Nora’s read-only filesystem

NROFS is a very simple filesystem intended for bootloaders with a focus on avoiding redundant copying.

Features

• Up to 4 billion files

• File sizes of up to 4GB.

• Adjustable block size.

• Maximum total size of 4 billion blocks.

Format

All integers are in little-endian format.

The filesystem begins with a 16-byte header.

Byte(s)	Description
7:0	Magic string “NrRdOnly”
8	Version, 0 as of writing.
9	Block size as a power of 2.
11:10	Reserved, must be all zeroes.
15:12	Amount of files as a little-endian integer.

Immediately after the header comes a list of entries. Each entry is 12 bytes large.

Byte(s)	Description
3:0	Address of the filename string in bytes.
7:4	Address of the first block.
11:8	Total size of the file.

Strings

Strings are located anywhere in the first 4GB. They are prefixed with a single byte indicating the length. The string’s contents come immediately after.