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, 19 insertions, 0 deletions

diff --git a/src/core/service.c b/src/core/service.c
index 58084e2f82..b46dd8bcdd 100644
--- a/src/core/service.c
+++ b/src/core/service.c
@@ -3195,6 +3195,22 @@ static int service_kill(Unit *u, KillWho who, int signo, sd_bus_error *error) {
         return unit_kill_common(u, who, signo, s->main_pid, s->control_pid, error);
 }
 
+static int service_main_pid(Unit *u) {
+        Service *s = SERVICE(u);
+
+        assert(s);
+
+        return s->main_pid;
+}
+
+static int service_control_pid(Unit *u) {
+        Service *s = SERVICE(u);
+
+        assert(s);
+
+        return s->control_pid;
+}
+
 static const char* const service_restart_table[_SERVICE_RESTART_MAX] = {
         [SERVICE_RESTART_NO] = "no",
         [SERVICE_RESTART_ON_SUCCESS] = "on-success",
@@ -3303,6 +3319,9 @@ const UnitVTable service_vtable = {
         .notify_cgroup_empty = service_notify_cgroup_empty_event,
         .notify_message = service_notify_message,
 
+        .main_pid = service_main_pid,
+        .control_pid = service_control_pid,
+
         .bus_name_owner_change = service_bus_name_owner_change,
 
         .bus_vtable = bus_service_vtable,