Report kqueue ebadf, epipe, and eperm as EV_READ events

When asked to add one side of a pipe, and the other side has been
closed, kqueue on NetBSD will say EBADF; kqueue on FreeBSD will say
EPIPE, and kqueue on OpenBSD will say EPERM.  So treat all of these
as EV_READ events, to give the user an opportunity to notice that
the pipe is closed.

Diagnosed by Nicholas Marriott and Dale Rahn; based on a patch by
Nicholas Marriott.

1 files changed, 46 insertions, 19 deletions

diff --git a/kqueue.c b/kqueue.c
index 8b486346..2e8b1724 100644
--- a/kqueue.c
+++ b/kqueue.c
@@ -51,8 +51,10 @@
  * easy way to tell them apart via autoconf, so we need to use OS macros. */
 #if defined(_EVENT_HAVE_INTTYPES_H) && !defined(__OpenBSD__) && !defined(__FreeBSD__) && !defined(__darwin__) && !defined(__APPLE__)
 #define PTR_TO_UDATA(x)	((intptr_t)(x))
+#define INT_TO_UDATA(x) ((intptr_t)(x))
 #else
 #define PTR_TO_UDATA(x)	(x)
+#define INT_TO_UDATA(x) ((void*)(x))
 #endif
 
 #include "event-internal.h"
@@ -169,6 +171,8 @@ kq_sighandler(int sig)
 	/* Do nothing here */
 }
 
+#define ADD_UDATA 0x30303
+
 static void
 kq_setup_kevent(struct kevent *out, evutil_socket_t fd, int filter, short change)
 {
@@ -178,6 +182,9 @@ kq_setup_kevent(struct kevent *out, evutil_socket_t fd, int filter, short change
 
 	if (change & EV_CHANGE_ADD) {
 		out->flags = EV_ADD;
+		/* We set a magic number here so that we can tell 'add'
+		 * errors from 'del' errors. */
+		out->udata = INT_TO_UDATA(ADD_UDATA);
 		if (change & EV_ET)
 			out->flags |= EV_CLEAR;
 #ifdef NOTE_EOF
@@ -316,27 +323,47 @@ kq_dispatch(struct event_base *base, struct timeval *tv)
 		int which = 0;
 
 		if (events[i].flags & EV_ERROR) {
-			/*
-			 * Error messages that can happen, when a delete fails.
-			 *   EBADF happens when the file descriptor has been
-			 *   closed,
-			 *   ENOENT when the file descriptor was closed and
-			 *   then reopened.
-			 *   EINVAL for some reasons not understood; EINVAL
-			 *   should not be returned ever; but FreeBSD does :-\
-			 * An error is also indicated when a callback deletes
-			 * an event we are still processing.  In that case
-			 * the data field is set to ENOENT.
-			 */
-			if (events[i].data == EBADF ||
-			    events[i].data == EINVAL ||
-			    events[i].data == ENOENT)
+			switch (events[i].data) {
+
+			/* Can occur on delete if we are not currently
+			 * watching any events on this fd.  That can
+			 * happen when the fd was closed and another
+			 * file was opened with that fd. */
+			case ENOENT:
+			/* Can occur for reasons not fully understood
+			 * on FreeBSD. */
+			case EINVAL:
 				continue;
-			errno = events[i].data;
-			return (-1);
-		}
 
-		if (events[i].filter == EVFILT_READ) {
+			/* Can occur on a delete if the fd is closed.  Can
+			 * occur on an add if the fd was one side of a pipe,
+			 * and the other side was closed. */
+			case EBADF:
+			/* These two can occur on an add if the fd was one side
+			 * of a pipe, and the other side was closed. */
+			case EPERM:
+			case EPIPE:
+				/* Report read events, if we're listening for
+				 * them, so that the user can learn about any
+				 * add errors.  (If the operation was a
+				 * delete, then udata should be cleared.) */
+				if (events[i].udata) {
+					/* The operation was an add:
+					 * report the error as a read. */
+					which |= EV_READ;
+					break;
+				} else {
+					/* The operation was a del:
+					 * report nothing. */
+					continue;
+				}
+
+			/* Other errors shouldn't occur. */
+			default:
+				errno = events[i].data;
+				return (-1);
+			}
+		} else if (events[i].filter == EVFILT_READ) {
 			which |= EV_READ;
 		} else if (events[i].filter == EVFILT_WRITE) {
 			which |= EV_WRITE;