source: bootcd/isolinux/syslinux-6.03/gpxe/src/net/tcpip.c

#include <stdint.h>
#include <string.h>
#include <errno.h>
#include <byteswap.h>
#include <gpxe/iobuf.h>
#include <gpxe/tables.h>
#include <gpxe/tcpip.h>

/** @file
 *
 * Transport-network layer interface
 *
 * This file contains functions and utilities for the
 * TCP/IP transport-network layer interface
 */

FILE_LICENCE ( GPL2_OR_LATER );

/** Process a received TCP/IP packet
 *
 * @v iobuf             I/O buffer
 * @v tcpip_proto       Transport-layer protocol number
 * @v st_src            Partially-filled source address
 * @v st_dest           Partially-filled destination address
 * @v pshdr_csum        Pseudo-header checksum
 * @ret rc              Return status code
 *
 * This function expects a transport-layer segment from the network
 * layer.  The network layer should fill in as much as it can of the
 * source and destination addresses (i.e. it should fill in the
 * address family and the network-layer addresses, but leave the ports
 * and the rest of the structures as zero).
 */
int tcpip_rx ( struct io_buffer *iobuf, uint8_t tcpip_proto, 
               struct sockaddr_tcpip *st_src,
               struct sockaddr_tcpip *st_dest,
               uint16_t pshdr_csum ) {
        struct tcpip_protocol *tcpip;

        /* Hand off packet to the appropriate transport-layer protocol */
        for_each_table_entry ( tcpip, TCPIP_PROTOCOLS ) {
                if ( tcpip->tcpip_proto == tcpip_proto ) {
                        DBG ( "TCP/IP received %s packet\n", tcpip->name );
                        return tcpip->rx ( iobuf, st_src, st_dest, pshdr_csum );
                }
        }

        DBG ( "Unrecognised TCP/IP protocol %d\n", tcpip_proto );
        free_iob ( iobuf );
        return -EPROTONOSUPPORT;
}

/** Transmit a TCP/IP packet
 *
 * @v iobuf             I/O buffer
 * @v tcpip_protocol    Transport-layer protocol
 * @v st_src            Source address, or NULL to use route default
 * @v st_dest           Destination address
 * @v netdev            Network device to use if no route found, or NULL
 * @v trans_csum        Transport-layer checksum to complete, or NULL
 * @ret rc              Return status code
 */
int tcpip_tx ( struct io_buffer *iobuf, struct tcpip_protocol *tcpip_protocol,
               struct sockaddr_tcpip *st_src, struct sockaddr_tcpip *st_dest,
               struct net_device *netdev, uint16_t *trans_csum ) {
        struct tcpip_net_protocol *tcpip_net;

        /* Hand off packet to the appropriate network-layer protocol */
        for_each_table_entry ( tcpip_net, TCPIP_NET_PROTOCOLS ) {
                if ( tcpip_net->sa_family == st_dest->st_family ) {
                        DBG ( "TCP/IP sending %s packet\n", tcpip_net->name );
                        return tcpip_net->tx ( iobuf, tcpip_protocol, st_src,
                                               st_dest, netdev, trans_csum );
                }
        }
        
        DBG ( "Unrecognised TCP/IP address family %d\n", st_dest->st_family );
        free_iob ( iobuf );
        return -EAFNOSUPPORT;
}

/**
 * Calculate continued TCP/IP checkum
 *
 * @v partial           Checksum of already-summed data, in network byte order
 * @v data              Data buffer
 * @v len               Length of data buffer
 * @ret cksum           Updated checksum, in network byte order
 *
 * Calculates a TCP/IP-style 16-bit checksum over the data block.  The
 * checksum is returned in network byte order.
 *
 * This function may be used to add new data to an existing checksum.
 * The function assumes that both the old data and the new data start
 * on even byte offsets; if this is not the case then you will need to
 * byte-swap either the input partial checksum, the output checksum,
 * or both.  Deciding which to swap is left as an exercise for the
 * interested reader.
 */
uint16_t tcpip_continue_chksum ( uint16_t partial, const void *data,
                                 size_t len ) {
        unsigned int cksum = ( ( ~partial ) & 0xffff );
        unsigned int value;
        unsigned int i;
        
        for ( i = 0 ; i < len ; i++ ) {
                value = * ( ( uint8_t * ) data + i );
                if ( i & 1 ) {
                        /* Odd bytes: swap on little-endian systems */
                        value = be16_to_cpu ( value );
                } else {
                        /* Even bytes: swap on big-endian systems */
                        value = le16_to_cpu ( value );
                }
                cksum += value;
                if ( cksum > 0xffff )
                        cksum -= 0xffff;
        }
        
        return ( ~cksum );
}

/**
 * Calculate TCP/IP checkum
 *
 * @v data              Data buffer
 * @v len               Length of data buffer
 * @ret cksum           Checksum, in network byte order
 *
 * Calculates a TCP/IP-style 16-bit checksum over the data block.  The
 * checksum is returned in network byte order.
 */
uint16_t tcpip_chksum ( const void *data, size_t len ) {
        return tcpip_continue_chksum ( TCPIP_EMPTY_CSUM, data, len );
}