mkdosfs 标记磁盘坏块

mkdosfs 标记磁盘坏块

static void check_blocks(void)
{
    int try, got;
    int i;
    static char blkbuf[BLOCK_SIZE * TEST_BUFFER_BLOCKS];

    printf("[BLOCK_SIZE = %d, TEST_BUFFER_BLOCKS = %d]\n",BLOCK_SIZE , TEST_BUFFER_BLOCKS);
    printf("start_data_block = %d,SECTORS_PER_BLOCK = %d\n",start_data_block,SECTORS_PER_BLOCK);

//[BLOCK_SIZE = 1024, TEST_BUFFER_BLOCKS = 16]
//start_data_block = 7992,SECTORS_PER_BLOCK = 2

    if (verbose) {
 printf("Searching for bad blocks ");
 fflush(stdout);
    }
    currently_testing = 0;
    if (verbose) {
 signal(SIGALRM, alarm_intr);
 alarm(5);
    }
    try = TEST_BUFFER_BLOCKS;
    while (currently_testing < blocks) {
 if (currently_testing + try > blocks)
     try = blocks - currently_testing;
 got = do_check(blkbuf, try, currently_testing);
 currently_testing += got;
 if (got == try) {          //try=16块一起读,读出来也是16块,说明没有坏块
     try = TEST_BUFFER_BLOCKS;
     continue;
 } else  //读出来不够try != 16块,说明读错误,存在坏块。
     try = 1;  //分成一块一块地检
 if (currently_testing < start_data_block)
     die("bad blocks before data-area: cannot make fs");

 for (i = 0; i < SECTORS_PER_BLOCK; i++) /* Mark all of the sectors in the block as bad */   //分成一个一个扇区
     mark_sector_bad(currently_testing * SECTORS_PER_BLOCK + i);
 badblocks++;
 currently_testing++;
    }

    if (verbose)
 printf("\n");

    if (badblocks)
 printf("%d bad block%s\n", badblocks, (badblocks > 1) ? "s" : "");
}

 

static long do_check(char *buffer, int try, off_t current_block)
{
    long got;

    if (llseek(dev, current_block * BLOCK_SIZE, SEEK_SET) /* Seek to the correct location */
 !=current_block * BLOCK_SIZE)
 die("seek failed during testing for blocks");

    got = read(dev, buffer, try * BLOCK_SIZE); /* Try reading! */
    if (got < 0)
 got = 0;

    if (got & (BLOCK_SIZE - 1))
 printf("Unexpected values in do_check: probably bugs\n");
    got /= BLOCK_SIZE;

    return got;
}

 

#define mark_sector_bad( sector ) mark_FAT_sector( sector, FAT_BAD )

static void mark_FAT_sector(int sector, unsigned int value)
{
    int cluster;

    cluster = (sector - start_data_sector) / (int)(bs.cluster_size) /
 (sector_size / HARD_SECTOR_SIZE);
    if (cluster < 0)
 die("Invalid cluster number in mark_FAT_sector: probably bug!");

    mark_FAT_cluster(cluster, value);   //扇区所在簇进行标记(标记以簇为单位),1簇=4块=8扇区
}

 

static void mark_FAT_cluster(int cluster, unsigned int value)
{
    switch (size_fat) {
    case 12:
 value &= 0x0fff;
 if (((cluster * 3) & 0x1) == 0) {
     fat[3 * cluster / 2] = (unsigned char)(value & 0x00ff);
     fat[(3 * cluster / 2) + 1] =
  (unsigned char)((fat[(3 * cluster / 2) + 1] & 0x00f0)
    | ((value & 0x0f00) >> 8));
 } else {
     fat[3 * cluster / 2] =
  (unsigned char)((fat[3 * cluster / 2] & 0x000f) |
    ((value & 0x000f) << 4));
     fat[(3 * cluster / 2) + 1] = (unsigned char)((value & 0x0ff0) >> 4);
 }
 break;

    case 16:
 value &= 0xffff;
 fat[2 * cluster] = (unsigned char)(value & 0x00ff);
 fat[(2 * cluster) + 1] = (unsigned char)(value >> 8);
 break;

    case 32:
 value &= 0xfffffff;
 fat[4 * cluster] = (unsigned char)(value & 0x000000ff);
 fat[(4 * cluster) + 1] = (unsigned char)((value & 0x0000ff00) >> 8);
 fat[(4 * cluster) + 2] = (unsigned char)((value & 0x00ff0000) >> 16);
 fat[(4 * cluster) + 3] = (unsigned char)((value & 0xff000000) >> 24);
 break;

    default:
 die("Bad FAT size (not 12, 16, or 32)");
    }
}


 

 



 

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