From f6475a290600ef07c4dcbd48ed8351a1cce51dff Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Mon, 24 Aug 2020 08:49:41 -0700
Subject: [PATCH] ircd::fs: Add interface to mmap fd.

---
 include/ircd/fs/fs.h  |   1 +
 include/ircd/fs/map.h |  57 +++++++++++++++++++
 ircd/fs.cc            | 126 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 184 insertions(+)
 create mode 100644 include/ircd/fs/map.h

diff --git a/include/ircd/fs/fs.h b/include/ircd/fs/fs.h
index c45da294d..eaba1f1f0 100644
--- a/include/ircd/fs/fs.h
+++ b/include/ircd/fs/fs.h
@@ -47,6 +47,7 @@ namespace ircd::fs
 #include "opts.h"
 #include "dev.h"
 #include "fd.h"
+#include "map.h"
 #include "wait.h"
 #include "read.h"
 #include "write.h"
diff --git a/include/ircd/fs/map.h b/include/ircd/fs/map.h
new file mode 100644
index 000000000..cfa0a3a13
--- /dev/null
+++ b/include/ircd/fs/map.h
@@ -0,0 +1,57 @@
+// The Construct
+//
+// Copyright (C) The Construct Developers, Authors & Contributors
+// Copyright (C) 2016-2020 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_MAP_H
+
+namespace ircd::fs
+{
+	struct map;
+}
+
+/// Interface to map file into memory.
+///
+/// Note that this was created specifically for file maps and not intended to
+/// be a generic mmap(2) interface, at least for now.
+struct ircd::fs::map
+:mutable_buffer
+{
+	struct opts;
+
+	map() = default;
+	map(const fd &, const opts &opts, const size_t &size = 0UL);
+	map(map &&) noexcept;
+	map(const map &) = delete;
+	map &operator=(map &&) noexcept;
+	map &operator=(const map &) = delete;
+	~map() noexcept;
+};
+
+/// Descriptor options (open options)
+struct ircd::fs::map::opts
+:fd::opts
+{
+	bool execute {false};
+	bool shared {false};
+	bool reserve {false};
+	bool populate {false};
+
+	opts(const fd::opts &opts = {std::ios::in})
+	:fd::opts(opts)
+	{}
+};
+
+inline
+ircd::fs::map::map(map &&other)
+noexcept
+:mutable_buffer{other}
+{
+	static_cast<mutable_buffer &>(other) = {};
+}
diff --git a/ircd/fs.cc b/ircd/fs.cc
index a05d38b45..b2af08b9a 100644
--- a/ircd/fs.cc
+++ b/ircd/fs.cc
@@ -1730,6 +1730,132 @@ noexcept
 }
 #endif
 
+///////////////////////////////////////////////////////////////////////////////
+//
+// fs/map.h
+//
+
+namespace ircd::fs
+{
+	static uint flags(const map::opts &);
+	static uint prot(const map::opts &);
+}
+
+ircd::fs::map::map(const fd &fd,
+                   const opts &opts,
+                   const size_t &size)
+{
+	const auto map_size
+	{
+		size?: fs::size(fd)
+	};
+
+	void *const &ptr
+	{
+		::mmap(nullptr, map_size, prot(opts), flags(opts), int(fd), opts.offset)
+	};
+
+	if(unlikely(ptr == MAP_FAILED))
+		throw_system_error(errno);
+
+	static_cast<mutable_buffer &>(*this) = mutable_buffer
+	{
+		reinterpret_cast<char *>(ptr),
+		map_size
+	};
+}
+
+ircd::fs::map::~map()
+noexcept try
+{
+	if(mutable_buffer::null())
+		return;
+
+	syscall(::munmap, data(*this), size(*this));
+}
+catch(const std::exception &e)
+{
+	log::critical
+	{
+		log, "munmap(%p, %zu) :%s",
+		data(static_cast<mutable_buffer &>(*this)),
+		size(static_cast<mutable_buffer &>(*this)),
+		e.what(),
+	};
+}
+
+ircd::fs::map &
+ircd::fs::map::operator=(map &&other)
+noexcept
+{
+	auto &ours
+	{
+		static_cast<mutable_buffer &>(*this)
+	};
+
+	auto &theirs
+	{
+		static_cast<mutable_buffer &>(other)
+	};
+
+	this->~map();
+	ours = theirs;
+	theirs = {};
+	return *this;
+}
+
+uint
+ircd::fs::prot(const map::opts &opts)
+{
+	uint ret
+	{
+		PROT_NONE
+	};
+
+	if(opts.mode & std::ios::in)
+		ret |= PROT_READ;
+
+	if(opts.mode & std::ios::out)
+		ret |= PROT_WRITE;
+
+	assert(!opts.execute);
+	if((false) && opts.execute)
+		ret |= PROT_EXEC;
+
+	return ret;
+}
+
+uint
+ircd::fs::flags(const map::opts &opts)
+{
+	uint ret
+	{
+		0
+	};
+
+	if(opts.shared)
+		ret |= MAP_SHARED;
+	else
+		ret |= MAP_PRIVATE;
+
+	#if defined(MAP_NONBLOCK)
+	if(!opts.blocking)
+		ret |= MAP_NONBLOCK;
+	#endif
+
+	#if defined(MAP_POPULATE)
+	if(opts.populate)
+		ret |= MAP_POPULATE;
+	#endif
+
+	#if defined(MAP_NORESERVE)
+	if(!opts.reserve)
+		ret |= MAP_NORESERVE;
+	#endif
+
+	return ret;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 //
 // fs/fd.h