This is the C implementation of a minimal filesystem for my Z80 homebrew box. It uses an Arduino nano and Microchip 24LC256 I2C EEPROMS.
At first I wanted to implement the CP/M or even the FAT filesystem for my system. But when reading some documentation for these FS I realized I didn't understand enough about filesystem operation to be able to reliable implement these.
Therefore I decided to implement a very simple FS on my own just to get the hang of it. It is neither very elegant, fast or appropriate for FLASH based storage. But my hopes are it is easy to implemnt in Z80 assembly language.
The FS specification is able to handle different block sizes, this implementation is hardcoded to support only the blocksize defined at compile time in config.h (64 byte right now).
The max number of blocks is 2^16, this can be adjusted by changing the size of block_t.
It can be compiled using Arduino IDE and the I2C EEPROM library. It should be no problem to compile with any C compiler and by re-implementing blockio it can be altered to use other means of storage.
The 'user' part of the filesystem is described in fileio.h.
- See z80fs.h for details about the data structures.
- All data is store little endian.
- File/Dir names are not NULL terminated if all 12 bytes are used.
- FileSystem.pdf contains (a little outdated) graphic representation of a FS example.
- The superblock contains metainformation about the filesystem.
- It always resides in block 0x00 of the medium.
- blk_size contains one of Z80FS_BSxx
- first_block points to the first used block of the filesystem. This is always the root-directory.
Directory nodes are marked by Z80FS_FNODE_DIRECTORY and are linked by block number. Child nodes are stored right after the fields in z80fs_dir_t. Unused entries are NULL. If the block containing the directory is filled the number of entries can be extended by allocating another block, marking it as Z80FS_FNODE_DIREXTEND and linking it via the extend field in the directory structure.
File nodes are marked by Z80FS_FNODE_FILE and the file data starts right after the metadata in z80fs_file_t. If more space is needed additional blocks can be chained with the extend field. These blocks are marked by Z80FS_FNODE_FEXTEND.
Free blocks are indicated by 0xFF in the first byte of the block. An occupied block is marked by one of the Z80FS_FNODE_xxx values.