title: iotop does not show any disk read statistics
body: <p>I am running a test to check disk read statistics. Here is the code for the same:</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  #include &lt;stdlib.h&gt;
  #include &lt;fcntl.h&gt;
  
  int main(int argc, char* argv)
  {
  int count=1000, size;
  char block[4096]="0";
  int fd = open("file1.txt",O_RDONLY | O_SYNC);
  //int pid = getpid();
  system("pid=$(ps -a | grep 'a.out' | awk '{print $1}'); iotop -bokp $pid &gt; test1c.out &amp;");
  system("echo 'Starts reading in 10'");
  srand(time(NULL));
  system("sleep 1");
      while(count--){
        int random = (rand()%16)*666;
        printf("%d;",random);
        lseek(fd, random, SEEK_SET);
        size = read(fd,block,4096);
        printf("Number of bytes read: %d\n", size);
        fsync(fd);
        //printf("Read 4kb from the file.\n");
      }
  system("sleep 1");
  system("killall iotop");
  }
  </code></pre>
  
  <p>As you can see, I am opening a large file, getting the PID of my a.out file, and passing it to iotop. After that I am randomly seeking to a 4kb block in the file and reading data.</p>
  
  <p>If you run this code on your system, you'll realize that iotop output shows 0kb reads throughout, which makes no sense. Am I doing something wrong?</p>