* \return \p -ENOTSUP if no parent node of \a btrn understands \a command.
* Otherwise the return value of the command handler is returned.
*
* \return \p -ENOTSUP if no parent node of \a btrn understands \a command.
* Otherwise the return value of the command handler is returned.
*
* \param type The supposed type of \a btrn.
*
* Most users of the buffer tree subsystem call this function from both
* \param type The supposed type of \a btrn.
*
* Most users of the buffer tree subsystem call this function from both
*
* \return Negative if an error condition was detected, zero if there
* is nothing to do and positive otherwise.
*
* \return Negative if an error condition was detected, zero if there
* is nothing to do and positive otherwise.