qvm/docs/virtio-fs-requirements.md

virtio-fs Prerequisites Verification

Date: 2026-01-26

This document verifies that all prerequisites for virtio-fs support are available in nixpkgs.

Requirements Summary

virtio-fs requires:

1. QEMU 4.2.0+ - vhost-user-fs device support introduced
2. virtiofsd daemon - User-space filesystem daemon for virtio-fs
3. Guest kernel CONFIG_VIRTIO_FS - Linux 5.4+ with virtio-fs driver enabled

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Verification Results

1. QEMU Version

Command:

nix eval nixpkgs#qemu.version --raw

Result:

10.1.2

Status: ✅ PASS - Version 10.1.2 is significantly newer than the required 4.2.0

Notes:

• QEMU 10.x includes full virtio-fs support with vhost-user-fs backend
• Package provides qemu-kvm as main program
• Multiple outputs available: out, doc, ga, debug

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2. virtiofsd Package

Command:

nix search nixpkgs virtiofsd --json

Result:

legacyPackages.x86_64-linux.virtiofsd

Version Check:

nix eval nixpkgs#virtiofsd.version --raw

Version:

1.13.2

Status: ✅ PASS - virtiofsd is available as a standalone package

Notes:

• virtiofsd is available in nixpkgs as a separate package
• Version 1.13.2 is a modern Rust-based implementation
• This is the newer rust-virtiofsd, not the original C implementation from QEMU

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3. Kernel CONFIG_VIRTIO_FS Support

Command:

nix-shell -p linux --run "zcat /proc/config.gz | grep CONFIG_VIRTIO_FS"

Kernel Version:

nix eval nixpkgs#linux.version --raw

Version: 6.12.63

Result:

CONFIG_VIRTIO_FS=m

Status: ✅ PASS - virtio-fs is enabled as a loadable kernel module

Notes:

• Linux kernel 6.12.63 is much newer than the required 5.4+
• CONFIG_VIRTIO_FS is compiled as a module (=m)
• Module will be available in NixOS VM builds by default
• virtio-fs driver can be loaded on-demand

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NixOS-Specific Considerations

Module Loading

• Kernel module virtiofs will need to be loaded in the guest
• NixOS typically handles this automatically via boot.initrd.availableKernelModules or runtime modprobe

QEMU Integration

• QEMU package in nixpkgs is the full-featured build
• Includes vhost-user-fs device support
• No custom QEMU build needed

virtiofsd Daemon

• Must be started on the host before launching VM
• Requires socket path for communication with QEMU
• NixOS can manage this via systemd if desired

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Conclusion

✅ ALL PREREQUISITES AVAILABLE

All required components for virtio-fs are present in nixpkgs:

• ✅ QEMU 10.1.2 (requirement: 4.2.0+)
• ✅ virtiofsd 1.13.2 (standalone package)
• ✅ Linux kernel 6.12.63 with CONFIG_VIRTIO_FS=m (requirement: 5.4+)

No blockers identified. We can proceed with virtio-fs implementation.

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Next Steps

1. Design virtiofsd socket/daemon management strategy
2. Update QEMU launch arguments to use vhost-user-fs-pci device
3. Configure guest kernel to mount virtio-fs filesystems
4. Update NixOS VM flake to include virtiofsd in systemPackages or as a service