libvirt: A potential problem in the package and looking for guidance

libvirt: A potential problem in the package and looking for guidance

[Allan Adair]

Hi Guix!

I am using a libvirt-service-type in my system configuration and it seems
to be working. I can launch VMs using virt-manager, for example. However I
have run into a potential problem, and I think it has to do with the
libvirt package.

Additionally, I would like to present a plea to others on this list that
perhaps someone could share their system configurations for libvirt-
service-type if they use it in a similar way that I am attempting.

My end goal is that I would like to be able to launch several VM guests,
for them to be able to see each other through a local network, and I would
like to be able to SSH from my my host to VM guests.

The configuration for my service-type might be relevant here, so I will
share it here. I don't think that "mdns-adv?" and "log-level" are
particularly relevant to my problem, just keeping it exactly as it is
defined on my system. My user is part of the "libvirt" group.

(service libvirt-service-type
  (libvirt-configuration
    (unix-sock-group "libvirt")
    (mdns-adv? #t)
    (log-level 1)))

I am trying to do everything through qemu://session in user space, not
qemu://system. However it's not that big of a deal to use either. I just
haven't gotten either to work!

The first thing that I am trying to do is to SSH into a single running
guest from my host, and I have so far been unsuccessful.

So, the potential problem that I want to mention is that after having
poked around a bit and created the default network under a qemu://system
connection, a bridge device called "virbr0" is created.

And then for my guest VM which runs under a qemu://session connection, it
has a virtual network interface defined in XML. It was generated by the
virt-manager GUI:


<interface type="bridge">
  <mac address="52:54:00:84:a5:5a"/>
  <source bridge="virbr0"/>
  <model type="virtio"/>
  <address type="pci" domain="0x0000" bus="0x01" slot="0x00"
function="0x0"/>
</interface>


When I try to restart the VM with this modification, I get the following
error:


Error starting domain: '/usr/libexec/qemu-bridge-helper' is not a suitable
bridge helper: No such file or directory

Traceback (most recent call last):
  File "/gnu/store/s15ahi35w0i274lima3dk41a7vr3kdbn-virt-manager-
3.2.0/share/virt-manager/virtManager/asyncjob.py", line 65, in cb_wrapper
    callback(asyncjob, *args, **kwargs)
  File "/gnu/store/s15ahi35w0i274lima3dk41a7vr3kdbn-virt-manager-
3.2.0/share/virt-manager/virtManager/asyncjob.py", line 101, in tmpcb
    callback(*args, **kwargs)
  File "/gnu/store/s15ahi35w0i274lima3dk41a7vr3kdbn-virt-manager-
3.2.0/share/virt-manager/virtManager/object/libvirtobject.py", line 57, in
newfn
    ret = fn(self, *args, **kwargs)
  File "/gnu/store/s15ahi35w0i274lima3dk41a7vr3kdbn-virt-manager-
3.2.0/share/virt-manager/virtManager/object/domain.py", line 1329, in
startup
    self._backend.create()
  File "/gnu/store/g2x37cxh2ag5h66f0p9zaz9pkz2vcvgg-python-libvirt-
7.9.0/lib/python3.9/site-packages/libvirt.py", line 1353, in create
    raise libvirtError('virDomainCreate() failed')
libvirt.libvirtError: '/usr/libexec/qemu-bridge-helper' is not a suitable
bridge helper: No such file or directory


Because the package is searching specifically for "/usr/libexec/qemu-
bridge-helper", I think this is a bug in the package definition. "/usr"
should probably be a prefix from the store, right?

Any comments or suggestions?


Thanks in advance for a response,

Allan

Re: libvirt: A potential problem in the package and looking for guidance

[Rene Saavedra]

Hi Allan,

Just an idea,
You can try to fix the package and try again.


--
Rene

Re: libvirt: A potential problem in the package and looking for guidance

[Ludovic Courtès]

Hi,

Allan Adair <allan@adair.no> skribis:

>   File "/gnu/store/g2x37cxh2ag5h66f0p9zaz9pkz2vcvgg-python-libvirt-
> 7.9.0/lib/python3.9/site-packages/libvirt.py", line 1353, in create
>     raise libvirtError('virDomainCreate() failed')
> libvirt.libvirtError: '/usr/libexec/qemu-bridge-helper' is not a suitable
> bridge helper: No such file or directory
>
>
> Because the package is searching specifically for "/usr/libexec/qemu-
> bridge-helper", I think this is a bug in the package definition. "/usr"
> should probably be a prefix from the store, right?
>
> Any comments or suggestions?

Presumably that “/usr/libexec/qemu-bridge-helper” reference is
hard-coded in the source.  The solution in situations like this is to
replace it (using ‘substitute*’) by the absolute file name of the
corresponding program in /gnu/store.

  (substitute* "some/file.py"
    (("/usr/libexec/qemu-bridge-helper")
     (search-input-file inputs "/bin/qemu-bridge-helper")))

HTH!

Ludo’.

Re: libvirt: A potential problem in the package and looking for guidance

[Maxime Devos]

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Ludovic Courtès schreef op ma 23-05-2022 om 17:28 [+0200]:
> Hi,
> 
> Allan Adair <allan@adair.no> skribis:
> 
> >    File "/gnu/store/g2x37cxh2ag5h66f0p9zaz9pkz2vcvgg-python-libvirt-
> > 7.9.0/lib/python3.9/site-packages/libvirt.py", line 1353, in create
> >      raise libvirtError('virDomainCreate() failed')
> > libvirt.libvirtError: '/usr/libexec/qemu-bridge-helper' is not a suitable
> > bridge helper: No such file or directory
> > 
> > 
> > Because the package is searching specifically for "/usr/libexec/qemu-
> > bridge-helper", I think this is a bug in the package definition. "/usr"
> > should probably be a prefix from the store, right?
> > 
> > Any comments or suggestions?
> 
> Presumably that “/usr/libexec/qemu-bridge-helper” reference is
> hard-coded in the source.  The solution in situations like this is to
> replace it (using ‘substitute*’) by the absolute file name of the
> corresponding program in /gnu/store.
> 
>   (substitute* "some/file.py"
>     (("/usr/libexec/qemu-bridge-helper")
>      (search-input-file inputs "/bin/qemu-bridge-helper")))

Additionally, you can do
"grep -RF /usr/libexec /gnu/store/g2x37cxh2ag5h66f0p9zaz9pkz2vcvgg-python-libvirt-7.9.0"
in a shell to find the name of the source file to substitutify.

Greetings,
Maxime.

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Re: libvirt: A potential problem in the package and looking for guidance

[Allan Adair]

Thanks! Looks like I was on a good track. The only reference that I could
find to /usr/libexec/qemu-bridge-helper was in the meson.build file of the
libvirt package. I wrote a package variant that looks like this, to test:

(define-public libvirt-with-qemu-bridge-helper
  (package
    (inherit libvirt)
    (name "libvirt-with-qemu-bridge-helper")
    (arguments
     (substitute-keyword-arguments (package-arguments libvirt)
       ((#:phases phases)
	#~(modify-phases #$phases
	    ;; libvirt needs to be able to find qemu's bridge helper
	    ;; this is hacky, perhaps a patch on meson.build would be
better.
	    (add-after 'unpack 'find-qemu-bridge-helper
	      (lambda* (#:key inputs #:allow-other-keys)
		(let* ((qemu (assoc-ref inputs "qemu")))
		  (substitute* "meson.build"
		    (("/usr/libexec/qemu-bridge-helper")
		     (format #f "~a/libexec/qemu-bridge-helper"
qemu))))))))))
    (inputs
     (modify-inputs (package-inputs libvirt)
		    (append qemu)))))

However the effort was fruitless, and my efforts on this are currently on
pause. If I am able to fix it I plan to submit a patch.

Re: libvirt: A potential problem in the package and looking for guidance

[Maxime Devos]

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Allan Adair schreef op ma 23-05-2022 om 21:44 [+0200]:
> (define-public libvirt-with-qemu-bridge-helper
>   (package
>     (inherit libvirt)
>     (name "libvirt-with-qemu-bridge-helper")

This fixes only a variant of the libvirt library itself, it doesn't
cause your modified  version to be used. You may need to modify the
package definition of 'libvirt' instead.  Another method is to set the
'libvirt' field of 'libvirt-configuration' to your 'libvirt-with-qemu-
bridge-helper'.

Greetings,
Maxime.

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