parport: check exclusive access before register

As of now we were starting the registration process and after the device
is registered we were checking if the device can be used by the
parport. Now lets check it first so that we do not need to go through
the registration process only to fail at the end.
The original exclusive access check at the end is still there so that we
do not get any surprises if two different process registers its device
with same parport and with exclusive access at the same time.
Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/parport/share.c

@@ -708,6 +708,20 @@ parport_register_device(struct parport *port, const char *name,
 		}
 	}
 
+	if (flags & PARPORT_DEV_EXCL) {
+		if (port->physport->devices) {
+			/*
+			 * If a device is already registered and this new
+			 * device wants exclusive access, then no need to
+			 * continue as we can not grant exclusive access to
+			 * this device.
+			 */
+			pr_err("%s: cannot grant exclusive access for device %s\n",
+			       port->name, name);
+			return NULL;
+		}
+	}
+
 	/* We up our own module reference count, and that of the port
            on which a device is to be registered, to ensure that
            neither of us gets unloaded while we sleep in (e.g.)
@@ -827,6 +841,20 @@ parport_register_dev_model(struct parport *port, const char *name,
 		}
 	}
 
+	if (par_dev_cb->flags & PARPORT_DEV_EXCL) {
+		if (port->physport->devices) {
+			/*
+			 * If a device is already registered and this new
+			 * device wants exclusive access, then no need to
+			 * continue as we can not grant exclusive access to
+			 * this device.
+			 */
+			pr_err("%s: cannot grant exclusive access for device %s\n",
+			       port->name, name);
+			return NULL;
+		}
+	}
+
 	if (!try_module_get(port->ops->owner))
 		return NULL;