construct/include/ircd/fs/opts.h

// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.

#pragma once
#define HAVE_IRCD_FS_SYNC_OPTS_H

namespace ircd::fs
{
	struct opts extern const opts_default;

	int reqprio(int) noexcept __attribute__((const));
}

/// Options common to all operations
struct ircd::fs::opts
{
	static const int highest_priority;

	/// Offset in the file. If this is -1, for writes, it indicates an append
	/// at the end of the file (RWF_APPEND or legacy non-atomic lseek()).
	off_t offset {0};

	/// The enumerated operation code to identify the type of request being
	/// made at runtime from any abstract list of requests. This is set by
	/// the fs:: interface call and not the user in most cases. The user
	/// should not rely on this value being preserved if, e.g. they set a read
	/// opcode and then pass the opts structure to write().
	enum op op {op::NOOP};

	/// Request priority. Lower value takes priority over higher. The lowest
	/// possible priority value is special, on supporting platforms (RWF_HIPRI).
	/// One can either simply set the integer minimum or use the extern value.
	int8_t priority {0};

	/// Submits the I/O request immediately rather than allowing IRCd to
	/// queue requests for a few iterations of the ircd::ios event loop.
	/// (only relevant to aio).
	bool nodelay {false};

	/// Setting this to false enables non-blocking behavior. If the operation
	/// would block, EAGAIN is returned. This is only available with RWF_NOWAIT
	/// on newer systems, otherwise this value is ignored and is always true.
	/// This feature makes up for the fact that O_NONBLOCK when opening the
	/// file is ineffective for regular files.
	bool blocking {true};

	/// Determines whether this operation is conducted via AIO/io_uring. If
	/// not, a direct syscall is made. Using AIO will only block one ircd::ctx
	/// while a direct syscall will block the thread (all contexts). If AIO is
	/// not available or not enabled, or doesn't support this operation,
	/// setting this has no effect. If this system supports io_uring this
	/// option is reused to indicate use of io_uring (as AIO and io_uring are
	/// not used simultaneously).
	bool aio {true};

	/// Suppress logging of some expected/tolerated failures. Set to false
	/// if the call should just silently rethrow.
	bool errlog {true};
};