
    if (br_is_root_bridge(br))
        bpdu.message_age = 0;
    else {
        struct net_bridge_port *root
            = br_get_port(br, br->root_port);
        bpdu.message_age = (jiffies - root->designated_age)
            + MESSAGE_AGE_INCR;
    }
    bpdu.max_age = br->max_age;
    bpdu.hello_time = br->hello_time;
    bpdu.forward_delay = br->forward_delay;

    if (bpdu.message_age < br->max_age) {
        br_send_config_bpdu(p, &bpdu);
        p->topology_change_ack = 0;
        p->config_pending = 0;
        mod_timer(&p->hold_timer,
              round_jiffies(jiffies + BR_HOLD_TIME));
    }
}

/* called under bridge lock */
static void br_record_config_information(struct net_bridge_port *p,
                     const struct br_config_bpdu *bpdu)
{
    p->designated_root = bpdu->root;
    p->designated_cost = bpdu->root_path_cost;
    p->designated_bridge = bpdu->bridge_id;
    p->designated_port = bpdu->port_id;
    p->designated_age = jiffies - bpdu->message_age;

    mod_timer(&p->message_age_timer, jiffies
          + (p->br->max_age - bpdu->message_age));
}

/* called under bridge lock */
static void br_record_config_timeout_values(struct net_bridge *br,
                        const struct br_config_bpdu *bpdu)
{
    br->max_age = bpdu->max_age;
    br->hello_time = bpdu->hello_time;
    br->forward_delay = bpdu->forward_delay;
    br->topology_change = bpdu->topology_change;
}

/* called under bridge lock */
void br_transmit_tcn(struct net_bridge *br)
{
    br_send_tcn_bpdu(br_get_port(br, br->root_port));
}

/* called under bridge lock */
static int br_should_become_designated_port(const struct net_bridge_port *p)
{
    struct net_bridge *br;
    int t;

    br = p->br;
    if (br_is_designated_port(p))
        return 1;

    if (memcmp(&p->designated_root, &br->designated_root, 8))
        return 1;

    if (br->root_path_cost < p->designated_cost)
        return 1;
    else if (br->root_path_cost > p->designated_cost)
        return 0;

    t = memcmp(&br->bridge_id, &p->designated_bridge, 8);
    if (t < 0)
        return 1;
    else if (t > 0)
        return 0;

    if (p->port_id < p->designated_port)
        return 1;

    return 0;
}

/* called under bridge lock */
static void br_designated_port_selection(struct net_bridge *br)
{
    struct net_bridge_port *p;

    list_for_each_entry(p, &br->port_list, list) {
        if (p->state != BR_STATE_DISABLED &&
            br_should_become_designated_port(p))
            br_become_designated_port(p);

    }
}

/* called under bridge lock */
static int br_supersedes_port_info(const struct net_bridge_port *p,
                   const struct br_config_bpdu *bpdu)
{
    int t;

    t = memcmp(&bpdu->root, &p->designated_root, 8);
    if (t < 0)
        return 1;
    else if (t > 0)
        return 0;

    if (bpdu->root_path_cost < p->designated_cost)
        return 1;
    else if (bpdu->root_path_cost > p->designated_cost)
        return 0;

    t = memcmp(&bpdu->bridge_id, &p->designated_bridge, 8);
    if (t < 0)
        return 1;
    else if (t > 0)
        return 0;

    if (memcmp(&bpdu->bridge_id, &p->br->bridge_id, 8))
        return 1;

    if (bpdu->port_id <= p->designated_port)
        return 1;

    return 0;
}

/* called under bridge lock */
static void br_topology_change_acknowledged(struct net_bridge *br)
{
    br->topology_change_detected = 0;
    del_timer(&br->tcn_timer);
}

/* called under bridge lock */
void br_topology_change_detection(struct net_bridge *br)
{
    int isroot = br_is_root_bridge(br);

    if (br->stp_enabled != BR_KERNEL_STP)
        return;

    br_info(br, "topology change detected, %s\n",
        isroot ? "propagating" : "sending tcn bpdu");

    if (isroot) {
        br->topology_change = 1;
        mod_timer(&br->topology_change_timer, jiffies
              + br->bridge_forward_delay + br->bridge_max_age);
    } else if (!br->topology_change_detected) {
        br_transmit_tcn(br);
        mod_timer(&br->tcn_timer, jiffies + br->bridge_hello_time);
    }

    br->topology_change_detected = 1;
}

/* called under bridge lock */
void br_config_bpdu_generation(struct net_bridge *br)
{
    struct net_bridge_port *p;

    list_for_each_entry(p, &br->port_list, list) {
        if (p->state != BR_STATE_DISABLED &&
            br_is_designated_port(p))
            br_transmit_config(p);
    }
}

/* called under bridge lock */
static void br_reply(struct net_bridge_port *p)
{
    br_transmit_config(p);
}

/* called under bridge lock */
void br_configuration_update(struct net_bridge *br)
{
    br_root_selection(br);
    br_designated_port_selection(br);
}

/* called under bridge lock */
void br_become_designated_port(struct net_bridge_port *p)
{
    struct net_bridge *br;

    br = p->br;
    p->designated_root = br->designated_root;
    p->designated_cost = br->root_path_cost;
    p->designated_bridge = br->bridge_id;
    p->designated_port = p->port_id;
}


/* called under bridge lock */
static void br_make_blocking(struct net_bridge_port *p)
{
    if (p->state != BR_STATE_DISABLED &&
        p->state != BR_STATE_BLOCKING) {
        if (p->state == BR_STATE_FORWARDING ||
            p->state == BR_STATE_LEARNING)
            br_topology_change_detection(p->br);

        p->state = BR_STATE_BLOCKING;
        br_log_state(p);
        br_ifinfo_notify(RTM_NEWLINK, p);

        del_timer(&p->forward_delay_timer);
    }
}

/* called under bridge lock */
static void br_make_forwarding(struct net_bridge_port *p)
{
    struct net_bridge *br = p->br;

    if (p->state != BR_STATE_BLOCKING)
        return;

    if (br->stp_enabled == BR_NO_STP || br->forward_delay == 0) {
        p->state = BR_STATE_FORWARDING;
        br_topology_change_detection(br);
        del_timer(&p->forward_delay_timer);
    } else if (br->stp_enabled == BR_KERNEL_STP)
        p->state = BR_STATE_LISTENING;
    else
        p->state = BR_STATE_LEARNING;

    br_multicast_enable_port(p);
    br_log_state(p);
    br_ifinfo_notify(RTM_NEWLINK, p);

    if (br->forward_delay != 0)
        mod_timer(&p->forward_delay_timer, jiffies + br->forward_delay);
}

/* called under bridge lock */
void br_port_state_selection(struct net_bridge *br)
{
    struct net_bridge_port *p;
    unsigned int liveports = 0;

    list_for_each_entry(p, &br->port_list, list) {
        if (p->state == BR_STATE_DISABLED)
            continue;

        /* Don't change port states if userspace is handling STP */
        if (br->stp_enabled != BR_USER_STP) {
            if (p->port_no == br->root_port) {
                p->config_pending = 0;
                p->topology_change_ack = 0;
                br_make_forwarding(p);
            } else if (br_is_designated_port(p)) {
                del_timer(&p->message_age_timer);
                br_make_forwarding(p);
            } else {
                p->config_pending = 0;
                p->topology_change_ack = 0;
                br_make_blocking(p);
            }
        }

        if (p->state == BR_STATE_FORWARDING)
            ++liveports;
    }

    if (liveports == 0)
        netif_carrier_off(br->dev);
    else
        netif_carrier_on(br->dev);
}

/* called under bridge lock */
static void br_topology_change_acknowledge(struct net_bridge_port *p)
{
    p->topology_change_ack = 1;
    br_transmit_config(p);
}

/* called under bridge lock */
void br_received_config_bpdu(struct net_bridge_port *p,
                 const struct br_config_bpdu *bpdu)
{
    struct net_bridge *br;
    int was_root;

    br = p->br;
    was_root = br_is_root_bridge(br);

    if (br_supersedes_port_info(p, bpdu)) {
        br_record_config_information(p, bpdu);
        br_configuration_update(br);
        br_port_state_selection(br);

        if (!br_is_root_bridge(br) && was_root) {
            del_timer(&br->hello_timer);
            if (br->topology_change_detected) {
                del_timer(&br->topology_change_timer);
                br_transmit_tcn(br);

                mod_timer(&br->tcn_timer,
                      jiffies + br->bridge_hello_time);
            }
        }

        if (p->port_no == br->root_port) {
            br_record_config_timeout_values(br, bpdu);
            br_config_bpdu_generation(br);
            if (bpdu->topology_change_ack)
                br_topology_change_acknowledged(br);
        }
    } else if (br_is_designated_port(p)) {
        br_reply(p);
    }
}

/* called under bridge lock */
void br_received_tcn_bpdu(struct net_bridge_port *p)
{
    if (br_is_designated_port(p)) {
        br_info(p->br, "port %u(%s) received tcn bpdu\n",
            (unsigned int) p->port_no, p->dev->name);

        br_topology_change_detection(p->br);
        br_topology_change_acknowledge(p);
    }
}

/* Change bridge STP parameter */
int br_set_hello_time(struct net_bridge *br, unsigned long val)
{
    unsigned long t = clock_t_to_jiffies(val);

    if (t < BR_MIN_HELLO_TIME || t > BR_MAX_HELLO_TIME)
        return -ERANGE;

    spin_lock_bh(&br->lock);
    br->bridge_hello_time = t;
    if (br_is_root_bridge(br))
        br->hello_time = br->bridge_hello_time;
    spin_unlock_bh(&br->lock);
    return 0;
}

int br_set_max_age(struct net_bridge *br, unsigned long val)
{
    unsigned long t = clock_t_to_jiffies(val);

    if (t < BR_MIN_MAX_AGE || t > BR_MAX_MAX_AGE)
        return -ERANGE;

    spin_lock_bh(&br->lock);
    br->bridge_max_age = t;
    if (br_is_root_bridge(br))
        br->max_age = br->bridge_max_age;
    spin_unlock_bh(&br->lock);
    return 0;

}

int br_set_forward_delay(struct net_bridge *br, unsigned long val)
{
    unsigned long t = clock_t_to_jiffies(val);

    if (br->stp_enabled != BR_NO_STP &&
        (t < BR_MIN_FORWARD_DELAY || t > BR_MAX_FORWARD_DELAY))
        return -ERANGE;

    spin_lock_bh(&br->lock);
    br->bridge_forward_delay = t;
    if (br_is_root_bridge(br))
        br->forward_delay = br->bridge_forward_delay;
    spin_unlock_bh(&br->lock);
    return 0;
}