Xen: consolidate and simplify struct xenbus_driver instantiation

The 'name', 'owner', and 'mod_name' members are redundant with the
identically named fields in the 'driver' sub-structure. Rather than
switching each instance to specify these fields explicitly, introduce
a macro to simplify this.

Eliminate further redundancy by allowing the drvname argument to
DEFINE_XENBUS_DRIVER() to be blank (in which case the first entry from
the ID table will be used for .driver.name).

Also eliminate the questionable xenbus_register_{back,front}end()
wrappers - their sole remaining purpose was the checking of the
'owner' field, proper setting of which shouldn't be an issue anymore
when the macro gets used.

v2: Restore DRV_NAME for the driver name in xen-pciback.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/pci/xen-pcifront.c

@@ -1126,14 +1126,11 @@ static const struct xenbus_device_id xenpci_ids[] = {
 	{""},
 };
 
-static struct xenbus_driver xenbus_pcifront_driver = {
-	.name			= "pcifront",
-	.owner			= THIS_MODULE,
-	.ids			= xenpci_ids,
+static DEFINE_XENBUS_DRIVER(xenpci, "pcifront",
 	.probe			= pcifront_xenbus_probe,
 	.remove			= pcifront_xenbus_remove,
 	.otherend_changed	= pcifront_backend_changed,
-};
+);
 
 static int __init pcifront_init(void)
 {
@@ -1142,12 +1139,12 @@ static int __init pcifront_init(void)
 
 	pci_frontend_registrar(1 /* enable */);
 
-	return xenbus_register_frontend(&xenbus_pcifront_driver);
+	return xenbus_register_frontend(&xenpci_driver);
 }
 
 static void __exit pcifront_cleanup(void)
 {
-	xenbus_unregister_driver(&xenbus_pcifront_driver);
+	xenbus_unregister_driver(&xenpci_driver);
 	pci_frontend_registrar(0 /* disable */);
 }
 module_init(pcifront_init);