T_DATA_REQ(D7tpi)

T_DATA_REQ -- Data Request

Synopsis

This message consists of one M_PROTO message block followed by zero or more M_DATA message blocks where each M_DATA message block contains zero or more bytes of data. The format of the M_PROTO message block is as follows:

   struct T_data_req {
   	long PRIM_type;	 /* always T_DATA_REQ */
   	long MORE_flag;	 /* indicates more data in TSDU */
   }

Description

This primitive indicates to the transport provider that this message contains a transport interface data unit. One or more transport interface data units form a transport service data unit (TSDU).

Note that the maximum transport service data unit size allowed by the transport provider is indicated to the transport user via the T_INFO_ACK primitive.

This primitive has a mechanism which indicates the beginning and end of a transport service data unit. However, not all transport providers support the concept of a transport service data unit.

Parameters

PRIM_type: identifies the primitive type.
MORE_flag: when greater than zero, indicates that the next T_DATA_REQ primitive is also part of this transport service data unit.

Rules

The transport provider must also recognize a message of one or more M_DATA message blocks without the leading M_PROTO message block as a T_DATA_REQ primitive. This message type will be initiated from the write operating system service routine.

In this example there are no implied transport service data unit boundaries, and the transport provider may view this message type as a self contained transport service data unit. If these two types of messages are intermixed, then transport service data boundaries may be lost.

This primitive does not require any acknowledgments, although it may generate a fatal error. This is indicated via a M_ERROR message type which results in the failure of all operating system service routines on the stream.

Errors

The allowable errors are as follows:

EPROTO

This indicates one of the following unrecoverable protocol conditions:

The transport service interface was found to be in an incorrect state. If the interface is in the T_IDLE state when the provider receives the T_DATA_REQ primitive, then the transport provider should just drop the message without generating a fatal error.
The amount of transport user data associated with the primitive defines a transport service data unit larger than that allowed by the transport provider.

Modes

Only connection-mode.

Originator

Transport user.

Notices

Hardware constraints

None

Applicability

N/A

Backward compatibility

UnixWare-specific TPI Message Formats

Forward compatibility

N/A