cgroup: add support for net_cls controllers

Add a new config directive called NetClass= to CGroup enabled units.
Allowed values are positive numbers for fix assignments and "auto" for
picking a free value automatically, for which we need to keep track of
dynamically assigned net class IDs of units. Introduce a hash table for
this, and also record the last ID that was given out, so the allocator
can start its search for the next 'hole' from there. This could
eventually be optimized with something like an irb.

The class IDs up to 65536 are considered reserved and won't be
assigned automatically by systemd. This barrier can be made a config
directive in the future.

Values set in unit files are stored in the CGroupContext of the
unit and considered read-only. The actually assigned number (which
may have been chosen dynamically) is stored in the unit itself and
is guaranteed to remain stable as long as the unit is active.

In the CGroup controller, set the configured CGroup net class to
net_cls.classid. Multiple unit may share the same net class ID,
and those which do are linked together.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/core/unit.h b/src/core/unit.h
index 3c7684411b..c868d75c79 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -161,6 +161,9 @@ struct Unit {
         /* CGroup realize members queue */
         LIST_FIELDS(Unit, cgroup_queue);
 
+        /* Units with the same CGroup netclass */
+        LIST_FIELDS(Unit, cgroup_netclass);
+
         /* PIDs we keep an eye on. Note that a unit might have many
          * more, but these are the ones we care enough about to
          * process SIGCHLD for */
@@ -189,6 +192,8 @@ struct Unit {
         CGroupMask cgroup_members_mask;
         int cgroup_inotify_wd;
 
+        uint32_t cgroup_netclass_id;
+
         /* How to start OnFailure units */
         JobMode on_failure_job_mode;