sd: implement unmapping Write Zeroes

Try to use a write same with unmap bit variant if the device supports it
and the caller allows for it.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NMartin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: NHannes Reinecke <hare@suse.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

drivers/scsi/sd.c

@@ -803,6 +803,15 @@ static int sd_setup_write_zeroes_cmnd(struct scsi_cmnd *cmd)
 	u64 sector = blk_rq_pos(rq) >> (ilog2(sdp->sector_size) - 9);
 	u32 nr_sectors = blk_rq_sectors(rq) >> (ilog2(sdp->sector_size) - 9);
 
+	if (!(rq->cmd_flags & REQ_NOUNMAP)) {
+		switch (sdkp->provisioning_mode) {
+		case SD_LBP_WS16:
+			return sd_setup_write_same16_cmnd(cmd, true);
+		case SD_LBP_WS10:
+			return sd_setup_write_same10_cmnd(cmd, true);
+		}
+	}
+
 	if (sdp->no_write_same)
 		return BLKPREP_INVALID;
 	if (sdkp->ws16 || sector > 0xffffffff || nr_sectors > 0xffff)