For KVM/QEMU, as of January 2023, virtio-fs is only available for virtual machines managed by the system libvirt instance (
qemu:///system)
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.
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.
Just as with other virtio devices, it requires specialized drivers to be written for the guest operating system.
<domain type="kvm">
[...]
<memoryBacking>
<source type="memfb"/>
<access mode="shared/>"
</memoryBacking>
[...]
</domain>
/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>
/opt/share host directory to the guest, using also the /mnt point:# mount -t virtiofs share /mnt/
/etc/fstab to look like the following:share /mnt/ virtiofs rw,noatime,_netdev 0 0
# umount /mnt/
# mount all