Crate easy_fuser 

easy_fuser

[!IMPORTANT] Breaking Changes in v0.5.0: The crate has been reorganized to support separate code generation structures per mode.

• Instead of a single prelude (easy_fuser::prelude), use the mode-specific preludes: easy_fuser::fuse_serial::prelude::*, easy_fuser::fuse_parallel::prelude::*, or easy_fuser::fuse_async::prelude::*.
• Template/Preset implementations (like DefaultFuseHandler and MirrorFs) are now located in the easy_fuser::fuse_presets module (instead of easy_fuser::templates).
• The presets no longer implement FuseHandler directly. Users now implement FuseHandler for their custom struct and delegate operations using the delegate_fs! macro from the easy_fuser_macro crate.

About

easy_fuser is a high-level, ergonomic wrapper around the fuser crate, designed to simplify the process of implementing FUSE (Filesystem in Userspace) filesystems in Rust. It abstracts away many of the complexities, offering a more intuitive and Rust-idiomatic approach to filesystem development.

Key Features

• Simplified API: Provides a higher-level interface compared to fuser, reducing boilerplate and making filesystem implementation more straightforward.

• Flexible Concurrency Models: Offers three distinct concurrency models to suit different use cases and performance requirements.

• Flexible File Identification: Supports both path-based and inode-based operations, allowing you to choose between Inode, PathBuf, or Vec<OsString> as your file identifier type. This offers flexibility in how you represent and manage file identities, suitable for different filesystem structures and performance requirements.

• Error Handling: Provides a structured error handling system, facilitating the management of filesystem-specific errors.

• Composable Presets and Examples: Includes pre-built, composable presets and a comprehensive examples folder to help you get started quickly, understand various implementation patterns, and easily combine different filesystem behaviors. These presets are designed to be mixed and matched via delegation, allowing for flexible and modular filesystem creation.

File Identification Flexibility

easy_fuser supports two main approaches for file identification:

1. Path-based Operations: Work with file paths directly, which can be more intuitive for certain use cases.
2. Inode-based Operations: Use inode numbers for more efficient control, especially useful for complex filesystem structures or when performance is critical.

You can choose the approach that best fits your filesystem’s needs and switch between them as necessary.

Usage

To use easy_fuser, follow these steps:

1. Import the appropriate prelude for your concurrency mode (e.g. easy_fuser::fuse_parallel::prelude::*).
2. Implement the FuseHandler trait for your filesystem structure, specifying the TId type (e.g. PathBuf).
3. (Optional) Compose presets (like DefaultFuseHandler or MirrorFs from easy_fuser::fuse_presets) and delegate operations to them using the delegate_fs! macro.
4. Mount or spawn-mount your filesystem.

Here’s a basic example:

#[cfg(feature = "serial")]
use easy_fuser::fuse_serial::prelude::*;
#[cfg(all(feature = "parallel", not(feature = "serial")))]
use easy_fuser::fuse_parallel::prelude::*;
#[cfg(all(feature = "async", not(feature = "parallel"), not(feature = "serial")))]
use easy_fuser::fuse_async::prelude::*;

use easy_fuser::fuse_presets::DefaultFuseHandler;
use easy_fuser_macro::delegate_fs;
use std::path::{Path, PathBuf};

struct MyFS {
    default_fs: DefaultFuseHandler<PathBuf>,
}

impl FuseHandler for MyFS {
    type TId = PathBuf;

    // Delegate all standard FUSE methods to default_fs
    delegate_fs! { default_fs, [
        access, bmap, copy_file_range, create, fallocate, flush, forget, fsync, fsyncdir,
        getattr, getlk, getxattr, ioctl, link, listxattr, lookup, lseek, mkdir, mknod,
        open, opendir, read, readdir, readlink, release, releasedir, removexattr, rename,
        rmdir, setattr, setlk, setxattr, statfs, symlink, unlink, write
    ]}
}

fn main() -> std::io::Result<()> {
    let fs = MyFS { default_fs: DefaultFuseHandler::new() };
    
    // Mount the filesystem, optionally configuring the number of threads.
    // In parallel mode, Some(4) runs FUSE handlers on 4 worker threads.
    // In serial mode, the thread count argument is ignored.
    // In async mode, the thread count argument configures tokio threads.
    // If you pass None, a default configuration is used.
    mount(fs, Path::new("/mnt/myfs"), &[], Some(4))?;
    
    Ok(())
}

Async Delegation

When using the async concurrency model, the FuseHandler trait is decorated with #[async_trait]. Because outer attribute macros expand before inner macro invocations, a standard delegation macro like delegate_fs! cannot be desugared by #[async_trait].

To solve this, easy_fuser provides two specialized async delegation macros that perform manual signature desugaring matching the expected output format of #[async_trait]:

1. delegate_fs_async!: Use this when delegating to a field/target that itself exposes asynchronous methods (returning Futures).
2. delegate_fs_sync_to_async!: Use this when delegating to a field/target that exposes synchronous/blocking methods. The macro automatically wraps the synchronous method call in a pinned async block.

Example for Async Mode

use easy_fuser::fuse_async::prelude::*;
use easy_fuser::fuse_presets::mirror_fs::MirrorFs;
use easy_fuser::fuse_presets::DefaultFuseHandler;
use easy_fuser_macro::delegate_fs_sync_to_async;
use std::path::PathBuf;

struct MyAsyncFS {
    // MirrorFs has standard synchronous/blocking methods
    mirror_fs: MirrorFs,
    default_fs: DefaultFuseHandler<PathBuf>,
}

#[async_trait]
impl FuseHandler for MyAsyncFS {
    type TId = PathBuf;

    // Delegate to the synchronous MirrorFs target inside an async handler
    delegate_fs_sync_to_async! { mirror_fs, [ read, write, getattr ] }

    // Delegate remaining methods to default_fs
    delegate_fs_sync_to_async! { default_fs, [ statfs, link ] }
}

Feature Flags

This crate provides three feature flags for different concurrency models:

• serial: Enables single-threaded operation. Use this for simplicity and when concurrent access is not required. The thread count argument (Option<usize>) is accepted for API consistency but ignored.

• parallel: Enables multi-threaded operation using a thread pool. This is suitable for scenarios where you want to handle multiple filesystem operations concurrently on separate threads. It can improve performance on multi-core systems. Pass Some(threads) to specify the pool size, or None to automatically use a default based on the system’s CPU count.

• async: Enables asynchronous operation using tokio. This is ideal for high-concurrency scenarios and when you want to integrate the filesystem with asynchronous Rust code. Pass Some(threads) to configure tokio’s worker threads, or None to use the default multi-threaded runtime. When this feature is enabled, you use easy_fuser::fuse_async::prelude::* which decorates FuseHandler with #[async_trait].

Example usage in Cargo.toml:

[dependencies]
easy_fuser = { version = "0.5.0", features = ["parallel"] }

By leveraging easy_fuser, you can focus more on your filesystem’s logic and less on the intricacies of FUSE implementation, making it easier to create robust, efficient, and maintainable filesystem solutions in Rust.

Presets / Templates

easy_fuser provides a set of template implementations (presets) under the easy_fuser::fuse_presets module to help you get started quickly:

• DefaultFuseHandler: A backbone implementation that acts as a NullFs, implementing every operation. It can also be used as a PanicFs for debugging purposes.
• FdHandlerHelper: Provides boilerplate for operations on open files (ReadOnly and ReadWrite variants available).
• MirrorFs: A passthrough filesystem template that can be leveraged for creating more complex filesystems.

These presets serve as composable building blocks, allowing you to mix and match functionalities to create custom, complex filesystem implementations with ease using delegation (via delegate_fs!).

Examples

Please check the README inside the examples folder for additional details and references.

Common Caveats

When working with FUSE filesystems, be aware of the following:

1. Crashes & Proper Unmounting: If a program crashes or is stopped abruptly (e.g., using Ctrl+C), it may leave the mountpoint in an inconsistent state.

To properly unmount the filesystem and stop the program (or to resolve a bad state after a crash), use the following command:

fusermount -u <mountpoint>

This is the preferred method for both unmounting and resolving any issues with the mountpoint. You will find more information in the documentation of mount and spawn_mount.

2. Modifying the source directory while mounted: This is not well-supported behavior and can result in unexpected outcomes.

Important Notes

libfuse and by extension fuser contains a lot of flags as arguments. We tried to identify them as much as possible, but cannot guarantee it due to the lack of clear documentation on this subject.

Re-exports

pub use session::FusePruner;

pub use session::FuseSession;

Modules

fuse_async

fuse_parallel

fuse_presets

Template Implementations for easy_fuser

fuse_serial

inode_mapper

inode_multi_mapper

session

types

Types and structures for FUSE filesystem operations.

unix_fs

POSIX Filesystem Operations Module compatible with FUSE signatures.

Macros

delegate_fs

Synchronously delegates FUSE handler trait methods to a target field.

delegate_fs_async

Asynchronously delegates FUSE handler trait methods to an asynchronous target field.

delegate_fs_sync_to_async

Asynchronously delegates FUSE handler trait methods to a synchronous target field.