FSK

FSK is a Rust toolkit for building real filesystems. You implement one trait, then mount it as a native volume: FSKit on macOS, FUSE on Linux, or ProjFS on Windows.

The crate owns the platform plumbing — mounting, IPC, authorization, directory encoding and lifecycle. Your backend owns the data. A read-only volume only needs five methods; writes are opt-in.

#Start here

• Getting started — install the crate and mount a filesystem with five methods
• Core concepts — inodes, names, metadata, errors and concurrency
• Implementing a filesystem — every trait method, required and defaulted
• Directories and lookup — cookies, verifiers and streamed enumeration
• Reading and writing — data paths, sparse files and permissions

#How it fits together

The adapter owns decoding, buffer bounds and error translation. Your backend never sees a native pointer unless it asked for raw events, and never returns a native error code.

#Platform support

On any other target authorization_status() returns io::ErrorKind::Unsupported and no MountSession exists.

#What FSK leaves to you

FSK does not impose a filesystem design. In particular, it does not provide:

• Storage — bytes live wherever you put them; the crate never persists anything.
• An inode index — you allocate inode numbers and decide how to find them again.
• A cache — no page cache, no attribute cache, no eviction policy of its own.
• Locking — adapters call methods concurrently; your state needs your own locks.
• Transactions — FSK provides no transaction boundary; a sequence of mutations is not atomic.
• A consistency policy — when to bump generation, invalidate a cookie or return STALE is your call.

This is deliberate. The same trait has to serve a Git server, a cloud drive, and a synthetic debug view, and those want different answers.

#Guide

• Getting started
• Core concepts
• Implementing a filesystem
• Directories and lookup
• Reading and writing
• Mounting and lifecycle
• Network filesystems
• Platform setup
• Raw events
• Testing a backend
• Examples
• Troubleshooting

#Reference

• Architecture — how the adapters, the C ABI and the Swift extension fit together

#Crates and examples

fsk requires Rust 1.85 or later and is MIT licensed. Mounting also requires the platform component listed above; see Platform setup.