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, 10 insertions, 0 deletions

diff --git a/src/core/busname.c b/src/core/busname.c
index bbe61af4f0..f4f433340c 100644
--- a/src/core/busname.c
+++ b/src/core/busname.c
@@ -999,6 +999,14 @@ static bool busname_supported(void) {
         return supported;
 }
 
+static int busname_control_pid(Unit *u) {
+        BusName *n = BUSNAME(u);
+
+        assert(n);
+
+        return n->control_pid;
+}
+
 static const char* const busname_result_table[_BUSNAME_RESULT_MAX] = {
         [BUSNAME_SUCCESS] = "success",
         [BUSNAME_FAILURE_RESOURCES] = "resources",
@@ -1052,6 +1060,8 @@ const UnitVTable busname_vtable = {
 
         .supported = busname_supported,
 
+        .control_pid = busname_control_pid,
+
         .bus_vtable = bus_busname_vtable,
 
         .status_message_formats = {