Argument cannot be negative

The negative argument will be interpreted as a very large unsigned value. Negative value used as argument to a function expecting a positive value (for example, size of buffer or allocation)
/bench/wtperf/wtperf_misc.c:157: REVERSE_NEGATIVE 138744 Passing "rfd" to a parameter that cannot be negative.
/bench/wtperf/wtperf_misc.c:166: REVERSE_NEGATIVE 138744 You might be using variable "rfd" before verifying that it is >= 0.