/** device to call, upper layer normally */
struct md_device *mu_upcall_dev;
/** upcall function */
int (*mu_upcall)(const struct lu_env *env, struct md_device *md,
/** device to call, upper layer normally */
struct md_device *mu_upcall_dev;
/** upcall function */
int (*mu_upcall)(const struct lu_env *env, struct md_device *md,