The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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

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    1 /*
    2  * Definitions for tcp compression routines.
    3  */
    4 /*-
    5  * Copyright (c) 1989, 1993
    6  *      The Regents of the University of California.  All rights reserved.
    7  *
    8  * Redistribution and use in source and binary forms, with or without
    9  * modification, are permitted provided that the following conditions
   10  * are met:
   11  * 1. Redistributions of source code must retain the above copyright
   12  *    notice, this list of conditions and the following disclaimer.
   13  * 2. Redistributions in binary form must reproduce the above copyright
   14  *    notice, this list of conditions and the following disclaimer in the
   15  *    documentation and/or other materials provided with the distribution.
   16  * 4. Neither the name of the University nor the names of its contributors
   17  *    may be used to endorse or promote products derived from this software
   18  *    without specific prior written permission.
   19  *
   20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   30  * SUCH DAMAGE.
   31  *
   32  *      Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
   33  *      - Initial distribution.
   34  * $FreeBSD: releng/6.2/sys/net/slcompress.h 139823 2005-01-07 01:45:51Z imp $
   35  */
   36 
   37 #ifndef _NET_SLCOMPRESS_H_
   38 #define _NET_SLCOMPRESS_H_
   39 
   40 #define MAX_STATES 16           /* must be > 2 and < 256 */
   41 #define MAX_HDR 128
   42 
   43 /*
   44  * Compressed packet format:
   45  *
   46  * The first octet contains the packet type (top 3 bits), TCP
   47  * 'push' bit, and flags that indicate which of the 4 TCP sequence
   48  * numbers have changed (bottom 5 bits).  The next octet is a
   49  * conversation number that associates a saved IP/TCP header with
   50  * the compressed packet.  The next two octets are the TCP checksum
   51  * from the original datagram.  The next 0 to 15 octets are
   52  * sequence number changes, one change per bit set in the header
   53  * (there may be no changes and there are two special cases where
   54  * the receiver implicitly knows what changed -- see below).
   55  *
   56  * There are 5 numbers which can change (they are always inserted
   57  * in the following order): TCP urgent pointer, window,
   58  * acknowledgement, sequence number and IP ID.  (The urgent pointer
   59  * is different from the others in that its value is sent, not the
   60  * change in value.)  Since typical use of SLIP links is biased
   61  * toward small packets (see comments on MTU/MSS below), changes
   62  * use a variable length coding with one octet for numbers in the
   63  * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
   64  * range 256 - 65535 or 0.  (If the change in sequence number or
   65  * ack is more than 65535, an uncompressed packet is sent.)
   66  */
   67 
   68 /*
   69  * Packet types (must not conflict with IP protocol version)
   70  *
   71  * The top nibble of the first octet is the packet type.  There are
   72  * three possible types: IP (not proto TCP or tcp with one of the
   73  * control flags set); uncompressed TCP (a normal IP/TCP packet but
   74  * with the 8-bit protocol field replaced by an 8-bit connection id --
   75  * this type of packet syncs the sender & receiver); and compressed
   76  * TCP (described above).
   77  *
   78  * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
   79  * is logically part of the 4-bit "changes" field that follows.  Top
   80  * three bits are actual packet type.  For backward compatibility
   81  * and in the interest of conserving bits, numbers are chosen so the
   82  * IP protocol version number (4) which normally appears in this nibble
   83  * means "IP packet".
   84  */
   85 
   86 /* packet types */
   87 #define TYPE_IP 0x40
   88 #define TYPE_UNCOMPRESSED_TCP 0x70
   89 #define TYPE_COMPRESSED_TCP 0x80
   90 #define TYPE_ERROR 0x00
   91 
   92 /* Bits in first octet of compressed packet */
   93 #define NEW_C   0x40    /* flag bits for what changed in a packet */
   94 #define NEW_I   0x20
   95 #define NEW_S   0x08
   96 #define NEW_A   0x04
   97 #define NEW_W   0x02
   98 #define NEW_U   0x01
   99 
  100 /* reserved, special-case values of above */
  101 #define SPECIAL_I (NEW_S|NEW_W|NEW_U)           /* echoed interactive traffic */
  102 #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U)     /* unidirectional data */
  103 #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
  104 
  105 #define TCP_PUSH_BIT 0x10
  106 
  107 
  108 /*
  109  * "state" data for each active tcp conversation on the wire.  This is
  110  * basically a copy of the entire IP/TCP header from the last packet
  111  * we saw from the conversation together with a small identifier
  112  * the transmit & receive ends of the line use to locate saved header.
  113  */
  114 struct cstate {
  115         struct cstate *cs_next; /* next most recently used cstate (xmit only) */
  116         u_int16_t cs_hlen;      /* size of hdr (receive only) */
  117         u_char cs_id;           /* connection # associated with this state */
  118         u_char cs_filler;
  119         union {
  120                 char csu_hdr[MAX_HDR];
  121                 struct ip csu_ip;       /* ip/tcp hdr from most recent packet */
  122         } slcs_u;
  123 };
  124 #define cs_ip slcs_u.csu_ip
  125 #define cs_hdr slcs_u.csu_hdr
  126 
  127 /*
  128  * all the state data for one serial line (we need one of these
  129  * per line).
  130  */
  131 struct slcompress {
  132         struct cstate *last_cs; /* most recently used tstate */
  133         u_char last_recv;       /* last rcvd conn. id */
  134         u_char last_xmit;       /* last sent conn. id */
  135         u_int16_t flags;
  136 #ifndef SL_NO_STATS
  137         int sls_packets;        /* outbound packets */
  138         int sls_compressed;     /* outbound compressed packets */
  139         int sls_searches;       /* searches for connection state */
  140         int sls_misses;         /* times couldn't find conn. state */
  141         int sls_uncompressedin; /* inbound uncompressed packets */
  142         int sls_compressedin;   /* inbound compressed packets */
  143         int sls_errorin;        /* inbound unknown type packets */
  144         int sls_tossed;         /* inbound packets tossed because of error */
  145 #endif
  146         struct cstate tstate[MAX_STATES];       /* xmit connection states */
  147         struct cstate rstate[MAX_STATES];       /* receive connection states */
  148 };
  149 /* flag values */
  150 #define SLF_TOSS 1              /* tossing rcvd frames because of input err */
  151 
  152 void     sl_compress_init(struct slcompress *, int);
  153 u_int    sl_compress_tcp(struct mbuf *, struct ip *, struct slcompress *, int);
  154 int      sl_uncompress_tcp(u_char **, int, u_int, struct slcompress *);
  155 int      sl_uncompress_tcp_core(u_char *, int, int, u_int,
  156             struct slcompress *, u_char **, u_int *);
  157 
  158 #endif /* !_NET_SLCOMPRESS_H_ */

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