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#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);
Optionally, write queue associated with the read queue to be used on failure (see below).
Optionally, the message to exchange.
Size of the returned message.
Type of the returned message.
Optionally, a 4 byte value to store at the beginning of the returned message.
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.
STREAMS Programming Guide