target: Fail UNMAP when emulate_tpu=0

This patch adds a check within sbc_parse_cdb() to fail a UNMAP op,
if the backend device has emulate_tpu disabled.

Cc: Martin Petersen <martin.petersen@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
diff --git a/drivers/target/target_core_sbc.c b/drivers/target/target_core_sbc.c
index 0d307c3..9661a66 100644
--- a/drivers/target/target_core_sbc.c
+++ b/drivers/target/target_core_sbc.c
@@ -962,6 +962,11 @@
 		if (!ops->execute_unmap)
 			return TCM_UNSUPPORTED_SCSI_OPCODE;
 
+		if (!dev->dev_attrib.emulate_tpu) {
+			pr_err("Got UNMAP, but backend device has"
+			       " emulate_tpu disabled\n");
+			return TCM_UNSUPPORTED_SCSI_OPCODE;
+		}
 		size = get_unaligned_be16(&cdb[7]);
 		cmd->execute_cmd = ops->execute_unmap;
 		break;