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/*
* OpenVPN -- An application to securely tunnel IP networks
* over a single TCP/UDP port, with support for SSL/TLS-based
* session authentication and key exchange,
* packet encryption, packet authentication, and
* packet compression.
*
* Copyright (C) 2010-2018 Fox Crypto B.V. <openvpn@fox-it.com>
*
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
/**
* @file
* Memory management strategies documentation file.
*/
/**
* @page memory_management OpenVPN's memory management strategies
*
* This section describes several implementation details relating to
* OpenVPN's memory management strategies.
*
* During operation, the OpenVPN process performs all kinds of operations
* on blocks of data. Receiving packets, encrypting content, prepending
* headers, etc. To make the programmer's job easier and to decrease the
* likelihood of memory-related bugs, OpenVPN uses its own memory %buffer
* library and garbage collection facilities. These are described in
* brief here.
*
* @section memory_management_buffer The buffer structure
*
* The \c buffer structure is a wrapper around a block of dynamically
* allocated memory which keeps track of the block's capacity \c
* buffer.capacity and location in memory \c buffer.data. This structure
* supports efficient prepending and appending within the allocated memory
* through the use of offset \c buffer.offset and length \c buffer.len
* fields. See the \c buffer documentation for more details on the
* structure itself.
*
* OpenVPN's %buffer library, implemented in the \c buffer.h and \c
* buffer.c files, contains many utility functions for working with \c
* buffer structures. These functions facilitate common operations, such
* as allocating, freeing, reading and writing to \c buffer structures,
* and even offer several more advanced operations, such as string
* matching and creating sub-buffers.
*
* Not only do these utility functions make working with \c buffer
* structures easy, they also perform extensive error checking. Each
* function, where necessary, checks whether enough space is available
* before performing its actions. This minimizes the chance of bugs
* leading to %buffer overflows and other vulnerabilities.
*
* @section memory_management_frame The frame structure
*
* The \c frame structure keeps track of the maximum allowed packet
* geometries of a network connection.
*
* It is used, for example, to determine the size of \c buffer structures
* in which to store data channel packets. This is done by having each
* data channel processing module register the maximum amount of extra
* space it will need for header prepending and content expansion in the
* \c frame structure. Once these parameters are known, \c buffer
* structures can be allocated, based on the \c frame parameters, so that
* they are large enough to allow efficient prepending of headers and
* processing of content.
*
* @section memory_management_garbage Garbage collection
*
* OpenVPN has many sizable functions which perform various actions
* depending on their %context. This makes it difficult to know in advance
* exactly how much memory must be allocated. The garbage collection
* facilities are used to keep track of dynamic allocations, thereby
* allowing easy collective freeing of the allocated memory.
*
* The garbage collection system is implemented by the \c gc_arena and \c
* gc_entry structures. The arena represents a garbage collecting unit,
* and contains a linked list of entries. Each entry represents one block
* of dynamically allocated memory.
*
* The garbage collection system also contains various utility functions
* for working with the garbage collection structures. These include
* functions for initializing new arenas, allocating memory of a given
* size and registering the allocation in an arena, and freeing all the
* allocated memory associated with an arena.
*/
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