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, 869 insertions, 0 deletions

diff --git a/net/rds/iw_recv.c b/net/rds/iw_recv.c
new file mode 100644
index 000000000000..a1931f0027a2
--- /dev/null
+++ b/net/rds/iw_recv.c
@@ -0,0 +1,869 @@
+/*
+ * 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/pci.h>
+#include <linux/dma-mapping.h>
+#include <rdma/rdma_cm.h>
+
+#include "rds.h"
+#include "iw.h"
+
+static struct kmem_cache *rds_iw_incoming_slab;
+static struct kmem_cache *rds_iw_frag_slab;
+static atomic_t rds_iw_allocation = ATOMIC_INIT(0);
+
+static void rds_iw_frag_drop_page(struct rds_page_frag *frag)
+{
+        rdsdebug("frag %p page %p\n", frag, frag->f_page);
+        __free_page(frag->f_page);
+        frag->f_page = NULL;
+}
+
+static void rds_iw_frag_free(struct rds_page_frag *frag)
+{
+        rdsdebug("frag %p page %p\n", frag, frag->f_page);
+        BUG_ON(frag->f_page != NULL);
+        kmem_cache_free(rds_iw_frag_slab, frag);
+}
+
+/*
+ * We map a page at a time.  Its fragments are posted in order.  This
+ * is called in fragment order as the fragments get send completion events.
+ * Only the last frag in the page performs the unmapping.
+ *
+ * It's OK for ring cleanup to call this in whatever order it likes because
+ * DMA is not in flight and so we can unmap while other ring entries still
+ * hold page references in their frags.
+ */
+static void rds_iw_recv_unmap_page(struct rds_iw_connection *ic,
+                                   struct rds_iw_recv_work *recv)
+{
+        struct rds_page_frag *frag = recv->r_frag;
+
+        rdsdebug("recv %p frag %p page %p\n", recv, frag, frag->f_page);
+        if (frag->f_mapped)
+                ib_dma_unmap_page(ic->i_cm_id->device,
+                               frag->f_mapped,
+                               RDS_FRAG_SIZE, DMA_FROM_DEVICE);
+        frag->f_mapped = 0;
+}
+
+void rds_iw_recv_init_ring(struct rds_iw_connection *ic)
+{
+        struct rds_iw_recv_work *recv;
+        u32 i;
+
+        for (i = 0, recv = ic->i_recvs; i < ic->i_recv_ring.w_nr; i++, recv++) {
+                struct ib_sge *sge;
+
+                recv->r_iwinc = NULL;
+                recv->r_frag = NULL;
+
+                recv->r_wr.next = NULL;
+                recv->r_wr.wr_id = i;
+                recv->r_wr.sg_list = recv->r_sge;
+                recv->r_wr.num_sge = RDS_IW_RECV_SGE;
+
+                sge = rds_iw_data_sge(ic, recv->r_sge);
+                sge->addr = 0;
+                sge->length = RDS_FRAG_SIZE;
+                sge->lkey = 0;
+
+                sge = rds_iw_header_sge(ic, recv->r_sge);
+                sge->addr = ic->i_recv_hdrs_dma + (i * sizeof(struct rds_header));
+                sge->length = sizeof(struct rds_header);
+                sge->lkey = 0;
+        }
+}
+
+static void rds_iw_recv_clear_one(struct rds_iw_connection *ic,
+                                  struct rds_iw_recv_work *recv)
+{
+        if (recv->r_iwinc) {
+                rds_inc_put(&recv->r_iwinc->ii_inc);
+                recv->r_iwinc = NULL;
+        }
+        if (recv->r_frag) {
+                rds_iw_recv_unmap_page(ic, recv);
+                if (recv->r_frag->f_page)
+                        rds_iw_frag_drop_page(recv->r_frag);
+                rds_iw_frag_free(recv->r_frag);
+                recv->r_frag = NULL;
+        }
+}
+
+void rds_iw_recv_clear_ring(struct rds_iw_connection *ic)
+{
+        u32 i;
+
+        for (i = 0; i < ic->i_recv_ring.w_nr; i++)
+                rds_iw_recv_clear_one(ic, &ic->i_recvs[i]);
+
+        if (ic->i_frag.f_page)
+                rds_iw_frag_drop_page(&ic->i_frag);
+}
+
+static int rds_iw_recv_refill_one(struct rds_connection *conn,
+                                  struct rds_iw_recv_work *recv,
+                                  gfp_t kptr_gfp, gfp_t page_gfp)
+{
+        struct rds_iw_connection *ic = conn->c_transport_data;
+        dma_addr_t dma_addr;
+        struct ib_sge *sge;
+        int ret = -ENOMEM;
+
+        if (recv->r_iwinc == NULL) {
+                if (atomic_read(&rds_iw_allocation) >= rds_iw_sysctl_max_recv_allocation) {
+                        rds_iw_stats_inc(s_iw_rx_alloc_limit);
+                        goto out;
+                }
+                recv->r_iwinc = kmem_cache_alloc(rds_iw_incoming_slab,
+                                                 kptr_gfp);
+                if (recv->r_iwinc == NULL)
+                        goto out;
+                atomic_inc(&rds_iw_allocation);
+                INIT_LIST_HEAD(&recv->r_iwinc->ii_frags);
+                rds_inc_init(&recv->r_iwinc->ii_inc, conn, conn->c_faddr);
+        }
+
+        if (recv->r_frag == NULL) {
+                recv->r_frag = kmem_cache_alloc(rds_iw_frag_slab, kptr_gfp);
+                if (recv->r_frag == NULL)
+                        goto out;
+                INIT_LIST_HEAD(&recv->r_frag->f_item);
+                recv->r_frag->f_page = NULL;
+        }
+
+        if (ic->i_frag.f_page == NULL) {
+                ic->i_frag.f_page = alloc_page(page_gfp);
+                if (ic->i_frag.f_page == NULL)
+                        goto out;
+                ic->i_frag.f_offset = 0;
+        }
+
+        dma_addr = ib_dma_map_page(ic->i_cm_id->device,
+                                  ic->i_frag.f_page,
+                                  ic->i_frag.f_offset,
+                                  RDS_FRAG_SIZE,
+                                  DMA_FROM_DEVICE);
+        if (ib_dma_mapping_error(ic->i_cm_id->device, dma_addr))
+                goto out;
+
+        /*
+         * Once we get the RDS_PAGE_LAST_OFF frag then rds_iw_frag_unmap()
+         * must be called on this recv.  This happens as completions hit
+         * in order or on connection shutdown.
+         */
+        recv->r_frag->f_page = ic->i_frag.f_page;
+        recv->r_frag->f_offset = ic->i_frag.f_offset;
+        recv->r_frag->f_mapped = dma_addr;
+
+        sge = rds_iw_data_sge(ic, recv->r_sge);
+        sge->addr = dma_addr;
+        sge->length = RDS_FRAG_SIZE;
+
+        sge = rds_iw_header_sge(ic, recv->r_sge);
+        sge->addr = ic->i_recv_hdrs_dma + (recv - ic->i_recvs) * sizeof(struct rds_header);
+        sge->length = sizeof(struct rds_header);
+
+        get_page(recv->r_frag->f_page);
+
+        if (ic->i_frag.f_offset < RDS_PAGE_LAST_OFF) {
+                ic->i_frag.f_offset += RDS_FRAG_SIZE;
+        } else {
+                put_page(ic->i_frag.f_page);
+                ic->i_frag.f_page = NULL;
+                ic->i_frag.f_offset = 0;
+        }
+
+        ret = 0;
+out:
+        return ret;
+}
+
+/*
+ * This tries to allocate and post unused work requests after making sure that
+ * they have all the allocations they need to queue received fragments into
+ * sockets.  The i_recv_mutex is held here so that ring_alloc and _unalloc
+ * pairs don't go unmatched.
+ *
+ * -1 is returned if posting fails due to temporary resource exhaustion.
+ */
+int rds_iw_recv_refill(struct rds_connection *conn, gfp_t kptr_gfp,
+                       gfp_t page_gfp, int prefill)
+{
+        struct rds_iw_connection *ic = conn->c_transport_data;
+        struct rds_iw_recv_work *recv;
+        struct ib_recv_wr *failed_wr;
+        unsigned int posted = 0;
+        int ret = 0;
+        u32 pos;
+
+        while ((prefill || rds_conn_up(conn))
+                        && rds_iw_ring_alloc(&ic->i_recv_ring, 1, &pos)) {
+                if (pos >= ic->i_recv_ring.w_nr) {
+                        printk(KERN_NOTICE "Argh - ring alloc returned pos=%u\n",
+                                        pos);
+                        ret = -EINVAL;
+                        break;
+                }
+
+                recv = &ic->i_recvs[pos];
+                ret = rds_iw_recv_refill_one(conn, recv, kptr_gfp, page_gfp);
+                if (ret) {
+                        ret = -1;
+                        break;
+                }
+
+                /* XXX when can this fail? */
+                ret = ib_post_recv(ic->i_cm_id->qp, &recv->r_wr, &failed_wr);
+                rdsdebug("recv %p iwinc %p page %p addr %lu ret %d\n", recv,
+                         recv->r_iwinc, recv->r_frag->f_page,
+                         (long) recv->r_frag->f_mapped, ret);
+                if (ret) {
+                        rds_iw_conn_error(conn, "recv post on "
+                               "%pI4 returned %d, disconnecting and "
+                               "reconnecting\n", &conn->c_faddr,
+                               ret);
+                        ret = -1;
+                        break;
+                }
+
+                posted++;
+        }
+
+        /* We're doing flow control - update the window. */
+        if (ic->i_flowctl && posted)
+                rds_iw_advertise_credits(conn, posted);
+
+        if (ret)
+                rds_iw_ring_unalloc(&ic->i_recv_ring, 1);
+        return ret;
+}
+
+void rds_iw_inc_purge(struct rds_incoming *inc)
+{
+        struct rds_iw_incoming *iwinc;
+        struct rds_page_frag *frag;
+        struct rds_page_frag *pos;
+
+        iwinc = container_of(inc, struct rds_iw_incoming, ii_inc);
+        rdsdebug("purging iwinc %p inc %p\n", iwinc, inc);
+
+        list_for_each_entry_safe(frag, pos, &iwinc->ii_frags, f_item) {
+                list_del_init(&frag->f_item);
+                rds_iw_frag_drop_page(frag);
+                rds_iw_frag_free(frag);
+        }
+}
+
+void rds_iw_inc_free(struct rds_incoming *inc)
+{
+        struct rds_iw_incoming *iwinc;
+
+        iwinc = container_of(inc, struct rds_iw_incoming, ii_inc);
+
+        rds_iw_inc_purge(inc);
+        rdsdebug("freeing iwinc %p inc %p\n", iwinc, inc);
+        BUG_ON(!list_empty(&iwinc->ii_frags));
+        kmem_cache_free(rds_iw_incoming_slab, iwinc);
+        atomic_dec(&rds_iw_allocation);
+        BUG_ON(atomic_read(&rds_iw_allocation) < 0);
+}
+
+int rds_iw_inc_copy_to_user(struct rds_incoming *inc, struct iovec *first_iov,
+                            size_t size)
+{
+        struct rds_iw_incoming *iwinc;
+        struct rds_page_frag *frag;
+        struct iovec *iov = first_iov;
+        unsigned long to_copy;
+        unsigned long frag_off = 0;
+        unsigned long iov_off = 0;
+        int copied = 0;
+        int ret;
+        u32 len;
+
+        iwinc = container_of(inc, struct rds_iw_incoming, ii_inc);
+        frag = list_entry(iwinc->ii_frags.next, struct rds_page_frag, f_item);
+        len = be32_to_cpu(inc->i_hdr.h_len);
+
+        while (copied < size && copied < len) {
+                if (frag_off == RDS_FRAG_SIZE) {
+                        frag = list_entry(frag->f_item.next,
+                                          struct rds_page_frag, f_item);
+                        frag_off = 0;
+                }
+                while (iov_off == iov->iov_len) {
+                        iov_off = 0;
+                        iov++;
+                }
+
+                to_copy = min(iov->iov_len - iov_off, RDS_FRAG_SIZE - frag_off);
+                to_copy = min_t(size_t, to_copy, size - copied);
+                to_copy = min_t(unsigned long, to_copy, len - copied);
+
+                rdsdebug("%lu bytes to user [%p, %zu] + %lu from frag "
+                         "[%p, %lu] + %lu\n",
+                         to_copy, iov->iov_base, iov->iov_len, iov_off,
+                         frag->f_page, frag->f_offset, frag_off);
+
+                /* XXX needs + offset for multiple recvs per page */
+                ret = rds_page_copy_to_user(frag->f_page,
+                                            frag->f_offset + frag_off,
+                                            iov->iov_base + iov_off,
+                                            to_copy);
+                if (ret) {
+                        copied = ret;
+                        break;
+                }
+
+                iov_off += to_copy;
+                frag_off += to_copy;
+                copied += to_copy;
+        }
+
+        return copied;
+}
+
+/* ic starts out kzalloc()ed */
+void rds_iw_recv_init_ack(struct rds_iw_connection *ic)
+{
+        struct ib_send_wr *wr = &ic->i_ack_wr;
+        struct ib_sge *sge = &ic->i_ack_sge;
+
+        sge->addr = ic->i_ack_dma;
+        sge->length = sizeof(struct rds_header);
+        sge->lkey = rds_iw_local_dma_lkey(ic);
+
+        wr->sg_list = sge;
+        wr->num_sge = 1;
+        wr->opcode = IB_WR_SEND;
+        wr->wr_id = RDS_IW_ACK_WR_ID;
+        wr->send_flags = IB_SEND_SIGNALED | IB_SEND_SOLICITED;
+}
+
+/*
+ * You'd think that with reliable IB connections you wouldn't need to ack
+ * messages that have been received.  The problem is that IB hardware generates
+ * an ack message before it has DMAed the message into memory.  This creates a
+ * potential message loss if the HCA is disabled for any reason between when it
+ * sends the ack and before the message is DMAed and processed.  This is only a
+ * potential issue if another HCA is available for fail-over.
+ *
+ * When the remote host receives our ack they'll free the sent message from
+ * their send queue.  To decrease the latency of this we always send an ack
+ * immediately after we've received messages.
+ *
+ * For simplicity, we only have one ack in flight at a time.  This puts
+ * pressure on senders to have deep enough send queues to absorb the latency of
+ * a single ack frame being in flight.  This might not be good enough.
+ *
+ * This is implemented by have a long-lived send_wr and sge which point to a
+ * statically allocated ack frame.  This ack wr does not fall under the ring
+ * accounting that the tx and rx wrs do.  The QP attribute specifically makes
+ * room for it beyond the ring size.  Send completion notices its special
+ * wr_id and avoids working with the ring in that case.
+ */
+static void rds_iw_set_ack(struct rds_iw_connection *ic, u64 seq,
+                                int ack_required)
+{
+        rds_iw_set_64bit(&ic->i_ack_next, seq);
+        if (ack_required) {
+                smp_mb__before_clear_bit();
+                set_bit(IB_ACK_REQUESTED, &ic->i_ack_flags);
+        }
+}
+
+static u64 rds_iw_get_ack(struct rds_iw_connection *ic)
+{
+        clear_bit(IB_ACK_REQUESTED, &ic->i_ack_flags);
+        smp_mb__after_clear_bit();
+
+        return ic->i_ack_next;
+}
+
+static void rds_iw_send_ack(struct rds_iw_connection *ic, unsigned int adv_credits)
+{
+        struct rds_header *hdr = ic->i_ack;
+        struct ib_send_wr *failed_wr;
+        u64 seq;
+        int ret;
+
+        seq = rds_iw_get_ack(ic);
+
+        rdsdebug("send_ack: ic %p ack %llu\n", ic, (unsigned long long) seq);
+        rds_message_populate_header(hdr, 0, 0, 0);
+        hdr->h_ack = cpu_to_be64(seq);
+        hdr->h_credit = adv_credits;
+        rds_message_make_checksum(hdr);
+        ic->i_ack_queued = jiffies;
+
+        ret = ib_post_send(ic->i_cm_id->qp, &ic->i_ack_wr, &failed_wr);
+        if (unlikely(ret)) {
+                /* Failed to send. Release the WR, and
+                 * force another ACK.
+                 */
+                clear_bit(IB_ACK_IN_FLIGHT, &ic->i_ack_flags);
+                set_bit(IB_ACK_REQUESTED, &ic->i_ack_flags);
+
+                rds_iw_stats_inc(s_iw_ack_send_failure);
+                /* Need to finesse this later. */
+                BUG();
+        } else
+                rds_iw_stats_inc(s_iw_ack_sent);
+}
+
+/*
+ * There are 3 ways of getting acknowledgements to the peer:
+ *  1.  We call rds_iw_attempt_ack from the recv completion handler
+ *      to send an ACK-only frame.
+ *      However, there can be only one such frame in the send queue
+ *      at any time, so we may have to postpone it.
+ *  2.  When another (data) packet is transmitted while there's
+ *      an ACK in the queue, we piggyback the ACK sequence number
+ *      on the data packet.
+ *  3.  If the ACK WR is done sending, we get called from the
+ *      send queue completion handler, and check whether there's
+ *      another ACK pending (postponed because the WR was on the
+ *      queue). If so, we transmit it.
+ *
+ * We maintain 2 variables:
+ *  -   i_ack_flags, which keeps track of whether the ACK WR
+ *      is currently in the send queue or not (IB_ACK_IN_FLIGHT)
+ *  -   i_ack_next, which is the last sequence number we received
+ *
+ * Potentially, send queue and receive queue handlers can run concurrently.
+ *
+ * Reconnecting complicates this picture just slightly. When we
+ * reconnect, we may be seeing duplicate packets. The peer
+ * is retransmitting them, because it hasn't seen an ACK for
+ * them. It is important that we ACK these.
+ *
+ * ACK mitigation adds a header flag "ACK_REQUIRED"; any packet with
+ * this flag set *MUST* be acknowledged immediately.
+ */
+
+/*
+ * When we get here, we're called from the recv queue handler.
+ * Check whether we ought to transmit an ACK.
+ */
+void rds_iw_attempt_ack(struct rds_iw_connection *ic)
+{
+        unsigned int adv_credits;
+
+        if (!test_bit(IB_ACK_REQUESTED, &ic->i_ack_flags))
+                return;
+
+        if (test_and_set_bit(IB_ACK_IN_FLIGHT, &ic->i_ack_flags)) {
+                rds_iw_stats_inc(s_iw_ack_send_delayed);
+                return;
+        }
+
+        /* Can we get a send credit? */
+        if (!rds_iw_send_grab_credits(ic, 1, &adv_credits, 0)) {
+                rds_iw_stats_inc(s_iw_tx_throttle);
+                clear_bit(IB_ACK_IN_FLIGHT, &ic->i_ack_flags);
+                return;
+        }
+
+        clear_bit(IB_ACK_REQUESTED, &ic->i_ack_flags);
+        rds_iw_send_ack(ic, adv_credits);
+}
+
+/*
+ * We get here from the send completion handler, when the
+ * adapter tells us the ACK frame was sent.
+ */
+void rds_iw_ack_send_complete(struct rds_iw_connection *ic)
+{
+        clear_bit(IB_ACK_IN_FLIGHT, &ic->i_ack_flags);
+        rds_iw_attempt_ack(ic);
+}
+
+/*
+ * This is called by the regular xmit code when it wants to piggyback
+ * an ACK on an outgoing frame.
+ */
+u64 rds_iw_piggyb_ack(struct rds_iw_connection *ic)
+{
+        if (test_and_clear_bit(IB_ACK_REQUESTED, &ic->i_ack_flags))
+                rds_iw_stats_inc(s_iw_ack_send_piggybacked);
+        return rds_iw_get_ack(ic);
+}
+
+/*
+ * It's kind of lame that we're copying from the posted receive pages into
+ * long-lived bitmaps.  We could have posted the bitmaps and rdma written into
+ * them.  But receiving new congestion bitmaps should be a *rare* event, so
+ * hopefully we won't need to invest that complexity in making it more
+ * efficient.  By copying we can share a simpler core with TCP which has to
+ * copy.
+ */
+static void rds_iw_cong_recv(struct rds_connection *conn,
+                              struct rds_iw_incoming *iwinc)
+{
+        struct rds_cong_map *map;
+        unsigned int map_off;
+        unsigned int map_page;
+        struct rds_page_frag *frag;
+        unsigned long frag_off;
+        unsigned long to_copy;
+        unsigned long copied;
+        uint64_t uncongested = 0;
+        void *addr;
+
+        /* catch completely corrupt packets */
+        if (be32_to_cpu(iwinc->ii_inc.i_hdr.h_len) != RDS_CONG_MAP_BYTES)
+                return;
+
+        map = conn->c_fcong;
+        map_page = 0;
+        map_off = 0;
+
+        frag = list_entry(iwinc->ii_frags.next, struct rds_page_frag, f_item);
+        frag_off = 0;
+
+        copied = 0;
+
+        while (copied < RDS_CONG_MAP_BYTES) {
+                uint64_t *src, *dst;
+                unsigned int k;
+
+                to_copy = min(RDS_FRAG_SIZE - frag_off, PAGE_SIZE - map_off);
+                BUG_ON(to_copy & 7); /* Must be 64bit aligned. */
+
+                addr = kmap_atomic(frag->f_page, KM_SOFTIRQ0);
+
+                src = addr + frag_off;
+                dst = (void *)map->m_page_addrs[map_page] + map_off;
+                for (k = 0; k < to_copy; k += 8) {
+                        /* Record ports that became uncongested, ie
+                         * bits that changed from 0 to 1. */
+                        uncongested |= ~(*src) & *dst;
+                        *dst++ = *src++;
+                }
+                kunmap_atomic(addr, KM_SOFTIRQ0);
+
+                copied += to_copy;
+
+                map_off += to_copy;
+                if (map_off == PAGE_SIZE) {
+                        map_off = 0;
+                        map_page++;
+                }
+
+                frag_off += to_copy;
+                if (frag_off == RDS_FRAG_SIZE) {
+                        frag = list_entry(frag->f_item.next,
+                                          struct rds_page_frag, f_item);
+                        frag_off = 0;
+                }
+        }
+
+        /* the congestion map is in little endian order */
+        uncongested = le64_to_cpu(uncongested);
+
+        rds_cong_map_updated(map, uncongested);
+}
+
+/*
+ * Rings are posted with all the allocations they'll need to queue the
+ * incoming message to the receiving socket so this can't fail.
+ * All fragments start with a header, so we can make sure we're not receiving
+ * garbage, and we can tell a small 8 byte fragment from an ACK frame.
+ */
+struct rds_iw_ack_state {
+        u64             ack_next;
+        u64             ack_recv;
+        unsigned int    ack_required:1;
+        unsigned int    ack_next_valid:1;
+        unsigned int    ack_recv_valid:1;
+};
+
+static void rds_iw_process_recv(struct rds_connection *conn,
+                                struct rds_iw_recv_work *recv, u32 byte_len,
+                                struct rds_iw_ack_state *state)
+{
+        struct rds_iw_connection *ic = conn->c_transport_data;
+        struct rds_iw_incoming *iwinc = ic->i_iwinc;
+        struct rds_header *ihdr, *hdr;
+
+        /* XXX shut down the connection if port 0,0 are seen? */
+
+        rdsdebug("ic %p iwinc %p recv %p byte len %u\n", ic, iwinc, recv,
+                 byte_len);
+
+        if (byte_len < sizeof(struct rds_header)) {
+                rds_iw_conn_error(conn, "incoming message "
+                       "from %pI4 didn't inclue a "
+                       "header, disconnecting and "
+                       "reconnecting\n",
+                       &conn->c_faddr);
+                return;
+        }
+        byte_len -= sizeof(struct rds_header);
+
+        ihdr = &ic->i_recv_hdrs[recv - ic->i_recvs];
+
+        /* Validate the checksum. */
+        if (!rds_message_verify_checksum(ihdr)) {
+                rds_iw_conn_error(conn, "incoming message "
+                       "from %pI4 has corrupted header - "
+                       "forcing a reconnect\n",
+                       &conn->c_faddr);
+                rds_stats_inc(s_recv_drop_bad_checksum);
+                return;
+        }
+
+        /* Process the ACK sequence which comes with every packet */
+        state->ack_recv = be64_to_cpu(ihdr->h_ack);
+        state->ack_recv_valid = 1;
+
+        /* Process the credits update if there was one */
+        if (ihdr->h_credit)
+                rds_iw_send_add_credits(conn, ihdr->h_credit);
+
+        if (ihdr->h_sport == 0 && ihdr->h_dport == 0 && byte_len == 0) {
+                /* This is an ACK-only packet. The fact that it gets
+                 * special treatment here is that historically, ACKs
+                 * were rather special beasts.
+                 */
+                rds_iw_stats_inc(s_iw_ack_received);
+
+                /*
+                 * Usually the frags make their way on to incs and are then freed as
+                 * the inc is freed.  We don't go that route, so we have to drop the
+                 * page ref ourselves.  We can't just leave the page on the recv
+                 * because that confuses the dma mapping of pages and each recv's use
+                 * of a partial page.  We can leave the frag, though, it will be
+                 * reused.
+                 *
+                 * FIXME: Fold this into the code path below.
+                 */
+                rds_iw_frag_drop_page(recv->r_frag);
+                return;
+        }
+
+        /*
+         * If we don't already have an inc on the connection then this
+         * fragment has a header and starts a message.. copy its header
+         * into the inc and save the inc so we can hang upcoming fragments
+         * off its list.
+         */
+        if (iwinc == NULL) {
+                iwinc = recv->r_iwinc;
+                recv->r_iwinc = NULL;
+                ic->i_iwinc = iwinc;
+
+                hdr = &iwinc->ii_inc.i_hdr;
+                memcpy(hdr, ihdr, sizeof(*hdr));
+                ic->i_recv_data_rem = be32_to_cpu(hdr->h_len);
+
+                rdsdebug("ic %p iwinc %p rem %u flag 0x%x\n", ic, iwinc,
+                         ic->i_recv_data_rem, hdr->h_flags);
+        } else {
+                hdr = &iwinc->ii_inc.i_hdr;
+                /* We can't just use memcmp here; fragments of a
+                 * single message may carry different ACKs */
+                if (hdr->h_sequence != ihdr->h_sequence
+                 || hdr->h_len != ihdr->h_len
+                 || hdr->h_sport != ihdr->h_sport
+                 || hdr->h_dport != ihdr->h_dport) {
+                        rds_iw_conn_error(conn,
+                                "fragment header mismatch; forcing reconnect\n");
+                        return;
+                }
+        }
+
+        list_add_tail(&recv->r_frag->f_item, &iwinc->ii_frags);
+        recv->r_frag = NULL;
+
+        if (ic->i_recv_data_rem > RDS_FRAG_SIZE)
+                ic->i_recv_data_rem -= RDS_FRAG_SIZE;
+        else {
+                ic->i_recv_data_rem = 0;
+                ic->i_iwinc = NULL;
+
+                if (iwinc->ii_inc.i_hdr.h_flags == RDS_FLAG_CONG_BITMAP)
+                        rds_iw_cong_recv(conn, iwinc);
+                else {
+                        rds_recv_incoming(conn, conn->c_faddr, conn->c_laddr,
+                                          &iwinc->ii_inc, GFP_ATOMIC,
+                                          KM_SOFTIRQ0);
+                        state->ack_next = be64_to_cpu(hdr->h_sequence);
+                        state->ack_next_valid = 1;
+                }
+
+                /* Evaluate the ACK_REQUIRED flag *after* we received
+                 * the complete frame, and after bumping the next_rx
+                 * sequence. */
+                if (hdr->h_flags & RDS_FLAG_ACK_REQUIRED) {
+                        rds_stats_inc(s_recv_ack_required);
+                        state->ack_required = 1;
+                }
+
+                rds_inc_put(&iwinc->ii_inc);
+        }
+}
+
+/*
+ * Plucking the oldest entry from the ring can be done concurrently with
+ * the thread refilling the ring.  Each ring operation is protected by
+ * spinlocks and the transient state of refilling doesn't change the
+ * recording of which entry is oldest.
+ *
+ * This relies on IB only calling one cq comp_handler for each cq so that
+ * there will only be one caller of rds_recv_incoming() per RDS connection.
+ */
+void rds_iw_recv_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_ack_state state = { 0, };
+        struct rds_iw_recv_work *recv;
+
+        rdsdebug("conn %p cq %p\n", conn, cq);
+
+        rds_iw_stats_inc(s_iw_rx_cq_call);
+
+        ib_req_notify_cq(cq, IB_CQ_SOLICITED);
+
+        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_rx_cq_event);
+
+                recv = &ic->i_recvs[rds_iw_ring_oldest(&ic->i_recv_ring)];
+
+                rds_iw_recv_unmap_page(ic, recv);
+
+                /*
+                 * Also process recvs in connecting state because it is possible
+                 * to get a recv completion _before_ the rdmacm ESTABLISHED
+                 * event is processed.
+                 */
+                if (rds_conn_up(conn) || rds_conn_connecting(conn)) {
+                        /* We expect errors as the qp is drained during shutdown */
+                        if (wc.status == IB_WC_SUCCESS) {
+                                rds_iw_process_recv(conn, recv, wc.byte_len, &state);
+                        } else {
+                                rds_iw_conn_error(conn, "recv completion on "
+                                       "%pI4 had status %u, disconnecting and "
+                                       "reconnecting\n", &conn->c_faddr,
+                                       wc.status);
+                        }
+                }
+
+                rds_iw_ring_free(&ic->i_recv_ring, 1);
+        }
+
+        if (state.ack_next_valid)
+                rds_iw_set_ack(ic, state.ack_next, state.ack_required);
+        if (state.ack_recv_valid && state.ack_recv > ic->i_ack_recv) {
+                rds_send_drop_acked(conn, state.ack_recv, NULL);
+                ic->i_ack_recv = state.ack_recv;
+        }
+        if (rds_conn_up(conn))
+                rds_iw_attempt_ack(ic);
+
+        /* If we ever end up with a really empty receive ring, we're
+         * in deep trouble, as the sender will definitely see RNR
+         * timeouts. */
+        if (rds_iw_ring_empty(&ic->i_recv_ring))
+                rds_iw_stats_inc(s_iw_rx_ring_empty);
+
+        /*
+         * If the ring is running low, then schedule the thread to refill.
+         */
+        if (rds_iw_ring_low(&ic->i_recv_ring))
+                queue_delayed_work(rds_wq, &conn->c_recv_w, 0);
+}
+
+int rds_iw_recv(struct rds_connection *conn)
+{
+        struct rds_iw_connection *ic = conn->c_transport_data;
+        int ret = 0;
+
+        rdsdebug("conn %p\n", conn);
+
+        /*
+         * If we get a temporary posting failure in this context then
+         * we're really low and we want the caller to back off for a bit.
+         */
+        mutex_lock(&ic->i_recv_mutex);
+        if (rds_iw_recv_refill(conn, GFP_KERNEL, GFP_HIGHUSER, 0))
+                ret = -ENOMEM;
+        else
+                rds_iw_stats_inc(s_iw_rx_refill_from_thread);
+        mutex_unlock(&ic->i_recv_mutex);
+
+        if (rds_conn_up(conn))
+                rds_iw_attempt_ack(ic);
+
+        return ret;
+}
+
+int __init rds_iw_recv_init(void)
+{
+        struct sysinfo si;
+        int ret = -ENOMEM;
+
+        /* Default to 30% of all available RAM for recv memory */
+        si_meminfo(&si);
+        rds_iw_sysctl_max_recv_allocation = si.totalram / 3 * PAGE_SIZE / RDS_FRAG_SIZE;
+
+        rds_iw_incoming_slab = kmem_cache_create("rds_iw_incoming",
+                                        sizeof(struct rds_iw_incoming),
+                                        0, 0, NULL);
+        if (rds_iw_incoming_slab == NULL)
+                goto out;
+
+        rds_iw_frag_slab = kmem_cache_create("rds_iw_frag",
+                                        sizeof(struct rds_page_frag),
+                                        0, 0, NULL);
+        if (rds_iw_frag_slab == NULL)
+                kmem_cache_destroy(rds_iw_incoming_slab);
+        else
+                ret = 0;
+out:
+        return ret;
+}
+
+void rds_iw_recv_exit(void)
+{
+        kmem_cache_destroy(rds_iw_incoming_slab);
+        kmem_cache_destroy(rds_iw_frag_slab);
+}