[libvirt PATCH 0/9] fix cgroups on systemd hosts

[Michal Privoznik]

On 2/9/21 2:26 PM, Pavel Hrdina wrote:
> When running on host with systemd there is an ownership issue of
> the root VM cgroup. When it is created for us by systemd using machined
> the owner of the root VM cgroup is systemd and we should not touch any
> of the files as systemd can and will modify any values configured there.
> 
> Basically we had the issue since introduction of machined support
> in libvirt 1.1.1 back in 2013. With systemd implementing more cgroup
> APIs the `systemctl daemon-reload` would change more values configured
> by libvirt.
> 
> The solution to the issue is to use systemd DBus APIs to configure
> cgroups but unfortunately they don't cover everything that libvirt
> needs.
> 
> For that reason we will use systemd DBus APIs only for values that
> affect sibling cgroups where the resources are distributed
> proportionally, such as blkio.weight or cpu.shares. For the remaining
> resources we will keep the current code where we work with the files
> directly but we move everything into a child cgroup of the VM root
> cgroup where we are free to do whatever we like including thread
> configuration.

Yeah, if only there was a way to tell machined to not touch CGroups 
we've created until they offer full set of features.

> 
> Pavel Hrdina (9):
>    virsystemd: export virSystemdHasMachined
>    virsystemd: introduce virSystemdGetMachineByPID
>    virsystemd: introduce virSystemdGetMachineUnitByPID
>    vircgroup: use DBus call to systemd for some APIs
>    vircgroupv1: refactor virCgroupV1DetectPlacement
>    vircgroupv2: move task into cgroup before enabling controllers
>    vircgroup: introduce virCgroupV1Exists and virCgroupV2Exists
>    vircgroup: introduce nested cgroup to properly work with systemd
>    tests: add cgroup nested tests
> 
>   docs/cgroups.html.in                          |  29 +-
>   src/libvirt_private.syms                      |   2 +
>   src/util/vircgroup.c                          | 300 ++++++++++++++----
>   src/util/vircgroupbackend.h                   |   5 +
>   src/util/vircgrouppriv.h                      |  10 +
>   src/util/vircgroupv1.c                        | 122 +++++--
>   src/util/vircgroupv2.c                        |  82 ++++-
>   src/util/virsystemd.c                         | 105 +++++-
>   src/util/virsystemd.h                         |   4 +
>   tests/vircgroupdata/systemd-legacy.cgroups    |  12 +
>   tests/vircgroupdata/systemd-legacy.mounts     |  11 +
>   .../vircgroupdata/systemd-legacy.self.cgroup  |  11 +
>   tests/vircgroupdata/systemd-unified.cgroups   |  13 +
>   tests/vircgroupdata/systemd-unified.mounts    |   1 +
>   .../vircgroupdata/systemd-unified.self.cgroup |   1 +
>   tests/vircgrouptest.c                         |  72 +++++
>   tests/virsystemdtest.c                        |  39 ++-
>   17 files changed, 687 insertions(+), 132 deletions(-)
>   create mode 100644 tests/vircgroupdata/systemd-legacy.cgroups
>   create mode 100644 tests/vircgroupdata/systemd-legacy.mounts
>   create mode 100644 tests/vircgroupdata/systemd-legacy.self.cgroup
>   create mode 100644 tests/vircgroupdata/systemd-unified.cgroups
>   create mode 100644 tests/vircgroupdata/systemd-unified.mounts
>   create mode 100644 tests/vircgroupdata/systemd-unified.self.cgroup
> 

Reviewed-by: Michal Privoznik <mprivozn at redhat.com>

Michal