Filesystem notes

These are just quick notes about how I'd like to implement the filesystem, based only on assumptions on how the storage will work. No real work has been done on this.

This assumes that we will have something like an SD card connected through SPI.

Goals

Simple (will be implemented in assembler)
- Specifically: Not COW :-)
Fun!

Design

Block size 1kWord = 2kB
- Matches the MMU page size
16b block pointers
=> 128MB max addressable space

Superblock

First block of the device
"PICKLEFS" magic
Parameters?
16b Pointer to first unused block
16b Pointer to root directory

Boot area

Optional?
Contiguous range of blocks starting at the second block of the device
Must have a corresponding directory entry and file header

Unused blocks

16b pointer to next unused block

Root directory

.. entry points to itself
Otherwise like normal directory

Directory

Creation date
- ?
Flags
- ?
16b refcount
List of entries
- Name
  - Length?
  - Format?
- 16b pointer to first block of entry (either file header or directory)
16b pointer to next block of directory
Special entry
- .. pointing to parent
Additional directory blocks only contain the entry list and next pointer

File header

Creation date
- ?
Flags
- ?
16b refcount
Size in B
- 32b?
List of 16b data block pointers
- Number of valid blocks can be calculated from file size
16b pointer to next block of file header
Additional file header blocks only contain the block pointer list and next pointer