driver-core: Introduce DEVICE_ATTR_ADMIN_{RO,RW}

A common pattern for using plain DEVICE_ATTR() instead of
DEVICE_ATTR_RO() and DEVICE_ATTR_RW() is for attributes that want to
limit read to only root.  I.e. many users of DEVICE_ATTR() are
specifying 0400 or 0600 for permissions.

Given the expectation that CAP_SYS_ADMIN is needed to access these
sensitive attributes and an explicit helper with the _ADMIN_ identifier
for DEVICE_ATTR_ADMIN_{RO,RW}.

Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Link: https://lore.kernel.org/r/159312906372.1850128.11611897078988158727.stgit@dwillia2-desk3.amr.corp.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/device.h

@@ -128,8 +128,12 @@ ssize_t device_store_bool(struct device *dev, struct device_attribute *attr,
 		__ATTR_PREALLOC(_name, _mode, _show, _store)
 #define DEVICE_ATTR_RW(_name) \
 	struct device_attribute dev_attr_##_name = __ATTR_RW(_name)
+#define DEVICE_ATTR_ADMIN_RW(_name) \
+	struct device_attribute dev_attr_##_name = __ATTR_RW_MODE(_name, 0600)
 #define DEVICE_ATTR_RO(_name) \
 	struct device_attribute dev_attr_##_name = __ATTR_RO(_name)
+#define DEVICE_ATTR_ADMIN_RO(_name) \
+	struct device_attribute dev_attr_##_name = __ATTR_RO_MODE(_name, 0400)
 #define DEVICE_ATTR_WO(_name) \
 	struct device_attribute dev_attr_##_name = __ATTR_WO(_name)
 #define DEVICE_ULONG_ATTR(_name, _mode, _var) \

include/linux/sysfs.h

@@ -123,6 +123,13 @@ struct attribute_group {
 	.show	= _name##_show,						\
 }
 
+#define __ATTR_RW_MODE(_name, _mode) {					\
+	.attr	= { .name = __stringify(_name),				\
+		    .mode = VERIFY_OCTAL_PERMISSIONS(_mode) },		\
+	.show	= _name##_show,						\
+	.store	= _name##_store,					\
+}
+
 #define __ATTR_WO(_name) {						\
 	.attr	= { .name = __stringify(_name), .mode = 0200 },		\
 	.store	= _name##_store,					\