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FreeDOS/kernel/fattab.c

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C
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/****************************************************************/
/* */
/* 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 1631 2011-06-13 16:27:34Z bartoldeman $";
#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
void clusterMessage(const char * msg, CLUSTER clussec)
{
put_string("Run chkdsk: Bad FAT ");
put_string(msg);
#ifdef WITHFAT32
put_unsigned((unsigned)(clussec >> 16), 16, 4);
#endif
put_unsigned((unsigned)(clussec & 0xffffu), 16, 4);
put_console('\n');
}
struct buffer FAR *getFATblock(struct dpb FAR * dpbp, CLUSTER clussec)
{
/* *** why dpbp->dpb_unit? only useful to know in context of the dpbp...? *** */
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; /* 0 for FAT32 but blockio.c knows that */
#ifdef WITHFAT32
if (ISFAT32(dpbp))
{
if (dpbp->dpb_xflags & FAT_NO_MIRRORING)
bp->b_copies = 1;
}
#endif
} else {
clusterMessage("I/O: 0x",clussec);
}
return bp;
}
#ifdef WITHFAT32
void read_fsinfo(struct dpb FAR * dpbp)
{
struct buffer FAR *bp;
struct fsinfo FAR *fip;
CLUSTER cluster;
if (dpbp->dpb_xfsinfosec == 0xffff)
return;
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];
/* need to range check values because they may not be correct */
cluster = fip->fi_nfreeclst;
if (cluster >= dpbp->dpb_xsize)
cluster = XUNKNCLSTFREE;
dpbp->dpb_xnfreeclst = cluster;
cluster = fip->fi_cluster;
if (cluster < 2 || cluster > dpbp->dpb_xsize)
cluster = UNKNCLUSTER;
dpbp->dpb_xcluster = cluster;
}
void write_fsinfo(struct dpb FAR * dpbp)
{
struct buffer FAR *bp;
struct fsinfo FAR *fip;
if (dpbp->dpb_xfsinfosec == 0xffff)
return;
bp = getblock(dpbp->dpb_xfsinfosec, dpbp->dpb_unit);
bp->b_flag &= ~(BFR_DATA | BFR_DIR | BFR_FAT);
bp->b_flag |= BFR_VALID;
fip = (struct fsinfo FAR *)&bp->b_buffer[0x1e4];
if (fip->fi_nfreeclst != dpbp->dpb_xnfreeclst ||
fip->fi_cluster != dpbp->dpb_xcluster)
bp->b_flag |= BFR_DIRTY; /* only flag for update if we had real news */
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 FATs, 12 bit and 16 bit. The 16 bit */
/* FAT is the easiest, since it is nothing more than a series */
/* of UWORDs. The 12 bit FAT is difficult, because it packs 3 */
/* FAT entries into two BYTEs. 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 */
/* */
/* either read the value at Cluster1 (if Cluster2 is READ_CLUSTER) */
/* or write the Cluster2 value to the FAT entry at Cluster1 */
/* Read is always via next_cluster wrapper which has extra checks */
/* It might make sense to manually check old values before a write */
/* returns: the cluster number (or 1 on error) for read mode */
/* returns: SUCCESS (or 1 on error) for write mode */
CLUSTER link_fat(struct dpb FAR * dpbp, CLUSTER Cluster1,
REG CLUSTER Cluster2)
{
struct buffer FAR *bp;
unsigned idx;
unsigned secdiv; /* FAT entries per sector; nibbles for FAT12! */
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) /* try to read out of range? */
{
clusterMessage("index: 0x",clussec); /* bad array offset */
return 1;
}
/* Cluster2 can 0 (FREE) or 1 (READ_CLUSTER), a cluster nr. >= 2, */
/* (range check this case!) LONG_LAST_CLUSTER or LONG_BAD here... */
if (Cluster2 < LONG_BAD && Cluster2 > max_cluster) /* writing bad value? */
{
clusterMessage("write: 0x",Cluster2); /* refuse to write bad value */
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]) & LONG_LAST_CLUSTER;
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 & LONG_LAST_CLUSTER);
wasfree = 0;
if (res == FREE)
wasfree = 1;
}
#endif
else {
put_string("Bad DPB!\n"); /* FAT1x size field > 65525U (see fat.h) */
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 or */
/* 0 if there is no chain, 1 on error, LONG_LAST_CLUSTER at end. */
CLUSTER next_cluster(struct dpb FAR * dpbp, CLUSTER ClusterNum)
{
CLUSTER candidate, following, max_cluster;
candidate = link_fat(dpbp, ClusterNum, READ_CLUSTER);
/* empty (0) error (1) bad (LONG_BAD) last (>LONG_BAD) need no checks */
#if 0
if (candidate == ClusterNum)
return 1; /* chain has a tiny loop - easy but boring error check */
#endif
if (candidate < 2 || candidate >= LONG_BAD)
return candidate;
max_cluster = dpbp->dpb_size;
#ifdef WITHFAT32
if (ISFAT32(dpbp))
max_cluster = dpbp->dpb_xsize;
#endif
/* FAT entry points to a possibly invalid next cluster */
following = link_fat(dpbp, candidate, READ_CLUSTER);
if (following<2 || (following < LONG_BAD && following > max_cluster))
{
/* chain must not contain free or out of range clusters */
clusterMessage("value: 0x",following); /* read returned bad value */
return 1; /* only possible error code here */
}
/* without checking "following", a chain can dangle to a free cluster: */
/* if that cluster is later used by another chain, you get cross links */
return candidate;
}
/* check if the selected cluster is free (faster than next_cluster) */
BOOL is_free_cluster(struct dpb FAR * dpbp, CLUSTER ClusterNum)
{
return (link_fat(dpbp, ClusterNum, READ_CLUSTER) == FREE);
}
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