dbus-launch: if using X to define the session lifetime, do not poll stdin

dbus-launch --exit-with-session attempts to scope the session length
to various things:

- if DISPLAY points to an X server, exit when the X session ends
- if stdin is a terminal, exit when end-of-file is reached
- if both are true, exit when one of them happens, whichever is first
- if neither is true, fail

These are not particularly useful semantics: if the session is scoped to
the X session, then the terminal from which dbus-launch was launched
is irrelevant. This also causes practical problems when dbus-launch
consumes characters from the terminal from which it happens to have
been launched (some display managers, like slim and nodm, run users' X
sessions with stdin pointing to the terminal from which the init daemon
happens to have started the display manager during boot, usually tty1
on Linux).

Reviewed-by: Will Thompson <will.thompson@collabora.co.uk>
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=39197

1 files changed, 13 insertions, 4 deletions

diff --git a/tools/dbus-launch.c b/tools/dbus-launch.c
index 7b1bb37b..1ec9ae59 100644
--- a/tools/dbus-launch.c
+++ b/tools/dbus-launch.c
@@ -492,11 +492,20 @@ kill_bus_when_session_ends (void)
   else
     tty_fd = -1;
 
-  if (tty_fd >= 0)
-    verbose ("stdin isatty(), monitoring it\n");
+  if (x_fd >= 0)
+    {
+      verbose ("session lifetime is defined by X, not monitoring stdin\n");
+      tty_fd = -1;
+    }
+  else if (tty_fd >= 0)
+    {
+      verbose ("stdin isatty(), monitoring it\n");
+    }
   else
-    verbose ("stdin was not a TTY, not monitoring it\n");  
-  
+    {
+      verbose ("stdin was not a TTY, not monitoring it\n");
+    }
+
   if (tty_fd < 0 && x_fd < 0)
     {
       fprintf (stderr, "No terminal on standard input and no X display; cannot attach message bus to session lifetime\n");