relating to O_RDWR file descriptors, which while not defined in POSIX,
are in fact used:
(1) Revise assumption that we have two file descriptors when testing I/O
operations on a fifo. Provide cleanup routines that handle either
two or three file descriptors (including a kqueue descriptor).
(2) Add an openfifo_rw() routine to supplement openfifo().
(3) kqueue_setup() now configures an existing kqueue to monitor a new
file descriptor, rather than allocating a new kqueue to monitor two
existing file descriptors.
(4) Wrap all direct poll/select/kqueue/FIONREAD interactions in a single
function, assert_status(), which takes a file descriptor, kqueue
descriptor, assertion of read/writable/exception states, and
test description, then tests the assertion. This reduces the bulk
of calls in many of the tests, making them shorter, more readable,
and easier to determine correct.
(5) Add a new test_events_rdwr() function, which performs a basic create/
write/read event test on a O_RDWR fifo file descriptor. This is
currently failed by our fifo code in HEAD due to a bug in FIONREAD
handling. Fix to be merged shortly.
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