Declarations

The service interface primitives are defined in the declarations:

#include <sys/types.h>
#include <sys/param.h>
#include <sys/stream.h>
#include <sys/errno.h>

/* Primitives initiated by the service user */

#define BIND_REQ								1		/* bind request */
#define UNITDATA_REQ							2		/* unitdata request */

 /* Primitives initiated by the service provider */

#define OK_ACK									3	/* bind acknowledgment */
#define ERROR_ACK								4	/* error acknowledgment */
#define UNITDATA_IND							5	/* unitdata indication */
/*
 * The following structures define the format of the
 * stream message block of the above primitives.

 */
struct bind_req {									/* bind request */
 	long			PRIM_type;						/* always BIND_REQ */
 	long			BIND_addr;						/* addr to bind	*/
};
struct unitdata_req {							/* unitdata request */
 	long			PRIM_type;						/* always UNITDATA_REQ */
 	long			DEST_addr;						/* dest addr */
};
struct ok_ack {									/* ok acknowledgment */
 	long			PRIM_type;						/* always OK_ACK */
};
struct error_ack {								/* error acknowledgment */
 	long			PRIM_type;						/* always ERROR_ACK */
 	long			UNIX_error;						/* UNIX system error code*/
};
struct unitdata_ind {							/* unitdata indication */
 	long			PRIM_type;						/* always UNITDATA_IND */
 	long			SRC_addr;						/* source addr */
};

union primitives {								/* union of all primitives */
 	long								type;
 	struct bind_req				bind_req;
 	struct unitdata_req			unitdata_req;
 	struct ok_ack					ok_ack;
 	struct error_ack				error_ack;
 	struct unitdata_ind			unitdata_ind;
};
struct dgproto {									/*structure minor device */
 	short state;									/*current provider state */
 	long addr;										/* net address */
};

/* Provider states */
#define IDLE 0
#define BOUND 1

In general, the M_PROTO or M_PCPROTO block is described by a data structure containing the service interface information. In this example, union primitives is that structure.

The module recognizes two commands:

BIND_REQ

Give this Stream a protocol address (for example, give it a name on the network). After a BIND_REQ is completed, data from other senders will find their way through the network to this particular Stream.

UNITDATA_REQ

Send data to the specified address.

The module generates three messages:

OK_ACK

A positive acknowledgment (ack) of BIND_REQ.

ERROR_ACK

A negative acknowledgment (nak) of BIND_REQ.

UNITDATA_IND

Data from the network have been received.

The acknowledgment of a BIND_REQ informs the user that the request was syntactically correct (or incorrect if ERROR_ACK). The receipt of a BIND_REQ is acknowledged with an M_PCPROTO to ensure that the acknowledgment reaches the user before any other message. For example, a UNITDATA_IND could come through before the bind has completed, and the application would be confused.

The driver uses a per-minor device data structure, dgproto, which contains the following:

state

current state of the service provider IDLE or BOUND

addr

network address that has been bound to this Stream

It is assumed (though not shown) that the module open procedure sets the write queue q_ptr to point at the appropriate private data structure.