core,systemctl: add bus API to retrieve processes of a unit

This adds a new GetProcesses() bus call to the Unit object which returns an
array consisting of all PIDs, their process names, as well as their full cgroup
paths. This is then used by "systemctl status" to show the per-unit process
tree.

This has the benefit that the client-side no longer needs to access the
cgroupfs directly to show the process tree of a unit. Instead, it now uses this
new API, which means it also works if -H or -M are used correctly, as the
information from the specific host is used, and not the one from the local
system.

Fixes: #2945

1 files changed, 9 insertions, 0 deletions

diff --git a/src/core/unit.h b/src/core/unit.h
index cfdac852a5..5909652976 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -390,6 +390,12 @@ struct UnitVTable {
         /* Returns the next timeout of a unit */
         int (*get_timeout)(Unit *u, usec_t *timeout);
 
+        /* Returns the main PID if there is any defined, or 0. */
+        pid_t (*main_pid)(Unit *u);
+
+        /* Returns the main PID if there is any defined, or 0. */
+        pid_t (*control_pid)(Unit *u);
+
         /* This is called for each unit type and should be used to
          * enumerate existing devices and load them. However,
          * everything that is loaded here should still stay in
@@ -601,6 +607,9 @@ bool unit_type_supported(UnitType t);
 
 bool unit_is_pristine(Unit *u);
 
+pid_t unit_control_pid(Unit *u);
+pid_t unit_main_pid(Unit *u);
+
 static inline bool unit_supported(Unit *u) {
         return unit_type_supported(u->type);
 }