Re: [PATCH] char: misc: Make the code for allocating minor in misc_register more concise

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Sep 09, 2025 at 04:58:35PM +0800, zhangjiao2 wrote:
> From: zhang jiao <zhangjiao2@cmss.chinamobile.com>
> 
> There is no need to check the registered misc dev in misc_list. 
> If misc_minor_alloc failed, it meens the minor is already alloced 
> and the misc dev is linked in misc_list.
> 
> Signed-off-by: zhang jiao <zhangjiao2@cmss.chinamobile.com>
> ---
>  drivers/char/misc.c | 32 +++++++-------------------------
>  1 file changed, 7 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/char/misc.c b/drivers/char/misc.c
> index a0aae0fc7926..fc2f5e8b2f95 100644
> --- a/drivers/char/misc.c
> +++ b/drivers/char/misc.c
> @@ -211,6 +211,7 @@ int misc_register(struct miscdevice *misc)
>  	dev_t dev;
>  	int err = 0;
>  	bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR);
> +	int minor = 0;
>  
>  	if (misc->minor > MISC_DYNAMIC_MINOR) {
>  		pr_err("Invalid fixed minor %d for miscdevice '%s'\n",
> @@ -221,32 +222,13 @@ int misc_register(struct miscdevice *misc)
>  	INIT_LIST_HEAD(&misc->list);
>  
>  	mutex_lock(&misc_mtx);
> -
> -	if (is_dynamic) {
> -		int i = misc_minor_alloc(misc->minor);
> -
> -		if (i < 0) {
> -			err = -EBUSY;
> -			goto out;
> -		}
> -		misc->minor = i;
> -	} else {
> -		struct miscdevice *c;
> -		int i;
> -
> -		list_for_each_entry(c, &misc_list, list) {
> -			if (c->minor == misc->minor) {
> -				err = -EBUSY;
> -				goto out;
> -			}
> -		}
> -
> -		i = misc_minor_alloc(misc->minor);
> -		if (i < 0) {
> -			err = -EBUSY;
> -			goto out;
> -		}
> +	minor = misc_minor_alloc(misc->minor);
> +	if (minor < 0) {
> +		err = -EBUSY;
> +		goto out;
>  	}
> +	if (is_dynamic)
> +		misc->minor = minor;
>  
>  	dev = MKDEV(MISC_MAJOR, misc->minor);
>  

Does this pass the new test suite for the misc code allocation logic
that we now have in the tree?  Or do we need to write a new test-case
for this codepath?

thanks,

greg k-h