Implement kqueue(2) for procdesc(4).

kqueue(2) already supports EVFILT_PROC. Add an EVFILT_PROCDESC that
behaves the same, but operates on a procdesc(4) instead. Only implement
NOTE_EXIT for now. The nice thing about NOTE_EXIT is that it also
returns the exit status of the process, meaning that we can now obtain
this value, even if pdwait4(2) is still unimplemented.

Notes:

- Simply reuse EVFILT_NETDEV for EVFILT_PROCDESC. As both of these will
  be used on totally different descriptor types, this should not clash.

- Let procdesc_kqops_event() reuse the same structure as filt_proc().
  The only difference is that procdesc_kqops_event() should also be able
  to deal with the case where the process was already terminated after
  registration. Simply test this when hint == 0.

- Fix some style(9) issues in filt_proc() to keep it consistent with the
  newly added procdesc_kqops_event().

- Save the exit status of the process in pd->pd_xstat, as we cannot pick
  up the proctree_lock from within procdesc_kqops_event().

Discussed on:	arch@
Reviewed by:	kib@

2 files changed, 27 insertions, 2 deletions

diff --git a/lib/libc/sys/kqueue.2 b/lib/libc/sys/kqueue.2
index 75c8207..1b2951e 100644
--- a/lib/libc/sys/kqueue.2
+++ b/lib/libc/sys/kqueue.2
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd November 4, 2013
+.Dd April 7, 2014
 .Dt KQUEUE 2
 .Os
 .Sh NAME
@@ -412,6 +412,24 @@ and the child process will not signal a NOTE_CHILD event.
 On return,
 .Va fflags
 contains the events which triggered the filter.
+.It EVFILT_PROCDESC
+Takes the process descriptor created by
+.Xr pdfork 2
+to monitor as the identifier and the events to watch for in
+.Va fflags ,
+and returns when the associated process performs one or more of the
+requested events.
+The events to monitor are:
+.Bl -tag -width XXNOTE_EXIT
+.It NOTE_EXIT
+The process has exited.
+The exit status will be stored in
+.Va data .
+.El
+.Pp
+On return,
+.Va fflags
+contains the events which triggered the filter.
 .It EVFILT_SIGNAL
 Takes the signal number to monitor as the identifier and returns
 when the given signal is delivered to the process.
diff --git a/lib/libc/sys/pdfork.2 b/lib/libc/sys/pdfork.2
index 87f2c8c..a489515 100644
--- a/lib/libc/sys/pdfork.2
+++ b/lib/libc/sys/pdfork.2
@@ -32,7 +32,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd April 4, 2014
+.Dd April 7, 2014
 .Dt PDFORK 2
 .Os
 .Sh NAME
@@ -117,6 +117,13 @@ and
 allow waiting for process state transitions; currently only
 .Dv POLLHUP
 is defined, and will be raised when the process dies.
+Process state transitions can also be monitored using
+.Xr kqueue 2
+filter
+.Dv EVFILT_PROCDESC ;
+currently only
+.Dv NOTE_EXIT
+is implemented.
 .Pp
 .Xr close 2
 will close the process descriptor unless