[libvirt] [REPOST] regarding cgroup v2 support in libvirt

(reposting w/ libvir-list cc'd, sorry about the delay in reposting, was traveling and then on vacation) Hello, Daniel. How have you been? We (facebook) are deploying cgroup v2 and internally use libvirt to manage virtual machines, so I'm trying to add cgroup v2 support to libvirt. Because cgroup v2's resource configurations differ from v1 in varying degrees depending on the specific resource type, it unfortunately introduces new configurations (some completely new configs, others just a different range / format). This means that adding cgroup v2 support to libvirt requires adding new config options to it and maybe implementing some form of translation mechanism between overlapping configs. The upcoming systemd release includes all that's necessary to support v1/v2 compatibility so that users setting resource configs through systemd don't have to worry about whether v1 or v2 is in use. I'm wondering whether it would make sense to make libvirt use dbus calls to systemd to set resource configs when systemd is in use, so that it can piggyback on systemd's v1/v2 compatibility. It is true that, as libvirt can be used without systemd, libvirt will probably want its own direct implementation down the line, but I think there are benefits to going through systemd for resource settings in general given that hierarchy setup is already done through systemd when available. What do you think? Thanks! -- tejun