linux-kernel - [PATCH RESEND v2 1/7] sysfs: attribute_group: allow registration of const attribute

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Message-Id: <20250713-sysfs-const-attr-prep-v2-1-2f42510318a5@weissschuh.net>
Date: Sun, 13 Jul 2025 11:52:13 +0200
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 "Rafael J. Wysocki" <rafael@...nel.org>, Danilo Krummrich <dakr@...nel.org>
Cc: linux-kernel@...r.kernel.org, 
 Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH RESEND v2 1/7] 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@...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 f418aae4f1134f8126783d9e8eb575ba4278e927..a47092e837d9eb014894d1f7e49f0fd0f9a2e350 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 {
 		const struct bin_attribute	*const *bin_attrs;
 		const struct bin_attribute	*const *bin_attrs_new;

-- 
2.50.1