|author||David Sommerseth <email@example.com>||2011-07-28 23:25:07 +0200|
|committer||David Sommerseth <firstname.lastname@example.org>||2011-07-28 23:25:07 +0200|
|parent||Added reliability layer documentation (diff)|
Added memory management documentation
Signed-off-by: Adriaan de Jong <email@example.com> Acked-by: James Yonan <firstname.lastname@example.org> Signed-off-by: David Sommerseth <email@example.com>
2 files changed, 147 insertions, 9 deletions
@@ -42,14 +42,30 @@
-/* basic buffer class for OpenVPN */
+ * Wrapper structure for dynamically allocated memory.
+ * The actual content stored in a \c buffer structure starts at the memory
+ * location \c buffer.data \c + \c buffer.offset, and has a length of \c
+ * buffer.len bytes. This, together with the space available before and
+ * after the content, is represented in the pseudocode below:
+uint8_t *content_start = buffer.data + buffer.offset;
+uint8_t *content_end = buffer.data + buffer.offset + buffer.len;
+int prepend_capacity = buffer.offset;
+int append_capacity = buffer.capacity - (buffer.offset + buffer.len);
- int capacity; /* size of buffer allocated by malloc */
- int offset; /* data starts at data + offset, offset > 0 to allow for efficient prepending */
- int len; /* length of data that starts at data + offset */
- uint8_t *data;
+ int capacity; /**< Size in bytes of memory allocated by
+ * \c malloc(). */
+ int offset; /**< Offset in bytes of the actual content
+ * within the allocated memory. */
+ int len; /**< Length in bytes of the actual content
+ * within the allocated memory. */
+ uint8_t *data; /**< Pointer to the allocated memory. */
const char *debug_file;
@@ -57,18 +73,41 @@ struct buffer
-/* for garbage collection */
+ * Garbage collection entry for one dynamically allocated block of memory.
+ * This structure represents one link in the linked list contained in a \c
+ * gc_arena structure. Each time the \c gc_malloc() function is called,
+ * it allocates \c sizeof(gc_entry) + the requested number of bytes. The
+ * \c gc_entry is then stored as a header in front of the memory address
+ * returned to the caller.
- struct gc_entry *next;
+ struct gc_entry *next; /**< Pointer to the next item in the
+ * linked list. */
+ * Garbage collection arena used to keep track of dynamically allocated
+ * memory.
+ * This structure contains a linked list of \c gc_entry structures. When
+ * a block of memory is allocated using the \c gc_malloc() function, the
+ * allocation is registered in the function's \c gc_arena argument. All
+ * the dynamically allocated memory registered in a \c gc_arena can be
+ * freed using the \c gc_free() function.
- struct gc_entry *list;
+ struct gc_entry *list; /**< First element of the linked list of
+ * \c gc_entry structures. */
#define BPTR(buf) (buf_bptr(buf))
#define BEND(buf) (buf_bend(buf))
#define BLAST(buf) (buf_blast(buf))
diff --git a/doc_memory_management.h b/doc_memory_management.h
new file mode 100644
@@ -0,0 +1,99 @@
+ * 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 Fox Crypto B.V. <firstname.lastname@example.org>
+ * 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 (see the file COPYING included with this
+ * distribution); if not, write to the Free Software Foundation, Inc.,
+ * 59 Temple Place, Suite 330, Boston, MA 02111-1307 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.