virtiofs

virtiofs is a shared file system designed for virtualized environments to provide high-performance, POSIX‑compliant file sharing between a host and its guest virtual machines. It is built on the Virtio framework, with a guest-side kernel driver (virtio_fs) and a host-side user-space daemon (virtiofsd) that exports host directories to the guest.

Architecture: The guest mounts a virtiofs filesystem via mount -t virtiofs, while the host runs virtiofsd to export selected paths. Communication uses virtio devices and the virtiofs protocol, enabling direct I/O between guest and host. The guest handles path resolution and metadata; the host mediates actual I/O via the exported directory.

Features: Provides POSIX-like semantics, including metadata and permissions, directory operations, file handles, and attribute caching. It supports reads, writes, creates, unlinks, and renames, aiming to reduce overhead compared with older 9p-based sharing.

Performance and deployment: Offers lower latency and higher throughput than legacy sharing methods. It is commonly used with QEMU and libvirt for development and production workloads that require fast access to host data from guests; security is controlled by export restrictions and mount options.

History: The project emerged in the Linux virtualization community as an alternative to 9p-based sharing, and was incorporated into the Linux kernel with user-space tooling. It is maintained as part of the Virtio ecosystem and is supported by major virtualization stacks.

Security and limitations: Access is limited by host exports and mount options; it is not a network filesystem. Performance depends on host storage and configuration. Best on Linux hosts and guests; cross-platform support is limited, and feature parity with full local filesystems varies by version.