Prefer vt(4) for UEFI boot

The UEFI framebuffer driver vt_efifb requires vt(4), so add a mechanism
for the startup routine to set the preferred console.  This change is
ugly because console init happens very early in the boot, making a
cleaner interface difficult.  This change is intended only to facilitate
the sc(4) / vt(4) transition, and can be reverted once vt(4) is the
default.

sys/amd64/amd64/machdep.c

@@ -1954,6 +1954,14 @@ hammer_time(u_int64_t modulep, u_int64_t physfree)
 	 */
 	clock_init();
 
+	/*
+	 * Use vt(4) by default for UEFI boot (during the sc(4)/vt(4)
+	 * transition).
+	 */
+	if (preload_search_info(kmdp, MODINFO_METADATA | MODINFOMD_EFI_MAP) !=
+	    NULL)
+		vty_set_preferred(VTY_VT);
+
 	/*
 	 * Initialize the console before we print anything out.
 	 */

sys/kern/kern_cons.c

@@ -652,6 +652,7 @@ sysbeep(int pitch __unused, int period __unused)
 /*
  * Temporary support for sc(4) to vt(4) transition.
  */
+static unsigned vty_prefer;
 static char vty_name[16];
 SYSCTL_STRING(_kern, OID_AUTO, vty, CTLFLAG_RDTUN | CTLFLAG_NOFETCH, vty_name,
     0, "Console vty driver");
@@ -676,6 +677,10 @@ vty_enabled(unsigned vty)
 				break;
 			}
 #endif
+			if (vty_prefer != 0) {
+				vty_selected = vty_prefer;
+				break;
+			}
 #if defined(DEV_SC)
 			vty_selected = VTY_SC;
 #elif defined(DEV_VT)
@@ -691,3 +696,16 @@ vty_enabled(unsigned vty)
 	return ((vty_selected & vty) != 0);
 }
 
+void
+vty_set_preferred(unsigned vty)
+{
+
+	vty_prefer = vty;
+#if !defined(DEV_SC)
+	vty_prefer &= ~DEV_SC;
+#endif
+#if !defined(DEV_VT)
+	vty_prefer &= ~DEV_VT;
+#endif
+}
+

sys/sys/cons.h

@@ -137,6 +137,7 @@ void	constty_clear(void);
 #define	VTY_SC 0x01
 #define	VTY_VT 0x02
 int	vty_enabled(unsigned int);
+void	vty_set_preferred(unsigned int);
 
 #endif /* _KERNEL */