Re: [libvirt-users] Questions regarding migration from QEMU to libvirt

Rodrigo Siqueira
Mon, 22 Oct 2018 15:07:13 -0000

Hi,

First of all, thanks for your feedback :)

On 10/17, Martin Kletzander wrote:
> On Wed, Oct 03, 2018 at 01:04:50PM -0300, Rodrigo Siqueira wrote:
> > Hi,
> >
> > My colleagues and I have a set of scripts that we use to automate our
> > daily tasks related to the Linux Kernel. As a result, most of our code
> > relies on the QEMU features; and recently we decided use libvirt
instead
> > of QEMU. However, we have some questions, and I would like to know if
> > someone could help us. Follows:
> >
>
> Could you explain how much do you rely on the VM looking the same from the
guest
> perspective (Guest ABI stability)?

Actually, we do not use any special feature from QEMU. Just basic
things. Just for illustrate, follows the command that we use for start a
VM:

qemu-system-x86_64 -enable-kvm -daemonize -m 3G -smp cores=4,cpus=4 -net nic \
-net user,hostfwd=tcp::2222-:22,smb=/home/USER /home/USER/p/DISK.qcow2

> If you only need the disk to stay the same and you want to easily migrate
> existing machines, then virt-v2v might be good to try.

Thanks! I will take a look on this.

> > 1) Import our QEMU images with virsh
> >
> > Currently, we import the QEMU VMs with virt-install.
> >
> > Is it possible to automatically discover the distro variant of a QEMU
> > image in order to use it in the “--os-variant” option?
> >
>
> You might be able to get that info using libguestfs (virt-v2v should be
able to
> do that for you).

Yes, I did it last week. I'm doing the following steps:

1. I mount the disk image using libguestfs
2. Print the value MOUNT_PATH_DISK/etc/*-release
3. Take the distro and version

Do you know a straightforward path?

> > Here is how we register a VM:
> >
https://github.com/rodrigosiqueira/kworkflow/pull/23/files#diff-70617d452b008bc71362804d54032f24R113
> >
> > 2) The requirement of sudo to create a network
> >
> > When we register our VM, we want to keep the ssh working well.
However,
> > every time we register a VM we create a new network bridge as a result
> > it requires sudo. Is it possible to avoid this? Or at least make this
a
> > single action?
> >
>
> You don't need to have a libvirt network for each VM, you can create a
bridge
> and use <interface type='bridge'/> or just use <interface
type='direct'/>.  Or
> you can have one network for multiple VMs.  What did you use with plain
QEMU?

When I use QEMU for work, I need two things: ssh and share a directory.
I'm using samba for sharing a directory and openssh. Again, this is the
command that I'm using:

qemu-system-x86_64 -enable-kvm -daemonize -m 3G -smp cores=4,cpus=4 -net nic \
-net user,hostfwd=tcp::2222-:22,smb=/home/USER /home/USER/p/DISK.qcow2

For our network configuration, we have:

<network>
  <name>kworkflow-network</name>
  <uuid>7d167334-7e36-475b-a0ae-9889b87848d7</uuid>
  <forward mode='nat'/>
  <bridge name='virbr-kworkflow' stp='on'
delay='0'/>
  <mac address='52:54:00:8a:da:00'/>
  <ip address='10.0.1.1' netmask='255.255.255.0'>
    <dhcp>
      <range start='10.0.1.2' end='10.0.1.2'/>
      <host mac='52:54:00:21:23:52' name='kworflow-vm'
ip='10.0.1.2'/>
    </dhcp>
  </ip>
</network>

This configuration file worked well on Debian, but when we tried it on
Archlinux things did not work. Actually, we want to keep these things as
simple as possible. Our requirements are only: share a directory and
access VM via ssh. In order to try to make things simples and
'portable', we think about the following approach:

1. Mount the disk image, and set a static IP
2. Our set of scripts, manage the static IPs

I feel that I'm reinventing the wheel, but this approach sounds easier
for me due to my lack of knowledge in the libvirt. Do you have any other
suggestion to make libvirt do the hard work for me?

> I'm not sure what the trouble is, also what the use cases are, so the
answers
> might not be fit for your needs.
>
> > Here is how we handled this:
> > * The code for register:
> >
https://github.com/rodrigosiqueira/kworkflow/pull/23/files#diff-70617d452b008bc71362804d54032f24R113
> > * The configuration file that we adopted as a default:
> >
https://github.com/rodrigosiqueira/kworkflow/pull/23/files#diff-d8c16482496875afc0d37b181487ae46R1
> >
> > 3) When using libvirt it changes the owner of our image
> >
> > If we try to use libvirt, it changes the ownership of our QEMU images
> > (root). We fixed it by changing the file “/etc/libvirt/qemu.conf”, and
> > switch the option dynamic_ownership to “0”. What is the impact of that
> > change? Is it dangerous? There is a way to avoid this change?
> >
>
> dynamic_ownership=0 keeps the owners as they are, but libvirt cannot
guarantee
> that the VM will have access to all its resources.  If you are taking care
of
> that, then keeping that turned off should be OK.
>
> > Finally, here is the full code of the libvirt part:
> > https://github.com/rodrigosiqueira/kworkflow/pull/23/files
> >
> > Thanks
> > Best Regards
> >
> > --
> > Rodrigo Siqueira
> > http://siqueira.tech
> > Graduate Student
> > Department of Computer Science
> > University of São Paulo
>
>
>
> > _______________________________________________
> > libvirt-users mailing list
> > libvirt-users@redhat.com
> > https://www.redhat.com/mailman/listinfo/libvirt-users
>



--
Rodrigo Siqueira
https://siqueira.tech
https://twitter.com/siqueirajordao
Graduate Student
Department of Computer Science
University of São Paulo