[PATCH v5 1/7] sysfs: attribute_group: allow registration of const attribute

["Thomas Weißschuh" <linux@weissschuh.net>]

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@weissschuh.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 9a25a2911652..e34d6af96abb 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_const;
+	};
 	const struct bin_attribute	*const *bin_attrs;
 };
 

-- 
2.51.1.dirty