What is virtio-fs?
For those unfamiliar, virtio-fs is a modern shared filesystem designed specifically for virtualised environments. It allows a virtual machine (the “guest”) to access a directory on the host system, but it does so with a focus on performance and providing local filesystem semantics.
Unlike traditional methods like network filesystems (e.g., NFS, Samba) or even the older virtio-9p protocol, virtio-fs is engineered to take advantage of the fact that the guest and host are running on the same machine. By leveraging shared memory and a design based on FUSE (Filesystem in Userspace), it bypasses much of the communication overhead that can slow down other solutions. The result is a faster, more seamless file sharing experience that is ideal for development, testing, and booting from a root filesystem located on the host.
virtio-fs arrives in U-Boot Concept
The recent merge request in U-Boot Concept introduces a new virtio-fs driver within U-Boot. This initial implementation enables two key functions:
- List directories on the host
- Read files from the host
This is made possible by a new filesystem driver that integrates with U-Boot’s new FS, DIR, and FILE uclasses. A compatibility layer is included so that existing command-line functionalities continue to work as expected.
This new capability in U-Boot opens up more flexible and efficient workflows. For example, developers can now more easily load kernels, device tree blobs, or other artifacts directly from their development workstation into a QEMU guest running U-Boot, streamlining the entire test and debug cycle. For cloud use cases, reading configuration files from via virtio-fs is a common requirement.
Overall this lays a strong foundation for future enhancements to virtio-fs support within U-Boot, promising even tighter integration between guest environments and the host system.
