The value by which the statistic is to be
incremented. For most probes, this argument is always 1, but for some
it may take other values; these probes are noted in Table 24-1
to the current value of the statistic to be incremented. This value
is a 64–bit quantity that will be incremented by the value in
arg0. Dereferencing this pointer allows consumers to determine the current count of
the statistic corresponding to the probe.