sysfs: attribute_group: allow registration of const attribute

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>
Link: https://patch.msgid.link/20251029-sysfs-const-attr-prep-v5-1-ea7d745acff4@weissschuh.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index 9a25a29116528fab77d667390dd3ef5957b86554..e34d6af96abb6aebf8b256ad13b18d652ff9291b 100644 (file)
--- 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;
 };