Difference between revisions of "VFF"

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(Add link to some old code I had lying around to dump VFF files)
 
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Following the header is two FATs, which are FAT12/FAT16 (depending on total volume size). Each FAT size is determined by the below algo. The format of the FAT is not regular FAT16, there's unknown flags and values, so it's currently not possible to process cluster chains. Following the FATs is the root [http://en.wikipedia.org/wiki/File_Allocation_Table#Directory_table directory] cluster, 0x1000 bytes long. Following the root cluster is the data "clusters". The data "clusters" have are 0x200 bytes long each. The size of the FAT is determined by the following algorithm:
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Following the header is two FATs, which are FAT12/FAT16 (depending on total volume size). Each FAT size is determined by the below algo. Following the FATs is the root [http://en.wikipedia.org/wiki/File_Allocation_Table#Directory_table directory] cluster, 0x1000 bytes long. Following the root cluster is the data "clusters". The data "clusters" have are 0x200 bytes long each. The size of the FAT is determined by the following algorithm:
u32 WC24_GetVFF_FATSize(u32 filesize)
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<source lang="c">
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#define ALIGN_FORWARD(x,align) \
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        ((typeof(x))((((u32)(x)) + (align) - 1) & (~((align)-1))))
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#define CLUSTER_SIZE 0x200
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 +
u32 WC24_GetVFF_FATSize(u32 filesize)
 
  {
 
  {
        if(filesize < 0x100000)
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    u32 num_clusters = filesize / CLUSTER_SIZE;
        {//This block is executed for filesizes less than 1MB.
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    u32 fat_bits = 32;
                u32 base = (filesize / 0x200) - 8;
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    if (num_clusters < 0xFFF5) fat_bits = 16;
                u32 fatsz = base;
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    if (num_clusters < 0xFF5) fat_bits = 12;
                if(base % 0x200)//Should always be executed.
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                {
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    return ALIGN_FORWARD(num_clusters * fat_bits / 8, CLUSTER_SIZE);
                    if(base<0x200)
 
                    {
 
                          fatsz = 0x200;
 
                    }
 
                    else
 
                    {
 
                          fatsz++;
 
                    }
 
                }
 
                return fatsz;
 
        }
 
        else
 
        {
 
                return filesize >> 8;//VFF files larger than 1MB must be aligned to a MB, since this algo doesn't work right with filesizes not aligned.
 
        }
 
 
  }
 
  }
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</source>
 +
 +
Trivial vff filesystem dumper (from marcan's old code stash): [https://mrcn.st/t/vffdump.py]
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 +
[[Category:File formats]]

Latest revision as of 11:03, 30 July 2015

VFF is a "virtual FAT filesystem", which is used as a container for primarily WC24 downloaded content, as well as E-Mail storage.

Header

Start Length Typical value Description
0 4 'VFF ' 4-byte magic
4 2 feff Byte-order-marker? (magic value, never checked by code)
6 2 0100 (length field? never checked by code)
8 4 01400000 Total file size
12 2 0020 Size of header
14 18 zeroes padding

Following the header is two FATs, which are FAT12/FAT16 (depending on total volume size). Each FAT size is determined by the below algo. Following the FATs is the root directory cluster, 0x1000 bytes long. Following the root cluster is the data "clusters". The data "clusters" have are 0x200 bytes long each. The size of the FAT is determined by the following algorithm:

#define ALIGN_FORWARD(x,align) \
        ((typeof(x))((((u32)(x)) + (align) - 1) & (~((align)-1))))
#define CLUSTER_SIZE 0x200

u32 WC24_GetVFF_FATSize(u32 filesize)
 {
    u32 num_clusters = filesize / CLUSTER_SIZE;
    u32 fat_bits = 32;
    if (num_clusters < 0xFFF5) fat_bits = 16;
    if (num_clusters < 0xFF5)  fat_bits = 12;

    return ALIGN_FORWARD(num_clusters * fat_bits / 8, CLUSTER_SIZE);
 }

Trivial vff filesystem dumper (from marcan's old code stash): [1]