dm sysfs: introduce ability to add writable attributes

Add DM_ATTR_RW() macro and establish .store method in dm_sysfs_ops.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-sysfs.c

@@ -11,7 +11,7 @@
 struct dm_sysfs_attr {
 	struct attribute attr;
 	ssize_t (*show)(struct mapped_device *, char *);
-	ssize_t (*store)(struct mapped_device *, char *);
+	ssize_t (*store)(struct mapped_device *, const char *, size_t count);
 };
 
 #define DM_ATTR_RO(_name) \
@@ -39,6 +39,31 @@ static ssize_t dm_attr_show(struct kobject *kobj, struct attribute *attr,
 	return ret;
 }
 
+#define DM_ATTR_RW(_name) \
+struct dm_sysfs_attr dm_attr_##_name = \
+	__ATTR(_name, S_IRUGO | S_IWUSR, dm_attr_##_name##_show, dm_attr_##_name##_store)
+
+static ssize_t dm_attr_store(struct kobject *kobj, struct attribute *attr,
+			     const char *page, size_t count)
+{
+	struct dm_sysfs_attr *dm_attr;
+	struct mapped_device *md;
+	ssize_t ret;
+
+	dm_attr = container_of(attr, struct dm_sysfs_attr, attr);
+	if (!dm_attr->store)
+		return -EIO;
+
+	md = dm_get_from_kobject(kobj);
+	if (!md)
+		return -EINVAL;
+
+	ret = dm_attr->store(md, page, count);
+	dm_put(md);
+
+	return ret;
+}
+
 static ssize_t dm_attr_name_show(struct mapped_device *md, char *buf)
 {
 	if (dm_copy_name_and_uuid(md, buf, NULL))
@@ -77,12 +102,9 @@ static struct attribute *dm_attrs[] = {
 
 static const struct sysfs_ops dm_sysfs_ops = {
 	.show	= dm_attr_show,
+	.store	= dm_attr_store,
 };
 
-/*
- * dm kobject is embedded in mapped_device structure
- * no need to define release function here
- */
 static struct kobj_type dm_ktype = {
 	.sysfs_ops	= &dm_sysfs_ops,
 	.default_attrs	= dm_attrs,