bsd_comp.c

讲述linux的初始化过程

/*
 * Update: The Berkeley copyright was changed, and the change 
 * is retroactive to all "true" BSD software (ie everything
 * from UCB as opposed to other peoples code that just carried
 * the same license). The new copyright doesn't clash with the
 * GPL, so the module-only restriction has been removed..
 */

/* Because this code is derived from the 4.3BSD compress source:
 *
 * Copyright (c) 1985, 1986 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * James A. Woods, derived from original work by Spencer Thomas
 * and Joseph Orost.
 *
 * 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 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.
 */

/*
 * This version is for use with contiguous buffers on Linux-derived systems.
 *
 *  ==FILEVERSION 20000226==
 *
 *  NOTE TO MAINTAINERS:
 *     If you modify this file at all, please set the number above to the
 *     date of the modification as YYMMDD (year month day).
 *     bsd_comp.c is shipped with a PPP distribution as well as with
 *     the kernel; if everyone increases the FILEVERSION number above,
 *     then scripts can do the right thing when deciding whether to
 *     install a new bsd_comp.c file. Don't change the format of that
 *     line otherwise, so the installation script can recognize it.
 *
 * From: bsd_comp.c,v 1.3 1994/12/08 01:59:58 paulus Exp
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/malloc.h>
#include <linux/vmalloc.h>

#include <linux/ppp_defs.h>

#undef   PACKETPTR
#define  PACKETPTR 1
#include <linux/ppp-comp.h>
#undef   PACKETPTR

/*
 * PPP "BSD compress" compression
 *  The differences between this compression and the classic BSD LZW
 *  source are obvious from the requirement that the classic code worked
 *  with files while this handles arbitrarily long streams that
 *  are broken into packets.  They are:
 *
 *	When the code size expands, a block of junk is not emitted by
 *	    the compressor and not expected by the decompressor.
 *
 *	New codes are not necessarily assigned every time an old
 *	    code is output by the compressor.  This is because a packet
 *	    end forces a code to be emitted, but does not imply that a
 *	    new sequence has been seen.
 *
 *	The compression ratio is checked at the first end of a packet
 *	    after the appropriate gap.	Besides simplifying and speeding
 *	    things up, this makes it more likely that the transmitter
 *	    and receiver will agree when the dictionary is cleared when
 *	    compression is not going well.
 */

/*
 * Macros to extract protocol version and number of bits
 * from the third byte of the BSD Compress CCP configuration option.
 */

#define BSD_VERSION(x)	((x) >> 5)
#define BSD_NBITS(x)	((x) & 0x1F)

#define BSD_CURRENT_VERSION	1

/*
 * A dictionary for doing BSD compress.
 */

struct bsd_dict {
    union {				/* hash value */
	unsigned long	fcode;
	struct {
#if defined(__LITTLE_ENDIAN)		/* Little endian order */
	    unsigned short	prefix;	/* preceding code */
	    unsigned char	suffix; /* last character of new code */
	    unsigned char	pad;
#elif defined(__BIG_ENDIAN)		/* Big endian order */
	    unsigned char	pad;
	    unsigned char	suffix; /* last character of new code */
	    unsigned short	prefix; /* preceding code */
#else
#error Endianness not defined...
#endif
	} hs;
    } f;
    unsigned short codem1;		/* output of hash table -1 */
    unsigned short cptr;		/* map code to hash table entry */
};

struct bsd_db {
    int	    totlen;			/* length of this structure */
    unsigned int   hsize;		/* size of the hash table */
    unsigned char  hshift;		/* used in hash function */
    unsigned char  n_bits;		/* current bits/code */
    unsigned char  maxbits;		/* maximum bits/code */
    unsigned char  debug;		/* non-zero if debug desired */
    unsigned char  unit;		/* ppp unit number */
    unsigned short seqno;		/* sequence # of next packet */
    unsigned int   mru;			/* size of receive (decompress) bufr */
    unsigned int   maxmaxcode;		/* largest valid code */
    unsigned int   max_ent;		/* largest code in use */
    unsigned int   in_count;		/* uncompressed bytes, aged */
    unsigned int   bytes_out;		/* compressed bytes, aged */
    unsigned int   ratio;		/* recent compression ratio */
    unsigned int   checkpoint;		/* when to next check the ratio */
    unsigned int   clear_count;		/* times dictionary cleared */
    unsigned int   incomp_count;	/* incompressible packets */
    unsigned int   incomp_bytes;	/* incompressible bytes */
    unsigned int   uncomp_count;	/* uncompressed packets */
    unsigned int   uncomp_bytes;	/* uncompressed bytes */
    unsigned int   comp_count;		/* compressed packets */
    unsigned int   comp_bytes;		/* compressed bytes */
    unsigned short  *lens;		/* array of lengths of codes */
    struct bsd_dict *dict;		/* dictionary */
};

#define BSD_OVHD	2		/* BSD compress overhead/packet */
#define MIN_BSD_BITS	9
#define BSD_INIT_BITS	MIN_BSD_BITS
#define MAX_BSD_BITS	15

static void	bsd_free (void *state);
static void	*bsd_alloc(unsigned char *options, int opt_len, int decomp);
static void	*bsd_comp_alloc (unsigned char *options, int opt_len);
static void	*bsd_decomp_alloc (unsigned char *options, int opt_len);

static int	bsd_init        (void *db, unsigned char *options,
			         int opt_len, int unit, int debug, int decomp);
static int	bsd_comp_init   (void *state, unsigned char *options,
			         int opt_len, int unit, int opthdr, int debug);
static int	bsd_decomp_init (void *state, unsigned char *options,
				 int opt_len, int unit, int opthdr, int mru,
				 int debug);

static void	bsd_reset (void *state);
static void	bsd_comp_stats (void *state, struct compstat *stats);

static int	bsd_compress (void *state, unsigned char *rptr,
			      unsigned char *obuf, int isize, int osize);
static void	bsd_incomp (void *state, unsigned char *ibuf, int icnt);

static int	bsd_decompress (void *state, unsigned char *ibuf, int isize,
				unsigned char *obuf, int osize);

/* These are in ppp.c */
extern int  ppp_register_compressor   (struct compressor *cp);
extern void ppp_unregister_compressor (struct compressor *cp);

/*
 * the next two codes should not be changed lightly, as they must not
 * lie within the contiguous general code space.
 */
#define CLEAR	256			/* table clear output code */
#define FIRST	257			/* first free entry */
#define LAST	255

#define MAXCODE(b)	((1 << (b)) - 1)
#define BADCODEM1	MAXCODE(MAX_BSD_BITS);

#define BSD_HASH(prefix,suffix,hshift) ((((unsigned long)(suffix))<<(hshift)) \
					 ^ (unsigned long)(prefix))
#define BSD_KEY(prefix,suffix)		((((unsigned long)(suffix)) << 16) \
					 + (unsigned long)(prefix))

#define CHECK_GAP	10000		/* Ratio check interval */

#define RATIO_SCALE_LOG	8
#define RATIO_SCALE	(1<<RATIO_SCALE_LOG)
#define RATIO_MAX	(0x7fffffff>>RATIO_SCALE_LOG)

/*
 * clear the dictionary
 */

static void
bsd_clear(struct bsd_db *db)
{
    db->clear_count++;
    db->max_ent      = FIRST-1;
    db->n_bits       = BSD_INIT_BITS;
    db->bytes_out    = 0;
    db->in_count     = 0;
    db->ratio	     = 0;
    db->checkpoint   = CHECK_GAP;
}

/*
 * If the dictionary is full, then see if it is time to reset it.
 *
 * Compute the compression ratio using fixed-point arithmetic
 * with 8 fractional bits.
 *
 * Since we have an infinite stream instead of a single file,
 * watch only the local compression ratio.
 *
 * Since both peers must reset the dictionary at the same time even in
 * the absence of CLEAR codes (while packets are incompressible), they
 * must compute the same ratio.
 */

static int bsd_check (struct bsd_db *db)	/* 1=output CLEAR */
  {
    unsigned int new_ratio;

    if (db->in_count >= db->checkpoint)
      {
	/* age the ratio by limiting the size of the counts */
	if (db->in_count >= RATIO_MAX || db->bytes_out >= RATIO_MAX)
	  {
	    db->in_count  -= (db->in_count  >> 2);
	    db->bytes_out -= (db->bytes_out >> 2);
	  }
	
	db->checkpoint = db->in_count + CHECK_GAP;
	
	if (db->max_ent >= db->maxmaxcode)
	  {
	    /* Reset the dictionary only if the ratio is worse,
	     * or if it looks as if it has been poisoned
	     * by incompressible data.
	     *
	     * This does not overflow, because
	     *	db->in_count <= RATIO_MAX.
	     */

	    new_ratio = db->in_count << RATIO_SCALE_LOG;
	    if (db->bytes_out != 0)
	      {
		new_ratio /= db->bytes_out;
	      }
	    
	    if (new_ratio < db->ratio || new_ratio < 1 * RATIO_SCALE)
	      {
		bsd_clear (db);
		return 1;
	      }
	    db->ratio = new_ratio;
	  }
      }
    return 0;
  }

/*
 * Return statistics.
 */

static void bsd_comp_stats (void *state, struct compstat *stats)
  {
    struct bsd_db *db = (struct bsd_db *) state;
    
    stats->unc_bytes    = db->uncomp_bytes;
    stats->unc_packets  = db->uncomp_count;
    stats->comp_bytes   = db->comp_bytes;
    stats->comp_packets = db->comp_count;
    stats->inc_bytes    = db->incomp_bytes;
    stats->inc_packets  = db->incomp_count;
    stats->in_count     = db->in_count;
    stats->bytes_out    = db->bytes_out;
  }

/*
 * Reset state, as on a CCP ResetReq.
 */

static void bsd_reset (void *state)
  {
    struct bsd_db *db = (struct bsd_db *) state;

    bsd_clear(db);

    db->seqno       = 0;
    db->clear_count = 0;
  }

/*
 * Release the compression structure
 */

static void bsd_free (void *state)
  {
    struct bsd_db *db = (struct bsd_db *) state;
    
    if (db)
      {
/*
 * Release the dictionary
 */
	if (db->dict)
	  {
	    vfree (db->dict);
	    db->dict = NULL;
	  }
/*
 * Release the string buffer
 */
	if (db->lens)
	  {
	    vfree (db->lens);
	    db->lens = NULL;
	  }
/*
 * Finally release the structure itself.
 */
	kfree (db);
	MOD_DEC_USE_COUNT;
      }
  }

/*
 * Allocate space for a (de) compressor.
 */

static void *bsd_alloc (unsigned char *options, int opt_len, int decomp)
  {
    int bits;
    unsigned int hsize, hshift, maxmaxcode;
    struct bsd_db *db;

    if (opt_len != 3 || options[0] != CI_BSD_COMPRESS || options[1] != 3
	|| BSD_VERSION(options[2]) != BSD_CURRENT_VERSION)
      {
	return NULL;
      }

    bits = BSD_NBITS(options[2]);

    switch (bits)
      {
    case 9:			/* needs 82152 for both directions */
    case 10:			/* needs 84144 */
    case 11:			/* needs 88240 */
    case 12:			/* needs 96432 */
	hsize = 5003;
	hshift = 4;
	break;
    case 13:			/* needs 176784 */
	hsize = 9001;
	hshift = 5;
	break;
    case 14:			/* needs 353744 */
	hsize = 18013;
	hshift = 6;
	break;
    case 15:			/* needs 691440 */
	hsize = 35023;
	hshift = 7;
	break;
    case 16:			/* needs 1366160--far too much, */
	/* hsize = 69001; */	/* and 69001 is too big for cptr */
	/* hshift = 8; */	/* in struct bsd_db */
	/* break; */
    default:
	return NULL;
      }
/*
 * Allocate the main control structure for this instance.
 */
    maxmaxcode = MAXCODE(bits);
    db         = (struct bsd_db *) kmalloc (sizeof (struct bsd_db),
					    GFP_KERNEL);
    if (!db)
      {
	return NULL;
      }

    memset (db, 0, sizeof(struct bsd_db));
/*
 * Allocate space for the dictionary. This may be more than one page in
 * length.
 */
    db->dict = (struct bsd_dict *) vmalloc (hsize *
					    sizeof (struct bsd_dict));
    if (!db->dict)
      {
	bsd_free (db);
	return NULL;
      }

    MOD_INC_USE_COUNT;
/*
 * If this is the compression buffer then there is no length data.
 */
    if (!decomp)
      {
	db->lens = NULL;
      }
/*
 * For decompression, the length information is needed as well.
 */
    else
      {
        db->lens = (unsigned short *) vmalloc ((maxmaxcode + 1) *
					       sizeof (db->lens[0]));
	if (!db->lens)
	  {
	    bsd_free (db);
	    return (NULL);
	  }
      }
/*
 * Initialize the data information for the compression code
 */
    db->totlen     = sizeof (struct bsd_db)   +
      		    (sizeof (struct bsd_dict) * hsize);

    db->hsize      = hsize;
    db->hshift     = hshift;
    db->maxmaxcode = maxmaxcode;
    db->maxbits    = bits;

    return (void *) db;
  }

static void *bsd_comp_alloc (unsigned char *options, int opt_len)
  {
    return bsd_alloc (options, opt_len, 0);
  }

static void *bsd_decomp_alloc (unsigned char *options, int opt_len)
  {
    return bsd_alloc (options, opt_len, 1);
  }

/*
 * Initialize the database.
 */

static int bsd_init (void *state, unsigned char *options,
		     int opt_len, int unit, int debug, int decomp)
  {
    struct bsd_db *db = state;
    int indx;
    
    if ((opt_len != 3) || (options[0] != CI_BSD_COMPRESS) || (options[1] != 3)
	|| (BSD_VERSION(options[2]) != BSD_CURRENT_VERSION)
	|| (BSD_NBITS(options[2]) != db->maxbits)
	|| (decomp && db->lens == NULL))
      {
	return 0;
      }

    if (decomp)
      {
	indx = LAST;
	do
	  {
	    db->lens[indx] = 1;
	  }
	while (indx-- > 0);
      }

    indx = db->hsize;
    while (indx-- != 0)
      {
	db->dict[indx].codem1 = BADCODEM1;
	db->dict[indx].cptr   = 0;
      }

    db->unit = unit;
    db->mru  = 0;
#ifndef DEBUG
    if (debug)
#endif
      db->debug = 1;
    
    bsd_reset(db);
    
    return 1;
  }

static int bsd_comp_init (void *state, unsigned char *options,
			  int opt_len, int unit, int opthdr, int debug)
  {
    return bsd_init (state, options, opt_len, unit, debug, 0);
  }

static int bsd_decomp_init (void *state, unsigned char *options,
			    int opt_len, int unit, int opthdr, int mru,
			    int debug)
  {
    return bsd_init (state, options, opt_len, unit, debug, 1);
  }

/*
 * Obtain pointers to the various structures in the compression tables
 */

#define dict_ptrx(p,idx) &(p->dict[idx])
#define lens_ptrx(p,idx) &(p->lens[idx])

#ifdef DEBUG
static unsigned short *lens_ptr(struct bsd_db *db, int idx)
  {
    if ((unsigned int) idx > (unsigned int) db->maxmaxcode)
      {
	printk ("<9>ppp: lens_ptr(%d) > max\n", idx);
	idx = 0;
      }
    return lens_ptrx (db, idx);
  }

static struct bsd_dict *dict_ptr(struct bsd_db *db, int idx)
  {
    if ((unsigned int) idx >= (unsigned int) db->hsize)
      {
	printk ("<9>ppp: dict_ptr(%d) > max\n", idx);
	idx = 0;
      }
    return dict_ptrx (db, idx);
  }

#else
#define lens_ptr(db,idx) lens_ptrx(db,idx)
#define dict_ptr(db,idx) dict_ptrx(db,idx)
#endif

/*
 * compress a packet
 *
 *	The result of this function is the size of the compressed
 *	packet. A zero is returned if the packet was not compressed
 *	for some reason, such as the size being larger than uncompressed.
 *
 *	One change from the BSD compress command is that when the
 *	code size expands, we do not output a bunch of padding.
 */

static int bsd_compress (void *state, unsigned char *rptr, unsigned char *obuf,
			 int isize, int osize)
  {
    struct bsd_db *db;
    int hshift;
    unsigned int max_ent;
    unsigned int n_bits;
    unsigned int bitno;
    unsigned long accm;
    int ent;
    unsigned long fcode;
    struct bsd_dict *dictp;
    unsigned char c;
    int hval;
    int disp;
    int ilen;
    int mxcode;
    unsigned char *wptr;