LLFS

The Linked-List File System (LLFS) is a compact file system designed for storage media with a capacity of up to 64KB, utilizing a 256-byte block size. This system is particularly suitable for environments with limited storage requirements, such as embedded systems.

Key Features of LLFS:

Block Partitioning:

Uses a 256-byte block size. The first sector is designated as the "index sector," serving as the file allocation table.

Index Sector:

Can contain up to 15 file descriptors. Supports multiple index sectors for scalability within the volume.

File Descriptor Structure:

Defined by the lf_record_t structure, which is packed and aligned for efficiency:

Field	Size (bytes)	Description
fptr	1	Sector pointer.
attr	1	File attribute.
rptr	2	Reference pointer, 0 for root.
name	12	File name.

Sector Management:

Designed for small volumes with a sector count up to 254. Sectors 0 and 255 are reserved for index sectors, optimizing file descriptor storage and retrieval.

LLFS provides a streamlined way to manage files on small-volume media, leveraging a linked-list structure for efficient file indexing and retrieval.

Offset	Size (bytes)	Description
0	16	lf_phy_t structure containing volume metadata.
16-31	16	lf_record_t - file descriptor (1st block).
32-47	16	lf_record_t - file descriptor (2nd block).
...	...	...
224-239	16	lf_record_t - file descriptor (15th block).
240-255	16	last lf_record_t descriptor with attr set to LLFS_ATTR_INDEX and last byte set to LLFS_MARK_INDEX_BYTE

The first record in the first index sector is a physical media description:

Field	Size (bytes)	Description
fsType	1	File system type, value 0xdb.
fsTypeN	1	Complement of fsType.
devID	2	Device identifier.
secCount	2	Number of sectors in the volume.
compress	1	Compression type, LLFS_COMPRESS_NONE.
ecc	1	ECC base size, LLFS_ECC_NONE.
name	8	Volume name.