core: add new .slice unit type for partitioning systems

In order to prepare for the kernel cgroup rework, let's introduce a new
unit type to systemd, the "slice". Slices can be arranged in a tree and
are useful to partition resources freely and hierarchally by the user.

Each service unit can now be assigned to one of these slices, and later
on login users and machines may too.

Slices translate pretty directly to the cgroup hierarchy, and the
various objects can be assigned to any of the slices in the tree.

1 files changed, 47 insertions, 6 deletions

diff --git a/src/core/unit.c b/src/core/unit.c
index 9b36b225fa..b97158ff06 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -60,7 +60,8 @@ const UnitVTable * const unit_vtable[_UNIT_TYPE_MAX] = {
         [UNIT_AUTOMOUNT] = &automount_vtable,
         [UNIT_SNAPSHOT] = &snapshot_vtable,
         [UNIT_SWAP] = &swap_vtable,
-        [UNIT_PATH] = &path_vtable
+        [UNIT_PATH] = &path_vtable,
+        [UNIT_SLICE] = &slice_vtable
 };
 
 Unit *unit_new(Manager *m, size_t size) {
@@ -853,6 +854,7 @@ int unit_add_default_target_dependency(Unit *u, Unit *target) {
 }
 
 static int unit_add_default_dependencies(Unit *u) {
+
         static const UnitDependency deps[] = {
                 UNIT_REQUIRED_BY,
                 UNIT_REQUIRED_BY_OVERRIDABLE,
@@ -868,9 +870,17 @@ static int unit_add_default_dependencies(Unit *u) {
         assert(u);
 
         for (k = 0; k < ELEMENTSOF(deps); k++)
-                SET_FOREACH(target, u->dependencies[deps[k]], i)
-                        if ((r = unit_add_default_target_dependency(u, target)) < 0)
+                SET_FOREACH(target, u->dependencies[deps[k]], i) {
+                        r = unit_add_default_target_dependency(u, target);
+                        if (r < 0)
                                 return r;
+                }
+
+        if (u->default_dependencies && UNIT_DEREF(u->slice)) {
+                r = unit_add_two_dependencies(u, UNIT_AFTER, UNIT_WANTS, UNIT_DEREF(u->slice), true);
+                if (r < 0)
+                        return r;
+        }
 
         return 0;
 }
@@ -1977,10 +1987,17 @@ static int unit_add_cgroup(Unit *u, CGroupBonding *b) {
 }
 
 char *unit_default_cgroup_path(Unit *u) {
-        _cleanup_free_ char *escaped_instance = NULL;
+        _cleanup_free_ char *escaped_instance = NULL, *slice = NULL;
+        int r;
 
         assert(u);
 
+        if (UNIT_DEREF(u->slice)) {
+                r = cg_slice_to_path(UNIT_DEREF(u->slice)->id, &slice);
+                if (r < 0)
+                        return NULL;
+        }
+
         escaped_instance = cg_escape(u->id);
         if (!escaped_instance)
                 return NULL;
@@ -1996,9 +2013,13 @@ char *unit_default_cgroup_path(Unit *u) {
                 if (!escaped_template)
                         return NULL;
 
-                return strjoin(u->manager->cgroup_hierarchy, "/", escaped_template, "/", escaped_instance, NULL);
+                return strjoin(u->manager->cgroup_hierarchy, "/",
+                               slice ? slice : "", slice ? "/" : "",
+                               escaped_template, "/", escaped_instance, NULL);
         } else
-                return strjoin(u->manager->cgroup_hierarchy, "/", escaped_instance, NULL);
+                return strjoin(u->manager->cgroup_hierarchy, "/",
+                               slice ? slice : "", slice ? "/" : "",
+                               escaped_instance, NULL);
 }
 
 int unit_add_cgroup_from_text(Unit *u, const char *name, bool overwrite, CGroupBonding **ret) {
@@ -2143,6 +2164,26 @@ fail:
         return r;
 }
 
+int unit_add_default_slice(Unit *u) {
+        Unit *slice;
+        int r;
+
+        assert(u);
+
+        if (UNIT_DEREF(u->slice))
+                return 0;
+
+        if (u->manager->running_as != SYSTEMD_SYSTEM)
+                return 0;
+
+        r = manager_load_unit(u->manager, SPECIAL_SYSTEM_SLICE, NULL, NULL, &slice);
+        if (r < 0)
+                return r;
+
+        unit_ref_set(&u->slice, slice);
+        return 0;
+}
+
 int unit_add_default_cgroups(Unit *u) {
         CGroupAttribute *a;
         char **c;