Comment # 13 on bug 1183247 from James Fehlig

FYI, Cole posted a patch to fix the NoMachineForPID issue

https://listman.redhat.com/archives/libvir-list/2021-October/msg00157.html

It works fine with hybrid mode in my testing. While testing the patch with V2
only, I noticed the following unrelated problem

virsh -c lxc:/// create lxc-test.xml 
error: Failed to create domain from lxc-test.xml
error: internal error: Unable to find 'memory' cgroups controller mount

From the libvirtd log

2021-10-07 20:16:00.521+0000: 4131: debug : virCgroupV2DetectPlacement:199 :
group=0x7f65580081a0 path= controllers= selfpath=/system.slice/libvirtd.service
2021-10-07 20:16:00.521+0000: 4131: debug : virCgroupV2DetectControllers:335 :
Controller 'cpu' present=no
2021-10-07 20:16:00.521+0000: 4131: debug : virCgroupV2DetectControllers:335 :
Controller 'cpuacct' present=yes
2021-10-07 20:16:00.521+0000: 4131: debug : virCgroupV2DetectControllers:335 :
Controller 'cpuset' present=no
2021-10-07 20:16:00.521+0000: 4131: debug : virCgroupV2DetectControllers:335 :
Controller 'memory' present=no
2021-10-07 20:16:00.521+0000: 4131: debug : virCgroupV2DetectControllers:335 :
Controller 'devices' present=yes
2021-10-07 20:16:00.521+0000: 4131: debug : virCgroupV2DetectControllers:335 :
Controller 'freezer' present=no
2021-10-07 20:16:00.521+0000: 4131: debug : virCgroupV2DetectControllers:335 :
Controller 'io' present=no
2021-10-07 20:16:00.521+0000: 4131: debug : virCgroupV2DetectControllers:335 :
Controller 'net_cls' present=no
2021-10-07 20:16:00.521+0000: 4131: debug : virCgroupV2DetectControllers:335 :
Controller 'perf_event' present=no
2021-10-07 20:16:00.521+0000: 4131: debug : virCgroupV2DetectControllers:335 :
Controller 'name=systemd' present=no
2021-10-07 20:16:00.521+0000: 4131: error : virLXCProcessStart:1236 : internal
error: Unable to find 'memory' cgroups controller mount

Hmm, what controllers are along the path to /system.slice/libvirtd.service?

# cat /sys/fs/cgroup/cgroup.controllers 
cpuset cpu io memory hugetlb pids rdma misc
# cat /sys/fs/cgroup/system.slice/cgroup.controllers
pids
# cat /sys/fs/cgroup/system.slice/libvirtd.service/cgroup.controllers
pids

So no memory controller, which along with cpuacct and devices, are required by
the lxc driver. I'm surprised there have been no complaints from other distros.
Could there be cgroup.subtree_control differences between distros?