Re: [PATCH] bcachefs: chardev: make bch_chardev_class constant

[Hongbo Li]

On 2024/3/6 4:21, Ricardo B. Marliere wrote:
> Since commit 43a7206b0963 ("driver core: class: make class_register() take
> a const *"), the driver core allows for struct class to be in read-only
> memory, so move the bch_chardev_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: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Suggested-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Ricardo B. Marliere <ricardo@xxxxxxxxxxxx>
> ---
>   fs/bcachefs/chardev.c | 23 ++++++++++++-----------
>   1 file changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/fs/bcachefs/chardev.c b/fs/bcachefs/chardev.c
> index 226b39c17667..af587453fd3d 100644
> --- a/fs/bcachefs/chardev.c
> +++ b/fs/bcachefs/chardev.c
> @@ -940,7 +940,9 @@ static const struct file_operations bch_chardev_fops = {
>   };
>   
>   static int bch_chardev_major;
> -static struct class *bch_chardev_class;
> +static const struct class bch_chardev_class = {
> +	.name = "bcachefs",
> +};
>   static struct device *bch_chardev;
>   
>   void bch2_fs_chardev_exit(struct bch_fs *c)
> @@ -957,7 +959,7 @@ int bch2_fs_chardev_init(struct bch_fs *c)
>   	if (c->minor < 0)
>   		return c->minor;
>   
> -	c->chardev = device_create(bch_chardev_class, NULL,
> +	c->chardev = device_create(&bch_chardev_class, NULL,
>   				   MKDEV(bch_chardev_major, c->minor), c,
>   				   "bcachefs%u-ctl", c->minor);
>   	if (IS_ERR(c->chardev))
> @@ -968,26 +970,25 @@ int bch2_fs_chardev_init(struct bch_fs *c)
>   
>   void bch2_chardev_exit(void)
>   {
> -	if (!IS_ERR_OR_NULL(bch_chardev_class))
> -		device_destroy(bch_chardev_class,
> -			       MKDEV(bch_chardev_major, U8_MAX));
> -	if (!IS_ERR_OR_NULL(bch_chardev_class))
> -		class_destroy(bch_chardev_class);
> +	device_destroy(&bch_chardev_class, MKDEV(bch_chardev_major, U8_MAX));
> +	class_unregister(&bch_chardev_class);
>   	if (bch_chardev_major > 0)
>   		unregister_chrdev(bch_chardev_major, "bcachefs");
>   }
>   
>   int __init bch2_chardev_init(void)
>   {
> +	int ret;
> +
>   	bch_chardev_major = register_chrdev(0, "bcachefs-ctl", &bch_chardev_fops);
>   	if (bch_chardev_major < 0)
>   		return bch_chardev_major;
>   
> -	bch_chardev_class = class_create("bcachefs");
> -	if (IS_ERR(bch_chardev_class))
> -		return PTR_ERR(bch_chardev_class);
> +	ret = class_register(&bch_chardev_class);
> +	if (ret)
Here, I think you should call class_unregister to relase resource which 
allocated before. And the same thing shoud be done in other exception exit.
> +		return ret;
>   
> -	bch_chardev = device_create(bch_chardev_class, NULL,
> +	bch_chardev = device_create(&bch_chardev_class, NULL,
>   				    MKDEV(bch_chardev_major, U8_MAX),
>   				    NULL, "bcachefs-ctl");
>   	if (IS_ERR(bch_chardev))
like here..
> ---
> base-commit: 90d35da658da8cff0d4ecbb5113f5fac9d00eb72
> change-id: 20240305-bcachefs-27a4bb8b9f4f
>
> Best regards,