Indicates that a jnr.ffi.Struct} parameter should be backed by a persistent native memory block.

Without the @Direct annotation, the native code will allocate a temporary native memory block for the parameter, and free it immediately after the call.

By using @Direct, the native memory block is permanently associated with the jnr.ffi.Struct instance, and will remain allocated for as long as the Struct instance remains strongly referenced by java code.