iser-target: Add iSCSI Extensions for RDMA (iSER) target driver

This patch adds support for iSCSI Extensions for RDMA target mode,
and includes CQ pooling per isert_device context distributed across
multiple active iser target sessions.

It also uses cmwq process context for RX / TX ib_post_cq() polling
via isert_cq_desc->cq_[rx,tx]_work invoked by isert_cq_[rx,tx]_callback()
hardIRQ context callbacks.

v5 changes:

- Use ISER_RECV_DATA_SEG_LEN instead of hardcoded value in ISER_RX_PAD_SIZE (Or)
- Fix make W=1 warnings (Or)
- Add missing depends on NET && INFINIBAND_ADDR_TRANS in Kconfig (Randy + Or)
- Make isert_device_find_by_ib_dev() return proper ERR_PTR (Wei Yongjun)
- Properly setup iscsi_np->np_sockaddr in isert_setup_np() (Shlomi + nab)
- Add special case for early ISCSI_OP_SCSI_CMD exception handling (nab)

v4 changes:
- Mark isert_cq_rx_work as static (Or)
- Drop unnecessary ib_dma_sync_single_for_cpu + ib_dma_sync_single_for_device
  calls for isert_cmd->sense_buf_dma from isert_put_response (Or)
- Use 12288 for ISER_RX_PAD_SIZE base to save extra page per
  struct iser_rx_desc (Or + nab)
- Drop now unnecessary isert_rx_desc usage, and convert RX users to
  iser_rx_desc (Or + nab)
- Move isert_[alloc,free]_rx_descriptors() ahead of
  isert_create_device_ib_res() usage (nab)
- Mark isert_cq_[rx,tx]_callback() + prototypes as static
- Fix 'warning: 'ret' may be used uninitialized' warning for
  isert_create_device_ib_res on powerpc allmodconfig (fengguang + nab)
- Fix 'warning: 'ret' may be used uninitialized' warning for
  isert_connect_request on i386 allyesconfig (fengguang + nab)
- Fix pr_debug conversion specification in isert_rx_completion()
  (fengguang + nab)
- Drop unnecessary isert_conn->conn_cm_id != NULL check in
  isert_connect_release causing the build warning:
  "variable dereferenced before check 'isert_conn->conn_cm_id'"
- Fix isert_lid + isert_np leak in isert_setup_np failure path
- Add isert_conn->conn_wait_comp_err usage in isert_free_conn()
  for isert_cq_comp_err completion path
- Add isert_conn->logout_posted bit to determine decrement of
  isert_conn->post_send_buf_count from logout response completion
- Always set ISER_CONN_DOWN from isert_disconnect_work() callback

v3 changes:

- Convert to use per isert_cq_desc->cq_[rx,tx]_work + drop tasklets (Or + nab)
- Move IB_EVENT_QP_LAST_WQE_REACHED warn into correct
  isert_qp_event_callback (Or)
- Drop unnecessary IB_ACCESS_REMOTE_* access flag usage in
  isert_create_device_ib_res (Or)
- Add common isert_init_send_wr(), and convert isert_put_* calls (Or)
- Move to verbs+core logic to single ib_isert.[c,h]  (Or + nab)
- Add kmem_cache isert_cmd_cache usage for descriptor allocation (nab)
- Move common ib_post_send() logic used by isert_put_*() to
  isert_post_response() (nab)
- Add isert_put_reject call in isert_response_queue() for posting
  ISCSI_REJECT response. (nab)
- Add ISTATE_SEND_REJECT checking in isert_do_control_comp. (nab)

v2 changes:

- Drop unused ISERT_ADDR_ROUTE_TIMEOUT define
- Add rdma_notify() call for IB_EVENT_COMM_EST in isert_qp_event_callback()
- Make isert_query_device() less verbose
- Drop unused RDMA_CM_EVENT_ADDR_ERROR and RDMA_CM_EVENT_ROUTE_ERROR
  cases from isert_cma_handler()
- Drop unused rdma/ib_fmr_pool.h include
- Update isert_conn_setup_qp() to assign cq based upon least used
- Add isert_create_device_ib_res() to setup PD, CQs and MRs for each
  underlying struct ib_device, instead of using per isert_conn resources.
- Add isert_free_device_ib_res() to release PD, CQs and MRs for each
  underlying struct ib_device.
- Add isert_device_find_by_ib_dev()
- Change isert_connect_request() to drop PD, CQs and MRs allocation,
  and use isert_device_find_by_ib_dev() instead.
- Add isert_device_try_release()
- Change isert_connect_release() to decrement cq_active_qps, and drop
  PD, CQs and MRs resource release.
- Update isert_connect_release() to call isert_device_try_release()
- Make isert_create_device_ib_res() determine device->cqs_used based
  upon num_online_cpus()
- Drop misleading isert_dump_ib_wc() usage
- Drop unused rdma/ib_fmr_pool.h include
- Use proper xfer_len for login PDUs in isert_rx_completion()
- Add isert_release_cmd() usage
- Change isert_alloc_cmd() to setup iscsi_cmd.release_cmd() pointer
- Change isert_put_cmd() to perform per iscsi_opcode specific release
  logic
- Add isert_unmap_cmd() call for ISCSI_OP_SCSI_CMD from isert_put_cmd()
- Change isert_send_completion() to call
  atomic_dec(&isert_conn->post_send_buf_count)
  based upon per iscsi_opcode logic
- Drop ISTATE_REMOVE processing from isert_immediate_queue()
- Drop ISTATE_SEND_DATAIN processing from isert_response_queue()
- Drop ISTATE_SEND_STATUS processing from isert_response_queue()
- Drop iscsit_transport->iscsit_unmap_cmd() and ->iscsit_free_cmd()
- Convert iser_cq_tx_tasklet() to use struct isert_cq_desc pooling logic
- Convert isert_cq_tx_callback() to use struct isert_cq_desc pooling
  logic
- Convert iser_cq_rx_tasklet() to use struct isert_cq_desc pooling logic
- Convert isert_cq_rx_callback() to use struct isert_cq_desc pooling
  logic
- Add explict iscsit_stop_dataout_timer() call to
  isert_do_rdma_read_comp()
- Use isert_get_dataout() for iscsit_transport->iscsit_get_dataout()
  caller
- Drop ISTATE_SEND_R2T processing from isert_immediate_queue()
- Drop unused rdma/ib_fmr_pool.h include
- Drop isert_cmd->cmd_kref in favor of se_cmd->cmd_kref usage
- Add struct isert_device in order to support multiple EQs + CQ pooling
- Add struct isert_cq_desc
- Drop tasklets and cqs from isert_conn
- Bump ISERT_MAX_CQ to 64
- Various minor checkpatch fixes

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

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