Merge lp:~mterry/lightdm/multi-seat-vt-0 into lp:lightdm

[Michael Terry]

If we aren't in a multi-seat environment, pass logind XDG_VTNR=0 instead of 1 when using surfaceflinger.

If we aren't in a multi-seat environment, pass logind XDG_VTNR=0 instead of 1 when using surfaceflinger.

Logind treats VT numbers very differently depending on whether it determines it is in a multi-seat environment. If we are multi-seat, it does things "normally". But if we aren't, then it only accepts VTNR=0 and rejects anything else. It will assume whatever session it has is active.

Our previous solution was designed and tested on a mako device, which has CONFIG_VT=y (and thus has a /dev/tty0 device, and thus logind thinks is multi-seat). Oddly enough, it doesn't actually have working switching VTs. It just is stuck on VT1. Which is why we originally forced VTNR=1 for logind.

But maguro has CONFIG_VT=n, which stops /dev/tty0 from appearing. Which puts logind in a completely different code path that requires VTNR=0. So this branch detects which mode we are in, and passes the right VTNR for logind's benefit.

Tested on both mako and maguro devices.

[Michael Terry (mterry)]

This is slightly time-sensitive, as this is blocking lightdm landing in Ubuntu Touch.

So Robert, if you don't like something in this branch, could you please fix directly if it's simple, rather than going back and forth. And a release, even if just for this, would be welcome.

[lp:~mterry/lightdm/multi-seat-vt-0]

1799. By Michael Terry on 2013-09-24

Same logic for normal session

[Michael Terry (mterry)]

Guh! I am so frazzled, I accidentally pushed this branch to trunk. (If we have autolanding turned on, maybe we should guard trunk so we can't make these mistakes...) I'll leave it there rather than overwriting or reverting immediately, until you review this.

[Michael Terry (mterry)]

(And to be clear, the code I pushed to trunk -- i.e. this branch including r1799) was tested on both devices and works to my knowledge.)

[Michael Terry (mterry)]

cwayne also tested on his maguro and it worked.

[Robert Ancell (robert-ancell)]

No problem having behaviour changes in seat-surfaceflinger - this is only used by the phone so if it works go for it.

The name 'vt_can_multi_seat' is a bit odd, since it's not clear to me what the check does and how it relates to multi-seat support. I'm guessing it's actually checking (indirectly) something like vt_support_is_available()? Not going to block on the naming though.

review: Approve

[Michael Terry (mterry)]

I stole the terms from logind. It's basically asking "can I switch VTs?"

=== modified file 'src/seat-surfaceflinger.c'
--- src/seat-surfaceflinger.c	2013-09-19 17:23:31 +0000
+++ src/seat-surfaceflinger.c	2013-09-24 17:32:52 +0000
@@ -13,6 +13,7 @@
 
 #include "seat-surfaceflinger.h"
 #include "surfaceflinger-server.h"
+#include "vt.h"
 
 G_DEFINE_TYPE (SeatSurfaceflinger, seat_surfaceflinger, SEAT_TYPE);
 
@@ -48,7 +49,7 @@
     session_set_env (SESSION (greeter_session), "XDG_SEAT", xdg_seat);
 
     /* Fake the VT */
-    session_set_env (SESSION (greeter_session), "XDG_VTNR", "1");
+    session_set_env (SESSION (greeter_session), "XDG_VTNR", vt_can_multi_seat() ? "1" : "0");
 
     return greeter_session;
 }

=== modified file 'src/vt.c'
--- src/vt.c	2012-06-05 04:25:47 +0000
+++ src/vt.c	2013-09-24 17:32:52 +0000
@@ -36,6 +36,20 @@
     return fd;
 }
 
+gboolean
+vt_can_multi_seat (void)
+{
+    /* Quick check to see if we can multi seat.  This is intentionally the
+       same check logind does, just without actually reading from the files.
+       Existence will prove whether we have CONFIG_VT built into the kernel.
+       (Reading /dev/console like the rest of the code in this file isn't
+       sufficient -- it may still exist if tty0 doesn't and it may not work
+       in situations where tty0 does exist and thus logind will think we are
+       multi seat.) */
+    return access ("/dev/tty0", F_OK) == 0 &&
+           access ("/sys/class/tty/tty0/active", F_OK) == 0;
+}
+
 gint
 vt_get_active (void)
 {

=== modified file 'src/vt.h'
--- src/vt.h	2013-04-23 03:07:03 +0000
+++ src/vt.h	2013-09-24 17:32:52 +0000
@@ -14,6 +14,8 @@
 
 #include <glib-object.h>
 
+gboolean vt_can_multi_seat (void);
+
 gint vt_get_active (void);
 
 gint vt_get_unused (void);