event/Loop: integrate io_uring support

src/event/Loop.hxx

@@ -38,6 +38,12 @@
 #include <cassert>
 #include <chrono>
 
+#include "io/uring/Features.h"
+#ifdef HAVE_URING
+#include <memory>
+namespace Uring { class Queue; class Manager; }
+#endif
+
 /**
  * An event loop that polls for events on file/socket descriptors.
  *
@@ -82,6 +88,10 @@ class EventLoop final : SocketMonitor
 				       boost::intrusive::constant_time_size<false>> DeferredList;
 	DeferredList deferred;
 
+#ifdef HAVE_URING
+	std::unique_ptr<Uring::Manager> uring;
+#endif
+
 	std::chrono::steady_clock::time_point now = std::chrono::steady_clock::now();
 
 	/**
@@ -108,6 +118,10 @@ class EventLoop final : SocketMonitor
 	 */
 	bool busy = true;
 
+#ifdef HAVE_URING
+	bool uring_initialized = false;
+#endif
+
 	PollGroup poll_group;
 	PollResult poll_result;
 
@@ -135,6 +149,11 @@ public:
 		return now;
 	}
 
+#ifdef HAVE_URING
+	gcc_pure
+	Uring::Queue *GetUring() noexcept;
+#endif
+
 	/**
 	 * Stop execution of this #EventLoop at the next chance.  This
 	 * method is thread-safe and non-blocking: after returning, it