Hello again,

The two patches attached create the cgroup directory needed and remove
the warning for the ip binary missing.  Still the following errors
are emitted to the log. 

--------------------8<-------------------
error : virConnectGetCPUModelNames:1109 : this function is not supported by the connection driver: virConnectGetCPUModelNames
error : virConnectGetAllDomainStats:11705 : this function is not supported by the connection driver: virConnectGetAllDomainStats
error : virCgroupSetValueRaw:473 : Unable to write to '/sys/fs/cgroup/unified/machine/qemu-1-Guix.libvirt-qemu/tasks': No such file or directory
error : virCgroupRemoveRecursively:2383 : Unable to remove /sys/fs/cgroup/unified/machine/qemu-1-Guix.libvirt-qemu/ (16) 
-------------------->8-------------------

The last two may indicate there may be lurking another bug in the
cgroups configuration, but at least the machines can be created and
started/stopped seamlessly.  What do you think?

Happy hacking!
Miguel