source: lib/hash_toeplitz.c @ 5ba34eb

/**
 * A implementation of Microsofts RSS standard for hashing.
 * See http://msdn.microsoft.com/en-us/library/windows/hardware/ff570726%28v=vs.85%29.aspx
 * and the Scalable Networking: Eliminating the Receive Processing Bottleneck—Introducing RSS
 * white paper.
 * 
 */
#include "hash_toeplitz.h"
#include <string.h>
#include <stdlib.h>
#include <time.h>

static inline uint8_t get_bit(uint8_t byte, size_t num) {
        return byte & (0x80>>num);
}

/**
 * Takes a key of length 40 bytes == (320bits)
 * and expands it into 320 32 bit ints
 * each shifted left by 1 byte more than the last
 */
void toeplitz_hash_expand_key(toeplitz_conf_t *conf) {
        size_t i = 0, j;
        // Don't destroy the existing key
        char *key_cpy = malloc(40);
        memcpy(key_cpy, conf->key, 40);
        
        do {
                conf->key_cache[i] = *((uint32_t *) key_cpy);
                
                for (j = 0; j < 39 ; ++j) {
                        key_cpy[j] <<= 1;
                        key_cpy[j] |= (0x80 & key_cpy[j+1])>>7;
                }
                key_cpy[39] <<= 1;
                ++i;
        } while (i < 320);
        free(key_cpy);
}


/**
 * Creates a random unidirectional RSS key - a ip or ip+port combination in
 * the opposite directions will most likely get different hashes.
 * @param key must have 40 bytes of space to retrieve random the key
 */ 
void toeplitz_create_unikey(uint8_t *key) {
        int i;
        unsigned int seed = time(NULL);
        for (i = 0; i < 40; i++) {
                key[i] = (uint8_t) rand_r(&seed);
        }
}

/**
 * Create a bidirectional RSS key, i.e. ip and ip+port configurations
 * in opposite directions will receive the same hash
 * @param key must have 40 bytes of space to retrieve random the key
 */
void toeplitz_create_bikey(uint8_t *key) {
        unsigned int seed = time(NULL);
        int i;
        // Every thing is 16bit (port=16, ipv4=32, ipv6=128 
        // aligned so this will make the hash bidirectional
        uint16_t bi_key = (uint16_t) rand_r(&seed);
        uint16_t *bi_rep = (uint16_t *) key;
        for (i = 0; i < 20; i++) {
                bi_rep[i] = bi_key;
        }
}

void toeplitz_init_config(toeplitz_conf_t *conf, bool bidirectional)
{
        if (bidirectional) {
                toeplitz_create_bikey(conf->key);
        } else {
                toeplitz_create_unikey(conf->key);
        }
        toeplitz_hash_expand_key(conf);
}

/**
 * n is bits
 */
uint32_t toeplitz_hash(const toeplitz_conf_t *tc, const uint8_t *data, size_t offset, size_t n, uint32_t result)
{
        size_t byte;
        size_t bit, i = 0;
        const uint32_t * key_array = tc->key_cache + offset*8;
        for (byte = 0; byte < n; ++byte) {
                for (bit = 0; bit < 8; ++bit,++i) {
                        if (get_bit(data[byte], bit))
                                result ^= key_array[i];
                }
        }
        return result;
}

uint32_t toeplitz_first_hash(const toeplitz_conf_t *tc, const uint8_t *data, size_t n)
{
        return toeplitz_hash(tc, data, 0, n, 0);
}

uint64_t toeplitz_hash_packet(const libtrace_packet_t * pkt, const toeplitz_conf_t *cnf) {
        uint8_t proto;
        uint16_t eth_type;
        uint32_t remaining;
        uint32_t res = 0; // shutup warning, logic was to complex for gcc to follow
        void *layer3 = trace_get_layer3(pkt, &eth_type, &remaining);
        void *transport = NULL;
        size_t offset = 0;
        bool accept_tcp = false, accept_udp = false;

        if (cnf->hash_ipv6_ex || cnf->hash_tcp_ipv6_ex || cnf->x_hash_udp_ipv6_ex)
        {
                perror("We don't support ipv6 ex hashing yet\n");
        }

        if (layer3) {
                switch (eth_type) {
                        case TRACE_ETHERTYPE_IP:
                                // The packet needs to include source and dest which
                                // are at the very end of the header
                                if ((cnf->hash_ipv4 || cnf->hash_tcp_ipv4 || cnf->x_hash_udp_ipv4)
                                                && remaining >= sizeof(libtrace_ip_t)) {        
                                        libtrace_ip_t * ip = (libtrace_ip_t *)layer3;
                                        // Order here is src dst as required by RSS
                                        res = toeplitz_first_hash(cnf, (uint8_t *)&ip->ip_src, 8);
                                        offset = 8;
                                        accept_tcp = cnf->hash_tcp_ipv4;
                                        accept_udp = cnf->x_hash_udp_ipv4;
                                }
                                break;
                        case TRACE_ETHERTYPE_IPV6:
                                // TODO IPv6 EX
                                if ((cnf->hash_ipv6 || cnf->hash_tcp_ipv6 || cnf->x_hash_udp_ipv6)
                                                && remaining >= sizeof(libtrace_ip6_t)) {
                                        libtrace_ip6_t * ip6 = (libtrace_ip6_t *)layer3;
                                        // Order here is src dst as required by RSS
                                        res = toeplitz_first_hash(cnf, (uint8_t *)&ip6->ip_src, 32);
                                        offset = 32;
                                        accept_tcp = cnf->hash_tcp_ipv6;
                                        accept_udp = cnf->x_hash_udp_ipv6;
                                }
                                break;
                        default:
                                return 0;
                }
        }

        transport = trace_get_transport(pkt, &proto, &remaining);

        if (transport) {
                switch(proto) {
                        // Hash src & dst port
                        case TRACE_IPPROTO_UDP:
                                if (accept_udp && remaining >= 4) {
                                        res = toeplitz_hash(cnf, (uint8_t *)transport, offset, 4, res);
                                }
                                break;
                        case TRACE_IPPROTO_TCP:
                                if (accept_tcp && remaining >= 4) {
                                        res = toeplitz_hash(cnf, (uint8_t *)transport, offset, 4, res);
                                }
                                break;
                }
        }

        return res;
}