logind: rework session shutdown logic

Simplify the shutdown logic a bit:

- Keep the session FIFO around in the PAM module, even after the session
  shutdown hook has been finished. This allows logind to track precisely
  when the PAM handler goes away.

- In the ReleaseSession() call start a timer, that will stop terminate
  the session when elapsed.

- Never fiddle with the KillMode of scopes to configure whether user
  processes should be killed or not. Instead, simply leave the scope
  units around when we terminate a session whose processes should not be
  killed.

- When killing is enabled, stop the session scope on FIFO EOF or after
  the ReleaseSession() timeout. When killing is disabled, simply tell
  PID 1 to abandon the scope.

Because the scopes stay around and hence all processes are always member
of a scope, the system shutdown logic should be more robust, as the
scopes can be shutdown as part of the usual shutdown logic.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/login/logind-session.h b/src/login/logind-session.h
index 7bf193203..42552bc2b 100644
--- a/src/login/logind-session.h
+++ b/src/login/logind-session.h
@@ -110,9 +110,12 @@ struct Session {
 
         bool in_gc_queue:1;
         bool started:1;
+        bool stopping:1;
 
         sd_bus_message *create_message;
 
+        sd_event_source *timer_event_source;
+
         char *controller;
         Hashmap *devices;
 
@@ -132,10 +135,10 @@ bool session_is_active(Session *s);
 int session_get_idle_hint(Session *s, dual_timestamp *t);
 void session_set_idle_hint(Session *s, bool b);
 int session_create_fifo(Session *s);
-void session_remove_fifo(Session *s);
 int session_start(Session *s);
 int session_stop(Session *s);
 int session_finalize(Session *s);
+void session_release(Session *s);
 int session_save(Session *s);
 int session_load(Session *s);
 int session_kill(Session *s, KillWho who, int signo);