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linux/net/bridge/br_stp.c
Stephen Hemminger ef647f1300 bridge: Eliminate unnecessary forward delay 
From: Stephen Hemminger <shemminger@vyatta.com>

Based upon original patch by Herbert Xu, which contained
the following problem description:

--------------------
When the forward delay is set to zero, we still delay the setting
of the forwarding state by one or possibly two timers depending
on whether STP is enabled.  This could either turn out to be
instantaneous, or horribly slow depending on the load of the
machine.

As there is nothing preventing us from enabling forwarding straight
away, this patch eliminates this potential delay by executing the
code directly if the forward delay is zero.

The effect of this problem is that immediately after the carrier
comes on a port, the bridge will drop all packets received from
that port until it enters forwarding mode, thus causing unnecessary
packet loss.

Note that this patch doesn't fully remove the delay due to the
link watcher.  We should also check the carrier state when we
are about to drop an incoming packet because the port is disabled.
But that's for another patch.
--------------------

This version of the fix takes a different approach, in that
it just does the state change directly.

Signed-off-by: David S. Miller <davem@davemloft.net>
2008-08-05 18:42:51 -07:00

474 lines
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/*
* Spanning tree protocol; generic parts
* Linux ethernet bridge
*
* Authors:
* Lennert Buytenhek <buytenh@gnu.org>
*
* 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.
*/
#define MESSAGE_AGE_INCR ((HZ < 256) ? 1 : (HZ/256))
static const char *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)
{
pr_info("%s: port %d(%s) entering %s state\n",
p->br->dev->name, 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 = br->max_age
- (root->message_age_timer.expires - jiffies)
+ 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 inline 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;
mod_timer(&p->message_age_timer, jiffies
+ (p->br->max_age - bpdu->message_age));
}
/* called under bridge lock */
static inline 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(struct net_bridge_port *p, 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 inline 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);
pr_info("%s: topology change detected, %s\n", br->dev->name,
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 inline 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);
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->forward_delay == 0) {
p->state = BR_STATE_FORWARDING;
br_topology_change_detection(br);
del_timer(&p->forward_delay_timer);
}
else if (p->br->stp_enabled == BR_KERNEL_STP)
p->state = BR_STATE_LISTENING;
else
p->state = BR_STATE_LEARNING;
br_log_state(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;
/* Don't change port states if userspace is handling STP */
if (br->stp_enabled == BR_USER_STP)
return;
list_for_each_entry(p, &br->port_list, list) {
if (p->state != BR_STATE_DISABLED) {
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);
}
}
}
}
/* called under bridge lock */
static inline 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, 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)) {
pr_info("%s: received tcn bpdu on port %i(%s)\n",
p->br->dev->name, p->port_no, p->dev->name);
br_topology_change_detection(p->br);
br_topology_change_acknowledge(p);
}
}
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