block/vpc: update comments to be compliant w/coding guidelines

    VHD_DIFFERENCING    = 4,

};

// Seconds since Jan 1, 2000 0:00:00 (UTC)

/* Seconds since Jan 1, 2000 0:00:00 (UTC) */

#define VHD_TIMESTAMP_BASE 946684800

#define VHD_CHS_MAX_C   65535LL

#define VPC_OPT_FORCE_SIZE "force_size"

// always big-endian

/* always big-endian */

typedef struct vhd_footer {

    char        creator[8]; // "conectix"

    char        creator[8]; /* "conectix" */

    uint32_t    features;

    uint32_t    version;

    // Offset of next header structure, 0xFFFFFFFF if none

    /* Offset of next header structure, 0xFFFFFFFF if none */

    uint64_t    data_offset;

    // Seconds since Jan 1, 2000 0:00:00 (UTC)

    /* Seconds since Jan 1, 2000 0:00:00 (UTC) */

    uint32_t    timestamp;

    char        creator_app[4]; // "vpc "

    char        creator_app[4]; /*  e.g., "vpc " */

    uint16_t    major;

    uint16_t    minor;

    char        creator_os[4]; // "Wi2k"

    char        creator_os[4]; /* "Wi2k" */

    uint64_t    orig_size;

    uint64_t    current_size;

    uint32_t    type;

    // Checksum of the Hard Disk Footer ("one's complement of the sum of all

    // the bytes in the footer without the checksum field")

    /* Checksum of the Hard Disk Footer ("one's complement of the sum of all

       the bytes in the footer without the checksum field") */

    uint32_t    checksum;

    // UUID used to identify a parent hard disk (backing file)

    /* UUID used to identify a parent hard disk (backing file) */

    uint8_t     uuid[16];

    uint8_t     in_saved_state;

} QEMU_PACKED VHDFooter;

typedef struct vhd_dyndisk_header {

    char        magic[8]; // "cxsparse"

    char        magic[8]; /* "cxsparse" */

    // Offset of next header structure, 0xFFFFFFFF if none

    /* Offset of next header structure, 0xFFFFFFFF if none */

    uint64_t    data_offset;

    // Offset of the Block Allocation Table (BAT)

    /* Offset of the Block Allocation Table (BAT) */

    uint64_t    table_offset;

    uint32_t    version;

    uint32_t    max_table_entries; // 32bit/entry

    uint32_t    max_table_entries; /* 32bit/entry */

    // 2 MB by default, must be a power of two

    /* 2 MB by default, must be a power of two */

    uint32_t    block_size;

    uint32_t    checksum;

    uint32_t    parent_timestamp;

    uint32_t    reserved;

    // Backing file name (in UTF-16)

    /* Backing file name (in UTF-16) */

    uint8_t     parent_name[512];

    struct {

    /* Write 'checksum' back to footer, or else will leave it with zero. */

    footer->checksum = cpu_to_be32(checksum);

    // The visible size of a image in Virtual PC depends on the geometry

    // rather than on the size stored in the footer (the size in the footer

    // is too large usually)

    /* The visible size of a image in Virtual PC depends on the geometry

       rather than on the size stored in the footer (the size in the footer

       is too large usually) */

    bs->total_sectors = (int64_t)

        be16_to_cpu(footer->cyls) * footer->heads * footer->secs_per_cyl;

    pageentry_index = (offset % s->block_size) / 512;

    if (pagetable_index >= s->max_table_entries || s->pagetable[pagetable_index] == 0xffffffff)

        return -1; // not allocated

        return -1; /* not allocated */

    bitmap_offset = 512 * (uint64_t) s->pagetable[pagetable_index];

    block_offset = bitmap_offset + s->bitmap_size + (512 * pageentry_index);

    // We must ensure that we don't write to any sectors which are marked as

    // unused in the bitmap. We get away with setting all bits in the block

    // bitmap each time we write to a new block. This might cause Virtual PC to

    // miss sparse read optimization, but it's not a problem in terms of

    // correctness.

    /* We must ensure that we don't write to any sectors which are marked as

       unused in the bitmap. We get away with setting all bits in the block

       bitmap each time we write to a new block. This might cause Virtual PC to

       miss sparse read optimization, but it's not a problem in terms of

       correctness. */

    if (write && (s->last_bitmap_offset != bitmap_offset)) {

        uint8_t bitmap[s->bitmap_size];

    int ret;

    uint8_t bitmap[s->bitmap_size];

    // Check if sector_num is valid

    /* Check if sector_num is valid */

    if ((sector_num < 0) || (sector_num > bs->total_sectors))

        return -1;

    // Write entry into in-memory BAT

    /* Write entry into in-memory BAT */

    index = (sector_num * 512) / s->block_size;

    if (s->pagetable[index] != 0xFFFFFFFF)

        return -1;

    s->pagetable[index] = s->free_data_block_offset / 512;

    // Initialize the block's bitmap

    /* Initialize the block's bitmap */

    memset(bitmap, 0xff, s->bitmap_size);

    ret = bdrv_pwrite_sync(bs->file->bs, s->free_data_block_offset, bitmap,

        s->bitmap_size);

        return ret;

    }

    // Write new footer (the old one will be overwritten)

    /* Write new footer (the old one will be overwritten) */

    s->free_data_block_offset += s->block_size + s->bitmap_size;

    ret = rewrite_footer(bs);

    if (ret < 0)

        goto fail;

    // Write BAT entry to disk

    /* Write BAT entry to disk */

    bat_offset = s->bat_offset + (4 * index);

    bat_value = cpu_to_be32(s->pagetable[index]);

    ret = bdrv_pwrite_sync(bs->file->bs, bat_offset, &bat_value, 4);

    int ret;

    int64_t offset = 0;

    // Write the footer (twice: at the beginning and at the end)

    /* Write the footer (twice: at the beginning and at the end) */

    block_size = 0x200000;

    num_bat_entries = (total_sectors + block_size / 512) / (block_size / 512);

        goto fail;

    }

    // Write the initial BAT

    /* Write the initial BAT */

    offset = 3 * 512;

    memset(buf, 0xFF, 512);

        offset += 512;

    }

    // Prepare the Dynamic Disk Header

    /* Prepare the Dynamic Disk Header */

    memset(buf, 0, 1024);

    memcpy(dyndisk_header->magic, "cxsparse", 8);

    dyndisk_header->checksum = cpu_to_be32(vpc_checksum(buf, 1024));

    // Write the header

    /* Write the header */

    offset = 512;

    ret = blk_pwrite(blk, offset, buf, 1024);