Committer: Michael Beasley <mike@snafu.setup>

[mikesnafu-overlay.git] / drivers / infiniband / ulp / iser / 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 - destroy/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 iser_device *device;

        mutex_lock(&ig.device_list_mutex);

        list_for_each_entry(device, &ig.device_list, ig_list)
                /* find if there's a match using the node GUID */
                if (device->ib_device->node_guid == cma_id->device->node_guid)
                        goto inc_refcnt;

        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);

inc_refcnt:
        device->refcount++;
out:
        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);
        if (!device) {
                iser_err("device lookup/creation failed\n");
                iser_connect_error(cma_id);
                return;
        }

        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);
        }
}

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:
                iser_err("Device removal is currently unsupported\n");
                BUG();
                break;
        default:
                iser_err("Unexpected RDMA CM event (%d)\n", event->event);
                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);
}