fuser-async

This crate, based on the fuser crate, allows building FUSE filesystems where the system calls are directed to async functions.

This can be particularly useful when the syscalls benefit from (or require) async IO. When using a multi-threaded [tokio] runtime, this can also be useful for CPU-bound code (although one should be careful with the interactions between IO- and CPU-bound tasks).

More precisely, this crate provides:

• a [Filesystem] trait, analogous to the fuser [fuser::Filesystem] trait, which has all its methods returning futures.
• a [FilesystemFUSE] struct, which can be constructed from any implementor of the [Filesystem] trait, and which implements the [fuser::Filesystem] trait, allowing to mount the filesystem using the fuser crate crate.

Behind the scenes, [FilesystemFUSE] wraps the inner filesystem into an [std::sync::Arc<tokio::sync::RwLock>] and stores a handle on the [tokio] runtime.

Usage

1. Implement the [Filesystem] trait.
2. Instantiate a [FilesystemFUSE] object from a instance implementing [Filesystem], with [FilesystemFUSE::new].
3. Mount the filesystem using [fuser], or use file handles programmatically with [FileHandle] (which implements [tokio::io::AsyncRead])

let fs = TestFs::new();
let fuse = FilesystemFUSE::new(fs);
let _mount = fuser::spawn_mount2(
    fuse,
    mountpoint,
    &[fuser::MountOption::RO, fuser::MountOption::Async],
  )?;
tokio::signal::ctrl_c().await?;

Implementations

Two example implementations are provided:

• Local filesystem passthrough.
• S3 object storage, using the rusty_s3 crate.

See the demo binary crate for a binary running these.

$ cargo run -r --features s3,demo --bin demo -- --help
USAGE:
    demo [OPTIONS] <MOUNTPOINT> <SUBCOMMAND>

ARGS:
    <MOUNTPOINT>    Mountpoint

OPTIONS:
    -d, --debug
    -h, --help     Print help information

SUBCOMMANDS:
    local
    s3

Difference with other solutions

fuse_mt

See https://github.com/wfraser/fuse-mt/issues/3. The implementation of this crate is fairly similar to the prototype linked in this issue, except that we use a recent [tokio] version and support different syscalls.

Limitations/TODO

• Not all methods from [fuser::Filesystem] are supported (they are however easy to add). In particular, the current focus of is on read operations.
• No tests yet beyond the demo and the dependent crates.