xen/pcifront: Process failure for pcifront_(re)scan_root()

When pcifront_try_connect() finds no PCI roots, it falls back to calling
pcifront_scan_root() for 0000:00.  If that fails, it used to switch to
XenbusStateConnected and return success (because xenbus_switch_state()
currently always succeeds).

If pcifront_scan_root() fails, leave the XenbusState unchanged and return
an error code.

Similarly, pcifront_attach_devices() falls back to calling
pcifront_rescan_root() for 0000:00.  If that fails, it used to switch to
XenbusStateConnected and return an error code.

If pcifront_rescan_root() fails, leave the XenbusState unchanged and return
the error code.

[bhelgaas: changelog]
Signed-off-by: NChen Gang <gang.chen.5i5j@gmail.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Reviewed-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/pci/xen-pcifront.c

@@ -866,6 +866,11 @@ static int pcifront_try_connect(struct pcifront_device *pdev)
 		xenbus_dev_error(pdev->xdev, err,
 				 "No PCI Roots found, trying 0000:00");
 		err = pcifront_scan_root(pdev, 0, 0);
+		if (err) {
+			xenbus_dev_fatal(pdev->xdev, err,
+					 "Error scanning PCI root 0000:00");
+			goto out;
+		}
 		num_roots = 0;
 	} else if (err != 1) {
 		if (err == 0)
@@ -947,6 +952,11 @@ static int pcifront_attach_devices(struct pcifront_device *pdev)
 		xenbus_dev_error(pdev->xdev, err,
 				 "No PCI Roots found, trying 0000:00");
 		err = pcifront_rescan_root(pdev, 0, 0);
+		if (err) {
+			xenbus_dev_fatal(pdev->xdev, err,
+					 "Error scanning PCI root 0000:00");
+			goto out;
+		}
 		num_roots = 0;
 	} else if (err != 1) {
 		if (err == 0)