path: root/drivers/char/ftape/compressor/zftape-compress.c

/*
 *      Copyright (C) 1994-1997 Claus-Justus Heine

 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, 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.  If not, write to
 the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139,
 USA.
 
 *
 *     This file implements a "generic" interface between the *
 *     zftape-driver and a compression-algorithm. The *
 *     compression-algorithm currently used is a LZ77. I use the *
 *     implementation lzrw3 by Ross N. Williams (Renaissance *
 *     Software). The compression program itself is in the file
 *     lzrw3.c * and lzrw3.h.  To adopt another compression algorithm
 *     the functions * zft_compress() and zft_uncompress() must be
 *     changed * appropriately. See below.
 */

#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/module.h>

#include <linux/zftape.h>

#include <asm/uaccess.h>

#include "../zftape/zftape-init.h"
#include "../zftape/zftape-eof.h"
#include "../zftape/zftape-ctl.h"
#include "../zftape/zftape-write.h"
#include "../zftape/zftape-read.h"
#include "../zftape/zftape-rw.h"
#include "../compressor/zftape-compress.h"
#include "../zftape/zftape-vtbl.h"
#include "../compressor/lzrw3.h"

/*
 *   global variables
 */

/* I handle the allocation of this buffer as a special case, because
 * it's size varies depending on the tape length inserted.
 */

/* local variables 
 */
static void *zftc_wrk_mem = NULL;
static __u8 *zftc_buf     = NULL;
static void *zftc_scratch_buf  = NULL;

/* compression statistics 
 */
static unsigned int zftc_wr_uncompressed = 0;
static unsigned int zftc_wr_compressed   = 0;
static unsigned int zftc_rd_uncompressed = 0;
static unsigned int zftc_rd_compressed   = 0;

/* forward */
static int  zftc_write(int *write_cnt,
		       __u8 *dst_buf, const int seg_sz,
		       const __u8 __user *src_buf, const int req_len,
		       const zft_position *pos, const zft_volinfo *volume);
static int  zftc_read(int *read_cnt,
		      __u8  __user *dst_buf, const int to_do,
		      const __u8 *src_buf, const int seg_sz,
		      const zft_position *pos, const zft_volinfo *volume);
static int  zftc_seek(unsigned int new_block_pos, 
		      zft_position *pos, const zft_volinfo *volume,
		      __u8 *buffer);
static void zftc_lock   (void);
static void zftc_reset  (void);
static void zftc_cleanup(void);
static void zftc_stats      (void);

/* compressed segment. This conforms to QIC-80-MC, Revision K.
 * 
 * Rev. K applies to tapes with `fixed length format' which is
 * indicated by format code 2,3 and 5. See below for format code 4 and 6
 *
 * 2 bytes: offset of compression segment structure
 *          29k > offset >= 29k-18: data from previous segment ens in this
 *                                  segment and no compressed block starts
 *                                  in this segment
 *                     offset == 0: data from previous segment occupies entire
 *                                  segment and continues in next segment
 * n bytes: remainder from previous segment
 * 
 * Rev. K:  
 * 4 bytes: 4 bytes: files set byte offset
 * Post Rev. K and QIC-3020/3020:
 * 8 bytes: 8 bytes: files set byte offset
 * 2 bytes: byte count N (amount of data following)
 *          bit 15 is set if data is compressed, bit 15 is not
 *          set if data is uncompressed
 * N bytes: data (as much as specified in the byte count)
 * 2 bytes: byte count N_1 of next cluster
 * N_1 bytes: data of next cluset
 * 2 bytes: byte count N_2 of next cluster
 * N_2 bytes: ...  
 *
 * Note that the `N' byte count accounts only for the bytes that in the
 * current segment if the cluster spans to the next segment.
 */

typedef struct
{
	int cmpr_pos;             /* actual position in compression buffer */
	int cmpr_sz;              /* what is left in the compression buffer
				   * when copying the compressed data to the
				   * deblock buffer
				   */
	unsigned int first_block; /* location of header information in
				   * this segment
				   */
	unsigned int count;       /* amount of data of current block
				   * contained in current segment 
				   */
	unsigned int offset;      /* offset in current segment */
	unsigned int spans:1;     /* might continue in next segment */
	unsigned int uncmpr;      /* 0x8000 if thi