io/uring: basic Linux io_uring support

src/io/uring/Queue.hxx

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+/*
+ * Copyright 2020 CM4all GmbH
+ * All rights reserved.
+ *
+ * author: Max Kellermann <mk@cm4all.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "Ring.hxx"
+
+#include <liburing.h>
+
+#include <boost/intrusive/list.hpp>
+
+namespace Uring {
+
+class Operation;
+class CancellableOperation;
+
+/**
+ * High-level C++ wrapper for a `struct io_uring`.  It supports a
+ * handler class, cancellation, ...
+ */
+class Queue {
+	Ring ring;
+
+	boost::intrusive::list<CancellableOperation,
+			       boost::intrusive::base_hook<boost::intrusive::list_base_hook<boost::intrusive::link_mode<boost::intrusive::normal_link>>>,
+			       boost::intrusive::constant_time_size<false>> operations;
+
+public:
+	Queue(unsigned entries, unsigned flags);
+	~Queue() noexcept;
+
+	FileDescriptor GetFileDescriptor() const noexcept {
+		return ring.GetFileDescriptor();
+	}
+
+	struct io_uring_sqe *GetSubmitEntry() noexcept {
+		return ring.GetSubmitEntry();
+	}
+
+	bool HasPending() const noexcept {
+		return !operations.empty();
+	}
+
+protected:
+	void AddPending(struct io_uring_sqe &sqe,
+			Operation &operation) noexcept;
+
+public:
+	virtual void Push(struct io_uring_sqe &sqe,
+			  Operation &operation) noexcept {
+		AddPending(sqe, operation);
+		Submit();
+	}
+
+	void Submit() {
+		ring.Submit();
+	}
+
+	bool DispatchOneCompletion();
+
+	void DispatchCompletions() {
+		while (DispatchOneCompletion()) {}
+	}
+
+	bool WaitDispatchOneCompletion();
+
+	void WaitDispatchCompletions() {
+		while (WaitDispatchOneCompletion()) {}
+	}
+
+private:
+	void DispatchOneCompletion(struct io_uring_cqe &cqe) noexcept;
+};
+
+} // namespace Uring