VirtFS 9P filesystem passthrough in CentOS 7

This document details the steps for setting up VirtFS 9P "virtio-9pfs" (Plan 9 folder sharing over Virtio - I/O virtualization framework) filesystem passthrough between CentOS 7 guest and CentOS 7 host operating systems.

Rebuild QEMU packages with VirtFS support

git clone https://github.com/AlekseyChudov/qemu-kvm-virtfs.git

cd qemu-kvm-virtfs

docker run -it --privileged -v "$PWD/rpmbuild:/root/rpmbuild" \
    docker.io/centos:7 /root/rpmbuild/build

Upon successful completion you will have the following packages

rpmbuild/RPMS/x86_64/qemu-img-virtfs-<version>.x86_64.rpm
rpmbuild/RPMS/x86_64/qemu-kvm-common-virtfs-<version>.x86_64.rpm
rpmbuild/RPMS/x86_64/qemu-kvm-tools-virtfs-<version>.x86_64.rpm
rpmbuild/RPMS/x86_64/qemu-kvm-virtfs-<version>.x86_64.rpm
rpmbuild/RPMS/x86_64/qemu-kvm-virtfs-debuginfo-<version>.x86_64.rpm
rpmbuild/SRPMS/qemu-kvm-virtfs-<version>.src.rpm

Install QEMU packages on the hypervisor host

Install the previously created QEMU packages on the hypervisor host as usual, using the files or local Yum repository. During installation, new packages remove previously installed packages, if any, and correctly replace them due to RPM dependencies.

yum -y install centos-release-qemu-ev

yum -y install \
    cloud-utils \
    libvirt-client \
    libvirt-daemon-config-network \
    libvirt-daemon-config-nwfilter \
    libvirt-daemon-driver-interface \
    libvirt-daemon-driver-qemu \
    virt-install \
    rpmbuild/RPMS/x86_64/qemu-img-virtfs-<version>.x86_64.rpm \
    rpmbuild/RPMS/x86_64/qemu-kvm-common-virtfs-<version>.x86_64.rpm \
    rpmbuild/RPMS/x86_64/qemu-kvm-virtfs-<version>.x86_64.rpm

systemctl restart libvirtd

Download the latest CentOS 7 cloud image and create a guest disk image

curl https://cloud.centos.org/centos/7/images/CentOS-7-x86_64-GenericCloud-1907.qcow2 \
    -o /var/lib/libvirt/images/CentOS-7-x86_64-GenericCloud-1907.qcow2

qemu-img resize /var/lib/libvirt/images/CentOS-7-x86_64-GenericCloud-1907.qcow2 10G

qemu-img convert -O qcow2 -o preallocation=falloc \
    /var/lib/libvirt/images/CentOS-7-x86_64-GenericCloud-1907.qcow2 \
    /var/lib/libvirt/images/centos7.localhost.qcow2

Create a cloud-init ISO image to automate guest configuration

mkdir -p cloud-init

cat << EOF > cloud-init/meta-data
instance-id: centos7.localhost
local-hostname: centos7.localhost
EOF

cat << EOF > cloud-init/user-data
#cloud-config
chpasswd:
  expire: false
password: your-ssh-password-is-here
ssh_pwauth: true
runcmd:
  - yum -y update
  - yum -y --enablerepo centosplus install kernel-plus
  - grub2-set-default 0
  - echo "virtfs /mnt/virtfs 9p trans=virtio,version=9p2000.L,nofail,_netdev,x-mount.mkdir 0 0" >> /etc/fstab
  - reboot
EOF

cloud-localds /var/lib/libvirt/images/centos7.localhost.iso \
    cloud-init/user-data cloud-init/meta-data

Create a folder to share with the guest

Note the DAC (user, group, access) and MAC (SELinux) permissions on the shared folder.

mkdir -p /var/lib/libvirt/qemu/virtfs/centos7.localhost

chown -R qemu:qemu /var/lib/libvirt/qemu/virtfs

chmod -R 0770 /var/lib/libvirt/qemu/virtfs

Provision a new virtual machine

virt-install \
    --name centos7.localhost \
    --memory 1024 \
    --vcpus 1 \
    --cpu host \
    --import \
    --disk /var/lib/libvirt/images/centos7.localhost.qcow2,device=disk,bus=virtio \
    --disk /var/lib/libvirt/images/centos7.localhost.iso,device=cdrom \
    --filesystem /var/lib/libvirt/qemu/virtfs/centos7.localhost,virtfs \
    --network default \
    --graphics none \
    --virt-type kvm \
    --os-variant centos7.0

Default username is "centos" and default password is "your-ssh-password-is-here". Press "Ctrl + ]" to exit the guest console.

Resources

Filesystem passthrough "virtio-9pfs" support in KVM in RHEL7

Virtualization Deployment and Administration Guide

Setting up cloud-init

VirtFS

v9fs: Plan 9 Resource Sharing for Linux