Re: [PATCH RFC 02/10] rtc: prepare for struct device member groups becoming a constant array

["yanjun.zhu" <yanjun.zhu@linux.dev>]

On 2/17/26 2:26 PM, Heiner Kallweit wrote:
> This prepares for making struct device member groups a constant array.
> The assignment groups = rtc->dev.groups would result in a "discarding
> const qualifier" warning with this change.
> No functional change intended.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
> ---
>   drivers/rtc/sysfs.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/rtc/sysfs.c b/drivers/rtc/sysfs.c
> index 4ab05e105a7..ae5e1252b4c 100644
> --- a/drivers/rtc/sysfs.c
> +++ b/drivers/rtc/sysfs.c
> @@ -308,7 +308,7 @@ const struct attribute_group **rtc_get_dev_attribute_groups(void)
>   int rtc_add_groups(struct rtc_device *rtc, const struct attribute_group **grps)
>   {
>   	size_t old_cnt = 0, add_cnt = 0, new_cnt;
> -	const struct attribute_group **groups, **old;
> +	const struct attribute_group **groups, *const *old;
>   
>   	if (grps) {
>   		for (groups = grps; *groups; groups++)
> @@ -320,9 +320,9 @@ int rtc_add_groups(struct rtc_device *rtc, const struct attribute_group **grps)
>   		return -EINVAL;
>   	}
>   
> -	groups = rtc->dev.groups;
> -	if (groups)
> -		for (; *groups; groups++)
> +	old = rtc->dev.groups;
> +	if (old)
> +		while (*old++)
>   			old_cnt++;

The change from for (; *groups; groups++) to while (*old++) is not 
functionally equivalent. In the while version, the post-increment old++ 
executes even when *old is NULL. This leaves the pointer old pointing 
one element past the NULL terminator. While old_cnt remains correct, 
this is a side-effect-heavy idiom that differs from standard kernel 
patterns and could be fragile if old is used later in the function.

Best Regards,
Zhu Yanjun

>   
>   	new_cnt = old_cnt + add_cnt + 1;