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-rw-r--r--openvpn/mtu.h304
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diff --git a/openvpn/mtu.h b/openvpn/mtu.h
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--- a/openvpn/mtu.h
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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) 2002-2005 OpenVPN Solutions LLC <info@openvpn.net>
- *
- * 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
- */
-
-#ifndef MTU_H
-#define MTU_H
-
-#include "buffer.h"
-
-/*
- *
- * Packet maninipulation routes such as encrypt, decrypt, compress, decompress
- * are passed a frame buffer that looks like this:
- *
- * [extra_frame bytes] [mtu bytes] [extra_frame_bytes] [compression overflow bytes]
- * ^
- * Pointer passed to function points here so that routine
- * can make use of extra_frame bytes before pointer
- * to prepend headers, etc.
- *
- * extra_frame bytes is large enough for all encryption related overhead.
- *
- * mtu bytes will be the MTU size set in the ifconfig statement that configures
- * the TUN or TAP device such as:
- *
- * ifconfig $1 10.1.0.2 pointopoint 10.1.0.1 mtu 1450
- *
- * Compression overflow bytes is the worst-case size expansion that would be
- * expected if we tried to compress mtu + extra_frame bytes of uncompressible data.
- */
-
-/*
- * Standard ethernet MTU
- */
-#define ETHERNET_MTU 1500
-
-/*
- * It is a fatal error if mtu is less than
- * this value for tun device.
- */
-#define TUN_MTU_MIN 100
-
-/*
- * Default MTU of network over which tunnel data will pass by TCP/UDP.
- */
-#define LINK_MTU_DEFAULT 1500
-
-/*
- * Default MTU of tunnel device.
- */
-#define TUN_MTU_DEFAULT 1500
-
-/*
- * MTU Defaults for TAP devices
- */
-#define TAP_MTU_EXTRA_DEFAULT 32
-
-/*
- * Default MSSFIX value, used for reducing TCP MTU size
- */
-#define MSSFIX_DEFAULT 1450
-
-/*
- * Alignment of payload data such as IP packet or
- * ethernet frame.
- */
-#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;
-
- /*
- * Alignment control
- */
-# define FRAME_HEADROOM_MARKER_DECRYPT (1<<0)
-# define FRAME_HEADROOM_MARKER_FRAGMENT (1<<1)
-# define FRAME_HEADROOM_MARKER_READ_LINK (1<<2)
-# define FRAME_HEADROOM_MARKER_READ_STREAM (1<<3)
- unsigned int align_flags;
- int align_adjust;
-};
-
-/* Routines which read struct frame should use the macros below */
-
-/*
- * Overhead added to packet payload due to encapsulation
- */
-#define EXTRA_FRAME(f) ((f)->extra_frame)
-
-/*
- * Delta between tun payload size and final TCP/UDP datagram size
- * (not including extra_link additions)
- */
-#define TUN_LINK_DELTA(f) ((f)->extra_frame + (f)->extra_tun)
-
-/*
- * This is the size to "ifconfig" the tun or tap device.
- */
-#define TUN_MTU_SIZE(f) ((f)->link_mtu - TUN_LINK_DELTA(f))
-#define TUN_MTU_SIZE_DYNAMIC(f) ((f)->link_mtu_dynamic - TUN_LINK_DELTA(f))
-
-/*
- * This is the maximum packet size that we need to be able to
- * read from or write to a tun or tap device. For example,
- * a tap device ifconfiged to an MTU of 1200 might actually want
- * to return a packet size of 1214 on a read().
- */
-#define PAYLOAD_SIZE(f) ((f)->link_mtu - (f)->extra_frame)
-#define PAYLOAD_SIZE_DYNAMIC(f) ((f)->link_mtu_dynamic - (f)->extra_frame)
-
-/*
- * Max size of a payload packet after encryption, compression, etc.
- * overhead is added.
- */
-#define EXPANDED_SIZE(f) ((f)->link_mtu)
-#define EXPANDED_SIZE_DYNAMIC(f) ((f)->link_mtu_dynamic)
-#define EXPANDED_SIZE_MIN(f) (TUN_MTU_MIN + TUN_LINK_DELTA(f))
-
-/*
- * These values are used as maximum size constraints
- * on read() or write() from TUN/TAP device or TCP/UDP port.
- */
-#define MAX_RW_SIZE_TUN(f) (PAYLOAD_SIZE(f))
-#define MAX_RW_SIZE_LINK(f) (EXPANDED_SIZE(f) + (f)->extra_link)
-
-/*
- * Control buffer headroom allocations to allow for efficient prepending.
- */
-#define FRAME_HEADROOM_BASE(f) (TUN_LINK_DELTA(f) + (f)->extra_buffer + (f)->extra_link)
-#define FRAME_HEADROOM(f) frame_headroom(f, 0)
-#define FRAME_HEADROOM_ADJ(f, fm) frame_headroom(f, fm)
-
-/*
- * Max size of a buffer used to build a packet for output to
- * the TCP/UDP port.
- */
-#define BUF_SIZE(f) (TUN_MTU_SIZE(f) + FRAME_HEADROOM_BASE(f) * 2)
-
-/*
- * Function prototypes.
- */
-
-void frame_finalize (struct frame *frame,
- bool link_mtu_defined,
- int link_mtu,
- bool tun_mtu_defined,
- int tun_mtu);
-
-void frame_subtract_extra (struct frame *frame, const struct frame *src);
-
-void frame_print (const struct frame *frame,
- int level,
- const char *prefix);
-
-void set_mtu_discover_type (int sd, int mtu_type);
-int translate_mtu_discover_type_name (const char *name);
-
-/*
- * frame_set_mtu_dynamic and flags
- */
-
-#define SET_MTU_TUN (1<<0) /* use tun/tap rather than link sizing */
-#define SET_MTU_UPPER_BOUND (1<<1) /* only decrease dynamic MTU */
-
-void frame_set_mtu_dynamic (struct frame *frame, int mtu, unsigned int flags);
-
-/*
- * allocate a buffer for socket or tun layer
- */
-void alloc_buf_sock_tun (struct buffer *buf,
- const struct frame *frame,
- const bool tuntap_buffer,
- const unsigned int align_mask);
-
-/*
- * EXTENDED_SOCKET_ERROR_CAPABILITY functions -- print extra error info
- * on socket errors, such as PMTU size. As of 2003.05.11, only works
- * on Linux 2.4+.
- */
-
-#if EXTENDED_SOCKET_ERROR_CAPABILITY
-
-void set_sock_extended_error_passing (int sd);
-const char *format_extended_socket_error (int fd, int *mtu, struct gc_arena *gc);
-
-#endif
-
-/*
- * Calculate a starting offset into a buffer object, dealing with
- * headroom and alignment issues.
- */
-static inline int
-frame_headroom (const struct frame *f, const unsigned int flag_mask)
-{
- const int offset = FRAME_HEADROOM_BASE (f);
- const int adjust = (flag_mask & f->align_flags) ? f->align_adjust : 0;
- const int delta = ((PAYLOAD_ALIGN << 24) - (offset + adjust)) & (PAYLOAD_ALIGN - 1);
- return offset + delta;
-}
-
-/*
- * frame member adjustment functions
- */
-
-static inline void
-frame_add_to_extra_frame (struct frame *frame, const int increment)
-{
- frame->extra_frame += increment;
-}
-
-static inline void
-frame_add_to_extra_tun (struct frame *frame, const int increment)
-{
- frame->extra_tun += increment;
-}
-
-static inline void
-frame_add_to_extra_link (struct frame *frame, const int increment)
-{
- frame->extra_link += increment;
-}
-
-static inline void
-frame_add_to_extra_buffer (struct frame *frame, const int increment)
-{
- frame->extra_buffer += increment;
-}
-
-static inline void
-frame_add_to_align_adjust (struct frame *frame, const int increment)
-{
- frame->align_adjust += increment;
-}
-
-static inline void
-frame_align_to_extra_frame (struct frame *frame)
-{
- frame->align_adjust = frame->extra_frame + frame->extra_link;
-}
-
-static inline void
-frame_or_align_flags (struct frame *frame, const unsigned int flag_mask)
-{
- frame->align_flags |= flag_mask;
-}
-
-static inline bool
-frame_defined (const struct frame *frame)
-{
- return frame->link_mtu > 0;
-}
-
-#endif
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