Copyright (C) Kristian Hart 2009

Introduction

RWFS is a filesystem specifically designed to hold large amounts of data(500 Million EB). It accomplishes this by add further dividing disks into large blocks called blocksections. Their size is determined by the block size used.

Layout

The first four sectors(2kb) of the disk are reserved for bootcode or whatever an OS wants to do with them. Next comes the FS_DESCRIPTOR structure in the first sector after the reserved sector. Next comes the DS_ENTRY blocks that define the directory structure. At the end of the first DS_ENTRY blocks is a BLOCK_ARRAY_ENTRY that points to another section of DS_ENTRIES that extend the directory structure (and so on with the next section of DS_ENTRIES). Next, comes the FD_ENTRIES that are organized much like the DS_ENTRIES. After all this comes the list of free blocks (Which also can be expanded like the DS_ENTRIES). You can see their structure below.

There is no entry for the root directory. It's ID is automatically 0 and has no name. Any file with a parent ID of zero belongs to the root directory.

Structures

These are the structures that define the filesystem.

 
/*Copyright (C) Kristian Hart 2009*/
typedef struct
{
    unsigned short version_id; //allow for reading different versions of the filesystem
    unsigned short system_id;//id that an operating system can use to know what os the filesystem originated on
    unsigned short m_ownerid;//the id of the person who is admin of the filesystem
    unsigned short sector_size;// size of a sector in bytes
    unsigned short  blocksize;//the size of a block in the fs in number of sectors
    unsigned int   blocksections;//number of block sections
    unsigned int   num_file_entry_sectors;
    unsigned int   num_dir_struct_entry_sectors;
    unsigned int   num_free_block_sectors;
    unsigned int   num_sec;//number of sectors in the last blocksection
}FS_DESCRIPTOR;//structure that defines a filesystems characteristics

typedef struct
{
    unsigned int idbase;//directory id base
    unsigned int idcalc;// a number to multiply the idbase by to get the actual id(usually 1 on small trees)
    unsigned int parent_idbase;
    unsigned int parent_idcalc;
    char         name[20];
}DS_ENTRY;//defines an entry in the directory tree

typedef struct
{
    unsigned int blocksection;
    unsigned int blockstart;// start block
    unsigned int blocks;//consecutive blocks in the block area
}BLOCK_ARRAY_ENTRY;//enty in a list of blocks

typedef struct
{
    char name[20];
    unsigned int owner_idbase;
    unsigned int owner_idcalc;  
    unsigned char system;//bits the system uses for characteristics
    unsigned int parent_idbase;//id base of the parent folder
    unsigned int parent_idcalc;//id calc of the parent folder
    unsigned int date;//last date edited in seconds past since (12PM Jan 1 2000)
    unsigned int num_barray_blks;// number of block entry array blocks (they are always consecutive)
    unsigned int blocksection;//the blocksection the array is in
    unsigned int blockstart;//first block in the array
}FD_ENTRY;//file descriptor entry

typedef struct
{
    unsigned int blocksection;
    unsigned int blockstart;// start block
    unsigned int blocks;//consecutive blocks in the array entry

}FREE_BLOCKS_ENTRY;