8634 epoll fails to wake on certain edge-triggered conditions
8635 epoll should not emit POLLNVAL
8636 recursive epoll should emit EPOLLRDNORM
Reviewed by: Jerry Jelinek <jerry.jelinek@joyent.com>
Reviewed by: Robert Mustacchi <rm@joyent.com>
Reviewed by: Toomas Soome <tsoome@me.com>
Reviewed by: Igor Kozhukhov <igor@dilos.org>

*** 105,120 ****
  
                      if (specified_events_are_satisfied_now) {
                            *reventsp = satisfied_events & events;
                      } else {
                            *reventsp = 0;
-                           if (!anyyet)
-                                 *phpp = &my_local_pollhead_structure;
                      }
                      return (0);
  
  
             2.     Allocate an instance of the pollhead structure. This
                    instance may be tied to the per-minor data structure defined
                    by the driver. The pollhead structure should be treated as a
                    "black box" by the driver. Initialize the pollhead structure
                    by filling it with zeroes. The size of this structure is
--- 105,135 ----
  
                      if (specified_events_are_satisfied_now) {
                            *reventsp = satisfied_events & events;
                      } else {
                            *reventsp = 0;
                      }
+                     if ((*reventsp == 0 && !anyyet) || (events & POLLET))
+                           *phpp = &my_local_pollhead_structure;
                      return (0);
  
+                   Note: Prior to the integration of epoll(5), which included
+                   edge-triggering via the POLLET flag, standard chpoll
+                   mechanisms would only provide a pollhead in phpp if there
+                   were no matching events.  Edge-triggered polling requires
+                   that pollwakeup() always be called for a resource, so if
+                   POLLET is set in the events of interest, the chpoll method
+                   must yield a pollhead and prepare to issue pollwakeup()
+                   calls on it.
  
+                   Drivers which are not wired up to make pollwakeup() calls on
+                   a pollhead when their status changes should emit one from
+                   their chpoll routine.  This will exclude the resource from
+                   caching by pollers, since it cannot alert them to new events
+                   without pollwakeup() notification.
+ 
+ 
             2.     Allocate an instance of the pollhead structure. This
                    instance may be tied to the per-minor data structure defined
                    by the driver. The pollhead structure should be treated as a
                    "black box" by the driver. Initialize the pollhead structure
                    by filling it with zeroes. The size of this structure is
*** 162,174 ****
  
  RETURN VALUES
         chpoll() should return 0 for success, or the appropriate error number.
  
  SEE ALSO
!        poll(2), nochpoll(9F), pollwakeup(9F)
  
  
         Writing Device Drivers
  
  
  
!                                   May 7, 2008                       CHPOLL(9E)
--- 177,189 ----
  
  RETURN VALUES
         chpoll() should return 0 for success, or the appropriate error number.
  
  SEE ALSO
!        poll(2), epoll(5), nochpoll(9F), pollwakeup(9F)
  
  
         Writing Device Drivers
  
  
  
!                                January 18, 2017                     CHPOLL(9E)