Wick (wick v0.1.0)

Build FUSE userspace filesystems on the BEAM.

Wick has two layers and deliberately stops there — it does not impose a filesystem abstraction. You drive the protocol loop yourself; the Writing a filesystem guide walks through a complete read-only example.

Transport

• Wick.Native — opens /dev/fuse, arms enif_select readiness notifications, and does bounded read_frame/1 / write_frame/2 of protocol frames.
• Wick.Fusermount — mounts and unmounts via the setuid fusermount3 helper.

Codec

• Wick.Protocol — a pure-Elixir codec for the Linux FUSE kernel protocol (FUSE_KERNEL_VERSION 7.31). decode_request/1 turns a kernel frame into an opcode, a Wick.Protocol.InHeader, and a request struct; encode_response/3 builds the reply frame.

The request/response loop

A FUSE server is an event loop over a single mounted fd:

1. Wick.Fusermount.mount/2 returns a handle.
2. Wick.Native.select_read/1 arms one read-readiness notification; the owning process then receives {:select, handle, :undefined, :ready_input} when a request is waiting.
3. Wick.Native.read_frame/1 reads one request frame.
4. Wick.Protocol.decode_request/1 decodes it.
5. You build a reply and write it with Wick.Protocol.encode_response/3 and Wick.Native.write_frame/2 (or Wick.Protocol.encode_error/2 for an errno).
6. Re-arm with select_read/1 and repeat — the notification is one-shot.

The INIT handshake

The kernel's first request after a mount is :init, and nothing else works until you answer it with a Wick.Protocol.Response.Init carrying a compatible version (clamp the minor to 31) and your negotiated max_write. See the guide for the full handshake.