event/SocketMonitor: Schedule() returns bool

src/event/SocketMonitor.cxx

@@ -68,20 +68,24 @@ SocketMonitor::Close() noexcept
 	Steal().Close();
 }
 
-void
+bool
 SocketMonitor::Schedule(unsigned flags) noexcept
 {
 	assert(IsDefined());
 
 	if (flags == GetScheduledFlags())
-		return;
+		return true;
 
+	bool success;
 	if (scheduled_flags == 0)
-		loop.AddFD(fd.Get(), flags, *this);
+		success = loop.AddFD(fd.Get(), flags, *this);
 	else if (flags == 0)
-		loop.RemoveFD(fd.Get(), *this);
+		success = loop.RemoveFD(fd.Get(), *this);
 	else
-		loop.ModifyFD(fd.Get(), flags, *this);
+		success = loop.ModifyFD(fd.Get(), flags, *this);
+
+	if (success)
+		scheduled_flags = flags;
 
-	scheduled_flags = flags;
+	return success;
 }

src/event/SocketMonitor.hxx

@@ -98,18 +98,22 @@ public:
 		return scheduled_flags;
 	}
 
-	void Schedule(unsigned flags) noexcept;
+	/**
+	 * @return true on success, false on error (with errno set if
+	 * USE_EPOLL is defined)
+	 */
+	bool Schedule(unsigned flags) noexcept;
 
 	void Cancel() noexcept {
 		Schedule(0);
 	}
 
-	void ScheduleRead() noexcept {
-		Schedule(GetScheduledFlags() | READ | HANGUP | ERROR);
+	bool ScheduleRead() noexcept {
+		return Schedule(GetScheduledFlags() | READ | HANGUP | ERROR);
 	}
 
-	void ScheduleWrite() noexcept {
-		Schedule(GetScheduledFlags() | WRITE);
+	bool ScheduleWrite() noexcept {
+		return Schedule(GetScheduledFlags() | WRITE);
 	}
 
 	void CancelRead() noexcept {