core: add basic infrastructure to record unit activation information

Not wired in by any unit type yet, just the basic to allocate,
ref, deref and plug in to other unit types.
Includes recording the trigger unit name and passing it to the
triggered unit as TRIGGER_UNIT= env var.

1 files changed, 73 insertions, 1 deletions

diff --git a/src/core/unit.h b/src/core/unit.h
index 4dabbb9a3c..fc8edaade5 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -110,6 +110,75 @@ typedef union UnitDependencyInfo {
         } _packed_;
 } UnitDependencyInfo;
 
+/* Store information about why a unit was activated.
+ * We start with trigger units (.path/.timer), eventually it will be expanded to include more metadata. */
+typedef struct ActivationDetails {
+        unsigned n_ref;
+        UnitType trigger_unit_type;
+        char *trigger_unit_name;
+} ActivationDetails;
+
+/* For casting an activation event into the various unit-specific types */
+#define DEFINE_ACTIVATION_DETAILS_CAST(UPPERCASE, MixedCase, UNIT_TYPE)         \
+        static inline MixedCase* UPPERCASE(ActivationDetails *a) {              \
+                if (_unlikely_(!a || a->trigger_unit_type != UNIT_##UNIT_TYPE)) \
+                        return NULL;                                            \
+                                                                                \
+                return (MixedCase*) a;                                          \
+        }
+
+/* For casting the various unit types into a unit */
+#define ACTIVATION_DETAILS(u)                                         \
+        ({                                                            \
+                typeof(u) _u_ = (u);                                  \
+                ActivationDetails *_w_ = _u_ ? &(_u_)->meta : NULL;   \
+                _w_;                                                  \
+        })
+
+ActivationDetails *activation_details_new(Unit *trigger_unit);
+ActivationDetails *activation_details_ref(ActivationDetails *p);
+ActivationDetails *activation_details_unref(ActivationDetails *p);
+void activation_details_serialize(ActivationDetails *p, FILE *f);
+int activation_details_deserialize(const char *key, const char *value, ActivationDetails **info);
+int activation_details_append_env(ActivationDetails *info, char ***strv);
+int activation_details_append_pair(ActivationDetails *info, char ***strv);
+DEFINE_TRIVIAL_CLEANUP_FUNC(ActivationDetails*, activation_details_unref);
+
+typedef struct ActivationDetailsVTable {
+        /* How much memory does an object of this activation type need */
+        size_t object_size;
+
+        /* This should reset all type-specific variables. This should not allocate memory, and is called
+         * with zero-initialized data. It should hence only initialize variables that need to be set != 0. */
+        void (*init)(ActivationDetails *info, Unit *trigger_unit);
+
+        /* This should free all type-specific variables. It should be idempotent. */
+        void (*done)(ActivationDetails *info);
+
+        /* This should serialize all type-specific variables. */
+        void (*serialize)(ActivationDetails *info, FILE *f);
+
+        /* This should deserialize all type-specific variables, one at a time. */
+        int (*deserialize)(const char *key, const char *value, ActivationDetails **info);
+
+        /* This should format the type-specific variables for the env block of the spawned service,
+         * and return the number of added items. */
+        int (*append_env)(ActivationDetails *info, char ***strv);
+
+        /* This should append type-specific variables as key/value pairs for the D-Bus property of the job,
+         * and return the number of added pairs. */
+        int (*append_pair)(ActivationDetails *info, char ***strv);
+} ActivationDetailsVTable;
+
+extern const ActivationDetailsVTable * const activation_details_vtable[_UNIT_TYPE_MAX];
+
+static inline const ActivationDetailsVTable* ACTIVATION_DETAILS_VTABLE(const ActivationDetails *a) {
+        assert(a);
+        assert(a->trigger_unit_type < _UNIT_TYPE_MAX);
+
+        return activation_details_vtable[a->trigger_unit_type];
+}
+
 /* Newer LLVM versions don't like implicit casts from large pointer types to smaller enums, hence let's add
  * explicit type-safe helpers for that. */
 static inline UnitDependency UNIT_DEPENDENCY_FROM_PTR(const void *p) {
@@ -363,6 +432,9 @@ typedef struct Unit {
         JobMode on_success_job_mode;
         JobMode on_failure_job_mode;
 
+        /* If the job had a specific trigger that needs to be advertised (eg: a path unit), store it. */
+        ActivationDetails *activation_details;
+
         /* Tweaking the GC logic */
         CollectMode collect_mode;
 
@@ -813,7 +885,7 @@ bool unit_can_start(Unit *u) _pure_;
 bool unit_can_stop(Unit *u) _pure_;
 bool unit_can_isolate(Unit *u) _pure_;
 
-int unit_start(Unit *u);
+int unit_start(Unit *u, ActivationDetails *details);
 int unit_stop(Unit *u);
 int unit_reload(Unit *u);