xenbus: don't rely on xen_initial_domain to detect local xenstore

The xenstore daemon does not have to run in the xen initial domain;
however, Linux currently uses xen_initial_domain to test if a loopback
event channel should be used instead of the event channel provided in
Xen's start_info structure. Instead, if the event channel passed in the
start_info structure is not valid, assume that this domain will run
xenstored locally and set up the event channel.
Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Reviewed-by: Ian Campbell <Ian.Campbell@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/xenbus/xenbus_probe.c

@@ -696,27 +696,19 @@ static int __init xenbus_probe_initcall(void)
 
 device_initcall(xenbus_probe_initcall);
 
-static int __init xenbus_init(void)
+/* Set up event channel for xenstored which is run as a local process
+ * (this is normally used only in dom0)
+ */
+static int __init xenstored_local_init(void)
 {
 	int err = 0;
 	unsigned long page = 0;
-
-	DPRINTK("");
-
-	err = -ENODEV;
-	if (!xen_domain())
-		return err;
-
-	/*
-	 * Domain0 doesn't have a store_evtchn or store_mfn yet.
-	 */
-	if (xen_initial_domain()) {
 	struct evtchn_alloc_unbound alloc_unbound;
 
 	/* Allocate Xenstore page */
 	page = get_zeroed_page(GFP_KERNEL);
 	if (!page)
-			goto out_error;
+		goto out_err;
 
 	xen_store_mfn = xen_start_info->store_mfn =
 		pfn_to_mfn(virt_to_phys((void *)page) >>
@@ -729,14 +721,27 @@ static int __init xenbus_init(void)
 	err = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound,
 					  &alloc_unbound);
 	if (err == -ENOSYS)
-			goto out_error;
+		goto out_err;
 
 	BUG_ON(err);
 	xen_store_evtchn = xen_start_info->store_evtchn =
 		alloc_unbound.port;
 
-		xen_store_interface = mfn_to_virt(xen_store_mfn);
-	} else {
+	return 0;
+
+ out_err:
+	if (page != 0)
+		free_page(page);
+	return err;
+}
+
+static int __init xenbus_init(void)
+{
+	int err = 0;
+
+	if (!xen_domain())
+		return -ENODEV;
+
 	if (xen_hvm_domain()) {
 		uint64_t v = 0;
 		err = hvm_get_parameter(HVM_PARAM_STORE_EVTCHN, &v);
@@ -751,9 +756,14 @@ static int __init xenbus_init(void)
 	} else {
 		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);
+		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);
 	}
 
 	/* Initialize the interface to xenstore. */
@@ -772,12 +782,7 @@ static int __init xenbus_init(void)
 	proc_mkdir("xen", NULL);
 #endif
 
-	return 0;
-
  out_error:
-	if (page != 0)
-		free_page(page);
-
 	return err;
 }