Tagged Queuing

For a definition of tagged queuing refer to the SCSI-2 specification. To support tagged queuing, first check the scsi_options flag SCSI_OPTIONS_TAG to see if tagged queuing is enabled globally. Next, check to see if the target is a SCSI-2 device and whether it has tagged queuing enabled. If this is all true, attempt to enable tagged queuing by using scsi_ifsetcap(9F). Example G-1 shows an example of supporting tagged queuing.

Example G-1 Supporting SCSI Tagged Queuing

#define ROUTE &sdp->sd_address
	...
	/*
	 * If SCSI-2 tagged queueing is supported by the disk drive and
	 * by the host adapter then we will enable it.
	 */ 
	xsp->tagflags = 0;
	if ((scsi_options & SCSI_OPTIONS_TAG) &&
		(devp->sd_inq->inq_rdf == RDF_SCSI2) &&
		(devp->sd_inq->inq_cmdque)) {
		if (scsi_ifsetcap(ROUTE, "tagged-qing", 1, 1) == 1) {
			xsp->tagflags = FLAG_STAG;
			xsp->throttle = 256;
		} else if (scsi_ifgetcap(ROUTE, "untagged-qing", 0) == 1) {
			xsp->dp->options |= XX_QUEUEING;
			xsp->throttle = 3;
		} else {
			xsp->dp->options &= ~XX_QUEUEING;
			xsp->throttle = 1;
		}
}