FreeBSD/Linux Kernel Cross Reference
sys/net/slcompress.h

     /*
      * Definitions for tcp compression routines.
      *
      * Copyright (c) 1989, 1993
      *      The Regents of the University of California.  All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 4. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
     *      - Initial distribution.
     * $FreeBSD: releng/5.3/sys/net/slcompress.h 136588 2004-10-16 08:43:07Z cvs2svn $
     */
    
    #ifndef _NET_SLCOMPRESS_H_
    #define _NET_SLCOMPRESS_H_
    
    #define MAX_STATES 16           /* must be > 2 and < 256 */
    #define MAX_HDR 128
    
    /*
     * Compressed packet format:
     *
     * The first octet contains the packet type (top 3 bits), TCP
     * 'push' bit, and flags that indicate which of the 4 TCP sequence
     * numbers have changed (bottom 5 bits).  The next octet is a
     * conversation number that associates a saved IP/TCP header with
     * the compressed packet.  The next two octets are the TCP checksum
     * from the original datagram.  The next 0 to 15 octets are
     * sequence number changes, one change per bit set in the header
     * (there may be no changes and there are two special cases where
     * the receiver implicitly knows what changed -- see below).
     *
     * There are 5 numbers which can change (they are always inserted
     * in the following order): TCP urgent pointer, window,
     * acknowledgement, sequence number and IP ID.  (The urgent pointer
     * is different from the others in that its value is sent, not the
     * change in value.)  Since typical use of SLIP links is biased
     * toward small packets (see comments on MTU/MSS below), changes
     * use a variable length coding with one octet for numbers in the
     * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
     * range 256 - 65535 or 0.  (If the change in sequence number or
     * ack is more than 65535, an uncompressed packet is sent.)
     */
    
    /*
     * Packet types (must not conflict with IP protocol version)
     *
     * The top nibble of the first octet is the packet type.  There are
     * three possible types: IP (not proto TCP or tcp with one of the
     * control flags set); uncompressed TCP (a normal IP/TCP packet but
     * with the 8-bit protocol field replaced by an 8-bit connection id --
     * this type of packet syncs the sender & receiver); and compressed
     * TCP (described above).
     *
     * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
     * is logically part of the 4-bit "changes" field that follows.  Top
     * three bits are actual packet type.  For backward compatibility
     * and in the interest of conserving bits, numbers are chosen so the
     * IP protocol version number (4) which normally appears in this nibble
     * means "IP packet".
     */
    
    /* packet types */
    #define TYPE_IP 0x40
    #define TYPE_UNCOMPRESSED_TCP 0x70
    #define TYPE_COMPRESSED_TCP 0x80
    #define TYPE_ERROR 0x00
    
    /* Bits in first octet of compressed packet */
    #define NEW_C   0x40    /* flag bits for what changed in a packet */
    #define NEW_I   0x20
    #define NEW_S   0x08
    #define NEW_A   0x04
    #define NEW_W   0x02
    #define NEW_U   0x01
    
    /* reserved, special-case values of above */
   #define SPECIAL_I (NEW_S|NEW_W|NEW_U)           /* echoed interactive traffic */
   #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U)     /* unidirectional data */
   #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
   
   #define TCP_PUSH_BIT 0x10
   
   
   /*
    * "state" data for each active tcp conversation on the wire.  This is
    * basically a copy of the entire IP/TCP header from the last packet
    * we saw from the conversation together with a small identifier
    * the transmit & receive ends of the line use to locate saved header.
    */
   struct cstate {
           struct cstate *cs_next; /* next most recently used cstate (xmit only) */
           u_int16_t cs_hlen;      /* size of hdr (receive only) */
           u_char cs_id;           /* connection # associated with this state */
           u_char cs_filler;
           union {
                   char csu_hdr[MAX_HDR];
                   struct ip csu_ip;       /* ip/tcp hdr from most recent packet */
           } slcs_u;
   };
   #define cs_ip slcs_u.csu_ip
   #define cs_hdr slcs_u.csu_hdr
   
   /*
    * all the state data for one serial line (we need one of these
    * per line).
    */
   struct slcompress {
           struct cstate *last_cs; /* most recently used tstate */
           u_char last_recv;       /* last rcvd conn. id */
           u_char last_xmit;       /* last sent conn. id */
           u_int16_t flags;
   #ifndef SL_NO_STATS
           int sls_packets;        /* outbound packets */
           int sls_compressed;     /* outbound compressed packets */
           int sls_searches;       /* searches for connection state */
           int sls_misses;         /* times couldn't find conn. state */
           int sls_uncompressedin; /* inbound uncompressed packets */
           int sls_compressedin;   /* inbound compressed packets */
           int sls_errorin;        /* inbound unknown type packets */
           int sls_tossed;         /* inbound packets tossed because of error */
   #endif
           struct cstate tstate[MAX_STATES];       /* xmit connection states */
           struct cstate rstate[MAX_STATES];       /* receive connection states */
   };
   /* flag values */
   #define SLF_TOSS 1              /* tossing rcvd frames because of input err */
   
   void     sl_compress_init(struct slcompress *, int);
   u_int    sl_compress_tcp(struct mbuf *, struct ip *, struct slcompress *, int);
   int      sl_uncompress_tcp(u_char **, int, u_int, struct slcompress *);
   int      sl_uncompress_tcp_core(u_char *, int, int, u_int,
               struct slcompress *, u_char **, u_int *);
   
   #endif /* !_NET_SLCOMPRESS_H_ */

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