bsg: make bsg_class a static const structure

Now that the driver core allows for struct class to be in read-only
memory, move the bsg_class structure to be declared at build time
placing it into read-only memory, instead of having to be dynamically
allocated at boot time.

Cc: FUJITA Tomonori <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Suggested-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Ivan Orlov <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jens Axboe <[e-mail]>

block/bsg.c

···
 #define BSG_MAX_DEVS		32768
 
 static DEFINE_IDA(bsg_minor_ida);
-static struct class *bsg_class;
+static const struct class bsg_class;
 static int bsg_major;
 
 static unsigned int bsg_timeout(struct bsg_device *bd, struct sg_io_v4 *hdr)
···
 		return ERR_PTR(ret);
 	}
 	bd->device.devt = MKDEV(bsg_major, ret);
-	bd->device.class = bsg_class;
+	bd->device.class = &bsg_class;
 	bd->device.parent = parent;
 	bd->device.release = bsg_device_release;
 	dev_set_name(&bd->device, "%s", name);
···
 	return kasprintf(GFP_KERNEL, "bsg/%s", dev_name(dev));
 }
 
+static const struct class bsg_class = {
+	.name		= "bsg",
+	.devnode	= bsg_devnode,
+};
+
 static int __init bsg_init(void)
 {
 	dev_t devid;
 	int ret;
 
-	bsg_class = class_create("bsg");
-	if (IS_ERR(bsg_class))
-		return PTR_ERR(bsg_class);
-	bsg_class->devnode = bsg_devnode;
+	ret = class_register(&bsg_class);
+	if (ret)
+		return ret;
 
 	ret = alloc_chrdev_region(&devid, 0, BSG_MAX_DEVS, "bsg");
 	if (ret)
···
 	return 0;
 
 destroy_bsg_class:
-	class_destroy(bsg_class);
+	class_unregister(&bsg_class);
 	return ret;
 }