[Libguestfs] Using libguestfs to sandbox VM builds

[Richard W.M. Jones]

On Thu, Sep 28, 2017 at 06:02:04PM +0200, Emmanuel Kasper wrote:
> Hi
> Debian has a couple of tools like fai-diskimage and vmdebootstrap, to
> build VM images, but they require being root, as these loopmounts
> partitions on which deboostrap is executed. Maybe installing grub2 needs
> access to block devices too.
> 
> I was thinking of using libguestfs to sandbox those processes, by
> passing a build VM as a disk image and my build directory as a 9pfs
> mount to the appliance, and calling the build command via $g->shell().
> 
> Any pitfalls I should be aware while doing this ?

In the general case that you want to build bootable disk images,
installing them using d-i, you can do that fully non-root using
virt-install:

https://github.com/libguestfs/libguestfs/blob/stable-1.34/builder/website/debian.sh#L66

You could also use virt-builder (either using our Debian 9 template as
a starting point, or your own created in the previous step).
Something like:

  $ virt-builder debian-9 \
          --install some,required,packages \
          --copy-in test-dir:/var/tmp \
          --firstboot-command /var/tmp/test-dir/run-the-tests.sh

  $ qemu-system-x86_64 \
          -nodefaults \
          -nographic \
          -machine accel=kvm:tcg \
          -cpu host \
          -m 2048 \
          -drive file=debian-9.img,format=raw,if=virtio \
          -serial stdio

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-builder quickly builds VMs from scratch
http://libguestfs.org/virt-builder.1.html