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, 1 insertions, 0 deletions

diff --git a/src/login/logind-user.h b/src/login/logind-user.h
index 0062880560..b0fefe9b9c 100644
--- a/src/login/logind-user.h
+++ b/src/login/logind-user.h
@@ -61,6 +61,7 @@ struct User {
 
         bool in_gc_queue:1;
         bool started:1;
+        bool stopping:1;
 
         LIST_HEAD(Session, sessions);
         LIST_FIELDS(User, gc_queue);