target: Add WRITE_SAME (10) parsing and refactor passthrough checks

This patch adds initial WRITE_SAME (10) w/ UNMAP=1 support following updates in
sbcr26 to allow UNMAP=1 for the non 16 + 32 byte CDB case.  It also refactors
current pSCSI passthrough passthrough checks into target_check_write_same_discard()
ahead of UNMAP=0 w/ write payload support into target_core_iblock.c.

This includes the support for handling WRITE_SAME in transport_emulate_control_cdb(),
and converts target_emulate_write_same to accept num_blocks directly for
WRITE_SAME, WRITE_SAME_16 and WRITE_SAME_32.
Reported-by: Eric Seppanen <eric@purestorage.com>
Cc: Roland Dreier <roland@purestorage.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@risingtidesystems.com>

drivers/target/target_core_cdb.c

@@ -1090,24 +1090,17 @@ target_emulate_unmap(struct se_task *task)
  * Note this is not used for TCM/pSCSI passthrough
  */
 static int
-target_emulate_write_same(struct se_task *task, int write_same32)
+target_emulate_write_same(struct se_task *task, u32 num_blocks)
 {
 	struct se_cmd *cmd = task->task_se_cmd;
 	struct se_device *dev = cmd->se_dev;
 	sector_t range;
 	sector_t lba = cmd->t_task_lba;
-	unsigned int num_blocks;
 	int ret;
 	/*
-	 * Extract num_blocks from the WRITE_SAME_* CDB.  Then use the explict
-	 * range when non zero is supplied, otherwise calculate the remaining
-	 * range based on ->get_blocks() - starting LBA.
+	 * Use the explicit range when non zero is supplied, otherwise calculate
+	 * the remaining range based on ->get_blocks() - starting LBA.
 	 */
-	if (write_same32)
-		num_blocks = get_unaligned_be32(&cmd->t_task_cdb[28]);
-	else
-		num_blocks = get_unaligned_be32(&cmd->t_task_cdb[10]);
-
 	if (num_blocks != 0)
 		range = num_blocks;
 	else
@@ -1170,13 +1163,23 @@ transport_emulate_control_cdb(struct se_task *task)
 		}
 		ret = target_emulate_unmap(task);
 		break;
+	case WRITE_SAME:
+		if (!dev->transport->do_discard) {
+			pr_err("WRITE_SAME emulation not supported"
+					" for: %s\n", dev->transport->name);
+			return PYX_TRANSPORT_UNKNOWN_SAM_OPCODE;
+		}
+		ret = target_emulate_write_same(task,
+				get_unaligned_be16(&cmd->t_task_cdb[7]));
+		break;
 	case WRITE_SAME_16:
 		if (!dev->transport->do_discard) {
 			pr_err("WRITE_SAME_16 emulation not supported"
 					" for: %s\n", dev->transport->name);
 			return PYX_TRANSPORT_UNKNOWN_SAM_OPCODE;
 		}
-		ret = target_emulate_write_same(task, 0);
+		ret = target_emulate_write_same(task,
+				get_unaligned_be32(&cmd->t_task_cdb[10]));
 		break;
 	case VARIABLE_LENGTH_CMD:
 		service_action =
@@ -1189,7 +1192,8 @@ transport_emulate_control_cdb(struct se_task *task)
 					dev->transport->name);
 				return PYX_TRANSPORT_UNKNOWN_SAM_OPCODE;
 			}
-			ret = target_emulate_write_same(task, 1);
+			ret = target_emulate_write_same(task,
+				get_unaligned_be32(&cmd->t_task_cdb[28]));
 			break;
 		default:
 			pr_err("Unsupported VARIABLE_LENGTH_CMD SA:"

drivers/target/target_core_transport.c

@@ -2861,6 +2861,38 @@ static int transport_cmd_get_valid_sectors(struct se_cmd *cmd)
 	return sectors;
 }
 
+static int target_check_write_same_discard(unsigned char *flags, struct se_device *dev)
+{
+	/*
+	 * Determine if the received WRITE_SAME is used to for direct
+	 * passthrough into Linux/SCSI with struct request via TCM/pSCSI
+	 * or we are signaling the use of internal WRITE_SAME + UNMAP=1
+	 * emulation for -> Linux/BLOCK disbard with TCM/IBLOCK code.
+	 */
+	int passthrough = (dev->transport->transport_type ==
+				TRANSPORT_PLUGIN_PHBA_PDEV);
+
+	if (!passthrough) {
+		if ((flags[0] & 0x04) || (flags[0] & 0x02)) {
+			pr_err("WRITE_SAME PBDATA and LBDATA"
+				" bits not supported for Block Discard"
+				" Emulation\n");
+			return -ENOSYS;
+		}
+		/*
+		 * Currently for the emulated case we only accept
+		 * tpws with the UNMAP=1 bit set.
+		 */
+		if (!(flags[0] & 0x08)) {
+			pr_err("WRITE_SAME w/o UNMAP bit not"
+				" supported for Block Discard Emulation\n");
+			return -ENOSYS;
+		}
+	}
+
+	return 0;
+}
+
 /*	transport_generic_cmd_sequencer():
  *
  *	Generic Command Sequencer that should work for most DAS transport
@@ -3081,27 +3113,9 @@ static int transport_generic_cmd_sequencer(
 			cmd->t_task_lba = get_unaligned_be64(&cdb[12]);
 			cmd->se_cmd_flags |= SCF_SCSI_CONTROL_SG_IO_CDB;
 
-			/*
-			 * Skip the remaining assignments for TCM/PSCSI passthrough
-			 */
-			if (passthrough)
-				break;
-
-			if ((cdb[10] & 0x04) || (cdb[10] & 0x02)) {
-				pr_err("WRITE_SAME PBDATA and LBDATA"
-					" bits not supported for Block Discard"
-					" Emulation\n");
+			if (target_check_write_same_discard(&cdb[10], dev) < 0)
 				goto out_invalid_cdb_field;
-			}
-			/*
-			 * Currently for the emulated case we only accept
-			 * tpws with the UNMAP=1 bit set.
-			 */
-			if (!(cdb[10] & 0x08)) {
-				pr_err("WRITE_SAME w/o UNMAP bit not"
-					" supported for Block Discard Emulation\n");
-				goto out_invalid_cdb_field;
-			}
+
 			break;
 		default:
 			pr_err("VARIABLE_LENGTH_CMD service action"
@@ -3358,33 +3372,31 @@ static int transport_generic_cmd_sequencer(
 		}
 
 		cmd->t_task_lba = get_unaligned_be64(&cdb[2]);
-		passthrough = (dev->transport->transport_type ==
-				TRANSPORT_PLUGIN_PHBA_PDEV);
-		/*
-		 * Determine if the received WRITE_SAME_16 is used to for direct
-		 * passthrough into Linux/SCSI with struct request via TCM/pSCSI
-		 * or we are signaling the use of internal WRITE_SAME + UNMAP=1
-		 * emulation for -> Linux/BLOCK disbard with TCM/IBLOCK and
-		 * TCM/FILEIO subsystem plugin backstores.
-		 */
-		if (!passthrough) {
-			if ((cdb[1] & 0x04) || (cdb[1] & 0x02)) {
-				pr_err("WRITE_SAME PBDATA and LBDATA"
-					" bits not supported for Block Discard"
-					" Emulation\n");
-				goto out_invalid_cdb_field;
-			}
-			/*
-			 * Currently for the emulated case we only accept
-			 * tpws with the UNMAP=1 bit set.
-			 */
-			if (!(cdb[1] & 0x08)) {
-				pr_err("WRITE_SAME w/o UNMAP bit not "
-					" supported for Block Discard Emulation\n");
-				goto out_invalid_cdb_field;
-			}
+		cmd->se_cmd_flags |= SCF_SCSI_CONTROL_SG_IO_CDB;
+
+		if (target_check_write_same_discard(&cdb[1], dev) < 0)
+			goto out_invalid_cdb_field;
+		break;
+	case WRITE_SAME:
+		sectors = transport_get_sectors_10(cdb, cmd, &sector_ret);
+		if (sector_ret)
+			goto out_unsupported_cdb;
+
+		if (sectors)
+			size = transport_get_size(sectors, cdb, cmd);
+		else {
+			pr_err("WSNZ=1, WRITE_SAME w/sectors=0 not supported\n");
+			goto out_invalid_cdb_field;
 		}
+
+		cmd->t_task_lba = get_unaligned_be32(&cdb[2]);
 		cmd->se_cmd_flags |= SCF_SCSI_CONTROL_SG_IO_CDB;
+		/*
+		 * Follow sbcr26 with WRITE_SAME (10) and check for the existence
+		 * of byte 1 bit 3 UNMAP instead of original reserved field
+		 */
+		if (target_check_write_same_discard(&cdb[1], dev) < 0)
+			goto out_invalid_cdb_field;
 		break;
 	case ALLOW_MEDIUM_REMOVAL:
 	case GPCMD_CLOSE_TRACK: