[PATCH 1/6] sysfs: attribute_group: allow registration of const attribute

[Thomas Weißschuh]

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@xxxxxxxxxxxxxx>
---
 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;
+	};
 	union {
 		struct bin_attribute		**bin_attrs;
 		const struct bin_attribute	*const *bin_attrs_new;

-- 
2.48.1