linux-kernel - Re: [PATCH 1/6] sysfs: attribute_group: allow registration of const attribute

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Message-ID: <2025011714-skeleton-bring-3e77@gregkh>
Date: Fri, 17 Jan 2025 08:01:00 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Thomas Weißschuh <linux@...ssschuh.net>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] sysfs: attribute_group: allow registration of const
 attribute

On Thu, Jan 16, 2025 at 06:32:27PM +0100, Thomas Weißschuh wrote:
> To be able to constify instances of struct attribute it has to be
> possible to add them to struct attribute_group.
> The current type of the attrs member however is not compatible with that.
> Introduce a union that allows registration of both const and non-const
> attributes to enable a piecewise transition.
> As both union member types are compatible no logic needs to be adapted.
> 
> Technically it is now possible register a const struct
> attribute and receive it as mutable pointer in the callbacks.
> This is a soundness issue.
> But this same soundness issue already exists today in
> sysfs_create_file().
> Also the struct definition and callback implementation are always
> closely linked and are meant to be moved to const in lockstep.
> 
> Similar to commit 906c508afdca ("sysfs: attribute_group: allow registration of const bin_attribute")
> 
> Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
> ---
>  include/linux/sysfs.h | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
> index 0f2fcd244523f050c5286f19d4fe1846506f9214..f5e25bed777a6a6e717f10973f1abcd12111f5c5 100644
> --- a/include/linux/sysfs.h
> +++ b/include/linux/sysfs.h
> @@ -105,7 +105,10 @@ struct attribute_group {
>  	size_t			(*bin_size)(struct kobject *,
>  					    const struct bin_attribute *,
>  					    int);
> -	struct attribute	**attrs;
> +	union {
> +		struct attribute	**attrs;
> +		const struct attribute	*const *attrs_new;
> +	};

I'm all for the idea, BUT, let's finish up doing this one:

>  	union {
>  		struct bin_attribute		**bin_attrs;
>  		const struct bin_attribute	*const *bin_attrs_new;

first please.

That way we can see just how "easy" the switch from _new to not-new goes :)

thanks,

greg k-h