// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * iSCSI lib functions
 *
 * Copyright (C) 2006 Red Hat, Inc.  All rights reserved.
 * Copyright (C) 2004 - 2006 Mike Christie
 * Copyright (C) 2004 - 2005 Dmitry Yusupov
 * Copyright (C) 2004 - 2005 Alex Aizman
 * maintained by open-iscsi@googlegroups.com
 */
#include <linux/types.h>
#include <linux/kfifo.h>
#include <linux/delay.h>
#include <linux/log2.h>
#include <linux/slab.h>
#include <linux/sched/signal.h>
#include <linux/module.h>
#include <asm/unaligned.h>
#include <net/tcp.h>
#include <scsi/scsi_cmnd.h>
#include <scsi/scsi_device.h>
#include <scsi/scsi_eh.h>
#include <scsi/scsi_tcq.h>
#include <scsi/scsi_host.h>
#include <scsi/scsi.h>
#include <scsi/iscsi_proto.h>
#include <scsi/scsi_transport.h>
#include <scsi/scsi_transport_iscsi.h>
#include <scsi/libiscsi.h>
#include <trace/events/iscsi.h>

static int iscsi_dbg_lib_conn;
module_param_named(debug_libiscsi_conn, iscsi_dbg_lib_conn, int,
                   S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(debug_libiscsi_conn,
                 "Turn on debugging for connections in libiscsi module. "
                 "Set to 1 to turn on, and zero to turn off. Default is off.");

static int iscsi_dbg_lib_session;
module_param_named(debug_libiscsi_session, iscsi_dbg_lib_session, int,
                   S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(debug_libiscsi_session,
                 "Turn on debugging for sessions in libiscsi module. "
                 "Set to 1 to turn on, and zero to turn off. Default is off.");

static int iscsi_dbg_lib_eh;
module_param_named(debug_libiscsi_eh, iscsi_dbg_lib_eh, int,
                   S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(debug_libiscsi_eh,
                 "Turn on debugging for error handling in libiscsi module. "
                 "Set to 1 to turn on, and zero to turn off. Default is off.");

#define ISCSI_DBG_CONN(_conn, dbg_fmt, arg...)                  \
        do {                                                    \
                if (iscsi_dbg_lib_conn)                         \
                        iscsi_conn_printk(KERN_INFO, _conn,     \
                                             "%s " dbg_fmt,     \
                                             __func__, ##arg);  \
                iscsi_dbg_trace(trace_iscsi_dbg_conn,           \
                                &(_conn)->cls_conn->dev,        \
                                "%s " dbg_fmt, __func__, ##arg);\
        } while (0);

#define ISCSI_DBG_SESSION(_session, dbg_fmt, arg...)                    \
        do {                                                            \
                if (iscsi_dbg_lib_session)                              \
                        iscsi_session_printk(KERN_INFO, _session,       \
                                             "%s " dbg_fmt,             \
                                             __func__, ##arg);          \
                iscsi_dbg_trace(trace_iscsi_dbg_session,                \
                                &(_session)->cls_session->dev,          \
                                "%s " dbg_fmt, __func__, ##arg);        \
        } while (0);

#define ISCSI_DBG_EH(_session, dbg_fmt, arg...)                         \
        do {                                                            \
                if (iscsi_dbg_lib_eh)                                   \
                        iscsi_session_printk(KERN_INFO, _session,       \
                                             "%s " dbg_fmt,             \
                                             __func__, ##arg);          \
                iscsi_dbg_trace(trace_iscsi_dbg_eh,                     \
                                &(_session)->cls_session->dev,          \
                                "%s " dbg_fmt, __func__, ##arg);        \
        } while (0);

inline void iscsi_conn_queue_work(struct iscsi_conn *conn)
{
        struct Scsi_Host *shost = conn->session->host;
        struct iscsi_host *ihost = shost_priv(shost);

        if (ihost->workq)
                queue_work(ihost->workq, &conn->xmitwork);
}
EXPORT_SYMBOL_GPL(iscsi_conn_queue_work);

static void __iscsi_update_cmdsn(struct iscsi_session *session,
                                 uint32_t exp_cmdsn, uint32_t max_cmdsn)
{
        /*
         * standard specifies this check for when to update expected and
         * max sequence numbers
         */
        if (iscsi_sna_lt(max_cmdsn, exp_cmdsn - 1))
                return;

        if (exp_cmdsn != session->exp_cmdsn &&
            !iscsi_sna_lt(exp_cmdsn, session->exp_cmdsn))
                session->exp_cmdsn = exp_cmdsn;

        if (max_cmdsn != session->max_cmdsn &&
            !iscsi_sna_lt(max_cmdsn, session->max_cmdsn))
                session->max_cmdsn = max_cmdsn;
}

void iscsi_update_cmdsn(struct iscsi_session *session, struct iscsi_nopin *hdr)
{
        __iscsi_update_cmdsn(session, be32_to_cpu(hdr->exp_cmdsn),
                             be32_to_cpu(hdr->max_cmdsn));
}
EXPORT_SYMBOL_GPL(iscsi_update_cmdsn);

/**
 * iscsi_prep_data_out_pdu - initialize Data-Out
 * @task: scsi command task
 * @r2t: R2T info
 * @hdr: iscsi data in pdu
 *
 * Notes:
 *      Initialize Data-Out within this R2T sequence and finds
 *      proper data_offset within this SCSI command.
 *
 *      This function is called with connection lock taken.
 **/
void iscsi_prep_data_out_pdu(struct iscsi_task *task, struct iscsi_r2t_info *r2t,
                           struct iscsi_data *hdr)
{
        struct iscsi_conn *conn = task->conn;
        unsigned int left = r2t->data_length - r2t->sent;

        task->hdr_len = sizeof(struct iscsi_data);

        memset(hdr, 0, sizeof(struct iscsi_data));
        hdr->ttt = r2t->ttt;
        hdr->datasn = cpu_to_be32(r2t->datasn);
        r2t->datasn++;
        hdr->opcode = ISCSI_OP_SCSI_DATA_OUT;
        hdr->lun = task->lun;
        hdr->itt = task->hdr_itt;
        hdr->exp_statsn = r2t->exp_statsn;
        hdr->offset = cpu_to_be32(r2t->data_offset + r2t->sent);
        if (left > conn->max_xmit_dlength) {
                hton24(hdr->dlength, conn->max_xmit_dlength);
                r2t->data_count = conn->max_xmit_dlength;
                hdr->flags = 0;
        } else {
                hton24(hdr->dlength, left);
                r2t->data_count = left;
                hdr->flags = ISCSI_FLAG_CMD_FINAL;
        }
        conn->dataout_pdus_cnt++;
}
EXPORT_SYMBOL_GPL(iscsi_prep_data_out_pdu);

static int iscsi_add_hdr(struct iscsi_task *task, unsigned len)
{
        unsigned exp_len = task->hdr_len + len;

        if (exp_len > task->hdr_max) {
                WARN_ON(1);
                return -EINVAL;
        }

        WARN_ON(len & (ISCSI_PAD_LEN - 1)); /* caller must pad the AHS */
        task->hdr_len = exp_len;
        return 0;
}

/*
 * make an extended cdb AHS
 */
static int iscsi_prep_ecdb_ahs(struct iscsi_task *task)
{
        struct scsi_cmnd *cmd = task->sc;
        unsigned rlen, pad_len;
        unsigned short ahslength;
        struct iscsi_ecdb_ahdr *ecdb_ahdr;
        int rc;

        ecdb_ahdr = iscsi_next_hdr(task);
        rlen = cmd->cmd_len - ISCSI_CDB_SIZE;

        BUG_ON(rlen > sizeof(ecdb_ahdr->ecdb));
        ahslength = rlen + sizeof(ecdb_ahdr->reserved);

        pad_len = iscsi_padding(rlen);

        rc = iscsi_add_hdr(task, sizeof(ecdb_ahdr->ahslength) +
                           sizeof(ecdb_ahdr->ahstype) + ahslength + pad_len);
        if (rc)
                return rc;

        if (pad_len)
                memset(&ecdb_ahdr->ecdb[rlen], 0, pad_len);

        ecdb_ahdr->ahslength = cpu_to_be16(ahslength);
        ecdb_ahdr->ahstype = ISCSI_AHSTYPE_CDB;
        ecdb_ahdr->reserved = 0;
        memcpy(ecdb_ahdr->ecdb, cmd->cmnd + ISCSI_CDB_SIZE, rlen);

        ISCSI_DBG_SESSION(task->conn->session,
                          "iscsi_prep_ecdb_ahs: varlen_cdb_len %d "
                          "rlen %d pad_len %d ahs_length %d iscsi_headers_size "
                          "%u\n", cmd->cmd_len, rlen, pad_len, ahslength,
                          task->hdr_len);
        return 0;
}

/**
 * iscsi_check_tmf_restrictions - check if a task is affected by TMF
 * @task: iscsi task
 * @opcode: opcode to check for
 *
 * During TMF a task has to be checked if it's affected.
 * All unrelated I/O can be passed through, but I/O to the
 * affected LUN should be restricted.
 * If 'fast_abort' is set we won't be sending any I/O to the
 * affected LUN.
 * Otherwise the target is waiting for all TTTs to be completed,
 * so we have to send all outstanding Data-Out PDUs to the target.
 */
static int iscsi_check_tmf_restrictions(struct iscsi_task *task, int opcode)
{
        struct iscsi_session *session = task->conn->session;
        struct iscsi_tm *tmf = &session->tmhdr;
        u64 hdr_lun;

        if (session->tmf_state == TMF_INITIAL)
                return 0;

        if ((tmf->opcode & ISCSI_OPCODE_MASK) != ISCSI_OP_SCSI_TMFUNC)
                return 0;

        switch (ISCSI_TM_FUNC_VALUE(tmf)) {
        case ISCSI_TM_FUNC_LOGICAL_UNIT_RESET:
                /*
                 * Allow PDUs for unrelated LUNs
                 */
                hdr_lun = scsilun_to_int(&tmf->lun);
                if (hdr_lun != task->sc->device->lun)
                        return 0;
                fallthrough;
        case ISCSI_TM_FUNC_TARGET_WARM_RESET:
                /*
                 * Fail all SCSI cmd PDUs
                 */
                if (opcode != ISCSI_OP_SCSI_DATA_OUT) {
                        iscsi_session_printk(KERN_INFO, session,
                                             "task [op %x itt 0x%x/0x%x] rejected.\n",
                                             opcode, task->itt, task->hdr_itt);
                        return -EACCES;
                }
                /*
                 * And also all data-out PDUs in response to R2T
                 * if fast_abort is set.
                 */
                if (session->fast_abort) {
                        iscsi_session_printk(KERN_INFO, session,
                                             "task [op %x itt 0x%x/0x%x] fast abort.\n",
                                             opcode, task->itt, task->hdr_itt);
                        return -EACCES;
                }
                break;
        case ISCSI_TM_FUNC_ABORT_TASK:
                /*
                 * the caller has already checked if the task
                 * they want to abort was in the pending queue so if
                 * we are here the cmd pdu has gone out already, and
                 * we will only hit this for data-outs
                 */
                if (opcode == ISCSI_OP_SCSI_DATA_OUT &&
                    task->hdr_itt == tmf->rtt) {
                        ISCSI_DBG_SESSION(session,
                                          "Preventing task %x/%x from sending "
                                          "data-out due to abort task in "
                                          "progress\n", task->itt,
                                          task->hdr_itt);
                        return -EACCES;
                }
                break;
        }

        return 0;
}

/**
 * iscsi_prep_scsi_cmd_pdu - prep iscsi scsi cmd pdu
 * @task: iscsi task
 *
 * Prep basic iSCSI PDU fields for a scsi cmd pdu. The LLD should set
 * fields like dlength or final based on how much data it sends
 */
static int iscsi_prep_scsi_cmd_pdu(struct iscsi_task *task)
{
        struct iscsi_conn *conn = task->conn;
        struct iscsi_session *session = conn->session;
        struct scsi_cmnd *sc = task->sc;
        struct iscsi_scsi_req *hdr;
        unsigned hdrlength, cmd_len, transfer_length;
        itt_t itt;
        int rc;

        rc = iscsi_check_tmf_restrictions(task, ISCSI_OP_SCSI_CMD);
        if (rc)
                return rc;

        if (conn->session->tt->alloc_pdu) {
                rc = conn->session->tt->alloc_pdu(task, ISCSI_OP_SCSI_CMD);
                if (rc)
                        return rc;
        }
        hdr = (struct iscsi_scsi_req *)task->hdr;
        itt = hdr->itt;
        memset(hdr, 0, sizeof(*hdr));

        if (session->tt->parse_pdu_itt)
                hdr->itt = task->hdr_itt = itt;
        else
                hdr->itt = task->hdr_itt = build_itt(task->itt,
                                                     task->conn->session->age);
        task->hdr_len = 0;
        rc = iscsi_add_hdr(task, sizeof(*hdr));
        if (rc)
                return rc;
        hdr->opcode = ISCSI_OP_SCSI_CMD;
        hdr->flags = ISCSI_ATTR_SIMPLE;
        int_to_scsilun(sc->device->lun, &hdr->lun);
        task->lun = hdr->lun;
        hdr->exp_statsn = cpu_to_be32(conn->exp_statsn);
        cmd_len = sc->cmd_len;
        if (cmd_len < ISCSI_CDB_SIZE)
                memset(&hdr->cdb[cmd_len], 0, ISCSI_CDB_SIZE - cmd_len);
        else if (cmd_len > ISCSI_CDB_SIZE) {
                rc = iscsi_prep_ecdb_ahs(task);
                if (rc)
                        return rc;
                cmd_len = ISCSI_CDB_SIZE;
        }
        memcpy(hdr->cdb, sc->cmnd, cmd_len);

        task->imm_count = 0;
        if (scsi_get_prot_op(sc) != SCSI_PROT_NORMAL)
                task->protected = true;

        transfer_length = scsi_transfer_length(sc);
        hdr->data_length = cpu_to_be32(transfer_length);
        if (sc->sc_data_direction == DMA_TO_DEVICE) {
                struct iscsi_r2t_info *r2t = &task->unsol_r2t;

                hdr->flags |= ISCSI_FLAG_CMD_WRITE;
                /*
                 * Write counters:
                 *
                 *      imm_count       bytes to be sent right after
                 *                      SCSI PDU Header
                 *
                 *      unsol_count     bytes(as Data-Out) to be sent
                 *                      without R2T ack right after
                 *                      immediate data
                 *
                 *      r2t data_length bytes to be sent via R2T ack's
                 *
                 *      pad_count       bytes to be sent as zero-padding
                 */
                memset(r2t, 0, sizeof(*r2t));

                if (session->imm_data_en) {
                        if (transfer_length >= session->first_burst)
                                task->imm_count = min(session->first_burst,
                                                        conn->max_xmit_dlength);
                        else
                                task->imm_count = min(transfer_length,
                                                      conn->max_xmit_dlength);
                        hton24(hdr->dlength, task->imm_count);
                } else
                        zero_data(hdr->dlength);

                if (!session->initial_r2t_en) {
                        r2t->data_length = min(session->first_burst,
                                               transfer_length) -
                                               task->imm_count;
                        r2t->data_offset = task->imm_count;
                        r2t->ttt = cpu_to_be32(ISCSI_RESERVED_TAG);
                        r2t->exp_statsn = cpu_to_be32(conn->exp_statsn);
                }

                if (!task->unsol_r2t.data_length)
                        /* No unsolicit Data-Out's */
                        hdr->flags |= ISCSI_FLAG_CMD_FINAL;
        } else {
                hdr->flags |= ISCSI_FLAG_CMD_FINAL;
                zero_data(hdr->dlength);

                if (sc->sc_data_direction == DMA_FROM_DEVICE)
                        hdr->flags |= ISCSI_FLAG_CMD_READ;
        }

        /* calculate size of additional header segments (AHSs) */
        hdrlength = task->hdr_len - sizeof(*hdr);

        WARN_ON(hdrlength & (ISCSI_PAD_LEN-1));
        hdrlength /= ISCSI_PAD_LEN;

        WARN_ON(hdrlength >= 256);
        hdr->hlength = hdrlength & 0xFF;
        hdr->cmdsn = task->cmdsn = cpu_to_be32(session->cmdsn);

        if (session->tt->init_task && session->tt->init_task(task))
                return -EIO;

        task->state = ISCSI_TASK_RUNNING;
        session->cmdsn++;

        conn->scsicmd_pdus_cnt++;
        ISCSI_DBG_SESSION(session, "iscsi prep [%s cid %d sc %p cdb 0x%x "
                          "itt 0x%x len %d cmdsn %d win %d]\n",
                          sc->sc_data_direction == DMA_TO_DEVICE ?
                          "write" : "read", conn->id, sc, sc->cmnd[0],
                          task->itt, transfer_length,
                          session->cmdsn,
                          session->max_cmdsn - session->exp_cmdsn + 1);
        return 0;
}

/**
 * iscsi_free_task - free a task
 * @task: iscsi cmd task
 *
 * Must be called with session back_lock.
 * This function returns the scsi command to scsi-ml or cleans
 * up mgmt tasks then returns the task to the pool.
 */
static void iscsi_free_task(struct iscsi_task *task)
{
        struct iscsi_conn *conn = task->conn;
        struct iscsi_session *session = conn->session;
        struct scsi_cmnd *sc = task->sc;
        int oldstate = task->state;

        ISCSI_DBG_SESSION(session, "freeing task itt 0x%x state %d sc %p\n",
                          task->itt, task->state, task->sc);

        session->tt->cleanup_task(task);
        task->state = ISCSI_TASK_FREE;
        task->sc = NULL;
        /*
         * login task is preallocated so do not free
         */
        if (conn->login_task == task)
                return;

        kfifo_in(&session->cmdpool.queue, (void*)&task, sizeof(void*));

        if (sc) {
                /* SCSI eh reuses commands to verify us */
                sc->SCp.ptr = NULL;
                /*
                 * queue command may call this to free the task, so
                 * it will decide how to return sc to scsi-ml.
                 */
                if (oldstate != ISCSI_TASK_REQUEUE_SCSIQ)
                        sc->scsi_done(sc);
        }
}

void __iscsi_get_task(struct iscsi_task *task)
{
        refcount_inc(&task->refcount);
}
EXPORT_SYMBOL_GPL(__iscsi_get_task);

void __iscsi_put_task(struct iscsi_task *task)
{
        if (refcount_dec_and_test(&task->refcount))
                iscsi_free_task(task);
}
EXPORT_SYMBOL_GPL(__iscsi_put_task);

void iscsi_put_task(struct iscsi_task *task)
{
        struct iscsi_session *session = task->conn->session;

        /* regular RX path uses back_lock */
        spin_lock_bh(&session->back_lock);
        __iscsi_put_task(task);
        spin_unlock_bh(&session->back_lock);
}
EXPORT_SYMBOL_GPL(iscsi_put_task);

/**
 * iscsi_complete_task - finish a task
 * @task: iscsi cmd task
 * @state: state to complete task with
 *
 * Must be called with session back_lock.
 */
static void iscsi_complete_task(struct iscsi_task *task, int state)
{
        struct iscsi_conn *conn = task->conn;

        ISCSI_DBG_SESSION(conn->session,
                          "complete task itt 0x%x state %d sc %p\n",
                          task->itt, task->state, task->sc);
        if (task->state == ISCSI_TASK_COMPLETED ||
            task->state == ISCSI_TASK_ABRT_TMF ||
            task->state == ISCSI_TASK_ABRT_SESS_RECOV ||
            task->state == ISCSI_TASK_REQUEUE_SCSIQ)
                return;
        WARN_ON_ONCE(task->state == ISCSI_TASK_FREE);
        task->state = state;

        if (READ_ONCE(conn->ping_task) == task)
                WRITE_ONCE(conn->ping_task, NULL);

        /* release get from queueing */
        __iscsi_put_task(task);
}

/**
 * iscsi_complete_scsi_task - finish scsi task normally
 * @task: iscsi task for scsi cmd
 * @exp_cmdsn: expected cmd sn in cpu format
 * @max_cmdsn: max cmd sn in cpu format
 *
 * This is used when drivers do not need or cannot perform
 * lower level pdu processing.
 *
 * Called with session back_lock
 */
void iscsi_complete_scsi_task(struct iscsi_task *task,
                              uint32_t exp_cmdsn, uint32_t max_cmdsn)
{
        struct iscsi_conn *conn = task->conn;

        ISCSI_DBG_SESSION(conn->session, "[itt 0x%x]\n", task->itt);

        conn->last_recv = jiffies;
        __iscsi_update_cmdsn(conn->session, exp_cmdsn, max_cmdsn);
        iscsi_complete_task(task, ISCSI_TASK_COMPLETED);
}
EXPORT_SYMBOL_GPL(iscsi_complete_scsi_task);

/*
 * Must be called with back and frwd lock
 */
static bool cleanup_queued_task(struct iscsi_task *task)
{
        struct iscsi_conn *conn = task->conn;
        bool early_complete = false;

        /* Bad target might have completed task while it was still running */
        if (task->state == ISCSI_TASK_COMPLETED)
                early_complete = true;

        if (!list_empty(&task->running)) {
                list_del_init(&task->running);
                /*
                 * If it's on a list but still running, this could be from
                 * a bad target sending a rsp early, cleanup from a TMF, or
                 * session recovery.
                 */
                if (task->state == ISCSI_TASK_RUNNING ||
                    task->state == ISCSI_TASK_COMPLETED)
                        __iscsi_put_task(task);
        }

        if (conn->session->running_aborted_task == task) {
                conn->session->running_aborted_task = NULL;
                __iscsi_put_task(task);
        }

        if (conn->task == task) {
                conn->task = NULL;
                __iscsi_put_task(task);
        }

        return early_complete;
}

/*
 * session frwd lock must be held and if not called for a task that is still
 * pending or from the xmit thread, then xmit thread must be suspended
 */
static void fail_scsi_task(struct iscsi_task *task, int err)
{
        struct iscsi_conn *conn = task->conn;
        struct scsi_cmnd *sc;
        int state;

        spin_lock_bh(&conn->session->back_lock);
        if (cleanup_queued_task(task)) {
                spin_unlock_bh(&conn->session->back_lock);
                return;
        }

        if (task->state == ISCSI_TASK_PENDING) {
                /*
                 * cmd never made it to the xmit thread, so we should not count
                 * the cmd in the sequencing
                 */
                conn->session->queued_cmdsn--;
                /* it was never sent so just complete like normal */
                state = ISCSI_TASK_COMPLETED;
        } else if (err == DID_TRANSPORT_DISRUPTED)
                state = ISCSI_TASK_ABRT_SESS_RECOV;
        else
                state = ISCSI_TASK_ABRT_TMF;

        sc = task->sc;
        sc->result = err << 16;
        scsi_set_resid(sc, scsi_bufflen(sc));
        iscsi_complete_task(task, state);
        spin_unlock_bh(&conn->session->back_lock);
}

static int iscsi_prep_mgmt_task(struct iscsi_conn *conn,
                                struct iscsi_task *task)
{
        struct iscsi_session *session = conn->session;
        struct iscsi_hdr *hdr = task->hdr;
        struct iscsi_nopout *nop = (struct iscsi_nopout *)hdr;
        uint8_t opcode = hdr->opcode & ISCSI_OPCODE_MASK;

        if (conn->session->state == ISCSI_STATE_LOGGING_OUT)
                return -ENOTCONN;

        if (opcode != ISCSI_OP_LOGIN && opcode != ISCSI_OP_TEXT)
                nop->exp_statsn = cpu_to_be32(conn->exp_statsn);
        /*
         * pre-format CmdSN for outgoing PDU.
         */
        nop->cmdsn = cpu_to_be32(session->cmdsn);
        if (hdr->itt != RESERVED_ITT) {
                /*
                 * TODO: We always use immediate for normal session pdus.
                 * If we start to send tmfs or nops as non-immediate then
                 * we should start checking the cmdsn numbers for mgmt tasks.
                 *
                 * During discovery sessions iscsid sends TEXT as non immediate,
                 * but we always only send one PDU at a time.
                 */
                if (conn->c_stage == ISCSI_CONN_STARTED &&
                    !(hdr->opcode & ISCSI_OP_IMMEDIATE)) {
                        session->queued_cmdsn++;
                        session->cmdsn++;
                }
        }

        if (session->tt->init_task && session->tt->init_task(task))
                return -EIO;

        if ((hdr->opcode & ISCSI_OPCODE_MASK) == ISCSI_OP_LOGOUT)
                session->state = ISCSI_STATE_LOGGING_OUT;

        task->state = ISCSI_TASK_RUNNING;
        ISCSI_DBG_SESSION(session, "mgmtpdu [op 0x%x hdr->itt 0x%x "
                          "datalen %d]\n", hdr->opcode & ISCSI_OPCODE_MASK,
                          hdr->itt, task->data_count);
        return 0;
}

static struct iscsi_task *
__iscsi_conn_send_pdu(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
                      char *data, uint32_t data_size)
{
        struct iscsi_session *session = conn->session;
        struct iscsi_host *ihost = shost_priv(session->host);
        uint8_t opcode = hdr->opcode & ISCSI_OPCODE_MASK;
        struct iscsi_task *task;
        itt_t itt;

        if (session->state == ISCSI_STATE_TERMINATE)
                return NULL;

        if (opcode == ISCSI_OP_LOGIN || opcode == ISCSI_OP_TEXT) {
                /*
                 * Login and Text are sent serially, in
                 * request-followed-by-response sequence.
                 * Same task can be used. Same ITT must be used.
                 * Note that login_task is preallocated at conn_create().
                 */
                if (conn->login_task->state != ISCSI_TASK_FREE) {
                        iscsi_conn_printk(KERN_ERR, conn, "Login/Text in "
                                          "progress. Cannot start new task.\n");
                        return NULL;
                }

                if (data_size > ISCSI_DEF_MAX_RECV_SEG_LEN) {
                        iscsi_conn_printk(KERN_ERR, conn, "Invalid buffer len of %u for login task. Max len is %u\n", data_size, ISCSI_DEF_MAX_RECV_SEG_LEN);
                        return NULL;
                }

                task = conn->login_task;
        } else {
                if (session->state != ISCSI_STATE_LOGGED_IN)
                        return NULL;

                if (data_size != 0) {
                        iscsi_conn_printk(KERN_ERR, conn, "Can not send data buffer of len %u for op 0x%x\n", data_size, opcode);
                        return NULL;
                }

                BUG_ON(conn->c_stage == ISCSI_CONN_INITIAL_STAGE);
                BUG_ON(conn->c_stage == ISCSI_CONN_STOPPED);

                if (!kfifo_out(&session->cmdpool.queue,
                                 (void*)&task, sizeof(void*)))
                        return NULL;
        }
        /*
         * released in complete pdu for task we expect a response for, and
         * released by the lld when it has transmitted the task for
         * pdus we do not expect a response for.
         */
        refcount_set(&task->refcount, 1);
        task->conn = conn;
        task->sc = NULL;
        INIT_LIST_HEAD(&task->running);
        task->state = ISCSI_TASK_PENDING;

        if (data_size) {
                memcpy(task->data, data, data_size);
                task->data_count = data_size;
        } else
                task->data_count = 0;

        if (conn->session->tt->alloc_pdu) {
                if (conn->session->tt->alloc_pdu(task, hdr->opcode)) {
                        iscsi_conn_printk(KERN_ERR, conn, "Could not allocate "
                                         "pdu for mgmt task.\n");
                        goto free_task;
                }
        }

        itt = task->hdr->itt;
        task->hdr_len = sizeof(struct iscsi_hdr);
        memcpy(task->hdr, hdr, sizeof(struct iscsi_hdr));

        if (hdr->itt != RESERVED_ITT) {
                if (session->tt->parse_pdu_itt)
                        task->hdr->itt = itt;
                else
                        task->hdr->itt = build_itt(task->itt,
                                                   task->conn->session->age);
        }

        if (unlikely(READ_ONCE(conn->ping_task) == INVALID_SCSI_TASK))
                WRITE_ONCE(conn->ping_task, task);

        if (!ihost->workq) {
                if (iscsi_prep_mgmt_task(conn, task))
                        goto free_task;

                if (session->tt->xmit_task(task))
                        goto free_task;
        } else {
                list_add_tail(&task->running, &conn->mgmtqueue);
                iscsi_conn_queue_work(conn);
        }

        return task;

free_task:
        /* regular RX path uses back_lock */
        spin_lock(&session->back_lock);
        __iscsi_put_task(task);
        spin_unlock(&session->back_lock);
        return NULL;
}

int iscsi_conn_send_pdu(struct iscsi_cls_conn *cls_conn, struct iscsi_hdr *hdr,
                        char *data, uint32_t data_size)
{
        struct iscsi_conn *conn = cls_conn->dd_data;
        struct iscsi_session *session = conn->session;
        int err = 0;

        spin_lock_bh(&session->frwd_lock);
        if (!__iscsi_conn_send_pdu(conn, hdr, data, data_size))
                err = -EPERM;
        spin_unlock_bh(&session->frwd_lock);
        return err;
}
EXPORT_SYMBOL_GPL(iscsi_conn_send_pdu);

/**
 * iscsi_scsi_cmd_rsp - SCSI Command Response processing
 * @conn: iscsi connection
 * @hdr: iscsi header
 * @task: scsi command task
 * @data: cmd data buffer
 * @datalen: len of buffer
 *
 * iscsi_cmd_rsp sets up the scsi_cmnd fields based on the PDU and
 * then completes the command and task. called under back_lock
 **/
static void iscsi_scsi_cmd_rsp(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
                               struct iscsi_task *task, char *data,
                               int datalen)
{
        struct iscsi_scsi_rsp *rhdr = (struct iscsi_scsi_rsp *)hdr;
        struct iscsi_session *session = conn->session;
        struct scsi_cmnd *sc = task->sc;

        iscsi_update_cmdsn(session, (struct iscsi_nopin*)rhdr);
        conn->exp_statsn = be32_to_cpu(rhdr->statsn) + 1;

        sc->result = (DID_OK << 16) | rhdr->cmd_status;

        if (task->protected) {
                sector_t sector;
                u8 ascq;

                /**
                 * Transports that didn't implement check_protection
                 * callback but still published T10-PI support to scsi-mid
                 * deserve this BUG_ON.
                 **/
                BUG_ON(!session->tt->check_protection);

                ascq = session->tt->check_protection(task, &sector);
                if (ascq) {
                        scsi_build_sense(sc, 1, ILLEGAL_REQUEST, 0x10, ascq);
                        scsi_set_sense_information(sc->sense_buffer,
                                                   SCSI_SENSE_BUFFERSIZE,
                                                   sector);
                        goto out;
                }
        }

        if (rhdr->response != ISCSI_STATUS_CMD_COMPLETED) {
                sc->result = DID_ERROR << 16;
                goto out;
        }

        if (rhdr->cmd_status == SAM_STAT_CHECK_CONDITION) {
                uint16_t senselen;

                if (datalen < 2) {
invalid_datalen:
                        iscsi_conn_printk(KERN_ERR,  conn,
                                         "Got CHECK_CONDITION but invalid data "
                                         "buffer size of %d\n", datalen);
                        sc->result = DID_BAD_TARGET << 16;
                        goto out;
                }

                senselen = get_unaligned_be16(data);
                if (datalen < senselen)
                        goto invalid_datalen;

                memcpy(sc->sense_buffer, data + 2,
                       min_t(uint16_t, senselen, SCSI_SENSE_BUFFERSIZE));
                ISCSI_DBG_SESSION(session, "copied %d bytes of sense\n",
                                  min_t(uint16_t, senselen,
                                  SCSI_SENSE_BUFFERSIZE));
        }

        if (rhdr->flags & (ISCSI_FLAG_CMD_BIDI_UNDERFLOW |
                           ISCSI_FLAG_CMD_BIDI_OVERFLOW)) {
                sc->result = (DID_BAD_TARGET << 16) | rhdr->cmd_status;
        }

        if (rhdr->flags & (ISCSI_FLAG_CMD_UNDERFLOW |
                           ISCSI_FLAG_CMD_OVERFLOW)) {
                int res_count = be32_to_cpu(rhdr->residual_count);

                if (res_count > 0 &&
                    (rhdr->flags & ISCSI_FLAG_CMD_OVERFLOW ||
                     res_count <= scsi_bufflen(sc)))
                        /* write side for bidi or uni-io set_resid */
                        scsi_set_resid(sc, res_count);
                else
                        sc->result = (DID_BAD_TARGET << 16) | rhdr->cmd_status;
        }
out:
        ISCSI_DBG_SESSION(session, "cmd rsp done [sc %p res %d itt 0x%x]\n",
                          sc, sc->result, task->itt);
        conn->scsirsp_pdus_cnt++;
        iscsi_complete_task(task, ISCSI_TASK_COMPLETED);
}

/**
 * iscsi_data_in_rsp - SCSI Data-In Response processing
 * @conn: iscsi connection
 * @hdr:  iscsi pdu
 * @task: scsi command task
 *
 * iscsi_data_in_rsp sets up the scsi_cmnd fields based on the data received
 * then completes the command and task. called under back_lock
 **/
static void
iscsi_data_in_rsp(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
                  struct iscsi_task *task)
{
        struct iscsi_data_rsp *rhdr = (struct iscsi_data_rsp *)hdr;
        struct scsi_cmnd *sc = task->sc;

        if (!(rhdr->flags & ISCSI_FLAG_DATA_STATUS))
                return;

        iscsi_update_cmdsn(conn->session, (struct iscsi_nopin *)hdr);
        sc->result = (DID_OK << 16) | rhdr->cmd_status;
        conn->exp_statsn = be32_to_cpu(rhdr->statsn) + 1;
        if (rhdr->flags & (ISCSI_FLAG_DATA_UNDERFLOW |
                           ISCSI_FLAG_DATA_OVERFLOW)) {
                int res_count = be32_to_cpu(rhdr->residual_count);

                if (res_count > 0 &&
                    (rhdr->flags & ISCSI_FLAG_CMD_OVERFLOW ||
                     res_count <= sc->sdb.length))
                        scsi_set_resid(sc, res_count);
                else
                        sc->result = (DID_BAD_TARGET << 16) | rhdr->cmd_status;
        }

        ISCSI_DBG_SESSION(conn->session, "data in with status done "
                          "[sc %p res %d itt 0x%x]\n",
                          sc, sc->result, task->itt);
        conn->scsirsp_pdus_cnt++;
        iscsi_complete_task(task, ISCSI_TASK_COMPLETED);
}

static void iscsi_tmf_rsp(struct iscsi_conn *conn, struct iscsi_hdr *hdr)
{
        struct iscsi_tm_rsp *tmf = (struct iscsi_tm_rsp *)hdr;
        struct iscsi_session *session = conn->session;

        conn->exp_statsn = be32_to_cpu(hdr->statsn) + 1;
        conn->tmfrsp_pdus_cnt++;

        if (session->tmf_state != TMF_QUEUED)
                return;

        if (tmf->response == ISCSI_TMF_RSP_COMPLETE)
                session->tmf_state = TMF_SUCCESS;
        else if (tmf->response == ISCSI_TMF_RSP_NO_TASK)
                session->tmf_state = TMF_NOT_FOUND;
        else
                session->tmf_state = TMF_FAILED;
        wake_up(&session->ehwait);
}

static int iscsi_send_nopout(struct iscsi_conn *conn, struct iscsi_nopin *rhdr)
{
        struct iscsi_nopout hdr;
        struct iscsi_task *task;

        if (!rhdr) {
                if (READ_ONCE(conn->ping_task))
                        return -EINVAL;
                WRITE_ONCE(conn->ping_task, INVALID_SCSI_TASK);
        }

        memset(&hdr, 0, sizeof(struct iscsi_nopout));
        hdr.opcode = ISCSI_OP_NOOP_OUT | ISCSI_OP_IMMEDIATE;
        hdr.flags = ISCSI_FLAG_CMD_FINAL;

        if (rhdr) {
                hdr.lun = rhdr->lun;
                hdr.ttt = rhdr->ttt;
                hdr.itt = RESERVED_ITT;
        } else
                hdr.ttt = RESERVED_ITT;

        task = __iscsi_conn_send_pdu(conn, (struct iscsi_hdr *)&hdr, NULL, 0);
        if (!task) {
                if (!rhdr)
                        WRITE_ONCE(conn->ping_task, NULL);
                iscsi_conn_printk(KERN_ERR, conn, "Could not send nopout\n");
                return -EIO;
        } else if (!rhdr) {
                /* only track our nops */
                conn->last_ping = jiffies;
        }

        return 0;
}

/**
 * iscsi_nop_out_rsp - SCSI NOP Response processing
 * @task: scsi command task
 * @nop: the nop structure
 * @data: where to put the data
 * @datalen: length of data
 *
 * iscsi_nop_out_rsp handles nop response from use or
 * from user space. called under back_lock
 **/
static int iscsi_nop_out_rsp(struct iscsi_task *task,
                             struct iscsi_nopin *nop, char *data, int datalen)

{
        struct iscsi_conn *conn = task->conn;
        int rc = 0;

        if (READ_ONCE(conn->ping_task) != task) {
                /*
                 * If this is not in response to one of our
                 * nops then it must be from userspace.
                 */
                if (iscsi_recv_pdu(conn->cls_conn, (struct iscsi_hdr *)nop,
                                   data, datalen))
                        rc = ISCSI_ERR_CONN_FAILED;
        } else
                mod_timer(&conn->transport_timer, jiffies + conn->recv_timeout);
        iscsi_complete_task(task, ISCSI_TASK_COMPLETED);
        return rc;
}

static int iscsi_handle_reject(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
                               char *data, int datalen)
{
        struct iscsi_reject *reject = (struct iscsi_reject *)hdr;
        struct iscsi_hdr rejected_pdu;
        int opcode, rc = 0;

        conn->exp_statsn = be32_to_cpu(reject->statsn) + 1;

        if (ntoh24(reject->dlength) > datalen ||
            ntoh24(reject->dlength) < sizeof(struct iscsi_hdr)) {
                iscsi_conn_printk(KERN_ERR, conn, "Cannot handle rejected "
                                  "pdu. Invalid data length (pdu dlength "
                                  "%u, datalen %d\n", ntoh24(reject->dlength),
                                  datalen);
                return ISCSI_ERR_PROTO;
        }
        memcpy(&rejected_pdu, data, sizeof(struct iscsi_hdr));
        opcode = rejected_pdu.opcode & ISCSI_OPCODE_MASK;

        switch (reject->reason) {
        case ISCSI_REASON_DATA_DIGEST_ERROR:
                iscsi_conn_printk(KERN_ERR, conn,
                                  "pdu (op 0x%x itt 0x%x) rejected "
                                  "due to DataDigest error.\n",
                                  opcode, rejected_pdu.itt);
                break;
        case ISCSI_REASON_IMM_CMD_REJECT:
                iscsi_conn_printk(KERN_ERR, conn,
                                  "pdu (op 0x%x itt 0x%x) rejected. Too many "
                                  "immediate commands.\n",
                                  opcode, rejected_pdu.itt);
                /*
                 * We only send one TMF at a time so if the target could not
                 * handle it, then it should get fixed (RFC mandates that
                 * a target can handle one immediate TMF per conn).
                 *
                 * For nops-outs, we could have sent more than one if
                 * the target is sending us lots of nop-ins
                 */
                if (opcode != ISCSI_OP_NOOP_OUT)
                        return 0;

                if (rejected_pdu.itt == cpu_to_be32(ISCSI_RESERVED_TAG)) {
                        /*
                         * nop-out in response to target's nop-out rejected.
                         * Just resend.
                         */
                        /* In RX path we are under back lock */
                        spin_unlock(&conn->session->back_lock);
                        spin_lock(&conn->session->frwd_lock);
                        iscsi_send_nopout(conn,
                                          (struct iscsi_nopin*)&rejected_pdu);
                        spin_unlock(&conn->session->frwd_lock);
                        spin_lock(&conn->session->back_lock);
                } else {
                        struct iscsi_task *task;
                        /*
                         * Our nop as ping got dropped. We know the target
                         * and transport are ok so just clean up
                         */
                        task = iscsi_itt_to_task(conn, rejected_pdu.itt);
                        if (!task) {
                                iscsi_conn_printk(KERN_ERR, conn,
                                                 "Invalid pdu reject. Could "
                                                 "not lookup rejected task.\n");
                                rc = ISCSI_ERR_BAD_ITT;
                        } else
                                rc = iscsi_nop_out_rsp(task,
                                        (struct iscsi_nopin*)&rejected_pdu,
                                        NULL, 0);
                }
                break;
        default:
                iscsi_conn_printk(KERN_ERR, conn,
                                  "pdu (op 0x%x itt 0x%x) rejected. Reason "
                                  "code 0x%x\n", rejected_pdu.opcode,
                                  rejected_pdu.itt, reject->reason);
                break;
        }
        return rc;
}

/**
 * iscsi_itt_to_task - look up task by itt
 * @conn: iscsi connection
 * @itt: itt
 *
 * This should be used for mgmt tasks like login and nops, or if
 * the LDD's itt space does not include the session age.
 *
 * The session back_lock must be held.
 */
struct iscsi_task *iscsi_itt_to_task(struct iscsi_conn *conn, itt_t itt)
{
        struct iscsi_session *session = conn->session;
        int i;

        if (itt == RESERVED_ITT)
                return NULL;

        if (session->tt->parse_pdu_itt)
                session->tt->parse_pdu_itt(conn, itt, &i, NULL);
        else
                i = get_itt(itt);
        if (i >= session->cmds_max)
                return NULL;

        return session->cmds[i];
}
EXPORT_SYMBOL_GPL(iscsi_itt_to_task);

/**
 * __iscsi_complete_pdu - complete pdu
 * @conn: iscsi conn
 * @hdr: iscsi header
 * @data: data buffer
 * @datalen: len of data buffer
 *
 * Completes pdu processing by freeing any resources allocated at
 * queuecommand or send generic. session back_lock must be held and verify
 * itt must have been called.
 */
int __iscsi_complete_pdu(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
                         char *data, int datalen)
{
        struct iscsi_session *session = conn->session;
        int opcode = hdr->opcode & ISCSI_OPCODE_MASK, rc = 0;
        struct iscsi_task *task;
        uint32_t itt;

        conn->last_recv = jiffies;
        rc = iscsi_verify_itt(conn, hdr->itt);
        if (rc)
                return rc;

        if (hdr->itt != RESERVED_ITT)
                itt = get_itt(hdr->itt);
        else
                itt = ~0U;

        ISCSI_DBG_SESSION(session, "[op 0x%x cid %d itt 0x%x len %d]\n",
                          opcode, conn->id, itt, datalen);

        if (itt == ~0U) {
                iscsi_update_cmdsn(session, (struct iscsi_nopin*)hdr);

                switch(opcode) {
                case ISCSI_OP_NOOP_IN:
                        if (datalen) {
                                rc = ISCSI_ERR_PROTO;
                                break;
                        }

                        if (hdr->ttt == cpu_to_be32(ISCSI_RESERVED_TAG))
                                break;

                        /* In RX path we are under back lock */
                        spin_unlock(&session->back_lock);
                        spin_lock(&session->frwd_lock);
                        iscsi_send_nopout(conn, (struct iscsi_nopin*)hdr);
                        spin_unlock(&session->frwd_lock);
                        spin_lock(&session->back_lock);
                        break;
                case ISCSI_OP_REJECT:
                        rc = iscsi_handle_reject(conn, hdr, data, datalen);
                        break;
                case ISCSI_OP_ASYNC_EVENT:
                        conn->exp_statsn = be32_to_cpu(hdr->statsn) + 1;
                        if (iscsi_recv_pdu(conn->cls_conn, hdr, data, datalen))
                                rc = ISCSI_ERR_CONN_FAILED;
                        break;
                default:
                        rc = ISCSI_ERR_BAD_OPCODE;
                        break;
                }
                goto out;
        }

        switch(opcode) {
        case ISCSI_OP_SCSI_CMD_RSP:
        case ISCSI_OP_SCSI_DATA_IN:
                task = iscsi_itt_to_ctask(conn, hdr->itt);
                if (!task)
                        return ISCSI_ERR_BAD_ITT;
                task->last_xfer = jiffies;
                break;
        case ISCSI_OP_R2T:
                /*
                 * LLD handles R2Ts if they need to.
                 */
                return 0;
        case ISCSI_OP_LOGOUT_RSP:
        case ISCSI_OP_LOGIN_RSP:
        case ISCSI_OP_TEXT_RSP:
        case ISCSI_OP_SCSI_TMFUNC_RSP:
        case ISCSI_OP_NOOP_IN:
                task = iscsi_itt_to_task(conn, hdr->itt);
                if (!task)
                        return ISCSI_ERR_BAD_ITT;
                break;
        default:
                return ISCSI_ERR_BAD_OPCODE;
        }

        switch(opcode) {
        case ISCSI_OP_SCSI_CMD_RSP:
                iscsi_scsi_cmd_rsp(conn, hdr, task, data, datalen);
                break;
        case ISCSI_OP_SCSI_DATA_IN:
                iscsi_data_in_rsp(conn, hdr, task);
                break;
        case ISCSI_OP_LOGOUT_RSP:
                iscsi_update_cmdsn(session, (struct iscsi_nopin*)hdr);
                if (datalen) {
                        rc = ISCSI_ERR_PROTO;
                        break;
                }
                conn->exp_statsn = be32_to_cpu(hdr->statsn) + 1;
                goto recv_pdu;
        case ISCSI_OP_LOGIN_RSP:
        case ISCSI_OP_TEXT_RSP:
                iscsi_update_cmdsn(session, (struct iscsi_nopin*)hdr);
                /*
                 * login related PDU's exp_statsn is handled in
                 * userspace
                 */
                goto recv_pdu;
        case ISCSI_OP_SCSI_TMFUNC_RSP:
                iscsi_update_cmdsn(session, (struct iscsi_nopin*)hdr);
                if (datalen) {
                        rc = ISCSI_ERR_PROTO;
                        break;
                }

                iscsi_tmf_rsp(conn, hdr);
                iscsi_complete_task(task, ISCSI_TASK_COMPLETED);
                break;
        case ISCSI_OP_NOOP_IN:
                iscsi_update_cmdsn(session, (struct iscsi_nopin*)hdr);
                if (hdr->ttt != cpu_to_be32(ISCSI_RESERVED_TAG) || datalen) {
                        rc = ISCSI_ERR_PROTO;
                        break;
                }
                conn->exp_statsn = be32_to_cpu(hdr->statsn) + 1;

                rc = iscsi_nop_out_rsp(task, (struct iscsi_nopin*)hdr,
                                       data, datalen);
                break;
        default:
                rc = ISCSI_ERR_BAD_OPCODE;
                break;
        }

out:
        return rc;
recv_pdu:
        if (iscsi_recv_pdu(conn->cls_conn, hdr, data, datalen))
                rc = ISCSI_ERR_CONN_FAILED;
        iscsi_complete_task(task, ISCSI_TASK_COMPLETED);
        return rc;
}
EXPORT_SYMBOL_GPL(__iscsi_complete_pdu);

int iscsi_complete_pdu(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
                       char *data, int datalen)
{
        int rc;

        spin_lock(&conn->session->back_lock);
        rc = __iscsi_complete_pdu(conn, hdr, data, datalen);
        spin_unlock(&conn->session->back_lock);
        return rc;
}
EXPORT_SYMBOL_GPL(iscsi_complete_pdu);

int iscsi_verify_itt(struct iscsi_conn *conn, itt_t itt)
{
        struct iscsi_session *session = conn->session;
        int age = 0, i = 0;

        if (itt == RESERVED_ITT)
                return 0;

        if (session->tt->parse_pdu_itt)
                session->tt->parse_pdu_itt(conn, itt, &i, &age);
        else {
                i = get_itt(itt);
                age = ((__force u32)itt >> ISCSI_AGE_SHIFT) & ISCSI_AGE_MASK;
        }

        if (age != session->age) {
                iscsi_conn_printk(KERN_ERR, conn,
                                  "received itt %x expected session age (%x)\n",
                                  (__force u32)itt, session->age);
                return ISCSI_ERR_BAD_ITT;
        }

        if (i >= session->cmds_max) {
                iscsi_conn_printk(KERN_ERR, conn,
                                  "received invalid itt index %u (max cmds "
                                   "%u.\n", i, session->cmds_max);
                return ISCSI_ERR_BAD_ITT;
        }
        return 0;
}
EXPORT_SYMBOL_GPL(iscsi_verify_itt);

/**
 * iscsi_itt_to_ctask - look up ctask by itt
 * @conn: iscsi connection
 * @itt: itt
 *
 * This should be used for cmd tasks.
 *
 * The session back_lock must be held.
 */
struct iscsi_task *iscsi_itt_to_ctask(struct iscsi_conn *conn, itt_t itt)
{
        struct iscsi_task *task;

        if (iscsi_verify_itt(conn, itt))
                return NULL;

        task = iscsi_itt_to_task(conn, itt);
        if (!task || !task->sc)
                return NULL;

        if (task->sc->SCp.phase != conn->session->age) {
                iscsi_session_printk(KERN_ERR, conn->session,
                                  "task's session age %d, expected %d\n",
                                  task->sc->SCp.phase, conn->session->age);
                return NULL;
        }

        return task;
}
EXPORT_SYMBOL_GPL(iscsi_itt_to_ctask);

void iscsi_session_failure(struct iscsi_session *session,
                           enum iscsi_err err)
{
        struct iscsi_conn *conn;

        spin_lock_bh(&session->frwd_lock);
        conn = session->leadconn;
        if (session->state == ISCSI_STATE_TERMINATE || !conn) {
                spin_unlock_bh(&session->frwd_lock);
                return;
        }

        iscsi_get_conn(conn->cls_conn);
        spin_unlock_bh(&session->frwd_lock);
        /*
         * if the host is being removed bypass the connection
         * recovery initialization because we are going to kill
         * the session.
         */
        if (err == ISCSI_ERR_INVALID_HOST)
                iscsi_conn_error_event(conn->cls_conn, err);
        else
                iscsi_conn_failure(conn, err);
        iscsi_put_conn(conn->cls_conn);
}
EXPORT_SYMBOL_GPL(iscsi_session_failure);

static bool iscsi_set_conn_failed(struct iscsi_conn *conn)
{
        struct iscsi_session *session = conn->session;

        if (session->state == ISCSI_STATE_FAILED)
                return false;

        if (conn->stop_stage == 0)
                session->state = ISCSI_STATE_FAILED;

        set_bit(ISCSI_SUSPEND_BIT, &conn->suspend_tx);
        set_bit(ISCSI_SUSPEND_BIT, &conn->suspend_rx);
        return true;
}

void iscsi_conn_failure(struct iscsi_conn *conn, enum iscsi_err err)
{
        struct iscsi_session *session = conn->session;
        bool needs_evt;

        spin_lock_bh(&session->frwd_lock);
        needs_evt = iscsi_set_conn_failed(conn);
        spin_unlock_bh(&session->frwd_lock);

        if (needs_evt)
                iscsi_conn_error_event(conn->cls_conn, err);
}
EXPORT_SYMBOL_GPL(iscsi_conn_failure);

static int iscsi_check_cmdsn_window_closed(struct iscsi_conn *conn)
{
        struct iscsi_session *session = conn->session;

        /*
         * Check for iSCSI window and take care of CmdSN wrap-around
         */
        if (!iscsi_sna_lte(session->queued_cmdsn, session->max_cmdsn)) {
                ISCSI_DBG_SESSION(session, "iSCSI CmdSN closed. ExpCmdSn "
                                  "%u MaxCmdSN %u CmdSN %u/%u\n",
                                  session->exp_cmdsn, session->max_cmdsn,
                                  session->cmdsn, session->queued_cmdsn);
                return -ENOSPC;
        }
        return 0;
}

static int iscsi_xmit_task(struct iscsi_conn *conn, struct iscsi_task *task,
                           bool was_requeue)
{
        int rc;

        spin_lock_bh(&conn->session->back_lock);

        if (!conn->task) {
                /* Take a ref so we can access it after xmit_task() */
                __iscsi_get_task(task);
        } else {
                /* Already have a ref from when we failed to send it last call */
                conn->task = NULL;
        }

        /*
         * If this was a requeue for a R2T we have an extra ref on the task in
         * case a bad target sends a cmd rsp before we have handled the task.
         */
        if (was_requeue)
                __iscsi_put_task(task);

        /*
         * Do this after dropping the extra ref because if this was a requeue
         * it's removed from that list and cleanup_queued_task would miss it.
         */
        if (test_bit(ISCSI_SUSPEND_BIT, &conn->suspend_tx)) {
                /*
                 * Save the task and ref in case we weren't cleaning up this
                 * task and get woken up again.
                 */
                conn->task = task;
                spin_unlock_bh(&conn->session->back_lock);
                return -ENODATA;
        }
        spin_unlock_bh(&conn->session->back_lock);

        spin_unlock_bh(&conn->session->frwd_lock);
        rc = conn->session->tt->xmit_task(task);
        spin_lock_bh(&conn->session->frwd_lock);
        if (!rc) {
                /* done with this task */
                task->last_xfer = jiffies;
        }
        /* regular RX path uses back_lock */
        spin_lock(&conn->session->back_lock);
        if (rc && task->state == ISCSI_TASK_RUNNING) {
                /*
                 * get an extra ref that is released next time we access it
                 * as conn->task above.
                 */
                __iscsi_get_task(task);
                conn->task = task;
        }

        __iscsi_put_task(task);
        spin_unlock(&conn->session->back_lock);
        return rc;
}

/**
 * iscsi_requeue_task - requeue task to run from session workqueue
 * @task: task to requeue
 *
 * Callers must have taken a ref to the task that is going to be requeued.
 */
void iscsi_requeue_task(struct iscsi_task *task)
{
        struct iscsi_conn *conn = task->conn;

        /*
         * this may be on the requeue list already if the xmit_task callout
         * is handling the r2ts while we are adding new ones
         */
        spin_lock_bh(&conn->session->frwd_lock);
        if (list_empty(&task->running)) {
                list_add_tail(&task->running, &conn->requeue);
        } else {
                /*
                 * Don't need the extra ref since it's already requeued and
                 * has a ref.
                 */
                iscsi_put_task(task);
        }
        iscsi_conn_queue_work(conn);
        spin_unlock_bh(&conn->session->frwd_lock);
}
EXPORT_SYMBOL_GPL(iscsi_requeue_task);

/**
 * iscsi_data_xmit - xmit any command into the scheduled connection
 * @conn: iscsi connection
 *
 * Notes:
 *      The function can return -EAGAIN in which case the caller must
 *      re-schedule it again later or recover. '0' return code means
 *      successful xmit.
 **/
static int iscsi_data_xmit(struct iscsi_conn *conn)
{
        struct iscsi_task *task;
        int rc = 0;

        spin_lock_bh(&conn->session->frwd_lock);
        if (test_bit(ISCSI_SUSPEND_BIT, &conn->suspend_tx)) {
                ISCSI_DBG_SESSION(conn->session, "Tx suspended!\n");
                spin_unlock_bh(&conn->session->frwd_lock);
                return -ENODATA;
        }

        if (conn->task) {
                rc = iscsi_xmit_task(conn, conn->task, false);
                if (rc)
                        goto done;
        }

        /*
         * process mgmt pdus like nops before commands since we should
         * only have one nop-out as a ping from us and targets should not
         * overflow us with nop-ins
         */
check_mgmt:
        while (!list_empty(&conn->mgmtqueue)) {
                task = list_entry(conn->mgmtqueue.next, struct iscsi_task,
                                  running);
                list_del_init(&task->running);
                if (iscsi_prep_mgmt_task(conn, task)) {
                        /* regular RX path uses back_lock */
                        spin_lock_bh(&conn->session->back_lock);
                        __iscsi_put_task(task);
                        spin_unlock_bh(&conn->session->back_lock);
                        continue;
                }
                rc = iscsi_xmit_task(conn, task, false);
                if (rc)
                        goto done;
        }

        /* process pending command queue */
        while (!list_empty(&conn->cmdqueue)) {
                task = list_entry(conn->cmdqueue.next, struct iscsi_task,
                                  running);
                list_del_init(&task->running);
                if (conn->session->state == ISCSI_STATE_LOGGING_OUT) {
                        fail_scsi_task(task, DID_IMM_RETRY);
                        continue;
                }
                rc = iscsi_prep_scsi_cmd_pdu(task);
                if (rc) {
                        if (rc == -ENOMEM || rc == -EACCES)
                                fail_scsi_task(task, DID_IMM_RETRY);
                        else
                                fail_scsi_task(task, DID_ABORT);
                        continue;
                }
                rc = iscsi_xmit_task(conn, task, false);
                if (rc)
                        goto done;
                /*
                 * we could continuously get new task requests so
                 * we need to check the mgmt queue for nops that need to
                 * be sent to aviod starvation
                 */
                if (!list_empty(&conn->mgmtqueue))
                        goto check_mgmt;
        }

        while (!list_empty(&conn->requeue)) {
                /*
                 * we always do fastlogout - conn stop code will clean up.
                 */
                if (conn->session->state == ISCSI_STATE_LOGGING_OUT)
                        break;

                task = list_entry(conn->requeue.next, struct iscsi_task,
                                  running);

                if (iscsi_check_tmf_restrictions(task, ISCSI_OP_SCSI_DATA_OUT))
                        break;

                list_del_init(&task->running);
                rc = iscsi_xmit_task(conn, task, true);
                if (rc)
                        goto done;
                if (!list_empty(&conn->mgmtqueue))
                        goto check_mgmt;
        }
        spin_unlock_bh(&conn->session->frwd_lock);
        return -ENODATA;

done:
        spin_unlock_bh(&conn->session->frwd_lock);
        return rc;
}

static void iscsi_xmitworker(struct work_struct *work)
{
        struct iscsi_conn *conn =
                container_of(work, struct iscsi_conn, xmitwork);
        int rc;
        /*
         * serialize Xmit worker on a per-connection basis.
         */
        do {
                rc = iscsi_data_xmit(conn);
        } while (rc >= 0 || rc == -EAGAIN);
}

static inline struct iscsi_task *iscsi_alloc_task(struct iscsi_conn *conn,
                                                  struct scsi_cmnd *sc)
{
        struct iscsi_task *task;

        if (!kfifo_out(&conn->session->cmdpool.queue,
                         (void *) &task, sizeof(void *)))
                return NULL;

        sc->SCp.phase = conn->session->age;
        sc->SCp.ptr = (char *) task;

        refcount_set(&task->refcount, 1);
        task->state = ISCSI_TASK_PENDING;
        task->conn = conn;
        task->sc = sc;
        task->have_checked_conn = false;
        task->last_timeout = jiffies;
        task->last_xfer = jiffies;
        task->protected = false;
        INIT_LIST_HEAD(&task->running);
        return task;
}

enum {
        FAILURE_BAD_HOST = 1,
        FAILURE_SESSION_FAILED,
        FAILURE_SESSION_FREED,
        FAILURE_WINDOW_CLOSED,
        FAILURE_OOM,
        FAILURE_SESSION_TERMINATE,
        FAILURE_SESSION_IN_RECOVERY,
        FAILURE_SESSION_RECOVERY_TIMEOUT,
        FAILURE_SESSION_LOGGING_OUT,
        FAILURE_SESSION_NOT_READY,
};

int iscsi_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *sc)
{
        struct iscsi_cls_session *cls_session;
        struct iscsi_host *ihost;
        int reason = 0;
        struct iscsi_session *session;
        struct iscsi_conn *conn;
        struct iscsi_task *task = NULL;

        sc->result = 0;
        sc->SCp.ptr = NULL;

        ihost = shost_priv(host);

        cls_session = starget_to_session(scsi_target(sc->device));
        session = cls_session->dd_data;
        spin_lock_bh(&session->frwd_lock);

        reason = iscsi_session_chkready(cls_session);
        if (reason) {
                sc->result = reason;
                goto fault;
        }

        if (session->state != ISCSI_STATE_LOGGED_IN) {
                /*
                 * to handle the race between when we set the recovery state
                 * and block the session we requeue here (commands could
                 * be entering our queuecommand while a block is starting
                 * up because the block code is not locked)
                 */
                switch (session->state) {
                case ISCSI_STATE_FAILED:
                        /*
                         * cmds should fail during shutdown, if the session
                         * state is bad, allowing completion to happen
                         */
                        if (unlikely(system_state != SYSTEM_RUNNING)) {
                                reason = FAILURE_SESSION_FAILED;
                                sc->result = DID_NO_CONNECT << 16;
                                break;
                        }
                        fallthrough;
                case ISCSI_STATE_IN_RECOVERY:
                        reason = FAILURE_SESSION_IN_RECOVERY;
                        sc->result = DID_IMM_RETRY << 16;
                        break;
                case ISCSI_STATE_LOGGING_OUT:
                        reason = FAILURE_SESSION_LOGGING_OUT;
                        sc->result = DID_IMM_RETRY << 16;
                        break;
                case ISCSI_STATE_RECOVERY_FAILED:
                        reason = FAILURE_SESSION_RECOVERY_TIMEOUT;
                        sc->result = DID_TRANSPORT_FAILFAST << 16;
                        break;
                case ISCSI_STATE_TERMINATE:
                        reason = FAILURE_SESSION_TERMINATE;
                        sc->result = DID_NO_CONNECT << 16;
                        break;
                default:
                        reason = FAILURE_SESSION_FREED;
                        sc->result = DID_NO_CONNECT << 16;
                }
                goto fault;
        }

        conn = session->leadconn;
        if (!conn) {
                reason = FAILURE_SESSION_FREED;
                sc->result = DID_NO_CONNECT << 16;
                goto fault;
        }

        if (test_bit(ISCSI_SUSPEND_BIT, &conn->suspend_tx)) {
                reason = FAILURE_SESSION_IN_RECOVERY;
                sc->result = DID_REQUEUE << 16;
                goto fault;
        }

        if (iscsi_check_cmdsn_window_closed(conn)) {
                reason = FAILURE_WINDOW_CLOSED;
                goto reject;
        }

        task = iscsi_alloc_task(conn, sc);
        if (!task) {
                reason = FAILURE_OOM;
                goto reject;
        }

        if (!ihost->workq) {
                reason = iscsi_prep_scsi_cmd_pdu(task);
                if (reason) {
                        if (reason == -ENOMEM ||  reason == -EACCES) {
                                reason = FAILURE_OOM;
                                goto prepd_reject;
                        } else {
                                sc->result = DID_ABORT << 16;
                                goto prepd_fault;
                        }
                }
                if (session->tt->xmit_task(task)) {
                        session->cmdsn--;
                        reason = FAILURE_SESSION_NOT_READY;
                        goto prepd_reject;
                }
        } else {
                list_add_tail(&task->running, &conn->cmdqueue);
                iscsi_conn_queue_work(conn);
        }

        session->queued_cmdsn++;
        spin_unlock_bh(&session->frwd_lock);
        return 0;

prepd_reject:
        spin_lock_bh(&session->back_lock);
        iscsi_complete_task(task, ISCSI_TASK_REQUEUE_SCSIQ);
        spin_unlock_bh(&session->back_lock);
reject:
        spin_unlock_bh(&session->frwd_lock);
        ISCSI_DBG_SESSION(session, "cmd 0x%x rejected (%d)\n",
                          sc->cmnd[0], reason);
        return SCSI_MLQUEUE_TARGET_BUSY;

prepd_fault:
        spin_lock_bh(&session->back_lock);
        iscsi_complete_task(task, ISCSI_TASK_REQUEUE_SCSIQ);
        spin_unlock_bh(&session->back_lock);
fault:
        spin_unlock_bh(&session->frwd_lock);
        ISCSI_DBG_SESSION(session, "iscsi: cmd 0x%x is not queued (%d)\n",
                          sc->cmnd[0], reason);
        scsi_set_resid(sc, scsi_bufflen(sc));
        sc->scsi_done(sc);
        return 0;
}
EXPORT_SYMBOL_GPL(iscsi_queuecommand);

int iscsi_target_alloc(struct scsi_target *starget)
{
        struct iscsi_cls_session *cls_session = starget_to_session(starget);
        struct iscsi_session *session = cls_session->dd_data;

        starget->can_queue = session->scsi_cmds_max;
        return 0;
}
EXPORT_SYMBOL_GPL(iscsi_target_alloc);

static void iscsi_tmf_timedout(struct timer_list *t)
{
        struct iscsi_session *session = from_timer(session, t, tmf_timer);

        spin_lock(&session->frwd_lock);
        if (session->tmf_state == TMF_QUEUED) {
                session->tmf_state = TMF_TIMEDOUT;
                ISCSI_DBG_EH(session, "tmf timedout\n");
                /* unblock eh_abort() */
                wake_up(&session->ehwait);
        }
        spin_unlock(&session->frwd_lock);
}

static int iscsi_exec_task_mgmt_fn(struct iscsi_conn *conn,
                                   struct iscsi_tm *hdr, int age,
                                   int timeout)
        __must_hold(&session->frwd_lock)
{
        struct iscsi_session *session = conn->session;
        struct iscsi_task *task;

        task = __iscsi_conn_send_pdu(conn, (struct iscsi_hdr *)hdr,
                                      NULL, 0);
        if (!task) {
                spin_unlock_bh(&session->frwd_lock);
                iscsi_conn_printk(KERN_ERR, conn, "Could not send TMF.\n");
                iscsi_conn_failure(conn, ISCSI_ERR_CONN_FAILED);
                spin_lock_bh(&session->frwd_lock);
                return -EPERM;
        }
        conn->tmfcmd_pdus_cnt++;
        session->tmf_timer.expires = timeout * HZ + jiffies;
        add_timer(&session->tmf_timer);
        ISCSI_DBG_EH(session, "tmf set timeout\n");

        spin_unlock_bh(&session->frwd_lock);
        mutex_unlock(&session->eh_mutex);

        /*
         * block eh thread until:
         *
         * 1) tmf response
         * 2) tmf timeout
         * 3) session is terminated or restarted or userspace has
         * given up on recovery
         */
        wait_event_interruptible(session->ehwait, age != session->age ||
                                 session->state != ISCSI_STATE_LOGGED_IN ||
                                 session->tmf_state != TMF_QUEUED);
        if (signal_pending(current))
                flush_signals(current);
        del_timer_sync(&session->tmf_timer);

        mutex_lock(&session->eh_mutex);
        spin_lock_bh(&session->frwd_lock);
        /* if the session drops it will clean up the task */
        if (age != session->age ||
            session->state != ISCSI_STATE_LOGGED_IN)
                return -ENOTCONN;
        return 0;
}

/*
 * Fail commands. session frwd lock held and xmit thread flushed.
 */
static void fail_scsi_tasks(struct iscsi_conn *conn, u64 lun, int error)
{
        struct iscsi_session *session = conn->session;
        struct iscsi_task *task;
        int i;

        spin_lock_bh(&session->back_lock);
        for (i = 0; i < session->cmds_max; i++) {
                task = session->cmds[i];
                if (!task->sc || task->state == ISCSI_TASK_FREE)
                        continue;

                if (lun != -1 && lun != task->sc->device->lun)
                        continue;

                __iscsi_get_task(task);
                spin_unlock_bh(&session->back_lock);

                ISCSI_DBG_SESSION(session,
                                  "failing sc %p itt 0x%x state %d\n",
                                  task->sc, task->itt, task->state);
                fail_scsi_task(task, error);

                spin_unlock_bh(&session->frwd_lock);
                iscsi_put_task(task);
                spin_lock_bh(&session->frwd_lock);

                spin_lock_bh(&session->back_lock);
        }

        spin_unlock_bh(&session->back_lock);
}

/**
 * iscsi_suspend_queue - suspend iscsi_queuecommand
 * @conn: iscsi conn to stop queueing IO on
 *
 * This grabs the session frwd_lock to make sure no one is in
 * xmit_task/queuecommand, and then sets suspend to prevent
 * new commands from being queued. This only needs to be called
 * by offload drivers that need to sync a path like ep disconnect
 * with the iscsi_queuecommand/xmit_task. To start IO again libiscsi
 * will call iscsi_start_tx and iscsi_unblock_session when in FFP.
 */
void iscsi_suspend_queue(struct iscsi_conn *conn)
{
        spin_lock_bh(&conn->session->frwd_lock);
        set_bit(ISCSI_SUSPEND_BIT, &conn->suspend_tx);
        spin_unlock_bh(&conn->session->frwd_lock);
}
EXPORT_SYMBOL_GPL(iscsi_suspend_queue);

/**
 * iscsi_suspend_tx - suspend iscsi_data_xmit
 * @conn: iscsi conn tp stop processing IO on.
 *
 * This function sets the suspend bit to prevent iscsi_data_xmit
 * from sending new IO, and if work is queued on the xmit thread
 * it will wait for it to be completed.
 */
void iscsi_suspend_tx(struct iscsi_conn *conn)
{
        struct Scsi_Host *shost = conn->session->host;
        struct iscsi_host *ihost = shost_priv(shost);

        set_bit(ISCSI_SUSPEND_BIT, &conn->suspend_tx);
        if (ihost->workq)
                flush_workqueue(ihost->workq);
}
EXPORT_SYMBOL_GPL(iscsi_suspend_tx);

static void iscsi_start_tx(struct iscsi_conn *conn)
{
        clear_bit(ISCSI_SUSPEND_BIT, &conn->suspend_tx);
        iscsi_conn_queue_work(conn);
}

/*
 * We want to make sure a ping is in flight. It has timed out.
 * And we are not busy processing a pdu that is making
 * progress but got started before the ping and is taking a while
 * to complete so the ping is just stuck behind it in a queue.
 */
static int iscsi_has_ping_timed_out(struct iscsi_conn *conn)
{
        if (READ_ONCE(conn->ping_task) &&
            time_before_eq(conn->last_recv + (conn->recv_timeout * HZ) +
                           (conn->ping_timeout * HZ), jiffies))
                return 1;
        else
                return 0;
}

enum blk_eh_timer_return iscsi_eh_cmd_timed_out(struct scsi_cmnd *sc)
{
        enum blk_eh_timer_return rc = BLK_EH_DONE;
        struct iscsi_task *task = NULL, *running_task;
        struct iscsi_cls_session *cls_session;
        struct iscsi_session *session;
        struct iscsi_conn *conn;
        int i;

        cls_session = starget_to_session(scsi_target(sc->device));
        session = cls_session->dd_data;

        ISCSI_DBG_EH(session, "scsi cmd %p timedout\n", sc);

        spin_lock_bh(&session->frwd_lock);
        spin_lock(&session->back_lock);
        task = (struct iscsi_task *)sc->SCp.ptr;

        if (!task) {
                /*
                 * Raced with completion. Blk layer has taken ownership
                 * so let timeout code complete it now.
                 */
                rc = BLK_EH_DONE;
                spin_unlock(&session->back_lock);
                goto done;
        }
        __iscsi_get_task(task);
        spin_unlock(&session->back_lock);

        if (session->state != ISCSI_STATE_LOGGED_IN) {
                /*
                 * During shutdown, if session is prematurely disconnected,
                 * recovery won't happen and there will be hung cmds. Not
                 * handling cmds would trigger EH, also bad in this case.
                 * Instead, handle cmd, allow completion to happen and let
                 * upper layer to deal with the result.
                 */
                if (unlikely(system_state != SYSTEM_RUNNING)) {
                        sc->result = DID_NO_CONNECT << 16;
                        ISCSI_DBG_EH(session, "sc on shutdown, handled\n");
                        rc = BLK_EH_DONE;
                        goto done;
                }
                /*
                 * We are probably in the middle of iscsi recovery so let
                 * that complete and handle the error.
                 */
                rc = BLK_EH_RESET_TIMER;
                goto done;
        }

        conn = session->leadconn;
        if (!conn) {
                /* In the middle of shuting down */
                rc = BLK_EH_RESET_TIMER;
                goto done;
        }

        /*
         * If we have sent (at least queued to the network layer) a pdu or
         * recvd one for the task since the last timeout ask for
         * more time. If on the next timeout we have not made progress
         * we can check if it is the task or connection when we send the
         * nop as a ping.
         */
        if (time_after(task->last_xfer, task->last_timeout)) {
                ISCSI_DBG_EH(session, "Command making progress. Asking "
                             "scsi-ml for more time to complete. "
                             "Last data xfer at %lu. Last timeout was at "
                             "%lu\n.", task->last_xfer, task->last_timeout);
                task->have_checked_conn = false;
                rc = BLK_EH_RESET_TIMER;
                goto done;
        }

        if (!conn->recv_timeout && !conn->ping_timeout)
                goto done;
        /*
         * if the ping timedout then we are in the middle of cleaning up
         * and can let the iscsi eh handle it
         */
        if (iscsi_has_ping_timed_out(conn)) {
                rc = BLK_EH_RESET_TIMER;
                goto done;
        }

        spin_lock(&session->back_lock);
        for (i = 0; i < conn->session->cmds_max; i++) {
                running_task = conn->session->cmds[i];
                if (!running_task->sc || running_task == task ||
                     running_task->state != ISCSI_TASK_RUNNING)
                        continue;

                /*
                 * Only check if cmds started before this one have made
                 * progress, or this could never fail
                 */
                if (time_after(running_task->sc->jiffies_at_alloc,
                               task->sc->jiffies_at_alloc))
                        continue;

                if (time_after(running_task->last_xfer, task->last_timeout)) {
                        /*
                         * This task has not made progress, but a task
                         * started before us has transferred data since
                         * we started/last-checked. We could be queueing
                         * too many tasks or the LU is bad.
                         *
                         * If the device is bad the cmds ahead of us on
                         * other devs will complete, and this loop will
                         * eventually fail starting the scsi eh.
                         */
                        ISCSI_DBG_EH(session, "Command has not made progress "
                                     "but commands ahead of it have. "
                                     "Asking scsi-ml for more time to "
                                     "complete. Our last xfer vs running task "
                                     "last xfer %lu/%lu. Last check %lu.\n",
                                     task->last_xfer, running_task->last_xfer,
                                     task->last_timeout);
                        spin_unlock(&session->back_lock);
                        rc = BLK_EH_RESET_TIMER;
                        goto done;
                }
        }
        spin_unlock(&session->back_lock);

        /* Assumes nop timeout is shorter than scsi cmd timeout */
        if (task->have_checked_conn)
                goto done;

        /*
         * Checking the transport already or nop from a cmd timeout still
         * running
         */
        if (READ_ONCE(conn->ping_task)) {
                task->have_checked_conn = true;
                rc = BLK_EH_RESET_TIMER;
                goto done;
        }

        /* Make sure there is a transport check done */
        iscsi_send_nopout(conn, NULL);
        task->have_checked_conn = true;
        rc = BLK_EH_RESET_TIMER;

done:
        spin_unlock_bh(&session->frwd_lock);

        if (task) {
                task->last_timeout = jiffies;
                iscsi_put_task(task);
        }
        ISCSI_DBG_EH(session, "return %s\n", rc == BLK_EH_RESET_TIMER ?
                     "timer reset" : "shutdown or nh");
        return rc;
}
EXPORT_SYMBOL_GPL(iscsi_eh_cmd_timed_out);

static void iscsi_check_transport_timeouts(struct timer_list *t)
{
        struct iscsi_conn *conn = from_timer(conn, t, transport_timer);
        struct iscsi_session *session = conn->session;
        unsigned long recv_timeout, next_timeout = 0, last_recv;

        spin_lock(&session->frwd_lock);
        if (session->state != ISCSI_STATE_LOGGED_IN)
                goto done;

        recv_timeout = conn->recv_timeout;
        if (!recv_timeout)
                goto done;

        recv_timeout *= HZ;
        last_recv = conn->last_recv;

        if (iscsi_has_ping_timed_out(conn)) {
                iscsi_conn_printk(KERN_ERR, conn, "ping timeout of %d secs "
                                  "expired, recv timeout %d, last rx %lu, "
                                  "last ping %lu, now %lu\n",
                                  conn->ping_timeout, conn->recv_timeout,
                                  last_recv, conn->last_ping, jiffies);
                spin_unlock(&session->frwd_lock);
                iscsi_conn_failure(conn, ISCSI_ERR_NOP_TIMEDOUT);
                return;
        }

        if (time_before_eq(last_recv + recv_timeout, jiffies)) {
                /* send a ping to try to provoke some traffic */
                ISCSI_DBG_CONN(conn, "Sending nopout as ping\n");
                if (iscsi_send_nopout(conn, NULL))
                        next_timeout = jiffies + (1 * HZ);
                else
                        next_timeout = conn->last_ping + (conn->ping_timeout * HZ);
        } else
                next_timeout = last_recv + recv_timeout;

        ISCSI_DBG_CONN(conn, "Setting next tmo %lu\n", next_timeout);
        mod_timer(&conn->transport_timer, next_timeout);
done:
        spin_unlock(&session->frwd_lock);
}

/**
 * iscsi_conn_unbind - prevent queueing to conn.
 * @cls_conn: iscsi conn ep is bound to.
 * @is_active: is the conn in use for boot or is this for EH/termination
 *
 * This must be called by drivers implementing the ep_disconnect callout.
 * It disables queueing to the connection from libiscsi in preparation for
 * an ep_disconnect call.
 */
void iscsi_conn_unbind(struct iscsi_cls_conn *cls_conn, bool is_active)
{
        struct iscsi_session *session;
        struct iscsi_conn *conn;

        if (!cls_conn)
                return;

        conn = cls_conn->dd_data;
        session = conn->session;
        /*
         * Wait for iscsi_eh calls to exit. We don't wait for the tmf to
         * complete or timeout. The caller just wants to know what's running
         * is everything that needs to be cleaned up, and no cmds will be
         * queued.
         */
        mutex_lock(&session->eh_mutex);

        iscsi_suspend_queue(conn);
        iscsi_suspend_tx(conn);

        spin_lock_bh(&session->frwd_lock);
        if (!is_active) {
                /*
                 * if logout timed out before userspace could even send a PDU
                 * the state might still be in ISCSI_STATE_LOGGED_IN and
                 * allowing new cmds and TMFs.
                 */
                if (session->state == ISCSI_STATE_LOGGED_IN)
                        iscsi_set_conn_failed(conn);
        }
        spin_unlock_bh(&session->frwd_lock);
        mutex_unlock(&session->eh_mutex);
}
EXPORT_SYMBOL_GPL(iscsi_conn_unbind);

static void iscsi_prep_abort_task_pdu(struct iscsi_task *task,
                                      struct iscsi_tm *hdr)
{
        memset(hdr, 0, sizeof(*hdr));
        hdr->opcode = ISCSI_OP_SCSI_TMFUNC | ISCSI_OP_IMMEDIATE;
        hdr->flags = ISCSI_TM_FUNC_ABORT_TASK & ISCSI_FLAG_TM_FUNC_MASK;
        hdr->flags |= ISCSI_FLAG_CMD_FINAL;
        hdr->lun = task->lun;
        hdr->rtt = task->hdr_itt;
        hdr->refcmdsn = task->cmdsn;
}

int iscsi_eh_abort(struct scsi_cmnd *sc)
{
        struct iscsi_cls_session *cls_session;
        struct iscsi_session *session;
        struct iscsi_conn *conn;
        struct iscsi_task *task;
        struct iscsi_tm *hdr;
        int age;

        cls_session = starget_to_session(scsi_target(sc->device));
        session = cls_session->dd_data;

        ISCSI_DBG_EH(session, "aborting sc %p\n", sc);

        mutex_lock(&session->eh_mutex);
        spin_lock_bh(&session->frwd_lock);
        /*
         * if session was ISCSI_STATE_IN_RECOVERY then we may not have
         * got the command.
         */
        if (!sc->SCp.ptr) {
                ISCSI_DBG_EH(session, "sc never reached iscsi layer or "
                                      "it completed.\n");
                spin_unlock_bh(&session->frwd_lock);
                mutex_unlock(&session->eh_mutex);
                return SUCCESS;
        }

        /*
         * If we are not logged in or we have started a new session
         * then let the host reset code handle this
         */
        if (!session->leadconn || session->state != ISCSI_STATE_LOGGED_IN ||
            sc->SCp.phase != session->age) {
                spin_unlock_bh(&session->frwd_lock);
                mutex_unlock(&session->eh_mutex);
                ISCSI_DBG_EH(session, "failing abort due to dropped "
                                  "session.\n");
                return FAILED;
        }

        spin_lock(&session->back_lock);
        task = (struct iscsi_task *)sc->SCp.ptr;
        if (!task || !task->sc) {
                /* task completed before time out */
                ISCSI_DBG_EH(session, "sc completed while abort in progress\n");

                spin_unlock(&session->back_lock);
                spin_unlock_bh(&session->frwd_lock);
                mutex_unlock(&session->eh_mutex);
                return SUCCESS;
        }

        conn = session->leadconn;
        iscsi_get_conn(conn->cls_conn);
        conn->eh_abort_cnt++;
        age = session->age;

        ISCSI_DBG_EH(session, "aborting [sc %p itt 0x%x]\n", sc, task->itt);
        __iscsi_get_task(task);
        spin_unlock(&session->back_lock);

        if (task->state == ISCSI_TASK_PENDING) {
                fail_scsi_task(task, DID_ABORT);
                goto success;
        }

        /* only have one tmf outstanding at a time */
        if (session->tmf_state != TMF_INITIAL)
                goto failed;
        session->tmf_state = TMF_QUEUED;

        hdr = &session->tmhdr;
        iscsi_prep_abort_task_pdu(task, hdr);

        if (iscsi_exec_task_mgmt_fn(conn, hdr, age, session->abort_timeout))
                goto failed;

        switch (session->tmf_state) {
        case TMF_SUCCESS:
                spin_unlock_bh(&session->frwd_lock);
                /*
                 * stop tx side incase the target had sent a abort rsp but
                 * the initiator was still writing out data.
                 */
                iscsi_suspend_tx(conn);
                /*
                 * we do not stop the recv side because targets have been
                 * good and have never sent us a successful tmf response
                 * then sent more data for the cmd.
                 */
                spin_lock_bh(&session->frwd_lock);
                fail_scsi_task(task, DID_ABORT);
                session->tmf_state = TMF_INITIAL;
                memset(hdr, 0, sizeof(*hdr));
                spin_unlock_bh(&session->frwd_lock);
                iscsi_start_tx(conn);
                goto success_unlocked;
        case TMF_TIMEDOUT:
                session->running_aborted_task = task;
                spin_unlock_bh(&session->frwd_lock);
                iscsi_conn_failure(conn, ISCSI_ERR_SCSI_EH_SESSION_RST);
                goto failed_unlocked;
        case TMF_NOT_FOUND:
                if (iscsi_task_is_completed(task)) {
                        session->tmf_state = TMF_INITIAL;
                        memset(hdr, 0, sizeof(*hdr));
                        /* task completed before tmf abort response */
                        ISCSI_DBG_EH(session, "sc completed while abort in "
                                              "progress\n");
                        goto success;
                }
                fallthrough;
        default:
                session->tmf_state = TMF_INITIAL;
                goto failed;
        }

success:
        spin_unlock_bh(&session->frwd_lock);
success_unlocked:
        ISCSI_DBG_EH(session, "abort success [sc %p itt 0x%x]\n",
                     sc, task->itt);
        iscsi_put_task(task);
        iscsi_put_conn(conn->cls_conn);
        mutex_unlock(&session->eh_mutex);
        return SUCCESS;

failed:
        spin_unlock_bh(&session->frwd_lock);
failed_unlocked:
        ISCSI_DBG_EH(session, "abort failed [sc %p itt 0x%x]\n", sc,
                     task ? task->itt : 0);
        /*
         * The driver might be accessing the task so hold the ref. The conn
         * stop cleanup will drop the ref after ep_disconnect so we know the
         * driver's no longer touching the task.
         */
        if (!session->running_aborted_task)
                iscsi_put_task(task);

        iscsi_put_conn(conn->cls_conn);
        mutex_unlock(&session->eh_mutex);
        return FAILED;
}
EXPORT_SYMBOL_GPL(iscsi_eh_abort);

static void iscsi_prep_lun_reset_pdu(struct scsi_cmnd *sc, struct iscsi_tm *hdr)
{
        memset(hdr, 0, sizeof(*hdr));
        hdr->opcode = ISCSI_OP_SCSI_TMFUNC | ISCSI_OP_IMMEDIATE;
        hdr->flags = ISCSI_TM_FUNC_LOGICAL_UNIT_RESET & ISCSI_FLAG_TM_FUNC_MASK;
        hdr->flags |= ISCSI_FLAG_CMD_FINAL;
        int_to_scsilun(sc->device->lun, &hdr->lun);
        hdr->rtt = RESERVED_ITT;
}

int iscsi_eh_device_reset(struct scsi_cmnd *sc)
{
        struct iscsi_cls_session *cls_session;
        struct iscsi_session *session;
        struct iscsi_conn *conn;
        struct iscsi_tm *hdr;
        int rc = FAILED;

        cls_session = starget_to_session(scsi_target(sc->device));
        session = cls_session->dd_data;

        ISCSI_DBG_EH(session, "LU Reset [sc %p lun %llu]\n", sc,
                     sc->device->lun);

        mutex_lock(&session->eh_mutex);
        spin_lock_bh(&session->frwd_lock);
        /*
         * Just check if we are not logged in. We cannot check for
         * the phase because the reset could come from a ioctl.
         */
        if (!session->leadconn || session->state != ISCSI_STATE_LOGGED_IN)
                goto unlock;
        conn = session->leadconn;

        /* only have one tmf outstanding at a time */
        if (session->tmf_state != TMF_INITIAL)
                goto unlock;
        session->tmf_state = TMF_QUEUED;

        hdr = &session->tmhdr;
        iscsi_prep_lun_reset_pdu(sc, hdr);

        if (iscsi_exec_task_mgmt_fn(conn, hdr, session->age,
                                    session->lu_reset_timeout)) {
                rc = FAILED;
                goto unlock;
        }

        switch (session->tmf_state) {
        case TMF_SUCCESS:
                break;
        case TMF_TIMEDOUT:
                spin_unlock_bh(&session->frwd_lock);
                iscsi_conn_failure(conn, ISCSI_ERR_SCSI_EH_SESSION_RST);
                goto done;
        default:
                session->tmf_state = TMF_INITIAL;
                goto unlock;
        }

        rc = SUCCESS;
        spin_unlock_bh(&session->frwd_lock);

        iscsi_suspend_tx(conn);

        spin_lock_bh(&session->frwd_lock);
        memset(hdr, 0, sizeof(*hdr));
        fail_scsi_tasks(conn, sc->device->lun, DID_ERROR);
        session->tmf_state = TMF_INITIAL;
        spin_unlock_bh(&session->frwd_lock);

        iscsi_start_tx(conn);
        goto done;

unlock:
        spin_unlock_bh(&session->frwd_lock);
done:
        ISCSI_DBG_EH(session, "dev reset result = %s\n",
                     rc == SUCCESS ? "SUCCESS" : "FAILED");
        mutex_unlock(&session->eh_mutex);
        return rc;
}
EXPORT_SYMBOL_GPL(iscsi_eh_device_reset);

void iscsi_session_recovery_timedout(struct iscsi_cls_session *cls_session)
{
        struct iscsi_session *session = cls_session->dd_data;

        spin_lock_bh(&session->frwd_lock);
        if (session->state != ISCSI_STATE_LOGGED_IN) {
                session->state = ISCSI_STATE_RECOVERY_FAILED;
                wake_up(&session->ehwait);
        }
        spin_unlock_bh(&session->frwd_lock);
}
EXPORT_SYMBOL_GPL(iscsi_session_recovery_timedout);

/**
 * iscsi_eh_session_reset - drop session and attempt relogin
 * @sc: scsi command
 *
 * This function will wait for a relogin, session termination from
 * userspace, or a recovery/replacement timeout.
 */
int iscsi_eh_session_reset(struct scsi_cmnd *sc)
{
        struct iscsi_cls_session *cls_session;
        struct iscsi_session *session;
        struct iscsi_conn *conn;

        cls_session = starget_to_session(scsi_target(sc->device));
        session = cls_session->dd_data;

        mutex_lock(&session->eh_mutex);
        spin_lock_bh(&session->frwd_lock);
        if (session->state == ISCSI_STATE_TERMINATE) {
failed:
                ISCSI_DBG_EH(session,
                             "failing session reset: Could not log back into "
                             "%s [age %d]\n", session->targetname,
                             session->age);
                spin_unlock_bh(&session->frwd_lock);
                mutex_unlock(&session->eh_mutex);
                return FAILED;
        }

        conn = session->leadconn;
        iscsi_get_conn(conn->cls_conn);

        spin_unlock_bh(&session->frwd_lock);
        mutex_unlock(&session->eh_mutex);

        iscsi_conn_failure(conn, ISCSI_ERR_SCSI_EH_SESSION_RST);
        iscsi_put_conn(conn->cls_conn);

        ISCSI_DBG_EH(session, "wait for relogin\n");
        wait_event_interruptible(session->ehwait,
                                 session->state == ISCSI_STATE_TERMINATE ||
                                 session->state == ISCSI_STATE_LOGGED_IN ||
                                 session->state == ISCSI_STATE_RECOVERY_FAILED);
        if (signal_pending(current))
                flush_signals(current);

        mutex_lock(&session->eh_mutex);
        spin_lock_bh(&session->frwd_lock);
        if (session->state == ISCSI_STATE_LOGGED_IN) {
                ISCSI_DBG_EH(session,
                             "session reset succeeded for %s,%s\n",
                             session->targetname, conn->persistent_address);
        } else
                goto failed;
        spin_unlock_bh(&session->frwd_lock);
        mutex_unlock(&session->eh_mutex);
        return SUCCESS;
}
EXPORT_SYMBOL_GPL(iscsi_eh_session_reset);

static void iscsi_prep_tgt_reset_pdu(struct scsi_cmnd *sc, struct iscsi_tm *hdr)
{
        memset(hdr, 0, sizeof(*hdr));
        hdr->opcode = ISCSI_OP_SCSI_TMFUNC | ISCSI_OP_IMMEDIATE;
        hdr->flags = ISCSI_TM_FUNC_TARGET_WARM_RESET & ISCSI_FLAG_TM_FUNC_MASK;
        hdr->flags |= ISCSI_FLAG_CMD_FINAL;
        hdr->rtt = RESERVED_ITT;
}

/**
 * iscsi_eh_target_reset - reset target
 * @sc: scsi command
 *
 * This will attempt to send a warm target reset.
 */
static int iscsi_eh_target_reset(struct scsi_cmnd *sc)
{
        struct iscsi_cls_session *cls_session;
        struct iscsi_session *session;
        struct iscsi_conn *conn;
        struct iscsi_tm *hdr;
        int rc = FAILED;

        cls_session = starget_to_session(scsi_target(sc->device));
        session = cls_session->dd_data;

        ISCSI_DBG_EH(session, "tgt Reset [sc %p tgt %s]\n", sc,
                     session->targetname);

        mutex_lock(&session->eh_mutex);
        spin_lock_bh(&session->frwd_lock);
        /*
         * Just check if we are not logged in. We cannot check for
         * the phase because the reset could come from a ioctl.
         */
        if (!session->leadconn || session->state != ISCSI_STATE_LOGGED_IN)
                goto unlock;
        conn = session->leadconn;

        /* only have one tmf outstanding at a time */
        if (session->tmf_state != TMF_INITIAL)
                goto unlock;
        session->tmf_state = TMF_QUEUED;

        hdr = &session->tmhdr;
        iscsi_prep_tgt_reset_pdu(sc, hdr);

        if (iscsi_exec_task_mgmt_fn(conn, hdr, session->age,
                                    session->tgt_reset_timeout)) {
                rc = FAILED;
                goto unlock;
        }

        switch (session->tmf_state) {
        case TMF_SUCCESS:
                break;
        case TMF_TIMEDOUT:
                spin_unlock_bh(&session->frwd_lock);
                iscsi_conn_failure(conn, ISCSI_ERR_SCSI_EH_SESSION_RST);
                goto done;
        default:
                session->tmf_state = TMF_INITIAL;
                goto unlock;
        }

        rc = SUCCESS;
        spin_unlock_bh(&session->frwd_lock);

        iscsi_suspend_tx(conn);

        spin_lock_bh(&session->frwd_lock);
        memset(hdr, 0, sizeof(*hdr));
        fail_scsi_tasks(conn, -1, DID_ERROR);
        session->tmf_state = TMF_INITIAL;
        spin_unlock_bh(&session->frwd_lock);

        iscsi_start_tx(conn);
        goto done;

unlock:
        spin_unlock_bh(&session->frwd_lock);
done:
        ISCSI_DBG_EH(session, "tgt %s reset result = %s\n", session->targetname,
                     rc == SUCCESS ? "SUCCESS" : "FAILED");
        mutex_unlock(&session->eh_mutex);
        return rc;
}

/**
 * iscsi_eh_recover_target - reset target and possibly the session
 * @sc: scsi command
 *
 * This will attempt to send a warm target reset. If that fails,
 * we will escalate to ERL0 session recovery.
 */
int iscsi_eh_recover_target(struct scsi_cmnd *sc)
{
        int rc;

        rc = iscsi_eh_target_reset(sc);
        if (rc == FAILED)
                rc = iscsi_eh_session_reset(sc);
        return rc;
}
EXPORT_SYMBOL_GPL(iscsi_eh_recover_target);

/*
 * Pre-allocate a pool of @max items of @item_size. By default, the pool
 * should be accessed via kfifo_{get,put} on q->queue.
 * Optionally, the caller can obtain the array of object pointers
 * by passing in a non-NULL @items pointer
 */
int
iscsi_pool_init(struct iscsi_pool *q, int max, void ***items, int item_size)
{
        int i, num_arrays = 1;

        memset(q, 0, sizeof(*q));

        q->max = max;

        /* If the user passed an items pointer, he wants a copy of
         * the array. */
        if (items)
                num_arrays++;
        q->pool = kvcalloc(num_arrays * max, sizeof(void *), GFP_KERNEL);
        if (q->pool == NULL)
                return -ENOMEM;

        kfifo_init(&q->queue, (void*)q->pool, max * sizeof(void*));

        for (i = 0; i < max; i++) {
                q->pool[i] = kzalloc(item_size, GFP_KERNEL);
                if (q->pool[i] == NULL) {
                        q->max = i;
                        goto enomem;
                }
                kfifo_in(&q->queue, (void*)&q->pool[i], sizeof(void*));
        }

        if (items) {
                *items = q->pool + max;
                memcpy(*items, q->pool, max * sizeof(void *));
        }

        return 0;

enomem:
        iscsi_pool_free(q);
        return -ENOMEM;
}
EXPORT_SYMBOL_GPL(iscsi_pool_init);

void iscsi_pool_free(struct iscsi_pool *q)
{
        int i;

        for (i = 0; i < q->max; i++)
                kfree(q->pool[i]);
        kvfree(q->pool);
}
EXPORT_SYMBOL_GPL(iscsi_pool_free);

int iscsi_host_get_max_scsi_cmds(struct Scsi_Host *shost,
                                 uint16_t requested_cmds_max)
{
        int scsi_cmds, total_cmds = requested_cmds_max;

check:
        if (!total_cmds)
                total_cmds = ISCSI_DEF_XMIT_CMDS_MAX;
        /*
         * The iscsi layer needs some tasks for nop handling and tmfs,
         * so the cmds_max must at least be greater than ISCSI_MGMT_CMDS_MAX
         * + 1 command for scsi IO.
         */
        if (total_cmds < ISCSI_TOTAL_CMDS_MIN) {
                printk(KERN_ERR "iscsi: invalid max cmds of %d. Must be a power of two that is at least %d.\n",
                       total_cmds, ISCSI_TOTAL_CMDS_MIN);
                return -EINVAL;
        }

        if (total_cmds > ISCSI_TOTAL_CMDS_MAX) {
                printk(KERN_INFO "iscsi: invalid max cmds of %d. Must be a power of 2 less than or equal to %d. Using %d.\n",
                       requested_cmds_max, ISCSI_TOTAL_CMDS_MAX,
                       ISCSI_TOTAL_CMDS_MAX);
                total_cmds = ISCSI_TOTAL_CMDS_MAX;
        }

        if (!is_power_of_2(total_cmds)) {
                total_cmds = rounddown_pow_of_two(total_cmds);
                if (total_cmds < ISCSI_TOTAL_CMDS_MIN) {
                        printk(KERN_ERR "iscsi: invalid max cmds of %d. Must be a power of 2 greater than %d.\n", requested_cmds_max, ISCSI_TOTAL_CMDS_MIN);
                        return -EINVAL;
                }

                printk(KERN_INFO "iscsi: invalid max cmds %d. Must be a power of 2. Rounding max cmds down to %d.\n",
                       requested_cmds_max, total_cmds);
        }

        scsi_cmds = total_cmds - ISCSI_MGMT_CMDS_MAX;
        if (shost->can_queue && scsi_cmds > shost->can_queue) {
                total_cmds = shost->can_queue;

                printk(KERN_INFO "iscsi: requested max cmds %u is higher than driver limit. Using driver limit %u\n",
                       requested_cmds_max, shost->can_queue);
                goto check;
        }

        return scsi_cmds;
}
EXPORT_SYMBOL_GPL(iscsi_host_get_max_scsi_cmds);

/**
 * iscsi_host_add - add host to system
 * @shost: scsi host
 * @pdev: parent device
 *
 * This should be called by partial offload and software iscsi drivers
 * to add a host to the system.
 */
int iscsi_host_add(struct Scsi_Host *shost, struct device *pdev)
{
        if (!shost->can_queue)
                shost->can_queue = ISCSI_DEF_XMIT_CMDS_MAX;

        if (!shost->cmd_per_lun)
                shost->cmd_per_lun = ISCSI_DEF_CMD_PER_LUN;

        return scsi_add_host(shost, pdev);
}
EXPORT_SYMBOL_GPL(iscsi_host_add);

/**
 * iscsi_host_alloc - allocate a host and driver data
 * @sht: scsi host template
 * @dd_data_size: driver host data size
 * @xmit_can_sleep: bool indicating if LLD will queue IO from a work queue
 *
 * This should be called by partial offload and software iscsi drivers.
 * To access the driver specific memory use the iscsi_host_priv() macro.
 */
struct Scsi_Host *iscsi_host_alloc(struct scsi_host_template *sht,
                                   int dd_data_size, bool xmit_can_sleep)
{
        struct Scsi_Host *shost;
        struct iscsi_host *ihost;

        shost = scsi_host_alloc(sht, sizeof(struct iscsi_host) + dd_data_size);
        if (!shost)
                return NULL;
        ihost = shost_priv(shost);

        if (xmit_can_sleep) {
                snprintf(ihost->workq_name, sizeof(ihost->workq_name),
                        "iscsi_q_%d", shost->host_no);
                ihost->workq = alloc_workqueue("%s",
                        WQ_SYSFS | __WQ_LEGACY | WQ_MEM_RECLAIM | WQ_UNBOUND,
                        1, ihost->workq_name);
                if (!ihost->workq)
                        goto free_host;
        }

        spin_lock_init(&ihost->lock);
        ihost->state = ISCSI_HOST_SETUP;
        ihost->num_sessions = 0;
        init_waitqueue_head(&ihost->session_removal_wq);
        return shost;

free_host:
        scsi_host_put(shost);
        return NULL;
}
EXPORT_SYMBOL_GPL(iscsi_host_alloc);

static void iscsi_notify_host_removed(struct iscsi_cls_session *cls_session)
{
        iscsi_session_failure(cls_session->dd_data, ISCSI_ERR_INVALID_HOST);
}

/**
 * iscsi_host_remove - remove host and sessions
 * @shost: scsi host
 *
 * If there are any sessions left, this will initiate the removal and wait
 * for the completion.
 */
void iscsi_host_remove(struct Scsi_Host *shost)
{
        struct iscsi_host *ihost = shost_priv(shost);
        unsigned long flags;

        spin_lock_irqsave(&ihost->lock, flags);
        ihost->state = ISCSI_HOST_REMOVED;
        spin_unlock_irqrestore(&ihost->lock, flags);

        iscsi_host_for_each_session(shost, iscsi_notify_host_removed);
        wait_event_interruptible(ihost->session_removal_wq,
                                 ihost->num_sessions == 0);
        if (signal_pending(current))
                flush_signals(current);

        scsi_remove_host(shost);
}
EXPORT_SYMBOL_GPL(iscsi_host_remove);

void iscsi_host_free(struct Scsi_Host *shost)
{
        struct iscsi_host *ihost = shost_priv(shost);

        if (ihost->workq)
                destroy_workqueue(ihost->workq);

        kfree(ihost->netdev);
        kfree(ihost->hwaddress);
        kfree(ihost->initiatorname);
        scsi_host_put(shost);
}
EXPORT_SYMBOL_GPL(iscsi_host_free);

static void iscsi_host_dec_session_cnt(struct Scsi_Host *shost)
{
        struct iscsi_host *ihost = shost_priv(shost);
        unsigned long flags;

        shost = scsi_host_get(shost);
        if (!shost) {
                printk(KERN_ERR "Invalid state. Cannot notify host removal "
                      "of session teardown event because host already "
                      "removed.\n");
                return;
        }

        spin_lock_irqsave(&ihost->lock, flags);
        ihost->num_sessions--;
        if (ihost->num_sessions == 0)
                wake_up(&ihost->session_removal_wq);
        spin_unlock_irqrestore(&ihost->lock, flags);
        scsi_host_put(shost);
}

/**
 * iscsi_session_setup - create iscsi cls session and host and session
 * @iscsit: iscsi transport template
 * @shost: scsi host
 * @cmds_max: session can queue
 * @dd_size: private driver data size, added to session allocation size
 * @cmd_task_size: LLD task private data size
 * @initial_cmdsn: initial CmdSN
 * @id: target ID to add to this session
 *
 * This can be used by software iscsi_transports that allocate
 * a session per scsi host.
 *
 * Callers should set cmds_max to the largest total numer (mgmt + scsi) of
 * tasks they support. The iscsi layer reserves ISCSI_MGMT_CMDS_MAX tasks
 * for nop handling and login/logout requests.
 */
struct iscsi_cls_session *
iscsi_session_setup(struct iscsi_transport *iscsit, struct Scsi_Host *shost,
                    uint16_t cmds_max, int dd_size, int cmd_task_size,
                    uint32_t initial_cmdsn, unsigned int id)
{
        struct iscsi_host *ihost = shost_priv(shost);
        struct iscsi_session *session;
        struct iscsi_cls_session *cls_session;
        int cmd_i, scsi_cmds;
        unsigned long flags;

        spin_lock_irqsave(&ihost->lock, flags);
        if (ihost->state == ISCSI_HOST_REMOVED) {
                spin_unlock_irqrestore(&ihost->lock, flags);
                return NULL;
        }
        ihost->num_sessions++;
        spin_unlock_irqrestore(&ihost->lock, flags);

        scsi_cmds = iscsi_host_get_max_scsi_cmds(shost, cmds_max);
        if (scsi_cmds < 0)
                goto dec_session_count;

        cls_session = iscsi_alloc_session(shost, iscsit,
                                          sizeof(struct iscsi_session) +
                                          dd_size);
        if (!cls_session)
                goto dec_session_count;
        session = cls_session->dd_data;
        session->cls_session = cls_session;
        session->host = shost;
        session->state = ISCSI_STATE_FREE;
        session->fast_abort = 1;
        session->tgt_reset_timeout = 30;
        session->lu_reset_timeout = 15;
        session->abort_timeout = 10;
        session->scsi_cmds_max = scsi_cmds;
        session->cmds_max = scsi_cmds + ISCSI_MGMT_CMDS_MAX;
        session->queued_cmdsn = session->cmdsn = initial_cmdsn;
        session->exp_cmdsn = initial_cmdsn + 1;
        session->max_cmdsn = initial_cmdsn + 1;
        session->max_r2t = 1;
        session->tt = iscsit;
        session->dd_data = cls_session->dd_data + sizeof(*session);

        session->tmf_state = TMF_INITIAL;
        timer_setup(&session->tmf_timer, iscsi_tmf_timedout, 0);
        mutex_init(&session->eh_mutex);

        spin_lock_init(&session->frwd_lock);
        spin_lock_init(&session->back_lock);

        /* initialize SCSI PDU commands pool */
        if (iscsi_pool_init(&session->cmdpool, session->cmds_max,
                            (void***)&session->cmds,
                            cmd_task_size + sizeof(struct iscsi_task)))
                goto cmdpool_alloc_fail;

        /* pre-format cmds pool with ITT */
        for (cmd_i = 0; cmd_i < session->cmds_max; cmd_i++) {
                struct iscsi_task *task = session->cmds[cmd_i];

                if (cmd_task_size)
                        task->dd_data = &task[1];
                task->itt = cmd_i;
                task->state = ISCSI_TASK_FREE;
                INIT_LIST_HEAD(&task->running);
        }

        if (!try_module_get(iscsit->owner))
                goto module_get_fail;

        if (iscsi_add_session(cls_session, id))
                goto cls_session_fail;

        return cls_session;

cls_session_fail:
        module_put(iscsit->owner);
module_get_fail:
        iscsi_pool_free(&session->cmdpool);
cmdpool_alloc_fail:
        iscsi_free_session(cls_session);
dec_session_count:
        iscsi_host_dec_session_cnt(shost);
        return NULL;
}
EXPORT_SYMBOL_GPL(iscsi_session_setup);

/**
 * iscsi_session_teardown - destroy session, host, and cls_session
 * @cls_session: iscsi session
 */
void iscsi_session_teardown(struct iscsi_cls_session *cls_session)
{
        struct iscsi_session *session = cls_session->dd_data;