+/**
+ * sd_prepare_discard - unmap blocks on thinly provisioned device
+ * @rq: Request to prepare
+ *
+ * Will issue either UNMAP or WRITE SAME(16) depending on preference
+ * indicated by target device.
+ **/
+static int sd_prepare_discard(struct request *rq)
+{
+ struct scsi_disk *sdkp = scsi_disk(rq->rq_disk);
+ struct bio *bio = rq->bio;
+ sector_t sector = bio->bi_sector;
+ unsigned int num = bio_sectors(bio);
+
+ if (sdkp->device->sector_size == 4096) {
+ sector >>= 3;
+ num >>= 3;
+ }
+
+ rq->cmd_type = REQ_TYPE_BLOCK_PC;
+ rq->timeout = SD_TIMEOUT;
+
+ memset(rq->cmd, 0, rq->cmd_len);
+
+ if (sdkp->unmap) {
+ char *buf = kmap_atomic(bio_page(bio), KM_USER0);
+
+ rq->cmd[0] = UNMAP;
+ rq->cmd[8] = 24;
+ rq->cmd_len = 10;
+
+ /* Ensure that data length matches payload */
+ rq->__data_len = bio->bi_size = bio->bi_io_vec->bv_len = 24;
+
+ put_unaligned_be16(6 + 16, &buf[0]);
+ put_unaligned_be16(16, &buf[2]);
+ put_unaligned_be64(sector, &buf[8]);
+ put_unaligned_be32(num, &buf[16]);
+
+ kunmap_atomic(buf, KM_USER0);
+ } else {
+ rq->cmd[0] = WRITE_SAME_16;
+ rq->cmd[1] = 0x8; /* UNMAP */
+ put_unaligned_be64(sector, &rq->cmd[2]);
+ put_unaligned_be32(num, &rq->cmd[10]);
+ rq->cmd_len = 16;
+ }
+
+ return BLKPREP_OK;
+}
+