dieid.c - Get die ID / generate random strings on Gumstix.

/* dieid.c:
 *   Tool to get die ID from Gumstix and to generate random strings from it.
 *
 * Copyright (C) 2013 Jason Cipriani, jason.cipriani@gmail.com
 *
 * If redistributed in source form please include this notice and the entire
 * source. If source is modified, a note must be added identifying the
 * author of the modifications.
 *
 * If redistributed in binary form, no attribution is required.
 *
 * This program can be used for any purpose. It is provided as-is and the
 * author is not responsible for any damage resulting from the use of this
 * software.
 *
 * Tested only on Gumstix Overo WaterSTORM COM.
 */

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

/* these may or may not be appropriate for all platforms... */
#define DIEID_OFFSET ((off_t)0x4830A218)
#define DIEID_LENGTH ((size_t)16)


/**
 * read dieid from /dev/mem.
 * @param dieid buffer to store result on success.
 * @return 0 on success, non-zero on error. prints message stderr on error.
 */
int read_dieid (unsigned char dieid[DIEID_LENGTH]) {

  int f, n;
  size_t pagesize, length;
  off_t start, dieaddr;
  void *m;

  if ((pagesize = sysconf(_SC_PAGESIZE)) == (size_t)-1) {
    perror("sysconf");
    return 1;
  }

  /* calculate page-aligned start and min # of pages required to get the id. */
  start = pagesize * (off_t)(DIEID_OFFSET / pagesize);
  dieaddr = DIEID_OFFSET - start;
  length = pagesize * (off_t)(1 + (DIEID_LENGTH - 1) / pagesize);

  if ((f = open("/dev/mem", O_RDONLY)) < 0) {
    perror("/dev/mem");
    return 1;
  }

  if ((m = mmap(NULL, length, PROT_READ, MAP_SHARED, f, start)) == (void *)-1) {
    perror("mmap");
    close(f);
    return 1;
  }

  /* bytes in memory are reversed from what u-boot prints on boot. */
  for (n = 0; n < (int)DIEID_LENGTH; ++ n)
    dieid[n] = ((const unsigned char *)m)[dieaddr + DIEID_LENGTH - n - 1];

  munmap(m, length);
  close(f);
  return 0;

}


/**
 * replace all ^ in template with random hex digit and print it. we use libc's
 * srand/rand. for libc independence or consistency, implement your own.
 * @param dieid die id, used as random seed.
 * @param template template string.
 */
void gen_template (const unsigned char dieid[DIEID_LENGTH], const char *template, int salt) {

  static const char hex[16] = "0123456789abcdef";
  unsigned long seed = 0, value = 0;
  int n;

  for (n = 0; n < (int)DIEID_LENGTH - 4; n += 4)
    seed += *(unsigned long *)(dieid + n);
  srand(seed + salt);

  while (*template) {
    if (*template == '^') {
      if (value == 0)
    value = rand();
      putchar(hex[value & 15]);
      value >>= 4;
    } else {
      putchar(*template);
    }
    ++ template;
  }

  putchar('\n');

}


int main (int argc, char **argv) {

  int salt = 0;
  const char *template = NULL;
  unsigned char dieid[DIEID_LENGTH];

  /** very basic arg parse. */
  if ((argc == 3 || argc == 4) && !strcmp(argv[1], "-m")) {
    template = argv[2];
    salt = (argc > 3) ? atoi(argv[3]) : 0;
  } else if (argc != 1) {
    fprintf(stderr, "usage: %s [ -m template [ salt ] ]\n\n", argv[0]);
    fprintf(stderr, "  no options: prints die id.\n");
    fprintf(stderr, "  -m template: replace all '^' in template with random hex digit.\n");
    fprintf(stderr, "               salt is an integer to produce different random output.\n\n");
    fprintf(stderr, "example: generate mac address with prefix:\n");
    fprintf(stderr, "  %s -m ab:cd:ef:^^:^^:^^\n\n", argv[0]);
    fprintf(stderr, "example: generate two random macs:\n");
    fprintf(stderr, "  %s -m ^^:^^:^^:^^:^^:^^ 1\n", argv[0]);
    fprintf(stderr, "  %s -m ^^:^^:^^:^^:^^:^^ 2\n\n", argv[0]);
    return 1;
  }

  if (read_dieid(dieid))
    return 1;

  if (template)
    gen_template(dieid, template, salt);
  else {
    int n;
    for (n = 0; n < (int)DIEID_LENGTH; ++ n)
      printf("%02x", (unsigned)dieid[n]);
    putchar('\n');
  }

  return 0;

}