mexchange(9F)						   Kernel Functions for Drivers 					     mexchange(9F)

NAME

       mexchange - Exchange one message for another

SYNOPSIS

       #include <sys/stream.h>
       #include <sys/strsun.h>

       mblk_t *mexchange(queue_t *wq, mblk_t *mp, size_t size,
	    uchar_t type, int32_t primtype);

INTERFACE LEVEL

       Solaris DDI specific (Solaris DDI).

PARAMETERS

       wq	   Optionally, write queue associated with the read queue to be used on failure (see below).

       mp	   Optionally, the message to exchange.

       size	   Size of the returned message.

       type	   Type of the returned message.

       primtype    Optionally, a 4 byte value to store at the beginning of the returned message.

DESCRIPTION

       The mexchange() function exchanges the passed in message for another message of the specified size and type.

       If  mp is not NULL, is of at least size bytes, and has only one reference (see dupmsg(9F)), mp is converted to be of the specified size and
       type. Otherwise, a new message of the specified size and type is allocated. If allocation fails, and wq is not NULL, merror(9F) attempts to
       send an error to the stream head.

       Finally,  if  primtype  is  not	-1 and size is at least 4 bytes, the first 4 bytes are assigned to be primtype. This is chiefly useful for
       STREAMS-based protocols such as DLPI and TPI which store the protocol message type in the first 4 bytes of each message.

RETURN VALUES

       A pointer to the requested message is returned on success. NULL is returned on failure.

CONTEXT

       This function can be called from user, kernel or interrupt context.

SEE ALSO

       dupmsg(9F), merror(9F)

       STREAMS Programming Guide

SunOS 5.11							    9 June 2004 						     mexchange(9F)