genode/repos/base/include/base/attached_ram_dataspace.h

/*
 * \brief  Utility to allocate and locally attach a RAM dataspace
 * \author Norman Feske
 * \date   2008-03-22
 */

/*
 * Copyright (C) 2008-2017 Genode Labs GmbH
 *
 * This file is part of the Genode OS framework, which is distributed
 * under the terms of the GNU Affero General Public License version 3.
 */

#ifndef _INCLUDE__BASE__ATTACHED_RAM_DATASPACE_H_
#define _INCLUDE__BASE__ATTACHED_RAM_DATASPACE_H_

#include <util/touch.h>
#include <base/ram_allocator.h>
#include <base/env.h>

namespace Genode { class Attached_ram_dataspace; }


/*
 * Utility for allocating and attaching a RAM dataspace
 *
 * The combination of RAM allocation and a local RM attachment is a frequent
 * use case. Each function may fail, which makes error handling inevitable.
 * This utility class encapsulates this functionality to handle both operations
 * as a transaction. When embedded as a member, this class also takes care
 * about freeing and detaching the dataspace at destruction time.
 */
class Genode::Attached_ram_dataspace
{
	private:

		size_t                    _size = 0;
		Ram_allocator            *_ram  = nullptr;
		Region_map               *_rm   = nullptr;
		Ram_dataspace_capability  _ds { };
		void                     *_local_addr = nullptr;
		Cache               const _cache = CACHED;

		template <typename T>
		static void _swap(T &v1, T &v2) { T tmp = v1; v1 = v2; v2 = tmp; }

		void _detach_and_free_dataspace()
		{
			if (_local_addr)
				_rm->detach(_local_addr);

			if (_ds.valid())
				_ram->free(_ds);
		}

		void _alloc_and_attach()
		{
			if (!_size) return;

			try {
				_ds         = _ram->alloc(_size, _cache);
				_local_addr = _rm->attach(_ds);
			}
			/* revert allocation if attaching the dataspace failed */
			catch (Region_map::Region_conflict)   { _ram->free(_ds); throw; }
			catch (Region_map::Invalid_dataspace) { _ram->free(_ds); throw; }

			/*
			 * Eagerly map dataspace if used for DMA
			 *
			 * On some platforms, namely Fiasco.OC on ARMv7, the handling
			 * of page faults interferes with the caching attributes used
			 * for uncached DMA memory. See issue #452 for more details
			 * (https://github.com/genodelabs/genode/issues/452). As a
			 * work-around for this issues, we eagerly map the whole
			 * dataspace before writing actual content to it.
			 */
			if (_cache != CACHED) {
				enum { PAGE_SIZE = 4096 };
				unsigned char volatile *base = (unsigned char volatile *)_local_addr;
				for (size_t i = 0; i < _size; i += PAGE_SIZE)
					touch_read_write(base + i);
			}
		}

		/*
		 * Noncopyable
		 */
		Attached_ram_dataspace(Attached_ram_dataspace const &);
		Attached_ram_dataspace &operator = (Attached_ram_dataspace const &);

	public:

		/**
		 * Constructor
		 *
		 * \throw Out_of_ram
		 * \throw Out_of_caps
		 * \throw Region_map::Region_conflict
		 * \throw Region_map::Invalid_dataspace
		 */
		Attached_ram_dataspace(Ram_allocator &ram, Region_map &rm,
		                       size_t size, Cache cache = CACHED)
		:
			_size(size), _ram(&ram), _rm(&rm), _cache(cache)
		{
			_alloc_and_attach();
		}

		/**
		 * Destructor
		 */
		~Attached_ram_dataspace() { _detach_and_free_dataspace(); }

		/**
		 * Return capability of the used RAM dataspace
		 */
		Ram_dataspace_capability cap() const { return _ds; }

		/**
		 * Request local address
		 *
		 * This is a template to avoid inconvenient casts at
		 * the caller. A newly allocated RAM dataspace is
		 * untyped memory anyway.
		 */
		template <typename T>
		T *local_addr() const { return static_cast<T *>(_local_addr); }

		/**
		 * Return size
		 */
		size_t size() const { return _size; }

		void swap(Attached_ram_dataspace &other)
		{
			_swap(_size,        other._size);
			_swap(_ram,         other._ram);
			_swap(_ds,          other._ds);
			_swap(_local_addr,  other._local_addr);
		}

		/**
		 * Re-allocate dataspace with a new size
		 *
		 * The content of the original dataspace is not retained.
		 */
		void realloc(Ram_allocator *ram_allocator, size_t new_size)
		{
			if (new_size < _size) return;

			_detach_and_free_dataspace();

			_size = new_size;
			_ram  = ram_allocator;

			_alloc_and_attach();
		}
};

#endif /* _INCLUDE__BASE__ATTACHED_RAM_DATASPACE_H_ */