/** @dir test4
This example probe tracks file opens, reads and writes.
It demonstrates maps, stats, and iterators.

This is a translation of on an old dtr probe.  Original source is
\verbatim
global {
  long @opens[string];
  sum @reads[string], @writes[string];
}

probe sys_open:entry {
  @opens[current->comm]++;
}

probe sys_read:entry {
  @reads[current->comm] << count;
}

probe sys_write:entry {
  @writes[current->comm] << count;
}
\endverbatim
*/