// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * iSCSI over TCP/IP Data-Path lib
 *
 * Copyright (C) 2004 Dmitry Yusupov
 * Copyright (C) 2004 Alex Aizman
 * Copyright (C) 2005 - 2006 Mike Christie
 * Copyright (C) 2006 Red Hat, Inc.  All rights reserved.
 * maintained by open-iscsi@googlegroups.com
 *
 * Credits:
 *      Christoph Hellwig
 *      FUJITA Tomonori
 *      Arne Redlich
 *      Zhenyu Wang
 */

#include <crypto/hash.h>
#include <linux/types.h>
#include <linux/list.h>
#include <linux/inet.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/blkdev.h>
#include <linux/delay.h>
#include <linux/kfifo.h>
#include <linux/scatterlist.h>
#include <linux/module.h>
#include <net/tcp.h>
#include <scsi/scsi_cmnd.h>
#include <scsi/scsi_device.h>
#include <scsi/scsi_host.h>
#include <scsi/scsi.h>
#include <scsi/scsi_transport_iscsi.h>
#include <trace/events/iscsi.h>

#include "iscsi_tcp.h"

MODULE_AUTHOR("Mike Christie <michaelc@cs.wisc.edu>, "
              "Dmitry Yusupov <dmitry_yus@yahoo.com>, "
              "Alex Aizman <itn780@yahoo.com>");
MODULE_DESCRIPTION("iSCSI/TCP data-path");
MODULE_LICENSE("GPL");

static int iscsi_dbg_libtcp;
module_param_named(debug_libiscsi_tcp, iscsi_dbg_libtcp, int,
                   S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(debug_libiscsi_tcp, "Turn on debugging for libiscsi_tcp "
                 "module. Set to 1 to turn on, and zero to turn off. Default "
                 "is off.");

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

static int iscsi_tcp_hdr_recv_done(struct iscsi_tcp_conn *tcp_conn,
                                   struct iscsi_segment *segment);

/*
 * Scatterlist handling: inside the iscsi_segment, we
 * remember an index into the scatterlist, and set data/size
 * to the current scatterlist entry. For highmem pages, we
 * kmap as needed.
 *
 * Note that the page is unmapped when we return from
 * TCP's data_ready handler, so we may end up mapping and
 * unmapping the same page repeatedly. The whole reason
 * for this is that we shouldn't keep the page mapped
 * outside the softirq.
 */

/**
 * iscsi_tcp_segment_init_sg - init indicated scatterlist entry
 * @segment: the buffer object
 * @sg: scatterlist
 * @offset: byte offset into that sg entry
 *
 * This function sets up the segment so that subsequent
 * data is copied to the indicated sg entry, at the given
 * offset.
 */
static inline void
iscsi_tcp_segment_init_sg(struct iscsi_segment *segment,
                          struct scatterlist *sg, unsigned int offset)
{
        segment->sg = sg;
        segment->sg_offset = offset;
        segment->size = min(sg->length - offset,
                            segment->total_size - segment->total_copied);
        segment->data = NULL;
}

/**
 * iscsi_tcp_segment_map - map the current S/G page
 * @segment: iscsi_segment
 * @recv: 1 if called from recv path
 *
 * We only need to possibly kmap data if scatter lists are being used,
 * because the iscsi passthrough and internal IO paths will never use high
 * mem pages.
 */
static void iscsi_tcp_segment_map(struct iscsi_segment *segment, int recv)
{
        struct scatterlist *sg;

        if (segment->data != NULL || !segment->sg)
                return;

        sg = segment->sg;
        BUG_ON(segment->sg_mapped);
        BUG_ON(sg->length == 0);

        /*
         * We always map for the recv path.
         *
         * If the page count is greater than one it is ok to send
         * to the network layer's zero copy send path. If not we
         * have to go the slow sendmsg path.
         *
         * Same goes for slab pages: skb_can_coalesce() allows
         * coalescing neighboring slab objects into a single frag which
         * triggers one of hardened usercopy checks.
         */
        if (!recv && sendpage_ok(sg_page(sg)))
                return;

        if (recv) {
                segment->atomic_mapped = true;
                segment->sg_mapped = kmap_atomic(sg_page(sg));
        } else {
                segment->atomic_mapped = false;
                /* the xmit path can sleep with the page mapped so use kmap */
                segment->sg_mapped = kmap(sg_page(sg));
        }

        segment->data = segment->sg_mapped + sg->offset + segment->sg_offset;
}

void iscsi_tcp_segment_unmap(struct iscsi_segment *segment)
{
        if (segment->sg_mapped) {
                if (segment->atomic_mapped)
                        kunmap_atomic(segment->sg_mapped);
                else
                        kunmap(sg_page(segment->sg));
                segment->sg_mapped = NULL;
                segment->data = NULL;
        }
}
EXPORT_SYMBOL_GPL(iscsi_tcp_segment_unmap);

/*
 * Splice the digest buffer into the buffer
 */
static inline void
iscsi_tcp_segment_splice_digest(struct iscsi_segment *segment, void *digest)
{
        segment->data = digest;
        segment->digest_len = ISCSI_DIGEST_SIZE;
        segment->total_size += ISCSI_DIGEST_SIZE;
        segment->size = ISCSI_DIGEST_SIZE;
        segment->copied = 0;
        segment->sg = NULL;
        segment->hash = NULL;
}

/**
 * iscsi_tcp_segment_done - check whether the segment is complete
 * @tcp_conn: iscsi tcp connection
 * @segment: iscsi segment to check
 * @recv: set to one of this is called from the recv path
 * @copied: number of bytes copied
 *
 * Check if we're done receiving this segment. If the receive
 * buffer is full but we expect more data, move on to the
 * next entry in the scatterlist.
 *
 * If the amount of data we received isn't a multiple of 4,
 * we will transparently receive the pad bytes, too.
 *
 * This function must be re-entrant.
 */
int iscsi_tcp_segment_done(struct iscsi_tcp_conn *tcp_conn,
                           struct iscsi_segment *segment, int recv,
                           unsigned copied)
{
        struct scatterlist sg;
        unsigned int pad;

        ISCSI_DBG_TCP(tcp_conn->iscsi_conn, "copied %u %u size %u %s\n",
                      segment->copied, copied, segment->size,
                      recv ? "recv" : "xmit");
        if (segment->hash && copied) {
                /*
                 * If a segment is kmapd we must unmap it before sending
                 * to the crypto layer since that will try to kmap it again.
                 */
                iscsi_tcp_segment_unmap(segment);

                if (!segment->data) {
                        sg_init_table(&sg, 1);
                        sg_set_page(&sg, sg_page(segment->sg), copied,
                                    segment->copied + segment->sg_offset +
                                                        segment->sg->offset);
                } else
                        sg_init_one(&sg, segment->data + segment->copied,
                                    copied);
                ahash_request_set_crypt(segment->hash, &sg, NULL, copied);
                crypto_ahash_update(segment->hash);
        }

        segment->copied += copied;
        if (segment->copied < segment->size) {
                iscsi_tcp_segment_map(segment, recv);
                return 0;
        }

        segment->total_copied += segment->copied;
        segment->copied = 0;
        segment->size = 0;

        /* Unmap the current scatterlist page, if there is one. */
        iscsi_tcp_segment_unmap(segment);

        /* Do we have more scatterlist entries? */
        ISCSI_DBG_TCP(tcp_conn->iscsi_conn, "total copied %u total size %u\n",
                      segment->total_copied, segment->total_size);
        if (segment->total_copied < segment->total_size) {
                /* Proceed to the next entry in the scatterlist. */
                iscsi_tcp_segment_init_sg(segment, sg_next(segment->sg),
                                          0);
                iscsi_tcp_segment_map(segment, recv);
                BUG_ON(segment->size == 0);
                return 0;
        }

        /* Do we need to handle padding? */
        if (!(tcp_conn->iscsi_conn->session->tt->caps & CAP_PADDING_OFFLOAD)) {
                pad = iscsi_padding(segment->total_copied);
                if (pad != 0) {
                        ISCSI_DBG_TCP(tcp_conn->iscsi_conn,
                                      "consume %d pad bytes\n", pad);
                        segment->total_size += pad;
                        segment->size = pad;
                        segment->data = segment->padbuf;
                        return 0;
                }
        }

        /*
         * Set us up for transferring the data digest. hdr digest
         * is completely handled in hdr done function.
         */
        if (segment->hash) {
                ahash_request_set_crypt(segment->hash, NULL,
                                        segment->digest, 0);
                crypto_ahash_final(segment->hash);
                iscsi_tcp_segment_splice_digest(segment,
                                 recv ? segment->recv_digest : segment->digest);
                return 0;
        }

        return 1;
}
EXPORT_SYMBOL_GPL(iscsi_tcp_segment_done);

/**
 * iscsi_tcp_segment_recv - copy data to segment
 * @tcp_conn: the iSCSI TCP connection
 * @segment: the buffer to copy to
 * @ptr: data pointer
 * @len: amount of data available
 *
 * This function copies up to @len bytes to the
 * given buffer, and returns the number of bytes
 * consumed, which can actually be less than @len.
 *
 * If hash digest is enabled, the function will update the
 * hash while copying.
 * Combining these two operations doesn't buy us a lot (yet),
 * but in the future we could implement combined copy+crc,
 * just way we do for network layer checksums.
 */
static int
iscsi_tcp_segment_recv(struct iscsi_tcp_conn *tcp_conn,
                       struct iscsi_segment *segment, const void *ptr,
                       unsigned int len)
{
        unsigned int copy = 0, copied = 0;

        while (!iscsi_tcp_segment_done(tcp_conn, segment, 1, copy)) {
                if (copied == len) {
                        ISCSI_DBG_TCP(tcp_conn->iscsi_conn,
                                      "copied %d bytes\n", len);
                        break;
                }

                copy = min(len - copied, segment->size - segment->copied);
                ISCSI_DBG_TCP(tcp_conn->iscsi_conn, "copying %d\n", copy);
                memcpy(segment->data + segment->copied, ptr + copied, copy);
                copied += copy;
        }
        return copied;
}

inline void
iscsi_tcp_dgst_header(struct ahash_request *hash, const void *hdr,
                      size_t hdrlen, unsigned char digest[ISCSI_DIGEST_SIZE])
{
        struct scatterlist sg;

        sg_init_one(&sg, hdr, hdrlen);
        ahash_request_set_crypt(hash, &sg, digest, hdrlen);
        crypto_ahash_digest(hash);
}
EXPORT_SYMBOL_GPL(iscsi_tcp_dgst_header);

static inline int
iscsi_tcp_dgst_verify(struct iscsi_tcp_conn *tcp_conn,
                      struct iscsi_segment *segment)
{
        if (!segment->digest_len)
                return 1;

        if (memcmp(segment->recv_digest, segment->digest,
                   segment->digest_len)) {
                ISCSI_DBG_TCP(tcp_conn->iscsi_conn, "digest mismatch\n");
                return 0;
        }

        return 1;
}

/*
 * Helper function to set up segment buffer
 */
static inline void
__iscsi_segment_init(struct iscsi_segment *segment, size_t size,
                     iscsi_segment_done_fn_t *done, struct ahash_request *hash)
{
        memset(segment, 0, sizeof(*segment));
        segment->total_size = size;
        segment->done = done;

        if (hash) {
                segment->hash = hash;
                crypto_ahash_init(hash);
        }
}

inline void
iscsi_segment_init_linear(struct iscsi_segment *segment, void *data,
                          size_t size, iscsi_segment_done_fn_t *done,
                          struct ahash_request *hash)
{
        __iscsi_segment_init(segment, size, done, hash);
        segment->data = data;
        segment->size = size;
}
EXPORT_SYMBOL_GPL(iscsi_segment_init_linear);

inline int
iscsi_segment_seek_sg(struct iscsi_segment *segment,
                      struct scatterlist *sg_list, unsigned int sg_count,
                      unsigned int offset, size_t size,
                      iscsi_segment_done_fn_t *done,
                      struct ahash_request *hash)
{
        struct scatterlist *sg;
        unsigned int i;

        __iscsi_segment_init(segment, size, done, hash);
        for_each_sg(sg_list, sg, sg_count, i) {
                if (offset < sg->length) {
                        iscsi_tcp_segment_init_sg(segment, sg, offset);
                        return 0;
                }
                offset -= sg->length;
        }

        return ISCSI_ERR_DATA_OFFSET;
}
EXPORT_SYMBOL_GPL(iscsi_segment_seek_sg);

/**
 * iscsi_tcp_hdr_recv_prep - prep segment for hdr reception
 * @tcp_conn: iscsi connection to prep for
 *
 * This function always passes NULL for the hash argument, because when this
 * function is called we do not yet know the final size of the header and want
 * to delay the digest processing until we know that.
 */
void iscsi_tcp_hdr_recv_prep(struct iscsi_tcp_conn *tcp_conn)
{
        ISCSI_DBG_TCP(tcp_conn->iscsi_conn,
                      "(%s)\n", tcp_conn->iscsi_conn->hdrdgst_en ?
                      "digest enabled" : "digest disabled");
        iscsi_segment_init_linear(&tcp_conn->in.segment,
                                tcp_conn->in.hdr_buf, sizeof(struct iscsi_hdr),
                                iscsi_tcp_hdr_recv_done, NULL);
}
EXPORT_SYMBOL_GPL(iscsi_tcp_hdr_recv_prep);

/*
 * Handle incoming reply to any other type of command
 */
static int
iscsi_tcp_data_recv_done(struct iscsi_tcp_conn *tcp_conn,
                         struct iscsi_segment *segment)
{
        struct iscsi_conn *conn = tcp_conn->iscsi_conn;
        int rc = 0;

        if (!iscsi_tcp_dgst_verify(tcp_conn, segment))
                return ISCSI_ERR_DATA_DGST;

        rc = iscsi_complete_pdu(conn, tcp_conn->in.hdr,
                        conn->data, tcp_conn->in.datalen);
        if (rc)
                return rc;

        iscsi_tcp_hdr_recv_prep(tcp_conn);
        return 0;
}

static void
iscsi_tcp_data_recv_prep(struct iscsi_tcp_conn *tcp_conn)
{
        struct iscsi_conn *conn = tcp_conn->iscsi_conn;
        struct ahash_request *rx_hash = NULL;

        if (conn->datadgst_en &&
            !(conn->session->tt->caps & CAP_DIGEST_OFFLOAD))
                rx_hash = tcp_conn->rx_hash;

        iscsi_segment_init_linear(&tcp_conn->in.segment,
                                conn->data, tcp_conn->in.datalen,
                                iscsi_tcp_data_recv_done, rx_hash);
}

/**
 * iscsi_tcp_cleanup_task - free tcp_task resources
 * @task: iscsi task
 *
 * must be called with session back_lock
 */
void iscsi_tcp_cleanup_task(struct iscsi_task *task)
{
        struct iscsi_tcp_task *tcp_task = task->dd_data;
        struct iscsi_r2t_info *r2t;

        /* nothing to do for mgmt */
        if (!task->sc)
                return;

        spin_lock_bh(&tcp_task->queue2pool);
        /* flush task's r2t queues */
        while (kfifo_out(&tcp_task->r2tqueue, (void*)&r2t, sizeof(void*))) {
                kfifo_in(&tcp_task->r2tpool.queue, (void*)&r2t,
                            sizeof(void*));
                ISCSI_DBG_TCP(task->conn, "pending r2t dropped\n");
        }

        r2t = tcp_task->r2t;
        if (r2t != NULL) {
                kfifo_in(&tcp_task->r2tpool.queue, (void*)&r2t,
                            sizeof(void*));
                tcp_task->r2t = NULL;
        }
        spin_unlock_bh(&tcp_task->queue2pool);
}
EXPORT_SYMBOL_GPL(iscsi_tcp_cleanup_task);

/**
 * iscsi_tcp_data_in - SCSI Data-In Response processing
 * @conn: iscsi connection
 * @task: scsi command task
 */
static int iscsi_tcp_data_in(struct iscsi_conn *conn, struct iscsi_task *task)
{
        struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
        struct iscsi_tcp_task *tcp_task = task->dd_data;
        struct iscsi_data_rsp *rhdr = (struct iscsi_data_rsp *)tcp_conn->in.hdr;
        int datasn = be32_to_cpu(rhdr->datasn);
        unsigned total_in_length = task->sc->sdb.length;

        /*
         * lib iscsi will update this in the completion handling if there
         * is status.
         */
        if (!(rhdr->flags & ISCSI_FLAG_DATA_STATUS))
                iscsi_update_cmdsn(conn->session, (struct iscsi_nopin*)rhdr);

        if (tcp_conn->in.datalen == 0)
                return 0;

        if (tcp_task->exp_datasn != datasn) {
                ISCSI_DBG_TCP(conn, "task->exp_datasn(%d) != rhdr->datasn(%d)"
                              "\n", tcp_task->exp_datasn, datasn);
                return ISCSI_ERR_DATASN;
        }

        tcp_task->exp_datasn++;

        tcp_task->data_offset = be32_to_cpu(rhdr->offset);
        if (tcp_task->data_offset + tcp_conn->in.datalen > total_in_length) {
                ISCSI_DBG_TCP(conn, "data_offset(%d) + data_len(%d) > "
                              "total_length_in(%d)\n", tcp_task->data_offset,
                              tcp_conn->in.datalen, total_in_length);
                return ISCSI_ERR_DATA_OFFSET;
        }

        conn->datain_pdus_cnt++;
        return 0;
}

/**
 * iscsi_tcp_r2t_rsp - iSCSI R2T Response processing
 * @conn: iscsi connection
 * @hdr: PDU header
 */
static int iscsi_tcp_r2t_rsp(struct iscsi_conn *conn, struct iscsi_hdr *hdr)
{
        struct iscsi_session *session = conn->session;
        struct iscsi_tcp_task *tcp_task;
        struct iscsi_tcp_conn *tcp_conn;
        struct iscsi_r2t_rsp *rhdr;
        struct iscsi_r2t_info *r2t;
        struct iscsi_task *task;
        u32 data_length;
        u32 data_offset;
        int r2tsn;
        int rc;

        spin_lock(&session->back_lock);
        task = iscsi_itt_to_ctask(conn, hdr->itt);
        if (!task) {
                spin_unlock(&session->back_lock);
                return ISCSI_ERR_BAD_ITT;
        } else if (task->sc->sc_data_direction != DMA_TO_DEVICE) {
                spin_unlock(&session->back_lock);
                return ISCSI_ERR_PROTO;
        }
        /*
         * A bad target might complete the cmd before we have handled R2Ts
         * so get a ref to the task that will be dropped in the xmit path.
         */
        if (task->state != ISCSI_TASK_RUNNING) {
                spin_unlock(&session->back_lock);
                /* Let the path that got the early rsp complete it */
                return 0;
        }
        task->last_xfer = jiffies;
        __iscsi_get_task(task);

        tcp_conn = conn->dd_data;
        rhdr = (struct iscsi_r2t_rsp *)tcp_conn->in.hdr;
        /* fill-in new R2T associated with the task */
        iscsi_update_cmdsn(session, (struct iscsi_nopin *)rhdr);
        spin_unlock(&session->back_lock);

        if (tcp_conn->in.datalen) {
                iscsi_conn_printk(KERN_ERR, conn,
                                  "invalid R2t with datalen %d\n",
                                  tcp_conn->in.datalen);
                rc = ISCSI_ERR_DATALEN;
                goto put_task;
        }

        tcp_task = task->dd_data;
        r2tsn = be32_to_cpu(rhdr->r2tsn);
        if (tcp_task->exp_datasn != r2tsn){
                ISCSI_DBG_TCP(conn, "task->exp_datasn(%d) != rhdr->r2tsn(%d)\n",
                              tcp_task->exp_datasn, r2tsn);
                rc = ISCSI_ERR_R2TSN;
                goto put_task;
        }

        if (session->state != ISCSI_STATE_LOGGED_IN) {
                iscsi_conn_printk(KERN_INFO, conn,
                                  "dropping R2T itt %d in recovery.\n",
                                  task->itt);
                rc = 0;
                goto put_task;
        }

        data_length = be32_to_cpu(rhdr->data_length);
        if (data_length == 0) {
                iscsi_conn_printk(KERN_ERR, conn,
                                  "invalid R2T with zero data len\n");
                rc = ISCSI_ERR_DATALEN;
                goto put_task;
        }

        if (data_length > session->max_burst)
                ISCSI_DBG_TCP(conn, "invalid R2T with data len %u and max "
                              "burst %u. Attempting to execute request.\n",
                              data_length, session->max_burst);

        data_offset = be32_to_cpu(rhdr->data_offset);
        if (data_offset + data_length > task->sc->sdb.length) {
                iscsi_conn_printk(KERN_ERR, conn,
                                  "invalid R2T with data len %u at offset %u "
                                  "and total length %d\n", data_length,
                                  data_offset, task->sc->sdb.length);
                rc = ISCSI_ERR_DATALEN;
                goto put_task;
        }

        spin_lock(&tcp_task->pool2queue);
        rc = kfifo_out(&tcp_task->r2tpool.queue, (void *)&r2t, sizeof(void *));
        if (!rc) {
                iscsi_conn_printk(KERN_ERR, conn, "Could not allocate R2T. "
                                  "Target has sent more R2Ts than it "
                                  "negotiated for or driver has leaked.\n");
                spin_unlock(&tcp_task->pool2queue);
                rc = ISCSI_ERR_PROTO;
                goto put_task;
        }

        r2t->exp_statsn = rhdr->statsn;
        r2t->data_length = data_length;
        r2t->data_offset = data_offset;

        r2t->ttt = rhdr->ttt; /* no flip */
        r2t->datasn = 0;
        r2t->sent = 0;

        tcp_task->exp_datasn = r2tsn + 1;
        kfifo_in(&tcp_task->r2tqueue, (void*)&r2t, sizeof(void*));
        conn->r2t_pdus_cnt++;
        spin_unlock(&tcp_task->pool2queue);

        iscsi_requeue_task(task);
        return 0;

put_task:
        iscsi_put_task(task);
        return rc;
}

/*
 * Handle incoming reply to DataIn command
 */
static int
iscsi_tcp_process_data_in(struct iscsi_tcp_conn *tcp_conn,
                          struct iscsi_segment *segment)
{
        struct iscsi_conn *conn = tcp_conn->iscsi_conn;
        struct iscsi_hdr *hdr = tcp_conn->in.hdr;
        int rc;

        if (!iscsi_tcp_dgst_verify(tcp_conn, segment))
                return ISCSI_ERR_DATA_DGST;

        /* check for non-exceptional status */
        if (hdr->flags & ISCSI_FLAG_DATA_STATUS) {
                rc = iscsi_complete_pdu(conn, tcp_conn->in.hdr, NULL, 0);
                if (rc)
                        return rc;
        }

        iscsi_tcp_hdr_recv_prep(tcp_conn);
        return 0;
}

/**
 * iscsi_tcp_hdr_dissect - process PDU header
 * @conn: iSCSI connection
 * @hdr: PDU header
 *
 * This function analyzes the header of the PDU received,
 * and performs several sanity checks. If the PDU is accompanied
 * by data, the receive buffer is set up to copy the incoming data
 * to the correct location.
 */
static int
iscsi_tcp_hdr_dissect(struct iscsi_conn *conn, struct iscsi_hdr *hdr)
{
        int rc = 0, opcode, ahslen;
        struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
        struct iscsi_task *task;

        /* verify PDU length */
        tcp_conn->in.datalen = ntoh24(hdr->dlength);
        if (tcp_conn->in.datalen > conn->max_recv_dlength) {
                iscsi_conn_printk(KERN_ERR, conn,
                                  "iscsi_tcp: datalen %d > %d\n",
                                  tcp_conn->in.datalen, conn->max_recv_dlength);
                return ISCSI_ERR_DATALEN;
        }

        /* Additional header segments. So far, we don't
         * process additional headers.
         */
        ahslen = hdr->hlength << 2;

        opcode = hdr->opcode & ISCSI_OPCODE_MASK;
        /* verify itt (itt encoding: age+cid+itt) */
        rc = iscsi_verify_itt(conn, hdr->itt);
        if (rc)
                return rc;

        ISCSI_DBG_TCP(conn, "opcode 0x%x ahslen %d datalen %d\n",
                      opcode, ahslen, tcp_conn->in.datalen);

        switch(opcode) {
        case ISCSI_OP_SCSI_DATA_IN:
                spin_lock(&conn->session->back_lock);
                task = iscsi_itt_to_ctask(conn, hdr->itt);
                if (!task)
                        rc = ISCSI_ERR_BAD_ITT;
                else
                        rc = iscsi_tcp_data_in(conn, task);
                if (rc) {
                        spin_unlock(&conn->session->back_lock);
                        break;
                }

                if (tcp_conn->in.datalen) {
                        struct iscsi_tcp_task *tcp_task = task->dd_data;
                        struct ahash_request *rx_hash = NULL;
                        struct scsi_data_buffer *sdb = &task->sc->sdb;

                        /*
                         * Setup copy of Data-In into the struct scsi_cmnd
                         * Scatterlist case:
                         * We set up the iscsi_segment to point to the next
                         * scatterlist entry to copy to. As we go along,
                         * we move on to the next scatterlist entry and
                         * update the digest per-entry.
                         */
                        if (conn->datadgst_en &&
                            !(conn->session->tt->caps & CAP_DIGEST_OFFLOAD))
                                rx_hash = tcp_conn->rx_hash;

                        ISCSI_DBG_TCP(conn, "iscsi_tcp_begin_data_in( "
                                     "offset=%d, datalen=%d)\n",
                                      tcp_task->data_offset,
                                      tcp_conn->in.datalen);
                        task->last_xfer = jiffies;
                        rc = iscsi_segment_seek_sg(&tcp_conn->in.segment,
                                                   sdb->table.sgl,
                                                   sdb->table.nents,
                                                   tcp_task->data_offset,
                                                   tcp_conn->in.datalen,
                                                   iscsi_tcp_process_data_in,
                                                   rx_hash);
                        spin_unlock(&conn->session->back_lock);
                        return rc;
                }
                rc = __iscsi_complete_pdu(conn, hdr, NULL, 0);
                spin_unlock(&conn->session->back_lock);
                break;
        case ISCSI_OP_SCSI_CMD_RSP:
                if (tcp_conn->in.datalen) {
                        iscsi_tcp_data_recv_prep(tcp_conn);
                        return 0;
                }
                rc = iscsi_complete_pdu(conn, hdr, NULL, 0);
                break;
        case ISCSI_OP_R2T:
                if (ahslen) {
                        rc = ISCSI_ERR_AHSLEN;
                        break;
                }
                rc = iscsi_tcp_r2t_rsp(conn, hdr);
                break;
        case ISCSI_OP_LOGIN_RSP:
        case ISCSI_OP_TEXT_RSP:
        case ISCSI_OP_REJECT:
        case ISCSI_OP_ASYNC_EVENT:
                /*
                 * It is possible that we could get a PDU with a buffer larger
                 * than 8K, but there are no targets that currently do this.
                 * For now we fail until we find a vendor that needs it
                 */
                if (ISCSI_DEF_MAX_RECV_SEG_LEN < tcp_conn->in.datalen) {
                        iscsi_conn_printk(KERN_ERR, conn,
                                          "iscsi_tcp: received buffer of "
                                          "len %u but conn buffer is only %u "
                                          "(opcode %0x)\n",
                                          tcp_conn->in.datalen,
                                          ISCSI_DEF_MAX_RECV_SEG_LEN, opcode);
                        rc = ISCSI_ERR_PROTO;
                        break;
                }

                /* If there's data coming in with the response,
                 * receive it to the connection's buffer.
                 */
                if (tcp_conn->in.datalen) {
                        iscsi_tcp_data_recv_prep(tcp_conn);
                        return 0;
                }
                fallthrough;
        case ISCSI_OP_LOGOUT_RSP:
        case ISCSI_OP_NOOP_IN:
        case ISCSI_OP_SCSI_TMFUNC_RSP:
                rc = iscsi_complete_pdu(conn, hdr, NULL, 0);
                break;
        default:
                rc = ISCSI_ERR_BAD_OPCODE;
                break;
        }

        if (rc == 0) {
                /* Anything that comes with data should have
                 * been handled above. */
                if (tcp_conn->in.datalen)
                        return ISCSI_ERR_PROTO;
                iscsi_tcp_hdr_recv_prep(tcp_conn);
        }

        return rc;
}

/**
 * iscsi_tcp_hdr_recv_done - process PDU header
 * @tcp_conn: iSCSI TCP connection
 * @segment: the buffer segment being processed
 *
 * This is the callback invoked when the PDU header has
 * been received. If the header is followed by additional
 * header segments, we go back for more data.
 */
static int
iscsi_tcp_hdr_recv_done(struct iscsi_tcp_conn *tcp_conn,
                        struct iscsi_segment *segment)
{
        struct iscsi_conn *conn = tcp_conn->iscsi_conn;
        struct iscsi_hdr *hdr;

        /* Check if there are additional header segments
         * *prior* to computing the digest, because we
         * may need to go back to the caller for more.
         */
        hdr = (struct iscsi_hdr *) tcp_conn->in.hdr_buf;
        if (segment->copied == sizeof(struct iscsi_hdr) && hdr->hlength) {
                /* Bump the header length - the caller will
                 * just loop around and get the AHS for us, and
                 * call again. */
                unsigned int ahslen = hdr->hlength << 2;

                /* Make sure we don't overflow */
                if (sizeof(*hdr) + ahslen > sizeof(tcp_conn->in.hdr_buf))
                        return ISCSI_ERR_AHSLEN;

                segment->total_size += ahslen;
                segment->size += ahslen;
                return 0;
        }

        /* We're done processing the header. See if we're doing
         * header digests; if so, set up the recv_digest buffer
         * and go back for more. */
        if (conn->hdrdgst_en &&
            !(conn->session->tt->caps & CAP_DIGEST_OFFLOAD)) {
                if (segment->digest_len == 0) {
                        /*
                         * Even if we offload the digest processing we
                         * splice it in so we can increment the skb/segment
                         * counters in preparation for the data segment.
                         */
                        iscsi_tcp_segment_splice_digest(segment,
                                                        segment->recv_digest);
                        return 0;
                }

                iscsi_tcp_dgst_header(tcp_conn->rx_hash, hdr,
                                      segment->total_copied - ISCSI_DIGEST_SIZE,
                                      segment->digest);

                if (!iscsi_tcp_dgst_verify(tcp_conn, segment))
                        return ISCSI_ERR_HDR_DGST;
        }

        tcp_conn->in.hdr = hdr;
        return iscsi_tcp_hdr_dissect(conn, hdr);
}

/**
 * iscsi_tcp_recv_segment_is_hdr - tests if we are reading in a header
 * @tcp_conn: iscsi tcp conn
 *
 * returns non zero if we are currently processing or setup to process
 * a header.
 */
inline int iscsi_tcp_recv_segment_is_hdr(struct iscsi_tcp_conn *tcp_conn)
{
        return tcp_conn->in.segment.done == iscsi_tcp_hdr_recv_done;
}
EXPORT_SYMBOL_GPL(iscsi_tcp_recv_segment_is_hdr);

/**
 * iscsi_tcp_recv_skb - Process skb
 * @conn: iscsi connection
 * @skb: network buffer with header and/or data segment
 * @offset: offset in skb
 * @offloaded: bool indicating if transfer was offloaded
 * @status: iscsi TCP status result
 *
 * Will return status of transfer in @status. And will return
 * number of bytes copied.
 */
int iscsi_tcp_recv_skb(struct iscsi_conn *conn, struct sk_buff *skb,
                       unsigned int offset, bool offloaded, int *status)
{
        struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
        struct iscsi_segment *segment = &tcp_conn->in.segment;
        struct skb_seq_state seq;
        unsigned int consumed = 0;
        int rc = 0;

        ISCSI_DBG_TCP(conn, "in %d bytes\n", skb->len - offset);
        /*
         * Update for each skb instead of pdu, because over slow networks a
         * data_in's data could take a while to read in. We also want to
         * account for r2ts.
         */
        conn->last_recv = jiffies;

        if (unlikely(conn->suspend_rx)) {
                ISCSI_DBG_TCP(conn, "Rx suspended!\n");
                *status = ISCSI_TCP_SUSPENDED;
                return 0;
        }

        if (offloaded) {
                segment->total_copied = segment->total_size;
                goto segment_done;
        }

        skb_prepare_seq_read(skb, offset, skb->len, &seq);
        while (1) {
                unsigned int avail;
                const u8 *ptr;

                avail = skb_seq_read(consumed, &ptr, &seq);
                if (avail == 0) {
                        ISCSI_DBG_TCP(conn, "no more data avail. Consumed %d\n",
                                      consumed);
                        *status = ISCSI_TCP_SKB_DONE;
                        goto skb_done;
                }
                BUG_ON(segment->copied >= segment->size);

                ISCSI_DBG_TCP(conn, "skb %p ptr=%p avail=%u\n", skb, ptr,
                              avail);
                rc = iscsi_tcp_segment_recv(tcp_conn, segment, ptr, avail);
                BUG_ON(rc == 0);
                consumed += rc;

                if (segment->total_copied >= segment->total_size) {
                        skb_abort_seq_read(&seq);
                        goto segment_done;
                }
        }

segment_done:
        *status = ISCSI_TCP_SEGMENT_DONE;
        ISCSI_DBG_TCP(conn, "segment done\n");
        rc = segment->done(tcp_conn, segment);
        if (rc != 0) {
                *status = ISCSI_TCP_CONN_ERR;
                ISCSI_DBG_TCP(conn, "Error receiving PDU, errno=%d\n", rc);
                iscsi_conn_failure(conn, rc);
                return 0;
        }
        /* The done() functions sets up the next segment. */

skb_done:
        conn->rxdata_octets += consumed;
        return consumed;
}
EXPORT_SYMBOL_GPL(iscsi_tcp_recv_skb);

/**
 * iscsi_tcp_task_init - Initialize iSCSI SCSI_READ or SCSI_WRITE commands
 * @task: scsi command task
 */
int iscsi_tcp_task_init(struct iscsi_task *task)
{
        struct iscsi_tcp_task *tcp_task = task->dd_data;
        struct iscsi_conn *conn = task->conn;
        struct scsi_cmnd *sc = task->sc;
        int err;

        if (!sc) {
                /*
                 * mgmt tasks do not have a scatterlist since they come
                 * in from the iscsi interface.
                 */

                ISCSI_DBG_TCP(conn, "mtask deq [itt 0x%x]\n", task->itt);

                return conn->session->tt->init_pdu(task, 0, task->data_count);
        }

        BUG_ON(kfifo_len(&tcp_task->r2tqueue));
        tcp_task->exp_datasn = 0;

        /* Prepare PDU, optionally w/ immediate data */
        ISCSI_DBG_TCP(conn, "task deq [itt 0x%x imm %d unsol %d]\n",
                      task->itt, task->imm_count, task->unsol_r2t.data_length);

        err = conn->session->tt->init_pdu(task, 0, task->imm_count);
        if (err)
                return err;
        task->imm_count = 0;
        return 0;
}
EXPORT_SYMBOL_GPL(iscsi_tcp_task_init);

static struct iscsi_r2t_info *iscsi_tcp_get_curr_r2t(struct iscsi_task *task)
{
        struct iscsi_tcp_task *tcp_task = task->dd_data;
        struct iscsi_r2t_info *r2t = NULL;

        if (iscsi_task_has_unsol_data(task))
                r2t = &task->unsol_r2t;
        else {
                spin_lock_bh(&tcp_task->queue2pool);
                if (tcp_task->r2t) {
                        r2t = tcp_task->r2t;
                        /* Continue with this R2T? */
                        if (r2t->data_length <= r2t->sent) {
                                ISCSI_DBG_TCP(task->conn,
                                              "  done with r2t %p\n", r2t);
                                kfifo_in(&tcp_task->r2tpool.queue,
                                            (void *)&tcp_task->r2t,
                                            sizeof(void *));
                                tcp_task->r2t = r2t = NULL;
                        }
                }

                if (r2t == NULL) {
                        if (kfifo_out(&tcp_task->r2tqueue,
                            (void *)&tcp_task->r2t, sizeof(void *)) !=
                            sizeof(void *))
                                r2t = NULL;
                        else
                                r2t = tcp_task->r2t;
                }
                spin_unlock_bh(&tcp_task->queue2pool);
        }

        return r2t;
}

/**
 * iscsi_tcp_task_xmit - xmit normal PDU task
 * @task: iscsi command task
 *
 * We're expected to return 0 when everything was transmitted successfully,
 * -EAGAIN if there's still data in the queue, or != 0 for any other kind
 * of error.
 */
int iscsi_tcp_task_xmit(struct iscsi_task *task)
{
        struct iscsi_conn *conn = task->conn;
        struct iscsi_session *session = conn->session;
        struct iscsi_r2t_info *r2t;
        int rc = 0;

flush:
        /* Flush any pending data first. */
        rc = session->tt->xmit_pdu(task);
        if (rc < 0)
                return rc;

        /* mgmt command */
        if (!task->sc) {
                if (task->hdr->itt == RESERVED_ITT)
                        iscsi_put_task(task);
                return 0;
        }

        /* Are we done already? */
        if (task->sc->sc_data_direction != DMA_TO_DEVICE)
                return 0;

        r2t = iscsi_tcp_get_curr_r2t(task);
        if (r2t == NULL) {
                /* Waiting for more R2Ts to arrive. */
                ISCSI_DBG_TCP(conn, "no R2Ts yet\n");
                return 0;
        }

        rc = conn->session->tt->alloc_pdu(task, ISCSI_OP_SCSI_DATA_OUT);
        if (rc)
                return rc;
        iscsi_prep_data_out_pdu(task, r2t, (struct iscsi_data *) task->hdr);

        ISCSI_DBG_TCP(conn, "sol dout %p [dsn %d itt 0x%x doff %d dlen %d]\n",
                      r2t, r2t->datasn - 1, task->hdr->itt,
                      r2t->data_offset + r2t->sent, r2t->data_count);

        rc = conn->session->tt->init_pdu(task, r2t->data_offset + r2t->sent,
                                         r2t->data_count);
        if (rc) {
                iscsi_conn_failure(conn, ISCSI_ERR_XMIT_FAILED);
                return rc;
        }

        r2t->sent += r2t->data_count;
        goto flush;
}
EXPORT_SYMBOL_GPL(iscsi_tcp_task_xmit);

struct iscsi_cls_conn *
iscsi_tcp_conn_setup(struct iscsi_cls_session *cls_session, int dd_data_size,
                      uint32_t conn_idx)

{
        struct iscsi_conn *conn;
        struct iscsi_cls_conn *cls_conn;
        struct iscsi_tcp_conn *tcp_conn;

        cls_conn = iscsi_conn_setup(cls_session,
                                    sizeof(*tcp_conn) + dd_data_size, conn_idx);
        if (!cls_conn)
                return NULL;
        conn = cls_conn->dd_data;
        /*
         * due to strange issues with iser these are not set
         * in iscsi_conn_setup
         */
        conn->max_recv_dlength = ISCSI_DEF_MAX_RECV_SEG_LEN;

        tcp_conn = conn->dd_data;
        tcp_conn->iscsi_conn = conn;
        tcp_conn->dd_data = conn->dd_data + sizeof(*tcp_conn);
        return cls_conn;
}
EXPORT_SYMBOL_GPL(iscsi_tcp_conn_setup);

void iscsi_tcp_conn_teardown(struct iscsi_cls_conn *cls_conn)
{
        iscsi_conn_teardown(cls_conn);
}
EXPORT_SYMBOL_GPL(iscsi_tcp_conn_teardown);

int iscsi_tcp_r2tpool_alloc(struct iscsi_session *session)
{
        int i;
        int cmd_i;

        /*
         * initialize per-task: R2T pool and xmit queue
         */
        for (cmd_i = 0; cmd_i < session->cmds_max; cmd_i++) {
                struct iscsi_task *task = session->cmds[cmd_i];
                struct iscsi_tcp_task *tcp_task = task->dd_data;

                /*
                 * pre-allocated x2 as much r2ts to handle race when
                 * target acks DataOut faster than we data_xmit() queues
                 * could replenish r2tqueue.
                 */

                /* R2T pool */
                if (iscsi_pool_init(&tcp_task->r2tpool,
                                    session->max_r2t * 2, NULL,
                                    sizeof(struct iscsi_r2t_info))) {
                        goto r2t_alloc_fail;
                }

                /* R2T xmit queue */
                if (kfifo_alloc(&tcp_task->r2tqueue,
                      session->max_r2t * 4 * sizeof(void*), GFP_KERNEL)) {
                        iscsi_pool_free(&tcp_task->r2tpool);
                        goto r2t_alloc_fail;
                }
                spin_lock_init(&tcp_task->pool2queue);
                spin_lock_init(&tcp_task->queue2pool);
        }

        return 0;

r2t_alloc_fail:
        for (i = 0; i < cmd_i; i++) {
                struct iscsi_task *task = session->cmds[i];
                struct iscsi_tcp_task *tcp_task = task->dd_data;

                kfifo_free(&tcp_task->r2tqueue);
                iscsi_pool_free(&tcp_task->r2tpool);
        }
        return -ENOMEM;
}
EXPORT_SYMBOL_GPL(iscsi_tcp_r2tpool_alloc);

void iscsi_tcp_r2tpool_free(struct iscsi_session *session)
{
        int i;

        for (i = 0; i < session->cmds_max; i++) {
                struct iscsi_task *task = session->cmds[i];
                struct iscsi_tcp_task *tcp_task = task->dd_data;

                kfifo_free(&tcp_task->r2tqueue);
                iscsi_pool_free(&tcp_task->r2tpool);
        }
}
EXPORT_SYMBOL_GPL(iscsi_tcp_r2tpool_free);

int iscsi_tcp_set_max_r2t(struct iscsi_conn *conn, char *buf)
{
        struct iscsi_session *session = conn->session;
        unsigned short r2ts = 0;

        sscanf(buf, "%hu", &r2ts);
        if (session->max_r2t == r2ts)
                return 0;

        if (!r2ts || !is_power_of_2(r2ts))
                return -EINVAL;

        session->max_r2t = r2ts;
        iscsi_tcp_r2tpool_free(session);
        return iscsi_tcp_r2tpool_alloc(session);
}
EXPORT_SYMBOL_GPL(iscsi_tcp_set_max_r2t);

void iscsi_tcp_conn_get_stats(struct iscsi_cls_conn *cls_conn,
                              struct iscsi_stats *stats)
{
        struct iscsi_conn *conn = cls_conn->dd_data;

        stats->txdata_octets = conn->txdata_octets;
        stats->rxdata_octets = conn->rxdata_octets;
        stats->scsicmd_pdus = conn->scsicmd_pdus_cnt;
        stats->dataout_pdus = conn->dataout_pdus_cnt;
        stats->scsirsp_pdus = conn->scsirsp_pdus_cnt;
        stats->datain_pdus = conn->datain_pdus_cnt;
        stats->r2t_pdus = conn->r2t_pdus_cnt;
        stats->tmfcmd_pdus = conn->tmfcmd_pdus_cnt;
        stats->tmfrsp_pdus = conn->tmfrsp_pdus_cnt;
}
EXPORT_SYMBOL_GPL(iscsi_tcp_conn_get_stats);