This option is used to set a low-water mark in the send buffer. The option value gives the minimal number of bytes that must have accumulated in the send buffer before they are sent. This request is not an absolute requirement. The implementation may place upper and lower limits on the option value. Requests that fall short of the lower limit are negotiated to the lower limit.
Legal values are all positive numbers.
The specified file descriptor does not refer to a transport endpoint. An invalid flag was specified. The specified options were in an incorrect format or contained illegal information. The information to be returned in ret will be discarded. This action is not supported by the transport provider.