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From 2f9e75564e04ed3e6f7aacb264ea69f5582050ca Mon Sep 17 00:00:00 2001
From: Anita Zhang <the.anitazha@gmail.com>
Date: Tue, 19 Oct 2021 18:00:58 -0700
Subject: [PATCH] Revert "core: convert Slice= into a proper dependency (and
 add a back dependency)"

This reverts commit d219a2b07cc5dc8ffd5010f08561fab2780d8616.
---
 man/org.freedesktop.systemd1.xml |  6 -----
 src/basic/unit-def.c             |  2 --
 src/basic/unit-def.h             |  4 ----
 src/core/cgroup.c                | 23 ++++++++++++++----
 src/core/dbus-unit.c             |  3 +--
 src/core/load-fragment.c         |  2 +-
 src/core/slice.c                 | 21 +++++++++++++----
 src/core/unit-dependency-atom.c  |  8 -------
 src/core/unit-dependency-atom.h  |  4 +---
 src/core/unit.c                  | 40 +++++++++-----------------------
 src/core/unit.h                  |  7 ++++--
 11 files changed, 54 insertions(+), 66 deletions(-)

diff --git a/man/org.freedesktop.systemd1.xml b/man/org.freedesktop.systemd1.xml
index c14c5b6601..c87feea201 100644
--- a/man/org.freedesktop.systemd1.xml
+++ b/man/org.freedesktop.systemd1.xml
@@ -1650,8 +1650,6 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2eservice {
       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
       readonly as JoinsNamespaceOf = ['...', ...];
       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
-      readonly as SliceOf = ['...', ...];
-      @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
       readonly as RequiresMountsFor = ['...', ...];
       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
       readonly as Documentation = ['...', ...];
@@ -1799,8 +1797,6 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2eservice {
 
     <!--property JoinsNamespaceOf is not documented!-->
 
-    <!--property SliceOf is not documented!-->
-
     <!--property FreezerState is not documented!-->
 
     <!--property DropInPaths is not documented!-->
@@ -1949,8 +1945,6 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2eservice {
 
     <variablelist class="dbus-property" generated="True" extra-ref="JoinsNamespaceOf"/>
 
-    <variablelist class="dbus-property" generated="True" extra-ref="SliceOf"/>
-
     <variablelist class="dbus-property" generated="True" extra-ref="RequiresMountsFor"/>
 
     <variablelist class="dbus-property" generated="True" extra-ref="Documentation"/>
diff --git a/src/basic/unit-def.c b/src/basic/unit-def.c
index 2667e61dc4..23e4825bd7 100644
--- a/src/basic/unit-def.c
+++ b/src/basic/unit-def.c
@@ -289,8 +289,6 @@ static const char* const unit_dependency_table[_UNIT_DEPENDENCY_MAX] = {
         [UNIT_JOINS_NAMESPACE_OF] = "JoinsNamespaceOf",
         [UNIT_REFERENCES] = "References",
         [UNIT_REFERENCED_BY] = "ReferencedBy",
-        [UNIT_IN_SLICE] = "InSlice",
-        [UNIT_SLICE_OF] = "SliceOf",
 };
 
 DEFINE_STRING_TABLE_LOOKUP(unit_dependency, UnitDependency);
diff --git a/src/basic/unit-def.h b/src/basic/unit-def.h
index 08651efa57..e72452702a 100644
--- a/src/basic/unit-def.h
+++ b/src/basic/unit-def.h
@@ -254,10 +254,6 @@ typedef enum UnitDependency {
         UNIT_REFERENCES,              /* Inverse of 'references' is 'referenced_by' */
         UNIT_REFERENCED_BY,
 
-        /* Slice= */
-        UNIT_IN_SLICE,
-        UNIT_SLICE_OF,
-
         _UNIT_DEPENDENCY_MAX,
         _UNIT_DEPENDENCY_INVALID = -EINVAL,
 } UnitDependency;
diff --git a/src/core/cgroup.c b/src/core/cgroup.c
index 5c07aa71d1..9033bea169 100644
--- a/src/core/cgroup.c
+++ b/src/core/cgroup.c
@@ -1706,8 +1706,12 @@ CGroupMask unit_get_members_mask(Unit *u) {
         if (u->type == UNIT_SLICE) {
                 Unit *member;
 
-                UNIT_FOREACH_DEPENDENCY(member, u, UNIT_ATOM_SLICE_OF)
+                UNIT_FOREACH_DEPENDENCY(member, u, UNIT_ATOM_BEFORE) {
+                        if (UNIT_DEREF(member->slice) != u)
+                                continue;
+
                         u->cgroup_members_mask |= unit_get_subtree_mask(member); /* note that this calls ourselves again, for the children */
+                }
         }
 
         u->cgroup_members_mask_valid = true;
@@ -2365,10 +2369,13 @@ static int unit_realize_cgroup_now_disable(Unit *u, ManagerState state) {
         if (u->type != UNIT_SLICE)
                 return 0;
 
-        UNIT_FOREACH_DEPENDENCY(m, u, UNIT_ATOM_SLICE_OF) {
+        UNIT_FOREACH_DEPENDENCY(m, u, UNIT_ATOM_BEFORE) {
                 CGroupMask target_mask, enable_mask, new_target_mask, new_enable_mask;
                 int r;
 
+                if (UNIT_DEREF(m->slice) != u)
+                        continue;
+
                 /* The cgroup for this unit might not actually be fully realised yet, in which case it isn't
                  * holding any controllers open anyway. */
                 if (!m->cgroup_realized)
@@ -2530,7 +2537,11 @@ void unit_add_family_to_cgroup_realize_queue(Unit *u) {
                 /* Children of u likely changed when we're called */
                 u->cgroup_members_mask_valid = false;
 
-                UNIT_FOREACH_DEPENDENCY(m, u, UNIT_ATOM_SLICE_OF) {
+                UNIT_FOREACH_DEPENDENCY(m, u, UNIT_ATOM_BEFORE) {
+
+                        /* Skip units that have a dependency on the slice but aren't actually in it. */
+                        if (UNIT_DEREF(m->slice) != u)
+                                continue;
 
                         /* No point in doing cgroup application for units without active processes. */
                         if (UNIT_IS_INACTIVE_OR_FAILED(unit_active_state(m)))
@@ -3869,8 +3880,12 @@ void unit_invalidate_cgroup_bpf(Unit *u) {
         if (u->type == UNIT_SLICE) {
                 Unit *member;
 
-                UNIT_FOREACH_DEPENDENCY(member, u, UNIT_ATOM_SLICE_OF)
+                UNIT_FOREACH_DEPENDENCY(member, u, UNIT_ATOM_BEFORE) {
+                        if (UNIT_DEREF(member->slice) != u)
+                                continue;
+
                         unit_invalidate_cgroup_bpf(member);
+                }
         }
 }
 
diff --git a/src/core/dbus-unit.c b/src/core/dbus-unit.c
index 124b9e496b..f861988bd8 100644
--- a/src/core/dbus-unit.c
+++ b/src/core/dbus-unit.c
@@ -875,7 +875,6 @@ const sd_bus_vtable bus_unit_vtable[] = {
         SD_BUS_PROPERTY("PropagatesStopTo", "as", property_get_dependencies, 0, SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("StopPropagatedFrom", "as", property_get_dependencies, 0, SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("JoinsNamespaceOf", "as", property_get_dependencies, 0, SD_BUS_VTABLE_PROPERTY_CONST),
-        SD_BUS_PROPERTY("SliceOf", "as", property_get_dependencies, 0, SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("RequiresMountsFor", "as", property_get_requires_mounts_for, offsetof(Unit, requires_mounts_for), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("Documentation", "as", NULL, offsetof(Unit, documentation), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("Description", "s", property_get_description, 0, SD_BUS_VTABLE_PROPERTY_CONST),
@@ -2273,7 +2272,7 @@ static int bus_unit_set_transient_property(
                         return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Unit name '%s' is not a slice", s);
 
                 if (!UNIT_WRITE_FLAGS_NOOP(flags)) {
-                        r = unit_set_slice(u, slice, UNIT_DEPENDENCY_FILE);
+                        r = unit_set_slice(u, slice);
                         if (r < 0)
                                 return r;
 
diff --git a/src/core/load-fragment.c b/src/core/load-fragment.c
index 8fb3c378ee..a068fdf313 100644
--- a/src/core/load-fragment.c
+++ b/src/core/load-fragment.c
@@ -3575,7 +3575,7 @@ int config_parse_unit_slice(
                 return 0;
         }
 
-        r = unit_set_slice(u, slice, UNIT_DEPENDENCY_FILE);
+        r = unit_set_slice(u, slice);
         if (r < 0) {
                 log_syntax(unit, LOG_WARNING, filename, line, r, "Failed to assign slice %s to unit %s, ignoring: %m", slice->id, u->id);
                 return 0;
diff --git a/src/core/slice.c b/src/core/slice.c
index 2e43c00119..009c98b434 100644
--- a/src/core/slice.c
+++ b/src/core/slice.c
@@ -47,7 +47,7 @@ static void slice_set_state(Slice *t, SliceState state) {
 }
 
 static int slice_add_parent_slice(Slice *s) {
-        Unit *u = UNIT(s);
+        Unit *u = UNIT(s), *parent;
         _cleanup_free_ char *a = NULL;
         int r;
 
@@ -60,7 +60,12 @@ static int slice_add_parent_slice(Slice *s) {
         if (r <= 0) /* 0 means root slice */
                 return r;
 
-        return unit_add_dependency_by_name(u, UNIT_IN_SLICE, a, true, UNIT_DEPENDENCY_IMPLICIT);
+        r = manager_load_unit(u->manager, a, NULL, NULL, &parent);
+        if (r < 0)
+                return r;
+
+        unit_ref_set(&u->slice, u, parent);
+        return 0;
 }
 
 static int slice_add_default_dependencies(Slice *s) {
@@ -349,11 +354,14 @@ static void slice_enumerate_perpetual(Manager *m) {
 
 static bool slice_freezer_action_supported_by_children(Unit *s) {
         Unit *member;
-        int r;
 
         assert(s);
 
-        UNIT_FOREACH_DEPENDENCY(member, s, UNIT_ATOM_SLICE_OF) {
+        UNIT_FOREACH_DEPENDENCY(member, s, UNIT_ATOM_BEFORE) {
+                int r;
+
+                if (UNIT_DEREF(member->slice) != s)
+                        continue;
 
                 if (member->type == UNIT_SLICE) {
                         r = slice_freezer_action_supported_by_children(member);
@@ -380,7 +388,10 @@ static int slice_freezer_action(Unit *s, FreezerAction action) {
                 return 0;
         }
 
-        UNIT_FOREACH_DEPENDENCY(member, s, UNIT_ATOM_SLICE_OF) {
+        UNIT_FOREACH_DEPENDENCY(member, s, UNIT_ATOM_BEFORE) {
+                if (UNIT_DEREF(member->slice) != s)
+                        continue;
+
                 if (action == FREEZER_FREEZE)
                         r = UNIT_VTABLE(member)->freeze(member);
                 else
diff --git a/src/core/unit-dependency-atom.c b/src/core/unit-dependency-atom.c
index 761835828a..9a8e4615f1 100644
--- a/src/core/unit-dependency-atom.c
+++ b/src/core/unit-dependency-atom.c
@@ -93,8 +93,6 @@ static const UnitDependencyAtom atom_map[_UNIT_DEPENDENCY_MAX] = {
         [UNIT_JOINS_NAMESPACE_OF]     = UNIT_ATOM_JOINS_NAMESPACE_OF,
         [UNIT_REFERENCES]             = UNIT_ATOM_REFERENCES,
         [UNIT_REFERENCED_BY]          = UNIT_ATOM_REFERENCED_BY,
-        [UNIT_IN_SLICE]               = UNIT_ATOM_IN_SLICE,
-        [UNIT_SLICE_OF]               = UNIT_ATOM_SLICE_OF,
 
         /* These are dependency types without effect on our state engine. We maintain them only to make
          * things discoverable/debuggable as they are the inverse dependencies to some of the above. As they
@@ -228,12 +226,6 @@ UnitDependency unit_dependency_from_unique_atom(UnitDependencyAtom atom) {
         case UNIT_ATOM_REFERENCED_BY:
                 return UNIT_REFERENCED_BY;
 
-        case UNIT_ATOM_IN_SLICE:
-                return UNIT_IN_SLICE;
-
-        case UNIT_ATOM_SLICE_OF:
-                return UNIT_SLICE_OF;
-
         default:
                 return _UNIT_DEPENDENCY_INVALID;
         }
diff --git a/src/core/unit-dependency-atom.h b/src/core/unit-dependency-atom.h
index c5f8f5d400..f79f1b732a 100644
--- a/src/core/unit-dependency-atom.h
+++ b/src/core/unit-dependency-atom.h
@@ -77,9 +77,7 @@ typedef enum UnitDependencyAtom {
         UNIT_ATOM_JOINS_NAMESPACE_OF                  = UINT64_C(1) << 29,
         UNIT_ATOM_REFERENCES                          = UINT64_C(1) << 30,
         UNIT_ATOM_REFERENCED_BY                       = UINT64_C(1) << 31,
-        UNIT_ATOM_IN_SLICE                            = UINT64_C(1) << 32,
-        UNIT_ATOM_SLICE_OF                            = UINT64_C(1) << 33,
-        _UNIT_DEPENDENCY_ATOM_MAX                     = (UINT64_C(1) << 34) - 1,
+        _UNIT_DEPENDENCY_ATOM_MAX                     = (UINT64_C(1) << 32) - 1,
         _UNIT_DEPENDENCY_ATOM_INVALID                 = -EINVAL,
 } UnitDependencyAtom;
 
diff --git a/src/core/unit.c b/src/core/unit.c
index 38d3eb703f..48810a2ba9 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -692,10 +692,11 @@ Unit* unit_free(Unit *u) {
                 job_free(j);
         }
 
+        unit_clear_dependencies(u);
+
         /* A unit is being dropped from the tree, make sure our family is realized properly. Do this after we
          * detach the unit from slice tree in order to eliminate its effect on controller masks. */
         slice = UNIT_GET_SLICE(u);
-        unit_clear_dependencies(u);
         if (slice)
                 unit_add_family_to_cgroup_realize_queue(slice);
 
@@ -721,6 +722,7 @@ Unit* unit_free(Unit *u) {
 
         unit_unwatch_all_pids(u);
 
+        unit_ref_unset(&u->slice);
         while (u->refs_by_target)
                 unit_ref_unset(u->refs_by_target);
 
@@ -3032,8 +3034,6 @@ int unit_add_dependency(
                 [UNIT_JOINS_NAMESPACE_OF] = UNIT_JOINS_NAMESPACE_OF, /* symmetric! 👓 */
                 [UNIT_REFERENCES] = UNIT_REFERENCED_BY,
                 [UNIT_REFERENCED_BY] = UNIT_REFERENCES,
-                [UNIT_IN_SLICE] = UNIT_SLICE_OF,
-                [UNIT_SLICE_OF] = UNIT_IN_SLICE,
         };
         Unit *original_u = u, *original_other = other;
         UnitDependencyAtom a;
@@ -3077,21 +3077,6 @@ int unit_add_dependency(
                 return log_unit_error_errno(u, SYNTHETIC_ERRNO(EINVAL),
                                             "Requested dependency TriggeredBy=%s refused (%s units cannot trigger other units).", other->id, unit_type_to_string(other->type));
 
-        if (FLAGS_SET(a, UNIT_ATOM_IN_SLICE) && other->type != UNIT_SLICE)
-                return log_unit_error_errno(u, SYNTHETIC_ERRNO(EINVAL),
-                                            "Requested dependency Slice=%s refused (%s is not a slice unit).", other->id, other->id);
-        if (FLAGS_SET(a, UNIT_ATOM_SLICE_OF) && u->type != UNIT_SLICE)
-                return log_unit_error_errno(u, SYNTHETIC_ERRNO(EINVAL),
-                                            "Requested dependency SliceOf=%s refused (%s is not a slice unit).", other->id, u->id);
-
-        if (FLAGS_SET(a, UNIT_ATOM_IN_SLICE) && !UNIT_HAS_CGROUP_CONTEXT(u))
-                return log_unit_error_errno(u, SYNTHETIC_ERRNO(EINVAL),
-                                            "Requested dependency Slice=%s refused (%s is not a cgroup unit).", other->id, u->id);
-
-        if (FLAGS_SET(a, UNIT_ATOM_SLICE_OF) && !UNIT_HAS_CGROUP_CONTEXT(other))
-                return log_unit_error_errno(u, SYNTHETIC_ERRNO(EINVAL),
-                                            "Requested dependency SliceOf=%s refused (%s is not a cgroup unit).", other->id, other->id);
-
         r = unit_add_dependency_hashmap(&u->dependencies, d, other, mask, 0);
         if (r < 0)
                 return r;
@@ -3270,15 +3255,15 @@ reset:
         return r;
 }
 
-int unit_set_slice(Unit *u, Unit *slice, UnitDependencyMask mask) {
-        int r;
-
+int unit_set_slice(Unit *u, Unit *slice) {
         assert(u);
         assert(slice);
 
-        /* Sets the unit slice if it has not been set before. Is extra careful, to only allow this for units
-         * that actually have a cgroup context. Also, we don't allow to set this for slices (since the parent
-         * slice is derived from the name). Make sure the unit we set is actually a slice. */
+        /* Sets the unit slice if it has not been set before. Is extra
+         * careful, to only allow this for units that actually have a
+         * cgroup context. Also, we don't allow to set this for slices
+         * (since the parent slice is derived from the name). Make
+         * sure the unit we set is actually a slice. */
 
         if (!UNIT_HAS_CGROUP_CONTEXT(u))
                 return -EOPNOTSUPP;
@@ -3303,10 +3288,7 @@ int unit_set_slice(Unit *u, Unit *slice, UnitDependencyMask mask) {
         if (UNIT_GET_SLICE(u) && u->cgroup_realized)
                 return -EBUSY;
 
-        r = unit_add_dependency(u, UNIT_IN_SLICE, slice, true, mask);
-        if (r < 0)
-                return r;
-
+        unit_ref_set(&u->slice, u, slice);
         return 1;
 }
 
@@ -3356,7 +3338,7 @@ int unit_set_default_slice(Unit *u) {
         if (r < 0)
                 return r;
 
-        return unit_set_slice(u, slice, UNIT_DEPENDENCY_FILE);
+        return unit_set_slice(u, slice);
 }
 
 const char *unit_slice_name(Unit *u) {
diff --git a/src/core/unit.h b/src/core/unit.h
index 759104ffa7..7a8bfd0568 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -202,6 +202,8 @@ typedef struct Unit {
         dual_timestamp active_exit_timestamp;
         dual_timestamp inactive_enter_timestamp;
 
+        UnitRef slice;
+
         /* Per type list */
         LIST_FIELDS(Unit, units_by_type);
 
@@ -716,7 +718,8 @@ static inline Unit* UNIT_TRIGGER(Unit *u) {
 }
 
 static inline Unit* UNIT_GET_SLICE(const Unit *u) {
-        return unit_has_dependency(u, UNIT_ATOM_IN_SLICE, NULL);
+        assert(u);
+        return u->slice.target;
 }
 
 Unit* unit_new(Manager *m, size_t size);
@@ -761,7 +764,7 @@ Unit *unit_follow_merge(Unit *u) _pure_;
 int unit_load_fragment_and_dropin(Unit *u, bool fragment_required);
 int unit_load(Unit *unit);
 
-int unit_set_slice(Unit *u, Unit *slice, UnitDependencyMask mask);
+int unit_set_slice(Unit *u, Unit *slice);
 int unit_set_default_slice(Unit *u);
 
 const char *unit_description(Unit *u) _pure_;
-- 
2.31.1