wiki/gofurther/virtiofs.md

title	description	published	date	tags	editor	dateCreated
Share a host directory with a guest using virtiofs		true	2023-05-29T09:14:51.426Z		markdown	2022-08-13T00:16:17.437Z

Sharing a directory between the host and the guest

Virtio-fs in a nutshell

Virtio-fs, shorts for Virtio shared FileSystem, allows for a directory located on the host to be shared with a guest.

It is designed to be fast and optimized for local usage, when the host and the guest are located on the same physical machine. It is therefore a perfect fit for Phyllome OS.

Just as with other virtio devices, virtio-fs requires specialized drivers to be written for the host and the guest operating system.

The guest

For KVM/QEMU, as of January 2023, virtio-fs is only available for virtual machines managed by the system libvirt instance (qemu:///system) {.is-warning}

As of January 2023, virtio-fs does not support read-only mode, meaning a guest will be able to write to the host's folder. {.is-warning}

Edit XML configuration

• Memory backing needs to be added to the XML definition:

<domain type="kvm">
[...]
    <memoryBacking>
        <source type="memfb"/>
        <access mode="shared/>"
    </memoryBacking>
[...]
</domain>

• Add the filesystem device to the guest. In this the following case, the directory /opt/share/ will be shared with the guest:

<domain type="kvm">
[...]
    <devices>
    [...]
        <filesystem type="mount" accessmode="passthrough">
            <driver type="virtiofs"/>
            <source dir="/opt/share"> # The host directory to be shared with the guest
            <target dir="share"> # The target dir value refers to the mount tag used inside the guest, not the target dir inside the guest
        </filesystem>
    [...]
    </devices>
[...]
</domain>    

Mount the folder inside the guest

• Inside the guest VM, mount the folder using the following command to mount the /opt/share host directory to the guest, using also the /mnt point:

# mount -t virtiofs share /mnt/

• To make it permanent, edit /etc/fstab to look like the following:

share /mnt/ virtiofs rw,noatime,_netdev 0 2

• Make sure it works before rebooting the guest virtual machine, by un-mounting the share

# umount /mnt/

• and then mounting all share available in fstab:

# mount all

Resources

• Official website: https://virtio-fs.gitlab.io/index.html#status
• In the context of a Windows guest: https://github.com/virtio-win/kvm-guest-drivers-windows/wiki/VirtIO-FS:-Shared-file-system
• https://wiki.archlinux.org/title/Libvirt#Sharing_data_between_host_and_guest

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