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iser_verbs.c

/*
 * Copyright (c) 2004, 2005, 2006 Voltaire, Inc. All rights reserved.
 * Copyright (c) 2005, 2006 Cisco Systems.  All rights reserved.
 *
 * This software is available to you under a choice of one of two
 * licenses.  You may choose to be licensed under the terms of the GNU
 * General Public License (GPL) Version 2, available from the file
 * COPYING in the main directory of this source tree, or the
 * OpenIB.org BSD license below:
 *
 *     Redistribution and use in source and binary forms, with or
 *     without modification, are permitted provided that the following
 *     conditions are met:
 *
 *    - Redistributions of source code must retain the above
 *      copyright notice, this list of conditions and the following
 *      disclaimer.
 *
 *    - Redistributions in binary form must reproduce the above
 *      copyright notice, this list of conditions and the following
 *      disclaimer in the documentation and/or other materials
 *      provided with the distribution.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 * $Id: iser_verbs.c 7051 2006-05-10 12:29:11Z ogerlitz $
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/delay.h>
#include <linux/version.h>

#include "iscsi_iser.h"

#define ISCSI_ISER_MAX_CONN   8
#define ISER_MAX_CQ_LEN       ((ISER_QP_MAX_RECV_DTOS + \
                        ISER_QP_MAX_REQ_DTOS) *   \
                         ISCSI_ISER_MAX_CONN)

static void iser_cq_tasklet_fn(unsigned long data);
static void iser_cq_callback(struct ib_cq *cq, void *cq_context);

static void iser_cq_event_callback(struct ib_event *cause, void *context)
{
      iser_err("got cq event %d \n", cause->event);
}

static void iser_qp_event_callback(struct ib_event *cause, void *context)
{
      iser_err("got qp event %d\n",cause->event);
}

/**
 * iser_create_device_ib_res - creates Protection Domain (PD), Completion
 * Queue (CQ), DMA Memory Region (DMA MR) with the device associated with
 * the adapator.
 *
 * returns 0 on success, -1 on failure
 */
static int iser_create_device_ib_res(struct iser_device *device)
{
      device->pd = ib_alloc_pd(device->ib_device);
      if (IS_ERR(device->pd))
            goto pd_err;

      device->cq = ib_create_cq(device->ib_device,
                          iser_cq_callback,
                          iser_cq_event_callback,
                          (void *)device,
                          ISER_MAX_CQ_LEN, 0);
      if (IS_ERR(device->cq))
            goto cq_err;

      if (ib_req_notify_cq(device->cq, IB_CQ_NEXT_COMP))
            goto cq_arm_err;

      tasklet_init(&device->cq_tasklet,
                 iser_cq_tasklet_fn,
                 (unsigned long)device);

      device->mr = ib_get_dma_mr(device->pd, IB_ACCESS_LOCAL_WRITE |
                           IB_ACCESS_REMOTE_WRITE |
                           IB_ACCESS_REMOTE_READ);
      if (IS_ERR(device->mr))
            goto dma_mr_err;

      return 0;

dma_mr_err:
      tasklet_kill(&device->cq_tasklet);
cq_arm_err:
      ib_destroy_cq(device->cq);
cq_err:
      ib_dealloc_pd(device->pd);
pd_err:
      iser_err("failed to allocate an IB resource\n");
      return -1;
}

/**
 * iser_free_device_ib_res - destory/dealloc/dereg the DMA MR,
 * CQ and PD created with the device associated with the adapator.
 */
static void iser_free_device_ib_res(struct iser_device *device)
{
      BUG_ON(device->mr == NULL);

      tasklet_kill(&device->cq_tasklet);

      (void)ib_dereg_mr(device->mr);
      (void)ib_destroy_cq(device->cq);
      (void)ib_dealloc_pd(device->pd);

      device->mr = NULL;
      device->cq = NULL;
      device->pd = NULL;
}

/**
 * iser_create_ib_conn_res - Creates FMR pool and Queue-Pair (QP)
 *
 * returns 0 on success, -1 on failure
 */
static int iser_create_ib_conn_res(struct iser_conn *ib_conn)
{
      struct iser_device      *device;
      struct ib_qp_init_attr  init_attr;
      int               ret;
      struct ib_fmr_pool_param params;

      BUG_ON(ib_conn->device == NULL);

      device = ib_conn->device;

      ib_conn->page_vec = kmalloc(sizeof(struct iser_page_vec) +
                            (sizeof(u64) * (ISCSI_ISER_SG_TABLESIZE +1)),
                            GFP_KERNEL);
      if (!ib_conn->page_vec) {
            ret = -ENOMEM;
            goto alloc_err;
      }
      ib_conn->page_vec->pages = (u64 *) (ib_conn->page_vec + 1);

      params.page_shift        = SHIFT_4K;
      /* when the first/last SG element are not start/end *
       * page aligned, the map whould be of N+1 pages     */
      params.max_pages_per_fmr = ISCSI_ISER_SG_TABLESIZE + 1;
      /* make the pool size twice the max number of SCSI commands *
       * the ML is expected to queue, watermark for unmap at 50%  */
      params.pool_size   = ISCSI_DEF_XMIT_CMDS_MAX * 2;
      params.dirty_watermark   = ISCSI_DEF_XMIT_CMDS_MAX;
      params.cache             = 0;
      params.flush_function    = NULL;
      params.access            = (IB_ACCESS_LOCAL_WRITE  |
                            IB_ACCESS_REMOTE_WRITE |
                            IB_ACCESS_REMOTE_READ);

      ib_conn->fmr_pool = ib_create_fmr_pool(device->pd, &params);
      if (IS_ERR(ib_conn->fmr_pool)) {
            ret = PTR_ERR(ib_conn->fmr_pool);
            goto fmr_pool_err;
      }

      memset(&init_attr, 0, sizeof init_attr);

      init_attr.event_handler = iser_qp_event_callback;
      init_attr.qp_context    = (void *)ib_conn;
      init_attr.send_cq = device->cq;
      init_attr.recv_cq = device->cq;
      init_attr.cap.max_send_wr  = ISER_QP_MAX_REQ_DTOS;
      init_attr.cap.max_recv_wr  = ISER_QP_MAX_RECV_DTOS;
      init_attr.cap.max_send_sge = MAX_REGD_BUF_VECTOR_LEN;
      init_attr.cap.max_recv_sge = 2;
      init_attr.sq_sig_type   = IB_SIGNAL_REQ_WR;
      init_attr.qp_type = IB_QPT_RC;

      ret = rdma_create_qp(ib_conn->cma_id, device->pd, &init_attr);
      if (ret)
            goto qp_err;

      ib_conn->qp = ib_conn->cma_id->qp;
      iser_err("setting conn %p cma_id %p: fmr_pool %p qp %p\n",
             ib_conn, ib_conn->cma_id,
             ib_conn->fmr_pool, ib_conn->cma_id->qp);
      return ret;

qp_err:
      (void)ib_destroy_fmr_pool(ib_conn->fmr_pool);
fmr_pool_err:
      kfree(ib_conn->page_vec);
alloc_err:
      iser_err("unable to alloc mem or create resource, err %d\n", ret);
      return ret;
}

/**
 * releases the FMR pool, QP and CMA ID objects, returns 0 on success,
 * -1 on failure
 */
static int iser_free_ib_conn_res(struct iser_conn *ib_conn)
{
      BUG_ON(ib_conn == NULL);

      iser_err("freeing conn %p cma_id %p fmr pool %p qp %p\n",
             ib_conn, ib_conn->cma_id,
             ib_conn->fmr_pool, ib_conn->qp);

      /* qp is created only once both addr & route are resolved */
      if (ib_conn->fmr_pool != NULL)
            ib_destroy_fmr_pool(ib_conn->fmr_pool);

      if (ib_conn->qp != NULL)
            rdma_destroy_qp(ib_conn->cma_id);

      if (ib_conn->cma_id != NULL)
            rdma_destroy_id(ib_conn->cma_id);

      ib_conn->fmr_pool = NULL;
      ib_conn->qp   = NULL;
      ib_conn->cma_id   = NULL;
      kfree(ib_conn->page_vec);

      return 0;
}

/**
 * based on the resolved device node GUID see if there already allocated
 * device for this device. If there's no such, create one.
 */
static
struct iser_device *iser_device_find_by_ib_device(struct rdma_cm_id *cma_id)
{
      struct list_head    *p_list;
      struct iser_device  *device = NULL;

      mutex_lock(&ig.device_list_mutex);

      p_list = ig.device_list.next;
      while (p_list != &ig.device_list) {
            device = list_entry(p_list, struct iser_device, ig_list);
            /* find if there's a match using the node GUID */
            if (device->ib_device->node_guid == cma_id->device->node_guid)
                  break;
      }

      if (device == NULL) {
            device = kzalloc(sizeof *device, GFP_KERNEL);
            if (device == NULL)
                  goto out;
            /* assign this device to the device */
            device->ib_device = cma_id->device;
            /* init the device and link it into ig device list */
            if (iser_create_device_ib_res(device)) {
                  kfree(device);
                  device = NULL;
                  goto out;
            }
            list_add(&device->ig_list, &ig.device_list);
      }
out:
      BUG_ON(device == NULL);
      device->refcount++;
      mutex_unlock(&ig.device_list_mutex);
      return device;
}

/* if there's no demand for this device, release it */
static void iser_device_try_release(struct iser_device *device)
{
      mutex_lock(&ig.device_list_mutex);
      device->refcount--;
      iser_err("device %p refcount %d\n",device,device->refcount);
      if (!device->refcount) {
            iser_free_device_ib_res(device);
            list_del(&device->ig_list);
            kfree(device);
      }
      mutex_unlock(&ig.device_list_mutex);
}

int iser_conn_state_comp(struct iser_conn *ib_conn,
                  enum iser_ib_conn_state comp)
{
      int ret;

      spin_lock_bh(&ib_conn->lock);
      ret = (ib_conn->state == comp);
      spin_unlock_bh(&ib_conn->lock);
      return ret;
}

static int iser_conn_state_comp_exch(struct iser_conn *ib_conn,
                             enum iser_ib_conn_state comp,
                             enum iser_ib_conn_state exch)
{
      int ret;

      spin_lock_bh(&ib_conn->lock);
      if ((ret = (ib_conn->state == comp)))
            ib_conn->state = exch;
      spin_unlock_bh(&ib_conn->lock);
      return ret;
}

/**
 * Frees all conn objects and deallocs conn descriptor
 */
static void iser_conn_release(struct iser_conn *ib_conn)
{
      struct iser_device  *device = ib_conn->device;

      BUG_ON(ib_conn->state != ISER_CONN_DOWN);

      mutex_lock(&ig.connlist_mutex);
      list_del(&ib_conn->conn_list);
      mutex_unlock(&ig.connlist_mutex);

      iser_free_ib_conn_res(ib_conn);
      ib_conn->device = NULL;
      /* on EVENT_ADDR_ERROR there's no device yet for this conn */
      if (device != NULL)
            iser_device_try_release(device);
      if (ib_conn->iser_conn)
            ib_conn->iser_conn->ib_conn = NULL;
      kfree(ib_conn);
}

/**
 * triggers start of the disconnect procedures and wait for them to be done
 */
void iser_conn_terminate(struct iser_conn *ib_conn)
{
      int err = 0;

      /* change the ib conn state only if the conn is UP, however always call
       * rdma_disconnect since this is the only way to cause the CMA to change
       * the QP state to ERROR
       */

      iser_conn_state_comp_exch(ib_conn, ISER_CONN_UP, ISER_CONN_TERMINATING);
      err = rdma_disconnect(ib_conn->cma_id);
      if (err)
            iser_err("Failed to disconnect, conn: 0x%p err %d\n",
                   ib_conn,err);

      wait_event_interruptible(ib_conn->wait,
                         ib_conn->state == ISER_CONN_DOWN);

      iser_conn_release(ib_conn);
}

static void iser_connect_error(struct rdma_cm_id *cma_id)
{
      struct iser_conn *ib_conn;
      ib_conn = (struct iser_conn *)cma_id->context;

      ib_conn->state = ISER_CONN_DOWN;
      wake_up_interruptible(&ib_conn->wait);
}

static void iser_addr_handler(struct rdma_cm_id *cma_id)
{
      struct iser_device *device;
      struct iser_conn   *ib_conn;
      int    ret;

      device = iser_device_find_by_ib_device(cma_id);
      ib_conn = (struct iser_conn *)cma_id->context;
      ib_conn->device = device;

      ret = rdma_resolve_route(cma_id, 1000);
      if (ret) {
            iser_err("resolve route failed: %d\n", ret);
            iser_connect_error(cma_id);
      }
      return;
}

static void iser_route_handler(struct rdma_cm_id *cma_id)
{
      struct rdma_conn_param conn_param;
      int    ret;

      ret = iser_create_ib_conn_res((struct iser_conn *)cma_id->context);
      if (ret)
            goto failure;

      iser_dbg("path.mtu is %d setting it to %d\n",
             cma_id->route.path_rec->mtu, IB_MTU_1024);

      /* we must set the MTU to 1024 as this is what the target is assuming */
      if (cma_id->route.path_rec->mtu > IB_MTU_1024)
            cma_id->route.path_rec->mtu = IB_MTU_1024;

      memset(&conn_param, 0, sizeof conn_param);
      conn_param.responder_resources = 4;
      conn_param.initiator_depth     = 1;
      conn_param.retry_count         = 7;
      conn_param.rnr_retry_count     = 6;

      ret = rdma_connect(cma_id, &conn_param);
      if (ret) {
            iser_err("failure connecting: %d\n", ret);
            goto failure;
      }

      return;
failure:
      iser_connect_error(cma_id);
}

static void iser_connected_handler(struct rdma_cm_id *cma_id)
{
      struct iser_conn *ib_conn;

      ib_conn = (struct iser_conn *)cma_id->context;
      ib_conn->state = ISER_CONN_UP;
      wake_up_interruptible(&ib_conn->wait);
}

static void iser_disconnected_handler(struct rdma_cm_id *cma_id)
{
      struct iser_conn *ib_conn;

      ib_conn = (struct iser_conn *)cma_id->context;
      ib_conn->disc_evt_flag = 1;

      /* getting here when the state is UP means that the conn is being *
       * terminated asynchronously from the iSCSI layer's perspective.  */
      if (iser_conn_state_comp_exch(ib_conn, ISER_CONN_UP,
                              ISER_CONN_TERMINATING))
            iscsi_conn_failure(ib_conn->iser_conn->iscsi_conn,
                           ISCSI_ERR_CONN_FAILED);

      /* Complete the termination process if no posts are pending */
      if ((atomic_read(&ib_conn->post_recv_buf_count) == 0) &&
          (atomic_read(&ib_conn->post_send_buf_count) == 0)) {
            ib_conn->state = ISER_CONN_DOWN;
            wake_up_interruptible(&ib_conn->wait);
      }
}

static int iser_cma_handler(struct rdma_cm_id *cma_id, struct rdma_cm_event *event)
{
      int ret = 0;

      iser_err("event %d conn %p id %p\n",event->event,cma_id->context,cma_id);

      switch (event->event) {
      case RDMA_CM_EVENT_ADDR_RESOLVED:
            iser_addr_handler(cma_id);
            break;
      case RDMA_CM_EVENT_ROUTE_RESOLVED:
            iser_route_handler(cma_id);
            break;
      case RDMA_CM_EVENT_ESTABLISHED:
            iser_connected_handler(cma_id);
            break;
      case RDMA_CM_EVENT_ADDR_ERROR:
      case RDMA_CM_EVENT_ROUTE_ERROR:
      case RDMA_CM_EVENT_CONNECT_ERROR:
      case RDMA_CM_EVENT_UNREACHABLE:
      case RDMA_CM_EVENT_REJECTED:
            iser_err("event: %d, error: %d\n", event->event, event->status);
            iser_connect_error(cma_id);
            break;
      case RDMA_CM_EVENT_DISCONNECTED:
            iser_disconnected_handler(cma_id);
            break;
      case RDMA_CM_EVENT_DEVICE_REMOVAL:
            BUG();
            break;
      case RDMA_CM_EVENT_CONNECT_RESPONSE:
            BUG();
            break;
      case RDMA_CM_EVENT_CONNECT_REQUEST:
      default:
            break;
      }
      return ret;
}

int iser_conn_init(struct iser_conn **ibconn)
{
      struct iser_conn *ib_conn;

      ib_conn = kzalloc(sizeof *ib_conn, GFP_KERNEL);
      if (!ib_conn) {
            iser_err("can't alloc memory for struct iser_conn\n");
            return -ENOMEM;
      }
      ib_conn->state = ISER_CONN_INIT;
      init_waitqueue_head(&ib_conn->wait);
      atomic_set(&ib_conn->post_recv_buf_count, 0);
      atomic_set(&ib_conn->post_send_buf_count, 0);
      INIT_LIST_HEAD(&ib_conn->conn_list);
      spin_lock_init(&ib_conn->lock);

      *ibconn = ib_conn;
      return 0;
}

 /**
 * starts the process of connecting to the target
 * sleeps untill the connection is established or rejected
 */
int iser_connect(struct iser_conn   *ib_conn,
             struct sockaddr_in *src_addr,
             struct sockaddr_in *dst_addr,
             int                 non_blocking)
{
      struct sockaddr *src, *dst;
      int err = 0;

      sprintf(ib_conn->name,"%d.%d.%d.%d:%d",
            NIPQUAD(dst_addr->sin_addr.s_addr), dst_addr->sin_port);

      /* the device is known only --after-- address resolution */
      ib_conn->device = NULL;

      iser_err("connecting to: %d.%d.%d.%d, port 0x%x\n",
             NIPQUAD(dst_addr->sin_addr), dst_addr->sin_port);

      ib_conn->state = ISER_CONN_PENDING;

      ib_conn->cma_id = rdma_create_id(iser_cma_handler,
                                   (void *)ib_conn,
                                   RDMA_PS_TCP);
      if (IS_ERR(ib_conn->cma_id)) {
            err = PTR_ERR(ib_conn->cma_id);
            iser_err("rdma_create_id failed: %d\n", err);
            goto id_failure;
      }

      src = (struct sockaddr *)src_addr;
      dst = (struct sockaddr *)dst_addr;
      err = rdma_resolve_addr(ib_conn->cma_id, src, dst, 1000);
      if (err) {
            iser_err("rdma_resolve_addr failed: %d\n", err);
            goto addr_failure;
      }

      if (!non_blocking) {
            wait_event_interruptible(ib_conn->wait,
                               (ib_conn->state != ISER_CONN_PENDING));

            if (ib_conn->state != ISER_CONN_UP) {
                  err =  -EIO;
                  goto connect_failure;
            }
      }

      mutex_lock(&ig.connlist_mutex);
      list_add(&ib_conn->conn_list, &ig.connlist);
      mutex_unlock(&ig.connlist_mutex);
      return 0;

id_failure:
      ib_conn->cma_id = NULL;
addr_failure:
      ib_conn->state = ISER_CONN_DOWN;
connect_failure:
      iser_conn_release(ib_conn);
      return err;
}

/**
 * iser_reg_page_vec - Register physical memory
 *
 * returns: 0 on success, errno code on failure
 */
int iser_reg_page_vec(struct iser_conn     *ib_conn,
                  struct iser_page_vec *page_vec,
                  struct iser_mem_reg  *mem_reg)
{
      struct ib_pool_fmr *mem;
      u64            io_addr;
      u64            *page_list;
      int            status;

      page_list = page_vec->pages;
      io_addr       = page_list[0];

      mem  = ib_fmr_pool_map_phys(ib_conn->fmr_pool,
                            page_list,
                            page_vec->length,
                            io_addr);

      if (IS_ERR(mem)) {
            status = (int)PTR_ERR(mem);
            iser_err("ib_fmr_pool_map_phys failed: %d\n", status);
            return status;
      }

      mem_reg->lkey  = mem->fmr->lkey;
      mem_reg->rkey  = mem->fmr->rkey;
      mem_reg->len   = page_vec->length * SIZE_4K;
      mem_reg->va    = io_addr;
      mem_reg->is_fmr = 1;
      mem_reg->mem_h = (void *)mem;

      mem_reg->va   += page_vec->offset;
      mem_reg->len   = page_vec->data_size;

      iser_dbg("PHYSICAL Mem.register, [PHYS p_array: 0x%p, sz: %d, "
             "entry[0]: (0x%08lx,%ld)] -> "
             "[lkey: 0x%08X mem_h: 0x%p va: 0x%08lX sz: %ld]\n",
             page_vec, page_vec->length,
             (unsigned long)page_vec->pages[0],
             (unsigned long)page_vec->data_size,
             (unsigned int)mem_reg->lkey, mem_reg->mem_h,
             (unsigned long)mem_reg->va, (unsigned long)mem_reg->len);
      return 0;
}

/**
 * Unregister (previosuly registered) memory.
 */
void iser_unreg_mem(struct iser_mem_reg *reg)
{
      int ret;

      iser_dbg("PHYSICAL Mem.Unregister mem_h %p\n",reg->mem_h);

      ret = ib_fmr_pool_unmap((struct ib_pool_fmr *)reg->mem_h);
      if (ret)
            iser_err("ib_fmr_pool_unmap failed %d\n", ret);

      reg->mem_h = NULL;
}

/**
 * iser_dto_to_iov - builds IOV from a dto descriptor
 */
static void iser_dto_to_iov(struct iser_dto *dto, struct ib_sge *iov, int iov_len)
{
      int              i;
      struct ib_sge          *sge;
      struct iser_regd_buf *regd_buf;

      if (dto->regd_vector_len > iov_len) {
            iser_err("iov size %d too small for posting dto of len %d\n",
                   iov_len, dto->regd_vector_len);
            BUG();
      }

      for (i = 0; i < dto->regd_vector_len; i++) {
            sge       = &iov[i];
            regd_buf  = dto->regd[i];

            sge->addr   = regd_buf->reg.va;
            sge->length = regd_buf->reg.len;
            sge->lkey   = regd_buf->reg.lkey;

            if (dto->used_sz[i] > 0)  /* Adjust size */
                  sge->length = dto->used_sz[i];

            /* offset and length should not exceed the regd buf length */
            if (sge->length + dto->offset[i] > regd_buf->reg.len) {
                  iser_err("Used len:%ld + offset:%d, exceed reg.buf.len:"
                         "%ld in dto:0x%p [%d], va:0x%08lX\n",
                         (unsigned long)sge->length, dto->offset[i],
                         (unsigned long)regd_buf->reg.len, dto, i,
                         (unsigned long)sge->addr);
                  BUG();
            }

            sge->addr += dto->offset[i]; /* Adjust offset */
      }
}

/**
 * iser_post_recv - Posts a receive buffer.
 *
 * returns 0 on success, -1 on failure
 */
int iser_post_recv(struct iser_desc *rx_desc)
{
      int           ib_ret, ret_val = 0;
      struct ib_recv_wr recv_wr, *recv_wr_failed;
      struct ib_sge       iov[2];
      struct iser_conn  *ib_conn;
      struct iser_dto   *recv_dto = &rx_desc->dto;

      /* Retrieve conn */
      ib_conn = recv_dto->ib_conn;

      iser_dto_to_iov(recv_dto, iov, 2);

      recv_wr.next      = NULL;
      recv_wr.sg_list = iov;
      recv_wr.num_sge = recv_dto->regd_vector_len;
      recv_wr.wr_id     = (unsigned long)rx_desc;

      atomic_inc(&ib_conn->post_recv_buf_count);
      ib_ret      = ib_post_recv(ib_conn->qp, &recv_wr, &recv_wr_failed);
      if (ib_ret) {
            iser_err("ib_post_recv failed ret=%d\n", ib_ret);
            atomic_dec(&ib_conn->post_recv_buf_count);
            ret_val = -1;
      }

      return ret_val;
}

/**
 * iser_start_send - Initiate a Send DTO operation
 *
 * returns 0 on success, -1 on failure
 */
int iser_post_send(struct iser_desc *tx_desc)
{
      int           ib_ret, ret_val = 0;
      struct ib_send_wr send_wr, *send_wr_failed;
      struct ib_sge       iov[MAX_REGD_BUF_VECTOR_LEN];
      struct iser_conn  *ib_conn;
      struct iser_dto   *dto = &tx_desc->dto;

      ib_conn = dto->ib_conn;

      iser_dto_to_iov(dto, iov, MAX_REGD_BUF_VECTOR_LEN);

      send_wr.next         = NULL;
      send_wr.wr_id        = (unsigned long)tx_desc;
      send_wr.sg_list      = iov;
      send_wr.num_sge      = dto->regd_vector_len;
      send_wr.opcode       = IB_WR_SEND;
      send_wr.send_flags = dto->notify_enable ? IB_SEND_SIGNALED : 0;

      atomic_inc(&ib_conn->post_send_buf_count);

      ib_ret = ib_post_send(ib_conn->qp, &send_wr, &send_wr_failed);
      if (ib_ret) {
            iser_err("Failed to start SEND DTO, dto: 0x%p, IOV len: %d\n",
                   dto, dto->regd_vector_len);
            iser_err("ib_post_send failed, ret:%d\n", ib_ret);
            atomic_dec(&ib_conn->post_send_buf_count);
            ret_val = -1;
      }

      return ret_val;
}

static void iser_handle_comp_error(struct iser_desc *desc)
{
      struct iser_dto  *dto     = &desc->dto;
      struct iser_conn *ib_conn = dto->ib_conn;

      iser_dto_buffs_release(dto);

      if (desc->type == ISCSI_RX) {
            kfree(desc->data);
            kmem_cache_free(ig.desc_cache, desc);
            atomic_dec(&ib_conn->post_recv_buf_count);
      } else { /* type is TX control/command/dataout */
            if (desc->type == ISCSI_TX_DATAOUT)
                  kmem_cache_free(ig.desc_cache, desc);
            atomic_dec(&ib_conn->post_send_buf_count);
      }

      if (atomic_read(&ib_conn->post_recv_buf_count) == 0 &&
          atomic_read(&ib_conn->post_send_buf_count) == 0) {
            /* getting here when the state is UP means that the conn is *
             * being terminated asynchronously from the iSCSI layer's   *
             * perspective.                                             */
            if (iser_conn_state_comp_exch(ib_conn, ISER_CONN_UP,
                ISER_CONN_TERMINATING))
                  iscsi_conn_failure(ib_conn->iser_conn->iscsi_conn,
                                 ISCSI_ERR_CONN_FAILED);

            /* complete the termination process if disconnect event was delivered *
             * note there are no more non completed posts to the QP               */
            if (ib_conn->disc_evt_flag) {
                  ib_conn->state = ISER_CONN_DOWN;
                  wake_up_interruptible(&ib_conn->wait);
            }
      }
}

static void iser_cq_tasklet_fn(unsigned long data)
{
       struct iser_device  *device = (struct iser_device *)data;
       struct ib_cq          *cq = device->cq;
       struct ib_wc          wc;
       struct iser_desc    *desc;
       unsigned long         xfer_len;

      while (ib_poll_cq(cq, 1, &wc) == 1) {
            desc   = (struct iser_desc *) (unsigned long) wc.wr_id;
            BUG_ON(desc == NULL);

            if (wc.status == IB_WC_SUCCESS) {
                  if (desc->type == ISCSI_RX) {
                        xfer_len = (unsigned long)wc.byte_len;
                        iser_rcv_completion(desc, xfer_len);
                  } else /* type == ISCSI_TX_CONTROL/SCSI_CMD/DOUT */
                        iser_snd_completion(desc);
            } else {
                  iser_err("comp w. error op %d status %d\n",desc->type,wc.status);
                  iser_handle_comp_error(desc);
            }
      }
      /* #warning "it is assumed here that arming CQ only once its empty" *
       * " would not cause interrupts to be missed"                       */
      ib_req_notify_cq(cq, IB_CQ_NEXT_COMP);
}

static void iser_cq_callback(struct ib_cq *cq, void *cq_context)
{
      struct iser_device  *device = (struct iser_device *)cq_context;

      tasklet_schedule(&device->cq_tasklet);
}

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