source: bootcd/isolinux/syslinux-6.03/gpxe/src/net/udp/dhcp.c @ dd1be7c

/*
 * Copyright (C) 2006 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * 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 any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

FILE_LICENCE ( GPL2_OR_LATER );

#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>
#include <errno.h>
#include <assert.h>
#include <byteswap.h>
#include <gpxe/if_ether.h>
#include <gpxe/netdevice.h>
#include <gpxe/device.h>
#include <gpxe/xfer.h>
#include <gpxe/open.h>
#include <gpxe/job.h>
#include <gpxe/retry.h>
#include <gpxe/tcpip.h>
#include <gpxe/ip.h>
#include <gpxe/uuid.h>
#include <gpxe/timer.h>
#include <gpxe/settings.h>
#include <gpxe/dhcp.h>
#include <gpxe/dhcpopts.h>
#include <gpxe/dhcppkt.h>
#include <gpxe/features.h>

/** @file
 *
 * Dynamic Host Configuration Protocol
 *
 */

struct dhcp_session;
static int dhcp_tx ( struct dhcp_session *dhcp );

/**
 * DHCP operation types
 *
 * This table maps from DHCP message types (i.e. values of the @c
 * DHCP_MESSAGE_TYPE option) to values of the "op" field within a DHCP
 * packet.
 */
static const uint8_t dhcp_op[] = {
        [DHCPDISCOVER]  = BOOTP_REQUEST,
        [DHCPOFFER]     = BOOTP_REPLY,
        [DHCPREQUEST]   = BOOTP_REQUEST,
        [DHCPDECLINE]   = BOOTP_REQUEST,
        [DHCPACK]       = BOOTP_REPLY,
        [DHCPNAK]       = BOOTP_REPLY,
        [DHCPRELEASE]   = BOOTP_REQUEST,
        [DHCPINFORM]    = BOOTP_REQUEST,
};

/** Raw option data for options common to all DHCP requests */
static uint8_t dhcp_request_options_data[] = {
        DHCP_MESSAGE_TYPE, DHCP_BYTE ( 0 ),
        DHCP_MAX_MESSAGE_SIZE,
        DHCP_WORD ( ETH_MAX_MTU - 20 /* IP header */ - 8 /* UDP header */ ),
        DHCP_CLIENT_ARCHITECTURE, DHCP_WORD ( 0 ),
        DHCP_CLIENT_NDI, DHCP_OPTION ( 1 /* UNDI */ , 2, 1 /* v2.1 */ ),
        DHCP_VENDOR_CLASS_ID,
        DHCP_STRING (  'P', 'X', 'E', 'C', 'l', 'i', 'e', 'n', 't', ':',
                       'A', 'r', 'c', 'h', ':', '0', '0', '0', '0', '0', ':',
                       'U', 'N', 'D', 'I', ':', '0', '0', '2', '0', '0', '1' ),
        DHCP_USER_CLASS_ID,
        DHCP_STRING ( 'g', 'P', 'X', 'E' ),
        DHCP_PARAMETER_REQUEST_LIST,
        DHCP_OPTION ( DHCP_SUBNET_MASK, DHCP_ROUTERS, DHCP_DNS_SERVERS,
                      DHCP_LOG_SERVERS, DHCP_HOST_NAME, DHCP_DOMAIN_NAME,
                      DHCP_ROOT_PATH, DHCP_VENDOR_ENCAP, DHCP_VENDOR_CLASS_ID,
                      DHCP_TFTP_SERVER_NAME, DHCP_BOOTFILE_NAME,
                      DHCP_EB_ENCAP, DHCP_ISCSI_INITIATOR_IQN ),
        DHCP_END
};

/** Version number feature */
FEATURE_VERSION ( VERSION_MAJOR, VERSION_MINOR, VERSION_PATCH );

/** DHCP server address setting */
struct setting dhcp_server_setting __setting = {
        .name = "dhcp-server",
        .description = "DHCP server address",
        .tag = DHCP_SERVER_IDENTIFIER,
        .type = &setting_type_ipv4,
};

/** DHCP user class setting */
struct setting user_class_setting __setting = {
        .name = "user-class",
        .description = "User class identifier",
        .tag = DHCP_USER_CLASS_ID,
        .type = &setting_type_string,
};

/** Use cached network settings */
struct setting use_cached_setting __setting = {
        .name = "use-cached",
        .description = "Use cached network settings",
        .tag = DHCP_EB_USE_CACHED,
        .type = &setting_type_uint8,
};

/**
 * Name a DHCP packet type
 *
 * @v msgtype           DHCP message type
 * @ret string          DHCP mesasge type name
 */
static inline const char * dhcp_msgtype_name ( unsigned int msgtype ) {
        switch ( msgtype ) {
        case DHCPNONE:          return "BOOTP"; /* Non-DHCP packet */
        case DHCPDISCOVER:      return "DHCPDISCOVER";
        case DHCPOFFER:         return "DHCPOFFER";
        case DHCPREQUEST:       return "DHCPREQUEST";
        case DHCPDECLINE:       return "DHCPDECLINE";
        case DHCPACK:           return "DHCPACK";
        case DHCPNAK:           return "DHCPNAK";
        case DHCPRELEASE:       return "DHCPRELEASE";
        case DHCPINFORM:        return "DHCPINFORM";
        default:                return "DHCP<invalid>";
        }
}

/**
 * Calculate DHCP transaction ID for a network device
 *
 * @v netdev            Network device
 * @ret xid             DHCP XID
 *
 * Extract the least significant bits of the hardware address for use
 * as the transaction ID.
 */
static uint32_t dhcp_xid ( struct net_device *netdev ) {
        uint32_t xid;

        memcpy ( &xid, ( netdev->ll_addr + netdev->ll_protocol->ll_addr_len
                         - sizeof ( xid ) ), sizeof ( xid ) );
        return xid;
}

/****************************************************************************
 *
 * DHCP session
 *
 */

struct dhcp_session;

/** DHCP session state operations */
struct dhcp_session_state {
        /** State name */
        const char *name;
        /**
         * Construct transmitted packet
         *
         * @v dhcp              DHCP session
         * @v dhcppkt           DHCP packet
         * @v peer              Destination address
         */
        int ( * tx ) ( struct dhcp_session *dhcp,
                       struct dhcp_packet *dhcppkt,
                       struct sockaddr_in *peer );
        /** Handle received packet
         *
         * @v dhcp              DHCP session
         * @v dhcppkt           DHCP packet
         * @v peer              DHCP server address
         * @v msgtype           DHCP message type
         * @v server_id         DHCP server ID
         */
        void ( * rx ) ( struct dhcp_session *dhcp,
                        struct dhcp_packet *dhcppkt,
                        struct sockaddr_in *peer,
                        uint8_t msgtype, struct in_addr server_id );
        /** Handle timer expiry
         *
         * @v dhcp              DHCP session
         */
        void ( * expired ) ( struct dhcp_session *dhcp );
        /** Transmitted message type */
        uint8_t tx_msgtype;
        /** Apply minimum timeout */
        uint8_t apply_min_timeout;
};

static struct dhcp_session_state dhcp_state_discover;
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 */
        struct refcnt refcnt;
        /** Job control interface */
        struct job_interface job;
        /** Data transfer interface */
        struct xfer_interface xfer;

        /** Network device being configured */
        struct net_device *netdev;
        /** Local socket address */
        struct sockaddr_in local;
        /** State of the session */
        struct dhcp_session_state *state;

        /** PXE Boot Server type */
        uint16_t pxe_type;
        /** List of PXE Boot Servers to attempt */
        struct in_addr *pxe_attempt;
        /** List of PXE Boot Servers to accept */
        struct in_addr *pxe_accept;

        /** Retransmission timer */
        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];
};

/**
 * Free DHCP session
 *
 * @v refcnt            Reference counter
 */
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 );
}

/**
 * Mark DHCP session as complete
 *
 * @v dhcp              DHCP session
 * @v rc                Return status code
 */
static void dhcp_finished ( struct dhcp_session *dhcp, int rc ) {

        /* Block futher incoming messages */
        job_nullify ( &dhcp->job );
        xfer_nullify ( &dhcp->xfer );

        /* Stop retry timer */
        stop_timer ( &dhcp->timer );

        /* Free resources and close interfaces */
        xfer_close ( &dhcp->xfer, rc );
        job_done ( &dhcp->job, rc );
}

/**
 * Transition to new DHCP session state
 *
 * @v dhcp              DHCP session
 * @v state             New session state
 */
static void dhcp_set_state ( struct dhcp_session *dhcp,
                             struct dhcp_session_state *state ) {

        DBGC ( dhcp, "DHCP %p entering %s state\n", dhcp, state->name );
        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;
        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
 *
 */

/**
 * Construct transmitted packet for DHCP discovery
 *
 * @v dhcp              DHCP session
 * @v dhcppkt           DHCP packet
 * @v peer              Destination address
 */
static int dhcp_discovery_tx ( struct dhcp_session *dhcp,
                               struct dhcp_packet *dhcppkt __unused,
                               struct sockaddr_in *peer ) {

        DBGC ( dhcp, "DHCP %p DHCPDISCOVER\n", dhcp );

        /* Set server address */
        peer->sin_addr.s_addr = INADDR_BROADCAST;
        peer->sin_port = htons ( BOOTPS_PORT );

        return 0;
}

/**
 * Handle received DHCPOFFER during any state
 *
 * @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_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;
        struct dhcp_offer *offer;
        int i;

        DBGC ( dhcp, "DHCP %p %s from %s:%d", dhcp,
               dhcp_msgtype_name ( msgtype ), inet_ntoa ( peer->sin_addr ),
               ntohs ( peer->sin_port ) );
        if ( server_id.s_addr != peer->sin_addr.s_addr )
                DBGC ( dhcp, " (%s)", inet_ntoa ( server_id ) );

        /* Identify offered IP address */
        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,
                                  vci, sizeof ( vci ) );
        has_pxeclient = ( ( vci_len >= ( int ) sizeof ( vci ) ) &&
                          ( strncmp ( "PXEClient", vci, sizeof (vci) ) == 0 ));

        /* Identify presence of PXE-specific options */
        pxeopts_len = dhcppkt_fetch ( dhcppkt, DHCP_PXE_BOOT_MENU, NULL, 0 );
        has_pxeopts = ( pxeopts_len >= 0 );
        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, &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, &offer->no_pxedhcp,
                        sizeof ( offer->no_pxedhcp ) );
        if ( offer->no_pxedhcp )
                DBGC ( dhcp, " nopxe" );
        DBGC ( dhcp, "\n" );

        /* 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;

        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:
         *
         *  o  The DHCPOFFER instructs us to ignore ProxyDHCPOFFERs, or
         *  o  We have a valid ProxyDHCPOFFER, or
         *  o  We have allowed sufficient time for ProxyDHCPOFFERs.
         */

        /* If we don't yet have a DHCPOFFER, do nothing */
        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 ( ! ( ip_offer->no_pxedhcp ||
                 dhcp_next_offer ( dhcp, DHCP_OFFER_PXE ) ||
                 ( elapsed > PROXYDHCP_MAX_TIMEOUT ) ) )
                return;

        /* Transition to DHCPREQUEST */
        dhcp_set_state ( dhcp, &dhcp_state_request );
}

/**
 * Handle timer expiry during DHCP discovery
 *
 * @v dhcp              DHCP session
 */
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_next_offer ( dhcp, DHCP_OFFER_IP ) &&
             ( elapsed > PROXYDHCP_MAX_TIMEOUT ) ) {
                dhcp_set_state ( dhcp, &dhcp_state_request );
                return;
        }

        /* Otherwise, retransmit current packet */
        dhcp_tx ( dhcp );
}

/** DHCP discovery state operations */
static struct dhcp_session_state dhcp_state_discover = {
        .name                   = "discovery",
        .tx                     = dhcp_discovery_tx,
        .rx                     = dhcp_discovery_rx,
        .expired                = dhcp_discovery_expired,
        .tx_msgtype             = DHCPDISCOVER,
        .apply_min_timeout      = 1,
};

/**
 * Construct transmitted packet for DHCP request
 *
 * @v dhcp              DHCP session
 * @v dhcppkt           DHCP packet
 * @v peer              Destination address
 */
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 ( offer->server ), BOOTPS_PORT );
        DBGC ( dhcp, " for %s\n", inet_ntoa ( offer->ip ) );

        /* Set server ID */
        if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_SERVER_IDENTIFIER,
                                    &offer->server,
                                    sizeof ( offer->server ) ) ) != 0 )
                return rc;

        /* Set requested IP address */
        if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_REQUESTED_ADDRESS,
                                    &offer->ip, sizeof ( offer->ip ) ) ) != 0 )
                return rc;

        /* Set server address */
        peer->sin_addr.s_addr = INADDR_BROADCAST;
        peer->sin_port = htons ( BOOTPS_PORT );

        return 0;
}

/**
 * Handle received packet during DHCP request
 *
 * @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_request_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;
        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 ),
               ntohs ( peer->sin_port ) );
        if ( server_id.s_addr != peer->sin_addr.s_addr )
                DBGC ( dhcp, " (%s)", inet_ntoa ( server_id ) );

        /* Identify leased IP address */
        ip = dhcppkt->dhcphdr->yiaddr;
        if ( ip.s_addr )
                DBGC ( dhcp, " for %s", inet_ntoa ( ip ) );
        DBGC ( dhcp, "\n" );

        /* Filter out unacceptable responses */
        if ( peer->sin_port != htons ( BOOTPS_PORT ) )
                return;
        if ( msgtype /* BOOTP */ && ( msgtype != DHCPACK ) )
                return;
        if ( server_id.s_addr != dhcp->current_offer->server.s_addr )
                return;

        /* Record assigned address */
        dhcp->local.sin_addr = ip;

        /* Register settings */
        parent = netdev_settings ( dhcp->netdev );
        if ( ( rc = register_settings ( &dhcppkt->settings, parent ) ) != 0 ){
                DBGC ( dhcp, "DHCP %p could not register settings: %s\n",
                       dhcp, strerror ( rc ) );
                dhcp_finished ( dhcp, rc );
                return;
        }

        /* Locate best source of PXE settings */
        pxe_offer = dhcp_next_offer ( dhcp, DHCP_OFFER_PXE );

        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 );
        }
}

/**
 * Handle timer expiry during DHCP discovery
 *
 * @v dhcp              DHCP session
 */
static void dhcp_request_expired ( struct dhcp_session *dhcp ) {

        /* Retransmit current packet */
        dhcp_tx ( dhcp );
}

/** DHCP request state operations */
static struct dhcp_session_state dhcp_state_request = {
        .name                   = "request",
        .tx                     = dhcp_request_tx,
        .rx                     = dhcp_request_rx,
        .expired                = dhcp_request_expired,
        .tx_msgtype             = DHCPREQUEST,
        .apply_min_timeout      = 0,
};

/**
 * Construct transmitted packet for ProxyDHCP request
 *
 * @v dhcp              DHCP session
 * @v dhcppkt           DHCP packet
 * @v peer              Destination address
 */
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 ( offer->server ), PXE_PORT );

        /* Set server ID */
        if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_SERVER_IDENTIFIER,
                                    &offer->server,
                                    sizeof ( offer->server ) ) )  != 0 )
                return rc;

        /* Set server address */
        peer->sin_addr = offer->server;
        peer->sin_port = htons ( PXE_PORT );

        return 0;
}

/**
 * Handle received packet during ProxyDHCP request
 *
 * @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_proxy_rx ( struct dhcp_session *dhcp,
                            struct dhcp_packet *dhcppkt,
                            struct sockaddr_in *peer, uint8_t msgtype,
                            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 ) );
        if ( server_id.s_addr != peer->sin_addr.s_addr )
                DBGC ( dhcp, " (%s)", inet_ntoa ( server_id ) );
        DBGC ( dhcp, "\n" );

        /* Filter out unacceptable responses */
        if ( peer->sin_port != htons ( PXE_PORT ) )
                return;
        if ( msgtype != DHCPACK && msgtype != DHCPOFFER )
                return;
        if ( server_id.s_addr /* Linux PXE server omits server ID */ &&
             ( server_id.s_addr != dhcp->current_offer->server.s_addr ) )
                return;

        /* Register settings */
        dhcppkt->settings.name = PROXYDHCP_SETTINGS_NAME;
        if ( ( rc = register_settings ( &dhcppkt->settings, NULL ) ) != 0 ) {
                DBGC ( dhcp, "DHCP %p could not register settings: %s\n",
                       dhcp, strerror ( rc ) );
                dhcp_finished ( dhcp, rc );
                return;
        }

        /* Terminate DHCP */
        dhcp_finished ( dhcp, 0 );
}

/**
 * Handle timer expiry during ProxyDHCP request
 *
 * @v dhcp              DHCP session
 */
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 ) {

                /* 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;
        }

        /* Retransmit current packet */
        dhcp_tx ( dhcp );
}

/** ProxyDHCP request state operations */
static struct dhcp_session_state dhcp_state_proxy = {
        .name                   = "ProxyDHCP",
        .tx                     = dhcp_proxy_tx,
        .rx                     = dhcp_proxy_rx,
        .expired                = dhcp_proxy_expired,
        .tx_msgtype             = DHCPREQUEST,
        .apply_min_timeout      = 0,
};

/**
 * Construct transmitted packet for PXE Boot Server Discovery
 *
 * @v dhcp              DHCP session
 * @v dhcppkt           DHCP packet
 * @v peer              Destination address
 */
static int dhcp_pxebs_tx ( struct dhcp_session *dhcp,
                           struct dhcp_packet *dhcppkt,
                           struct sockaddr_in *peer ) {
        struct dhcp_pxe_boot_menu_item menu_item = { 0, 0 };
        int rc;

        /* Set server address */
        peer->sin_addr = *(dhcp->pxe_attempt);
        peer->sin_port = ( ( peer->sin_addr.s_addr == INADDR_BROADCAST ) ?
                           htons ( BOOTPS_PORT ) : htons ( PXE_PORT ) );

        DBGC ( dhcp, "DHCP %p PXEBS REQUEST to %s:%d for type %d\n",
               dhcp, inet_ntoa ( peer->sin_addr ), ntohs ( peer->sin_port ),
               le16_to_cpu ( dhcp->pxe_type ) );

        /* Set boot menu item */
        menu_item.type = dhcp->pxe_type;
        if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_PXE_BOOT_MENU_ITEM,
                                    &menu_item, sizeof ( menu_item ) ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Check to see if PXE Boot Server address is acceptable
 *
 * @v dhcp              DHCP session
 * @v bs                Boot Server address
 * @ret accept          Boot Server is acceptable
 */
static int dhcp_pxebs_accept ( struct dhcp_session *dhcp,
                               struct in_addr bs ) {
        struct in_addr *accept;

        /* Accept if we have no acceptance filter */
        if ( ! dhcp->pxe_accept )
                return 1;

        /* Scan through acceptance list */
        for ( accept = dhcp->pxe_accept ; accept->s_addr ; accept++ ) {
                if ( accept->s_addr == bs.s_addr )
                        return 1;
        }

        DBGC ( dhcp, "DHCP %p rejecting server %s\n",
               dhcp, inet_ntoa ( bs ) );
        return 0;
}

/**
 * Handle received packet during PXE Boot Server 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_pxebs_rx ( struct dhcp_session *dhcp,
                            struct dhcp_packet *dhcppkt,
                            struct sockaddr_in *peer, uint8_t msgtype,
                            struct in_addr server_id ) {
        struct dhcp_pxe_boot_menu_item menu_item = { 0, 0 };
        int rc;

        DBGC ( dhcp, "DHCP %p %s from %s:%d", dhcp,
               dhcp_msgtype_name ( msgtype ), inet_ntoa ( peer->sin_addr ),
               ntohs ( peer->sin_port ) );
        if ( server_id.s_addr != peer->sin_addr.s_addr )
                DBGC ( dhcp, " (%s)", inet_ntoa ( server_id ) );

        /* Identify boot menu item */
        dhcppkt_fetch ( dhcppkt, DHCP_PXE_BOOT_MENU_ITEM,
                        &menu_item, sizeof ( menu_item ) );
        if ( menu_item.type )
                DBGC ( dhcp, " for type %d", ntohs ( menu_item.type ) );
        DBGC ( dhcp, "\n" );

        /* Filter out unacceptable responses */
        if ( ( peer->sin_port != htons ( BOOTPS_PORT ) ) &&
             ( peer->sin_port != htons ( PXE_PORT ) ) )
                return;
        if ( msgtype != DHCPACK )
                return;
        if ( menu_item.type != dhcp->pxe_type )
                return;
        if ( ! dhcp_pxebs_accept ( dhcp, ( server_id.s_addr ?
                                           server_id : peer->sin_addr ) ) )
                return;

        /* Register settings */
        dhcppkt->settings.name = PXEBS_SETTINGS_NAME;
        if ( ( rc = register_settings ( &dhcppkt->settings, NULL ) ) != 0 ) {
                DBGC ( dhcp, "DHCP %p could not register settings: %s\n",
                       dhcp, strerror ( rc ) );
                dhcp_finished ( dhcp, rc );
                return;
        }

        /* Terminate DHCP */
        dhcp_finished ( dhcp, 0 );
}

/**
 * Handle timer expiry during PXE Boot Server Discovery
 *
 * @v dhcp              DHCP session
 */
static void dhcp_pxebs_expired ( struct dhcp_session *dhcp ) {
        unsigned long elapsed = ( currticks() - dhcp->start );

        /* 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 ) {
                dhcp->pxe_attempt++;
                if ( dhcp->pxe_attempt->s_addr ) {
                        dhcp_set_state ( dhcp, &dhcp_state_pxebs );
                        return;
                } else {
                        dhcp_finished ( dhcp, -ETIMEDOUT );
                        return;
                }
        }

        /* Retransmit current packet */
        dhcp_tx ( dhcp );
}

/** PXE Boot Server Discovery state operations */
static struct dhcp_session_state dhcp_state_pxebs = {
        .name                   = "PXEBS",
        .tx                     = dhcp_pxebs_tx,
        .rx                     = dhcp_pxebs_rx,
        .expired                = dhcp_pxebs_expired,
        .tx_msgtype             = DHCPREQUEST,
        .apply_min_timeout      = 1,
};

/****************************************************************************
 *
 * Packet construction
 *
 */

/**
 * Construct DHCP client hardware address field and broadcast flag
 *
 * @v netdev            Network device
 * @v hlen              DHCP hardware address length to fill in
 * @v flags             DHCP flags to fill in
 * @ret chaddr          DHCP client hardware address
 */
void * dhcp_chaddr ( struct net_device *netdev, uint8_t *hlen,
                     uint16_t *flags ) {
        struct ll_protocol *ll_protocol = netdev->ll_protocol;
        typeof ( ( ( struct dhcphdr * ) NULL )->chaddr ) chaddr;

        /* If the link-layer address cannot fit into the chaddr field
         * (as is the case for IPoIB) then try using the hardware
         * address instead.  If we do this, set the broadcast flag,
         * since chaddr then does not represent a valid link-layer
         * address for the return path.
         *
         * If even the hardware address is too large, use an empty
         * chaddr field and set the broadcast flag.
         *
         * This goes against RFC4390, but RFC4390 mandates that we use
         * a DHCP client identifier that conforms with RFC4361, which
         * we cannot do without either persistent (NIC-independent)
         * storage, or by eliminating the hardware address completely
         * from the DHCP packet, which seems unfriendly to users.
         */
        if ( ( *hlen = ll_protocol->ll_addr_len ) <= sizeof ( chaddr ) ) {
                return netdev->ll_addr;
        }
        *flags = htons ( BOOTP_FL_BROADCAST );
        if ( ( *hlen = ll_protocol->hw_addr_len ) <= sizeof ( chaddr ) ) {
                return netdev->hw_addr;
        } else {
                *hlen = 0;
                return NULL;
        }
}

/**
 * Create a DHCP packet
 *
 * @v dhcppkt           DHCP packet structure to fill in
 * @v netdev            Network device
 * @v msgtype           DHCP message type
 * @v options           Initial options to include (or NULL)
 * @v options_len       Length of initial options
 * @v data              Buffer for DHCP packet
 * @v max_len           Size of DHCP packet buffer
 * @ret rc              Return status code
 *
 * Creates a DHCP packet in the specified buffer, and initialise a
 * DHCP packet structure.
 */
int dhcp_create_packet ( struct dhcp_packet *dhcppkt,
                         struct net_device *netdev, uint8_t msgtype,
                         const void *options, size_t options_len,
                         void *data, size_t max_len ) {
        struct dhcphdr *dhcphdr = data;
        void *chaddr;
        int rc;

        /* Sanity check */
        if ( max_len < ( sizeof ( *dhcphdr ) + options_len ) )
                return -ENOSPC;

        /* Initialise DHCP packet content */
        memset ( dhcphdr, 0, max_len );
        dhcphdr->xid = dhcp_xid ( netdev );
        dhcphdr->magic = htonl ( DHCP_MAGIC_COOKIE );
        dhcphdr->htype = ntohs ( netdev->ll_protocol->ll_proto );
        dhcphdr->op = dhcp_op[msgtype];
        chaddr = dhcp_chaddr ( netdev, &dhcphdr->hlen, &dhcphdr->flags );
        memcpy ( dhcphdr->chaddr, chaddr, dhcphdr->hlen );
        memcpy ( dhcphdr->options, options, options_len );

        /* Initialise DHCP packet structure */
        memset ( dhcppkt, 0, sizeof ( *dhcppkt ) );
        dhcppkt_init ( dhcppkt, data, max_len );
        
        /* Set DHCP_MESSAGE_TYPE option */
        if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_MESSAGE_TYPE,
                                    &msgtype, sizeof ( msgtype ) ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Create DHCP request packet
 *
 * @v dhcppkt           DHCP packet structure to fill in
 * @v netdev            Network device
 * @v msgtype           DHCP message type
 * @v ciaddr            Client IP address
 * @v data              Buffer for DHCP packet
 * @v max_len           Size of DHCP packet buffer
 * @ret rc              Return status code
 *
 * Creates a DHCP request packet in the specified buffer, and
 * initialise a DHCP packet structure.
 */
int dhcp_create_request ( struct dhcp_packet *dhcppkt,
                          struct net_device *netdev, unsigned int msgtype,
                          struct in_addr ciaddr, void *data, size_t max_len ) {
        struct dhcp_netdev_desc dhcp_desc;
        struct dhcp_client_id client_id;
        struct dhcp_client_uuid client_uuid;
        uint8_t *dhcp_features;
        size_t dhcp_features_len;
        size_t ll_addr_len;
        ssize_t len;
        int rc;

        /* Create DHCP packet */
        if ( ( rc = dhcp_create_packet ( dhcppkt, netdev, msgtype,
                                         dhcp_request_options_data,
                                         sizeof ( dhcp_request_options_data ),
                                         data, max_len ) ) != 0 ) {
                DBG ( "DHCP could not create DHCP packet: %s\n",
                      strerror ( rc ) );
                return rc;
        }

        /* Set client IP address */
        dhcppkt->dhcphdr->ciaddr = ciaddr;

        /* Add options to identify the feature list */
        dhcp_features = table_start ( DHCP_FEATURES );
        dhcp_features_len = table_num_entries ( DHCP_FEATURES );
        if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_EB_ENCAP, dhcp_features,
                                    dhcp_features_len ) ) != 0 ) {
                DBG ( "DHCP could not set features list option: %s\n",
                      strerror ( rc ) );
                return rc;
        }

        /* Add options to identify the network device */
        fetch_setting ( &netdev->settings.settings, &busid_setting, &dhcp_desc,
                sizeof ( dhcp_desc ) );
        if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_EB_BUS_ID, &dhcp_desc,
                                    sizeof ( dhcp_desc ) ) ) != 0 ) {
                DBG ( "DHCP could not set bus ID option: %s\n",
                      strerror ( rc ) );
                return rc;
        }

        /* Add DHCP client identifier.  Required for Infiniband, and
         * doesn't hurt other link layers.
         */
        client_id.ll_proto = ntohs ( netdev->ll_protocol->ll_proto );
        ll_addr_len = netdev->ll_protocol->ll_addr_len;
        assert ( ll_addr_len <= sizeof ( client_id.ll_addr ) );
        memcpy ( client_id.ll_addr, netdev->ll_addr, ll_addr_len );
        if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_CLIENT_ID, &client_id,
                                    ( ll_addr_len + 1 ) ) ) != 0 ) {
                DBG ( "DHCP could not set client ID: %s\n",
                      strerror ( rc ) );
                return rc;
        }

        /* Add client UUID, if we have one.  Required for PXE. */
        client_uuid.type = DHCP_CLIENT_UUID_TYPE;
        if ( ( len = fetch_uuid_setting ( NULL, &uuid_setting,
                                          &client_uuid.uuid ) ) >= 0 ) {
                if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_CLIENT_UUID,
                                            &client_uuid,
                                            sizeof ( client_uuid ) ) ) != 0 ) {
                        DBG ( "DHCP could not set client UUID: %s\n",
                              strerror ( rc ) );
                        return rc;
                }
        }

        /* Add user class, if we have one. */
        if ( ( len = fetch_setting_len ( NULL, &user_class_setting ) ) >= 0 ) {
                char user_class[len];
                fetch_setting ( NULL, &user_class_setting, user_class,
                                sizeof ( user_class ) );
                if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_USER_CLASS_ID,
                                            &user_class,
                                            sizeof ( user_class ) ) ) != 0 ) {
                        DBG ( "DHCP could not set user class: %s\n",
                              strerror ( rc ) );
                        return rc;
                }
        }

        return 0;
}

/****************************************************************************
 *
 * Data transfer interface
 *
 */

/**
 * Transmit DHCP request
 *
 * @v dhcp              DHCP session
 * @ret rc              Return status code
 */
static int dhcp_tx ( struct dhcp_session *dhcp ) {
        static struct sockaddr_in peer = {
                .sin_family = AF_INET,
        };
        struct xfer_metadata meta = {
                .netdev = dhcp->netdev,
                .src = ( struct sockaddr * ) &dhcp->local,
                .dest = ( struct sockaddr * ) &peer,
        };
        struct io_buffer *iobuf;
        uint8_t msgtype = dhcp->state->tx_msgtype;
        struct dhcp_packet dhcppkt;
        int rc;

        /* Start retry timer.  Do this first so that failures to
         * transmit will be retried.
         */
        start_timer ( &dhcp->timer );

        /* Allocate buffer for packet */
        iobuf = xfer_alloc_iob ( &dhcp->xfer, DHCP_MIN_LEN );
        if ( ! iobuf )
                return -ENOMEM;

        /* Create basic DHCP packet in temporary buffer */
        if ( ( rc = dhcp_create_request ( &dhcppkt, dhcp->netdev, msgtype,
                                          dhcp->local.sin_addr, iobuf->data,
                                          iob_tailroom ( iobuf ) ) ) != 0 ) {
                DBGC ( dhcp, "DHCP %p could not construct DHCP request: %s\n",
                       dhcp, strerror ( rc ) );
                goto done;
        }

        /* Fill in packet based on current state */
        if ( ( rc = dhcp->state->tx ( dhcp, &dhcppkt, &peer ) ) != 0 ) {
                DBGC ( dhcp, "DHCP %p could not fill DHCP request: %s\n",
                       dhcp, strerror ( rc ) );
                goto done;
        }

        /* Transmit the packet */
        iob_put ( iobuf, dhcppkt.len );
        if ( ( rc = xfer_deliver_iob_meta ( &dhcp->xfer, iob_disown ( iobuf ),
                                            &meta ) ) != 0 ) {
                DBGC ( dhcp, "DHCP %p could not transmit UDP packet: %s\n",
                       dhcp, strerror ( rc ) );
                goto done;
        }

 done:
        free_iob ( iobuf );
        return rc;
}

/**
 * Receive new data
 *
 * @v xfer              Data transfer interface
 * @v iobuf             I/O buffer
 * @v meta              Transfer metadata
 * @ret rc              Return status code
 */
static int dhcp_deliver_iob ( struct xfer_interface *xfer,
                              struct io_buffer *iobuf,
                              struct xfer_metadata *meta ) {
        struct dhcp_session *dhcp =
                container_of ( xfer, struct dhcp_session, xfer );
        struct sockaddr_in *peer;
        size_t data_len;
        struct dhcp_packet *dhcppkt;
        struct dhcphdr *dhcphdr;
        uint8_t msgtype = 0;
        struct in_addr server_id = { 0 };
        int rc = 0;

        /* Sanity checks */
        if ( ! meta->src ) {
                DBGC ( dhcp, "DHCP %p received packet without source port\n",
                       dhcp );
                rc = -EINVAL;
                goto err_no_src;
        }
        peer = ( struct sockaddr_in * ) meta->src;

        /* Create a DHCP packet containing the I/O buffer contents.
         * Whilst we could just use the original buffer in situ, that
         * would waste the unused space in the packet buffer, and also
         * waste a relatively scarce fully-aligned I/O buffer.
         */
        data_len = iob_len ( iobuf );
        dhcppkt = zalloc ( sizeof ( *dhcppkt ) + data_len );
        if ( ! dhcppkt ) {
                rc = -ENOMEM;
                goto err_alloc_dhcppkt;
        }
        dhcphdr = ( ( ( void * ) dhcppkt ) + sizeof ( *dhcppkt ) );
        memcpy ( dhcphdr, iobuf->data, data_len );
        dhcppkt_init ( dhcppkt, dhcphdr, data_len );

        /* Identify message type */
        dhcppkt_fetch ( dhcppkt, DHCP_MESSAGE_TYPE, &msgtype,
                        sizeof ( msgtype ) );

        /* Identify server ID */
        dhcppkt_fetch ( dhcppkt, DHCP_SERVER_IDENTIFIER,
                        &server_id, sizeof ( server_id ) );

        /* Check for matching transaction ID */
        if ( dhcphdr->xid != dhcp_xid ( dhcp->netdev ) ) {
                DBGC ( dhcp, "DHCP %p %s from %s:%d has bad transaction "
                       "ID\n", dhcp, dhcp_msgtype_name ( msgtype ),
                       inet_ntoa ( peer->sin_addr ),
                       ntohs ( peer->sin_port ) );
                rc = -EINVAL;
                goto err_xid;
        };

        /* Handle packet based on current state */
        dhcp->state->rx ( dhcp, dhcppkt, peer, msgtype, server_id );

 err_xid:
        dhcppkt_put ( dhcppkt );
 err_alloc_dhcppkt:
 err_no_src:
        free_iob ( iobuf );
        return rc;
}

/** DHCP data transfer interface operations */
static struct xfer_interface_operations dhcp_xfer_operations = {
        .close          = ignore_xfer_close,
        .vredirect      = xfer_vreopen,
        .window         = unlimited_xfer_window,
        .alloc_iob      = default_xfer_alloc_iob,
        .deliver_iob    = dhcp_deliver_iob,
        .deliver_raw    = xfer_deliver_as_iob,
};

/**
 * Handle DHCP retry timer expiry
 *
 * @v timer             DHCP retry timer
 * @v fail              Failure indicator
 */
static void dhcp_timer_expired ( struct retry_timer *timer, int fail ) {
        struct dhcp_session *dhcp =
                container_of ( timer, struct dhcp_session, timer );

        /* If we have failed, terminate DHCP */
        if ( fail ) {
                dhcp_finished ( dhcp, -ETIMEDOUT );
                return;
        }

        /* Handle timer expiry based on current state */
        dhcp->state->expired ( dhcp );
}

/****************************************************************************
 *
 * Job control interface
 *
 */

/**
 * Handle kill() event received via job control interface
 *
 * @v job               DHCP job control interface
 */
static void dhcp_job_kill ( struct job_interface *job ) {
        struct dhcp_session *dhcp =
                container_of ( job, struct dhcp_session, job );

        /* Terminate DHCP session */
        dhcp_finished ( dhcp, -ECANCELED );
}

/** DHCP job control interface operations */
static struct job_interface_operations dhcp_job_operations = {
        .done           = ignore_job_done,
        .kill           = dhcp_job_kill,
        .progress       = ignore_job_progress,
};

/****************************************************************************
 *
 * Instantiators
 *
 */

/**
 * DHCP peer address for socket opening
 *
 * This is a dummy address; the only useful portion is the socket
 * family (so that we get a UDP connection).  The DHCP client will set
 * the IP address and source port explicitly on each transmission.
 */
static struct sockaddr dhcp_peer = {
        .sa_family = AF_INET,
};

/**
 * Start DHCP state machine on a network device
 *
 * @v job               Job control interface
 * @v netdev            Network device
 * @ret rc              Return status code, or positive if cached
 *
 * Starts DHCP on the specified network device.  If successful, the
 * DHCPACK (and ProxyDHCPACK, if applicable) will be registered as
 * option sources.
 *
 * On a return of 0, a background job has been started to perform the
 * DHCP request. Any nonzero return means the job has not been
 * started; a positive return value indicates the success condition of
 * having fetched the appropriate data from cached information.
 */
int start_dhcp ( struct job_interface *job, struct net_device *netdev ) {
        struct dhcp_session *dhcp;
        int rc;

        /* Check for cached DHCP information */
        get_cached_dhcpack();
        if ( fetch_uintz_setting ( NULL, &use_cached_setting ) ) {
                DBG ( "DHCP using cached network settings\n" );
                return 1;
        }

        /* Allocate and initialise structure */
        dhcp = zalloc ( sizeof ( *dhcp ) );
        if ( ! dhcp )
                return -ENOMEM;
        dhcp->refcnt.free = dhcp_free;
        job_init ( &dhcp->job, &dhcp_job_operations, &dhcp->refcnt );
        xfer_init ( &dhcp->xfer, &dhcp_xfer_operations, &dhcp->refcnt );
        dhcp->netdev = netdev_get ( netdev );
        dhcp->local.sin_family = AF_INET;
        dhcp->local.sin_port = htons ( BOOTPC_PORT );
        dhcp->timer.expired = dhcp_timer_expired;

        /* Instantiate child objects and attach to our interfaces */
        if ( ( rc = xfer_open_socket ( &dhcp->xfer, SOCK_DGRAM, &dhcp_peer,
                                  ( struct sockaddr * ) &dhcp->local ) ) != 0 )
                goto err;

        /* Enter DHCPDISCOVER state */
        dhcp_set_state ( dhcp, &dhcp_state_discover );

        /* Attach parent interface, mortalise self, and return */
        job_plug_plug ( &dhcp->job, job );
        ref_put ( &dhcp->refcnt );
        return 0;

 err:
        dhcp_finished ( dhcp, rc );
        ref_put ( &dhcp->refcnt );
        return rc;
}

/**
 * Retrieve list of PXE boot servers for a given server type
 *
 * @v dhcp              DHCP session
 * @v raw               DHCP PXE boot server list
 * @v raw_len           Length of DHCP PXE boot server list
 * @v ip                IP address list to fill in
 *
 * The caller must ensure that the IP address list has sufficient
 * space.
 */
static void pxebs_list ( struct dhcp_session *dhcp, void *raw,
                         size_t raw_len, struct in_addr *ip ) {
        struct dhcp_pxe_boot_server *server = raw;
        size_t server_len;
        unsigned int i;

        while ( raw_len ) {
                if ( raw_len < sizeof ( *server ) ) {
                        DBGC ( dhcp, "DHCP %p malformed PXE server list\n",
                               dhcp );
                        break;
                }
                server_len = offsetof ( typeof ( *server ),
                                        ip[ server->num_ip ] );
                if ( raw_len < server_len ) {
                        DBGC ( dhcp, "DHCP %p malformed PXE server list\n",
                               dhcp );
                        break;
                }
                if ( server->type == dhcp->pxe_type ) {
                        for ( i = 0 ; i < server->num_ip ; i++ )
                                *(ip++) = server->ip[i];
                }
                server = ( ( ( void * ) server ) + server_len );
                raw_len -= server_len;
        }
}

/**
 * Start PXE Boot Server Discovery on a network device
 *
 * @v job               Job control interface
 * @v netdev            Network device
 * @v pxe_type          PXE server type
 * @ret rc              Return status code
 *
 * Starts PXE Boot Server Discovery on the specified network device.
 * If successful, the Boot Server ACK will be registered as an option
 * source.
 */
int start_pxebs ( struct job_interface *job, struct net_device *netdev,
                  unsigned int pxe_type ) {
        struct setting pxe_discovery_control_setting =
                { .tag = DHCP_PXE_DISCOVERY_CONTROL };
        struct setting pxe_boot_servers_setting =
                { .tag = DHCP_PXE_BOOT_SERVERS };
        struct setting pxe_boot_server_mcast_setting =
                { .tag = DHCP_PXE_BOOT_SERVER_MCAST };
        ssize_t pxebs_list_len;
        struct dhcp_session *dhcp;
        struct in_addr *ip;
        unsigned int pxe_discovery_control;
        int rc;

        /* Get upper bound for PXE boot server IP address list */
        pxebs_list_len = fetch_setting_len ( NULL, &pxe_boot_servers_setting );
        if ( pxebs_list_len < 0 )
                pxebs_list_len = 0;

        /* Allocate and initialise structure */
        dhcp = zalloc ( sizeof ( *dhcp ) + sizeof ( *ip ) /* mcast */ +
                        sizeof ( *ip ) /* bcast */ + pxebs_list_len +
                        sizeof ( *ip ) /* terminator */ );
        if ( ! dhcp )
                return -ENOMEM;
        dhcp->refcnt.free = dhcp_free;
        job_init ( &dhcp->job, &dhcp_job_operations, &dhcp->refcnt );
        xfer_init ( &dhcp->xfer, &dhcp_xfer_operations, &dhcp->refcnt );
        dhcp->netdev = netdev_get ( netdev );
        dhcp->local.sin_family = AF_INET;
        fetch_ipv4_setting ( netdev_settings ( netdev ), &ip_setting,
                             &dhcp->local.sin_addr );
        dhcp->local.sin_port = htons ( BOOTPC_PORT );
        dhcp->pxe_type = cpu_to_le16 ( pxe_type );
        dhcp->timer.expired = dhcp_timer_expired;

        /* Construct PXE boot server IP address lists */
        pxe_discovery_control =
                fetch_uintz_setting ( NULL, &pxe_discovery_control_setting );
        ip = ( ( ( void * ) dhcp ) + sizeof ( *dhcp ) );
        dhcp->pxe_attempt = ip;
        if ( ! ( pxe_discovery_control & PXEBS_NO_MULTICAST ) ) {
                fetch_ipv4_setting ( NULL, &pxe_boot_server_mcast_setting, ip);
                if ( ip->s_addr )
                        ip++;
        }
        if ( ! ( pxe_discovery_control & PXEBS_NO_BROADCAST ) )
                (ip++)->s_addr = INADDR_BROADCAST;
        if ( pxe_discovery_control & PXEBS_NO_UNKNOWN_SERVERS )
                dhcp->pxe_accept = ip;
        if ( pxebs_list_len ) {
                uint8_t buf[pxebs_list_len];

                fetch_setting ( NULL, &pxe_boot_servers_setting,
                                buf, sizeof ( buf ) );
                pxebs_list ( dhcp, buf, sizeof ( buf ), ip );
        }
        if ( ! dhcp->pxe_attempt->s_addr ) {
                DBGC ( dhcp, "DHCP %p has no PXE boot servers for type %04x\n",
                       dhcp, pxe_type );
                rc = -EINVAL;
                goto err;
        }

        /* Dump out PXE server lists */
        DBGC ( dhcp, "DHCP %p attempting", dhcp );
        for ( ip = dhcp->pxe_attempt ; ip->s_addr ; ip++ )
                DBGC ( dhcp, " %s", inet_ntoa ( *ip ) );
        DBGC ( dhcp, "\n" );
        if ( dhcp->pxe_accept ) {
                DBGC ( dhcp, "DHCP %p accepting", dhcp );
                for ( ip = dhcp->pxe_accept ; ip->s_addr ; ip++ )
                        DBGC ( dhcp, " %s", inet_ntoa ( *ip ) );
                DBGC ( dhcp, "\n" );
        }

        /* Instantiate child objects and attach to our interfaces */
        if ( ( rc = xfer_open_socket ( &dhcp->xfer, SOCK_DGRAM, &dhcp_peer,
                                  ( struct sockaddr * ) &dhcp->local ) ) != 0 )
                goto err;

        /* Enter PXEBS state */
        dhcp_set_state ( dhcp, &dhcp_state_pxebs );

        /* Attach parent interface, mortalise self, and return */
        job_plug_plug ( &dhcp->job, job );
        ref_put ( &dhcp->refcnt );
        return 0;

 err:
        dhcp_finished ( dhcp, rc );
        ref_put ( &dhcp->refcnt );
        return rc;
}