sd: use READ_16 or WRITE_16 when transfer length is greater than 0xffff

This change makes the scsi disk driver handle the requests whose
transfer length is greater than 0xffff with READ_16 or WRITE_16.

However, this is a preparation for extending the data type of
max_sectors in struct Scsi_Host and scsi_host_template.  So, it is
impossible to happen this condition for now, because SCSI low-level
drivers can not specify max_sectors greater than 0xffff due to the
data type limitation.
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/scsi/sd.c

@@ -1042,7 +1042,7 @@ static int sd_init_command(struct scsi_cmnd *SCpnt)
 		SCpnt->cmnd[29] = (unsigned char) (this_count >> 16) & 0xff;
 		SCpnt->cmnd[30] = (unsigned char) (this_count >> 8) & 0xff;
 		SCpnt->cmnd[31] = (unsigned char) this_count & 0xff;
-	} else if (sdp->use_16_for_rw) {
+	} else if (sdp->use_16_for_rw || (this_count > 0xffff)) {
 		SCpnt->cmnd[0] += READ_16 - READ_6;
 		SCpnt->cmnd[1] = protect | ((rq->cmd_flags & REQ_FUA) ? 0x8 : 0);
 		SCpnt->cmnd[2] = sizeof(block) > 4 ? (unsigned char) (block >> 56) & 0xff : 0;
@@ -1061,9 +1061,6 @@ static int sd_init_command(struct scsi_cmnd *SCpnt)
 	} else if ((this_count > 0xff) || (block > 0x1fffff) ||
 		   scsi_device_protection(SCpnt->device) ||
 		   SCpnt->device->use_10_for_rw) {
-		if (this_count > 0xffff)
-			this_count = 0xffff;
-
 		SCpnt->cmnd[0] += READ_10 - READ_6;
 		SCpnt->cmnd[1] = protect | ((rq->cmd_flags & REQ_FUA) ? 0x8 : 0);
 		SCpnt->cmnd[2] = (unsigned char) (block >> 24) & 0xff;