Voidelle Filesystem

Voidelle is meant to be a simple to implement filesystem, without focusing on disk or speed efficiency.

Important

This uses FUSE. You can mount this on your host computer and mess around through GUI and most CLI interactions. Some features might be missing, and bugs are to be expected.

Design

Voidelle revolves around a linked list design to represent data.

Note

All positions must be absolute relative to the partition.

For example, a directory listing such as

>
| etc
| | files
| | environment

• etc is a voidelle with the directory flag.
  • the next member is set to 0 as there is no following entry.
  • the content member is set to the files position.
• files is a voidelle with the directory flag.
  • the next member is set to the environment position.
  • the content member is set to 0 as it does not contain any content.
• environment is a voidelle with no special flags.
  • the next member is set to 0 as there is no following entry.
  • the content member is set to 0 as it does not contain any content.

Types of entries

Voidlet

Note

The term void is used as an umbrella term for all types of entries.

This is the header of the current mounted filesystem. It contains crucial metadata such as the voidmap's position and a void's maximum size. It is also used to identify a voidelle filesystem.

Warning

Voidlet must always be placed at the beginning of the current partition!

Explanation and order of members

• header (4 bytes): It should spell out VOID.
• void_size (8 bytes): this is the maximum size of each void. By default it is 512. Padding done on each void is according to this value.
• voidmap_size (8 bytes): the size of the voidmap.
• voidmap (8 bytes): the position of the voidmap.
  • The voidmap is a bitmap that determines whether a void is occupied or not. The first two bits are always marked as occupied (1), as voidlet and the root take it up.

Voidelle

This is the basic entry for files and directories. It contains metadata such as creation/modification timestamps, a header to ensure its integrity and permissions/owner.

Explanation and order of members

• header (5 bytes): It should spell out VELLE.
• flags (8 bytes):
  • 0x1: directory.
  • 0x2: hidden.
  • 0x4: system-reserved entry.
  • 0x8: deleted/invalid entry (rarely used).
  • An OS can choose to use the remaining bits for its own flags.
• name_voidelle (8 bytes): contains the name's voidite position.
  • Names should include the null terminator.
• name_voidelle_size (8 bytes): the total size of the current entry's name + the null terminator.
• content_voidelle (8 bytes): contains the content's position.
  • the content presented can be a voidite or voidelle.
• content_voidelle_size (8 bytes): the total size of the current entry's content.
• next_voidelle (8 bytes): the neighbouring voidelle.
• position (8 bytes): the current entry's position.
• creation_seconds (8 bytes): epoch seconds since it's creation.
• modification_seconds (8 bytes): epoch seconds since it's last modification.
• access_seconds (8 bytes): epoch seconds since it's last access.
• owner_id (8 bytes): the ID of the current entry's owner.
  • A superuser's ID could be 0 as an example.
• other_permission (1 byte): the permissions of other users other than the owner.
  • The usual values are:
    • 0x4: write permissions.
    • 0x2: read permissions.
    • 0x1: execute permissions.
    • 0x7: all of above.
  • An OS can choose to use the rest of bits for its own purposes.
• owner_permission (1 byte): the permissions of the owner.
  • The usual values are similar to others_permission.
  • An OS can choose to use the rest of bits for its own purposes.

Voidite

This is the structure of any content required by voidelle. It is used primarily for the name, as well as for a file's content.

Explanation and order of members

• position (8 bytes): the position of the current voidite.
• next_voidite (8 bytes): the position of the next voidite.
  • A voidite uses the next member in order to expand on the content presented if it does not fit in the data's size.
• data (void_size - 16 bytes): the data being held.

This tool

It is meant to be used as a way to interact with a voidelle filesystem. The Filesystem folder contains a drop-in for baremetal kernels. (certain modifications may be necessary)

Build

1. Clone the repository.
2. Run make.

Caution

Make sure the disk you're using is not of essential use as the initialization command will corrupt existing data.

3. Run sudo chown $USER <DISK>
   • <DISK> is the disk you want to initialize the filesystem on. This is a required step as to avoid sudo later on.
4. Run ./voidelle <MOUNT_POSITION> --init --disk=<DISK> --user=$(id -u) in order to initialize the disk.
   • <DISK> is the disk you want to initialize the filesystem on.
   • <MOUNT_POSITION> is where fuse should mount the disk. You can create a mnt folder in your home directory.
   • The argument --user sets the owner UID of files. id -u gets your current UID.
5. In order to mount, run ./voidelle <MOUNT_POSITION> --disk=<DISK> --user=$(id -u)
   • <MOUNT_POSITION>, <DISK> and the UID should remain the same as in the init command.
   • The command can be ran with -f -d for debugging purposes.