genode/repos/os/include/ram_fs/file.h

/*
 * \brief  File node
 * \author Norman Feske
 * \date   2012-04-11
 */

/*
 * Copyright (C) 2012-2017 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__RAM_FS__FILE_H_
#define _INCLUDE__RAM_FS__FILE_H_

/* Genode includes */
#include <file_system_session/file_system_session.h>
#include <base/allocator.h>

/* local includes */
#include <ram_fs/node.h>
#include <ram_fs/chunk.h>

namespace File_system { class File; }


class File_system::File : public Node
{
	private:

		typedef Chunk<4096>                     Chunk_level_3;
		typedef Chunk_index<128, Chunk_level_3> Chunk_level_2;
		typedef Chunk_index<64,  Chunk_level_2> Chunk_level_1;
		typedef Chunk_index<64,  Chunk_level_1> Chunk_level_0;

		Chunk_level_0 _chunk;

		file_size_t _length;

	public:

		File(Allocator &alloc, char const *name)
		: _chunk(alloc, 0), _length(0) { Node::name(name); }

		size_t read(char *dst, size_t len, seek_off_t seek_offset)
		{
			file_size_t const chunk_used_size = _chunk.used_size();

			if (seek_offset == SEEK_TAIL)
				seek_offset = (len < _length) ? (_length - len) : 0;
			else if (seek_offset >= _length)
				return 0;

			/*
			 * Constrain read transaction to available chunk data
			 *
			 * Note that 'chunk_used_size' may be lower than '_length'
			 * because 'Chunk' may have truncated tailing zeros.
			 */
			if (seek_offset + len >= _length)
				len = _length - seek_offset;

			file_size_t read_len = len;

			if (seek_offset + read_len > chunk_used_size) {
				if (chunk_used_size >= seek_offset)
					read_len = chunk_used_size - seek_offset;
				else
					read_len = 0;
			}

			_chunk.read(dst, read_len, seek_offset);

			/* add zero padding if needed */
			if (read_len < len)
				memset(dst + read_len, 0, len - read_len);

			return len;
		}

		size_t write(char const *src, size_t len, seek_off_t seek_offset)
		{
			if (seek_offset == SEEK_TAIL)
				seek_offset = _length;

			if (seek_offset + len >= Chunk_level_0::SIZE) {
				len = (Chunk_level_0::SIZE-1) - seek_offset;
				Genode::error(name(), ": size limit ", (long)Chunk_level_0::SIZE, " reached");
			}

			_chunk.write(src, len, (size_t)seek_offset);

			/*
			 * Keep track of file length. We cannot use 'chunk.used_size()'
			 * as file length because trailing zeros may by represented
			 * by zero chunks, which do not contribute to 'used_size()'.
			 */
			_length = max(_length, seek_offset + len);

			mark_as_updated();
			return len;
		}

		file_size_t length() const { return _length; }

		void truncate(file_size_t size)
		{
			if (size < _chunk.used_size())
				_chunk.truncate(size);

			_length = size;

			mark_as_updated();
		}
};

#endif /* _INCLUDE__RAM_FS__FILE_H_ */