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authorDavid Sommerseth <dazo@users.sourceforge.net>2011-07-28 23:56:24 +0200
committerDavid Sommerseth <dazo@users.sourceforge.net>2011-07-28 23:56:24 +0200
commit98619012e242176bcbdc3215fa462fa2cf882e36 (patch)
tree0b5178b62a70fb162a1afe44b0608018a4d92c52
parentAdded data channel fragmentation docs (diff)
downloadopenvpn-98619012e242176bcbdc3215fa462fa2cf882e36.tar.gz
Added main/control docs
Signed-off-by: Adriaan de Jong <dejong@fox-it.com> Acked-by: James Yonan <james@openvpn.net> Signed-off-by: David Sommerseth <dazo@users.sourceforge.net>
-rw-r--r--doc_control_processor.h189
-rw-r--r--doc_data_control.h103
-rw-r--r--doc_eventloop.h67
-rw-r--r--doc_external_multiplexer.h46
-rw-r--r--doc_internal_multiplexer.h44
-rw-r--r--doc_mainpage.h162
-rw-r--r--doc_protocol_overview.h199
-rw-r--r--doc_tunnel_state.h155
-rw-r--r--forward.h163
-rw-r--r--mtcp.h9
-rw-r--r--mtu.h68
-rw-r--r--mudp.c14
-rw-r--r--mudp.h29
-rw-r--r--multi.h161
-rw-r--r--openvpn.c31
-rw-r--r--openvpn.h153
16 files changed, 1476 insertions, 117 deletions
diff --git a/doc_control_processor.h b/doc_control_processor.h
new file mode 100644
index 0000000..072dc37
--- /dev/null
+++ b/doc_control_processor.h
@@ -0,0 +1,189 @@
+/*
+ * 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. <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 (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
+ * Control Channel Processor module documentation file.
+ */
+
+/**
+ * @defgroup control_processor Control Channel Processor module
+ *
+ * This module controls the setup and maintenance of VPN tunnels and the
+ * associated security parameters.
+ *
+ * @par This module's role
+ * The Control Channel Processor module lies at the core of OpenVPN's
+ * activities. It handles the setup of new VPN tunnels, the negotiation
+ * of data channel security parameters, the managing of active VPN
+ * tunnels, and finally the cleanup of expired VPN tunnels.
+ *
+ * @par State structures
+ * A large amount of VPN tunnel state information must be stored within an
+ * OpenVPN process. A wide variety of container structures are used by
+ * this module for that purpose. Several of these structures are listed
+ * below, and the function of the first three VPN tunnel state containers
+ * is described in more detail later.
+ * - VPN tunnel state containers:
+ * - \c tls_multi, security parameter state for a single VPN tunnel.
+ * Contains three instances of the \c tls_session structure.
+ * - \c tls_session, security parameter state of a single session
+ * within a VPN tunnel. Contains two instances of the \c key_state
+ * structure.
+ * - \c key_state, security parameter state of one TLS and data
+ * channel %key set.
+ * - Data channel security parameter containers:
+ * - \c key_ctx_bi, container for two sets of OpenSSL cipher and/or
+ * HMAC context (both directions). Contains two instances of the \c
+ * key_ctx structure.
+ * - \c key_ctx, container for one set of OpenSSL cipher and/or HMAC
+ * context (one directions.
+ * - Key material containers:
+ * - \c key2, container for two sets of cipher and/or HMAC %key
+ * material (both directions). Contains two instances of the \c key
+ * structure.
+ * - \c key, container for one set of cipher and/or HMAC %key material
+ * (one direction).
+ * - \c key_direction_state, ordering of %key material within the \c
+ * key2.key array.
+ * - Key method 2 random material containers:
+ * - \c key_source2, container for both halves of random material used
+ * for %key method 2. Contains two instances of the \c key_source
+ * structure.
+ * - \c key_source, container for one half of random material used for
+ * %key method 2.
+ *
+ * @par The life of a \c tls_multi object
+ * A \c tls_multi structure contains all the security parameter state
+ * information related to the control and data channels of one VPN tunnel.
+ * Its life cycle can be summarized as follows:
+ * -# Initialization: \c tls_multi_init() and \c
+ * tls_multi_init_finalize(), which are called (indirectly) from \c
+ * init_instance() when initializing a new \c context structure.
+ * - Initializes a \c tls_multi structure.
+ * - Allocates the three \c tls_session objects contained by the \c
+ * tls_multi structure, and initializes as appropriate.
+ * -# Management: \c tls_multi_process() and \c tls_pre_decrypt()
+ * - If a new session is initiated by the remote peer, then \c
+ * tls_pre_decrypt() starts the new session negotiation in the
+ * un-trusted \c tls_session.
+ * - If the, as yet, un-trusted \c tls_session authenticates
+ * successfully, then \c tls_multi_process() moves it so as to be
+ * the active \c tls_session.
+ * - If an error occurs during processing of a \c key_state object,
+ * then \c tls_multi_process() cleans up and initializes the
+ * associated \c tls_session object. If the error occurred in the
+ * active \c key_state of the active \c tls_session and the
+ * lame-duck \c key_state of that \c tls_session has not yet
+ * expired, it is preserved as fallback.
+ * -# Cleanup: \c tls_multi_free(), which is called (indirectly) from \c
+ * close_instance() when cleaning up a \c context structure.
+ * - Cleans up a \c tls_multi structure.
+ * - Cleans up the three \c tls_session objects contained by the \c
+ * tls_multi structure.
+ *
+ * @par The life of a \c tls_session object
+ * A \c tls_session structure contains the state information related to an
+ * active and a lame-duck \c key_state. Its life cycle can be summarized
+ * as follows:
+ * -# Initialization: \c tls_session_init()
+ * - Initializes a \c tls_session structure.
+ * - Initializes the primary \c key_state by calling \c
+ * key_state_init().
+ * -# Renegotiation: \c key_state_soft_reset()
+ * - Cleans up the old lame-duck \c key_state by calling \c
+ * key_state_free().
+ * - Moves the old primary \c key_state to be the new lame-duck \c
+ * key_state.
+ * - Initializes a new primary \c key_state by calling \c
+ * key_state_init().
+ * -# Cleanup: \c tls_session_free()
+ * - Cleans up a \c tls_session structure.
+ * - Cleans up all \c key_state objects associated with the session by
+ * calling \c key_state_free() for each.
+ *
+ * @par The life of a \c key_state object
+ * A \c key_state structure represents one control and data channel %key
+ * set. It contains an OpenSSL TLS object that encapsulates the control
+ * channel, and the data channel security parameters needed by the \link
+ * data_crypto Data Channel Crypto module\endlink to perform cryptographic
+ * operations on data channel packets. Its life cycle can be summarized
+ * as follows:
+ * -# Initialization: \c key_state_init()
+ * - Initializes a \c key_state structure.
+ * - Creates a new OpenSSL TLS object to encapsulate this new control
+ * channel session.
+ * - Sets \c key_state.state to \c S_INITIAL.
+ * - Allocates several internal buffers.
+ * - Initializes new reliability layer structures for this key set.
+ * -# Negotiation: \c tls_process()
+ * - The OpenSSL TLS object negotiates a TLS session between itself
+ * and the remote peer's TLS object.
+ * - Key material is generated and exchanged through the TLS session
+ * between OpenVPN peers.
+ * - Both peers initialize their data channel cipher and HMAC key
+ * contexts.
+ * - On successful negotiation, the \c key_state.state will progress
+ * from \c S_INITIAL to \c S_ACTIVE and \c S_NORMAL.
+ * -# Active tunneling: \link data_crypto Data Channel Crypto
+ * module\endlink
+ * - Data channel packet to be sent to a remote OpenVPN peer:
+ * - \c tls_pre_encrypt() loads the security parameters from the \c
+ * key_state into a \c crypto_options structure.
+ * - \c openvpn_encrypt() uses the \c crypto_options to an encrypt
+ * and HMAC sign the data channel packet.
+ * - Data channel packet received from a remote OpenVPN peer:
+ * - \c tls_pre_decrypt() loads the security parameters from the \c
+ * key_state into a \c crypto_options structure.
+ * - \c openvpn_encrypt() uses the \c crypto_options to
+ * authenticate and decrypt the data channel packet.
+ * -# Cleanup: \c key_state_free()
+ * - Cleans up a \c key_state structure together with its OpenSSL TLS
+ * object, key material, internal buffers, and reliability layer
+ * structures.
+ *
+ * @par Control functions
+ * The following two functions drive the Control Channel Processor's
+ * activities.
+ * - \c tls_multi_process(), iterates through the \c tls_session objects
+ * within a given \c tls_multi of a VPN tunnel, and calls \c
+ * tls_process() for each \c tls_session which is being set up, is
+ * already active, or is busy expiring.
+ * - \c tls_process(), performs the Control Channel Processor module's
+ * core handling of received control channel messages, and generates
+ * appropriate messages to be sent.
+ *
+ * @par Functions which control data channel key generation
+ * - Key method 1 key exchange functions:
+ * - \c key_method_1_write(), generates and processes key material to
+ * be sent to the remote OpenVPN peer.
+ * - \c key_method_1_read(), processes key material received from the
+ * remote OpenVPN peer.
+ * - Key method 2 key exchange functions:
+ * - \c key_method_2_write(), generates and processes key material to
+ * be sent to the remote OpenVPN peer.
+ * - \c key_method_2_read(), processes key material received from the
+ * remote OpenVPN peer.
+ */
diff --git a/doc_data_control.h b/doc_data_control.h
new file mode 100644
index 0000000..d0f65ba
--- /dev/null
+++ b/doc_data_control.h
@@ -0,0 +1,103 @@
+/*
+ * 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. <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 (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
+ * Data Channel Control module documentation file.
+ */
+
+/**
+ * @defgroup data_control Data Channel Control module
+ *
+ * This module controls the processing of packets as they pass through the
+ * data channel.
+ *
+ * The Data Channel Control module controls the processing of packets as
+ * they pass through the data channel. The processing includes packet
+ * compression, fragmentation, and the performing of security operations
+ * on the packets. This module does not do the processing itself, but
+ * passes the packet to other data channel modules to perform the
+ * appropriate actions.
+ *
+ * Packets can travel in two directions through the data channel. They
+ * can be going to a remote destination which is reachable through a VPN
+ * tunnel, in which case this module prepares them to be sent out through
+ * a VPN tunnel. On the other hand, they can have been received through a
+ * VPN tunnel from a remote OpenVPN peer, in which case this module
+ * retrieves the packet in its original form as it was before entering the
+ * VPN tunnel on the remote OpenVPN peer. How this module processes
+ * packets traveling in the two directions is discussed in more detail
+ * below.
+ *
+ * @par Packets to be sent to a remote OpenVPN peer
+ * This module's main function for processing packets traveling in this
+ * direction is \c encrypt_sign(), which performs the following processing
+ * steps:
+ * - Call the \link compression Data Channel Compression module\endlink to
+ * perform packet compression if necessary.
+ * - Call the \link fragmentation Data Channel Fragmentation
+ * module\endlink to perform packet fragmentation if necessary.
+ * - Call the \link data_crypto Data Channel Crypto module\endlink to
+ * perform the required security operations.
+ *
+ * @par
+ * See the \c encrypt_sign() documentation for details of these
+ * interactions.
+ *
+ * @par
+ * After the above processing is complete, the packet is ready to be sent
+ * to a remote OpenVPN peer as a VPN tunnel packet. The actual sending of
+ * the packet is handled by the \link external_multiplexer External
+ * Multiplexer\endlink.
+ *
+ * @par Packets received from a remote OpenVPN peer
+ * The function that controls how packets traveling in this direction are
+ * processed is \c process_incoming_link(). That function, however, also
+ * performs some of the tasks required for the \link external_multiplexer
+ * External Multiplexer\endlink and is therefore listed as part of that
+ * module, instead of here.
+ *
+ * @par
+ * After the \c process_incoming_link() function has determined that a
+ * received packet is a data channel packet, it performs the following
+ * processing steps:
+ * - Call the \link data_crypto Data Channel Crypto module\endlink to
+ * perform the required security operations.
+ * - Call the \link fragmentation Data Channel Fragmentation
+ * module\endlink to perform packet reassembly if necessary.
+ * - Call the \link compression Data Channel Compression module\endlink to
+ * perform packet decompression if necessary.
+ *
+ * @par
+ * See the \c process_incoming_link() documentation for details of these
+ * interactions.
+ *
+ * @par
+ * After the above processing is complete, the packet is in its original
+ * form again as it was received by the remote OpenVPN peer. It can now
+ * be routed further to its final destination. If that destination is a
+ * locally reachable host, then the \link internal_multiplexer Internal
+ * Multiplexer\endlink will send it there.
+ */
diff --git a/doc_eventloop.h b/doc_eventloop.h
new file mode 100644
index 0000000..a860db6
--- /dev/null
+++ b/doc_eventloop.h
@@ -0,0 +1,67 @@
+/*
+ * 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. <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 (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
+ * Main Event Loop module documentation file.
+ */
+
+/**
+ * @defgroup eventloop Main Event Loop module
+ *
+ * This main event loop module drives the packet processing of OpenVPN.
+ *
+ * OpenVPN is an event driven system. Its activities are driven by a main
+ * event loop, which repeatedly waits for one of several predefined events
+ * to occur, and then calls the appropriate module to handle the event.
+ * The major types of network events that OpenVPN processes are:
+ * - A packet can be read from the external network interface.
+ * - The main event loop activates the \link external_multiplexer
+ * External Multiplexer\endlink to read and process the packet.
+ * - A packet can be read from the virtual tun/tap network interface.
+ * - The main event loop activates the \link internal_multiplexer
+ * Internal Multiplexer\endlink to read and process the packet.
+ * - If a packet is ready to be sent out as a VPN tunnel packet: the
+ * external network interface can be written to.
+ * - The main event loop activates the \link external_multiplexer
+ * External Multiplexer\endlink to send the packet.
+ * - If a packet is ready to be sent to a locally reachable destination:
+ * the virtual tun/tap network interface can be written to.
+ * - The main event loop activates the \link internal_multiplexer
+ * Internal Multiplexer\endlink to send the packet.
+ *
+ * Beside these external events, OpenVPN also processes other types of
+ * internal events. These include scheduled events, such as resending of
+ * non-acknowledged control channel messages.
+ *
+ * @par Main event loop implementations
+ *
+ * Depending on the mode in which OpenVPN is running, a different main
+ * event loop function is called to drive the event processing. The
+ * following implementations are available:
+ * - Client mode using UDP or TCP: \c tunnel_point_to_point()
+ * - Server mode using UDP: \c tunnel_server_udp_single_threaded()
+ * - Server mode using TCP: \c tunnel_server_tcp()
+ */
diff --git a/doc_external_multiplexer.h b/doc_external_multiplexer.h
new file mode 100644
index 0000000..7653255
--- /dev/null
+++ b/doc_external_multiplexer.h
@@ -0,0 +1,46 @@
+/*
+ * 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. <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 (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
+ * External Multiplexer module documentation file.
+ */
+
+/**
+ * @addtogroup external_multiplexer External Multiplexer module
+ *
+ * The External Multiplexer is the link between the external network
+ * interface and the other OpenVPN modules. It reads packets from the
+ * external network interface, determines which remote OpenVPN peer and
+ * VPN tunnel they are associated with, and whether they are data channel
+ * or control channel packets. It then passes the packets on to the
+ * appropriate processing module.
+ *
+ * This module also handles packets traveling in the reverse direction,
+ * which have been generated by the local control channel or which have
+ * already been processed by the \link data_control Data Channel Control
+ * module\endlink and are destined for a remote host reachable through a
+ * VPN tunnel.
+ */
diff --git a/doc_internal_multiplexer.h b/doc_internal_multiplexer.h
new file mode 100644
index 0000000..5142dd0
--- /dev/null
+++ b/doc_internal_multiplexer.h
@@ -0,0 +1,44 @@
+/*
+ * 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. <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 (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
+ * Internal Multiplexer module documentation file.
+ */
+
+/**
+ * @addtogroup internal_multiplexer Internal Multiplexer module
+ *
+ * The Internal Multiplexer is the link between the virtual tun/tap
+ * network interface and the \link data_control Data Channel Control
+ * module\endlink. It reads packets from the virtual network interface,
+ * determines for which remote OpenVPN peer they are destined, and then
+ * passes the packets on to the Data Channel Control module together with
+ * information about their destination VPN tunnel instance.
+ *
+ * This module also handles packets traveling in the reverse direction,
+ * which have already been processed by the Data Channel Control module
+ * and are destined for a locally reachable host.
+ */
diff --git a/doc_mainpage.h b/doc_mainpage.h
new file mode 100644
index 0000000..821b2e8
--- /dev/null
+++ b/doc_mainpage.h
@@ -0,0 +1,162 @@
+/*
+ * 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. <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 (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
+ * Main page documentation file.
+ */
+
+/**
+ * @mainpage OpenVPN v2.1 source code documentation
+ *
+ * This documentation describes the internal structure of OpenVPN. It was
+ * automatically generated from specially formatted comment blocks in
+ * OpenVPN's source code using Doxygen. (See
+ * http://www.stack.nl/~dimitri/doxygen/ for more information on Doxygen)
+ *
+ * The \ref mainpage_modules "Modules section" below gives an introduction
+ * into the high-level module concepts used throughout this documentation.
+ * The \ref mainpage_relatedpages "Related Pages section" below describes
+ * various special subjects related to OpenVPN's implementation which are
+ * discussed in the related pages section.
+ *
+ * @section mainpage_modules Modules
+ *
+ * For the purpose of describing the internal structure of OpenVPN, this
+ * documentation and the underlying source code has been broken up into a
+ * number of conceptually well-defined parts, known as modules. Each
+ * module plays a specific role within the OpenVPN process, and in most
+ * cases each module has a clear interfacing strategy for interacting with
+ * other modules.
+ *
+ * The following modules have been defined:
+ * - Driver module:
+ * - The \link eventloop Main Event Loop\endlink: this module drives the
+ * event handling of OpenVPN. It implements various types of
+ * select-loop which wait until an event happens, and then delegate
+ * the handling of that event to the appropriate module.
+ * - Network interface modules:
+ * - The \link external_multiplexer External Multiplexer\endlink: this
+ * module sends and receives packets to and from remote OpenVPN peers
+ * over the external network interface. It also takes care of
+ * demultiplexing received packets to their appropriate VPN tunnel and
+ * splitting control channel and data channel packets.
+ * - The \link internal_multiplexer Internal Multiplexer\endlink: this
+ * module sends and receives packets to and from locally reachable
+ * posts over the virtual tun/tap network interface. It also takes
+ * care of determining through which VPN tunnel a received packet must
+ * be sent to reach its destination.
+ * - Control channel modules:
+ * - The \link reliable Reliability Layer\endlink: this module offers a
+ * %reliable and sequential transport layer for control channel
+ * messages.
+ * - The \link control_tls Control Channel TLS module\endlink: this
+ * module offers a secure encapsulation of control channel messages
+ * using the TLS protocol.
+ * - The \link control_processor Control Channel Processor\endlink: his
+ * module manages the setup, maintenance, and shut down of VPN
+ * tunnels.
+ * - Data channel modules:
+ * - The \link data_control Data Channel Control module\endlink: this
+ * module controls the processing of data channel packets and,
+ * depending on the settings of the packet's VPN tunnel, passes the
+ * packet to the three modules below for handling.
+ * - The \link data_crypto Data Channel Crypto module\endlink: this
+ * module performs security operations on data channel packets.
+ * - The \link fragmentation Data Channel Fragmentation module\endlink:
+ * this module offers fragmentation of data channel packets larger
+ * than the VPN tunnel's MTU.
+ * - The \link compression Data Channel Compression module\endlink: this
+ * module offers compression of data channel packets.
+ *
+ * @subsection mainpage_modules_example Example event: receiving a packet
+ *
+ * OpenVPN handles many types of events during operation. These include
+ * external events, such as network traffic being received, and internal
+ * events, such as a %key session timing out causing renegotiation. An
+ * example event, receiving a packet over the network, is described here
+ * together with which modules play what roles:
+ * -# The \link eventloop Main Event Loop\endlink detects that a packet
+ * can be read from the external or the virtual tun/tap network
+ * interface.
+ * -# The \link eventloop Main Event Loop\endlink calls the \link
+ * external_multiplexer External Multiplexer\endlink or \link
+ * internal_multiplexer Internal Multiplexer\endlink to read and
+ * process the packet.
+ * -# The multiplexer module determines the type of packet and its
+ * destination, and passes the packet on to the appropriate handling
+ * module:
+ * - A control channel packet received by the \link
+ * external_multiplexer External Multiplexer\endlink is passed on
+ * through the \link reliable Reliability Layer\endlink and the \link
+ * control_tls Control Channel TLS module\endlink to the \link
+ * control_processor Control Channel Processor\endlink.
+ * - A data channel packet received by either multiplexer module is
+ * passed on to the \link data_control Data Channel Control
+ * module\endlink.
+ * -# The packet is processed by the appropriate control channel or data
+ * channel modules.
+ * -# If, after processing the packet, a resulting packet is generated
+ * that needs to be sent to a local or remote destination, it is given
+ * to the \link external_multiplexer External Multiplexer\endlink or
+ * \link internal_multiplexer Internal Multiplexer\endlink for sending.
+ * -# If a packet is waiting to be sent by either multiplexer module and
+ * the \link eventloop Main Event Loop\endlink detects that data can be
+ * written to the associated network interface, it calls the
+ * multiplexer module to send the packet.
+ *
+ * @section mainpage_relatedpages Related pages
+ *
+ * This documentation includes a number of descriptions of various aspects
+ * of OpenVPN and its implementation. These are not directly related to
+ * one module, function, or data structure, and are therefore listed
+ * separately under "Related Pages".
+ *
+ * @subsection mainpage_relatedpages_key_generation Data channel key generation
+ *
+ * The @ref key_generation "Data channel key generation" related page
+ * describes how, during VPN tunnel setup and renegotiation, OpenVPN peers
+ * generate and exchange the %key material required for the symmetric
+ * encryption/decryption and HMAC signing/verifying security operations
+ * performed on data channel packets.
+ *
+ * @subsection mainpage_relatedpages_tunnel_state VPN tunnel state
+ *
+ * The @ref tunnel_state "Structure of VPN tunnel state storage" related
+ * page describes how an OpenVPN process manages the state information
+ * associated with its active VPN tunnels.
+ *
+ * @subsection mainpage_relatedpages_network_protocol Network protocol
+ *
+ * The @ref network_protocol "Network protocol" related page describes the
+ * format and content of VPN tunnel packets exchanged between OpenVPN
+ * peers.
+ *
+ * @subsection mainpage_relatedpages_memory_management Memory management
+ *
+ * The @ref memory_management "Memory management strategies" related page
+ * gives a brief introduction into OpenVPN's memory %buffer library and
+ * garbage collection facilities.
+ */
diff --git a/doc_protocol_overview.h b/doc_protocol_overview.h
new file mode 100644
index 0000000..26fed33
--- /dev/null
+++ b/doc_protocol_overview.h
@@ -0,0 +1,199 @@
+/*
+ * 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. <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 (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 Network protocol overview documentation file.
+ */
+
+/**
+ * @page network_protocol OpenVPN's network protocol
+ *
+ * Description of packet structure in OpenVPN's network protocol.
+ *
+ * This document describes the structure of packets exchanged between
+ * OpenVPN peers. It is based on the protocol description in the \c ssl.h
+ * file.
+ *
+ * @section network_protocol_external Outer structure of packets exchanged between OpenVPN peers
+ *
+ * VPN tunnel packets are transported between OpenVPN peers using the UDP
+ * or TCP protocols. Their structure is described below.
+ *
+ * @subsection network_protocol_external_structure External packet structure
+ *
+ * - packet length (16 bits, unsigned) [TCP-mode only]: always sent as
+ * plain text. Since TCP is a stream protocol, this packet length
+ * defines the packetization of the stream.
+ * - packet opcode and key_id (8 bits) [TLS-mode only]:
+ * - package message type (high 5 bits)
+ * - key_id (low 3 bits): the key_id refers to an already negotiated
+ * TLS session. OpenVPN seamlessly renegotiates the TLS session by
+ * using a new key_id for the new session. Overlap (controlled by
+ * user definable parameters) between old and new TLS sessions is
+ * allowed, providing a seamless transition during tunnel operation.
+ * - payload (n bytes)
+ *
+ * @subsection network_protocol_external_types Message types
+ *
+ * The type of a VPN tunnel packet is indicated by its opcode. The
+ * following describes the various opcodes available.
+ *
+ * - Control channel messages:
+ * - \c P_CONTROL_HARD_RESET_CLIENT_V1 -- %Key method 1, initial %key
+ * from client, forget previous state.
+ * - \c P_CONTROL_HARD_RESET_SERVER_V1 -- %Key method 1, initial %key
+ * from server, forget previous state.
+ * - \c P_CONTROL_HARD_RESET_CLIENT_V2 -- %Key method 2, initial %key
+ * from client, forget previous state.
+ * - \c P_CONTROL_HARD_RESET_SERVER_V2 -- %Key method 2, initial %key
+ * from server, forget previous state.
+ * - \c P_CONTROL_SOFT_RESET_V1 -- New %key, with a graceful
+ * transition from old to new %key in the sense that a transition
+ * window exists where both the old or new key_id can be used.
+ * - \c P_CONTROL_V1 -- Control channel packet (usually TLS
+ * ciphertext).
+ * - \c P_ACK_V1 -- Acknowledgement for control channel packets
+ * received.
+ * - Data channel messages:
+ * - \c P_DATA_V1 -- Data channel packet containing data channel
+ * ciphertext.
+ *
+ * @subsection network_protocol_external_key_id Session IDs and Key IDs
+ *
+ * OpenVPN uses two different forms of packet identifiers:
+ * - The first form is 64 bits and is used for all control channel
+ * messages. This form is referred to as a \c session_id.
+ * - Data channel messages on the other hand use a shortened form of 3
+ * bits for efficiency reasons since the vast majority of OpenVPN
+ * packets in an active tunnel will be data channel messages. This
+ * form is referred to as a \c key_id.
+ *
+ * The control and data channels use independent packet-id sequences,
+ * because the data channel is an unreliable channel while the control
+ * channel is a %reliable channel. Each use their own independent HMAC
+ * keys.
+ *
+ * @subsection network_protocol_external_reliable Control channel reliability layer
+ *
+ * Control channel messages (\c P_CONTROL_* and \c P_ACK_* message types)
+ * are TLS ciphertext packets which have been encapsulated inside of a
+ * reliability layer. The reliability layer is implemented as a
+ * straightforward acknowledge and retransmit model.
+ *
+ * Acknowledgments of received messages can be encoded in either the
+ * dedicated \c P_ACK_* record or they can be prepended to a \c
+ * P_CONTROL_* message.
+ *
+ * See the \link reliable Reliability Layer\endlink module for a detailed
+ * description.
+ *
+ * @section network_protocol_control Structure of control channel messages
+ *
+ * @subsection network_protocol_control_ciphertext Structure of ciphertext control channel messages
+ *
+ * Control channel packets in ciphertext form consist of the following
+ * parts:
+ *
+ * - local \c session_id (random 64 bit value to identify TLS session).
+ * - HMAC signature of entire encapsulation header for HMAC firewall
+ * [only if \c --tls-auth is specified] (usually 16 or 20 bytes).
+ * - packet-id for replay protection (4 or 8 bytes, includes sequence
+ * number and optional \c time_t timestamp).
+ * - acknowledgment packet-id array length (1 byte).
+ * - acknowledgment packet-id array (if length > 0).
+ * - acknowledgment remote session-id (if length > 0).
+ * - packet-id of this message (4 bytes).
+ * - TLS payload ciphertext (n bytes) (only for \c P_CONTROL_V1).
+ *
+ * Note that when \c --tls-auth is used, all message types are protected
+ * with an HMAC signature, even the initial packets of the TLS handshake.
+ * This makes it easy for OpenVPN to throw away bogus packets quickly,
+ * without wasting resources on attempting a TLS handshake which will
+ * ultimately fail.
+ *
+ * @subsection network_protocol_control_key_methods Control channel key methods and
+ *
+ * Once the TLS session has been initialized and authenticated, the TLS
+ * channel is used to exchange random %key material for bidirectional
+ * cipher and HMAC keys which will be used to secure data channel packets.
+ * OpenVPN currently implements two %key methods. %Key method 1 directly
+ * derives keys using random bits obtained from the \c RAND_bytes()
+ * OpenSSL function. %Key method 2 mixes random %key material from both
+ * sides of the connection using the TLS PRF mixing function. %Key method
+ * 2 is the preferred method and is the default for OpenVPN 2.0.
+ *
+ * The @ref key_generation "Data channel key generation" related page
+ * describes the %key methods in more detail.
+ *
+ * @subsection network_protocol_control_plaintext Structure of plaintext control channel messages
+ *
+ * - %Key method 1:
+ * - Cipher %key length in bytes (1 byte).
+ * - Cipher %key (n bytes).
+ * - HMAC %key length in bytes (1 byte).
+ * - HMAC %key (n bytes).
+ * - %Options string (n bytes, null terminated, client/server %options
+ * string should match).
+ * - %Key method 2:
+ * - Literal 0 (4 bytes).
+ * - %Key method (1 byte).
+ * - \c key_source structure (\c key_source.pre_master only defined
+ * for client -> server).
+ * - %Options string length, including null (2 bytes).
+ * - %Options string (n bytes, null terminated, client/server %options
+ * string must match).
+ * - [The username/password data below is optional, record can end at
+ * this point.]
+ * - Username string length, including null (2 bytes).
+ * - Username string (n bytes, null terminated).
+ * - Password string length, including null (2 bytes).
+ * - Password string (n bytes, null terminated).
+ *
+ * @section network_protocol_data Structure of data channel messages
+ *
+ * @subsection network_protocol_data_ciphertext Structure of ciphertext data channel messages
+ *
+ * The P_DATA_* payload represents encrypted, encapsulated tunnel packets
+ * which tend to be either IP packets or Ethernet frames. This is
+ * essentially the "payload" of the VPN.
+ *
+ * Data channel packets in ciphertext form consist of the following parts:
+ * - HMAC of ciphertext IV + ciphertext (if not disabled by \c --auth
+ * none).
+ * - Ciphertext IV (size is cipher-dependent, if not disabled by \c
+ * --no-iv).
+ * - Tunnel packet ciphertext.
+ *
+ * @subsection network_protocol_data_plaintext Structure of plaintext data channel messages
+ *
+ * Data channel packets in plaintext form consist of the following parts:
+ * - packet-id (4 or 8 bytes, if not disabled by --no-replay).
+ * - In TLS mode, 4 bytes are used because the implementation can
+ * force a TLS renegotation before \c 2^32 packets are sent.
+ * - In pre-shared %key mode, 8 bytes are used (sequence number and \c
+ * time_t value) to allow long-term %key usage without packet-id
+ * collisions.
+ * - User plaintext (n bytes).
+ */
diff --git a/doc_tunnel_state.h b/doc_tunnel_state.h
new file mode 100644
index 0000000..6c93e71
--- /dev/null
+++ b/doc_tunnel_state.h
@@ -0,0 +1,155 @@
+/*
+ * 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. <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 (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
+ * VPN tunnel state documentation file.
+ */
+
+/**
+ * @page tunnel_state Structure of the VPN tunnel state storage
+ *
+ * This section describes how OpenVPN stores its VPN tunnel state during
+ * operation.
+ *
+ * OpenVPN uses several data structures as storage containers for state
+ * information of active VPN tunnels. These are described in this
+ * section, together with a little bit of history to help understand the
+ * origin of the current architecture.
+ *
+ * Whether an OpenVPN process is running in client-mode or server-mode
+ * determines whether it can support only one or multiple simultaneously
+ * active VPN tunnels. This consequently also determines how the
+ * associated state information is wrapped up internally. This section
+ * gives an overview of the differences.
+ *
+ * @section tunnel_state_history Historic developments
+ *
+ * In the old v1.x series, an OpenVPN process managed only one single VPN
+ * tunnel. This allowed the VPN tunnel state to be stored together with
+ * process-global information in one single \c context structure.
+ *
+ * This changed, however, in the v2.x series, as new OpenVPN versions
+ * running in server-mode can support multiple simultaneously active VPN
+ * tunnels. This necessitated a redesign of the VPN tunnel state
+ * container structures, and modification of the \link
+ * external_multiplexer External Multiplexer\endlink and \link
+ * internal_multiplexer Internal Multiplexer\endlink systems. The
+ * majority of these changes are only relevant for OpenVPN processes
+ * running in server-mode, and the client-mode structure has remained very
+ * similar to the v1.x single-tunnel form.
+ *
+ * @section tunnel_state_client Client-mode state
+ *
+ * An OpenVPN process running in client-mode can manage at most one single
+ * VPN tunnel at any one time. The state information for a client's VPN
+ * tunnel is stored in a \c context structure.
+ *
+ * The \c context structure is created in the \c main() function. That is
+ * also where process-wide initialization takes place, such as parsing
+ * command line %options and reading configuration files. The \c context
+ * is then passed to \c tunnel_point_to_point() which drives OpenVPN's
+ * main event processing loop. These functions are both part of the \link
+ * eventloop Main Event Loop\endlink module.
+ *
+ * @subsection tunnel_state_client_init Initialization and cleanup
+ *
+ * Because there is only one \c context structure present, it can be
+ * initialized and cleaned up from the client's main event processing
+ * function. Before the \c tunnel_point_to_point() function enters its
+ * event loop, it calls \c init_instance_handle_signals() which calls \c
+ * init_instance() to initialize the single \c context structure. After
+ * the event loop stops, it calls \c close_instance() to clean up the \c
+ * context.
+ *
+ * @subsection tunnel_state_client_event Event processing
+ *
+ * When the main event processing loop activates the external or internal
+ * multiplexer to handle a network event, it is not necessary to determine
+ * which VPN tunnel the event is associated with, because there is only
+ * one VPN tunnel active.
+ *
+ * @section tunnel_state_server Server-mode state
+ *
+ * An OpenVPN process running in server-mode can manage multiple
+ * simultaneously active VPN tunnels. For every VPN tunnel active, in
+ * other words for every OpenVPN client which is connected to a server,
+ * the OpenVPN server has one \c context structure in which it stores that
+ * particular VPN tunnel's state information.
+ *
+ * @subsection tunnel_state_server_multi Multi_context and multi_instance structures
+ *
+ * To support multiple \c context structures, each is wrapped in a \c
+ * multi_instance structure, and all the \c multi_instance structures are
+ * registered in one single \c multi_context structure. The \link
+ * external_multiplexer External Multiplexer\endlink and \link
+ * internal_multiplexer Internal Multiplexer\endlink then use the \c
+ * multi_context to retrieve the correct \c multi_instance and \c context
+ * associated with a given network address.
+ *
+ * @subsection tunnel_state_server_init Startup and initialization
+ *
+ * An OpenVPN process running in server-mode starts in the same \c main()
+ * function as it would in client-mode. The same process-wide
+ * initialization is performed, and the resulting state and configuration
+ * is stored in a \c context structure. The server-mode and client-mode
+ * processes diverge when the \c main() function calls one of \c
+ * tunnel_point_to_point() or \c tunnel_server().
+ *
+ * In server-mode, \c main() calls the \c tunnel_server() function, which
+ * transfers control to \c tunnel_server_udp_single_threaded() or \c
+ * tunnel_server_tcp() depending on the external transport protocol.
+ *
+ * These functions receive the \c context created in \c main(). This
+ * object has a special status in server-mode, as it does not represent an
+ * active VPN tunnel, but does contain process-wide configuration
+ * parameters. In the source code, it is often stored in "top" variables.
+ * To distinguish this object from other instances of the same type, its
+ * \c context.mode value is set to \c CM_TOP. Other \c context objects,
+ * which do represent active VPN tunnels, have a \c context.mode set to \c
+ * CM_CHILD_UDP or \c CM_CHILD_TCP, depending on the external transport
+ * protocol.
+ *
+ * Both \c tunnel_server_udp_single_threaded() and \c tunnel_server_tcp()
+ * perform similar initialization. In either case, a \c multi_context
+ * structure is created, and it is initialized according to the
+ * configuration stored in the top \c context by the \c multi_init() and
+ * \c multi_top_init() functions.
+ *
+ * @subsection tunnel_state_server_tunnels Creating and destroying VPN tunnels
+ *
+ * When an OpenVPN client makes a new connection to a server, the server
+ * creates a new \c context and \c multi_instance. The latter is
+ * registered in the \c multi_context, which makes it possible for the
+ * external and internal multiplexers to retrieve the correct \c
+ * multi_instance and \c context when a network event occurs.
+ *
+ * @subsection tunnel_state_server_cleanup Final cleanup
+ *
+ * After the main event loop exits, both \c
+ * tunnel_server_udp_single_threaded() and \c tunnel_server_tcp() perform
+ * similar cleanup. They call \c multi_uninit() followed by \c
+ * multi_top_free() to clean up the \c multi_context structure.
+ */
diff --git a/forward.h b/forward.h
index 76d8b9e..0f829bd 100644
--- a/forward.h
+++ b/forward.h
@@ -22,6 +22,13 @@
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
+
+/**
+ * @file
+ * Interface functions to the internal and external multiplexers.
+ */
+
+
#ifndef FORWARD_H
#define FORWARD_H
@@ -54,22 +61,170 @@
#define IOW_READ (IOW_READ_TUN|IOW_READ_LINK)
-void pre_select (struct context *c);
+void pre_select (struct context *c);
void process_io (struct context *c);
-void encrypt_sign (struct context *c, bool comp_frag);
-
const char *wait_status_string (struct context *c, struct gc_arena *gc);
void show_wait_status (struct context *c);
+
+/**********************************************************************/
+/**
+ * Process a data channel packet that will be sent through a VPN tunnel.
+ * @ingroup data_control
+ *
+ * This function controls the processing of a data channel packet which
+ * will be sent through a VPN tunnel to a remote OpenVPN peer. It's
+ * general structure is as follows:
+ * - Check that the client authentication has succeeded; if not, drop the
+ * packet.
+ * - If the \a comp_frag argument is true:
+ * - Call \c lzo_compress() of the \link Data Channel Compression
+ * module\endlink to (possibly) compress the packet.
+ * - Call \c fragment_outgoing() of the \link Data Channel Fragmentation
+ * module\endlink to (possibly) fragment the packet.
+ * - Activate the \link Data Channel Crypto module\endlink to perform
+ * security operations on the packet.
+ * - Call \c tls_pre_encrypt() to choose the appropriate security
+ * parameters for this packet.
+ * - Call \c openvpn_encrypt() to encrypt and HMAC signed the packet.
+ * - Call \c tls_post_encrypt() to prepend the one-byte OpenVPN header
+ * and do some TLS accounting.
+ * - Place the resulting packet in \c c->c2.to_link so that it can be sent
+ * over the external network interface to its remote destination by the
+ * \link external_multiplexer External Multiplexer\endlink.
+ *
+ * @param c - The context structure of the VPN tunnel associated with this
+ * packet.
+ * @param comp_frag - Whether to do packet compression and fragmentation.
+ * This flag is set to true the first time a packet is processed. If
+ * the packet then gets fragmented, this function will be called again
+ * once for each remaining fragment with this parameter set to false.
+ */
+void encrypt_sign (struct context *c, bool comp_frag);
+
+
+/**********************************************************************/
+/**
+ * Read a packet from the external network interface.
+ * @ingroup external_multiplexer
+ *
+ * The packet read from the external network interface is stored in \c
+ * c->c2.buf and its source address in \c c->c2.from. If an error
+ * occurred, the length of \c c->c2.buf will be 0.
+ *
+ * OpenVPN running as client or as UDP server only has a single external
+ * network socket, so this function can be called with the single (client
+ * mode) or top level (UDP server) context as its argument. OpenVPN
+ * running as TCP server, on the other hand, has a network socket for each
+ * active VPN tunnel. In that case this function must be called with the
+ * context associated with the appropriate VPN tunnel for which data is
+ * available to be read.
+ *
+ * @param c - The context structure which contains the external
+ * network socket from which to read incoming packets.
+ */
void read_incoming_link (struct context *c);
+
+
+/**
+ * Process a packet read from the external network interface.
+ * @ingroup external_multiplexer
+ *
+ * This function controls the processing of a data channel packet which
+ * has come out of a VPN tunnel. It's high-level structure is as follows:
+ * - Verify that a nonzero length packet has been received from a valid
+ * source address for the given context \a c.
+ * - Call \c tls_pre_decrypt(), which splits data channel and control
+ * channel packets:
+ * - If a data channel packet, the appropriate security parameters are
+ * loaded.
+ * - If a control channel packet, this function process is it and
+ * afterwards sets the packet's buffer length to 0, so that the data
+ * channel processing steps below will ignore it.
+ * - Call \c openvpn_decrypt() of the \link data_crypto Data Channel
+ * Crypto module\endlink to authenticate and decrypt the packet using
+ * the security parameters loaded by \c tls_pre_decrypt() above.
+ * - Call \c fragment_incoming() of the \link fragmentation Data Channel
+ * Fragmentation module\endlink to reassemble the packet if it's
+ * fragmented.
+ * - Call \c lzo_decompress() of the \link compression Data Channel
+ * Compression module\endlink to decompress the packet if it's
+ * compressed.
+ * - Place the resulting packet in \c c->c2.to_tun so that it can be sent
+ * over the virtual tun/tap network interface to its local destination
+ * by the \link internal_multiplexer Internal Multiplexer\endlink.
+ *
+ * @param c - The context structure of the VPN tunnel associated with the
+ * packet.
+ */
void process_incoming_link (struct context *c);
+
+
+/**
+ * Write a packet to the external network interface.
+ * @ingroup external_multiplexer
+ *
+ * This function writes the packet stored in \c c->c2.to_link to the
+ * external network device contained within \c c->c1.link_socket.
+ *
+ * If an error occurs, it is logged and the packet is dropped.
+ *
+ * @param c - The context structure of the VPN tunnel associated with the
+ * packet.
+ */
+void process_outgoing_link (struct context *c);
+
+
+/**************************************************************************/
+/**
+ * Read a packet from the virtual tun/tap network interface.
+ * @ingroup internal_multiplexer
+ *
+ * This function reads a packet from the virtual tun/tap network device \c
+ * c->c1.tuntap and stores it in \c c->c2.buf.
+ *
+ * If an error occurs, it is logged and the packet is dropped.
+ *
+ * @param c - The context structure in which to store the received
+ * packet.
+ */
void read_incoming_tun (struct context *c);
+
+
+/**
+ * Process a packet read from the virtual tun/tap network interface.
+ * @ingroup internal_multiplexer
+ *
+ * This function calls \c encrypt_sign() of the \link data_control Data
+ * Channel Control module\endlink to process the packet.
+ *
+ * If an error occurs, it is logged and the packet is dropped.
+ *
+ * @param c - The context structure of the VPN tunnel associated with the
+ * packet.
+ */
void process_incoming_tun (struct context *c);
-void process_outgoing_link (struct context *c);
+
+
+/**
+ * Write a packet to the virtual tun/tap network interface.
+ * @ingroup internal_multiplexer
+ *
+ * This function writes the packet stored in \c c->c2.to_tun to the
+ * virtual tun/tap network device \c c->c1.tuntap.
+ *
+ * If an error occurs, it is logged and the packet is dropped.
+ *
+ * @param c - The context structure of the VPN tunnel associated with
+ * the packet.
+ */
void process_outgoing_tun (struct context *c);
+
+/**************************************************************************/
+
bool send_control_channel_string (struct context *c, const char *str, int msglevel);
#define PIPV4_PASSTOS (1<<0)
diff --git a/mtcp.h b/mtcp.h
index 3585af4..b677b48 100644
--- a/mtcp.h
+++ b/mtcp.h
@@ -60,8 +60,17 @@ void multi_tcp_instance_specific_free (struct multi_instance *mi);
void multi_tcp_link_out_deferred (struct multi_context *m, struct multi_instance *mi);
+
+/**************************************************************************/
+/**
+ * Main event loop for OpenVPN in TCP server mode.
+ * @ingroup eventloop
+ *
+ * @param top - Top-level context structure.
+ */
void tunnel_server_tcp (struct context *top);
+
void multi_tcp_delete_event (struct multi_tcp *mtcp, event_t event);
#endif
diff --git a/mtu.h b/mtu.h
index d9fa020..29ec21f 100644
--- a/mtu.h
+++ b/mtu.h
@@ -86,39 +86,43 @@
*/
#define PAYLOAD_ALIGN 4
-struct frame {
- /*
- * Maximum datagram size to be sent over the tunnel TCP/UDP channel.
- */
- int link_mtu;
- int link_mtu_dynamic;
-
- /*
- * How many extra bytes might each subsystem (crypto, TLS, or, compression)
- * add to frame in worst case?
- *
- * mtu + extra_frame = MTU of TCP/UDP transport
- */
- int extra_frame;
-
- /*
- * Worst case size added to internal buffer due to functions
- * such as compression which can potentially expand the size of uncompressible
- * data.
- */
- int extra_buffer;
-
- /*
- * Max number of bytes in excess of tun mtu size that we might read
- * or write from TUN/TAP device.
- */
- int extra_tun;
- /*
- * Max number of bytes in excess of link mtu size that we might read
- * or write from UDP/TCP link.
- */
- int extra_link;
+/**************************************************************************/
+/**
+ * Packet geometry parameters.
+ */
+struct frame {
+ int link_mtu; /**< Maximum packet size to be sent over
+ * the external network interface. */
+
+ int link_mtu_dynamic; /**< Dynamic MTU value for the external
+ * network interface. */
+
+ int extra_frame; /**< Maximum number of bytes that all
+ * processing steps together could add.
+ * @code
+ * frame.link_mtu = "socket MTU" - extra_frame;
+ * @endcode
+ */
+
+ int extra_buffer; /**< Maximum number of bytes that
+ * processing steps could expand the
+ * internal work buffer.
+ *
+ * This is used by the \link compression
+ * Data Channel Compression
+ * module\endlink to give enough working
+ * space for worst-case expansion of
+ * incompressible content. */
+
+ int extra_tun; /**< Maximum number of bytes in excess of
+ * the tun/tap MTU that might be read
+ * from or written to the virtual
+ * tun/tap network interface. */
+
+ int extra_link; /**< Maximum number of bytes in excess of
+ * external network interface's MTU that
+ * might be read from or written to it. */
/*
* Alignment control
diff --git a/mudp.c b/mudp.c
index a478b29..7648ec6 100644
--- a/mudp.c
+++ b/mudp.c
@@ -199,9 +199,17 @@ p2mp_iow_flags (const struct multi_context *m)
return flags;
}
-/*
- * Top level event loop for single-threaded operation.
- * UDP mode.
+
+/**************************************************************************/
+/**
+ * Main event loop for OpenVPN in UDP server mode.
+ * @ingroup eventloop
+ *
+ * This function implements OpenVPN's main event loop for UDP server mode.
+ * At this time, OpenVPN does not yet support multithreading. This
+ * function's name is therefore slightly misleading.
+ *
+ * @param top - Top-level context structure.
*/
static void
tunnel_server_udp_single_threaded (struct context *top)
diff --git a/mudp.h b/mudp.h
index dc9cfde..97f961b 100644
--- a/mudp.h
+++ b/mudp.h
@@ -34,8 +34,37 @@
struct context;
struct multi_context;
+
+/**************************************************************************/
+/**
+ * Main event loop wrapper function for OpenVPN in UDP server mode.
+ * @ingroup eventloop
+ *
+ * This function simply calls \c tunnel_server_udp_single_threaded().
+ *
+ * @param top - Top-level context structure.
+ */
void tunnel_server_udp (struct context *top);
+
+/**************************************************************************/
+/**
+ * Get, and if necessary create, the multi_instance associated with a
+ * packet's source address.
+ * @ingroup external_multiplexer
+ *
+ * This function extracts the source address of a recently read packet
+ * from \c m->top.c2.from and uses that source address as a hash key for
+ * the hash table \c m->hash. If an entry exists, this function returns
+ * it. If no entry exists, this function handles its creation, and if
+ * successful, returns the newly created instance.
+ *
+ * @param m - The single multi_context structure.
+ *
+ * @return A pointer to a multi_instance if one already existed for the
+ * packet's source address or if one was a newly created successfully.
+ * NULL if one did not yet exist and a new one was not created.
+ */
struct multi_instance *multi_get_create_instance_udp (struct multi_context *m);
#endif
diff --git a/multi.h b/multi.h
index 08964a2..58e65a3 100644
--- a/multi.h
+++ b/multi.h
@@ -22,6 +22,10 @@
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
+/**
+ * @file Header file for server-mode related structures and functions.
+ */
+
#ifndef MULTI_H
#define MULTI_H
@@ -50,8 +54,16 @@ struct multi_reap
time_t last_call;
};
-/*
- * One multi_instance object per client instance.
+
+/**
+ * Server-mode state structure for one single VPN tunnel.
+ *
+ * This structure is used by OpenVPN processes running in server-mode to
+ * store state information related to one single VPN tunnel.
+ *
+ * The @ref tunnel_state "Structure of VPN tunnel state storage" related
+ * page describes the role the structure plays when OpenVPN is running in
+ * server-mode.
*/
struct multi_instance {
struct schedule_entry se; /* this must be the first element of the structure */
@@ -60,9 +72,13 @@ struct multi_instance {
bool halt;
int refcount;
int route_count; /* number of routes (including cached routes) owned by this instance */
- time_t created;
+ time_t created; /**< Time at which a VPN tunnel instance
+ * was created. This parameter is set
+ * by the \c multi_create_instance()
+ * function. */
struct timeval wakeup; /* absolute time */
- struct mroute_addr real;
+ struct mroute_addr real; /**< External network address of the
+ * remote peer. */
ifconfig_pool_handle vaddr_handle;
const char *msg_prefix;
@@ -84,11 +100,20 @@ struct multi_instance {
bool did_iroutes;
int n_clients_delta; /* added to multi_context.n_clients when instance is closed */
- struct context context;
+ struct context context; /**< The context structure storing state
+ * for this VPN tunnel. */
};
-/*
- * One multi_context object per server daemon thread.
+
+/**
+ * Main OpenVPN server state structure.
+ *
+ * This structure is used by OpenVPN processes running in server-mode to
+ * store all the VPN tunnel and process-wide state.
+ *
+ * The @ref tunnel_state "Structure of VPN tunnel state storage" related
+ * page describes the role the structure plays when OpenVPN is running in
+ * server-mode.
*/
struct multi_context {
# define MC_UNDEF 0
@@ -99,12 +124,19 @@ struct multi_context {
# define MC_WORK_THREAD (MC_MULTI_THREADED_WORKER|MC_MULTI_THREADED_SCHEDULER)
int thread_mode;
- struct hash *hash; /* client instances indexed by real address */
- struct hash *vhash; /* client instances indexed by virtual address */
- struct hash *iter; /* like real address hash but optimized for iteration */
+ struct hash *hash; /**< VPN tunnel instances indexed by real
+ * address of the remote peer. */
+ struct hash *vhash; /**< VPN tunnel instances indexed by
+ * virtual address of remote hosts. */
+ struct hash *iter; /**< VPN tunnel instances indexed by real
+ * address of the remote peer, optimized
+ * for iteration. */
struct schedule *schedule;
- struct mbuf_set *mbuf;
- struct multi_tcp *mtcp;
+ struct mbuf_set *mbuf; /**< Set of buffers for passing data
+ * channel packets between VPN tunnel
+ * instances. */
+ struct multi_tcp *mtcp; /**< State specific to OpenVPN using TCP
+ * as external transport. */
struct ifconfig_pool *ifconfig_pool;
struct frequency_limit *new_connection_limiter;
struct mroute_helper *route_helper;
@@ -127,7 +159,8 @@ struct multi_context {
struct context_buffers *context_buffers;
time_t per_second_trigger;
- struct context top;
+ struct context top; /**< Storage structure for process-wide
+ * configuration. */
};
/*
@@ -146,11 +179,22 @@ struct multi_route
time_t last_reference;
};
-/*
- * top level function, called by openvpn.c
+
+/**************************************************************************/
+/**
+ * Main event loop for OpenVPN in server mode.
+ * @ingroup eventloop
+ *
+ * This function calls the appropriate main event loop function depending
+ * on the transport protocol used:
+ * - \c tunnel_server_udp()
+ * - \c tunnel_server_tcp()
+ *
+ * @param top - Top-level context structure.
*/
void tunnel_server (struct context *top);
+
const char *multi_instance_string (const struct multi_instance *mi, bool null, struct gc_arena *gc);
/*
@@ -172,11 +216,77 @@ bool multi_process_timeout (struct multi_context *m, const unsigned int mpp_flag
#define MPP_CONDITIONAL_PRE_SELECT (1<<1)
#define MPP_CLOSE_ON_SIGNAL (1<<2)
#define MPP_RECORD_TOUCH (1<<3)
+
+
+/**************************************************************************/
+/**
+ * Perform postprocessing of a VPN tunnel instance.
+ *
+ * After some VPN tunnel activity has taken place, the VPN tunnel's state
+ * may need updating and some follow-up action may be required. This
+ * function controls the necessary postprocessing. It is called by many
+ * other functions that handle VPN tunnel related activity, such as \c
+ * multi_process_incoming_link(), \c multi_process_outgoing_link(), \c
+ * multi_process_incoming_tun(), \c multi_process_outgoing_tun(), and \c
+ * multi_process_timeout(), among others.
+ *
+ * @param m - The single \c multi_context structure.
+ * @param mi - The \c multi_instance of the VPN tunnel to be
+ * postprocessed.
+ * @param flags - Fast I/O optimization flags.
+ *
+ * @return
+ * - True, if the VPN tunnel instance \a mi was not closed due to a
+ * signal during processing.
+ * - False, if the VPN tunnel instance \a mi was closed.
+ */
bool multi_process_post (struct multi_context *m, struct multi_instance *mi, const unsigned int flags);
+
+/**************************************************************************/
+/**
+ * Demultiplex and process a packet received over the external network
+ * interface.
+ * @ingroup external_multiplexer
+ *
+ * This function determines which VPN tunnel instance the incoming packet
+ * is associated with, and then calls \c process_incoming_link() to handle
+ * it. Afterwards, if the packet is destined for a broadcast/multicast
+ * address or a remote host reachable through a different VPN tunnel, this
+ * function takes care of sending it they are.
+ *
+ * @note This function is only used by OpenVPN processes which are running
+ * in server mode, and can therefore sustain multiple active VPN
+ * tunnels.
+ *
+ * @param m - The single \c multi_context structure.
+ * @param instance - The VPN tunnel state structure associated with
+ * the incoming packet, if known, as is the case
+ * when using TCP transport. Otherwise NULL, as is
+ * the case when using UDP transport.
+ * @param mpp_flags - Fast I/O optimization flags.
+ */
bool multi_process_incoming_link (struct multi_context *m, struct multi_instance *instance, const unsigned int mpp_flags);
+
+
+/**
+ * Determine the destination VPN tunnel of a packet received over the
+ * virtual tun/tap network interface and then process it accordingly.
+ * @ingroup internal_multiplexer
+ *
+ * This function determines which VPN tunnel instance the packet is
+ * destined for, and then calls \c process_outgoing_tun() to handle it.
+ *
+ * @note This function is only used by OpenVPN processes which are running
+ * in server mode, and can therefore sustain multiple active VPN
+ * tunnels.
+ *
+ * @param m - The single \c multi_context structure.
+ * @param mpp_flags - Fast I/O optimization flags.
+ */
bool multi_process_incoming_tun (struct multi_context *m, const unsigned int mpp_flags);
+
void multi_process_drop_outgoing_tun (struct multi_context *m, const unsigned int mpp_flags);
void multi_print_status (struct multi_context *m, struct status_output *so, const int version);
@@ -397,8 +507,23 @@ multi_get_timeout (struct multi_context *m, struct timeval *dest)
}
}
-/*
- * Send a packet to TUN/TAP interface.
+
+/**
+ * Send a packet over the virtual tun/tap network interface to its locally
+ * reachable destination.
+ * @ingroup internal_multiplexer
+ *
+ * This function calls \c process_outgoing_tun() to perform the actual
+ * sending of the packet. Afterwards, it calls \c multi_process_post() to
+ * perform server-mode postprocessing.
+ *
+ * @param m - The single \c multi_context structure.
+ * @param mpp_flags - Fast I/O optimization flags.
+ *
+ * @return
+ * - True, if the \c multi_instance associated with the packet sent was
+ * not closed due to a signal during processing.
+ * - Falls, if the \c multi_instance was closed.
*/
static inline bool
multi_process_outgoing_tun (struct multi_context *m, const unsigned int mpp_flags)
@@ -419,6 +544,8 @@ multi_process_outgoing_tun (struct multi_context *m, const unsigned int mpp_flag
return ret;
}
+
+
static inline bool
multi_process_outgoing_link_dowork (struct multi_context *m, struct multi_instance *mi, const unsigned int mpp_flags)
{
diff --git a/openvpn.c b/openvpn.c
index 99b343b..520fda1 100644
--- a/openvpn.c
+++ b/openvpn.c
@@ -42,6 +42,16 @@ process_signal_p2p (struct context *c)
return process_signal (c);
}
+
+
+/**************************************************************************/
+/**
+ * Main event loop for OpenVPN in client mode, where only one VPN tunnel
+ * is active.
+ * @ingroup eventloop
+ *
+ * @param c - The context structure of the single active VPN tunnel.
+ */
static void
tunnel_point_to_point (struct context *c)
{
@@ -90,6 +100,27 @@ tunnel_point_to_point (struct context *c)
#undef PROCESS_SIGNAL_P2P
+
+/**************************************************************************/
+/**
+ * OpenVPN's main init-run-cleanup loop.
+ * @ingroup eventloop
+ *
+ * This function contains the two outer OpenVPN loops. Its structure is
+ * as follows:
+ * - Once-per-process initialization.
+ * - Outer loop, run at startup and then once per \c SIGHUP:
+ * - Level 1 initialization
+ * - Inner loop, run at startup and then once per \c SIGUSR1:
+ * - Call event loop function depending on client or server mode:
+ * - \c tunnel_point_to_point()
+ * - \c tunnel_server()
+ * - Level 1 cleanup
+ * - Once-per-process cleanup.
+ *
+ * @param argc - Commandline argument count.
+ * @param argv - Commandline argument values.
+ */
int
main (int argc, char *argv[])
{
diff --git a/openvpn.h b/openvpn.h
index 33661df..bd6e873 100644
--- a/openvpn.h
+++ b/openvpn.h
@@ -126,10 +126,14 @@ struct context_persist
int restart_sleep_seconds;
};
-/*
- * level 0 context contains data related to
- * once-per OpenVPN instantiation events
- * such as daemonization.
+
+/**************************************************************************/
+/**
+ * Level 0 %context containing information related to the OpenVPN process.
+ *
+ * Level 0 state is initialized once at program startup, and then remains
+ * throughout the lifetime of the OpenVPN process. This structure
+ * contains information related to the process's PID, user, and group.
*/
struct context_0
{
@@ -143,14 +147,21 @@ struct context_0
struct group_state group_state;
};
-/*
- * Contains the persist-across-restart OpenVPN tunnel instance state.
- * Reset only for SIGHUP restarts.
+
+/**
+ * Level 1 %context containing state that persists across \c SIGUSR1
+ * restarts.
+ *
+ * Level 1 state is reset on \c SIGHUP restarts. This structure is
+ * initialized for every iteration of the \c main() function's outer \c
+ * SIGHUP loop, but persists over iteration of that function's inner \c
+ * SIGUSR1 loop.
*/
struct context_1
{
- /* local and remote addresses */
struct link_socket_addr link_socket_addr;
+ /**< Local and remote addresses on the
+ * external network. */
/* tunnel session keys */
struct key_schedule ks;
@@ -158,12 +169,14 @@ struct context_1
/* persist crypto sequence number to/from file */
struct packet_id_persist pid_persist;
- /* TUN/TAP interface */
- struct tuntap *tuntap;
- bool tuntap_owned;
+ struct tuntap *tuntap; /**< Tun/tap virtual network interface. */
+ bool tuntap_owned; /**< Whether the tun/tap interface should
+ * be cleaned up when this %context is
+ * cleaned up. */
- /* list of --route directives */
struct route_list *route_list;
+ /**< List of routing information. See the
+ * \c --route command line option. */
/* list of --route-ipv6 directives */
struct route_ipv6_list *route_ipv6_list;
@@ -194,20 +207,30 @@ struct context_1
/* if client mode, hash of option strings we pulled from server */
struct md5_digest pulled_options_digest_save;
+ /**< Hash of option strings received from the
+ * remote OpenVPN server. Only used in
+ * client-mode. */
- /* save user/pass for authentication */
struct user_pass *auth_user_pass;
+ /**< Username and password for
+ * authentication. */
#endif
};
-/*
- * Contains the OpenVPN tunnel instance state, wiped across
- * SIGUSR1 and SIGHUP restarts.
+/**
+ * Level 2 %context containing state that is reset on both \c SIGHUP and
+ * \c SIGUSR1 restarts.
+ *
+ * This structure is initialized at the top of the \c
+ * tunnel_point_to_point(), \c tunnel_server_udp_single_threaded(), and \c
+ * tunnel_server_tcp() functions. In other words, it is reset for every
+ * iteration of the \c main() function's inner \c SIGUSR1 loop.
*/
struct context_2
{
- /* garbage collection arena for context_2 scope */
- struct gc_arena gc;
+ struct gc_arena gc; /**< Garbage collection arena for
+ * allocations done in the level 2 scope
+ * of this context_2 structure. */
/* our global wait events */
struct event_set *event_set;
@@ -315,12 +338,19 @@ struct context_2
*/
#ifdef USE_SSL
- /* master OpenVPN SSL/TLS object */
- struct tls_multi *tls_multi;
+ struct tls_multi *tls_multi; /**< TLS state structure for this VPN
+ * tunnel. */
- /* check --tls-auth signature without needing
- a full-size tls_multi object */
struct tls_auth_standalone *tls_auth_standalone;
+ /**< TLS state structure required for the
+ * initial authentication of a client's
+ * connection attempt. This structure
+ * is used by the \c
+ * tls_pre_decrypt_lite() function when
+ * it performs the HMAC firewall check
+ * on the first connection packet
+ * received from a new client. See the
+ * \c --tls-auth commandline option. */
/* used to optimize calls to tls_multi_process */
struct interval tmp_int;
@@ -330,10 +360,11 @@ struct context_2
#endif /* USE_SSL */
- /* passed to encrypt or decrypt, contains all
- crypto-related command line options related
- to data channel encryption/decryption */
struct crypto_options crypto_options;
+ /**< Security parameters and crypto state
+ * used by the \link data_crypto Data
+ * Channel Crypto module\endlink to
+ * process data channel packet. */
/* used to keep track of data channel packet sequence numbers */
struct packet_id packet_id;
@@ -341,11 +372,11 @@ struct context_2
#endif /* USE_CRYPTO */
- /*
- * LZO compression library workspace.
- */
#ifdef USE_LZO
struct lzo_compress_workspace lzo_compwork;
+ /**< Compression workspace used by the
+ * \link compression Data Channel
+ * Compression module\endlink. */
#endif
/*
@@ -462,16 +493,25 @@ struct context_2
#endif
};
-/*
+
+/**
* Contains all state information for one tunnel.
+ *
+ * This structure represents one VPN tunnel. It is used to store state
+ * information related to a VPN tunnel, but also includes process-wide
+ * data, such as configuration options.
+ *
+ * The @ref tunnel_state "Structure of VPN tunnel state storage" related
+ * page describes how this structure is used in client-mode and
+ * server-mode.
*/
struct context
{
- /* command line or config file options */
- struct options options;
+ struct options options; /**< Options loaded from command line or
+ * configuration file. */
- /* true on initial VPN iteration */
- bool first_time;
+ bool first_time; /**< True on the first iteration of
+ * OpenVPN's main loop. */
/* context modes */
# define CM_P2P 0 /* standalone point-to-point session or client */
@@ -479,41 +519,32 @@ struct context
# define CM_TOP_CLONE 2 /* clone of a CM_TOP context for one thread */
# define CM_CHILD_UDP 3 /* child context of a CM_TOP or CM_THREAD */
# define CM_CHILD_TCP 4 /* child context of a CM_TOP or CM_THREAD */
- int mode;
+ int mode; /**< Role of this context within the
+ * OpenVPN process. Valid values are \c
+ * CM_P2P, \c CM_TOP, \c CM_TOP_CLONE,
+ * \c CM_CHILD_UDP, and \c CM_CHILD_TCP. */
- /* garbage collection for context scope
- allocations */
- struct gc_arena gc;
+ struct gc_arena gc; /**< Garbage collection arena for
+ * allocations done in the scope of this
+ * context structure. */
- /* environmental variable settings */
- struct env_set *es;
+ struct env_set *es; /**< Set of environment variables. */
- /* signal info */
- struct signal_info *sig;
+ struct signal_info *sig; /**< Internal error signaling object. */
- /* shared object plugins */
- struct plugin_list *plugins;
- bool plugins_owned;
+ struct plugin_list *plugins; /**< List of plug-ins. */
+ bool plugins_owned; /**< Whether the plug-ins should be
+ * cleaned up when this %context is
+ * cleaned up. */
- /* set to true after we daemonize */
- bool did_we_daemonize;
+ bool did_we_daemonize; /**< Whether demonization has already
+ * taken place. */
- /* persistent across SIGHUP */
struct context_persist persist;
-
- /* level 0 context contains data related to
- once-per OpenVPN instantiation events
- such as daemonization */
- struct context_0 *c0;
-
- /* level 1 context is preserved for
- SIGUSR1 restarts, but initialized
- for SIGHUP restarts */
- struct context_1 c1;
-
- /* level 2 context is initialized for all
- restarts (SIGUSR1 and SIGHUP) */
- struct context_2 c2;
+ /**< Persistent %context. */
+ struct context_0 *c0; /**< Level 0 %context. */
+ struct context_1 c1; /**< Level 1 %context. */
+ struct context_2 c2; /**< Level 2 %context. */
};
/*