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

Simplify pcifront's shared page 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/pci/xen-pcifront.c

···
 	if (pdev == NULL)
 		goto out;
 
-	pdev->sh_info =
-	    (struct xen_pci_sharedinfo *)__get_free_page(GFP_KERNEL);
-	if (pdev->sh_info == NULL) {
+	if (xenbus_setup_ring(xdev, GFP_KERNEL, (void **)&pdev->sh_info, 1,
+			      &pdev->gnt_ref)) {
 		kfree(pdev);
 		pdev = NULL;
 		goto out;
···
 	spin_lock_init(&pdev->sh_info_lock);
 
 	pdev->evtchn = INVALID_EVTCHN;
-	pdev->gnt_ref = INVALID_GRANT_REF;
 	pdev->irq = -1;
 
 	INIT_WORK(&pdev->op_work, pcifront_do_aer);
···
 	if (pdev->evtchn != INVALID_EVTCHN)
 		xenbus_free_evtchn(pdev->xdev, pdev->evtchn);
 
-	if (pdev->gnt_ref != INVALID_GRANT_REF)
-		gnttab_end_foreign_access(pdev->gnt_ref,
-					  (unsigned long)pdev->sh_info);
-	else
-		free_page((unsigned long)pdev->sh_info);
+	xenbus_teardown_ring((void **)&pdev->sh_info, 1, &pdev->gnt_ref);
 
 	dev_set_drvdata(&pdev->xdev->dev, NULL);
 
···
 {
 	int err = 0;
 	struct xenbus_transaction trans;
-	grant_ref_t gref;
-
-	err = xenbus_grant_ring(pdev->xdev, pdev->sh_info, 1, &gref);
-	if (err < 0)
-		goto out;
-
-	pdev->gnt_ref = gref;
 
 	err = xenbus_alloc_evtchn(pdev->xdev, &pdev->evtchn);
 	if (err)