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[dhcp] Keep multiple DHCP offers received, and use them intelligently

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Instead of keeping only the best IP and PXE offers, store all of them,
and pick the best to use just before a request is sent. This allows
priority differentiation to work even when lower-priority offers
provide PXE options, and improves robustness at sites with broken PXE
servers intermingled with working ones: when a ProxyDHCP request times
out, instead of giving up, we try the next PXE offer we've received.
It also allows us to avoid breaking up combined IP+PXE offers, which
can be important with some firewall configurations. This behavior
matches that of most vendor PXE ROMs.

Store a reference to the DHCPOFFER packet in the offer structure, so
that when registering settings after a successful ACK we can register
the proxy PXE settings we originally received; this removes the need
for a nonstandard duplicate REQUEST/ACK to port 67 of proxy servers
like dnsmasq that provide PXE options in the OFFER.

Total cost: 450 bytes uncompressed.

Signed-off-by: Marty Connor <mdc@etherboot.org>
This commit is contained in:
Joshua Oreman 2009-11-03 13:45:58 -05:00 committed by Marty Connor
parent 466d8fc234
commit 5efc2fcb60
1 changed files with 229 additions and 87 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

316
src/net/udp/dhcp.c
View File

@ -206,6 +206,36 @@ static struct dhcp_session_state dhcp_state_request;
static struct dhcp_session_state dhcp_state_proxy;
static struct dhcp_session_state dhcp_state_pxebs;
/** DHCP offer is valid for IP lease */
#define DHCP_OFFER_IP 1
/** DHCP offer is valid for PXE options */
#define DHCP_OFFER_PXE 2
/** A DHCP offer */
struct dhcp_offer {
/** IP address of server granting offer */
struct in_addr server;
/** IP address being offered, or 0.0.0.0 for a pure proxy */
struct in_addr ip;
/** DHCP packet containing PXE options; NULL if missing or proxied */
struct dhcp_packet *pxe;
/** Valid uses for this offer, a combination of DHCP_OFFER bits */
uint8_t valid;
/** Priority of this offer */
int8_t priority;
/** Whether to ignore PXE DHCP extensions */
uint8_t no_pxedhcp;
};
/** Maximum number of DHCP offers to queue */
#define DHCP_MAX_OFFERS 6
/** A DHCP session */
struct dhcp_session {
/** Reference counter */
@ -222,22 +252,6 @@ struct dhcp_session {
/** State of the session */
struct dhcp_session_state *state;
/** Offered IP address */
struct in_addr offer;
/** DHCP server */
struct in_addr server;
/** DHCP offer priority */
int priority;
/** ProxyDHCP protocol extensions should be ignored */
int no_pxedhcp;
/** ProxyDHCP server */
struct in_addr proxy_server;
/** ProxyDHCP port */
uint16_t proxy_port;
/** ProxyDHCP server priority */
int proxy_priority;
/** PXE Boot Server type */
uint16_t pxe_type;
/** List of PXE Boot Servers to attempt */
@ -249,6 +263,11 @@ struct dhcp_session {
struct retry_timer timer;
/** Start time of the current state (in ticks) */
unsigned long start;
/** DHCP offer just requested */
struct dhcp_offer *current_offer;
/** List of DHCP offers received */
struct dhcp_offer offers[DHCP_MAX_OFFERS];
};
/**
@ -259,6 +278,12 @@ struct dhcp_session {
static void dhcp_free ( struct refcnt *refcnt ) {
struct dhcp_session *dhcp =
container_of ( refcnt, struct dhcp_session, refcnt );
int i;
for ( i = 0 ; i < DHCP_MAX_OFFERS ; i++ ) {
if ( dhcp->offers[i].pxe )
dhcppkt_put ( dhcp->offers[i].pxe );
}
netdev_put ( dhcp->netdev );
free ( dhcp );
@ -303,6 +328,35 @@ static void dhcp_set_state ( struct dhcp_session *dhcp,
start_timer_nodelay ( &dhcp->timer );
}
/**
* Determine next DHCP offer to try
*
* @v dhcp DHCP session
* @v type DHCP offer type
* @ret offer Next DHCP offer to try
*
* Offers are ranked by priority, then by completeness (combined
* IP+PXE are tried before @a type alone), then by order of receipt.
*/
static struct dhcp_offer * dhcp_next_offer ( struct dhcp_session *dhcp,
uint8_t type ) {
struct dhcp_offer *offer;
struct dhcp_offer *best = NULL;
for ( offer = dhcp->offers ; offer < dhcp->offers + DHCP_MAX_OFFERS ;
offer++ ) {
if ( ( offer->valid & type ) &&
( ( best == NULL ) ||
( offer->priority > best->priority ) ||
( ( offer->priority == best->priority ) &&
( offer->valid & ~best->valid ) ) ) )
best = offer;
}
return best;
}
/****************************************************************************
*
* DHCP state machine
@ -330,7 +384,7 @@ static int dhcp_discovery_tx ( struct dhcp_session *dhcp,
}
/**
* Handle received packet during DHCP discovery
* Handle received DHCPOFFER during any state
*
* @v dhcp DHCP session
* @v dhcppkt DHCP packet
@ -338,19 +392,17 @@ static int dhcp_discovery_tx ( struct dhcp_session *dhcp,
* @v msgtype DHCP message type
* @v server_id DHCP server ID
*/
static void dhcp_discovery_rx ( struct dhcp_session *dhcp,
struct dhcp_packet *dhcppkt,
struct sockaddr_in *peer, uint8_t msgtype,
struct in_addr server_id ) {
struct in_addr ip;
static void dhcp_rx_offer ( struct dhcp_session *dhcp,
struct dhcp_packet *dhcppkt,
struct sockaddr_in *peer, uint8_t msgtype,
struct in_addr server_id ) {
char vci[9]; /* "PXEClient" */
int vci_len;
int has_pxeclient;
int pxeopts_len;
int has_pxeopts;
int8_t priority = 0;
uint8_t no_pxedhcp = 0;
unsigned long elapsed;
struct dhcp_offer *offer;
int i;
DBGC ( dhcp, "DHCP %p %s from %s:%d", dhcp,
dhcp_msgtype_name ( msgtype ), inet_ntoa ( peer->sin_addr ),
@ -359,9 +411,27 @@ static void dhcp_discovery_rx ( struct dhcp_session *dhcp,
DBGC ( dhcp, " (%s)", inet_ntoa ( server_id ) );
/* Identify offered IP address */
ip = dhcppkt->dhcphdr->yiaddr;
if ( ip.s_addr )
DBGC ( dhcp, " for %s", inet_ntoa ( ip ) );
if ( dhcppkt->dhcphdr->yiaddr.s_addr )
DBGC ( dhcp, " for %s", inet_ntoa ( dhcppkt->dhcphdr->yiaddr ));
/* Enqueue an offer to be filled in */
for ( i = 0 ; i < DHCP_MAX_OFFERS ; i++ ) {
if ( dhcp->offers[i].server.s_addr == server_id.s_addr ) {
DBGC ( dhcp, " dup\n" );
return;
}
if ( ! dhcp->offers[i].valid )
break;
}
if ( i == DHCP_MAX_OFFERS ) {
DBGC ( dhcp, " dropped\n" );
return;
}
offer = &dhcp->offers[i];
offer->server = server_id;
offer->ip = dhcppkt->dhcphdr->yiaddr;
/* Identify "PXEClient" vendor class */
vci_len = dhcppkt_fetch ( dhcppkt, DHCP_VENDOR_CLASS_ID,
@ -375,43 +445,53 @@ static void dhcp_discovery_rx ( struct dhcp_session *dhcp,
if ( has_pxeclient )
DBGC ( dhcp, "%s", ( has_pxeopts ? " pxe" : " proxy" ) );
if ( has_pxeclient && has_pxeopts ) {
/* Save reference to packet for future use */
if ( offer->pxe )
dhcppkt_put ( offer->pxe );
offer->pxe = dhcppkt_get ( dhcppkt );
}
/* Identify priority */
dhcppkt_fetch ( dhcppkt, DHCP_EB_PRIORITY, &priority,
sizeof ( priority ) );
if ( priority )
DBGC ( dhcp, " pri %d", priority );
dhcppkt_fetch ( dhcppkt, DHCP_EB_PRIORITY, &offer->priority,
sizeof ( offer->priority ) );
if ( offer->priority )
DBGC ( dhcp, " pri %d", offer->priority );
/* Identify ignore-PXE flag */
dhcppkt_fetch ( dhcppkt, DHCP_EB_NO_PXEDHCP, &no_pxedhcp,
sizeof ( no_pxedhcp ) );
if ( no_pxedhcp )
dhcppkt_fetch ( dhcppkt, DHCP_EB_NO_PXEDHCP, &offer->no_pxedhcp,
sizeof ( offer->no_pxedhcp ) );
if ( offer->no_pxedhcp )
DBGC ( dhcp, " nopxe" );
DBGC ( dhcp, "\n" );
/* Select as DHCP offer, if applicable */
if ( ip.s_addr && ( peer->sin_port == htons ( BOOTPS_PORT ) ) &&
( ( msgtype == DHCPOFFER ) || ( ! msgtype /* BOOTP */ ) ) &&
( priority >= dhcp->priority ) ) {
dhcp->offer = ip;
dhcp->server = server_id;
dhcp->priority = priority;
dhcp->no_pxedhcp = no_pxedhcp;
}
/* Determine roles this offer can fill */
if ( offer->ip.s_addr &&
( peer->sin_port == htons ( BOOTPS_PORT ) ) &&
( ( msgtype == DHCPOFFER ) || ( ! msgtype /* BOOTP */ ) ) )
offer->valid |= DHCP_OFFER_IP;
/* Select as ProxyDHCP offer, if applicable */
if ( has_pxeclient && ( msgtype == DHCPOFFER ) &&
( priority >= dhcp->proxy_priority ) ) {
/* If the offer already includes the PXE options, then
* assume that we can send the ProxyDHCPREQUEST to
* port 67 (since the DHCPDISCOVER that triggered this
* ProxyDHCPOFFER was sent to port 67). Otherwise,
* send the ProxyDHCPREQUEST to port 4011.
*/
dhcp->proxy_server = server_id;
dhcp->proxy_port = ( has_pxeopts ? htons ( BOOTPS_PORT )
: htons ( PXE_PORT ) );
dhcp->proxy_priority = priority;
}
if ( has_pxeclient && ( msgtype == DHCPOFFER ) )
offer->valid |= DHCP_OFFER_PXE;
}
/**
* Handle received packet during DHCP discovery
*
* @v dhcp DHCP session
* @v dhcppkt DHCP packet
* @v peer DHCP server address
* @v msgtype DHCP message type
* @v server_id DHCP server ID
*/
static void dhcp_discovery_rx ( struct dhcp_session *dhcp,
struct dhcp_packet *dhcppkt,
struct sockaddr_in *peer, uint8_t msgtype,
struct in_addr server_id ) {
unsigned long elapsed;
struct dhcp_offer *ip_offer;
dhcp_rx_offer ( dhcp, dhcppkt, peer, msgtype, server_id );
/* We can exit the discovery state when we have a valid
* DHCPOFFER, and either:
@ -422,12 +502,14 @@ static void dhcp_discovery_rx ( struct dhcp_session *dhcp,
*/
/* If we don't yet have a DHCPOFFER, do nothing */
if ( ! dhcp->offer.s_addr )
ip_offer = dhcp_next_offer ( dhcp, DHCP_OFFER_IP );
if ( ! ip_offer )
return;
/* If we can't yet transition to DHCPREQUEST, do nothing */
elapsed = ( currticks() - dhcp->start );
if ( ! ( dhcp->no_pxedhcp || dhcp->proxy_server.s_addr ||
if ( ! ( ip_offer->no_pxedhcp ||
dhcp_next_offer ( dhcp, DHCP_OFFER_PXE ) ||
( elapsed > PROXYDHCP_MAX_TIMEOUT ) ) )
return;
@ -444,7 +526,8 @@ 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_next_offer ( dhcp, DHCP_OFFER_IP ) &&
( elapsed > PROXYDHCP_MAX_TIMEOUT ) ) {
dhcp_set_state ( dhcp, &dhcp_state_request );
return;
}
@ -474,21 +557,23 @@ static int dhcp_request_tx ( struct dhcp_session *dhcp,
struct dhcp_packet *dhcppkt,
struct sockaddr_in *peer ) {
int rc;
struct dhcp_offer *offer;
offer = dhcp->current_offer = dhcp_next_offer ( dhcp, DHCP_OFFER_IP );
DBGC ( dhcp, "DHCP %p DHCPREQUEST to %s:%d",
dhcp, inet_ntoa ( dhcp->server ), BOOTPS_PORT );
DBGC ( dhcp, " for %s\n", inet_ntoa ( dhcp->offer ) );
dhcp, inet_ntoa ( offer->server ), BOOTPS_PORT );
DBGC ( dhcp, " for %s\n", inet_ntoa ( offer->ip ) );
/* Set server ID */
if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_SERVER_IDENTIFIER,
&dhcp->server,
sizeof ( dhcp->server ) ) ) != 0 )
&offer->server,
sizeof ( offer->server ) ) ) != 0 )
return rc;
/* Set requested IP address */
if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_REQUESTED_ADDRESS,
&dhcp->offer,
sizeof ( dhcp->offer ) ) ) != 0 )
&offer->ip, sizeof ( offer->ip ) ) ) != 0 )
return rc;
/* Set server address */
@ -514,6 +599,18 @@ static void dhcp_request_rx ( struct dhcp_session *dhcp,
struct in_addr ip;
struct settings *parent;
int rc;
struct dhcp_offer *pxe_offer;
if ( msgtype == DHCPOFFER ) {
dhcp_rx_offer ( dhcp, dhcppkt, peer, msgtype, server_id );
if ( dhcp_next_offer ( dhcp, DHCP_OFFER_IP ) !=
dhcp->current_offer ) {
/* Restart due to higher-priority offer received */
DBGC ( dhcp, "DHCP %p re-requesting\n", dhcp );
dhcp_set_state ( dhcp, &dhcp_state_request );
}
return;
}
DBGC ( dhcp, "DHCP %p %s from %s:%d", dhcp,
dhcp_msgtype_name ( msgtype ), inet_ntoa ( peer->sin_addr ),
@ -532,7 +629,7 @@ static void dhcp_request_rx ( struct dhcp_session *dhcp,
return;
if ( msgtype /* BOOTP */ && ( msgtype != DHCPACK ) )
return;
if ( server_id.s_addr != dhcp->server.s_addr )
if ( server_id.s_addr != dhcp->current_offer->server.s_addr )
return;
/* Record assigned address */
@ -547,18 +644,31 @@ static void dhcp_request_rx ( struct dhcp_session *dhcp,
return;
}
/* Start ProxyDHCPREQUEST if applicable */
if ( dhcp->proxy_server.s_addr /* Have ProxyDHCP server */ &&
( ! dhcp->no_pxedhcp ) /* ProxyDHCP not disabled */ &&
( /* ProxyDHCP server is not just the DHCP server itself */
( dhcp->proxy_server.s_addr != dhcp->server.s_addr ) ||
( dhcp->proxy_port != htons ( BOOTPS_PORT ) ) ) ) {
dhcp_set_state ( dhcp, &dhcp_state_proxy );
return;
}
/* Locate best source of PXE settings */
pxe_offer = dhcp_next_offer ( dhcp, DHCP_OFFER_PXE );
/* Terminate DHCP */
dhcp_finished ( dhcp, 0 );
if ( ( ! pxe_offer ) || /* No PXE available */
/* IP offer instructs us to ignore PXE */
dhcp->current_offer->no_pxedhcp ||
/* PXE settings already registered with IP offer */
( ( dhcp->current_offer == pxe_offer ) && ( pxe_offer->pxe ) ) ) {
/* Terminate DHCP */
dhcp_finished ( dhcp, 0 );
} else if ( pxe_offer->pxe ) {
/* Register PXE settings and terminate DHCP */
pxe_offer->pxe->settings.name = PROXYDHCP_SETTINGS_NAME;
if ( ( rc = register_settings ( &pxe_offer->pxe->settings,
NULL ) ) != 0 ) {
DBGC ( dhcp, "DHCP %p could not register settings: "
"%s\n", dhcp, strerror ( rc ) );
}
dhcp_finished ( dhcp, rc );
} else {
/* Start ProxyDHCP */
dhcp_set_state ( dhcp, &dhcp_state_proxy );
}
}
/**
@ -593,19 +703,22 @@ static int dhcp_proxy_tx ( struct dhcp_session *dhcp,
struct dhcp_packet *dhcppkt,
struct sockaddr_in *peer ) {
int rc;
struct dhcp_offer *offer;
offer = dhcp->current_offer = dhcp_next_offer ( dhcp, DHCP_OFFER_PXE );
DBGC ( dhcp, "DHCP %p ProxyDHCP REQUEST to %s:%d\n", dhcp,
inet_ntoa ( dhcp->proxy_server ), ntohs ( dhcp->proxy_port ) );
inet_ntoa ( offer->server ), PXE_PORT );
/* Set server ID */
if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_SERVER_IDENTIFIER,
&dhcp->proxy_server,
sizeof ( dhcp->proxy_server ) ) ) != 0 )
&offer->server,
sizeof ( offer->server ) ) ) != 0 )
return rc;
/* Set server address */
peer->sin_addr = dhcp->proxy_server;
peer->sin_port = dhcp->proxy_port;
peer->sin_addr = offer->server;
peer->sin_port = htons ( PXE_PORT );
return 0;
}
@ -625,6 +738,13 @@ static void dhcp_proxy_rx ( struct dhcp_session *dhcp,
struct in_addr server_id ) {
int rc;
/* Enqueue last-minute DHCPOFFERs for use in case of failure */
if ( peer->sin_port == htons ( BOOTPS_PORT ) &&
msgtype == DHCPOFFER ) {
dhcp_rx_offer ( dhcp, dhcppkt, peer, msgtype, server_id );
return;
}
DBGC ( dhcp, "DHCP %p %s from %s:%d", dhcp,
dhcp_msgtype_name ( msgtype ), inet_ntoa ( peer->sin_addr ),
ntohs ( peer->sin_port ) );
@ -633,12 +753,12 @@ static void dhcp_proxy_rx ( struct dhcp_session *dhcp,
DBGC ( dhcp, "\n" );
/* Filter out unacceptable responses */
if ( peer->sin_port != dhcp->proxy_port )
if ( peer->sin_port != htons ( PXE_PORT ) )
return;
if ( ( msgtype != DHCPOFFER ) && ( msgtype != DHCPACK ) )
if ( msgtype != DHCPACK && msgtype != DHCPOFFER )
return;
if ( server_id.s_addr /* Linux PXE server omits server ID */ &&
( server_id.s_addr != dhcp->proxy_server.s_addr ) )
( server_id.s_addr != dhcp->current_offer->server.s_addr ) )
return;
/* Register settings */
@ -664,6 +784,28 @@ static void dhcp_proxy_expired ( struct dhcp_session *dhcp ) {
/* Give up waiting for ProxyDHCP before we reach the failure point */
if ( elapsed > PROXYDHCP_MAX_TIMEOUT ) {
/* Mark failed offer as unsuitable for ProxyDHCP */
dhcp->current_offer->valid &= ~DHCP_OFFER_PXE;
/* Prefer not to use only half of a PXE+IP offer if we
* have other offers available
*/
dhcp->current_offer->priority = -1;
/* If we have any other PXE offers we can try, go back
* to DHCPREQUEST (since they might not be proxied
* offers, or might be coupled to a new IP address).
* We should probably DHCPRELEASE our old IP, but the
* standard does not require it.
*/
if ( dhcp_next_offer ( dhcp, DHCP_OFFER_PXE ) ) {
dhcp->local.sin_addr.s_addr = 0;
dhcp_set_state ( dhcp, &dhcp_state_request );
return;
}
/* No possibilities left; finish without PXE options */
dhcp_finished ( dhcp, 0 );
return;
}