iscsi-target: Add iSCSI fabric support for target v4.1

The Linux-iSCSI.org target module is a full featured in-kernel
software implementation of iSCSI target mode (RFC-3720) for the
current WIP mainline target v4.1 infrastructure code for the v3.1
kernel.  More information can be found here:

http://linux-iscsi.org/wiki/ISCSI

This includes support for:

   * RFC-3720 defined request / response state machines and support for
     all defined iSCSI operation codes from Section 10.2.1.2 using libiscsi
     include/scsi/iscsi_proto.h PDU definitions
   * Target v4.1 compatible control plane using the generic layout in
     target_core_fabric_configfs.c and fabric dependent attributes
     within /sys/kernel/config/target/iscsi/ subdirectories.
   * Target v4.1 compatible iSCSI statistics based on RFC-4544 (iSCSI MIBS)
   * Support for IPv6 and IPv4 network portals in M:N mapping to TPGs
   * iSCSI Error Recovery Hierarchy support
   * Per iSCSI connection RX/TX thread pair scheduling affinity
   * crc32c + crc32c_intel SSEv4 instruction offload support using libcrypto
   * CHAP Authentication support using libcrypto
   * Conversion to use internal SGl allocation with iscsit_alloc_buffs() ->
     transport_generic_map_mem_to_cmd()

(nab: Fix iscsi_proto.h struct scsi_lun usage from linux-next in commit:
      iscsi: Use struct scsi_lun in iscsi structs instead of u8[8])
(nab: Fix 32-bit compile warnings)

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Andy Grover <agrover@redhat.com>
Acked-by: Roland Dreier <roland@kernel.org>
Signed-off-by: Nicholas A. Bellinger <nab@linux-iscsi.org>

1 files changed, 849 insertions, 0 deletions

diff --git a/drivers/target/iscsi/iscsi_target_tmr.c b/drivers/target/iscsi/iscsi_target_tmr.c
new file mode 100644
index 000000000000..db1fe1ec84df
--- /dev/null
+++ b/drivers/target/iscsi/iscsi_target_tmr.c
@@ -0,0 +1,849 @@
+/*******************************************************************************
+ * This file contains the iSCSI Target specific Task Management functions.
+ *
+ * \u00a9 Copyright 2007-2011 RisingTide Systems LLC.
+ *
+ * Licensed to the Linux Foundation under the General Public License (GPL) version 2.
+ *
+ * Author: Nicholas A. Bellinger <nab@linux-iscsi.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ ******************************************************************************/
+
+#include <asm/unaligned.h>
+#include <scsi/iscsi_proto.h>
+#include <target/target_core_base.h>
+#include <target/target_core_transport.h>
+
+#include "iscsi_target_core.h"
+#include "iscsi_target_seq_pdu_list.h"
+#include "iscsi_target_datain_values.h"
+#include "iscsi_target_device.h"
+#include "iscsi_target_erl0.h"
+#include "iscsi_target_erl1.h"
+#include "iscsi_target_erl2.h"
+#include "iscsi_target_tmr.h"
+#include "iscsi_target_tpg.h"
+#include "iscsi_target_util.h"
+#include "iscsi_target.h"
+
+u8 iscsit_tmr_abort_task(
+	struct iscsi_cmd *cmd,
+	unsigned char *buf)
+{
+	struct iscsi_cmd *ref_cmd;
+	struct iscsi_conn *conn = cmd->conn;
+	struct iscsi_tmr_req *tmr_req = cmd->tmr_req;
+	struct se_tmr_req *se_tmr = cmd->se_cmd.se_tmr_req;
+	struct iscsi_tm *hdr = (struct iscsi_tm *) buf;
+
+	ref_cmd = iscsit_find_cmd_from_itt(conn, hdr->rtt);
+	if (!ref_cmd) {
+		pr_err("Unable to locate RefTaskTag: 0x%08x on CID:"
+			" %hu.\n", hdr->rtt, conn->cid);
+		return ((hdr->refcmdsn >= conn->sess->exp_cmd_sn) &&
+			(hdr->refcmdsn <= conn->sess->max_cmd_sn)) ?
+			ISCSI_TMF_RSP_COMPLETE : ISCSI_TMF_RSP_NO_TASK;
+	}
+	if (ref_cmd->cmd_sn != hdr->refcmdsn) {
+		pr_err("RefCmdSN 0x%08x does not equal"
+			" task's CmdSN 0x%08x. Rejecting ABORT_TASK.\n",
+			hdr->refcmdsn, ref_cmd->cmd_sn);
+		return ISCSI_TMF_RSP_REJECTED;
+	}
+
+	se_tmr->ref_task_tag		= hdr->rtt;
+	se_tmr->ref_cmd			= &ref_cmd->se_cmd;
+	tmr_req->ref_cmd_sn		= hdr->refcmdsn;
+	tmr_req->exp_data_sn		= hdr->exp_datasn;
+
+	return ISCSI_TMF_RSP_COMPLETE;
+}
+
+/*
+ *	Called from iscsit_handle_task_mgt_cmd().
+ */
+int iscsit_tmr_task_warm_reset(
+	struct iscsi_conn *conn,
+	struct iscsi_tmr_req *tmr_req,
+	unsigned char *buf)
+{
+	struct iscsi_session *sess = conn->sess;
+	struct iscsi_node_attrib *na = iscsit_tpg_get_node_attrib(sess);
+#if 0
+	struct iscsi_init_task_mgt_cmnd *hdr =
+		(struct iscsi_init_task_mgt_cmnd *) buf;
+#endif
+	if (!na->tmr_warm_reset) {
+		pr_err("TMR Opcode TARGET_WARM_RESET authorization"
+			" failed for Initiator Node: %s\n",
+			sess->se_sess->se_node_acl->initiatorname);
+		 return -1;
+	}
+	/*
+	 * Do the real work in transport_generic_do_tmr().
+	 */
+	return 0;
+}
+
+int iscsit_tmr_task_cold_reset(
+	struct iscsi_conn *conn,
+	struct iscsi_tmr_req *tmr_req,
+	unsigned char *buf)
+{
+	struct iscsi_session *sess = conn->sess;
+	struct iscsi_node_attrib *na = iscsit_tpg_get_node_attrib(sess);
+
+	if (!na->tmr_cold_reset) {
+		pr_err("TMR Opcode TARGET_COLD_RESET authorization"
+			" failed for Initiator Node: %s\n",
+			sess->se_sess->se_node_acl->initiatorname);
+		return -1;
+	}
+	/*
+	 * Do the real work in transport_generic_do_tmr().
+	 */
+	return 0;
+}
+
+u8 iscsit_tmr_task_reassign(
+	struct iscsi_cmd *cmd,
+	unsigned char *buf)
+{
+	struct iscsi_cmd *ref_cmd = NULL;
+	struct iscsi_conn *conn = cmd->conn;
+	struct iscsi_conn_recovery *cr = NULL;
+	struct iscsi_tmr_req *tmr_req = cmd->tmr_req;
+	struct se_tmr_req *se_tmr = cmd->se_cmd.se_tmr_req;
+	struct iscsi_tm *hdr = (struct iscsi_tm *) buf;
+	int ret;
+
+	pr_debug("Got TASK_REASSIGN TMR ITT: 0x%08x,"
+		" RefTaskTag: 0x%08x, ExpDataSN: 0x%08x, CID: %hu\n",
+		hdr->itt, hdr->rtt, hdr->exp_datasn, conn->cid);
+
+	if (conn->sess->sess_ops->ErrorRecoveryLevel != 2) {
+		pr_err("TMR TASK_REASSIGN not supported in ERL<2,"
+				" ignoring request.\n");
+		return ISCSI_TMF_RSP_NOT_SUPPORTED;
+	}
+
+	ret = iscsit_find_cmd_for_recovery(conn->sess, &ref_cmd, &cr, hdr->rtt);
+	if (ret == -2) {
+		pr_err("Command ITT: 0x%08x is still alligent to CID:"
+			" %hu\n", ref_cmd->init_task_tag, cr->cid);
+		return ISCSI_TMF_RSP_TASK_ALLEGIANT;
+	} else if (ret == -1) {
+		pr_err("Unable to locate RefTaskTag: 0x%08x in"
+			" connection recovery command list.\n", hdr->rtt);
+		return ISCSI_TMF_RSP_NO_TASK;
+	}
+	/*
+	 * Temporary check to prevent connection recovery for
+	 * connections with a differing MaxRecvDataSegmentLength.
+	 */
+	if (cr->maxrecvdatasegmentlength !=
+	    conn->conn_ops->MaxRecvDataSegmentLength) {
+		pr_err("Unable to perform connection recovery for"
+			" differing MaxRecvDataSegmentLength, rejecting"
+			" TMR TASK_REASSIGN.\n");
+		return ISCSI_TMF_RSP_REJECTED;
+	}
+
+	se_tmr->ref_task_tag		= hdr->rtt;
+	se_tmr->ref_cmd			= &ref_cmd->se_cmd;
+	se_tmr->ref_task_lun		= get_unaligned_le64(&hdr->lun);
+	tmr_req->ref_cmd_sn		= hdr->refcmdsn;
+	tmr_req->exp_data_sn		= hdr->exp_datasn;
+	tmr_req->conn_recovery		= cr;
+	tmr_req->task_reassign		= 1;
+	/*
+	 * Command can now be reassigned to a new connection.
+	 * The task management response must be sent before the
+	 * reassignment actually happens.  See iscsi_tmr_post_handler().
+	 */
+	return ISCSI_TMF_RSP_COMPLETE;
+}
+
+static void iscsit_task_reassign_remove_cmd(
+	struct iscsi_cmd *cmd,
+	struct iscsi_conn_recovery *cr,
+	struct iscsi_session *sess)
+{
+	int ret;
+
+	spin_lock(&cr->conn_recovery_cmd_lock);
+	ret = iscsit_remove_cmd_from_connection_recovery(cmd, sess);
+	spin_unlock(&cr->conn_recovery_cmd_lock);
+	if (!ret) {
+		pr_debug("iSCSI connection recovery successful for CID:"
+			" %hu on SID: %u\n", cr->cid, sess->sid);
+		iscsit_remove_active_connection_recovery_entry(cr, sess);
+	}
+}
+
+static int iscsit_task_reassign_complete_nop_out(
+	struct iscsi_tmr_req *tmr_req,
+	struct iscsi_conn *conn)
+{
+	struct se_tmr_req *se_tmr = tmr_req->se_tmr_req;
+	struct se_cmd *se_cmd = se_tmr->ref_cmd;
+	struct iscsi_cmd *cmd = container_of(se_cmd, struct iscsi_cmd, se_cmd);
+	struct iscsi_conn_recovery *cr;
+
+	if (!cmd->cr) {
+		pr_err("struct iscsi_conn_recovery pointer for ITT: 0x%08x"
+			" is NULL!\n", cmd->init_task_tag);
+		return -1;
+	}
+	cr = cmd->cr;
+
+	/*
+	 * Reset the StatSN so a new one for this commands new connection
+	 * will be assigned.
+	 * Reset the ExpStatSN as well so we may receive Status SNACKs.
+	 */
+	cmd->stat_sn = cmd->exp_stat_sn = 0;
+
+	iscsit_task_reassign_remove_cmd(cmd, cr, conn->sess);
+
+	spin_lock_bh(&conn->cmd_lock);
+	list_add_tail(&cmd->i_list, &conn->conn_cmd_list);
+	spin_unlock_bh(&conn->cmd_lock);
+
+	cmd->i_state = ISTATE_SEND_NOPIN;
+	iscsit_add_cmd_to_response_queue(cmd, conn, cmd->i_state);
+	return 0;
+}
+
+static int iscsit_task_reassign_complete_write(
+	struct iscsi_cmd *cmd,
+	struct iscsi_tmr_req *tmr_req)
+{
+	int no_build_r2ts = 0;
+	u32 length = 0, offset = 0;
+	struct iscsi_conn *conn = cmd->conn;
+	struct se_cmd *se_cmd = &cmd->se_cmd;
+	/*
+	 * The Initiator must not send a R2T SNACK with a Begrun less than
+	 * the TMR TASK_REASSIGN's ExpDataSN.
+	 */
+	if (!tmr_req->exp_data_sn) {
+		cmd->cmd_flags &= ~ICF_GOT_DATACK_SNACK;
+		cmd->acked_data_sn = 0;
+	} else {
+		cmd->cmd_flags |= ICF_GOT_DATACK_SNACK;
+		cmd->acked_data_sn = (tmr_req->exp_data_sn - 1);
+	}
+
+	/*
+	 * The TMR TASK_REASSIGN's ExpDataSN contains the next R2TSN the
+	 * Initiator is expecting.  The Target controls all WRITE operations
+	 * so if we have received all DataOUT we can safety ignore Initiator.
+	 */
+	if (cmd->cmd_flags & ICF_GOT_LAST_DATAOUT) {
+		if (!atomic_read(&cmd->transport_sent)) {
+			pr_debug("WRITE ITT: 0x%08x: t_state: %d"
+				" never sent to transport\n",
+				cmd->init_task_tag, cmd->se_cmd.t_state);
+			return transport_generic_handle_data(se_cmd);
+		}
+
+		cmd->i_state = ISTATE_SEND_STATUS;
+		iscsit_add_cmd_to_response_queue(cmd, conn, cmd->i_state);
+		return 0;
+	}
+
+	/*
+	 * Special case to deal with DataSequenceInOrder=No and Non-Immeidate
+	 * Unsolicited DataOut.
+	 */
+	if (cmd->unsolicited_data) {
+		cmd->unsolicited_data = 0;
+
+		offset = cmd->next_burst_len = cmd->write_data_done;
+
+		if ((conn->sess->sess_ops->FirstBurstLength - offset) >=
+		     cmd->data_length) {
+			no_build_r2ts = 1;
+			length = (cmd->data_length - offset);
+		} else
+			length = (conn->sess->sess_ops->FirstBurstLength - offset);
+
+		spin_lock_bh(&cmd->r2t_lock);
+		if (iscsit_add_r2t_to_list(cmd, offset, length, 0, 0) < 0) {
+			spin_unlock_bh(&cmd->r2t_lock);
+			return -1;
+		}
+		cmd->outstanding_r2ts++;
+		spin_unlock_bh(&cmd->r2t_lock);
+
+		if (no_build_r2ts)
+			return 0;
+	}
+	/*
+	 * iscsit_build_r2ts_for_cmd() can handle the rest from here.
+	 */
+	return iscsit_build_r2ts_for_cmd(cmd, conn, 2);
+}
+
+static int iscsit_task_reassign_complete_read(
+	struct iscsi_cmd *cmd,
+	struct iscsi_tmr_req *tmr_req)
+{
+	struct iscsi_conn *conn = cmd->conn;
+	struct iscsi_datain_req *dr;
+	struct se_cmd *se_cmd = &cmd->se_cmd;
+	/*
+	 * The Initiator must not send a Data SNACK with a BegRun less than
+	 * the TMR TASK_REASSIGN's ExpDataSN.
+	 */
+	if (!tmr_req->exp_data_sn) {
+		cmd->cmd_flags &= ~ICF_GOT_DATACK_SNACK;
+		cmd->acked_data_sn = 0;
+	} else {
+		cmd->cmd_flags |= ICF_GOT_DATACK_SNACK;
+		cmd->acked_data_sn = (tmr_req->exp_data_sn - 1);
+	}
+
+	if (!atomic_read(&cmd->transport_sent)) {
+		pr_debug("READ ITT: 0x%08x: t_state: %d never sent to"
+			" transport\n", cmd->init_task_tag,
+			cmd->se_cmd.t_state);
+		transport_generic_handle_cdb(se_cmd);
+		return 0;
+	}
+
+	if (!atomic_read(&se_cmd->t_transport_complete)) {
+		pr_err("READ ITT: 0x%08x: t_state: %d, never returned"
+			" from transport\n", cmd->init_task_tag,
+			cmd->se_cmd.t_state);
+		return -1;
+	}
+
+	dr = iscsit_allocate_datain_req();
+	if (!dr)
+		return -1;
+	/*
+	 * The TMR TASK_REASSIGN's ExpDataSN contains the next DataSN the
+	 * Initiator is expecting.
+	 */
+	dr->data_sn = dr->begrun = tmr_req->exp_data_sn;
+	dr->runlength = 0;
+	dr->generate_recovery_values = 1;
+	dr->recovery = DATAIN_CONNECTION_RECOVERY;
+
+	iscsit_attach_datain_req(cmd, dr);
+
+	cmd->i_state = ISTATE_SEND_DATAIN;
+	iscsit_add_cmd_to_response_queue(cmd, conn, cmd->i_state);
+	return 0;
+}
+
+static int iscsit_task_reassign_complete_none(
+	struct iscsi_cmd *cmd,
+	struct iscsi_tmr_req *tmr_req)
+{
+	struct iscsi_conn *conn = cmd->conn;
+
+	cmd->i_state = ISTATE_SEND_STATUS;
+	iscsit_add_cmd_to_response_queue(cmd, conn, cmd->i_state);
+	return 0;
+}
+
+static int iscsit_task_reassign_complete_scsi_cmnd(
+	struct iscsi_tmr_req *tmr_req,
+	struct iscsi_conn *conn)
+{
+	struct se_tmr_req *se_tmr = tmr_req->se_tmr_req;
+	struct se_cmd *se_cmd = se_tmr->ref_cmd;
+	struct iscsi_cmd *cmd = container_of(se_cmd, struct iscsi_cmd, se_cmd);
+	struct iscsi_conn_recovery *cr;
+
+	if (!cmd->cr) {
+		pr_err("struct iscsi_conn_recovery pointer for ITT: 0x%08x"
+			" is NULL!\n", cmd->init_task_tag);
+		return -1;
+	}
+	cr = cmd->cr;
+
+	/*
+	 * Reset the StatSN so a new one for this commands new connection
+	 * will be assigned.
+	 * Reset the ExpStatSN as well so we may receive Status SNACKs.
+	 */
+	cmd->stat_sn = cmd->exp_stat_sn = 0;
+
+	iscsit_task_reassign_remove_cmd(cmd, cr, conn->sess);
+
+	spin_lock_bh(&conn->cmd_lock);
+	list_add_tail(&cmd->i_list, &conn->conn_cmd_list);
+	spin_unlock_bh(&conn->cmd_lock);
+
+	if (se_cmd->se_cmd_flags & SCF_SENT_CHECK_CONDITION) {
+		cmd->i_state = ISTATE_SEND_STATUS;
+		iscsit_add_cmd_to_response_queue(cmd, conn, cmd->i_state);
+		return 0;
+	}
+
+	switch (cmd->data_direction) {
+	case DMA_TO_DEVICE:
+		return iscsit_task_reassign_complete_write(cmd, tmr_req);
+	case DMA_FROM_DEVICE:
+		return iscsit_task_reassign_complete_read(cmd, tmr_req);
+	case DMA_NONE:
+		return iscsit_task_reassign_complete_none(cmd, tmr_req);
+	default:
+		pr_err("Unknown cmd->data_direction: 0x%02x\n",
+				cmd->data_direction);
+		return -1;
+	}
+
+	return 0;
+}
+
+static int iscsit_task_reassign_complete(
+	struct iscsi_tmr_req *tmr_req,
+	struct iscsi_conn *conn)
+{
+	struct se_tmr_req *se_tmr = tmr_req->se_tmr_req;
+	struct se_cmd *se_cmd;
+	struct iscsi_cmd *cmd;
+	int ret = 0;
+
+	if (!se_tmr->ref_cmd) {
+		pr_err("TMR Request is missing a RefCmd struct iscsi_cmd.\n");
+		return -1;
+	}
+	se_cmd = se_tmr->ref_cmd;
+	cmd = container_of(se_cmd, struct iscsi_cmd, se_cmd);
+
+	cmd->conn = conn;
+
+	switch (cmd->iscsi_opcode) {
+	case ISCSI_OP_NOOP_OUT:
+		ret = iscsit_task_reassign_complete_nop_out(tmr_req, conn);
+		break;
+	case ISCSI_OP_SCSI_CMD:
+		ret = iscsit_task_reassign_complete_scsi_cmnd(tmr_req, conn);
+		break;
+	default:
+		 pr_err("Illegal iSCSI Opcode 0x%02x during"
+			" command realligence\n", cmd->iscsi_opcode);
+		return -1;
+	}
+
+	if (ret != 0)
+		return ret;
+
+	pr_debug("Completed connection realligence for Opcode: 0x%02x,"
+		" ITT: 0x%08x to CID: %hu.\n", cmd->iscsi_opcode,
+			cmd->init_task_tag, conn->cid);
+
+	return 0;
+}
+
+/*
+ *	Handles special after-the-fact actions related to TMRs.
+ *	Right now the only one that its really needed for is
+ *	connection recovery releated TASK_REASSIGN.
+ */
+extern int iscsit_tmr_post_handler(struct iscsi_cmd *cmd, struct iscsi_conn *conn)
+{
+	struct iscsi_tmr_req *tmr_req = cmd->tmr_req;
+	struct se_tmr_req *se_tmr = cmd->se_cmd.se_tmr_req;
+
+	if (tmr_req->task_reassign &&
+	   (se_tmr->response == ISCSI_TMF_RSP_COMPLETE))
+		return iscsit_task_reassign_complete(tmr_req, conn);
+
+	return 0;
+}
+
+/*
+ *	Nothing to do here, but leave it for good measure. :-)
+ */
+int iscsit_task_reassign_prepare_read(
+	struct iscsi_tmr_req *tmr_req,
+	struct iscsi_conn *conn)
+{
+	return 0;
+}
+
+static void iscsit_task_reassign_prepare_unsolicited_dataout(
+	struct iscsi_cmd *cmd,
+	struct iscsi_conn *conn)
+{
+	int i, j;
+	struct iscsi_pdu *pdu = NULL;
+	struct iscsi_seq *seq = NULL;
+
+	if (conn->sess->sess_ops->DataSequenceInOrder) {
+		cmd->data_sn = 0;
+
+		if (cmd->immediate_data)
+			cmd->r2t_offset += (cmd->first_burst_len -
+				cmd->seq_start_offset);
+
+		if (conn->sess->sess_ops->DataPDUInOrder) {
+			cmd->write_data_done -= (cmd->immediate_data) ?
+						(cmd->first_burst_len -
+						 cmd->seq_start_offset) :
+						 cmd->first_burst_len;
+			cmd->first_burst_len = 0;
+			return;
+		}
+
+		for (i = 0; i < cmd->pdu_count; i++) {
+			pdu = &cmd->pdu_list[i];
+
+			if (pdu->status != ISCSI_PDU_RECEIVED_OK)
+				continue;
+
+			if ((pdu->offset >= cmd->seq_start_offset) &&
+			   ((pdu->offset + pdu->length) <=
+			     cmd->seq_end_offset)) {
+				cmd->first_burst_len -= pdu->length;
+				cmd->write_data_done -= pdu->length;
+				pdu->status = ISCSI_PDU_NOT_RECEIVED;
+			}
+		}
+	} else {
+		for (i = 0; i < cmd->seq_count; i++) {
+			seq = &cmd->seq_list[i];
+
+			if (seq->type != SEQTYPE_UNSOLICITED)
+				continue;
+
+			cmd->write_data_done -=
+					(seq->offset - seq->orig_offset);
+			cmd->first_burst_len = 0;
+			seq->data_sn = 0;
+			seq->offset = seq->orig_offset;
+			seq->next_burst_len = 0;
+			seq->status = DATAOUT_SEQUENCE_WITHIN_COMMAND_RECOVERY;
+
+			if (conn->sess->sess_ops->DataPDUInOrder)
+				continue;
+
+			for (j = 0; j < seq->pdu_count; j++) {
+				pdu = &cmd->pdu_list[j+seq->pdu_start];
+
+				if (pdu->status != ISCSI_PDU_RECEIVED_OK)
+					continue;
+
+				pdu->status = ISCSI_PDU_NOT_RECEIVED;
+			}
+		}
+	}
+}
+
+int iscsit_task_reassign_prepare_write(
+	struct iscsi_tmr_req *tmr_req,
+	struct iscsi_conn *conn)
+{
+	struct se_tmr_req *se_tmr = tmr_req->se_tmr_req;
+	struct se_cmd *se_cmd = se_tmr->ref_cmd;
+	struct iscsi_cmd *cmd = container_of(se_cmd, struct iscsi_cmd, se_cmd);
+	struct iscsi_pdu *pdu = NULL;
+	struct iscsi_r2t *r2t = NULL, *r2t_tmp;
+	int first_incomplete_r2t = 1, i = 0;
+
+	/*
+	 * The command was in the process of receiving Unsolicited DataOUT when
+	 * the connection failed.
+	 */
+	if (cmd->unsolicited_data)
+		iscsit_task_reassign_prepare_unsolicited_dataout(cmd, conn);
+
+	/*
+	 * The Initiator is requesting R2Ts starting from zero,  skip
+	 * checking acknowledged R2Ts and start checking struct iscsi_r2ts
+	 * greater than zero.
+	 */
+	if (!tmr_req->exp_data_sn)
+		goto drop_unacknowledged_r2ts;
+
+	/*
+	 * We now check that the PDUs in DataOUT sequences below
+	 * the TMR TASK_REASSIGN ExpDataSN (R2TSN the Initiator is
+	 * expecting next) have all the DataOUT they require to complete
+	 * the DataOUT sequence.  First scan from R2TSN 0 to TMR
+	 * TASK_REASSIGN ExpDataSN-1.
+	 *
+	 * If we have not received all DataOUT in question,  we must
+	 * make sure to make the appropriate changes to values in
+	 * struct iscsi_cmd (and elsewhere depending on session parameters)
+	 * so iscsit_build_r2ts_for_cmd() in iscsit_task_reassign_complete_write()
+	 * will resend a new R2T for the DataOUT sequences in question.
+	 */
+	spin_lock_bh(&cmd->r2t_lock);
+	if (list_empty(&cmd->cmd_r2t_list)) {
+		spin_unlock_bh(&cmd->r2t_lock);
+		return -1;
+	}
+
+	list_for_each_entry(r2t, &cmd->cmd_r2t_list, r2t_list) {
+
+		if (r2t->r2t_sn >= tmr_req->exp_data_sn)
+			continue;
+		/*
+		 * Safely ignore Recovery R2Ts and R2Ts that have completed
+		 * DataOUT sequences.
+		 */
+		if (r2t->seq_complete)
+			continue;
+
+		if (r2t->recovery_r2t)
+			continue;
+
+		/*
+		 *                 DataSequenceInOrder=Yes:
+		 *
+		 * Taking into account the iSCSI implementation requirement of
+		 * MaxOutstandingR2T=1 while ErrorRecoveryLevel>0 and
+		 * DataSequenceInOrder=Yes, we must take into consideration
+		 * the following:
+		 *
+		 *                  DataSequenceInOrder=No:
+		 *
+		 * Taking into account that the Initiator controls the (possibly
+		 * random) PDU Order in (possibly random) Sequence Order of
+		 * DataOUT the target requests with R2Ts,  we must take into
+		 * consideration the following:
+		 *
+		 *      DataPDUInOrder=Yes for DataSequenceInOrder=[Yes,No]:
+		 *
+		 * While processing non-complete R2T DataOUT sequence requests
+		 * the Target will re-request only the total sequence length
+		 * minus current received offset.  This is because we must
+		 * assume the initiator will continue sending DataOUT from the
+		 * last PDU before the connection failed.
+		 *
+		 *      DataPDUInOrder=No for DataSequenceInOrder=[Yes,No]:
+		 *
+		 * While processing non-complete R2T DataOUT sequence requests
+		 * the Target will re-request the entire DataOUT sequence if
+		 * any single PDU is missing from the sequence.  This is because
+		 * we have no logical method to determine the next PDU offset,
+		 * and we must assume the Initiator will be sending any random
+		 * PDU offset in the current sequence after TASK_REASSIGN
+		 * has completed.
+		 */
+		if (conn->sess->sess_ops->DataSequenceInOrder) {
+			if (!first_incomplete_r2t) {
+				cmd->r2t_offset -= r2t->xfer_len;
+				goto next;
+			}
+
+			if (conn->sess->sess_ops->DataPDUInOrder) {
+				cmd->data_sn = 0;
+				cmd->r2t_offset -= (r2t->xfer_len -
+					cmd->next_burst_len);
+				first_incomplete_r2t = 0;
+				goto next;
+			}
+
+			cmd->data_sn = 0;
+			cmd->r2t_offset -= r2t->xfer_len;
+
+			for (i = 0; i < cmd->pdu_count; i++) {
+				pdu = &cmd->pdu_list[i];
+
+				if (pdu->status != ISCSI_PDU_RECEIVED_OK)
+					continue;
+
+				if ((pdu->offset >= r2t->offset) &&
+				    (pdu->offset < (r2t->offset +
+						r2t->xfer_len))) {
+					cmd->next_burst_len -= pdu->length;
+					cmd->write_data_done -= pdu->length;
+					pdu->status = ISCSI_PDU_NOT_RECEIVED;
+				}
+			}
+
+			first_incomplete_r2t = 0;
+		} else {
+			struct iscsi_seq *seq;
+
+			seq = iscsit_get_seq_holder(cmd, r2t->offset,
+					r2t->xfer_len);
+			if (!seq) {
+				spin_unlock_bh(&cmd->r2t_lock);
+				return -1;
+			}
+
+			cmd->write_data_done -=
+					(seq->offset - seq->orig_offset);
+			seq->data_sn = 0;
+			seq->offset = seq->orig_offset;
+			seq->next_burst_len = 0;
+			seq->status = DATAOUT_SEQUENCE_WITHIN_COMMAND_RECOVERY;
+
+			cmd->seq_send_order--;
+
+			if (conn->sess->sess_ops->DataPDUInOrder)
+				goto next;
+
+			for (i = 0; i < seq->pdu_count; i++) {
+				pdu = &cmd->pdu_list[i+seq->pdu_start];
+
+				if (pdu->status != ISCSI_PDU_RECEIVED_OK)
+					continue;
+
+				pdu->status = ISCSI_PDU_NOT_RECEIVED;
+			}
+		}
+
+next:
+		cmd->outstanding_r2ts--;
+	}
+	spin_unlock_bh(&cmd->r2t_lock);
+
+	/*
+	 * We now drop all unacknowledged R2Ts, ie: ExpDataSN from TMR
+	 * TASK_REASSIGN to the last R2T in the list..  We are also careful
+	 * to check that the Initiator is not requesting R2Ts for DataOUT
+	 * sequences it has already completed.
+	 *
+	 * Free each R2T in question and adjust values in struct iscsi_cmd
+	 * accordingly so iscsit_build_r2ts_for_cmd() do the rest of
+	 * the work after the TMR TASK_REASSIGN Response is sent.
+	 */
+drop_unacknowledged_r2ts:
+
+	cmd->cmd_flags &= ~ICF_SENT_LAST_R2T;
+	cmd->r2t_sn = tmr_req->exp_data_sn;
+
+	spin_lock_bh(&cmd->r2t_lock);
+	list_for_each_entry_safe(r2t, r2t_tmp, &cmd->cmd_r2t_list, r2t_list) {
+		/*
+		 * Skip up to the R2T Sequence number provided by the
+		 * iSCSI TASK_REASSIGN TMR
+		 */
+		if (r2t->r2t_sn < tmr_req->exp_data_sn)
+			continue;
+
+		if (r2t->seq_complete) {
+			pr_err("Initiator is requesting R2Ts from"
+				" R2TSN: 0x%08x, but R2TSN: 0x%08x, Offset: %u,"
+				" Length: %u is already complete."
+				"   BAD INITIATOR ERL=2 IMPLEMENTATION!\n",
+				tmr_req->exp_data_sn, r2t->r2t_sn,
+				r2t->offset, r2t->xfer_len);
+			spin_unlock_bh(&cmd->r2t_lock);
+			return -1;
+		}
+
+		if (r2t->recovery_r2t) {
+			iscsit_free_r2t(r2t, cmd);
+			continue;
+		}
+
+		/*		   DataSequenceInOrder=Yes:
+		 *
+		 * Taking into account the iSCSI implementation requirement of
+		 * MaxOutstandingR2T=1 while ErrorRecoveryLevel>0 and
+		 * DataSequenceInOrder=Yes, it's safe to subtract the R2Ts
+		 * entire transfer length from the commands R2T offset marker.
+		 *
+		 *		   DataSequenceInOrder=No:
+		 *
+		 * We subtract the difference from struct iscsi_seq between the
+		 * current offset and original offset from cmd->write_data_done
+		 * for account for DataOUT PDUs already received.  Then reset
+		 * the current offset to the original and zero out the current
+		 * burst length,  to make sure we re-request the entire DataOUT
+		 * sequence.
+		 */
+		if (conn->sess->sess_ops->DataSequenceInOrder)
+			cmd->r2t_offset -= r2t->xfer_len;
+		else
+			cmd->seq_send_order--;
+
+		cmd->outstanding_r2ts--;
+		iscsit_free_r2t(r2t, cmd);
+	}
+	spin_unlock_bh(&cmd->r2t_lock);
+
+	return 0;
+}
+
+/*
+ *	Performs sanity checks TMR TASK_REASSIGN's ExpDataSN for
+ *	a given struct iscsi_cmd.
+ */
+int iscsit_check_task_reassign_expdatasn(
+	struct iscsi_tmr_req *tmr_req,
+	struct iscsi_conn *conn)
+{
+	struct se_tmr_req *se_tmr = tmr_req->se_tmr_req;
+	struct se_cmd *se_cmd = se_tmr->ref_cmd;
+	struct iscsi_cmd *ref_cmd = container_of(se_cmd, struct iscsi_cmd, se_cmd);
+
+	if (ref_cmd->iscsi_opcode != ISCSI_OP_SCSI_CMD)
+		return 0;
+
+	if (se_cmd->se_cmd_flags & SCF_SENT_CHECK_CONDITION)
+		return 0;
+
+	if (ref_cmd->data_direction == DMA_NONE)
+		return 0;
+
+	/*
+	 * For READs the TMR TASK_REASSIGNs ExpDataSN contains the next DataSN
+	 * of DataIN the Initiator is expecting.
+	 *
+	 * Also check that the Initiator is not re-requesting DataIN that has
+	 * already been acknowledged with a DataAck SNACK.
+	 */
+	if (ref_cmd->data_direction == DMA_FROM_DEVICE) {
+		if (tmr_req->exp_data_sn > ref_cmd->data_sn) {
+			pr_err("Received ExpDataSN: 0x%08x for READ"
+				" in TMR TASK_REASSIGN greater than command's"
+				" DataSN: 0x%08x.\n", tmr_req->exp_data_sn,
+				ref_cmd->data_sn);
+			return -1;
+		}
+		if ((ref_cmd->cmd_flags & ICF_GOT_DATACK_SNACK) &&
+		    (tmr_req->exp_data_sn <= ref_cmd->acked_data_sn)) {
+			pr_err("Received ExpDataSN: 0x%08x for READ"
+				" in TMR TASK_REASSIGN for previously"
+				" acknowledged DataIN: 0x%08x,"
+				" protocol error\n", tmr_req->exp_data_sn,
+				ref_cmd->acked_data_sn);
+			return -1;
+		}
+		return iscsit_task_reassign_prepare_read(tmr_req, conn);
+	}
+
+	/*
+	 * For WRITEs the TMR TASK_REASSIGNs ExpDataSN contains the next R2TSN
+	 * for R2Ts the Initiator is expecting.
+	 *
+	 * Do the magic in iscsit_task_reassign_prepare_write().
+	 */
+	if (ref_cmd->data_direction == DMA_TO_DEVICE) {
+		if (tmr_req->exp_data_sn > ref_cmd->r2t_sn) {
+			pr_err("Received ExpDataSN: 0x%08x for WRITE"
+				" in TMR TASK_REASSIGN greater than command's"
+				" R2TSN: 0x%08x.\n", tmr_req->exp_data_sn,
+					ref_cmd->r2t_sn);
+			return -1;
+		}
+		return iscsit_task_reassign_prepare_write(tmr_req, conn);
+	}
+
+	pr_err("Unknown iSCSI data_direction: 0x%02x\n",
+			ref_cmd->data_direction);
+
+	return -1;
+}