Internships/ProjectIdeas/RustVMMVhostUserMacOSBSD

vhost-user devices in Rust on macOS and *BSD

Expected outcome: Extend rust-vmm crates to support vhost-user devices running on POSIX system like macOS and *BSD.

VIRTIO devices can be emulated in an external process to QEMU thanks to the vhost-user protocol, which allows QEMU to offload the entire emulation to a daemon. This is done through an AF_UNIX socket used as a control path between the frontend (i.e. QEMU) and the backend (i.e. the vhost-user daemon). QEMU will share guest memory with the daemon, provide all the information for data path setup, and notification mechanisms.

Moving the emulation of VIRTIO devices to a separate process from QEMU offers significant advantages, primarily in terms of safety, if a device crashes, we can restart it without affecting QEMU. Additionally, this approach simplifies updating device implementations, allows development in other languages (such as Rust as we do in the rust-vmm community), and enhances isolation through seccomp, cgroups, and similar mechanisms.

The rust-vmm community already provides several crates (e.g. vhost, vhost-user-backend, etc.) to implement a vhost-user backend in an external daemon. For example, these crates are used by virtiofsd (virtio-fs vhost-user device) but also by all vhost-user devices maintained by the rust-vmm community in the rust-vmm/vhost-device workspace. These crates work great on Linux, but unfortunately they use some Linux-specific system calls such as epoll(7) and eventfd(2) that make them impossible to use on other POSIX systems.

The goal of this project is to make sure that we can use rust-vmm's vhost and vhost-user-backend crates on other POSIX systems besides Linux. If time permits, we could also fix up simple devices such as vhost-device-console or vhost-device-vsock to run on any POSIX systems.

Tasks:

Run QEMU with a vhost-user device on macOS or FreeBSD/OpenBSD as covered in the FOSDEM 2025 talk
Analyze rust-vmm crates (vmm-sys-util, vhost, vhost-user-backend) to understand which components are Linux-specific
Replace epoll(7) with alternatives such as https://github.com/smol-rs/polling
Automatic fallback to pipe()/pipe2() if eventfd(2) is not available as QEMU already does
Handle any other cases discovered during the analysis
Adapt a simple device such as vhost-device-console or vhost-device-vsock to test that everything works on macOS or FreeBSD/OpenBSD

Links:

Details:

Project size: 350 hours
Skill level: intermediate
Language: Rust
Mentors: Stefano Garzarella <sgarzare@redhat.com>, German Maglione <gmaglione@redhat.com>, Oliver Steffen <osteffen@redhat.com>