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):

use fuse_backend_rs::api::{server::Server, Vfs, VfsOptions};
use fuse_backend_rs::transport::fusedev::{FuseSession, FuseChannel};

struct FuseServer {
    server: Arc<Server<Arc<Vfs>>>,
    ch: FuseChannel,
}

impl FuseServer {
    fn svc_loop(&self) -> Result<()> {
      // Given error EBADF, it means kernel has shut down this session.
      let _ebadf = std::io::Error::from_raw_os_error(libc::EBADF);
      loop {
        if let Some((reader, writer)) = self
                .ch
                .get_request()
                .map_err(|_| std::io::Error::from_raw_os_error(libc::EINVAL))?
        {
          if let Err(e) = self.server.handle_message(reader, writer, None, None) {
            match e {
              fuse_backend_rs::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