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[dhcp] Extract timing parameters out to config/dhcp.h
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iPXE uses DHCP timeouts loosely based on values recommended by the
specification, but often abbreviated to reduce timeouts for reliable
and/or simple network topologies.  Extract the DHCP timing parameters
to config/dhcp.h and document them.  The resulting default iPXE
behavior is exactly the same, but downstreams are now afforded the
opportunity to implement spec-compliant behavior via config file
overrides.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Modified-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
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@awilliam @mcb30
awilliam authored and mcb30 committed Feb 25, 2015
1 parent 5350b65 commit 47aebc2
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Showing 3 changed files with 106 additions and 23 deletions.
87 changes: 87 additions & 0 deletions src/config/dhcp.h
View file
@@ -0,0 +1,87 @@
#ifndef CONFIG_DHCP_H
#define CONFIG_DHCP_H

/** @file
*
* DHCP configuration
*
*/

FILE_LICENCE ( GPL2_OR_LATER );

#include <config/defaults.h>

/*
* DHCP and PXE Boot Server timeout parameters
*
* Initial and final timeout for DHCP discovery
*
* The PXE spec indicates discover request are sent 4 times, with
* timeouts of 4, 8, 16, 32 seconds. iPXE by default uses 1, 2, 4, 8.
*/
#define DHCP_DISC_START_TIMEOUT_SEC 1
#define DHCP_DISC_END_TIMEOUT_SEC 10
//#define DHCP_DISC_START_TIMEOUT_SEC 4 /* as per PXE spec */
//#define DHCP_DISC_END_TIMEOUT_SEC 32 /* as per PXE spec */

/*
* ProxyDHCP offers are given precedence by continue to wait for them
* after a valid DHCPOFFER is received. We'll wait through this
* timeout for it. The PXE spec indicates waiting through the 4 & 8
* second timeouts, iPXE by default stops after 2.
*/
#define DHCP_DISC_PROXY_TIMEOUT_SEC 2
//#define DHCP_DISC_PROXY_TIMEOUT_SEC 11 /* as per PXE spec */

/*
* Per the PXE spec, requests are also tried 4 times, but at timeout
* intervals of 1, 2, 3, 4 seconds. To adapt this to an exponential
* backoff timer, we can either do 1, 2, 4, 8, ie. 4 retires with a
* longer interval or start at 0 (0.25s) for 0.25, 0.5, 1, 2, 4,
* ie. one extra try and shorter initial timeouts. iPXE by default
* does a combination of both, starting at 0 and going through the 8
* second timeout.
*/
#define DHCP_REQ_START_TIMEOUT_SEC 0
#define DHCP_REQ_END_TIMEOUT_SEC 10
//#define DHCP_REQ_END_TIMEOUT_SEC 4 /* as per PXE spec */

/*
* A ProxyDHCP offer without PXE options also goes through a request
* phase using these same parameters, but note the early break below.
*/
#define DHCP_PROXY_START_TIMEOUT_SEC 0
#define DHCP_PROXY_END_TIMEOUT_SEC 10
//#define DHCP_PROXY_END_TIMEOUT_SEC 8 /* as per PXE spec */

/*
* A ProxyDHCP request timeout should not induce a failure condition,
* so we always want to break before the above set of timers expire.
* The iPXE default value of 2 breaks at the first timeout after 2
* seconds, which will be after the 2 second timeout.
*/
#define DHCP_REQ_PROXY_TIMEOUT_SEC 2
//#define DHCP_REQ_PROXY_TIMEOUT_SEC 7 /* as per PXE spec */

/*
* Per the PXE spec, a PXE boot server request is also be retried 4
* times at timeouts of 1, 2, 3, 4. iPXE uses the same timeouts as
* discovery, 1, 2, 4, 8, but will move on to the next server if
* available after an elapsed time greater than 3 seconds, therefore
* effectively only sending 3 tries at timeouts of 1, 2, 4.
*/
#define PXEBS_START_TIMEOUT_SEC 1
#define PXEBS_END_TIMEOUT_SEC 10
//#define PXEBS_START_TIMEOUT_SEC 0 /* as per PXE spec */
//#define PXEBS_END_TIMEOUT_SEC 8 /* as per PXE spec */

/*
* Increment to the next PXE Boot server, if available, after this
* this much time has elapsed.
*/
#define PXEBS_MAX_TIMEOUT_SEC 3
//#define PXEBS_MAX_TIMEOUT_SEC 7 /* as per PXE spec */

#include <config/local/dhcp.h>

#endif /* CONFIG_DHCP_H */
10 changes: 0 additions & 10 deletions src/include/ipxe/dhcp.h
View file
Expand Up @@ -639,16 +639,6 @@ struct dhcphdr {
*/
#define DHCP_MIN_LEN 552

/** Timeouts for sending DHCP packets */
#define DHCP_MIN_TIMEOUT ( 1 * TICKS_PER_SEC )
#define DHCP_MAX_TIMEOUT ( 10 * TICKS_PER_SEC )

/** Maximum time that we will wait for ProxyDHCP responses */
#define PROXYDHCP_MAX_TIMEOUT ( 2 * TICKS_PER_SEC )

/** Maximum time that we will wait for Boot Server responses */
#define PXEBS_MAX_TIMEOUT ( 3 * TICKS_PER_SEC )

/** Settings block name used for DHCP responses */
#define DHCP_SETTINGS_NAME "dhcp"

Expand Down
32 changes: 19 additions & 13 deletions src/net/udp/dhcp.c
View file
Expand Up @@ -44,6 +44,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
#include <ipxe/dhcppkt.h>
#include <ipxe/dhcp_arch.h>
#include <ipxe/features.h>
#include <config/dhcp.h>

/** @file
*
Expand Down Expand Up @@ -171,8 +172,9 @@ struct dhcp_session_state {
void ( * expired ) ( struct dhcp_session *dhcp );
/** Transmitted message type */
uint8_t tx_msgtype;
/** Apply minimum timeout */
uint8_t apply_min_timeout;
/** Timeout parameters */
uint8_t min_timeout_sec;
uint8_t max_timeout_sec;
};

static struct dhcp_session_state dhcp_state_discover;
Expand Down Expand Up @@ -272,9 +274,8 @@ static void dhcp_set_state ( struct dhcp_session *dhcp,
dhcp->state = state;
dhcp->start = currticks();
stop_timer ( &dhcp->timer );
dhcp->timer.min_timeout =
( state->apply_min_timeout ? DHCP_MIN_TIMEOUT : 0 );
dhcp->timer.max_timeout = DHCP_MAX_TIMEOUT;
dhcp->timer.min_timeout = state->min_timeout_sec * TICKS_PER_SEC;
dhcp->timer.max_timeout = state->max_timeout_sec * TICKS_PER_SEC;
start_timer_nodelay ( &dhcp->timer );
}

Expand Down Expand Up @@ -415,7 +416,7 @@ static void dhcp_discovery_rx ( struct dhcp_session *dhcp,
/* If we can't yet transition to DHCPREQUEST, do nothing */
elapsed = ( currticks() - dhcp->start );
if ( ! ( dhcp->no_pxedhcp || dhcp->proxy_offer ||
( elapsed > PROXYDHCP_MAX_TIMEOUT ) ) )
( elapsed > DHCP_DISC_PROXY_TIMEOUT_SEC * TICKS_PER_SEC ) ) )
return;

/* Transition to DHCPREQUEST */
Expand All @@ -431,7 +432,8 @@ static void dhcp_discovery_expired ( struct dhcp_session *dhcp ) {
unsigned long elapsed = ( currticks() - dhcp->start );

/* Give up waiting for ProxyDHCP before we reach the failure point */
if ( dhcp->offer.s_addr && ( elapsed > PROXYDHCP_MAX_TIMEOUT ) ) {
if ( dhcp->offer.s_addr &&
( elapsed > DHCP_DISC_PROXY_TIMEOUT_SEC * TICKS_PER_SEC ) ) {
dhcp_set_state ( dhcp, &dhcp_state_request );
return;
}
Expand All @@ -447,7 +449,8 @@ static struct dhcp_session_state dhcp_state_discover = {
.rx = dhcp_discovery_rx,
.expired = dhcp_discovery_expired,
.tx_msgtype = DHCPDISCOVER,
.apply_min_timeout = 1,
.min_timeout_sec = DHCP_DISC_START_TIMEOUT_SEC,
.max_timeout_sec = DHCP_DISC_END_TIMEOUT_SEC,
};

/**
Expand Down Expand Up @@ -584,7 +587,8 @@ static struct dhcp_session_state dhcp_state_request = {
.rx = dhcp_request_rx,
.expired = dhcp_request_expired,
.tx_msgtype = DHCPREQUEST,
.apply_min_timeout = 0,
.min_timeout_sec = DHCP_REQ_START_TIMEOUT_SEC,
.max_timeout_sec = DHCP_REQ_END_TIMEOUT_SEC,
};

/**
Expand Down Expand Up @@ -669,7 +673,7 @@ static void dhcp_proxy_expired ( struct dhcp_session *dhcp ) {
unsigned long elapsed = ( currticks() - dhcp->start );

/* Give up waiting for ProxyDHCP before we reach the failure point */
if ( elapsed > PROXYDHCP_MAX_TIMEOUT ) {
if ( elapsed > DHCP_REQ_PROXY_TIMEOUT_SEC * TICKS_PER_SEC ) {
dhcp_finished ( dhcp, 0 );
return;
}
Expand All @@ -685,7 +689,8 @@ static struct dhcp_session_state dhcp_state_proxy = {
.rx = dhcp_proxy_rx,
.expired = dhcp_proxy_expired,
.tx_msgtype = DHCPREQUEST,
.apply_min_timeout = 0,
.min_timeout_sec = DHCP_PROXY_START_TIMEOUT_SEC,
.max_timeout_sec = DHCP_PROXY_END_TIMEOUT_SEC,
};

/**
Expand Down Expand Up @@ -810,7 +815,7 @@ static void dhcp_pxebs_expired ( struct dhcp_session *dhcp ) {
/* Give up waiting before we reach the failure point, and fail
* over to the next server in the attempt list
*/
if ( elapsed > PXEBS_MAX_TIMEOUT ) {
if ( elapsed > PXEBS_MAX_TIMEOUT_SEC * TICKS_PER_SEC ) {
dhcp->pxe_attempt++;
if ( dhcp->pxe_attempt->s_addr ) {
dhcp_set_state ( dhcp, &dhcp_state_pxebs );
Expand All @@ -832,7 +837,8 @@ static struct dhcp_session_state dhcp_state_pxebs = {
.rx = dhcp_pxebs_rx,
.expired = dhcp_pxebs_expired,
.tx_msgtype = DHCPREQUEST,
.apply_min_timeout = 1,
.min_timeout_sec = PXEBS_START_TIMEOUT_SEC,
.max_timeout_sec = PXEBS_END_TIMEOUT_SEC,
};

/****************************************************************************
Expand Down

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