Re: [PATCH v3 6/7] samples/kobject: constify 'struct foo_attribute'

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Aug 11, 2025 at 11:14:32AM +0200, Thomas Weißschuh wrote:
> Showcase and test the new 'struct attribute' constification facilities.
> 
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> ---
>  samples/kobject/kset-example.c | 33 +++++++++++++++++----------------
>  1 file changed, 17 insertions(+), 16 deletions(-)
> 
> diff --git a/samples/kobject/kset-example.c b/samples/kobject/kset-example.c
> index 1aac595ed9498b30448485a60d9376cb5b5ea1d3..98aac6940f51f3312b44083a9d4ffe7afed1dba7 100644
> --- a/samples/kobject/kset-example.c
> +++ b/samples/kobject/kset-example.c
> @@ -37,10 +37,11 @@ struct foo_obj {
>  /* a custom attribute that works just for a struct foo_obj. */
>  struct foo_attribute {
>  	struct attribute attr;
> -	ssize_t (*show)(struct foo_obj *foo, struct foo_attribute *attr, char *buf);
> -	ssize_t (*store)(struct foo_obj *foo, struct foo_attribute *attr, const char *buf, size_t count);
> +	ssize_t (*show)(struct foo_obj *foo, const struct foo_attribute *attr, char *buf);
> +	ssize_t (*store)(struct foo_obj *foo, const struct foo_attribute *attr,
> +			 const char *buf, size_t count);
>  };
> -#define to_foo_attr(x) container_of(x, struct foo_attribute, attr)
> +#define to_foo_attr(x) container_of_const(x, struct foo_attribute, attr)
>  
>  /*
>   * The default show function that must be passed to sysfs.  This will be
> @@ -53,7 +54,7 @@ static ssize_t foo_attr_show(struct kobject *kobj,
>  			     struct attribute *attr,
>  			     char *buf)
>  {
> -	struct foo_attribute *attribute;
> +	const struct foo_attribute *attribute;
>  	struct foo_obj *foo;
>  
>  	attribute = to_foo_attr(attr);
> @@ -73,7 +74,7 @@ static ssize_t foo_attr_store(struct kobject *kobj,
>  			      struct attribute *attr,
>  			      const char *buf, size_t len)
>  {
> -	struct foo_attribute *attribute;
> +	const struct foo_attribute *attribute;
>  	struct foo_obj *foo;
>  
>  	attribute = to_foo_attr(attr);
> @@ -109,13 +110,13 @@ static void foo_release(struct kobject *kobj)
>  /*
>   * The "foo" file where the .foo variable is read from and written to.
>   */
> -static ssize_t foo_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
> +static ssize_t foo_show(struct foo_obj *foo_obj, const struct foo_attribute *attr,
>  			char *buf)
>  {
>  	return sysfs_emit(buf, "%d\n", foo_obj->foo);
>  }
>  
> -static ssize_t foo_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
> +static ssize_t foo_store(struct foo_obj *foo_obj, const struct foo_attribute *attr,
>  			 const char *buf, size_t count)
>  {
>  	int ret;
> @@ -128,14 +129,14 @@ static ssize_t foo_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
>  }
>  
>  /* Sysfs attributes cannot be world-writable. */
> -static struct foo_attribute foo_attribute =
> +static const struct foo_attribute foo_attribute =
>  	__ATTR(foo, 0664, foo_show, foo_store);
>  
>  /*
>   * More complex function where we determine which variable is being accessed by
>   * looking at the attribute for the "baz" and "bar" files.
>   */
> -static ssize_t b_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
> +static ssize_t b_show(struct foo_obj *foo_obj, const struct foo_attribute *attr,
>  		      char *buf)
>  {
>  	int var;
> @@ -147,7 +148,7 @@ static ssize_t b_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
>  	return sysfs_emit(buf, "%d\n", var);
>  }
>  
> -static ssize_t b_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
> +static ssize_t b_store(struct foo_obj *foo_obj, const struct foo_attribute *attr,
>  		       const char *buf, size_t count)
>  {
>  	int var, ret;
> @@ -163,16 +164,16 @@ static ssize_t b_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
>  	return count;
>  }
>  
> -static struct foo_attribute baz_attribute =
> +static const struct foo_attribute baz_attribute =
>  	__ATTR(baz, 0664, b_show, b_store);

We really should make this ATTR_RW() one of these days.

> -static struct foo_attribute bar_attribute =
> +static const struct foo_attribute bar_attribute =
>  	__ATTR(bar, 0664, b_show, b_store);

This one too.

Actually almost all existing users of __ATTR() should be fixed up so we
can just remove that (special modes can use the __ATTR_*_MODE() macro)

But that's separate from this series, sorry for the noise.

greg k-h