pcapgen-i2c.c

/*BINFMTC:-Wall -std=gnu99 -I/d/src/wireshark-1.12.1+g01b65bf -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -lpcap
 *
 * Test to generate dummy pcap data for I2C communication.
 *
 * Usage:
 * $ ./pcapgen-i2c.c hoge.pcap
 * $ tshark -V -d wtap_encap==103,i2c -r hoge.pcap
 *
 * NOTE:
 * Not sure where WTAP_ENCAP value of 103 came from.
 * I had to use something for -d option to apply "decode-as" function, and
 * just happen to find that it can be used.
 */

#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <endian.h>
#include <pcap/pcap.h>
#include <wiretap/wtap.h>

/*
 * I2C link-layer on-disk format - from wiretap/pcap-common.c
 */
struct i2c_file_hdr {
    guint8 bus;
    guint8 flags[4];
};

int
main(int argc, char **argv) {
    pcap_dumper_t *pd;
    pcap_t *pc;

    struct {
        struct i2c_file_hdr header;
        uint8_t payload[1];
    } frame;

    int snaplen = sizeof(frame);
    pc = pcap_open_dead(DLT_IPMB, snaplen);
    pd = pcap_dump_open(pc, argv[1]);

    char msg[] = "hello, pcap";

    for (int i = 0; i < sizeof(msg); i++) {
        frame.payload[0] = msg[i];

        //
        // 0b00000000
        //   ^event bit
        //    ^^^^^^^bus address
        //
        frame.header.bus  = 0x17; // dummy address

        //
        // 0xaaaabbbb
        //   ^^^^I2C_EVENT_ERR_* bits
        //       ^^^^if is_event: I2C_EVENT_* non-ERR bits
        //                  else: I2C_FLAG_* bits
        //
        memset(frame.header.flags, 0, 4);

        struct pcap_pkthdr ph;

        // add timestamp
        gettimeofday(&ph.ts, NULL);

        // captured caplen out of len bytes
        ph.caplen = sizeof(frame);
        ph.len    = sizeof(frame);

        pcap_dump((u_char *)pd, &ph, (u_char *)&frame);
    }
    pcap_dump_close(pd);
    pcap_close(pc);

    return 0;
}