Rust FUSE library for server, virtio-fs and vhost-user-fs

Design

The fuse-backend-rs crate is an rust library to implement Fuse daemons based on the Linux FUSE device (/dev/fuse) or the virtiofs draft specification.

Linux FUSE is an userspace filesystem framework, and the /dev/fuse device node is the interface for userspace filesystem daemons to communicate with the in-kernel fuse driver.

And the virito-fs specification extends the FUSE framework into the virtualization world, which uses the Virtio protocol to transfer FUSE requests and responses between the Fuse client and server. With virtio-fs, the Fuse client runs within the guest kernel and the Fuse server runs on the host userspace or hardware.

So the fuse-rs crate is a library to communicate with the Linux FUSE clients, which includes: - ABI layer, which defines all data structures shared between linux Fuse framework and Fuse daemons. - API layer, defines the interfaces for Fuse daemons to implement a userspace file system. - Transport layer, which supports both the Linux Fuse device and virtio-fs protocol. - VFS/pseudo_fs, an abstraction layer to support multiple file systems by a single virtio-fs device. - A sample passthrough file system implementation, which passes through files from daemons to clients.

Examples

Filesystem Drivers

• Virtual File System for an example of union file system.
• Pseudo File System for an example of pseudo file system.
• Passthrough File System for an example of passthrough(stacked) file system.
• Registry Accelerated File System for an example of readonly file system for container images.

Fuse Servers

• Dragonfly Image Service fusedev Server for an example of implementing a fuse server based on the fuse-backend-rs crate.
• Dragonfly Image Service vhost-user-fs Server for an example of implementing vhost-user-fs server based on the fuse-backend-rs crate.

Fuse Server and Main Service Loop

A sample fuse server based on the Linux Fuse device (/dev/fuse):

```rust use fusebackendrs::api::{server::Server, Vfs, VfsOptions}; use fusebackendrs::transport::fusedev::{FuseSession, FuseChannel};

struct FuseServer { server: Arc>>, ch: FuseChannel, }

impl FuseServer { fn svcloop(&self) -> Result<()> { // Given error EBADF, it means kernel has shut down this session. let _ebadf = std::io::Error::fromrawoserror(libc::EBADF); loop { if let Some((reader, writer)) = self .ch .getrequest() .maperr(|| std::io::Error::fromrawoserror(libc::EINVAL))? { if let Err(e) = self.server.handlemessage(reader, writer, None, None) { match e { fusebackendrs::Error::EncodeMessage(ebadf) => { break; } _ => { error!("Handling fuse message failed"); continue; } } } } else { info!("fuse server exits"); break; } } Ok(()) } } ```

License

This project is licensed under - Apache License, Version 2.0 - BSD-3-Clause License

Source code under [src/tokio-uring] is temporarily copied from tokio-uring with modifications, which is licensed under MIT.

We will use crate.io directly instead of this temporary copy when the pendding PRs is merged. https://github.com/tokio-rs/tokio-uring/pull/87 https://github.com/tokio-rs/tokio-uring/pull/88