Virt

(A library for) Virtual machines (using qemu) in minetest!

Dependencies

• a linux system, this will not work on windows, i will make no attempt to support windows but if you want to contribute you absolutely can (good luck...)
• luajit FFI
• theese commands: mkfifo, qemu_system-x86_64, qemu-img, timeout, cat (yes the use of timeout and cat are as dumb as you think they are :>)
• trusted mod status

Security

this mod TRIES to not leak io.popen or os.execute
but with lua that probably won't matter, because one can change out the many global functions that virt depends on and also there are like infinitely many ways to go about attacking it

so make sure you trust all your mods to not abuse virt even if virt tries to not leak anything

also, by default, support for qmp is enabled, untrusted mods could abuse that, if you don't want support for qmp being enabled, see line 2 of init.lua

Setup

• verify that you have all the dependancies
• give it the trusted mod status
• make/download at least one base image, base images are not included because my internet isn't great..., and even then, i can't trust that yours will be good, the base image is just too big

Making your own base image (with arch linux)

1) create a qemu image

• qemu-img create -f qcow2 base_images/archlinux.img 2G

2) Follow the standard arch install guide on the image

• use qemu-system-x86_64 -cpu host -enable-kvm -m 2G -cdrom <the arch iso> -drive file=base_images/archlinux.img -boot menu=on to launch the virtual machine, or whatever way you prefer

3) Install a bootloader and make sure you include console=ttyS0 in the kernel command line

• when using grub, before doing grub-mkconfig, go to /etc/default/grub and change GRUB_CMDLINE_LINUX_DEFAULT="loglevel=3 quiet" to GRUB_CMDLINE_LINUX_DEFAULT="console=ttyS0", then run grub-mkconfig -o /boot/grub/grub.cfg

4) also make sure to have nothing graphical installed, and KEEP IT MINIMAL as the size of the base image is basically the minimum size for all images based on it (unless you want to risk data loss) 5) you can optionally do /make_vm_from_base test archlinux 3G and enable the example frontend (see first line of init.lua, and yes in the example frontend, the vm name is hardcoded to be test), that was the UI in the screenshot

Faq

Q: Why can't you just use the arch iso
A: the arch linux iso does not have console=ttyS0 in their kernel command line

Q: How does it work
A: It uses named pipes (the .in/.out files) to communicate with qemu, it launches qemu with io.popen and kills it by seeing the pid in the pid file

Q: Why have rxi's json library when you can just use minetest's
A: minetest's is weird, when i try to do minetest.write_json({a=5}) it returns {"a":5.0} when it should be {"a":5} and yes it matters for qemu

Q: will you develop this
A: If you message me with a list of features, probably

TODOs

• more CPU limiting (like idk only x% cpu usage, can be achieved with systemd-run)
• better security
• testing