[ChuckMcM]

This is a nice structure, It also suggests something like closures where you inverse stacked the functions and did something like:

   int do_command(sdio_command_chain *cmd) {
           int err = 0;
           if (cmd->next) {
              err = do_command(cmd->next);
           }
           return (err) ? err : call_command(cmd->parms);
     }

Thanks for that!