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 <fujita.tomonori@lab.ntt.co.jp>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: linux-scsi@vger.kernel.org
Cc: linux-block@vger.kernel.org
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ivan Orlov <ivan.orlov0322@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20230620180129.645646-8-gregkh@linuxfoundation.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/bsg.c

@@ -39,7 +39,7 @@ static inline struct bsg_device *to_bsg_device(struct inode *inode)
 #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)
@@ -208,7 +208,7 @@ struct bsg_device *bsg_register_queue(struct request_queue *q,
 		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);
@@ -242,15 +242,19 @@ static char *bsg_devnode(const struct device *dev, umode_t *mode)
 	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)
@@ -262,7 +266,7 @@ static int __init bsg_init(void)
 	return 0;
 
 destroy_bsg_class:
-	class_destroy(bsg_class);
+	class_unregister(&bsg_class);
 	return ret;
 }