These rules are intended to answer awkward questions.
"w"
,
"t"
and "p"
.
"r"
or "rw"
.
"w"
descriptors are automatically changed to "r"
descriptors.
If the function you are passing the descriptor to uses WIO (see
§3.8.6), then "p"
descriptors become "t"
.
If the function you are passing the descriptor to uses PIO, then "p"
descriptors are unchanged.