GotenksFS

GotenksFS is a file system built for learning purposes. The disk is represented as a regular file which is created using the mkfs command provided by this binary. A mount command is also available for mounting the file system using FUSE.

For a more in-depth overview of this project, read the blog post: Writing a file system from scratch in Rust.

Layout

The first 1024 bytes of the "disk" hold the superblock with the metadata about the file system. When mkfs is executed, the "disk" is divided into fixed-size blocks. With the exception of the superblock, all data is written in these blocks. The size can be configured to be either 1 KiB, 2 KiB, or 4 KiB.

Blocks are grouped in block groups. The first two blocks in each block group are used for the data and inode bitmaps. Following that, there is the appropriate number of blocks for storing the inode table. As an example, inodes have a size of 128 bytes which means that for a block size of 4 KiB there will 32768 inodes in the bitmap which will require 1024 blocks for the inode table. After the inode table, the remaining blocks are used for user data. In this example, 32768 blocks taking 128 MiB to be exact.

Each inode has 12 direct pointers. The system supports larger files by using double indirect pointers. Considering blocks of 4 KiB, this means the maximum size a file can have is 4 GiB. The file system could theoretically be up to 16 TiB in size.

Example

First we need to create the disk image:

$ ./gotenksfs mkfs disk.img -s "10 GiB" -b 4096

Then mount it:

$ ./gotenksfs mount disk.img gotenks

The following image shows the file system in action.

Usage

gotenksfs
A file system on top of your file system

USAGE:
    gotenksfs [SUBCOMMAND]

FLAGS:
    -h, --help       Prints help information
    -V, --version    Prints version information

SUBCOMMANDS:
    help     Prints this message or the help of the given subcommand(s)
    mkfs     Create a new file system
    mount    Mount a file system