[PATCH 3/4] kobject: Allow the constification of kobject attributes

[Thomas Weißschuh]

Allow kobject attribute to reside in read-only memory.
Both const and non-const attributes are handled by the utility macros
and attributes can be migrated one-by-one.

Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
---
 include/linux/kobject.h | 57 +++++++++++++++++++++++++++++++++++++++++++------
 lib/kobject.c           |  8 +++++--
 2 files changed, 57 insertions(+), 8 deletions(-)

diff --git a/include/linux/kobject.h b/include/linux/kobject.h
index 975a5361fb60..2c5b386d441c 100644
--- a/include/linux/kobject.h
+++ b/include/linux/kobject.h
@@ -138,17 +138,62 @@ struct kset_uevent_ops {
 
 struct kobj_attribute {
 	struct attribute attr;
-	ssize_t (*show)(struct kobject *kobj, struct kobj_attribute *attr,
-			char *buf);
-	ssize_t (*store)(struct kobject *kobj, struct kobj_attribute *attr,
-			 const char *buf, size_t count);
+	__SYSFS_FUNCTION_ALTERNATIVE(
+		ssize_t (*show)(struct kobject *kobj, struct kobj_attribute *attr, char *buf);
+		ssize_t (*show_const)(struct kobject *kobj, const struct kobj_attribute *attr,
+				      char *buf);
+	);
+	__SYSFS_FUNCTION_ALTERNATIVE(
+		ssize_t (*store)(struct kobject *kobj, struct kobj_attribute *attr,
+				 const char *buf, size_t count);
+		ssize_t (*store_const)(struct kobject *kobj, const struct kobj_attribute *attr,
+				       const char *buf, size_t count);
+	);
 };
 
+typedef ssize_t __kobj_show_handler_const(struct kobject *kobj, const struct kobj_attribute *attr,
+					  char *buf);
+typedef ssize_t __kobj_store_handler_const(struct kobject *kobj, const struct kobj_attribute *attr,
+					   const char *buf, size_t count);
+
+#ifdef CONFIG_CFI
+
+#define __KOBJ_ATTR_SHOW_STORE(_show, _store)						\
+	.show		= _Generic(_show,						\
+			  __kobj_show_handler_const * : NULL,				\
+			  default : _show						\
+	),										\
+	.show_const	= _Generic(_show,						\
+			  __kobj_show_handler_const * : _show,				\
+			  default : NULL						\
+	),										\
+	.store		= _Generic(_store,						\
+			  __kobj_store_handler_const * : NULL,				\
+			  default : _store						\
+	),										\
+	.store_const	= _Generic(_store,						\
+			  __kobj_store_handler_const * : _store,			\
+			  default : NULL \
+	),
+
+#else
+
+#define __KOBJ_ATTR_SHOW_STORE(_show, _store)						\
+	.show		= _Generic(_show,						\
+			  __kobj_show_handler_const * : (void *)_show,			\
+			  default : _show						\
+	),										\
+	.store		= _Generic(_store,						\
+			  __kobj_store_handler_const * : (void *)_store,		\
+			  default : _store						\
+	),										\
+
+#endif
+
 #define __KOBJ_ATTR(_name, _mode, _show, _store) {			\
 	.attr	= { .name = __stringify(_name),				\
 		    .mode = VERIFY_OCTAL_PERMISSIONS(_mode) },		\
-	.show	= _show,						\
-	.store	= _store,						\
+	__KOBJ_ATTR_SHOW_STORE(_show, _store)				\
 }
 
 #define __KOBJ_ATTR_RO_MODE(_name, _mode) {				\
diff --git a/lib/kobject.c b/lib/kobject.c
index 9c9ff0f5175f..e7b010a989fb 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -823,9 +823,11 @@ static ssize_t kobj_attr_show(struct kobject *kobj, struct attribute *attr,
 	struct kobj_attribute *kattr;
 	ssize_t ret = -EIO;
 
-	kattr = container_of(attr, struct kobj_attribute, attr);
+	kattr = container_of_const(attr, struct kobj_attribute, attr);
 	if (kattr->show)
 		ret = kattr->show(kobj, kattr, buf);
+	else if (kattr->show_const)
+		ret = kattr->show_const(kobj, kattr, buf);
 	return ret;
 }
 
@@ -835,9 +837,11 @@ static ssize_t kobj_attr_store(struct kobject *kobj, struct attribute *attr,
 	struct kobj_attribute *kattr;
 	ssize_t ret = -EIO;
 
-	kattr = container_of(attr, struct kobj_attribute, attr);
+	kattr = container_of_const(attr, struct kobj_attribute, attr);
 	if (kattr->store)
 		ret = kattr->store(kobj, kattr, buf, count);
+	else if (kattr->store_const)
+		ret = kattr->store_const(kobj, kattr, buf, count);
 	return ret;
 }
 

-- 
2.54.0