Lennart Poettering
27adcc9737
This changes cg_enable_everywhere() to return which controllers are enabled for the specified cgroup. This information is then used to correctly track the enablement mask currently in effect for a unit. Moreover, when we try to turn off a controller, and this works, then this is indicates that the parent unit might succesfully turn it off now, too as our unit might have kept it busy. So far, when realizing cgroups, i.e. when syncing up the kernel representation of relevant cgroups with our own idea we would strictly work from the root to the leaves. This is generally a good approach, as when controllers are enabled this has to happen in root-to-leaves order. However, when controllers are disabled this has to happen in the opposite order: in leaves-to-root order (this is because controllers can only be enabled in a child if it is already enabled in the parent, and if it shall be disabled in the parent then it has to be disabled in the child first, otherwise it is considered busy when it is attempted to remove it in the parent). To make things complicated when invalidating a unit's cgroup membershup systemd can actually turn off some controllers previously turned on at the very same time as it turns on other controllers previously turned off. In such a case we have to work up leaves-to-root *and* root-to-leaves right after each other. With this patch this is implemented: we still generally operate root-to-leaves, but as soon as we noticed we successfully turned off a controller previously turned on for a cgroup we'll re-enqueue the cgroup realization for all parents of a unit, thus implementing leaves-to-root where necessary.
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