From 41c0bbab130fe5416755caab24897affc28a93e3 Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@musicpd.org>
Date: Thu, 8 Oct 2020 21:14:42 +0200
Subject: [PATCH] event/SocketMonitor: don't filter out ERROR/HANGUP

By bit-wise ANDing the reported flags with GetScheduledFlags(),
ERROR/HANGUP always get cleared.  This means the MPD event loop could
never report those conditions.
---
 src/event/SocketMonitor.cxx | 2 +-
 src/event/SocketMonitor.hxx | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/event/SocketMonitor.cxx b/src/event/SocketMonitor.cxx
index 018f7330e..5d78d85fe 100644
--- a/src/event/SocketMonitor.cxx
+++ b/src/event/SocketMonitor.cxx
@@ -30,7 +30,7 @@
 void
 SocketMonitor::Dispatch(unsigned flags) noexcept
 {
-	flags &= GetScheduledFlags();
+	flags &= GetScheduledFlags() | IMPLICIT_FLAGS;
 
 	if (flags != 0)
 		OnSocketReady(flags);
diff --git a/src/event/SocketMonitor.hxx b/src/event/SocketMonitor.hxx
index bb1e84354..eb8fcddb6 100644
--- a/src/event/SocketMonitor.hxx
+++ b/src/event/SocketMonitor.hxx
@@ -57,6 +57,12 @@ public:
 	static constexpr unsigned ERROR = PollGroup::ERROR;
 	static constexpr unsigned HANGUP = PollGroup::HANGUP;
 
+	/**
+	 * These flags are always reported by epoll_wait() and don't
+	 * need to be registered with epoll_ctl().
+	 */
+	static constexpr unsigned IMPLICIT_FLAGS = ERROR|HANGUP;
+
 	typedef std::make_signed<size_t>::type ssize_t;
 
 	explicit SocketMonitor(EventLoop &_loop) noexcept