initdisk.c

开源DOS的C代码源程序

/****************************************************************/
/*                                                              */
/*                            initDISK.c                        */
/*                                                              */
/*                      Copyright (c) 2001                      */
/*                      tom ehlert                              */
/*                      All Rights Reserved                     */
/*                                                              */
/* This file is part of DOS-C.                                  */
/*                                                              */
/* DOS-C 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.                    */
/*                                                              */
/* DOS-C 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 DOS-C; see the file COPYING.  If not,     */
/* write to the Free Software Foundation, 675 Mass Ave,         */
/* Cambridge, MA 02139, USA.                                    */
/****************************************************************/

#include "portab.h"
#include "init-mod.h"
#include "dyndata.h"
#ifdef VERSION_STRINGS
static BYTE *dskRcsId =
    "$Id: initdisk.c,v 1.33 2004/05/25 19:24:55 bartoldeman Exp $";
#endif

UBYTE InitDiskTransferBuffer[SEC_SIZE] BSS_INIT({0});
COUNT nUnits BSS_INIT(0);

/*
 *    Rev 1.0   13 May 2001  tom ehlert
 * Initial revision.
 *
 * this module implements the disk scanning for DOS accesible partitions
 * the drive letter ordering is somewhat chaotic, but like MSDOS does it.
 *
 * this module expects to run with CS = INIT_TEXT, like other init_code,
 * but SS = DS = DATA = DOS_DS, unlike other init_code.
 *
 * history:
 * 1.0 extracted the disk init code from DSK.C
 *     added LBA support
 *     moved code to INIT_TEXT
 *     done the funny code segment stuff to switch between INIT_TEXT and TEXT
 *     added a couple of snity checks for partitions
 *
 ****************************************************************************
 *
 * Implementation note:
 * this module needs some interfacing to INT 13
 * how to implement them
 *    
 * a) using inline assembly 
 *        _ASM mov ax,0x1314
 *
 * b) using assembly routines in some external FLOPPY.ASM
 *
 * c) using the funny TURBO-C style
 *        _AX = 0x1314
 *
 * d) using intr(intno, &regs) method.
 *
 * whynot's
 *
 * a) this is my personal favorite, combining the best aof all worlds.
 *    TURBO-C does support inline assembly, but only by using TASM,
 *    which is not free. 
 *    so - unfortunately- its excluded.
 *
 * b) keeping funny memory model in sync with external assembly
 *    routines is everything, but not fun
 *
 * c) you never know EXACT, what the compiler does, if its a bit
 *    more complicated. does
 *      _DL = drive & 0xff    
 *      _BL = driveParam.chs.Sector;
 *    destroy any other register? sure? _really_ sure?
 *    at least, it has it's surprises.
 *    and - I found a couple of optimizer induced bugs (TC 2.01)
 *      believe me.
 *    it was coded - and operational that way.
 *    but - there are many surprises waiting there. so I opted against.
 *
 *
 * d) this method is somewhat clumsy and certainly not the
 *    fastest way to do things.
 *    on the other hand, this is INIT code, executed once.
 *    and scince it's the only portable method, I opted for it.
 *
 * e) and all this is my private opinion. tom ehlert.
 *
 *
 * Some thoughts about LBA vs. CHS. by Bart Oldeman 2001/Nov/11
 * Matthias Paul writes in www.freedos.org/freedos/news/technote/113.html:
 * (...) MS-DOS 7.10+, which will always access logical drives in a type
 * 05h extended partition via CHS, even if the individual logical drives
 * in there are of LBA type, or go beyond 8 Gb... (Although this workaround
 * is sometimes used in conjunction with OS/2, using a 05h partition going
 * beyond 8 Gb may cause MS-DOS 7.10 to hang or corrupt your data...) (...)
 *
 * Also at http://www.win.tue.nl/~aeb/partitions/partition_types-1.html:
 * (...) 5 DOS 3.3+ Extended Partition
 *   Supports at most 8.4 GB disks: with type 5 DOS/Windows will not use the
 *   extended BIOS call, even if it is available. (...)
 *
 * So MS-DOS 7.10+ is brain-dead in this respect, but we knew that ;-)
 * However there is one reason to use old-style CHS calls:
 * some programs intercept int 13 and do not support LBA addressing. So
 * it is worth using CHS if possible, unless the user asks us not to,
 * either by specifying a 0x0c/0x0e/0x0f partition type or enabling
 * the ForceLBA setting in the fd kernel (sys) config. This will make
 * multi-sector reads and BIOS computations more efficient, at the cost
 * of some compatibility.
 *
 * However we need to be safe, and with varying CHS at different levels
 * that might be difficult. Hence we _only_ trust the LBA values in the
 * partition tables and the heads and sectors values the BIOS gives us.
 * After all these are the values the BIOS uses to process our CHS values.
 * So unless the BIOS is buggy, using CHS on one partition and LBA on another
 * should be safe. The CHS values in the partition table are NOT trusted.
 * We print a warning if there is a mismatch with the calculated values.
 *
 * The CHS values in the boot sector are used at a higher level. The CHS
 * that DOS uses in various INT21/AH=44 IOCTL calls are converted to LBA
 * using the boot sector values and then converted back to CHS using BIOS
 * values if necessary. Internally we do LBA as much as possible.
 *
 * However if the partition extends beyond cylinder 1023 and is not labelled
 * as one of the LBA types, we can't use CHS and print a warning, using LBA
 * instead if possible, and otherwise refuse to use it.
 *
 * As for EXTENDED_LBA vs. EXTENDED, FreeDOS makes no difference. This is
 * boot time - there is no reason not to use LBA for reading partition tables,
 * and the MSDOS 7.10 behaviour is not desirable.
 *
 * Note: for floppies we need the boot sector values though and the boot sector
 * code does not use LBA addressing yet.
 *
 * Conclusion: with all this implemented, FreeDOS should be able to gracefully
 * handle and read foreign hard disks moved across computers, whether using
 * CHS or LBA, strengthening its role as a rescue environment.
 */

/* #define DEBUG */

#define _BETA_                  /* messages for initial phase only */

#if defined(DEBUG)
#define DebugPrintf(x) printf x
#else
#define DebugPrintf(x)
#endif

#if defined(_BETA_)
#define BetaPrintf(x) printf x
#else
#define BetaPrintf(x)
#endif

#define LBA_to_CHS   init_LBA_to_CHS

/*
    interesting macros - used internally only
*/

#define SCAN_PRIMARYBOOT 0x00
#define SCAN_PRIMARY     0x01
#define SCAN_EXTENDED    0x02
#define SCAN_PRIMARY2    0x03

#define FAT12           0x01
#define FAT16SMALL      0x04
#define EXTENDED        0x05
#define FAT16LARGE      0x06
#define FAT32           0x0b    /* FAT32 partition that ends before the 8.4  */
                              /* GB boundary                               */
#define FAT32_LBA       0x0c    /* FAT32 partition that ends after the 8.4GB */
                              /* boundary.  LBA is needed to access this.  */
#define FAT16_LBA       0x0e    /* like 0x06, but it is supposed to end past */
                              /* the 8.4GB boundary                        */
#define FAT12_LBA       0xff    /* fake FAT12 LBA entry for internal use     */
#define EXTENDED_LBA    0x0f    /* like 0x05, but it is supposed to end past */

/* Let's play it safe and do not allow partitions with clusters above  *
 * or equal to 0xff0/0xfff0/0xffffff0 to be created		       *
 * the problem with fff0-fff6 is that they might be interpreted as BAD *
 * even though the standard BAD value is ...ff7                        */

#define FAT12MAX	(FAT_MAGIC-6)
#define FAT16MAX	(FAT_MAGIC16-6)
#define FAT32MAX	(FAT_MAGIC32-6)

#define IsExtPartition(parttyp) ((parttyp) == EXTENDED || \
                                 (parttyp) == EXTENDED_LBA )

#define IsLBAPartition(parttyp) ((parttyp) == FAT12_LBA  || \
                                 (parttyp) == FAT16_LBA  || \
                                 (parttyp) == FAT32_LBA)

#ifdef WITHFAT32
#define IsFATPartition(parttyp) ((parttyp) == FAT12      || \
                                 (parttyp) == FAT16SMALL || \
                                 (parttyp) == FAT16LARGE || \
                                 (parttyp) == FAT16_LBA  || \
                                 (parttyp) == FAT32      || \
                                 (parttyp) == FAT32_LBA)
#else
#define IsFATPartition(parttyp) ((parttyp) == FAT12      || \
                                 (parttyp) == FAT16SMALL || \
                                 (parttyp) == FAT16LARGE || \
                                 (parttyp) == FAT16_LBA)
#endif

#define MSDOS_EXT_SIGN 0x29     /* extended boot sector signature */
#define MSDOS_FAT12_SIGN "FAT12   "     /* FAT12 filesystem signature */
#define MSDOS_FAT16_SIGN "FAT16   "     /* FAT16 filesystem signature */
#define MSDOS_FAT32_SIGN "FAT32   "     /* FAT32 filesystem signature */

/* local - returned and used for BIOS interface INT 13, AH=48*/
struct _bios_LBA_disk_parameterS {
  UWORD size;
  UWORD information;
  ULONG cylinders;
  ULONG heads;
  ULONG sectors;

  ULONG totalSect;
  ULONG totalSectHigh;
  UWORD BytesPerSector;

  ULONG eddparameters;
};

/* physical characteristics of a drive */

struct DriveParamS {
  UBYTE driveno;                /* = 0x8x                           */
  UWORD descflags;
  ULONG total_sectors;

  struct CHS chs;               /* for normal   INT 13 */
};

struct PartTableEntry           /* INTERNAL representation of partition table entry */
{
  UBYTE Bootable;
  UBYTE FileSystem;
  struct CHS Begin;
  struct CHS End;
  ULONG RelSect;
  ULONG NumSect;
};

/*
    internal global data
*/

BOOL ExtLBAForce = FALSE;

COUNT init_readdasd(UBYTE drive)
{
  static iregs regs;

  regs.a.b.h = 0x15;
  regs.d.b.l = drive;
  init_call_intr(0x13, &regs);
  if ((regs.flags & 1) == 0)
    switch (regs.a.b.h)
    {
      case 2:
        return DF_CHANGELINE;
      case 3:
        return DF_FIXED;
    }
  return 0;
}

typedef struct {
  UWORD bpb_nbyte;              /* Bytes per Sector             */
  UBYTE bpb_nsector;            /* Sectors per Allocation Unit  */
  UWORD bpb_nreserved;          /* # Reserved Sectors           */
  UBYTE bpb_nfat;               /* # FAT's                      */
  UWORD bpb_ndirent;            /* # Root Directory entries     */
  UWORD bpb_nsize;              /* Size in sectors              */
  UBYTE bpb_mdesc;              /* MEDIA Descriptor Byte        */
  UWORD bpb_nfsect;             /* FAT size in sectors          */
  UWORD bpb_nsecs;              /* Sectors per track            */
  UWORD bpb_nheads;             /* Number of heads              */
} floppy_bpb;

floppy_bpb floppy_bpbs[5] = {
/* copied from Brian Reifsnyder's FORMAT, bpb.h */
  {SEC_SIZE, 2, 1, 2, 112, 720, 0xfd, 2, 9, 2}, /* FD360  5.25 DS   */
  {SEC_SIZE, 1, 1, 2, 224, 2400, 0xf9, 7, 15, 2},       /* FD1200 5.25 HD   */
  {SEC_SIZE, 2, 1, 2, 112, 1440, 0xf9, 3, 9, 2},        /* FD720  3.5  LD   */
  {SEC_SIZE, 1, 1, 2, 224, 2880, 0xf0, 9, 18, 2},       /* FD1440 3.5  HD   */
  {SEC_SIZE, 2, 1, 2, 240, 5760, 0xf0, 9, 36, 2}        /* FD2880 3.5  ED   */
};

COUNT init_getdriveparm(UBYTE drive, bpb * pbpbarray)
{
  static iregs regs;
  REG UBYTE type;

  if (drive & 0x80)
    return 5;
  regs.a.b.h = 0x08;
  regs.d.b.l = drive;
  init_call_intr(0x13, &regs);
  type = regs.b.b.l - 1;
  if (regs.flags & 1)
    type = 0;                   /* return 320-360 for XTs */
  else if (type > 6)
    type = 8;                   /* any odd ball drives get 8&7=0: the 320-360 table */
  else if (type == 5)
    type = 4;                   /* 5 and 4 are both 2.88 MB */

  memcpy(pbpbarray, &floppy_bpbs[type & 7], sizeof(floppy_bpb));

  if (type == 3)
    return 7;                   /* 1.44 MB */

  if (type == 4)
    return 9;                   /* 2.88 almost forgot this one */

  /* 0=320-360kB, 1=1.2MB, 2=720kB, 8=any odd ball drives */
  return type;
}

/*
    translate LBA sectors into CHS addressing
    copied and pasted from dsk.c!
*/

void init_LBA_to_CHS(struct CHS *chs, ULONG LBA_address,
                     struct DriveParamS *driveparam)
{
  unsigned hs = driveparam->chs.Sector * driveparam->chs.Head;
  unsigned hsrem = (unsigned)(LBA_address % hs);
  
  LBA_address /= hs;

  chs->Cylinder = LBA_address >= 0x10000ul ? 0xffffu : (unsigned)LBA_address;
  chs->Head = hsrem / driveparam->chs.Sector;
  chs->Sector = hsrem % driveparam->chs.Sector + 1;