xen/scsifront: use xenbus_setup_ring() and xenbus_teardown_ring()

Simplify scsifront's ring creation and removal via xenbus_setup_ring()
and xenbus_teardown_ring().

Signed-off-by: Juergen Gross <[e-mail]>
Reviewed-by: Boris Ostrovsky <[e-mail]>
Signed-off-by: Juergen Gross <[e-mail]>

drivers/scsi/xen-scsifront.c

···
 {
 	struct xenbus_device *dev = info->dev;
 	struct vscsiif_sring *sring;
-	grant_ref_t gref;
-	int err = -ENOMEM;
+	int err;
 
 	/***** Frontend to Backend ring start *****/
-	sring = (struct vscsiif_sring *)__get_free_page(GFP_KERNEL);
-	if (!sring) {
-		xenbus_dev_fatal(dev, err,
-			"fail to allocate shared ring (Front to Back)");
+	err = xenbus_setup_ring(dev, GFP_KERNEL, (void **)&sring, 1,
+				&info->ring_ref);
+	if (err)
 		return err;
-	}
-	SHARED_RING_INIT(sring);
-	FRONT_RING_INIT(&info->ring, sring, PAGE_SIZE);
 
-	err = xenbus_grant_ring(dev, sring, 1, &gref);
-	if (err < 0) {
-		free_page((unsigned long)sring);
-		xenbus_dev_fatal(dev, err,
-			"fail to grant shared ring (Front to Back)");
-		return err;
-	}
-	info->ring_ref = gref;
+	XEN_FRONT_RING_INIT(&info->ring, sring, PAGE_SIZE);
 
 	err = xenbus_alloc_evtchn(dev, &info->evtchn);
 	if (err) {
···
 free_irq:
 	unbind_from_irqhandler(info->irq, info);
 free_gnttab:
-	gnttab_end_foreign_access(info->ring_ref,
-				  (unsigned long)info->ring.sring);
+	xenbus_teardown_ring((void **)&sring, 1, &info->ring_ref);
 
 	return err;
 }
···
 static void scsifront_free_ring(struct vscsifrnt_info *info)
 {
 	unbind_from_irqhandler(info->irq, info);
-	gnttab_end_foreign_access(info->ring_ref,
-				  (unsigned long)info->ring.sring);
+	xenbus_teardown_ring((void **)&info->ring.sring, 1, &info->ring_ref);
 }
 
 static int scsifront_init_ring(struct vscsifrnt_info *info)