bsd-comp.c

unix and linux net driver

    u_char *cp_end;
    int olen;
    NETBUF_T m;

#define PUTBYTE(v) {					\
    ++olen;						\
    if (wptr) {						\
	*wptr++ = (v);					\
	if (wptr >= cp_end)				\
	    wptr = NULL;				\
    }							\
}

#define OUTPUT(ent) {					\
    bitno -= n_bits;					\
    accm |= ((ent) << bitno);				\
    do {						\
	PUTBYTE(accm >> 24);				\
	accm <<= 8;					\
	bitno += 8;					\
    } while (bitno <= 24);				\
}

    /*
     * If the protocol is not in the range we're interested in,
     * just return without compressing the packet.  If it is,
     * the protocol becomes the first byte to compress.
     */
    rptr = mtod(mp, u_char *);
    ent = PPP_PROTOCOL(rptr);
    if (ent < CI_BSD_COMPRESS || ent > 0xf9) {
	*mret = NULL;
	return slen;
    }

    /* Don't generate compressed packets which are larger than
       the uncompressed packet. */
    if (maxolen > slen)
	maxolen = slen;

    /* Allocate one mbuf to start with. (don't forget space for the FCS!) */
    m = NB_ALLOC(maxolen + db->hdrlen + PPP_FCSLEN);
    *mret = m;
    if (m != NULL) {
      if (db->hdrlen > 0)
	NB_SHRINK_TOP(m, db->hdrlen);
      NB_SHRINK_BOT(m, PPP_FCSLEN);  /* grown by pppstart() */
	wptr = mtod(m, u_char *);
	cp_end = wptr + maxolen;
    } else
	wptr = cp_end = NULL;

    /*
     * Copy the PPP header over, changing the protocol,
     * and install the 2-byte packet sequence number.
     */
    if (wptr) {
	*wptr++ = PPP_ADDRESS(rptr);	/* assumes the ppp header is */
	*wptr++ = PPP_CONTROL(rptr);	/* all in one mbuf */
	*wptr++ = 0;			/* change the protocol */
	*wptr++ = PPP_COMP;
	*wptr++ = db->seqno >> 8;
	*wptr++ = db->seqno;
    }
    ++db->seqno;

    olen = 0;
    rptr += PPP_HDRLEN;
    slen = NB_SIZE(mp) - PPP_HDRLEN;
    ilen = slen + 1;
    while (slen > 0) {
	slen--;
	c = *rptr++;
	fcode = BSD_KEY(ent, c);
	hval = BSD_HASH(ent, c, hshift);
	dictp = &db->dict[hval];

	/* Validate and then check the entry. */
	if (dictp->codem1 >= max_ent)
	    goto nomatch;
	if (dictp->f.fcode == fcode) {
	    ent = dictp->codem1+1;
	    continue;	/* found (prefix,suffix) */
	}

	/* continue probing until a match or invalid entry */
	disp = (hval == 0) ? 1 : hval;
	do {
	    hval += disp;
	    if (hval >= db->hsize)
		hval -= db->hsize;
	    dictp = &db->dict[hval];
	    if (dictp->codem1 >= max_ent)
		goto nomatch;
	} while (dictp->f.fcode != fcode);
	ent = dictp->codem1 + 1;	/* finally found (prefix,suffix) */
	continue;

    nomatch:
	OUTPUT(ent);		/* output the prefix */

	/* code -> hashtable */
	if (max_ent < db->maxmaxcode) {
	    struct bsd_dict *dictp2;
	    /* expand code size if needed */
	    if (max_ent >= MAXCODE(n_bits))
		db->n_bits = ++n_bits;

	    /* Invalidate old hash table entry using
	     * this code, and then take it over.
	     */
	    dictp2 = &db->dict[max_ent+1];
	    if (db->dict[dictp2->cptr].codem1 == max_ent)
		db->dict[dictp2->cptr].codem1 = BADCODEM1;
	    dictp2->cptr = hval;
	    dictp->codem1 = max_ent;
	    dictp->f.fcode = fcode;

	    db->max_ent = ++max_ent;
	}
	ent = c;
    }

    OUTPUT(ent);		/* output the last code */
    db->bytes_out += olen;
    db->in_count += ilen;
    if (bitno < 32)
	++db->bytes_out;	/* count complete bytes */

    if (bsd_check(db))
	OUTPUT(CLEAR);		/* do not count the CLEAR */

    /*
     * Pad dribble bits of last code with ones.
     * Do not emit a completely useless byte of ones.
     */
    if (bitno != 32)
	PUTBYTE((accm | (0xff << (bitno-8))) >> 24);

    /*
     * Increase code size if we would have without the packet
     * boundary and as the decompressor will.
     */
    if (max_ent >= MAXCODE(n_bits) && max_ent < db->maxmaxcode)
	db->n_bits++;

    db->uncomp_bytes += ilen;
    ++db->uncomp_count;
    if (olen + PPP_HDRLEN + BSD_OVHD > maxolen || wptr == NULL) {
	/* throw away the compressed stuff if it is longer than uncompressed */
	if (*mret != NULL) {
	    NB_FREE(*mret);
	    *mret = NULL;
	}
	++db->incomp_count;
	db->incomp_bytes += ilen;
    } else {
	NB_SHRINK_BOT(m, NB_SIZE(m) - (wptr - mtod(m, u_char *)));
	++db->comp_count;
	db->comp_bytes += olen + BSD_OVHD;
    }

    return olen + PPP_HDRLEN + BSD_OVHD;
#undef OUTPUT
#undef PUTBYTE
}


/*
 * Update the "BSD Compress" dictionary on the receiver for
 * incompressible data by pretending to compress the incoming data.
 */
static void
bsd_incomp(state, dmsg)
    void *state;
    NETBUF_T dmsg;
{
    struct bsd_db *db = (struct bsd_db *) state;
    u_int hshift = db->hshift;
    u_int max_ent = db->max_ent;
    u_int n_bits = db->n_bits;
    struct bsd_dict *dictp;
    u_int32_t fcode;
    u_char c;
    u_int32_t hval, disp;
    int slen, ilen;
    u_int bitno = 7;
    u_char *rptr;
    u_int ent;

    /*
     * If the protocol is not in the range we're interested in,
     * just return without looking at the packet.  If it is,
     * the protocol becomes the first byte to "compress".
     */
    rptr = mtod(dmsg, u_char *);
    ent = PPP_PROTOCOL(rptr);
    if (ent < CI_BSD_COMPRESS || ent > 0xf9)
	return;

    db->incomp_count++;
    db->seqno++;
    ilen = 1;		/* count the protocol as 1 byte */
    rptr += PPP_HDRLEN;
    slen = NB_SIZE(dmsg) - PPP_HDRLEN;
    ilen += slen;

    do {
	c = *rptr++;
	fcode = BSD_KEY(ent, c);
	hval = BSD_HASH(ent, c, hshift);
	dictp = &db->dict[hval];

	/* validate and then check the entry */
	if (dictp->codem1 >= max_ent)
	    goto nomatch;
	if (dictp->f.fcode == fcode) {
	    ent = dictp->codem1+1;
	    continue;   /* found (prefix,suffix) */
	}

	/* continue probing until a match or invalid entry */
	disp = (hval == 0) ? 1 : hval;
	do {
	    hval += disp;
	    if (hval >= db->hsize)
		hval -= db->hsize;
	    dictp = &db->dict[hval];
	    if (dictp->codem1 >= max_ent)
		goto nomatch;
	} while (dictp->f.fcode != fcode);
	ent = dictp->codem1+1;
	continue;	/* finally found (prefix,suffix) */

    nomatch:		/* output (count) the prefix */
	bitno += n_bits;

	/* code -> hashtable */
	if (max_ent < db->maxmaxcode) {
	    struct bsd_dict *dictp2;
	    /* expand code size if needed */
	    if (max_ent >= MAXCODE(n_bits))
		db->n_bits = ++n_bits;

	    /* Invalidate previous hash table entry
	     * assigned this code, and then take it over.
	     */
	    dictp2 = &db->dict[max_ent+1];
	    if (db->dict[dictp2->cptr].codem1 == max_ent)
		db->dict[dictp2->cptr].codem1 = BADCODEM1;
	    dictp2->cptr = hval;
	    dictp->codem1 = max_ent;
	    dictp->f.fcode = fcode;

	    db->max_ent = ++max_ent;
	    db->lens[max_ent] = db->lens[ent]+1;
	}
	ent = c;
    } while (--slen != 0);
    bitno += n_bits;		/* output (count) the last code */
    db->bytes_out += bitno/8;
    db->in_count += ilen;
    (void)bsd_check(db);

    ++db->incomp_count;
    db->incomp_bytes += ilen;
    ++db->uncomp_count;
    db->uncomp_bytes += ilen;

    /* Increase code size if we would have without the packet
     * boundary and as the decompressor will.
     */
    if (max_ent >= MAXCODE(n_bits) && max_ent < db->maxmaxcode)
	db->n_bits++;
}


/*
 * Decompress "BSD Compress".
 *
 * Because of patent problems, we return DECOMP_ERROR for errors
 * found by inspecting the input data and for system problems, but
 * DECOMP_FATALERROR for any errors which could possibly be said to
 * be being detected "after" decompression.  For DECOMP_ERROR,
 * we can issue a CCP reset-request; for DECOMP_FATALERROR, we may be
 * infringing a patent of Motorola's if we do, so we take CCP down
 * instead.
 *
 * Given that the frame has the correct sequence number and a good FCS,
 * errors such as invalid codes in the input most likely indicate a
 * bug, so we return DECOMP_FATALERROR for them in order to turn off
 * compression, even though they are detected by inspecting the input.
 */
int
bsd_decompress(state, cmp, dmpp)
    void *state;
    NETBUF_T cmp, *dmpp;
{
    struct bsd_db *db = (struct bsd_db *) state;
    u_int max_ent = db->max_ent;
    u_int32_t accm = 0;
    u_int bitno = 32;		/* 1st valid bit in accm */
    u_int n_bits = db->n_bits;
    u_int tgtbitno = 32-n_bits;	/* bitno when we have a code */
    struct bsd_dict *dictp;
    int explen, seq, len;
    u_int incode, oldcode, finchar;
    u_char *p, *rptr, *wptr;
    NETBUF_T dmp, mret;
    int adrs, ctrl, ilen;
    int space, codelen, extra, maxilen;

    /*
     * Save the address/control from the PPP header
     * and then get the sequence number.
     */
    *dmpp = NULL;
    rptr = mtod(cmp, u_char *);
    adrs = PPP_ADDRESS(rptr);
    ctrl = PPP_CONTROL(rptr);
    rptr += PPP_HDRLEN;
    len = NB_SIZE(cmp) - PPP_HDRLEN;
    seq = (rptr[0] << 8) + rptr[1];
    rptr += BSD_OVHD;
    len -= BSD_OVHD;

    /*
     * Check the sequence number and give up if it differs from
     * the value we're expecting.
     */
    if (seq != db->seqno) {
	IOLogDbg("bsd_decomp%d: bad sequence # %d, expected %d\n",
		   db->unit, seq, db->seqno - 1);
	return DECOMP_ERROR;
    }
    ++db->seqno;

    /*
     * Allocate an netbuf large enough for all the data.
     */
    maxilen = db->mru + db->hdrlen + PPP_HDRLEN;	/* no FCS */
    dmp = NB_ALLOC(maxilen);			/* XXX */
    if (dmp == NULL)
	return DECOMP_ERROR;
    if (db->hdrlen > 0)
   	NB_SHRINK_TOP(dmp, db->hdrlen);
    mret = dmp;
    wptr = mtod(dmp, u_char *);
    space = NB_SIZE(dmp) - PPP_HDRLEN + 1;

    /*
     * Fill in the ppp header, but not the last byte of the protocol
     * (that comes from the decompressed data).
     */
    wptr[0] = adrs;
    wptr[1] = ctrl;
    wptr[2] = 0;
    wptr += PPP_HDRLEN - 1;

    ilen = len;
    oldcode = CLEAR;
    explen = 0;
    while (len > 0) {
	/*
	 * Accumulate bytes until we have a complete code.
	 * Then get the next code, relying on the 32-bit,
	 * unsigned accm to mask the result.
	 */
	bitno -= 8;
	accm |= *rptr++ << bitno;
	--len;
	if (tgtbitno < bitno)
	    continue;
	incode = accm >> tgtbitno;
	accm <<= n_bits;
	bitno += n_bits;

	if (incode == CLEAR) {
	    /*
	     * The dictionary must only be cleared at
	     * the end of a packet.  But there could be an
	     * empty mbuf at the end.
	     */
	    if (len > 0) {
		NB_FREE(mret);
		IOLogDbg("bsd_decomp%d: bad CLEAR\n", db->unit);
		return DECOMP_FATALERROR;	/* probably a bug */
	    }
	    bsd_clear(db);
	    explen = ilen = 0;
	    break;
	}

	if (incode > max_ent + 2 || incode > db->maxmaxcode
	    || incode > max_ent && oldcode == CLEAR) {
	    NB_FREE(mret);
	    IOLogDbg("bsd_decomp%d: bad code 0x%x oldcode=0x%x max_ent=0x%x explen=%d seqno=%d\n",
		     db->unit, incode, oldcode, max_ent, explen, db->seqno);
	    return DECOMP_FATALERROR;	/* probably a bug */
	}

	/* Special case for KwKwK string. */
	if (incode > max_ent) {
	    finchar = oldcode;
	    extra = 1;
	} else {
	    finchar = incode;
	    extra = 0;
	}

	codelen = db->lens[finchar];
	explen += codelen + extra;
	if (explen > db->mru + 1) {
	    NB_FREE(mret);
	    IOLogDbg("bsd_decomp%d: ran out of mru\n  len=%d, finchar=0x%x, codelen=%d, explen=%d\n",
		       db->unit, len, finchar, codelen, explen);
	    return DECOMP_FATALERROR;
	}

	/*
	 * If we have no space left, then we've overflowed...
	 */
	if ((space -= codelen + extra) < 0) {
	    IOLog("bsd_decompress%d: no space left in netbuf (need %d bytes)\n",
		  db->unit, (codelen + extra) - space);
	    NB_FREE(mret);
	    return DECOMP_ERROR;
	}

	/*
	 * Decode this code and install it in the decompressed buffer.
	 */
	p = (wptr += codelen);
	while (finchar > LAST) {
	    dictp = &db->dict[db->dict[finchar].cptr];
#ifdef DEBUG
	    if (--codelen <= 0 || dictp->codem1 != finchar-1)
		goto bad;
#endif
	    *--p = dictp->f.hs.suffix;
	    finchar = dictp->f.hs.prefix;
	}
	*--p = finchar;

#ifdef DEBUG
	if (--codelen != 0)
	    IOLog("bsd_decomp%d: short by %d after code 0x%x, max_ent=0x%x\n",
		   db->unit, codelen, incode, max_ent);
#endif

	if (extra)		/* the KwKwK case again */
	    *wptr++ = finchar;

	/*
	 * If not first code in a packet, and
	 * if not out of code space, then allocate a new code.
	 *
	 * Keep the hash table correct so it can be used
	 * with uncompressed packets.
	 */
	if (oldcode != CLEAR && max_ent < db->maxmaxcode) {
	    struct bsd_dict *dictp2;
	    u_int32_t fcode;
	    u_int32_t hval, disp;

	    fcode = BSD_KEY(oldcode,finchar);
	    hval = BSD_HASH(oldcode,finchar,db->hshift);
	    dictp = &db->dict[hval];

	    /* look for a free hash table entry */
	    if (dictp->codem1 < max_ent) {
		disp = (hval == 0) ? 1 : hval;
		do {
		    hval += disp;
		    if (hval >= db->hsize)
			hval -= db->hsize;
		    dictp = &db->dict[hval];
		} while (dictp->codem1 < max_ent);
	    }

	    /*
	     * Invalidate previous hash table entry
	     * assigned this code, and then take it over
	     */
	    dictp2 = &db->dict[max_ent+1];
	    if (db->dict[dictp2->cptr].codem1 == max_ent) {
		db->dict[dictp2->cptr].codem1 = BADCODEM1;
	    }
	    dictp2->cptr = hval;
	    dictp->codem1 = max_ent;
	    dictp->f.fcode = fcode;

	    db->max_ent = ++max_ent;
	    db->lens[max_ent] = db->lens[oldcode]+1;

	    /* Expand code size if needed. */
	    if (max_ent >= MAXCODE(n_bits) && max_ent < db->maxmaxcode) {
		db->n_bits = ++n_bits;
		tgtbitno = 32-n_bits;
	    }
	}
	oldcode = incode;
    }
    NB_SHRINK_BOT(dmp, NB_SIZE(dmp) - (wptr - mtod(dmp, u_char *)));

    /*
     * Keep the checkpoint right so that incompressible packets
     * clear the dictionary at the right times.
     */
    db->bytes_out += ilen;
    db->in_count += explen;
    if (bsd_check(db)) {
	IOLogDbg("bsd_decomp%d: peer should have cleared dictionary\n",
	       db->unit);
    }

    ++db->comp_count;
    db->comp_bytes += ilen + BSD_OVHD;
    ++db->uncomp_count;
    db->uncomp_bytes += explen;

    *dmpp = mret;
    return DECOMP_OK;

#ifdef DEBUG
 bad:
    if (codelen <= 0) {
	IOLog("bsd_decomp%d: fell off end of chain 0x%x at 0x%x by 0x%x, max_ent=0x%x\n",
	      db->unit, incode, finchar, db->dict[finchar].cptr, max_ent);
    } else if (dictp->codem1 != finchar-1) {
	IOLog("bsd_decomp%d: bad code chain 0x%x finchar=0x%x oldcode=0x%x cptr=0x%x codem1=0x%x\n",
	      db->unit, incode, finchar, oldcode, db->dict[finchar].cptr,
	      dictp->codem1);
    }
    NB_FREE(mret);
    return DECOMP_FATALERROR;
#endif /* DEBUG */
}
#endif /* DO_BSD_COMPRESS */