kqueue EVFILT_PROC: avoid collision between NOTE_CHILD and NOTE_EXIT

[vangyzen]

Summary

NOTE_CHILD and NOTE_EXIT return something in kevent.data: the parent
pid (ppid) for NOTE_CHILD and the exit status for NOTE_EXIT.
Do not let the two events be combined, since one would overwrite
the other's data.

PR: 180385
MFC after: 2 weeks
Submitted by: David A. Bright <[e-mail]>
Sponsored by: Dell Inc.

Test Plan

A unit test is included.

[jhb]

On the surface I think this looks good. Keeping NOTE_CHILD and NOTE_EXIT separate is definitely the right approach to avoid losing data.

tests/sys/kqueue/proc.c

98

I would probably say that a pipe() is best for a test, even if it is more work than a bare sleep().

194

s/CHILD/EXIT/

[vangyzen]

Use a pipe, instead of sleeping, for process synchronization.

Fix a copy-and-paste-o.

[vangyzen]

tests/sys/kqueue/proc.c

98

Agreed. In fact, the code that found this uses a pipe.