/* *  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) 2002-2004 James Yonan <jim@yonan.net> * *  This program is free software; you can redistribute it and/or modify *  it under the terms of the GNU General Public License as published by *  the Free Software Foundation; either version 2 of the License, or *  (at your option) any later version. * *  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     1450struct frame {  /*   * Maximum datagram size to be sent over the tunnel TCP/UDP channel.   */  int link_mtu;  int link_mtu_dynamic;  /*   * extra_frame: 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;  /*   * extra_buffer: 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;  /*   * extra_tun: max number of bytes in excess of tun mtu size that we might read   * or write from TUN/TAP device.   */  int extra_tun;  /*   * extra_link: max number of bytes in excess on link mtu size that we might read   * or write from UDP/TCP link.   */  int extra_link;};/* 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)/* * In general, OpenVPN packet building routines set the initial * buffer store point this many bytes into the data buffer to * allow for efficient prepending. */#define FRAME_HEADROOM(f)        (TUN_LINK_DELTA(f) + (f)->extra_buffer + (f)->extra_link)/* * 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(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, bool tuntap_buffer);/* * 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_CAPABILITYvoid set_sock_extended_error_passing (int sd);const char *format_extended_socket_error (int fd, int *mtu, struct gc_arena *gc);#endif/* * Inline functions */static inline voidframe_add_to_extra_frame (struct frame *frame, int increment){  frame->extra_frame += increment;}static inline voidframe_add_to_extra_tun (struct frame *frame, int increment){  frame->extra_tun += increment;}static inline voidframe_add_to_extra_link (struct frame *frame, int increment){  frame->extra_link += increment;}static inline voidframe_add_to_extra_buffer (struct frame *frame, int increment){  frame->extra_buffer += increment;}static inline boolframe_defined (const struct frame *frame){  return frame->link_mtu > 0;}#endif