fattab.c

来自「开源DOS的C代码源程序」· C语言 代码 · 共 339 行

/****************************************************************/
/*                                                              */
/*                          fattab.c                            */
/*                                                              */
/*                 FAT File System Table Functions              */
/*                                                              */
/*                      Copyright (c) 1995                      */
/*                      Pasquale J. Villani                     */
/*                      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 "globals.h"

#ifdef VERSION_STRINGS
static BYTE *RcsId =
    "$Id: fattab.c,v 1.31 2004/05/04 09:43:06 bartoldeman Exp $";
#endif

/************************************************************************/
/*                                                                      */
/*                      cluster/sector routines                         */
/*                                                                      */
/************************************************************************/

/* special "impossible" "Cluster2" value of 1 denotes reading the
   cluster number rather than overwriting it */
#define READ_CLUSTER 1

#ifndef ISFAT32
int ISFAT32(struct dpb FAR * dpbp)
{
  return _ISFAT32(dpbp);
}
#endif

struct buffer FAR *getFATblock(struct dpb FAR * dpbp, CLUSTER clussec)
{
  struct buffer FAR *bp = getblock(clussec, dpbp->dpb_unit);

  if (bp)
  {
    bp->b_flag &= ~(BFR_DATA | BFR_DIR);
    bp->b_flag |= BFR_FAT | BFR_VALID;
    bp->b_dpbp = dpbp;
    bp->b_copies = dpbp->dpb_fats;
    bp->b_offset = dpbp->dpb_fatsize;
#ifdef WITHFAT32
    if (ISFAT32(dpbp))
    {
      if (dpbp->dpb_xflags & FAT_NO_MIRRORING)
        bp->b_copies = 1;
    }
#endif
  }
  return bp;
}

#ifdef WITHFAT32
void read_fsinfo(struct dpb FAR * dpbp)
{
  struct buffer FAR *bp;
  struct fsinfo FAR *fip;

  bp = getblock(dpbp->dpb_xfsinfosec, dpbp->dpb_unit);
  bp->b_flag &= ~(BFR_DATA | BFR_DIR | BFR_FAT | BFR_DIRTY);
  bp->b_flag |= BFR_VALID;

  fip = (struct fsinfo FAR *)&bp->b_buffer[0x1e4];
  dpbp->dpb_xnfreeclst = fip->fi_nfreeclst;
  dpbp->dpb_xcluster = fip->fi_cluster;
}

void write_fsinfo(struct dpb FAR * dpbp)
{
  struct buffer FAR *bp;
  struct fsinfo FAR *fip;

  bp = getblock(dpbp->dpb_xfsinfosec, dpbp->dpb_unit);
  bp->b_flag &= ~(BFR_DATA | BFR_DIR | BFR_FAT);
  bp->b_flag |= BFR_VALID | BFR_DIRTY;

  fip = (struct fsinfo FAR *)&bp->b_buffer[0x1e4];
  fip->fi_nfreeclst = dpbp->dpb_xnfreeclst;
  fip->fi_cluster = dpbp->dpb_xcluster;
}
#endif

/*                                                              */
/* The FAT file system is difficult to trace through FAT table. */
/* There are two kinds of FAT's, 12 bit and 16 bit. The 16 bit  */
/* FAT is the easiest, since it is nothing more than a series   */
/* of UWORD's. The 12 bit FAT is difficult, because it packs 3  */
/* FAT entries into two BYTE's. These are packed as follows:    */
/*                                                              */
/*      0x0003 0x0004 0x0005 0x0006 0x0007 0x0008 0x0009 ...    */
/*                                                              */
/*      are packed as                                           */
/*                                                              */
/*      0x03 0x40 0x00 0x05 0x60 0x00 0x07 0x80 0x00 0x09 ...   */
/*                                                              */
/*      12 bytes are compressed to 9 bytes                      */
/*                                                              */

CLUSTER link_fat(struct dpb FAR * dpbp, CLUSTER Cluster1,
                 REG CLUSTER Cluster2)
{
  struct buffer FAR *bp;
  unsigned idx;
  unsigned secdiv;
  unsigned char wasfree;
  CLUSTER clussec = Cluster1;
  CLUSTER max_cluster = dpbp->dpb_size;

#ifdef WITHFAT32
  if (ISFAT32(dpbp))
    max_cluster = dpbp->dpb_xsize;
#endif
 
  if (clussec <= 1 || clussec > max_cluster)
  {
    put_string("run CHKDSK: trying to access invalid cluster 0x");
#ifdef WITHFAT32
    put_unsigned((unsigned)(clussec >> 16), 16, 4);
#endif
    put_unsigned((unsigned)(clussec & 0xffffu), 16, 4);
    put_console('\n');
    return 1;
  }

  secdiv = dpbp->dpb_secsize;
  if (ISFAT12(dpbp))
  {
    clussec = (unsigned)clussec * 3;
    secdiv *= 2;
  }
  else /* FAT16 or FAT32 */
  {
    secdiv /= 2;
#ifdef WITHFAT32
    if (ISFAT32(dpbp))
      secdiv /= 2;
#endif
  }

  /* idx is a pointer to an index which is the nibble offset of the FAT
     entry within the sector for FAT12, or word offset for FAT16, or
     dword offset for FAT32 */
  idx = (unsigned)(clussec % secdiv);
  clussec /= secdiv;
  clussec += dpbp->dpb_fatstrt;
#ifdef WITHFAT32
  if (ISFAT32(dpbp) && (dpbp->dpb_xflags & FAT_NO_MIRRORING))
  {
    /* we must modify the active fat,
       it's number is in the 0-3 bits of dpb_xflags */
    clussec += (dpbp->dpb_xflags & 0xf) * dpbp->dpb_xfatsize;
  }
#endif

  /* Get the block that this cluster is in                */
  bp = getFATblock(dpbp, clussec);

  if (bp == NULL)
    return 1; /* the only error code possible here */

  if (ISFAT12(dpbp))
  {
    REG UBYTE FAR *fbp0, FAR * fbp1;
    struct buffer FAR * bp1;
    unsigned cluster, cluster2;

    /* form an index so that we can read the block as a     */
    /* byte array                                           */
    idx /= 2;

    /* Test to see if the cluster straddles the block. If   */
    /* it does, get the next block and use both to form the */
    /* the FAT word. Otherwise, just point to the next      */
    /* block.                                               */
    fbp0 = &bp->b_buffer[idx];

    /* pointer to next byte, will be overwritten, if not valid */
    fbp1 = fbp0 + 1;

    if (idx >= (unsigned)dpbp->dpb_secsize - 1)
    {
      /* blockio.c LRU logic ensures that bp != bp1 */
      bp1 = getFATblock(dpbp, (unsigned)clussec + 1);
      if (bp1 == 0)
        return 1; /* the only error code possible here */
      
      if (Cluster2 != READ_CLUSTER)
        bp1->b_flag |= BFR_DIRTY | BFR_VALID;
      
      fbp1 = &bp1->b_buffer[0];
    }

    cluster = *fbp0 | (*fbp1 << 8);
    {
      unsigned res = cluster;

      /* Now to unpack the contents of the FAT entry. Odd and */
      /* even bytes are packed differently.                   */

      if (Cluster1 & 0x01)
        cluster >>= 4;
      cluster &= 0x0fff;

      if ((unsigned)Cluster2 == READ_CLUSTER)
      {
        if (cluster >= MASK12)
          return LONG_LAST_CLUSTER;
        if (cluster == BAD12)
          return LONG_BAD;
        return cluster;
      }

      wasfree = 0;
      if (cluster == FREE)
        wasfree = 1;

      cluster = res;
    }

    /* Cluster2 may be set to LONG_LAST_CLUSTER == 0x0FFFFFFFUL or 0xFFFF */
    /* -- please don't remove this mask!                                  */
    cluster2 = (unsigned)Cluster2 & 0x0fff;

    /* Now pack the value in                                */
    if ((unsigned)Cluster1 & 0x01)
    {
      cluster &= 0x000f;
      cluster2 <<= 4;
    }
    else
    {
      cluster &= 0xf000;
    }
    cluster |= cluster2;
    *fbp0 = (UBYTE)cluster;
    *fbp1 = (UBYTE)(cluster >> 8);
  }
  else if (ISFAT16(dpbp)) 
  {
    /* form an index so that we can read the block as a     */
    /* byte array                                           */
    /* and get the cluster number                           */
    UWORD res = fgetword(&bp->b_buffer[idx * 2]);
    if ((unsigned)Cluster2 == READ_CLUSTER)
    {
      if (res >= MASK16)
        return LONG_LAST_CLUSTER;
      if (res == BAD16)
        return LONG_BAD;

      return res;
    }
    /* Finally, put the word into the buffer and mark the   */
    /* buffer as dirty.                                     */
    fputword(&bp->b_buffer[idx * 2], (UWORD)Cluster2);
    wasfree = 0;
    if (res == FREE)
      wasfree = 1;
  }
#ifdef WITHFAT32
  else if (ISFAT32(dpbp))
  {
    /* form an index so that we can read the block as a     */
    /* byte array                                           */
    UDWORD res = fgetlong(&bp->b_buffer[idx * 4]);
    if (Cluster2 == READ_CLUSTER)
    {
      if (res > LONG_BAD)
        return LONG_LAST_CLUSTER;

      return res;
    }
    /* Finally, put the word into the buffer and mark the   */
    /* buffer as dirty.                                     */
    fputlong(&bp->b_buffer[idx * 4], Cluster2);
    wasfree = 0;
    if (res == FREE)
      wasfree = 1;
  }
#endif
  else
    return 1;

  /* update the free space count                          */
  bp->b_flag |= BFR_DIRTY | BFR_VALID;
  if (Cluster2 == FREE || wasfree)
  {
    int adjust = 0;
    if (!wasfree)
      adjust = 1;
    else if (Cluster2 != FREE)
      adjust = -1;
#ifdef WITHFAT32
    if (ISFAT32(dpbp) && dpbp->dpb_xnfreeclst != XUNKNCLSTFREE)
    {
      /* update the free space count for returned     */
      /* cluster                                      */
      dpbp->dpb_xnfreeclst += adjust;
      write_fsinfo(dpbp);
    }
    else
#endif
    if (dpbp->dpb_nfreeclst != UNKNCLSTFREE)
      dpbp->dpb_nfreeclst += adjust;
  }
  return SUCCESS;
}

/* Given the disk parameters, and a cluster number, this function
   looks at the FAT, and returns the next cluster in the clain. */
CLUSTER next_cluster(struct dpb FAR * dpbp, CLUSTER ClusterNum)
{
  return link_fat(dpbp, ClusterNum, READ_CLUSTER);
}