#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
#include <strings.h>
#include <sys/file.h>

extern const char *__progname;

static int fd;
static char sbuf[512];
static unsigned long long int min;
static unsigned long long int max;

static int readable(unsigned long long int o)
{
 int rrv;

#ifdef LB_SET
 static int lb_set_works = -1;

 if (o > 0x003fffff)
  { if (lb_set_works < 0)
     { lb_set_works = (lseek(fd,o,LB_SET) >= 0);
     }
    if (lb_set_works)
     { lseek(fd,o,LB_SET);
     }
    else
     { lseek(fd,o*(off_t)512,L_SET);
     }
  }
 else
#endif
  { lseek(fd,o*(off_t)512,L_SET);
  }
 rrv = read(fd,sbuf,512);
 if (rrv < 0)
  { printf("%llu: %s\n",o,strerror(errno));
    return(0);
  }
 else if (rrv == 0)
  { printf("%llu: EOF\n",o);
    return(0);
  }
 else if (rrv != 512)
  { printf("%llu: read %d\n",o,rrv);
    return(0);
  }
 else
  { printf("%llu: ok\n",o);
    return(1);
  }
}

int main(int, char **);
int main(int ac, char **av)
{
 if (ac < 2)
  { fprintf(stderr,"Usage: %s <raw-device>\n",__progname);
    exit(1);
  }
 fd = open(av[1],O_RDONLY|O_NDELAY,0);
 if (fd < 0)
  { perror(av[1]);
    exit(1);
  }
 min = 0;
 max = 1;
 while (readable(max))
  { min = max;
    max *= 2;
    if (max == 0)
     { fprintf(stderr,"%s: no end found\n",__progname);
       exit(1);
     }
  }
 while (max-min > 1)
  { unsigned long long int m;
    m = min + ((max-min)/2); /* (min+max)/2 may overflow! */
    if (readable(m))
     { min = m;
     }
    else
     { max = m;
     }
  }
 printf("%llu\n",max);
 exit(0);
}