arp.c

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/*
 * 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 <stdint.h>
#include <string.h>
#include <byteswap.h>
#include <errno.h>
#include <gpxe/if_ether.h>
#include <gpxe/if_arp.h>
#include <gpxe/iobuf.h>
#include <gpxe/netdevice.h>
#include <gpxe/arp.h>

/** @file
 *
 * Address Resolution Protocol
 *
 * This file implements the address resolution protocol as defined in
 * RFC826.  The implementation is media-independent and
 * protocol-independent; it is not limited to Ethernet or to IPv4.
 *
 */

/** An ARP cache entry */
struct arp_entry {
        /** Network-layer protocol */
        struct net_protocol *net_protocol;
        /** Link-layer protocol */
        struct ll_protocol *ll_protocol;
        /** Network-layer address */
        uint8_t net_addr[MAX_NET_ADDR_LEN];
        /** Link-layer address */
        uint8_t ll_addr[MAX_LL_ADDR_LEN];
};

/** Number of entries in the ARP cache
 *
 * This is a global cache, covering all network interfaces,
 * network-layer protocols and link-layer protocols.
 */
#define NUM_ARP_ENTRIES 4

/** The ARP cache */
static struct arp_entry arp_table[NUM_ARP_ENTRIES];
#define arp_table_end &arp_table[NUM_ARP_ENTRIES]

static unsigned int next_new_arp_entry = 0;

struct net_protocol arp_protocol;

/**
 * Find entry in the ARP cache
 *
 * @v ll_protocol       Link-layer protocol
 * @v net_protocol      Network-layer protocol
 * @v net_addr          Network-layer address
 * @ret arp             ARP cache entry, or NULL if not found
 *
 */
static struct arp_entry *
arp_find_entry ( struct ll_protocol *ll_protocol,
                 struct net_protocol *net_protocol,
                 const void *net_addr ) {
        struct arp_entry *arp;

        for ( arp = arp_table ; arp < arp_table_end ; arp++ ) {
                if ( ( arp->ll_protocol == ll_protocol ) &&
                     ( arp->net_protocol == net_protocol ) &&
                     ( memcmp ( arp->net_addr, net_addr,
                                net_protocol->net_addr_len ) == 0 ) )
                        return arp;
        }
        return NULL;
}

/**
 * Look up media-specific link-layer address in the ARP cache
 *
 * @v netdev            Network device
 * @v net_protocol      Network-layer protocol
 * @v dest_net_addr     Destination network-layer address
 * @v source_net_addr   Source network-layer address
 * @ret dest_ll_addr    Destination link layer address
 * @ret rc              Return status code
 *
 * This function will use the ARP cache to look up the link-layer
 * address for the link-layer protocol associated with the network
 * device and the given network-layer protocol and addresses.  If
 * found, the destination link-layer address will be filled in in @c
 * dest_ll_addr.
 *
 * If no address is found in the ARP cache, an ARP request will be
 * transmitted on the specified network device and -ENOENT will be
 * returned.
 */
int arp_resolve ( struct net_device *netdev, struct net_protocol *net_protocol,
                  const void *dest_net_addr, const void *source_net_addr,
                  void *dest_ll_addr ) {
        struct ll_protocol *ll_protocol = netdev->ll_protocol;
        const struct arp_entry *arp;
        struct io_buffer *iobuf;
        struct arphdr *arphdr;
        int rc;

        /* Look for existing entry in ARP table */
        arp = arp_find_entry ( ll_protocol, net_protocol, dest_net_addr );
        if ( arp ) {
                DBG ( "ARP cache hit: %s %s => %s %s\n",
                      net_protocol->name, net_protocol->ntoa ( arp->net_addr ),
                      ll_protocol->name, ll_protocol->ntoa ( arp->ll_addr ) );
                memcpy ( dest_ll_addr, arp->ll_addr, ll_protocol->ll_addr_len);
                return 0;
        }
        DBG ( "ARP cache miss: %s %s\n", net_protocol->name,
              net_protocol->ntoa ( dest_net_addr ) );

        /* Allocate ARP packet */
        iobuf = alloc_iob ( MAX_LL_HEADER_LEN + sizeof ( *arphdr ) +
                          2 * ( MAX_LL_ADDR_LEN + MAX_NET_ADDR_LEN ) );
        if ( ! iobuf )
                return -ENOMEM;
        iob_reserve ( iobuf, MAX_LL_HEADER_LEN );

        /* Build up ARP request */
        arphdr = iob_put ( iobuf, sizeof ( *arphdr ) );
        arphdr->ar_hrd = ll_protocol->ll_proto;
        arphdr->ar_hln = ll_protocol->ll_addr_len;
        arphdr->ar_pro = net_protocol->net_proto;
        arphdr->ar_pln = net_protocol->net_addr_len;
        arphdr->ar_op = htons ( ARPOP_REQUEST );
        memcpy ( iob_put ( iobuf, ll_protocol->ll_addr_len ),
                 netdev->ll_addr, ll_protocol->ll_addr_len );
        memcpy ( iob_put ( iobuf, net_protocol->net_addr_len ),
                 source_net_addr, net_protocol->net_addr_len );
        memset ( iob_put ( iobuf, ll_protocol->ll_addr_len ),
                 0, ll_protocol->ll_addr_len );
        memcpy ( iob_put ( iobuf, net_protocol->net_addr_len ),
                 dest_net_addr, net_protocol->net_addr_len );

        /* Transmit ARP request */
        if ( ( rc = net_tx ( iobuf, netdev, &arp_protocol, 
                             netdev->ll_broadcast ) ) != 0 )
                return rc;

        return -ENOENT;
}

/**
 * Identify ARP protocol
 *
 * @v net_proto                 Network-layer protocol, in network-endian order
 * @ret arp_net_protocol        ARP protocol, or NULL
 *
 */
static struct arp_net_protocol * arp_find_protocol ( uint16_t net_proto ) {
        struct arp_net_protocol *arp_net_protocol;

        for_each_table_entry ( arp_net_protocol, ARP_NET_PROTOCOLS ) {
                if ( arp_net_protocol->net_protocol->net_proto == net_proto ) {
                        return arp_net_protocol;
                }
        }
        return NULL;
}

/**
 * Process incoming ARP packets
 *
 * @v iobuf             I/O buffer
 * @v netdev            Network device
 * @v ll_source         Link-layer source address
 * @ret rc              Return status code
 *
 * This handles ARP requests and responses as detailed in RFC826.  The
 * method detailed within the RFC is pretty optimised, handling
 * requests and responses with basically a single code path and
 * avoiding the need for extraneous ARP requests; read the RFC for
 * details.
 */
static int arp_rx ( struct io_buffer *iobuf, struct net_device *netdev,
                    const void *ll_source __unused ) {
        struct arphdr *arphdr = iobuf->data;
        struct arp_net_protocol *arp_net_protocol;
        struct net_protocol *net_protocol;
        struct ll_protocol *ll_protocol;
        struct arp_entry *arp;
        int merge = 0;

        /* Identify network-layer and link-layer protocols */
        arp_net_protocol = arp_find_protocol ( arphdr->ar_pro );
        if ( ! arp_net_protocol )
                goto done;
        net_protocol = arp_net_protocol->net_protocol;
        ll_protocol = netdev->ll_protocol;

        /* Sanity checks */
        if ( ( arphdr->ar_hrd != ll_protocol->ll_proto ) ||
             ( arphdr->ar_hln != ll_protocol->ll_addr_len ) ||
             ( arphdr->ar_pln != net_protocol->net_addr_len ) )
                goto done;

        /* See if we have an entry for this sender, and update it if so */
        arp = arp_find_entry ( ll_protocol, net_protocol,
                               arp_sender_pa ( arphdr ) );
        if ( arp ) {
                memcpy ( arp->ll_addr, arp_sender_ha ( arphdr ),
                         arphdr->ar_hln );
                merge = 1;
                DBG ( "ARP cache update: %s %s => %s %s\n",
                      net_protocol->name, net_protocol->ntoa ( arp->net_addr ),
                      ll_protocol->name, ll_protocol->ntoa ( arp->ll_addr ) );
        }

        /* See if we own the target protocol address */
        if ( arp_net_protocol->check ( netdev, arp_target_pa ( arphdr ) ) != 0)
                goto done;
        
        /* Create new ARP table entry if necessary */
        if ( ! merge ) {
                arp = &arp_table[next_new_arp_entry++ % NUM_ARP_ENTRIES];
                arp->ll_protocol = ll_protocol;
                arp->net_protocol = net_protocol;
                memcpy ( arp->ll_addr, arp_sender_ha ( arphdr ),
                         arphdr->ar_hln );
                memcpy ( arp->net_addr, arp_sender_pa ( arphdr ),
                         arphdr->ar_pln);
                DBG ( "ARP cache add: %s %s => %s %s\n",
                      net_protocol->name, net_protocol->ntoa ( arp->net_addr ),
                      ll_protocol->name, ll_protocol->ntoa ( arp->ll_addr ) );
        }

        /* If it's not a request, there's nothing more to do */
        if ( arphdr->ar_op != htons ( ARPOP_REQUEST ) )
                goto done;

        /* Change request to a reply */
        DBG ( "ARP reply: %s %s => %s %s\n", net_protocol->name,
              net_protocol->ntoa ( arp_target_pa ( arphdr ) ),
              ll_protocol->name, ll_protocol->ntoa ( netdev->ll_addr ) );
        arphdr->ar_op = htons ( ARPOP_REPLY );
        memswap ( arp_sender_ha ( arphdr ), arp_target_ha ( arphdr ),
                 arphdr->ar_hln + arphdr->ar_pln );
        memcpy ( arp_sender_ha ( arphdr ), netdev->ll_addr, arphdr->ar_hln );

        /* Send reply */
        net_tx ( iob_disown ( iobuf ), netdev, &arp_protocol,
                 arp_target_ha ( arphdr ) );

 done:
        free_iob ( iobuf );
        return 0;
}

/**
 * Transcribe ARP address
 *
 * @v net_addr  ARP address
 * @ret string  "<ARP>"
 *
 * This operation is meaningless for the ARP protocol.
 */
static const char * arp_ntoa ( const void *net_addr __unused ) {
        return "<ARP>";
}

/** ARP protocol */
struct net_protocol arp_protocol __net_protocol = {
        .name = "ARP",
        .net_proto = htons ( ETH_P_ARP ),
        .rx = arp_rx,
        .ntoa = arp_ntoa,
};