text: /*
   * Copyright (c) 2006, 2019 Oracle and/or its affiliates. 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.
   *
   */
  #include <linux/kernel.h>
  #include <linux/in.h>
  #include <linux/device.h>
  #include <linux/dmapool.h>
  #include <linux/ratelimit.h>
  
  #include "rds_single_path.h"
  #include "rds.h"
  #include "ib.h"
  
  /*
   * Convert IB-specific error message to RDS error message and call core
   * completion handler.
   */
  static void rds_ib_send_complete(struct rds_message *rm,
  				 int wc_status,
  				 void (*complete)(struct rds_message *rm, int status))
  {
  	int notify_status;
  
  	switch (wc_status) {
  	case IB_WC_WR_FLUSH_ERR:
  		return;
  
  	case IB_WC_SUCCESS:
  		notify_status = RDS_RDMA_SUCCESS;
  		break;
  
  	case IB_WC_REM_ACCESS_ERR:
  		notify_status = RDS_RDMA_REMOTE_ERROR;
  		break;
  
  	default:
  		notify_status = RDS_RDMA_OTHER_ERROR;
  		break;
  	}
  	complete(rm, notify_status);
  }
  
  static void rds_ib_send_unmap_data(struct rds_ib_connection *ic,
  				   struct rm_data_op *op,
  				   int wc_status)
  {
  	if (op->op_nents)
  		ib_dma_unmap_sg(ic->i_cm_id->device,
  				op->op_sg, op->op_nents,
  				DMA_TO_DEVICE);
  }
  
  static void rds_ib_send_unmap_rdma(struct rds_ib_connection *ic,
  				   struct rm_rdma_op *op,
  				   int wc_status)
  {
  	if (op->op_mapped) {
  		ib_dma_unmap_sg(ic->i_cm_id->device,
  				op->op_sg, op->op_nents,
  				op->op_write ? DMA_TO_DEVICE : DMA_FROM_DEVICE);
  		op->op_mapped = 0;
  	}
  
  	/* If the user asked for a completion notification on this
  	 * message, we can implement three different semantics:
  	 *  1.	Notify when we received the ACK on the RDS message
  	 *	that was queued with the RDMA. This provides reliable
  	 *	notification of RDMA status at the expense of a one-way
  	 *	packet delay.
  	 *  2.	Notify when the IB stack gives us the completion event for
  	 *	the RDMA operation.
  	 *  3.	Notify when the IB stack gives us the completion event for
  	 *	the accompanying RDS messages.
  	 * Here, we implement approach #3. To implement approach #2,
  	 * we would need to take an event for the rdma WR. To implement #1,
  	 * don't call rds_rdma_send_complete at all, and fall back to the notify
  	 * handling in the ACK processing code.
  	 *
  	 * Note: There's no need to explicitly sync any RDMA buffers using
  	 * ib_dma_sync_sg_for_cpu - the completion for the RDMA
  	 * operation itself unmapped the RDMA buffers, which takes care
  	 * of synching.
  	 */
  	rds_ib_send_complete(container_of(op, struct rds_message, rdma),
  			     wc_status, rds_rdma_send_complete);
  
  	if (op->op_write)
  		rds_stats_add(s_send_rdma_bytes, op->op_bytes);
  	else
  		rds_stats_add(s_recv_rdma_bytes, op->op_bytes);
  }
  
  static void rds_ib_send_unmap_atomic(struct rds_ib_connection *ic,
  				     struct rm_atomic_op *op,
  				     int wc_status)
  {
  	/* unmap atomic recvbuf */
  	if (op->op_mapped) {
  		ib_dma_unmap_sg(ic->i_cm_id->device, op->op_sg, 1,
  				DMA_FROM_DEVICE);
  		op->op_mapped = 0;
  	}
  
  	rds_ib_send_complete(container_of(op, struct rds_message, atomic),
  			     wc_status, rds_atomic_send_complete);
  
  	if (op->op_type == RDS_ATOMIC_TYPE_CSWP)
  		rds_ib_stats_inc(s_ib_atomic_cswp);
  	else
  		rds_ib_stats_inc(s_ib_atomic_fadd);
  }
  
  /*
   * Unmap the resources associated with a struct send_work.
   *
   * Returns the rm for no good reason other than it is unobtainable
   * other than by switching on wr.opcode, currently, and the caller,
   * the event handler, needs it.
   */
  static struct rds_message *rds_ib_send_unmap_op(struct rds_ib_connection *ic,
  						struct rds_ib_send_work *send,
  						int wc_status)
  {
  	struct rds_message *rm = NULL;
  
  	/* In the error case, wc.opcode sometimes contains garbage */
  	switch (send->s_wr.opcode) {
  	case IB_WR_SEND:
  		if (send->s_op) {
  			rm = container_of(send->s_op, struct rds_message, data);
  			rds_ib_send_unmap_data(ic, send->s_op, wc_status);
  		}
  		break;
  	case IB_WR_RDMA_WRITE:
  	case IB_WR_RDMA_READ:
  		if (send->s_op) {
  			rm = container_of(send->s_op, struct rds_message, rdma);
  			rds_ib_send_unmap_rdma(ic, send->s_op, wc_status);
  		}
  		break;
  	case IB_WR_ATOMIC_FETCH_AND_ADD:
  	case IB_WR_ATOMIC_CMP_AND_SWP:
  		if (send->s_op) {
  			rm = container_of(send->s_op, struct rds_message, atomic);
  			rds_ib_send_unmap_atomic(ic, send->s_op, wc_status);
  		}
  		break;
  	default:
  		printk_ratelimited(KERN_NOTICE
  			       "RDS/IB: %s: unexpected opcode 0x%x in WR!\n",
  			       __func__, send->s_wr.opcode);
  		break;
  	}
  
  	send->s_wr.opcode = 0xdead;
  
  	return rm;
  }
  
  void rds_ib_send_init_ring(struct rds_ib_connection *ic)
  {
  	struct rds_ib_send_work *send;
  	u32 i;
  
  	for (i = 0, send = ic->i_sends; i < ic->i_send_ring.w_nr; i++, send++) {
  		struct ib_sge *sge;
  
  		send->s_op = NULL;
  
  		send->s_wr.wr_id = i;
  		send->s_wr.sg_list = send->s_sge;
  		send->s_wr.ex.imm_data = 0;
  
  		sge = &send->s_sge[0];
  		sge->addr = ic->i_send_hdrs_dma[i];
  
  		sge->length = sizeof(struct rds_header);
  		sge->lkey = ic->i_pd->local_dma_lkey;
  
  		send->s_sge[1].lkey = ic->i_pd->local_dma_lkey;
  	}
  }
  
  void rds_ib_send_clear_ring(struct rds_ib_connection *ic)
  {
  	struct rds_ib_send_work *send;
  	u32 i;
  
  	for (i = 0, send = ic->i_sends; i < ic->i_send_ring.w_nr; i++, send++) {
  		if (send->s_op && send->s_wr.opcode != 0xdead)
  			rds_ib_send_unmap_op(ic, send, IB_WC_WR_FLUSH_ERR);
  	}
  }
  
  /*
   * The only fast path caller always has a non-zero nr, so we don't
   * bother testing nr before performing the atomic sub.
   */
  static void rds_ib_sub_signaled(struct rds_ib_connection *ic, int nr)
  {
  	if ((atomic_sub_return(nr, &ic->i_signaled_sends) == 0) &&
  	    waitqueue_active(&rds_ib_ring_empty_wait))
  		wake_up(&rds_ib_ring_empty_wait);
  	BUG_ON(atomic_read(&ic->i_signaled_sends) < 0);
  }
  
  /*
   * The _oldest/_free ring operations here race cleanly with the alloc/unalloc
   * operations performed in the send path.  As the sender allocs and potentially
   * unallocs the next free entry in the ring it doesn't alter which is
   * the next to be freed, which is what this is concerned with.
   */
  void rds_ib_send_cqe_handler(struct rds_ib_connection *ic, struct ib_wc *wc)
  {
  	struct rds_message *rm = NULL;
  	struct rds_connection *conn = ic->conn;
  	struct rds_ib_send_work *send;
  	u32 completed;
  	u32 oldest;
  	u32 i = 0;
  	int nr_sig = 0;
  
  
  	rdsdebug("wc wr_id 0x%llx status %u (%s) byte_len %u imm_data %u\n",
  		 (unsigned long long)wc->wr_id, wc->status,
  		 ib_wc_status_msg(wc->status), wc->byte_len,
  		 be32_to_cpu(wc->ex.imm_data));
  	rds_ib_stats_inc(s_ib_tx_cq_event);
  
  	if (wc->wr_id == RDS_IB_ACK_WR_ID) {
  		if (time_after(jiffies, ic->i_ack_queued + HZ / 2))
  			rds_ib_stats_inc(s_ib_tx_stalled);
  		rds_ib_ack_send_complete(ic);
  		return;
  	}
  
  	oldest = rds_ib_ring_oldest(&ic->i_send_ring);
  
  	completed = rds_ib_ring_completed(&ic->i_send_ring, wc->wr_id, oldest);
  
  	for (i = 0; i < completed; i++) {
  		send = &ic->i_sends[oldest];
  		if (send->s_wr.send_flags & IB_SEND_SIGNALED)
  			nr_sig++;
  
  		rm = rds_ib_send_unmap_op(ic, send, wc->status);
  
  		if (time_after(jiffies, send->s_queued + HZ / 2))
  			rds_ib_stats_inc(s_ib_tx_stalled);
  
  		if (send->s_op) {
  			if (send->s_op == rm->m_final_op) {
  				/* If anyone waited for this message to get
  				 * flushed out, wake them up now
  				 */
  				rds_message_unmapped(rm);
  			}
  			rds_message_put(rm);
  			send->s_op = NULL;
  		}
  
  		oldest = (oldest + 1) % ic->i_send_ring.w_nr;
  	}
  
  	rds_ib_ring_free(&ic->i_send_ring, completed);
  	rds_ib_sub_signaled(ic, nr_sig);
  	nr_sig = 0;
  
  	if (test_and_clear_bit(RDS_LL_SEND_FULL, &conn->c_flags) ||
  	    test_bit(0, &conn->c_map_queued))
  		queue_delayed_work(rds_wq, &conn->c_send_w, 0);
  
  	/* We expect errors as the qp is drained during shutdown */
  	if (wc->status != IB_WC_SUCCESS && rds_conn_up(conn)) {
  		rds_ib_conn_error(conn, "send completion on <%pI6c,%pI6c,%d> had status %u (%s), vendor err 0x%x, disconnecting and reconnecting\n",
  				  &conn->c_laddr, &conn->c_faddr,
  				  conn->c_tos, wc->status,
  				  ib_wc_status_msg(wc->status), wc->vendor_err);
  	}
  }
  
  /*
   * This is the main function for allocating credits when sending
   * messages.
   *
   * Conceptually, we have two counters:
   *  -	send credits: this tells us how many WRs we're allowed
   *	to submit without overruning the receiver's queue. For
   *	each SEND WR we post, we decrement this by one.
   *
   *  -	posted credits: this tells us how many WRs we recently
   *	posted to the receive queue. This value is transferred
   *	to the peer as a "credit update" in a RDS header field.
   *	Every time we transmit credits to the peer, we subtract
   *	the amount of transferred credits from this counter.
   *
   * It is essential that we avoid situations where both sides have
   * exhausted their send credits, and are unable to send new credits
   * to the peer. We achieve this by requiring that we send at least
   * one credit update to the peer before exhausting our credits.
   * When new credits arrive, we subtract one credit that is withheld
   * until we've posted new buffers and are ready to transmit these
   * credits (see rds_ib_send_add_credits below).
   *
   * The RDS send code is essentially single-threaded; rds_send_xmit
   * sets RDS_IN_XMIT to ensure exclusive access to the send ring.
   * However, the ACK sending code is independent and can race with
   * message SENDs.
   *
   * In the send path, we need to update the counters for send credits
   * and the counter of posted buffers atomically - when we use the
   * last available credit, we cannot allow another thread to race us
   * and grab the posted credits counter.  Hence, we have to use a
   * spinlock to protect the credit counter, or use atomics.
   *
   * Spinlocks shared between the send and the receive path are bad,
   * because they create unnecessary delays. An early implementation
   * using a spinlock showed a 5% degradation in throughput at some
   * loads.
   *
   * This implementation avoids spinlocks completely, putting both
   * counters into a single atomic, and updating that atomic using
   * atomic_add (in the receive path, when receiving fresh credits),
   * and using atomic_cmpxchg when updating the two counters.
   */
  int rds_ib_send_grab_credits(struct rds_ib_connection *ic,
  			     u32 wanted, u32 *adv_credits, int need_posted, int max_posted)
  {
  	unsigned int avail, posted, got = 0, advertise;
  	long oldval, newval;
  
  	*adv_credits = 0;
  	if (!ic->i_flowctl)
  		return wanted;
  
  try_again:
  	advertise = 0;
  	oldval = newval = atomic_read(&ic->i_credits);
  	posted = IB_GET_POST_CREDITS(oldval);
  	avail = IB_GET_SEND_CREDITS(oldval);
  
  	rdsdebug("wanted=%u credits=%u posted=%u\n",
  			wanted, avail, posted);
  
  	/* The last credit must be used to send a credit update. */
  	if (avail && !posted)
  		avail--;
  
  	if (avail < wanted) {
  		struct rds_connection *conn = ic->i_cm_id->context;
  
  		/* Oops, there aren't that many credits left! */
  		set_bit(RDS_LL_SEND_FULL, &conn->c_flags);
  		got = avail;
  	} else {
  		/* Sometimes you get what you want, lalala. */
  		got = wanted;
  	}
  	newval -= IB_SET_SEND_CREDITS(got);
  
  	/*
  	 * If need_posted is non-zero, then the caller wants
  	 * the posted regardless of whether any send credits are
  	 * available.
  	 */
  	if (posted && (got || need_posted)) {
  		advertise = min_t(unsigned int, posted, max_posted);
  		newval -= IB_SET_POST_CREDITS(advertise);
  	}
  
  	/* Finally bill everything */
  	if (atomic_cmpxchg(&ic->i_credits, oldval, newval) != oldval)
  		goto try_again;
  
  	*adv_credits = advertise;
  	return got;
  }
  
  void rds_ib_send_add_credits(struct rds_connection *conn, unsigned int credits)
  {
  	struct rds_ib_connection *ic = conn->c_transport_data;
  
  	if (credits == 0)
  		return;
  
  	rdsdebug("credits=%u current=%u%s\n",
  			credits,
  			IB_GET_SEND_CREDITS(atomic_read(&ic->i_credits)),
  			test_bit(RDS_LL_SEND_FULL, &conn->c_flags) ? ", ll_send_full" : "");
  
  	atomic_add(IB_SET_SEND_CREDITS(credits), &ic->i_credits);
  	if (test_and_clear_bit(RDS_LL_SEND_FULL, &conn->c_flags))
  		queue_delayed_work(rds_wq, &conn->c_send_w, 0);
  
  	WARN_ON(IB_GET_SEND_CREDITS(credits) >= 16384);
  
  	rds_ib_stats_inc(s_ib_rx_credit_updates);
  }
  
  void rds_ib_advertise_credits(struct rds_connection *conn, unsigned int posted)
  {
  	struct rds_ib_connection *ic = conn->c_transport_data;
  
  	if (posted == 0)
  		return;
  
  	atomic_add(IB_SET_POST_CREDITS(posted), &ic->i_credits);
  
  	/* Decide whether to send an update to the peer now.
  	 * If we would send a credit update for every single buffer we
  	 * post, we would end up with an ACK storm (ACK arrives,
  	 * consumes buffer, we refill the ring, send ACK to remote
  	 * advertising the newly posted buffer... ad inf)
  	 *
  	 * Performance pretty much depends on how often we send
  	 * credit updates - too frequent updates mean lots of ACKs.
  	 * Too infrequent updates, and the peer will run out of
  	 * credits and has to throttle.
  	 * For the time being, 16 seems to be a good compromise.
  	 */
  	if (IB_GET_POST_CREDITS(atomic_read(&ic->i_credits)) >= 16)
  		set_bit(IB_ACK_REQUESTED, &ic->i_ack_flags);
  }
  
  static inline int rds_ib_set_wr_signal_state(struct rds_ib_connection *ic,
  					     struct rds_ib_send_work *send,
  					     bool notify)
  {
  	/*
  	 * We want to delay signaling completions just enough to get
  	 * the batching benefits but not so much that we create dead time
  	 * on the wire.
  	 */
  	if (ic->i_unsignaled_wrs-- == 0 || notify) {
  		ic->i_unsignaled_wrs = rds_ib_sysctl_max_unsig_wrs;
  		send->s_wr.send_flags |= IB_SEND_SIGNALED;
  		return 1;
  	}
  	return 0;
  }
  
  /*
   * This can be called multiple times for a given message.  The first time
   * we see a message we map its scatterlist into the IB device so that
   * we can provide that mapped address to the IB scatter gather entries
   * in the IB work requests.  We translate the scatterlist into a series
   * of work requests that fragment the message.  These work requests complete
   * in order so we pass ownership of the message to the completion handler
   * once we send the final fragment.
   *
   * The RDS core uses the c_send_lock to only enter this function once
   * per connection.  This makes sure that the tx ring alloc/unalloc pairs
   * don't get out of sync and confuse the ring.
   */
  int rds_ib_xmit(struct rds_connection *conn, struct rds_message *rm,
  		unsigned int hdr_off, unsigned int sg, unsigned int off)
  {
  	struct rds_ib_connection *ic = conn->c_transport_data;
  	struct ib_device *dev = ic->i_cm_id->device;
  	struct rds_ib_send_work *send = NULL;
  	struct rds_ib_send_work *first;
  	struct rds_ib_send_work *prev;
  	const struct ib_send_wr *failed_wr;
  	struct scatterlist *scat;
  	u32 pos;
  	u32 i;
  	u32 work_alloc;
  	u32 credit_alloc = 0;
  	u32 posted;
  	u32 adv_credits = 0;
  	int send_flags = 0;
  	int bytes_sent = 0;
  	int ret;
  	int flow_controlled = 0;
  	int nr_sig = 0;
  
  	BUG_ON(off % RDS_FRAG_SIZE);
  	BUG_ON(hdr_off != 0 && hdr_off != sizeof(struct rds_header));
  
  	/* Do not send cong updates to IB loopback */
  	if (conn->c_loopback
  	    && rm->m_inc.i_hdr.h_flags & RDS_FLAG_CONG_BITMAP) {
  		rds_cong_map_updated(conn->c_fcong, ~(u64) 0);
  		scat = &rm->data.op_sg[sg];
  		ret = max_t(int, RDS_CONG_MAP_BYTES, scat->length);
  		return sizeof(struct rds_header) + ret;
  	}
  
  	/* FIXME we may overallocate here */
  	if (be32_to_cpu(rm->m_inc.i_hdr.h_len) == 0)
  		i = 1;
  	else
  		i = DIV_ROUND_UP(be32_to_cpu(rm->m_inc.i_hdr.h_len), RDS_FRAG_SIZE);
  
  	work_alloc = rds_ib_ring_alloc(&ic->i_send_ring, i, &pos);
  	if (work_alloc == 0) {
  		set_bit(RDS_LL_SEND_FULL, &conn->c_flags);
  		rds_ib_stats_inc(s_ib_tx_ring_full);
  		ret = -ENOMEM;
  		goto out;
  	}
  
  	if (ic->i_flowctl) {
  		credit_alloc = rds_ib_send_grab_credits(ic, work_alloc, &posted, 0, RDS_MAX_ADV_CREDIT);
  		adv_credits += posted;
  		if (credit_alloc < work_alloc) {
  			rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc - credit_alloc);
  			work_alloc = credit_alloc;
  			flow_controlled = 1;
  		}
  		if (work_alloc == 0) {
  			set_bit(RDS_LL_SEND_FULL, &conn->c_flags);
  			rds_ib_stats_inc(s_ib_tx_throttle);
  			ret = -ENOMEM;
  			goto out;
  		}
  	}
  
  	/* map the message the first time we see it */
  	if (!ic->i_data_op) {
  		if (rm->data.op_nents) {
  			rm->data.op_count = ib_dma_map_sg(dev,
  							  rm->data.op_sg,
  							  rm->data.op_nents,
  							  DMA_TO_DEVICE);
  			rdsdebug("ic %p mapping rm %p: %d\n", ic, rm, rm->data.op_count);
  			if (rm->data.op_count == 0) {
  				rds_ib_stats_inc(s_ib_tx_sg_mapping_failure);
  				rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc);
  				ret = -ENOMEM; /* XXX ? */
  				goto out;
  			}
  		} else {
  			rm->data.op_count = 0;
  		}
  
  		rds_message_addref(rm);
  		rm->data.op_dmasg = 0;
  		rm->data.op_dmaoff = 0;
  		ic->i_data_op = &rm->data;
  
  		/* Finalize the header */
  		if (test_bit(RDS_MSG_ACK_REQUIRED, &rm->m_flags))
  			rm->m_inc.i_hdr.h_flags |= RDS_FLAG_ACK_REQUIRED;
  		if (test_bit(RDS_MSG_RETRANSMITTED, &rm->m_flags))
  			rm->m_inc.i_hdr.h_flags |= RDS_FLAG_RETRANSMITTED;
  
  		/* If it has a RDMA op, tell the peer we did it. This is
  		 * used by the peer to release use-once RDMA MRs. */
  		if (rm->rdma.op_active) {
  			struct rds_ext_header_rdma ext_hdr;
  
  			ext_hdr.h_rdma_rkey = cpu_to_be32(rm->rdma.op_rkey);
  			rds_message_add_extension(&rm->m_inc.i_hdr,
  					RDS_EXTHDR_RDMA, &ext_hdr, sizeof(ext_hdr));
  		}
  		if (rm->m_rdma_cookie) {
  			rds_message_add_rdma_dest_extension(&rm->m_inc.i_hdr,
  					rds_rdma_cookie_key(rm->m_rdma_cookie),
  					rds_rdma_cookie_offset(rm->m_rdma_cookie));
  		}
  
  		/* Note - rds_ib_piggyb_ack clears the ACK_REQUIRED bit, so
  		 * we should not do this unless we have a chance of at least
  		 * sticking the header into the send ring. Which is why we
  		 * should call rds_ib_ring_alloc first. */
  		rm->m_inc.i_hdr.h_ack = cpu_to_be64(rds_ib_piggyb_ack(ic));
  		rds_message_make_checksum(&rm->m_inc.i_hdr);
  
  		/*
  		 * Update adv_credits since we reset the ACK_REQUIRED bit.
  		 */
  		if (ic->i_flowctl) {
  			rds_ib_send_grab_credits(ic, 0, &posted, 1, RDS_MAX_ADV_CREDIT - adv_credits);
  			adv_credits += posted;
  			BUG_ON(adv_credits > 255);
  		}
  	}
  
  	/* Sometimes you want to put a fence between an RDMA
  	 * READ and the following SEND.
  	 * We could either do this all the time
  	 * or when requested by the user. Right now, we let
  	 * the application choose.
  	 */
  	if (rm->rdma.op_active && rm->rdma.op_fence)
  		send_flags = IB_SEND_FENCE;
  
  	/* Each frag gets a header. Msgs may be 0 bytes */
  	send = &ic->i_sends[pos];
  	first = send;
  	prev = NULL;
  	scat = &ic->i_data_op->op_sg[rm->data.op_dmasg];
  	i = 0;
  	do {
  		unsigned int len = 0;
  
  		/* Set up the header */
  		send->s_wr.send_flags = send_flags;
  		send->s_wr.opcode = IB_WR_SEND;
  		send->s_wr.num_sge = 1;
  		send->s_wr.next = NULL;
  		send->s_queued = jiffies;
  		send->s_op = NULL;
  
  		send->s_sge[0].addr = ic->i_send_hdrs_dma[pos];
  
  		send->s_sge[0].length = sizeof(struct rds_header);
  
  		memcpy(ic->i_send_hdrs[pos], &rm->m_inc.i_hdr,
  		       sizeof(struct rds_header));
  
  
  		/* Set up the data, if present */
  		if (i < work_alloc
  		    && scat != &rm->data.op_sg[rm->data.op_count]) {
  			len = min(RDS_FRAG_SIZE,
  				  sg_dma_len(scat) - rm->data.op_dmaoff);
  			send->s_wr.num_sge = 2;
  
  			send->s_sge[1].addr = sg_dma_address(scat);
  			send->s_sge[1].addr += rm->data.op_dmaoff;
  			send->s_sge[1].length = len;
  
  			bytes_sent += len;
  			rm->data.op_dmaoff += len;
  			if (rm->data.op_dmaoff == sg_dma_len(scat)) {
  				scat++;
  				rm->data.op_dmasg++;
  				rm->data.op_dmaoff = 0;
  			}
  		}
  
  		rds_ib_set_wr_signal_state(ic, send, false);
  
  		/*
  		 * Always signal the last one if we're stopping due to flow control.
  		 */
  		if (ic->i_flowctl && flow_controlled && i == (work_alloc - 1)) {
  			rds_ib_set_wr_signal_state(ic, send, true);
  			send->s_wr.send_flags |= IB_SEND_SOLICITED;
  		}
  
  		if (send->s_wr.send_flags & IB_SEND_SIGNALED)
  			nr_sig++;
  
  		rdsdebug("send %p wr %p num_sge %u next %p\n", send,
  			 &send->s_wr, send->s_wr.num_sge, send->s_wr.next);
  
  		if (ic->i_flowctl && adv_credits) {
  			struct rds_header *hdr = ic->i_send_hdrs[pos];
  
  			/* add credit and redo the header checksum */
  			hdr->h_credit = adv_credits;
  			rds_message_make_checksum(hdr);
  			adv_credits = 0;
  			rds_ib_stats_inc(s_ib_tx_credit_updates);
  		}
  
  		if (prev)
  			prev->s_wr.next = &send->s_wr;
  		prev = send;
  
  		pos = (pos + 1) % ic->i_send_ring.w_nr;
  		send = &ic->i_sends[pos];
  		i++;
  
  	} while (i < work_alloc
  		 && scat != &rm->data.op_sg[rm->data.op_count]);
  
  	/* Account the RDS header in the number of bytes we sent, but just once.
  	 * The caller has no concept of fragmentation. */
  	if (hdr_off == 0)
  		bytes_sent += sizeof(struct rds_header);
  
  	/* if we finished the message then send completion owns it */
  	if (scat == &rm->data.op_sg[rm->data.op_count]) {
  		prev->s_op = ic->i_data_op;
  		prev->s_wr.send_flags |= IB_SEND_SOLICITED;
  		if (!(prev->s_wr.send_flags & IB_SEND_SIGNALED))
  			nr_sig += rds_ib_set_wr_signal_state(ic, prev, true);
  		ic->i_data_op = NULL;
  	}
  
  	/* Put back wrs & credits we didn't use */
  	if (i < work_alloc) {
  		rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc - i);
  		work_alloc = i;
  	}
  	if (ic->i_flowctl && i < credit_alloc)
  		rds_ib_send_add_credits(conn, credit_alloc - i);
  
  	if (nr_sig)
  		atomic_add(nr_sig, &ic->i_signaled_sends);
  
  	/* XXX need to worry about failed_wr and partial sends. */
  	failed_wr = &first->s_wr;
  	ret = ib_post_send(ic->i_cm_id->qp, &first->s_wr, &failed_wr);
  	rdsdebug("ic %p first %p (wr %p) ret %d wr %p\n", ic,
  		 first, &first->s_wr, ret, failed_wr);
  	BUG_ON(failed_wr != &first->s_wr);
  	if (ret) {
  		printk(KERN_WARNING "RDS/IB: ib_post_send to %pI6c "
  		       "returned %d\n", &conn->c_faddr, ret);
  		rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc);
  		rds_ib_sub_signaled(ic, nr_sig);
  		if (prev->s_op) {
  			ic->i_data_op = prev->s_op;
  			prev->s_op = NULL;
  		}
  
  		rds_ib_conn_error(ic->conn, "ib_post_send failed\n");
  		goto out;
  	}
  
  	ret = bytes_sent;
  out:
  	BUG_ON(adv_credits);
  	return ret;
  }
  
  /*
   * Issue atomic operation.
   * A simplified version of the rdma case, we always map 1 SG, and
   * only 8 bytes, for the return value from the atomic operation.
   */
  int rds_ib_xmit_atomic(struct rds_connection *conn, struct rm_atomic_op *op)
  {
  	struct rds_ib_connection *ic = conn->c_transport_data;
  	struct rds_ib_send_work *send = NULL;
  	const struct ib_send_wr *failed_wr;
  	u32 pos;
  	u32 work_alloc;
  	int ret;
  	int nr_sig = 0;
  
  	work_alloc = rds_ib_ring_alloc(&ic->i_send_ring, 1, &pos);
  	if (work_alloc != 1) {
  		rds_ib_stats_inc(s_ib_tx_ring_full);
  		ret = -ENOMEM;
  		goto out;
  	}
  
  	/* address of send request in ring */
  	send = &ic->i_sends[pos];
  	send->s_queued = jiffies;
  
  	if (op->op_type == RDS_ATOMIC_TYPE_CSWP) {
  		send->s_atomic_wr.wr.opcode = IB_WR_MASKED_ATOMIC_CMP_AND_SWP;
  		send->s_atomic_wr.compare_add = op->op_m_cswp.compare;
  		send->s_atomic_wr.swap = op->op_m_cswp.swap;
  		send->s_atomic_wr.compare_add_mask = op->op_m_cswp.compare_mask;
  		send->s_atomic_wr.swap_mask = op->op_m_cswp.swap_mask;
  	} else { /* FADD */
  		send->s_atomic_wr.wr.opcode = IB_WR_MASKED_ATOMIC_FETCH_AND_ADD;
  		send->s_atomic_wr.compare_add = op->op_m_fadd.add;
  		send->s_atomic_wr.swap = 0;
  		send->s_atomic_wr.compare_add_mask = op->op_m_fadd.nocarry_mask;
  		send->s_atomic_wr.swap_mask = 0;
  	}
  	send->s_wr.send_flags = 0;
  	nr_sig = rds_ib_set_wr_signal_state(ic, send, op->op_notify);
  	send->s_atomic_wr.wr.num_sge = 1;
  	send->s_atomic_wr.wr.next = NULL;
  	send->s_atomic_wr.remote_addr = op->op_remote_addr;
  	send->s_atomic_wr.rkey = op->op_rkey;
  	send->s_op = op;
  	rds_message_addref(container_of(send->s_op, struct rds_message, atomic));
  
  	/* map 8 byte retval buffer to the device */
  	ret = ib_dma_map_sg(ic->i_cm_id->device, op->op_sg, 1, DMA_FROM_DEVICE);
  	rdsdebug("ic %p mapping atomic op %p. mapped %d pg\n", ic, op, ret);
  	if (ret != 1) {
  		rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc);
  		rds_ib_stats_inc(s_ib_tx_sg_mapping_failure);
  		ret = -ENOMEM; /* XXX ? */
  		goto out;
  	}
  
  	/* Convert our struct scatterlist to struct ib_sge */
  	send->s_sge[0].addr = sg_dma_address(op->op_sg);
  	send->s_sge[0].length = sg_dma_len(op->op_sg);
  	send->s_sge[0].lkey = ic->i_pd->local_dma_lkey;
  
  	rdsdebug("rva %Lx rpa %Lx len %u\n", op->op_remote_addr,
  		 send->s_sge[0].addr, send->s_sge[0].length);
  
  	if (nr_sig)
  		atomic_add(nr_sig, &ic->i_signaled_sends);
  
  	failed_wr = &send->s_atomic_wr.wr;
  	ret = ib_post_send(ic->i_cm_id->qp, &send->s_atomic_wr.wr, &failed_wr);
  	rdsdebug("ic %p send %p (wr %p) ret %d wr %p\n", ic,
  		 send, &send->s_atomic_wr, ret, failed_wr);
  	BUG_ON(failed_wr != &send->s_atomic_wr.wr);
  	if (ret) {
  		printk(KERN_WARNING "RDS/IB: atomic ib_post_send to %pI6c "
  		       "returned %d\n", &conn->c_faddr, ret);
  		rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc);
  		rds_ib_sub_signaled(ic, nr_sig);
  		goto out;
  	}
  
  	if (unlikely(failed_wr != &send->s_atomic_wr.wr)) {
  		printk(KERN_WARNING "RDS/IB: atomic ib_post_send() rc=%d, but failed_wqe updated!\n", ret);
  		BUG_ON(failed_wr != &send->s_atomic_wr.wr);
  	}
  
  out:
  	return ret;
  }
  
  int rds_ib_xmit_rdma(struct rds_connection *conn, struct rm_rdma_op *op)
  {
  	struct rds_ib_connection *ic = conn->c_transport_data;
  	struct rds_ib_send_work *send = NULL;
  	struct rds_ib_send_work *first;
  	struct rds_ib_send_work *prev;
  	const struct ib_send_wr *failed_wr;
  	struct scatterlist *scat;
  	unsigned long len;
  	u64 remote_addr = op->op_remote_addr;
  	u32 max_sge = ic->rds_ibdev->max_sge;
  	u32 pos;
  	u32 work_alloc;
  	u32 i;
  	u32 j;
  	int sent;
  	int ret;
  	int num_sge;
  	int nr_sig = 0;
  
  	/* map the op the first time we see it */
  	if (!op->op_mapped) {
  		op->op_count = ib_dma_map_sg(ic->i_cm_id->device,
  					     op->op_sg, op->op_nents, (op->op_write) ?
  					     DMA_TO_DEVICE : DMA_FROM_DEVICE);
  		rdsdebug("ic %p mapping op %p: %d\n", ic, op, op->op_count);
  		if (op->op_count == 0) {
  			rds_ib_stats_inc(s_ib_tx_sg_mapping_failure);
  			ret = -ENOMEM; /* XXX ? */
  			goto out;
  		}
  
  		op->op_mapped = 1;
  	}
  
  	/*
  	 * Instead of knowing how to return a partial rdma read/write we insist that there
  	 * be enough work requests to send the entire message.
  	 */
  	i = DIV_ROUND_UP(op->op_count, max_sge);
  
  	work_alloc = rds_ib_ring_alloc(&ic->i_send_ring, i, &pos);
  	if (work_alloc != i) {
  		rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc);
  		rds_ib_stats_inc(s_ib_tx_ring_full);
  		ret = -ENOMEM;
  		goto out;
  	}
  
  	send = &ic->i_sends[pos];
  	first = send;
  	prev = NULL;
  	scat = &op->op_sg[0];
  	sent = 0;
  	num_sge = op->op_count;
  
  	for (i = 0; i < work_alloc && scat != &op->op_sg[op->op_count]; i++) {
  		send->s_wr.send_flags = 0;
  		send->s_queued = jiffies;
  		send->s_op = NULL;
  
  		if (!op->op_notify)
  			nr_sig += rds_ib_set_wr_signal_state(ic, send,
  							     op->op_notify);
  
  		send->s_wr.opcode = op->op_write ? IB_WR_RDMA_WRITE : IB_WR_RDMA_READ;
  		send->s_rdma_wr.remote_addr = remote_addr;
  		send->s_rdma_wr.rkey = op->op_rkey;
  
  		if (num_sge > max_sge) {
  			send->s_rdma_wr.wr.num_sge = max_sge;
  			num_sge -= max_sge;
  		} else {
  			send->s_rdma_wr.wr.num_sge = num_sge;
  		}
  
  		send->s_rdma_wr.wr.next = NULL;
  
  		if (prev)
  			prev->s_rdma_wr.wr.next = &send->s_rdma_wr.wr;
  
  		for (j = 0; j < send->s_rdma_wr.wr.num_sge &&
  		     scat != &op->op_sg[op->op_count]; j++) {
  			len = sg_dma_len(scat);
  			send->s_sge[j].addr = sg_dma_address(scat);
  			send->s_sge[j].length = len;
  			send->s_sge[j].lkey = ic->i_pd->local_dma_lkey;
  
  			sent += len;
  			rdsdebug("ic %p sent %d remote_addr %llu\n", ic, sent, remote_addr);
  
  			remote_addr += len;
  			scat++;
  		}
  
  		rdsdebug("send %p wr %p num_sge %u next %p\n", send,
  			&send->s_rdma_wr.wr,
  			send->s_rdma_wr.wr.num_sge,
  			send->s_rdma_wr.wr.next);
  
  		prev = send;
  		if (++send == &ic->i_sends[ic->i_send_ring.w_nr])
  			send = ic->i_sends;
  	}
  
  	/* give a reference to the last op */
  	if (scat == &op->op_sg[op->op_count]) {
  		prev->s_op = op;
  		rds_message_addref(container_of(op, struct rds_message, rdma));
  	}
  
  	if (i < work_alloc) {
  		rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc - i);
  		work_alloc = i;
  	}
  
  	if (nr_sig)
  		atomic_add(nr_sig, &ic->i_signaled_sends);
  
  	failed_wr = &first->s_rdma_wr.wr;
  	ret = ib_post_send(ic->i_cm_id->qp, &first->s_rdma_wr.wr, &failed_wr);
  	rdsdebug("ic %p first %p (wr %p) ret %d wr %p\n", ic,
  		 first, &first->s_rdma_wr.wr, ret, failed_wr);
  	BUG_ON(failed_wr != &first->s_rdma_wr.wr);
  	if (ret) {
  		printk(KERN_WARNING "RDS/IB: rdma ib_post_send to %pI6c "
  		       "returned %d\n", &conn->c_faddr, ret);
  		rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc);
  		rds_ib_sub_signaled(ic, nr_sig);
  		goto out;
  	}
  
  	if (unlikely(failed_wr != &first->s_rdma_wr.wr)) {
  		printk(KERN_WARNING "RDS/IB: ib_post_send() rc=%d, but failed_wqe updated!\n", ret);
  		BUG_ON(failed_wr != &first->s_rdma_wr.wr);
  	}
  
  
  out:
  	return ret;
  }
  
  void rds_ib_xmit_path_complete(struct rds_conn_path *cp)
  {
  	struct rds_connection *conn = cp->cp_conn;
  	struct rds_ib_connection *ic = conn->c_transport_data;
  
  	/* We may have a pending ACK or window update we were unable
  	 * to send previously (due to flow control). Try again. */
  	rds_ib_attempt_ack(ic);
  }
  