target: reintroduce some obsolete SCSI-2 commands

With kernel 3.6 some obsolete SCSI-2 commands including SEEK_10 have
have been removed by commit 1fd032ee10
"target: move code for CDB emulation".

There are still clients out there which use these old SCSI-2 commands.
This mainly happens when running VMs with legacy guest systems,
connected via SCSI command pass-through to iSCSI targets. Make them
happy and return status GOOD.

Many real SCSI disks or external iSCSI storage devices still support
these old commands. So let's make LIO backward compatible as well.

This patch adds support for the previously removed SEEK_10 and
additionally the SEEK_6 and REZERO_UNIT commands.

Signed-off-by: Bernhard Kohl <bernhard.kohl@nsn.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_sbc.c

@@ -135,6 +135,12 @@ static int sbc_emulate_verify(struct se_cmd *cmd)
 	return 0;
 }
 
+static int sbc_emulate_noop(struct se_cmd *cmd)
+{
+	target_complete_cmd(cmd, GOOD);
+	return 0;
+}
+
 static inline u32 sbc_get_size(struct se_cmd *cmd, u32 sectors)
 {
 	return cmd->se_dev->se_sub_dev->se_dev_attrib.block_size * sectors;
@@ -531,6 +537,18 @@ int sbc_parse_cdb(struct se_cmd *cmd, struct spc_ops *ops)
 		size = 0;
 		cmd->execute_cmd = sbc_emulate_verify;
 		break;
+	case REZERO_UNIT:
+	case SEEK_6:
+	case SEEK_10:
+		/*
+		 * There are still clients out there which use these old SCSI-2
+		 * commands. This mainly happens when running VMs with legacy
+		 * guest systems, connected via SCSI command pass-through to
+		 * iSCSI targets. Make them happy and return status GOOD.
+		 */
+		size = 0;
+		cmd->execute_cmd = sbc_emulate_noop;
+		break;
 	default:
 		ret = spc_parse_cdb(cmd, &size);
 		if (ret)