core: unified cgroup hierarchy support

This patch set adds full support the new unified cgroup hierarchy logic
of modern kernels.

A new kernel command line option "systemd.unified_cgroup_hierarchy=1" is
added. If specified the unified hierarchy is mounted to /sys/fs/cgroup
instead of a tmpfs. No further hierarchies are mounted. The kernel
command line option defaults to off. We can turn it on by default as
soon as the kernel's APIs regarding this are stabilized (but even then
downstream distros might want to turn this off, as this will break any
tools that access cgroupfs directly).

It is possibly to choose for each boot individually whether the unified
or the legacy hierarchy is used. nspawn will by default provide the
legacy hierarchy to containers if the host is using it, and the unified
otherwise. However it is possible to run containers with the unified
hierarchy on a legacy host and vice versa, by setting the
$UNIFIED_CGROUP_HIERARCHY environment variable for nspawn to 1 or 0,
respectively.

The unified hierarchy provides reliable cgroup empty notifications for
the first time, via inotify. To make use of this we maintain one
manager-wide inotify fd, and each cgroup to it.

This patch also removes cg_delete() which is unused now.

On kernel 4.2 only the "memory" controller is compatible with the
unified hierarchy, hence that's the only controller systemd exposes when
booted in unified heirarchy mode.

This introduces a new enum for enumerating supported controllers, plus a
related enum for the mask bits mapping to it. The core is changed to
make use of this everywhere.

This moves PID 1 into a new "init.scope" implicit scope unit in the root
slice. This is necessary since on the unified hierarchy cgroups may
either contain subgroups or processes but not both. PID 1 hence has to
move out of the root cgroup (strictly speaking the root cgroup is the
only one where processes and subgroups are still allowed, but in order
to support containers nicey, we move PID 1 into the new scope in all
cases.) This new unit is also used on legacy hierarchy setups. It's
actually pretty useful on all systems, as it can then be used to filter
journal messages coming from PID 1, and so on.

The root slice ("-.slice") is now implicitly created and started (and
does not require a unit file on disk anymore), since
that's where "init.scope" is located and the slice needs to be started
before the scope can.

To check whether we are in unified or legacy hierarchy mode we use
statfs() on /sys/fs/cgroup. If the .f_type field reports tmpfs we are in
legacy mode, if it reports cgroupfs we are in unified mode.

This patch set carefuly makes sure that cgls and cgtop continue to work
as desired.

When invoking nspawn as a service it will implicitly create two
subcgroups in the cgroup it is using, one to move the nspawn process
into, the other to move the actual container processes into. This is
done because of the requirement that cgroups may either contain
processes or other subgroups.

1 files changed, 22 insertions, 10 deletions

diff --git a/src/core/cgroup.h b/src/core/cgroup.h
index 7b38d210fb..1ce21f43f2 100644
--- a/src/core/cgroup.h
+++ b/src/core/cgroup.h
@@ -96,22 +96,32 @@ struct CGroupContext {
 void cgroup_context_init(CGroupContext *c);
 void cgroup_context_done(CGroupContext *c);
 void cgroup_context_dump(CGroupContext *c, FILE* f, const char *prefix);
-void cgroup_context_apply(CGroupContext *c, CGroupControllerMask mask, const char *path, ManagerState state);
+void cgroup_context_apply(CGroupContext *c, CGroupMask mask, const char *path, ManagerState state);
 
-CGroupControllerMask cgroup_context_get_mask(CGroupContext *c);
+CGroupMask cgroup_context_get_mask(CGroupContext *c);
 
 void cgroup_context_free_device_allow(CGroupContext *c, CGroupDeviceAllow *a);
 void cgroup_context_free_blockio_device_weight(CGroupContext *c, CGroupBlockIODeviceWeight *w);
 void cgroup_context_free_blockio_device_bandwidth(CGroupContext *c, CGroupBlockIODeviceBandwidth *b);
 
-CGroupControllerMask unit_get_cgroup_mask(Unit *u);
-CGroupControllerMask unit_get_siblings_mask(Unit *u);
-CGroupControllerMask unit_get_members_mask(Unit *u);
-CGroupControllerMask unit_get_target_mask(Unit *u);
+CGroupMask unit_get_own_mask(Unit *u);
+CGroupMask unit_get_siblings_mask(Unit *u);
+CGroupMask unit_get_members_mask(Unit *u);
+CGroupMask unit_get_subtree_mask(Unit *u);
+
+CGroupMask unit_get_target_mask(Unit *u);
+CGroupMask unit_get_enable_mask(Unit *u);
 
 void unit_update_cgroup_members_masks(Unit *u);
+
+char *unit_default_cgroup_path(Unit *u);
+int unit_set_cgroup_path(Unit *u, const char *path);
+
 int unit_realize_cgroup(Unit *u);
-void unit_destroy_cgroup_if_empty(Unit *u);
+void unit_release_cgroup(Unit *u);
+void unit_prune_cgroup(Unit *u);
+int unit_watch_cgroup(Unit *u);
+
 int unit_attach_pids_to_cgroup(Unit *u);
 
 int manager_setup_cgroup(Manager *m);
@@ -122,9 +132,8 @@ unsigned manager_dispatch_cgroup_queue(Manager *m);
 Unit *manager_get_unit_by_cgroup(Manager *m, const char *cgroup);
 Unit* manager_get_unit_by_pid(Manager *m, pid_t pid);
 
-pid_t unit_search_main_pid(Unit *u);
-
-int manager_notify_cgroup_empty(Manager *m, const char *group);
+int unit_search_main_pid(Unit *u, pid_t *ret);
+int unit_watch_all_pids(Unit *u);
 
 int unit_get_memory_current(Unit *u, uint64_t *ret);
 int unit_get_cpu_usage(Unit *u, nsec_t *ret);
@@ -132,5 +141,8 @@ int unit_reset_cpu_usage(Unit *u);
 
 bool unit_cgroup_delegate(Unit *u);
 
+int unit_notify_cgroup_empty(Unit *u);
+int manager_notify_cgroup_empty(Manager *m, const char *group);
+
 const char* cgroup_device_policy_to_string(CGroupDevicePolicy i) _const_;
 CGroupDevicePolicy cgroup_device_policy_from_string(const char *s) _pure_;