xen/arm: compile and run xenbus

bind_evtchn_to_irqhandler can legitimately return 0 (irq 0): it is not
an error.

If Linux is running as an HVM domain and is running as Dom0, use
xenstored_local_init to initialize the xenstore page and event channel.

Changes in v4:
- do not xs_reset_watches on dom0.

Changes in v2:
- refactor xenbus_init.

Signed-off-by: Stefano Stabellini <[e-mail]>
[v5: Fixed case switch indentations]
Signed-off-by: Konrad Rzeszutek Wilk <[e-mail]>

drivers/xen/xenbus/xenbus_comms.c

···
 		int err;
 		err = bind_evtchn_to_irqhandler(xen_store_evtchn, wake_waiting,
 						0, "xenbus", &xb_waitq);
-		if (err <= 0) {
+		if (err < 0) {
 			printk(KERN_ERR "XENBUS request irq failed %i\n", err);
 			return err;
 		}

drivers/xen/xenbus/xenbus_probe.c

···
 	return err;
 }
 
+enum xenstore_init {
+	UNKNOWN,
+	PV,
+	HVM,
+	LOCAL,
+};
 static int __init xenbus_init(void)
 {
 	int err = 0;
+	enum xenstore_init usage = UNKNOWN;
+	uint64_t v = 0;
 
 	if (!xen_domain())
 		return -ENODEV;
 
 	xenbus_ring_ops_init();
 
-	if (xen_hvm_domain()) {
-		uint64_t v = 0;
+	if (xen_pv_domain())
+		usage = PV;
+	if (xen_hvm_domain())
+		usage = HVM;
+	if (xen_hvm_domain() && xen_initial_domain())
+		usage = LOCAL;
+	if (xen_pv_domain() && !xen_start_info->store_evtchn)
+		usage = LOCAL;
+	if (xen_pv_domain() && xen_start_info->store_evtchn)
+		xenstored_ready = 1;
+
+	switch (usage) {
+	case LOCAL:
+		err = xenstored_local_init();
+		if (err)
+			goto out_error;
+		xen_store_interface = mfn_to_virt(xen_store_mfn);
+		break;
+	case PV:
+		xen_store_evtchn = xen_start_info->store_evtchn;
+		xen_store_mfn = xen_start_info->store_mfn;
+		xen_store_interface = mfn_to_virt(xen_store_mfn);
+		break;
+	case HVM:
 		err = hvm_get_parameter(HVM_PARAM_STORE_EVTCHN, &v);
 		if (err)
 			goto out_error;
···
 		if (err)
 			goto out_error;
 		xen_store_mfn = (unsigned long)v;
-		xen_store_interface = ioremap(xen_store_mfn << PAGE_SHIFT, PAGE_SIZE);
-	} else {
-		xen_store_evtchn = xen_start_info->store_evtchn;
-		xen_store_mfn = xen_start_info->store_mfn;
-		if (xen_store_evtchn)
-			xenstored_ready = 1;
-		else {
-			err = xenstored_local_init();
-			if (err)
-				goto out_error;
-		}
-		xen_store_interface = mfn_to_virt(xen_store_mfn);
+		xen_store_interface =
+			ioremap(xen_store_mfn << PAGE_SHIFT, PAGE_SIZE);
+		break;
+	default:
+		pr_warn("Xenstore state unknown\n");
+		break;
 	}
 
 	/* Initialize the interface to xenstore. */

drivers/xen/xenbus/xenbus_xs.c

···
 #include <linux/rwsem.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <asm/xen/hypervisor.h>
 #include <xen/xenbus.h>
 #include <xen/xen.h>
 #include "xenbus_comms.h"
···
 {
 	int err, supported = 0;
 
-	if (!xen_hvm_domain())
+	if (!xen_hvm_domain() || xen_initial_domain())
 		return;
 
 	err = xenbus_scanf(XBT_NIL, "control",