On Wed, Mar 25, 2020 at 04:27:07PM +0800, Jason Wang wrote:

+struct vdpa_device *__vdpa_alloc_device(struct device *parent,
+					const struct vdpa_config_ops *config,
+					size_t size);
+
+#define vdpa_alloc_device(dev_struct, member, parent, config)   \
+			  container_of(__vdpa_alloc_device( \
+				       parent, config, \
+				       sizeof(struct dev_struct) + \
+				       BUILD_BUG_ON_ZERO(offsetof( \
+				       struct dev_struct, member))), \
+				       struct dev_struct, member)

This all looks robust now, one minor remark is to not do 'struct
dev_struct' here so the caller has to do

   vdpa_alloc_device(struct foo, vpda, ...)

Which suggests to the reader something unusual is happening

Jason