fat.c

linux dosfs 工具,可以移植到嵌入式系统下检查存储状态下的磁盘状况,修复文件系统

/* fat.c  -  Read/write access to the FAT */

/* Written 1993 by Werner Almesberger */

/* FAT32, VFAT, Atari format support, and various fixes additions May 1998
 * by Roman Hodek <[e-mail]> */


#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "common.h"
#include "dosfsck.h"
#include "io.h"
#include "check.h"
#include "fat.h"


static void get_fat(FAT_ENTRY *entry,void *fat,unsigned long cluster,DOS_FS *fs)
{
    unsigned char *ptr;

    switch(fs->fat_bits) {
      case 12:
	ptr = &((unsigned char *) fat)[cluster*3/2];
	entry->value = 0xfff & (cluster & 1 ? (ptr[0] >> 4) | (ptr[1] << 4) :
	  (ptr[0] | ptr[1] << 8));
	break;
      case 16:
	entry->value = CF_LE_W(((unsigned short *) fat)[cluster]);
	break;
      case 32:
	/* According to M$, the high 4 bits of a FAT32 entry are reserved and
	 * are not part of the cluster number. So we cut them off. */
	{
	    unsigned long e = CF_LE_L(((unsigned int *) fat)[cluster]);
	    entry->value = e & 0xfffffff;
	    entry->reserved = e >> 28;
	}
	break;
      default:
	die("Bad FAT entry size: %d bits.",fs->fat_bits);
    }
    entry->owner = NULL;
}


void read_fat(DOS_FS *fs)
{
    int eff_size;
    unsigned long i;
    void *first,*second,*use;
    int first_ok,second_ok;

    eff_size = ((fs->clusters+2)*fs->fat_bits+7)/8;
    first = alloc(eff_size);
    fs_read(fs->fat_start,eff_size,first);
    use = first;
    if (fs->nfats > 1) {
	second = alloc(eff_size);
	fs_read(fs->fat_start+fs->fat_size,eff_size,second);
    }
    else
	second = NULL;
    if (second && memcmp(first,second,eff_size) != 0) {
	FAT_ENTRY first_media, second_media;
	get_fat(&first_media,first,0,fs);
	get_fat(&second_media,second,0,fs);
	first_ok = (first_media.value & FAT_EXTD(fs)) == FAT_EXTD(fs);
	second_ok = (second_media.value & FAT_EXTD(fs)) == FAT_EXTD(fs);
	if (first_ok && !second_ok) {
	    printf("FATs differ - using first FAT.\n");
	    fs_write(fs->fat_start+fs->fat_size,eff_size,use = first);
	}
	if (!first_ok && second_ok) {
	    printf("FATs differ - using second FAT.\n");
	    fs_write(fs->fat_start,eff_size,use = second);
	}
	if (first_ok && second_ok) {
	    if (interactive) {
		printf("FATs differ but appear to be intact. Use which FAT ?\n"
		  "1) Use first FAT\n2) Use second FAT\n");
		if (get_key("12","?") == '1')
		    fs_write(fs->fat_start+fs->fat_size,eff_size,use = first);
		else fs_write(fs->fat_start,eff_size,use = second);
	    }
	    else {
		printf("FATs differ but appear to be intact. Using first "
		  "FAT.\n");
		fs_write(fs->fat_start+fs->fat_size,eff_size,use = first);
	    }
	}
	if (!first_ok && !second_ok) {
	    printf("Both FATs appear to be corrupt. Giving up.\n");
	    exit(1);
	}
    }
    fs->fat = qalloc(&mem_queue,sizeof(FAT_ENTRY)*(fs->clusters+2));
    for (i = 2; i < fs->clusters+2; i++) get_fat(&fs->fat[i],use,i,fs);
    for (i = 2; i < fs->clusters+2; i++)
	if (fs->fat[i].value >= fs->clusters+2 &&
	    (fs->fat[i].value < FAT_MIN_BAD(fs))) {
	    printf("Cluster %ld out of range (%ld > %ld). Setting to EOF.\n",
		   i-2,fs->fat[i].value,fs->clusters+2-1);
	    set_fat(fs,i,-1);
	}
    free(first);
    if (second)
	free(second);
}


void set_fat(DOS_FS *fs,unsigned long cluster,unsigned long new)
{
    unsigned char data[4];
    int size;
    loff_t offs;

    if ((long)new == -1)
	new = FAT_EOF(fs);
    else if ((long)new == -2)
	new = FAT_BAD(fs);
    switch( fs->fat_bits ) {
      case 12:
	offs = fs->fat_start+cluster*3/2;
	if (cluster & 1) {
	    data[0] = ((new & 0xf) << 4) | (fs->fat[cluster-1].value >> 8);
	    data[1] = new >> 4;
	}
	else {
	    data[0] = new & 0xff;
	    data[1] = (new >> 8) | (cluster == fs->clusters-1 ? 0 :
	      (0xff & fs->fat[cluster+1].value) << 4);
	}
	size = 2;
	break;
      case 16:
	offs = fs->fat_start+cluster*2;
	*(unsigned short *) data = CT_LE_W(new);
	size = 2;
	break;
      case 32:
	offs = fs->fat_start+cluster*4;
	/* According to M$, the high 4 bits of a FAT32 entry are reserved and
	 * are not part of the cluster number. So we never touch them. */
	*(unsigned long *) data = CT_LE_L( (new & 0xfffffff) |
					   (fs->fat[cluster].reserved << 28) );
	size = 4;
	break;
      default:
	die("Bad FAT entry size: %d bits.",fs->fat_bits);
    }
    fs->fat[cluster].value = new;
    fs_write(offs,size,&data);
    fs_write(offs+fs->fat_size,size,&data);
}


int bad_cluster(DOS_FS *fs,unsigned long cluster)
{
    return FAT_IS_BAD(fs,fs->fat[cluster].value);
}


unsigned long next_cluster(DOS_FS *fs,unsigned long cluster)
{
    unsigned long value;

    value = fs->fat[cluster].value;
    if (FAT_IS_BAD(fs,value))
	die("Internal error: next_cluster on bad cluster");
    return FAT_IS_EOF(fs,value) ? -1 : value;
}


loff_t cluster_start(DOS_FS *fs,unsigned long cluster)
{
    return fs->data_start+((loff_t)cluster-2)*fs->cluster_size;
}


void set_owner(DOS_FS *fs,unsigned long cluster,DOS_FILE *owner)
{
    if (owner && fs->fat[cluster].owner)
	die("Internal error: attempt to change file owner");
    fs->fat[cluster].owner = owner;
}


DOS_FILE *get_owner(DOS_FS *fs,unsigned long cluster)
{
    return fs->fat[cluster].owner;
}


void fix_bad(DOS_FS *fs)
{
    unsigned long i;

    if (verbose)
	printf("Checking for bad clusters.\n");
    for (i = 2; i < fs->clusters+2; i++)
	if (!get_owner(fs,i) && !FAT_IS_BAD(fs,fs->fat[i].value))
	    if (!fs_test(cluster_start(fs,i),fs->cluster_size)) {
		printf("Cluster %lu is unreadable.\n",i);
		set_fat(fs,i,-2);
	    }
}


void reclaim_free(DOS_FS *fs)
{
    int reclaimed;
    unsigned long i;

    if (verbose)
	printf("Checking for unused clusters.\n");
    reclaimed = 0;
    for (i = 2; i < fs->clusters+2; i++)
	if (!get_owner(fs,i) && fs->fat[i].value &&
	    !FAT_IS_BAD(fs,fs->fat[i].value)) {
	    set_fat(fs,i,0);
	    reclaimed++;
	}
    if (reclaimed)
	printf("Reclaimed %d unused cluster%s (%d bytes).\n",reclaimed,
	  reclaimed == 1 ?  "" : "s",reclaimed*fs->cluster_size);
}


static void tag_free(DOS_FS *fs,DOS_FILE *ptr)
{
    DOS_FILE *owner;
    int prev;
    unsigned long i,walk;

    for (i = 2; i < fs->clusters+2; i++)
	if (fs->fat[i].value && !FAT_IS_BAD(fs,fs->fat[i].value) &&
	    !get_owner(fs,i) && !fs->fat[i].prev) {
	    prev = 0;
	    for (walk = i; walk > 0 && walk != -1;
		 walk = next_cluster(fs,walk)) {
		if (!(owner = get_owner(fs,walk))) set_owner(fs,walk,ptr);
		else if (owner != ptr)
		        die("Internal error: free chain collides with file");
		    else {
			set_fat(fs,prev,-1);
			break;
		    }
		prev = walk;
	    }
	}
}


void reclaim_file(DOS_FS *fs)
{
    DOS_FILE dummy;
    int reclaimed,files,changed;
    unsigned long i,next,walk;

    if (verbose)
	printf("Reclaiming unconnected clusters.\n");
    for (i = 2; i < fs->clusters+2; i++) fs->fat[i].prev = 0;
    for (i = 2; i < fs->clusters+2; i++) {
	next = fs->fat[i].value;
	if (!get_owner(fs,i) && next && next < fs->clusters+2) {
	    if (get_owner(fs,next) || !fs->fat[next].value ||
		FAT_IS_BAD(fs,fs->fat[next].value)) set_fat(fs,i,-1);
	    else fs->fat[next].prev++;
	}
    }
    do {
	tag_free(fs,&dummy);
	changed = 0;
	for (i = 2; i < fs->clusters+2; i++)
	    if (fs->fat[i].value && !FAT_IS_BAD(fs,fs->fat[i].value) &&
		!get_owner(fs, i)) {
		if (!fs->fat[fs->fat[i].value].prev--)
		    die("Internal error: prev going below zero");
		set_fat(fs,i,-1);
		changed = 1;
		printf("Broke cycle at cluster %lu in free chain.\n",i);
		break;
	    }
    }
    while (changed);
    files = reclaimed = 0;
    for (i = 2; i < fs->clusters+2; i++)
	if (get_owner(fs,i) == &dummy && !fs->fat[i].prev) {
	    DIR_ENT de;
	    loff_t offset;
	    files++;
	    offset = alloc_rootdir_entry(fs,&de,"FSCK%04dREC");
	    de.start = CT_LE_W(i&0xffff);
	    if (fs->fat_bits == 32)
		de.starthi = CT_LE_W(i>>16);
	    for (walk = i; walk > 0 && walk != -1;
		 walk = next_cluster(fs,walk)) {
		de.size = CT_LE_L(CF_LE_L(de.size)+fs->cluster_size);
		reclaimed++;
	    }
	    fs_write(offset,sizeof(DIR_ENT),&de);
	}
    if (reclaimed)
	printf("Reclaimed %d unused cluster%s (%d bytes) in %d chain%s.\n",
	  reclaimed,reclaimed == 1 ? "" : "s",reclaimed*fs->cluster_size,files,
	  files == 1 ? "" : "s");
}


unsigned long update_free(DOS_FS *fs)
{
    unsigned long i;
    unsigned long free = 0;
    int do_set = 0;

    for (i = 2; i < fs->clusters+2; i++)
	if (!get_owner(fs,i) && !FAT_IS_BAD(fs,fs->fat[i].value))
	    ++free;

    if (!fs->fsinfo_start)
	return free;

    if (verbose)
	printf("Checking free cluster summary.\n");
    if (fs->free_clusters >= 0) {
	if (free != fs->free_clusters) {
	    printf( "Free cluster summary wrong (%ld vs. really %ld)\n",
		    fs->free_clusters,free);
	    if (interactive)
		printf( "1) Correct\n2) Don't correct\n" );
	    else printf( "  Auto-correcting.\n" );
	    if (!interactive || get_key("12","?") == '1')
		do_set = 1;
	}
    }
    else {
	printf( "Free cluster summary uninitialized (should be %ld)\n", free );
	if (interactive)
	    printf( "1) Set it\n2) Leave it uninitialized\n" );
	else printf( "  Auto-setting.\n" );
	if (!interactive || get_key("12","?") == '1')
	    do_set = 1;
    }

    if (do_set) {
	fs->free_clusters = free;
	free = CT_LE_L(free);
	fs_write(fs->fsinfo_start+offsetof(struct info_sector,free_clusters),
		 sizeof(free),&free);
    }

    return free;
}

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