xen-console: add save/restore

Add code to:

 1. Deal with the console page being canonicalized.  During save, the
    console's mfn in the start_info structure is canonicalized to a pfn.
    In order to deal with that, we always use a copy of the pfn and
    indirect off that all the time.  However, we fall back to using the
    mfn if the pfn hasn't been initialized yet.

 2. Restore the console event channel, and rebind it to the existing irq.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

drivers/char/hvc_xen.c

@@ -39,9 +39,14 @@ static int xencons_irq;
 
 /* ------------------------------------------------------------------ */
 
+static unsigned long console_pfn = ~0ul;
+
 static inline struct xencons_interface *xencons_interface(void)
 {
+	if (console_pfn == ~0ul)
 		return mfn_to_virt(xen_start_info->console.domU.mfn);
+	else
+		return __va(console_pfn << PAGE_SHIFT);
 }
 
 static inline void notify_daemon(void)
@@ -101,20 +106,32 @@ static int __init xen_init(void)
 {
 	struct hvc_struct *hp;
 
-	if (!is_running_on_xen())
-		return 0;
+	if (!is_running_on_xen() ||
+	    is_initial_xendomain() ||
+	    !xen_start_info->console.domU.evtchn)
+		return -ENODEV;
 
 	xencons_irq = bind_evtchn_to_irq(xen_start_info->console.domU.evtchn);
 	if (xencons_irq < 0)
-		xencons_irq = 0 /* NO_IRQ */;
+		xencons_irq = 0; /* NO_IRQ */
+
 	hp = hvc_alloc(HVC_COOKIE, xencons_irq, &hvc_ops, 256);
 	if (IS_ERR(hp))
 		return PTR_ERR(hp);
 
 	hvc = hp;
+
+	console_pfn = mfn_to_pfn(xen_start_info->console.domU.mfn);
+
 	return 0;
 }
 
+void xen_console_resume(void)
+{
+	if (xencons_irq)
+		rebind_evtchn_irq(xen_start_info->console.domU.evtchn, xencons_irq);
+}
+
 static void __exit xen_fini(void)
 {
 	if (hvc)

include/xen/hvc-console.h

@@ -3,6 +3,8 @@
 
 extern struct console xenboot_console;
 
+void xen_console_resume(void);
+
 void xen_raw_console_write(const char *str);
 void xen_raw_printk(const char *fmt, ...);