Difference between revisions of "VFF"

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(Corrected info regarding sector size.)
Line 17: Line 17:
 
| 2
 
| 2
 
| feff
 
| feff
| Byte-order-marker?
+
| Byte-order-marker? (magic value, never checked by code)
 
|-
 
|-
 
| 6
 
| 6
 
| 2
 
| 2
 
| 0100
 
| 0100
| ? (2's complement of previous field ?)
+
| (length field? never checked by code)
 
|-
 
|-
 
| 8
 
| 8
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|}
 
|}
  
Following the header is two FATs, which are FAT16. 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:
+
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:
 
  u32 WC24_GetVFF_FATSize(u32 filesize)
 
  u32 WC24_GetVFF_FATSize(u32 filesize)
 
  {
 
  {

Revision as of 11:41, 10 June 2010

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. 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 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)
{
       if(filesize < 0x100000)
       {//This block is executed for filesizes less than 1MB.
               u32 base = (filesize / 0x200) - 8;
               u32 fatsz = base;
               if(base % 0x200)//Should always be executed.
               {
                    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.
       }
}