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92 lines
3.2 KiB
Markdown
92 lines
3.2 KiB
Markdown
# HOWTO VirtioFS rootfs
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A quick guide for using virtiofs as a cloud-hypervisor guest's rootfs (i.e.
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with no root block device). This document is a quick getting started guide.
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There are many more steps to take to make this a production ready, secure
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setup.
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## Prerequisites
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1. virtiofsd from the qemu project
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* We are using the Qemu version for now
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* There is a Rust version being worked on that may be a better option in the future
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* Part of the qemu-system-common package on Ubuntu
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* Part of the qemu-common package on Fedora
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2. cloud-hypervisor - the newer the better, but I tested with 0.12
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3. a rootfs - This howto uses an alpine rootfs available here:
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* https://dl-cdn.alpinelinux.org/alpine/v3.13/releases/x86_64/alpine-minirootfs-3.13.2-x86_64.tar.gz
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* Others should work
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## To create the VM rootfs
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```bash
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mkdir rootfs/
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cd rootfs
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# this needs sudo to be able to set root permissions on fs components
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sudo tar -xf /path/to/alpine-minirootfs-3.13.1-x86_64.tar.gz
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# this will get created when the VM actually boots by the dhcp client
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# but we need it in the chroot to download packages
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sudo cp /etc/resolv.conf etc/
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# the alpine mini rootfs is meant for docker containers, we need a few extra
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# things for a working rootfs
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sudo chroot $PWD apk add openrc busybox-initscripts
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# we are using the paravirt console in cloud-hypervisor, so enable it in init
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# append it after the other console since it doesn't work just appending it
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sudo sed -i '/vt100/a \n# paravirt console\nhvc0::respawn:/sbin/getty -L hvc0 115200 vt100' etc/inittab
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# set no password for root user... you obviously don't want to do this for
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# any sort of production setup
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sudo sed -i 's/root:!::0:::::/root:::0:::::/' etc/shadow
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# set up init scripts
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for i in acpid crond
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sudo ln -sf /etc/init.d/$i etc/runlevels/default/$i
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end
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for i in bootmisc hostname hwclock loadkmap modules networking swap sysctl syslog urandom
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sudo ln -sf /etc/init.d/$i etc/runlevels/boot/$i
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end
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for i in killprocs mount-ro savecache
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sudo ln -sf /etc/init.d/$i etc/runlevels/shutdown/$i
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end
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for i in devfs dmesg hwdrivers mdev
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sudo ln -sf /etc/init.d/$i etc/runlevels/sysinit/$i
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end
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# setup network config
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echo 'auto lo
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iface lo inet loopback
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auto eth0
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iface eth0 inet dhcp
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' | sudo tee etc/network/interfaces
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```
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## To run the VM
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```bash
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# starting in the directory above rootfs
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sudo virtiofsd --socket-path=$PWD/virtiofs-rootfs.sock --shared-dir=$PWD/rootfs --cache=never &
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sudo cloud-hypervisor \
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--cpus boot=1,max=1 \
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--kernel vmlinux \
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--fs tag=/dev/root,socket=$PWD/virtiofs-rootfs.sock \
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--memory size=2G,shared=on \
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--cmdline "console=hvc0 rootfstype=virtiofs root=/dev/root ro debug" \
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--api-socket $PWD/ch.sock \
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--rng \
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--net ...
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```
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Note: an important part of the above is the `tag=/dev/root` and
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`root=/dev/root` parts. For whatever reason, it would only work with that as
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the tag.
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Note: another important bit is that the memory is shared. This is required for
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virtiofs
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## Message from the author
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If you find any issues or have suggestions, feel free to reach out to @iggy on
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the cloud-hypervisor slack. Also if this works for you, I'd like to know as
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well. It would also be nice to get steps for preparing other distribution root
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filesystems. |