RDS: Add iWARP support

Support for iWARP NICs is implemented as a separate
RDS transport from IB. The code, however, is very
similar to IB (it was forked, basically.) so let's keep
it in one changeset.

The reason for this duplicationis that despite its similarity
to IB, there are a number of places where it has different
semantics. iwarp zcopy support is still under development,
and giving it its own sandbox ensures that IB code isn't
disrupted while iwarp changes. Over time these transports
will re-converge.

Signed-off-by: Andy Grover <andy.grover@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 975 insertions, 0 deletions

diff --git a/net/rds/iw_send.c b/net/rds/iw_send.c
new file mode 100644
index 00000000000..22dd38ffd60
--- /dev/null
+++ b/net/rds/iw_send.c
@@ -0,0 +1,975 @@
+/*
+ * Copyright (c) 2006 Oracle.  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 "rds.h"
+#include "rdma.h"
+#include "iw.h"
+
+static void rds_iw_send_rdma_complete(struct rds_message *rm,
+				      int wc_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;
+	}
+	rds_rdma_send_complete(rm, notify_status);
+}
+
+static void rds_iw_send_unmap_rdma(struct rds_iw_connection *ic,
+				   struct rds_rdma_op *op)
+{
+	if (op->r_mapped) {
+		ib_dma_unmap_sg(ic->i_cm_id->device,
+			op->r_sg, op->r_nents,
+			op->r_write ? DMA_TO_DEVICE : DMA_FROM_DEVICE);
+		op->r_mapped = 0;
+	}
+}
+
+static void rds_iw_send_unmap_rm(struct rds_iw_connection *ic,
+			  struct rds_iw_send_work *send,
+			  int wc_status)
+{
+	struct rds_message *rm = send->s_rm;
+
+	rdsdebug("ic %p send %p rm %p\n", ic, send, rm);
+
+	ib_dma_unmap_sg(ic->i_cm_id->device,
+		     rm->m_sg, rm->m_nents,
+		     DMA_TO_DEVICE);
+
+	if (rm->m_rdma_op != NULL) {
+		rds_iw_send_unmap_rdma(ic, rm->m_rdma_op);
+
+		/* 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,
+		 * call rds_rdma_send_complete from the cq_handler. 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_iw_send_rdma_complete(rm, wc_status);
+
+		if (rm->m_rdma_op->r_write)
+			rds_stats_add(s_send_rdma_bytes, rm->m_rdma_op->r_bytes);
+		else
+			rds_stats_add(s_recv_rdma_bytes, rm->m_rdma_op->r_bytes);
+	}
+
+	/* If anyone waited for this message to get flushed out, wake
+	 * them up now */
+	rds_message_unmapped(rm);
+
+	rds_message_put(rm);
+	send->s_rm = NULL;
+}
+
+void rds_iw_send_init_ring(struct rds_iw_connection *ic)
+{
+	struct rds_iw_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_rm = NULL;
+		send->s_op = NULL;
+		send->s_mapping = NULL;
+
+		send->s_wr.next = NULL;
+		send->s_wr.wr_id = i;
+		send->s_wr.sg_list = send->s_sge;
+		send->s_wr.num_sge = 1;
+		send->s_wr.opcode = IB_WR_SEND;
+		send->s_wr.send_flags = 0;
+		send->s_wr.ex.imm_data = 0;
+
+		sge = rds_iw_data_sge(ic, send->s_sge);
+		sge->lkey = 0;
+
+		sge = rds_iw_header_sge(ic, send->s_sge);
+		sge->addr = ic->i_send_hdrs_dma + (i * sizeof(struct rds_header));
+		sge->length = sizeof(struct rds_header);
+		sge->lkey = 0;
+
+		send->s_mr = ib_alloc_fast_reg_mr(ic->i_pd, fastreg_message_size);
+		if (IS_ERR(send->s_mr)) {
+			printk(KERN_WARNING "RDS/IW: ib_alloc_fast_reg_mr failed\n");
+			break;
+		}
+
+		send->s_page_list = ib_alloc_fast_reg_page_list(
+			ic->i_cm_id->device, fastreg_message_size);
+		if (IS_ERR(send->s_page_list)) {
+			printk(KERN_WARNING "RDS/IW: ib_alloc_fast_reg_page_list failed\n");
+			break;
+		}
+	}
+}
+
+void rds_iw_send_clear_ring(struct rds_iw_connection *ic)
+{
+	struct rds_iw_send_work *send;
+	u32 i;
+
+	for (i = 0, send = ic->i_sends; i < ic->i_send_ring.w_nr; i++, send++) {
+		BUG_ON(!send->s_mr);
+		ib_dereg_mr(send->s_mr);
+		BUG_ON(!send->s_page_list);
+		ib_free_fast_reg_page_list(send->s_page_list);
+		if (send->s_wr.opcode == 0xdead)
+			continue;
+		if (send->s_rm)
+			rds_iw_send_unmap_rm(ic, send, IB_WC_WR_FLUSH_ERR);
+		if (send->s_op)
+			rds_iw_send_unmap_rdma(ic, send->s_op);
+	}
+}
+
+/*
+ * 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_iw_send_cq_comp_handler(struct ib_cq *cq, void *context)
+{
+	struct rds_connection *conn = context;
+	struct rds_iw_connection *ic = conn->c_transport_data;
+	struct ib_wc wc;
+	struct rds_iw_send_work *send;
+	u32 completed;
+	u32 oldest;
+	u32 i;
+	int ret;
+
+	rdsdebug("cq %p conn %p\n", cq, conn);
+	rds_iw_stats_inc(s_iw_tx_cq_call);
+	ret = ib_req_notify_cq(cq, IB_CQ_NEXT_COMP);
+	if (ret)
+		rdsdebug("ib_req_notify_cq send failed: %d\n", ret);
+
+	while (ib_poll_cq(cq, 1, &wc) > 0) {
+		rdsdebug("wc wr_id 0x%llx status %u byte_len %u imm_data %u\n",
+			 (unsigned long long)wc.wr_id, wc.status, wc.byte_len,
+			 be32_to_cpu(wc.ex.imm_data));
+		rds_iw_stats_inc(s_iw_tx_cq_event);
+
+		if (wc.status != IB_WC_SUCCESS) {
+			printk(KERN_ERR "WC Error:  status = %d opcode = %d\n", wc.status, wc.opcode);
+			break;
+		}
+
+		if (wc.opcode == IB_WC_LOCAL_INV && wc.wr_id == RDS_IW_LOCAL_INV_WR_ID) {
+			ic->i_fastreg_posted = 0;
+			continue;
+		}
+
+		if (wc.opcode == IB_WC_FAST_REG_MR && wc.wr_id == RDS_IW_FAST_REG_WR_ID) {
+			ic->i_fastreg_posted = 1;
+			continue;
+		}
+
+		if (wc.wr_id == RDS_IW_ACK_WR_ID) {
+			if (ic->i_ack_queued + HZ/2 < jiffies)
+				rds_iw_stats_inc(s_iw_tx_stalled);
+			rds_iw_ack_send_complete(ic);
+			continue;
+		}
+
+		oldest = rds_iw_ring_oldest(&ic->i_send_ring);
+
+		completed = rds_iw_ring_completed(&ic->i_send_ring, wc.wr_id, oldest);
+
+		for (i = 0; i < completed; i++) {
+			send = &ic->i_sends[oldest];
+
+			/* In the error case, wc.opcode sometimes contains garbage */
+			switch (send->s_wr.opcode) {
+			case IB_WR_SEND:
+				if (send->s_rm)
+					rds_iw_send_unmap_rm(ic, send, wc.status);
+				break;
+			case IB_WR_FAST_REG_MR:
+			case IB_WR_RDMA_WRITE:
+			case IB_WR_RDMA_READ:
+			case IB_WR_RDMA_READ_WITH_INV:
+				/* Nothing to be done - the SG list will be unmapped
+				 * when the SEND completes. */
+				break;
+			default:
+				if (printk_ratelimit())
+					printk(KERN_NOTICE
+						"RDS/IW: %s: unexpected opcode 0x%x in WR!\n",
+						__func__, send->s_wr.opcode);
+				break;
+			}
+
+			send->s_wr.opcode = 0xdead;
+			send->s_wr.num_sge = 1;
+			if (send->s_queued + HZ/2 < jiffies)
+				rds_iw_stats_inc(s_iw_tx_stalled);
+
+			/* If a RDMA operation produced an error, signal this right
+			 * away. If we don't, the subsequent SEND that goes with this
+			 * RDMA will be canceled with ERR_WFLUSH, and the application
+			 * never learn that the RDMA failed. */
+			if (unlikely(wc.status == IB_WC_REM_ACCESS_ERR && send->s_op)) {
+				struct rds_message *rm;
+
+				rm = rds_send_get_message(conn, send->s_op);
+				if (rm)
+					rds_iw_send_rdma_complete(rm, wc.status);
+			}
+
+			oldest = (oldest + 1) % ic->i_send_ring.w_nr;
+		}
+
+		rds_iw_ring_free(&ic->i_send_ring, completed);
+
+		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_iw_conn_error(conn,
+				"send completion on %pI4 "
+				"had status %u, disconnecting and reconnecting\n",
+				&conn->c_faddr, wc.status);
+		}
+	}
+}
+
+/*
+ * 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 reciever'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_iw_send_add_credits below).
+ *
+ * The RDS send code is essentially single-threaded; rds_send_xmit
+ * grabs c_send_lock 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_iw_send_grab_credits(struct rds_iw_connection *ic,
+			     u32 wanted, u32 *adv_credits, int need_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("rds_iw_send_grab_credits(%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, RDS_MAX_ADV_CREDIT);
+		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_iw_send_add_credits(struct rds_connection *conn, unsigned int credits)
+{
+	struct rds_iw_connection *ic = conn->c_transport_data;
+
+	if (credits == 0)
+		return;
+
+	rdsdebug("rds_iw_send_add_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_iw_stats_inc(s_iw_rx_credit_updates);
+}
+
+void rds_iw_advertise_credits(struct rds_connection *conn, unsigned int posted)
+{
+	struct rds_iw_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 void
+rds_iw_xmit_populate_wr(struct rds_iw_connection *ic,
+		struct rds_iw_send_work *send, unsigned int pos,
+		unsigned long buffer, unsigned int length,
+		int send_flags)
+{
+	struct ib_sge *sge;
+
+	WARN_ON(pos != send - ic->i_sends);
+
+	send->s_wr.send_flags = send_flags;
+	send->s_wr.opcode = IB_WR_SEND;
+	send->s_wr.num_sge = 2;
+	send->s_wr.next = NULL;
+	send->s_queued = jiffies;
+	send->s_op = NULL;
+
+	if (length != 0) {
+		sge = rds_iw_data_sge(ic, send->s_sge);
+		sge->addr = buffer;
+		sge->length = length;
+		sge->lkey = rds_iw_local_dma_lkey(ic);
+
+		sge = rds_iw_header_sge(ic, send->s_sge);
+	} else {
+		/* We're sending a packet with no payload. There is only
+		 * one SGE */
+		send->s_wr.num_sge = 1;
+		sge = &send->s_sge[0];
+	}
+
+	sge->addr = ic->i_send_hdrs_dma + (pos * sizeof(struct rds_header));
+	sge->length = sizeof(struct rds_header);
+	sge->lkey = rds_iw_local_dma_lkey(ic);
+}
+
+/*
+ * 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_iw_xmit(struct rds_connection *conn, struct rds_message *rm,
+		unsigned int hdr_off, unsigned int sg, unsigned int off)
+{
+	struct rds_iw_connection *ic = conn->c_transport_data;
+	struct ib_device *dev = ic->i_cm_id->device;
+	struct rds_iw_send_work *send = NULL;
+	struct rds_iw_send_work *first;
+	struct rds_iw_send_work *prev;
+	struct ib_send_wr *failed_wr;
+	struct scatterlist *scat;
+	u32 pos;
+	u32 i;
+	u32 work_alloc;
+	u32 credit_alloc;
+	u32 posted;
+	u32 adv_credits = 0;
+	int send_flags = 0;
+	int sent;
+	int ret;
+	int flow_controlled = 0;
+
+	BUG_ON(off % RDS_FRAG_SIZE);
+	BUG_ON(hdr_off != 0 && hdr_off != sizeof(struct rds_header));
+
+	/* Fastreg support */
+	if (rds_rdma_cookie_key(rm->m_rdma_cookie)
+	 && !ic->i_fastreg_posted) {
+		ret = -EAGAIN;
+		goto out;
+	}
+
+	/* FIXME we may overallocate here */
+	if (be32_to_cpu(rm->m_inc.i_hdr.h_len) == 0)
+		i = 1;
+	else
+		i = ceil(be32_to_cpu(rm->m_inc.i_hdr.h_len), RDS_FRAG_SIZE);
+
+	work_alloc = rds_iw_ring_alloc(&ic->i_send_ring, i, &pos);
+	if (work_alloc == 0) {
+		set_bit(RDS_LL_SEND_FULL, &conn->c_flags);
+		rds_iw_stats_inc(s_iw_tx_ring_full);
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	credit_alloc = work_alloc;
+	if (ic->i_flowctl) {
+		credit_alloc = rds_iw_send_grab_credits(ic, work_alloc, &posted, 0);
+		adv_credits += posted;
+		if (credit_alloc < work_alloc) {
+			rds_iw_ring_unalloc(&ic->i_send_ring, work_alloc - credit_alloc);
+			work_alloc = credit_alloc;
+			flow_controlled++;
+		}
+		if (work_alloc == 0) {
+			rds_iw_ring_unalloc(&ic->i_send_ring, work_alloc);
+			rds_iw_stats_inc(s_iw_tx_throttle);
+			ret = -ENOMEM;
+			goto out;
+		}
+	}
+
+	/* map the message the first time we see it */
+	if (ic->i_rm == NULL) {
+		/*
+		printk(KERN_NOTICE "rds_iw_xmit prep msg dport=%u flags=0x%x len=%d\n",
+				be16_to_cpu(rm->m_inc.i_hdr.h_dport),
+				rm->m_inc.i_hdr.h_flags,
+				be32_to_cpu(rm->m_inc.i_hdr.h_len));
+		   */
+		if (rm->m_nents) {
+			rm->m_count = ib_dma_map_sg(dev,
+					 rm->m_sg, rm->m_nents, DMA_TO_DEVICE);
+			rdsdebug("ic %p mapping rm %p: %d\n", ic, rm, rm->m_count);
+			if (rm->m_count == 0) {
+				rds_iw_stats_inc(s_iw_tx_sg_mapping_failure);
+				rds_iw_ring_unalloc(&ic->i_send_ring, work_alloc);
+				ret = -ENOMEM; /* XXX ? */
+				goto out;
+			}
+		} else {
+			rm->m_count = 0;
+		}
+
+		ic->i_unsignaled_wrs = rds_iw_sysctl_max_unsig_wrs;
+		ic->i_unsignaled_bytes = rds_iw_sysctl_max_unsig_bytes;
+		rds_message_addref(rm);
+		ic->i_rm = rm;
+
+		/* 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->m_rdma_op) {
+			struct rds_ext_header_rdma ext_hdr;
+
+			ext_hdr.h_rdma_rkey = cpu_to_be32(rm->m_rdma_op->r_key);
+			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_iw_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_iw_ring_alloc first. */
+		rm->m_inc.i_hdr.h_ack = cpu_to_be64(rds_iw_piggyb_ack(ic));
+		rds_message_make_checksum(&rm->m_inc.i_hdr);
+
+		/*
+		 * Update adv_credits since we reset the ACK_REQUIRED bit.
+		 */
+		rds_iw_send_grab_credits(ic, 0, &posted, 1);
+		adv_credits += posted;
+		BUG_ON(adv_credits > 255);
+	} else if (ic->i_rm != rm)
+		BUG();
+
+	send = &ic->i_sends[pos];
+	first = send;
+	prev = NULL;
+	scat = &rm->m_sg[sg];
+	sent = 0;
+	i = 0;
+
+	/* 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->m_rdma_op && rm->m_rdma_op->r_fence)
+		send_flags = IB_SEND_FENCE;
+
+	/*
+	 * We could be copying the header into the unused tail of the page.
+	 * That would need to be changed in the future when those pages might
+	 * be mapped userspace pages or page cache pages.  So instead we always
+	 * use a second sge and our long-lived ring of mapped headers.  We send
+	 * the header after the data so that the data payload can be aligned on
+	 * the receiver.
+	 */
+
+	/* handle a 0-len message */
+	if (be32_to_cpu(rm->m_inc.i_hdr.h_len) == 0) {
+		rds_iw_xmit_populate_wr(ic, send, pos, 0, 0, send_flags);
+		goto add_header;
+	}
+
+	/* if there's data reference it with a chain of work reqs */
+	for (; i < work_alloc && scat != &rm->m_sg[rm->m_count]; i++) {
+		unsigned int len;
+
+		send = &ic->i_sends[pos];
+
+		len = min(RDS_FRAG_SIZE, ib_sg_dma_len(dev, scat) - off);
+		rds_iw_xmit_populate_wr(ic, send, pos,
+				ib_sg_dma_address(dev, scat) + off, len,
+				send_flags);
+
+		/*
+		 * 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) {
+			ic->i_unsignaled_wrs = rds_iw_sysctl_max_unsig_wrs;
+			send->s_wr.send_flags |= IB_SEND_SIGNALED | IB_SEND_SOLICITED;
+		}
+
+		ic->i_unsignaled_bytes -= len;
+		if (ic->i_unsignaled_bytes <= 0) {
+			ic->i_unsignaled_bytes = rds_iw_sysctl_max_unsig_bytes;
+			send->s_wr.send_flags |= IB_SEND_SIGNALED | IB_SEND_SOLICITED;
+		}
+
+		/*
+		 * Always signal the last one if we're stopping due to flow control.
+		 */
+		if (flow_controlled && i == (work_alloc-1))
+			send->s_wr.send_flags |= IB_SEND_SIGNALED | IB_SEND_SOLICITED;
+
+		rdsdebug("send %p wr %p num_sge %u next %p\n", send,
+			 &send->s_wr, send->s_wr.num_sge, send->s_wr.next);
+
+		sent += len;
+		off += len;
+		if (off == ib_sg_dma_len(dev, scat)) {
+			scat++;
+			off = 0;
+		}
+
+add_header:
+		/* Tack on the header after the data. The header SGE should already
+		 * have been set up to point to the right header buffer. */
+		memcpy(&ic->i_send_hdrs[pos], &rm->m_inc.i_hdr, sizeof(struct rds_header));
+
+		if (0) {
+			struct rds_header *hdr = &ic->i_send_hdrs[pos];
+
+			printk(KERN_NOTICE "send WR dport=%u flags=0x%x len=%d\n",
+				be16_to_cpu(hdr->h_dport),
+				hdr->h_flags,
+				be32_to_cpu(hdr->h_len));
+		}
+		if (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_iw_stats_inc(s_iw_tx_credit_updates);
+		}
+
+		if (prev)
+			prev->s_wr.next = &send->s_wr;
+		prev = send;
+
+		pos = (pos + 1) % ic->i_send_ring.w_nr;
+	}
+
+	/* 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)
+		sent += sizeof(struct rds_header);
+
+	/* if we finished the message then send completion owns it */
+	if (scat == &rm->m_sg[rm->m_count]) {
+		prev->s_rm = ic->i_rm;
+		prev->s_wr.send_flags |= IB_SEND_SIGNALED | IB_SEND_SOLICITED;
+		ic->i_rm = NULL;
+	}
+
+	if (i < work_alloc) {
+		rds_iw_ring_unalloc(&ic->i_send_ring, work_alloc - i);
+		work_alloc = i;
+	}
+	if (ic->i_flowctl && i < credit_alloc)
+		rds_iw_send_add_credits(conn, credit_alloc - i);
+
+	/* 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/IW: ib_post_send to %pI4 "
+		       "returned %d\n", &conn->c_faddr, ret);
+		rds_iw_ring_unalloc(&ic->i_send_ring, work_alloc);
+		if (prev->s_rm) {
+			ic->i_rm = prev->s_rm;
+			prev->s_rm = NULL;
+		}
+		goto out;
+	}
+
+	ret = sent;
+out:
+	BUG_ON(adv_credits);
+	return ret;
+}
+
+static void rds_iw_build_send_fastreg(struct rds_iw_device *rds_iwdev, struct rds_iw_connection *ic, struct rds_iw_send_work *send, int nent, int len, u64 sg_addr)
+{
+	BUG_ON(nent > send->s_page_list->max_page_list_len);
+	/*
+	 * Perform a WR for the fast_reg_mr. Each individual page
+	 * in the sg list is added to the fast reg page list and placed
+	 * inside the fast_reg_mr WR.
+	 */
+	send->s_wr.opcode = IB_WR_FAST_REG_MR;
+	send->s_wr.wr.fast_reg.length = len;
+	send->s_wr.wr.fast_reg.rkey = send->s_mr->rkey;
+	send->s_wr.wr.fast_reg.page_list = send->s_page_list;
+	send->s_wr.wr.fast_reg.page_list_len = nent;
+	send->s_wr.wr.fast_reg.page_shift = rds_iwdev->page_shift;
+	send->s_wr.wr.fast_reg.access_flags = IB_ACCESS_REMOTE_WRITE;
+	send->s_wr.wr.fast_reg.iova_start = sg_addr;
+
+	ib_update_fast_reg_key(send->s_mr, send->s_remap_count++);
+}
+
+int rds_iw_xmit_rdma(struct rds_connection *conn, struct rds_rdma_op *op)
+{
+	struct rds_iw_connection *ic = conn->c_transport_data;
+	struct rds_iw_send_work *send = NULL;
+	struct rds_iw_send_work *first;
+	struct rds_iw_send_work *prev;
+	struct ib_send_wr *failed_wr;
+	struct rds_iw_device *rds_iwdev;
+	struct scatterlist *scat;
+	unsigned long len;
+	u64 remote_addr = op->r_remote_addr;
+	u32 pos, fr_pos;
+	u32 work_alloc;
+	u32 i;
+	u32 j;
+	int sent;
+	int ret;
+	int num_sge;
+
+	rds_iwdev = ib_get_client_data(ic->i_cm_id->device, &rds_iw_client);
+
+	/* map the message the first time we see it */
+	if (!op->r_mapped) {
+		op->r_count = ib_dma_map_sg(ic->i_cm_id->device,
+					op->r_sg, op->r_nents, (op->r_write) ?
+					DMA_TO_DEVICE : DMA_FROM_DEVICE);
+		rdsdebug("ic %p mapping op %p: %d\n", ic, op, op->r_count);
+		if (op->r_count == 0) {
+			rds_iw_stats_inc(s_iw_tx_sg_mapping_failure);
+			ret = -ENOMEM; /* XXX ? */
+			goto out;
+		}
+
+		op->r_mapped = 1;
+	}
+
+	if (!op->r_write) {
+		/* Alloc space on the send queue for the fastreg */
+		work_alloc = rds_iw_ring_alloc(&ic->i_send_ring, 1, &fr_pos);
+		if (work_alloc != 1) {
+			rds_iw_ring_unalloc(&ic->i_send_ring, work_alloc);
+			rds_iw_stats_inc(s_iw_tx_ring_full);
+			ret = -ENOMEM;
+			goto out;
+		}
+	}
+
+	/*
+	 * 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 = ceil(op->r_count, rds_iwdev->max_sge);
+
+	work_alloc = rds_iw_ring_alloc(&ic->i_send_ring, i, &pos);
+	if (work_alloc != i) {
+		rds_iw_ring_unalloc(&ic->i_send_ring, work_alloc);
+		rds_iw_stats_inc(s_iw_tx_ring_full);
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	send = &ic->i_sends[pos];
+	if (!op->r_write) {
+		first = prev = &ic->i_sends[fr_pos];
+	} else {
+		first = send;
+		prev = NULL;
+	}
+	scat = &op->r_sg[0];
+	sent = 0;
+	num_sge = op->r_count;
+
+	for (i = 0; i < work_alloc && scat != &op->r_sg[op->r_count]; i++) {
+		send->s_wr.send_flags = 0;
+		send->s_queued = jiffies;
+
+		/*
+		 * 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) {
+			ic->i_unsignaled_wrs = rds_iw_sysctl_max_unsig_wrs;
+			send->s_wr.send_flags = IB_SEND_SIGNALED;
+		}
+
+		/* To avoid the need to have the plumbing to invalidate the fastreg_mr used
+		 * for local access after RDS is finished with it, using
+		 * IB_WR_RDMA_READ_WITH_INV will invalidate it after the read has completed.
+		 */
+		if (op->r_write)
+			send->s_wr.opcode = IB_WR_RDMA_WRITE;
+		else
+			send->s_wr.opcode = IB_WR_RDMA_READ_WITH_INV;
+
+		send->s_wr.wr.rdma.remote_addr = remote_addr;
+		send->s_wr.wr.rdma.rkey = op->r_key;
+		send->s_op = op;
+
+		if (num_sge > rds_iwdev->max_sge) {
+			send->s_wr.num_sge = rds_iwdev->max_sge;
+			num_sge -= rds_iwdev->max_sge;
+		} else
+			send->s_wr.num_sge = num_sge;
+
+		send->s_wr.next = NULL;
+
+		if (prev)
+			prev->s_wr.next = &send->s_wr;
+
+		for (j = 0; j < send->s_wr.num_sge && scat != &op->r_sg[op->r_count]; j++) {
+			len = ib_sg_dma_len(ic->i_cm_id->device, scat);
+
+			if (send->s_wr.opcode == IB_WR_RDMA_READ_WITH_INV)
+				send->s_page_list->page_list[j] = ib_sg_dma_address(ic->i_cm_id->device, scat);
+			else {
+				send->s_sge[j].addr = ib_sg_dma_address(ic->i_cm_id->device, scat);
+				send->s_sge[j].length = len;
+				send->s_sge[j].lkey = rds_iw_local_dma_lkey(ic);
+			}
+
+			sent += len;
+			rdsdebug("ic %p sent %d remote_addr %llu\n", ic, sent, remote_addr);
+			remote_addr += len;
+
+			scat++;
+		}
+
+		if (send->s_wr.opcode == IB_WR_RDMA_READ_WITH_INV) {
+			send->s_wr.num_sge = 1;
+			send->s_sge[0].addr = conn->c_xmit_rm->m_rs->rs_user_addr;
+			send->s_sge[0].length = conn->c_xmit_rm->m_rs->rs_user_bytes;
+			send->s_sge[0].lkey = ic->i_sends[fr_pos].s_mr->lkey;
+		}
+
+		rdsdebug("send %p wr %p num_sge %u next %p\n", send,
+			&send->s_wr, send->s_wr.num_sge, send->s_wr.next);
+
+		prev = send;
+		if (++send == &ic->i_sends[ic->i_send_ring.w_nr])
+			send = ic->i_sends;
+	}
+
+	/* if we finished the message then send completion owns it */
+	if (scat == &op->r_sg[op->r_count])
+		first->s_wr.send_flags = IB_SEND_SIGNALED;
+
+	if (i < work_alloc) {
+		rds_iw_ring_unalloc(&ic->i_send_ring, work_alloc - i);
+		work_alloc = i;
+	}
+
+	/* On iWARP, local memory access by a remote system (ie, RDMA Read) is not
+	 * recommended.  Putting the lkey on the wire is a security hole, as it can
+	 * allow for memory access to all of memory on the remote system.  Some
+	 * adapters do not allow using the lkey for this at all.  To bypass this use a
+	 * fastreg_mr (or possibly a dma_mr)
+	 */
+	if (!op->r_write) {
+		rds_iw_build_send_fastreg(rds_iwdev, ic, &ic->i_sends[fr_pos],
+			op->r_count, sent, conn->c_xmit_rm->m_rs->rs_user_addr);
+		work_alloc++;
+	}
+
+	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/IW: rdma ib_post_send to %pI4 "
+		       "returned %d\n", &conn->c_faddr, ret);
+		rds_iw_ring_unalloc(&ic->i_send_ring, work_alloc);
+		goto out;
+	}
+
+out:
+	return ret;
+}
+
+void rds_iw_xmit_complete(struct rds_connection *conn)
+{
+	struct rds_iw_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_iw_attempt_ack(ic);
+}