[PATCH net-next 06/10] device: add device_change_owner()

[Christian Brauner]

Add a helper to change the owner of a device's sysfs entries. This
needs to happen when the ownership of a device is changed, e.g. when
moving network devices between network namespaces.
The ownership of a device is determined based on the ownership of
the corresponding kobject, i.e. only if the ownership of a kobject is
changed will this function change the ownership of the corresponding
device's sysfs entries.
This function will be used to correctly account for ownership changes,
e.g. when moving network devices between network namespaces.

Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
---
 drivers/base/core.c    | 73 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/device.h |  1 +
 2 files changed, 74 insertions(+)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 42a672456432..262217287a09 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -3458,6 +3458,79 @@ int device_move(struct device *dev, struct device *new_parent,
 }
 EXPORT_SYMBOL_GPL(device_move);
 
+static int device_attrs_change_owner(struct device *dev)
+{
+	struct kobject *kobj = &dev->kobj;
+	struct class *class = dev->class;
+	const struct device_type *type = dev->type;
+	int error;
+
+	if (class) {
+		error = sysfs_groups_change_owner(kobj, class->dev_groups);
+		if (error)
+			return error;
+	}
+
+	if (type) {
+		error = sysfs_groups_change_owner(kobj, type->groups);
+		if (error)
+			return error;
+	}
+
+	error = sysfs_groups_change_owner(kobj, dev->groups);
+	if (error)
+		return error;
+
+	if (device_supports_offline(dev) && !dev->offline_disabled) {
+		error = sysfs_file_change_owner(kobj, dev_attr_online.attr.name);
+		if (error)
+			return error;
+	}
+
+	return 0;
+}
+
+/**
+ * device_change_owner - change the owner of an existing device.
+ * @dev: device.
+ */
+int device_change_owner(struct device *dev)
+{
+	int error;
+	struct kobject *kobj = &dev->kobj;
+
+	dev = get_device(dev);
+	if (!dev)
+		return -EINVAL;
+
+	error = sysfs_change_owner(kobj);
+	if (error)
+		goto out;
+
+	error = sysfs_file_change_owner(kobj, dev_attr_uevent.attr.name);
+	if (error)
+		goto out;
+
+	error = device_attrs_change_owner(dev);
+	if (error)
+		goto out;
+
+#ifdef CONFIG_BLOCK
+	if (sysfs_deprecated && dev->class == &block_class)
+		goto out;
+#endif
+
+	error = sysfs_link_change_owner(&dev->class->p->subsys.kobj, &dev->kobj,
+					dev_name(dev));
+	if (error)
+		goto out;
+
+out:
+	put_device(dev);
+	return error;
+}
+EXPORT_SYMBOL_GPL(device_change_owner);
+
 /**
  * device_shutdown - call ->shutdown() on each device to shutdown.
  */
diff --git a/include/linux/device.h b/include/linux/device.h
index 0cd7c647c16c..63ebd9e3f6b0 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -817,6 +817,7 @@ extern struct device *device_find_child_by_name(struct device *parent,
 extern int device_rename(struct device *dev, const char *new_name);
 extern int device_move(struct device *dev, struct device *new_parent,
 		       enum dpm_order dpm_order);
+extern int device_change_owner(struct device *dev);
 extern const char *device_get_devnode(struct device *dev,
 				      umode_t *mode, kuid_t *uid, kgid_t *gid,
 				      const char **tmp);
-- 
2.25.0