/*
 * 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/slab.h>
#include <linux/pci.h>
#include <linux/dma-mapping.h>
#include <rdma/rdma_cm.h>

#include "rds_single_path.h"
#include "rds.h"
#include "ib.h"

static struct kmem_cache *rds_ib_incoming_slab;
static struct kmem_cache *rds_ib_frag_slab;
static atomic_t rds_ib_allocation = ATOMIC_INIT(0);

void rds_ib_recv_init_ring(struct rds_ib_connection *ic)
{
        struct rds_ib_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_ibinc = 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_IB_RECV_SGE;

                sge = &recv->r_sge[0];
                sge->addr = ic->i_recv_hdrs_dma[i];
                sge->length = sizeof(struct rds_header);
                sge->lkey = ic->i_pd->local_dma_lkey;

                sge = &recv->r_sge[1];
                sge->addr = 0;
                sge->length = RDS_FRAG_SIZE;
                sge->lkey = ic->i_pd->local_dma_lkey;
        }
}

/*
 * The entire 'from' list, including the from element itself, is put on
 * to the tail of the 'to' list.
 */
static void list_splice_entire_tail(struct list_head *from,
                                    struct list_head *to)
{
        struct list_head *from_last = from->prev;

        list_splice_tail(from_last, to);
        list_add_tail(from_last, to);
}

static void rds_ib_cache_xfer_to_ready(struct rds_ib_refill_cache *cache)
{
        struct list_head *tmp;

        tmp = xchg(&cache->xfer, NULL);
        if (tmp) {
                if (cache->ready)
                        list_splice_entire_tail(tmp, cache->ready);
                else
                        cache->ready = tmp;
        }
}

static int rds_ib_recv_alloc_cache(struct rds_ib_refill_cache *cache, gfp_t gfp)
{
        struct rds_ib_cache_head *head;
        int cpu;

        cache->percpu = alloc_percpu_gfp(struct rds_ib_cache_head, gfp);
        if (!cache->percpu)
               return -ENOMEM;

        for_each_possible_cpu(cpu) {
                head = per_cpu_ptr(cache->percpu, cpu);
                head->first = NULL;
                head->count = 0;
        }
        cache->xfer = NULL;
        cache->ready = NULL;

        return 0;
}

int rds_ib_recv_alloc_caches(struct rds_ib_connection *ic, gfp_t gfp)
{
        int ret;

        ret = rds_ib_recv_alloc_cache(&ic->i_cache_incs, gfp);
        if (!ret) {
                ret = rds_ib_recv_alloc_cache(&ic->i_cache_frags, gfp);
                if (ret)
                        free_percpu(ic->i_cache_incs.percpu);
        }

        return ret;
}

static void rds_ib_cache_splice_all_lists(struct rds_ib_refill_cache *cache,
                                          struct list_head *caller_list)
{
        struct rds_ib_cache_head *head;
        int cpu;

        for_each_possible_cpu(cpu) {
                head = per_cpu_ptr(cache->percpu, cpu);
                if (head->first) {
                        list_splice_entire_tail(head->first, caller_list);
                        head->first = NULL;
                }
        }

        if (cache->ready) {
                list_splice_entire_tail(cache->ready, caller_list);
                cache->ready = NULL;
        }
}

void rds_ib_recv_free_caches(struct rds_ib_connection *ic)
{
        struct rds_ib_incoming *inc;
        struct rds_ib_incoming *inc_tmp;
        struct rds_page_frag *frag;
        struct rds_page_frag *frag_tmp;
        LIST_HEAD(list);

        rds_ib_cache_xfer_to_ready(&ic->i_cache_incs);
        rds_ib_cache_splice_all_lists(&ic->i_cache_incs, &list);
        free_percpu(ic->i_cache_incs.percpu);

        list_for_each_entry_safe(inc, inc_tmp, &list, ii_cache_entry) {
                list_del(&inc->ii_cache_entry);
                WARN_ON(!list_empty(&inc->ii_frags));
                kmem_cache_free(rds_ib_incoming_slab, inc);
                atomic_dec(&rds_ib_allocation);
        }

        rds_ib_cache_xfer_to_ready(&ic->i_cache_frags);
        rds_ib_cache_splice_all_lists(&ic->i_cache_frags, &list);
        free_percpu(ic->i_cache_frags.percpu);

        list_for_each_entry_safe(frag, frag_tmp, &list, f_cache_entry) {
                list_del(&frag->f_cache_entry);
                WARN_ON(!list_empty(&frag->f_item));
                kmem_cache_free(rds_ib_frag_slab, frag);
        }
}

/* fwd decl */
static void rds_ib_recv_cache_put(struct list_head *new_item,
                                  struct rds_ib_refill_cache *cache);
static struct list_head *rds_ib_recv_cache_get(struct rds_ib_refill_cache *cache);


/* Recycle frag and attached recv buffer f_sg */
static void rds_ib_frag_free(struct rds_ib_connection *ic,
                             struct rds_page_frag *frag)
{
        rdsdebug("frag %p page %p\n", frag, sg_page(&frag->f_sg));

        rds_ib_recv_cache_put(&frag->f_cache_entry, &ic->i_cache_frags);
        atomic_add(RDS_FRAG_SIZE / SZ_1K, &ic->i_cache_allocs);
        rds_ib_stats_add(s_ib_recv_added_to_cache, RDS_FRAG_SIZE);
}

/* Recycle inc after freeing attached frags */
void rds_ib_inc_free(struct rds_incoming *inc)
{
        struct rds_ib_incoming *ibinc;
        struct rds_page_frag *frag;
        struct rds_page_frag *pos;
        struct rds_ib_connection *ic = inc->i_conn->c_transport_data;

        ibinc = container_of(inc, struct rds_ib_incoming, ii_inc);

        /* Free attached frags */
        list_for_each_entry_safe(frag, pos, &ibinc->ii_frags, f_item) {
                list_del_init(&frag->f_item);
                rds_ib_frag_free(ic, frag);
        }
        BUG_ON(!list_empty(&ibinc->ii_frags));

        rdsdebug("freeing ibinc %p inc %p\n", ibinc, inc);
        rds_ib_recv_cache_put(&ibinc->ii_cache_entry, &ic->i_cache_incs);
}

static void rds_ib_recv_clear_one(struct rds_ib_connection *ic,
                                  struct rds_ib_recv_work *recv)
{
        if (recv->r_ibinc) {
                rds_inc_put(&recv->r_ibinc->ii_inc);
                recv->r_ibinc = NULL;
        }
        if (recv->r_frag) {
                ib_dma_unmap_sg(ic->i_cm_id->device, &recv->r_frag->f_sg, 1, DMA_FROM_DEVICE);
                rds_ib_frag_free(ic, recv->r_frag);
                recv->r_frag = NULL;
        }
}

void rds_ib_recv_clear_ring(struct rds_ib_connection *ic)
{
        u32 i;

        for (i = 0; i < ic->i_recv_ring.w_nr; i++)
                rds_ib_recv_clear_one(ic, &ic->i_recvs[i]);
}

static struct rds_ib_incoming *rds_ib_refill_one_inc(struct rds_ib_connection *ic,
                                                     gfp_t slab_mask)
{
        struct rds_ib_incoming *ibinc;
        struct list_head *cache_item;
        int avail_allocs;

        cache_item = rds_ib_recv_cache_get(&ic->i_cache_incs);
        if (cache_item) {
                ibinc = container_of(cache_item, struct rds_ib_incoming, ii_cache_entry);
        } else {
                avail_allocs = atomic_add_unless(&rds_ib_allocation,
                                                 1, rds_ib_sysctl_max_recv_allocation);
                if (!avail_allocs) {
                        rds_ib_stats_inc(s_ib_rx_alloc_limit);
                        return NULL;
                }
                ibinc = kmem_cache_alloc(rds_ib_incoming_slab, slab_mask);
                if (!ibinc) {
                        atomic_dec(&rds_ib_allocation);
                        return NULL;
                }
                rds_ib_stats_inc(s_ib_rx_total_incs);
        }
        INIT_LIST_HEAD(&ibinc->ii_frags);
        rds_inc_init(&ibinc->ii_inc, ic->conn, &ic->conn->c_faddr);

        return ibinc;
}

static struct rds_page_frag *rds_ib_refill_one_frag(struct rds_ib_connection *ic,
                                                    gfp_t slab_mask, gfp_t page_mask)
{
        struct rds_page_frag *frag;
        struct list_head *cache_item;
        int ret;

        cache_item = rds_ib_recv_cache_get(&ic->i_cache_frags);
        if (cache_item) {
                frag = container_of(cache_item, struct rds_page_frag, f_cache_entry);
                atomic_sub(RDS_FRAG_SIZE / SZ_1K, &ic->i_cache_allocs);
                rds_ib_stats_add(s_ib_recv_added_to_cache, RDS_FRAG_SIZE);
        } else {
                frag = kmem_cache_alloc(rds_ib_frag_slab, slab_mask);
                if (!frag)
                        return NULL;

                sg_init_table(&frag->f_sg, 1);
                ret = rds_page_remainder_alloc(&frag->f_sg,
                                               RDS_FRAG_SIZE, page_mask);
                if (ret) {
                        kmem_cache_free(rds_ib_frag_slab, frag);
                        return NULL;
                }
                rds_ib_stats_inc(s_ib_rx_total_frags);
        }

        INIT_LIST_HEAD(&frag->f_item);

        return frag;
}

static int rds_ib_recv_refill_one(struct rds_connection *conn,
                                  struct rds_ib_recv_work *recv, gfp_t gfp)
{
        struct rds_ib_connection *ic = conn->c_transport_data;
        struct ib_sge *sge;
        int ret = -ENOMEM;
        gfp_t slab_mask = gfp;
        gfp_t page_mask = gfp;

        if (gfp & __GFP_DIRECT_RECLAIM) {
                slab_mask = GFP_KERNEL;
                page_mask = GFP_HIGHUSER;
        }

        if (!ic->i_cache_incs.ready)
                rds_ib_cache_xfer_to_ready(&ic->i_cache_incs);
        if (!ic->i_cache_frags.ready)
                rds_ib_cache_xfer_to_ready(&ic->i_cache_frags);

        /*
         * ibinc was taken from recv if recv contained the start of a message.
         * recvs that were continuations will still have this allocated.
         */
        if (!recv->r_ibinc) {
                recv->r_ibinc = rds_ib_refill_one_inc(ic, slab_mask);
                if (!recv->r_ibinc)
                        goto out;
        }

        WARN_ON(recv->r_frag); /* leak! */
        recv->r_frag = rds_ib_refill_one_frag(ic, slab_mask, page_mask);
        if (!recv->r_frag)
                goto out;

        ret = ib_dma_map_sg(ic->i_cm_id->device, &recv->r_frag->f_sg,
                            1, DMA_FROM_DEVICE);
        WARN_ON(ret != 1);

        sge = &recv->r_sge[0];
        sge->addr = ic->i_recv_hdrs_dma[recv - ic->i_recvs];
        sge->length = sizeof(struct rds_header);

        sge = &recv->r_sge[1];
        sge->addr = sg_dma_address(&recv->r_frag->f_sg);
        sge->length = sg_dma_len(&recv->r_frag->f_sg);

        ret = 0;
out:
        return ret;
}

static int acquire_refill(struct rds_connection *conn)
{
        return test_and_set_bit(RDS_RECV_REFILL, &conn->c_flags) == 0;
}

static void release_refill(struct rds_connection *conn)
{
        clear_bit(RDS_RECV_REFILL, &conn->c_flags);

        /* We don't use wait_on_bit()/wake_up_bit() because our waking is in a
         * hot path and finding waiters is very rare.  We don't want to walk
         * the system-wide hashed waitqueue buckets in the fast path only to
         * almost never find waiters.
         */
        if (waitqueue_active(&conn->c_waitq))
                wake_up_all(&conn->c_waitq);
}

/*
 * 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.
 */
void rds_ib_recv_refill(struct rds_connection *conn, int prefill, gfp_t gfp)
{
        struct rds_ib_connection *ic = conn->c_transport_data;
        struct rds_ib_recv_work *recv;
        unsigned int posted = 0;
        int ret = 0;
        bool can_wait = !!(gfp & __GFP_DIRECT_RECLAIM);
        bool must_wake = false;
        u32 pos;

        /* the goal here is to just make sure that someone, somewhere
         * is posting buffers.  If we can't get the refill lock,
         * let them do their thing
         */
        if (!acquire_refill(conn))
                return;

        while ((prefill || rds_conn_up(conn)) &&
               rds_ib_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);
                        break;
                }

                recv = &ic->i_recvs[pos];
                ret = rds_ib_recv_refill_one(conn, recv, gfp);
                if (ret) {
                        must_wake = true;
                        break;
                }

                rdsdebug("recv %p ibinc %p page %p addr %lu\n", recv,
                         recv->r_ibinc, sg_page(&recv->r_frag->f_sg),
                         (long)sg_dma_address(&recv->r_frag->f_sg));

                /* XXX when can this fail? */
                ret = ib_post_recv(ic->i_cm_id->qp, &recv->r_wr, NULL);
                if (ret) {
                        rds_ib_conn_error(conn, "recv post on "
                               "%pI6c returned %d, disconnecting and "
                               "reconnecting\n", &conn->c_faddr,
                               ret);
                        break;
                }

                posted++;

                if ((posted > 128 && need_resched()) || posted > 8192) {
                        must_wake = true;
                        break;
                }
        }

        /* We're doing flow control - update the window. */
        if (ic->i_flowctl && posted)
                rds_ib_advertise_credits(conn, posted);

        if (ret)
                rds_ib_ring_unalloc(&ic->i_recv_ring, 1);

        release_refill(conn);

        /* if we're called from the softirq handler, we'll be GFP_NOWAIT.
         * in this case the ring being low is going to lead to more interrupts
         * and we can safely let the softirq code take care of it unless the
         * ring is completely empty.
         *
         * if we're called from krdsd, we'll be GFP_KERNEL.  In this case
         * we might have raced with the softirq code while we had the refill
         * lock held.  Use rds_ib_ring_low() instead of ring_empty to decide
         * if we should requeue.
         */
        if (rds_conn_up(conn) &&
            (must_wake ||
            (can_wait && rds_ib_ring_low(&ic->i_recv_ring)) ||
            rds_ib_ring_empty(&ic->i_recv_ring))) {
                queue_delayed_work(rds_wq, &conn->c_recv_w, 1);
        }
        if (can_wait)
                cond_resched();
}

/*
 * We want to recycle several types of recv allocations, like incs and frags.
 * To use this, the *_free() function passes in the ptr to a list_head within
 * the recyclee, as well as the cache to put it on.
 *
 * First, we put the memory on a percpu list. When this reaches a certain size,
 * We move it to an intermediate non-percpu list in a lockless manner, with some
 * xchg/compxchg wizardry.
 *
 * N.B. Instead of a list_head as the anchor, we use a single pointer, which can
 * be NULL and xchg'd. The list is actually empty when the pointer is NULL, and
 * list_empty() will return true with one element is actually present.
 */
static void rds_ib_recv_cache_put(struct list_head *new_item,
                                 struct rds_ib_refill_cache *cache)
{
        unsigned long flags;
        struct list_head *old, *chpfirst;

        local_irq_save(flags);

        chpfirst = __this_cpu_read(cache->percpu->first);
        if (!chpfirst)
                INIT_LIST_HEAD(new_item);
        else /* put on front */
                list_add_tail(new_item, chpfirst);

        __this_cpu_write(cache->percpu->first, new_item);
        __this_cpu_inc(cache->percpu->count);

        if (__this_cpu_read(cache->percpu->count) < RDS_IB_RECYCLE_BATCH_COUNT)
                goto end;

        /*
         * Return our per-cpu first list to the cache's xfer by atomically
         * grabbing the current xfer list, appending it to our per-cpu list,
         * and then atomically returning that entire list back to the
         * cache's xfer list as long as it's still empty.
         */
        do {
                old = xchg(&cache->xfer, NULL);
                if (old)
                        list_splice_entire_tail(old, chpfirst);
                old = cmpxchg(&cache->xfer, NULL, chpfirst);
        } while (old);


        __this_cpu_write(cache->percpu->first, NULL);
        __this_cpu_write(cache->percpu->count, 0);
end:
        local_irq_restore(flags);
}

static struct list_head *rds_ib_recv_cache_get(struct rds_ib_refill_cache *cache)
{
        struct list_head *head = cache->ready;

        if (head) {
                if (!list_empty(head)) {
                        cache->ready = head->next;
                        list_del_init(head);
                } else
                        cache->ready = NULL;
        }

        return head;
}

int rds_ib_inc_copy_to_user(struct rds_incoming *inc, struct iov_iter *to)
{
        struct rds_ib_incoming *ibinc;
        struct rds_page_frag *frag;
        unsigned long to_copy;
        unsigned long frag_off = 0;
        int copied = 0;
        int ret;
        u32 len;

        ibinc = container_of(inc, struct rds_ib_incoming, ii_inc);
        frag = list_entry(ibinc->ii_frags.next, struct rds_page_frag, f_item);
        len = be32_to_cpu(inc->i_hdr.h_len);

        while (iov_iter_count(to) && copied < len) {
                if (frag_off == RDS_FRAG_SIZE) {
                        frag = list_entry(frag->f_item.next,
                                          struct rds_page_frag, f_item);
                        frag_off = 0;
                }
                to_copy = min_t(unsigned long, iov_iter_count(to),
                                RDS_FRAG_SIZE - frag_off);
                to_copy = min_t(unsigned long, to_copy, len - copied);

                /* XXX needs + offset for multiple recvs per page */
                rds_stats_add(s_copy_to_user, to_copy);
                ret = copy_page_to_iter(sg_page(&frag->f_sg),
                                        frag->f_sg.offset + frag_off,
                                        to_copy,
                                        to);
                if (ret != to_copy)
                        return -EFAULT;

                frag_off += to_copy;
                copied += to_copy;
        }

        return copied;
}

/* ic starts out kzalloc()ed */
void rds_ib_recv_init_ack(struct rds_ib_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 = ic->i_pd->local_dma_lkey;

        wr->sg_list = sge;
        wr->num_sge = 1;
        wr->opcode = IB_WR_SEND;
        wr->wr_id = RDS_IB_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.
 */
#ifndef KERNEL_HAS_ATOMIC64
void rds_ib_set_ack(struct rds_ib_connection *ic, u64 seq, int ack_required)
{
        unsigned long flags;

        spin_lock_irqsave(&ic->i_ack_lock, flags);
        ic->i_ack_next = seq;
        if (ack_required)
                set_bit(IB_ACK_REQUESTED, &ic->i_ack_flags);
        spin_unlock_irqrestore(&ic->i_ack_lock, flags);
}

static u64 rds_ib_get_ack(struct rds_ib_connection *ic)
{
        unsigned long flags;
        u64 seq;

        clear_bit(IB_ACK_REQUESTED, &ic->i_ack_flags);

        spin_lock_irqsave(&ic->i_ack_lock, flags);
        seq = ic->i_ack_next;
        spin_unlock_irqrestore(&ic->i_ack_lock, flags);

        return seq;
}
#else
void rds_ib_set_ack(struct rds_ib_connection *ic, u64 seq, int ack_required)
{
        atomic64_set(&ic->i_ack_next, seq);
        if (ack_required) {
                smp_mb__before_atomic();
                set_bit(IB_ACK_REQUESTED, &ic->i_ack_flags);
        }
}

static u64 rds_ib_get_ack(struct rds_ib_connection *ic)
{
        clear_bit(IB_ACK_REQUESTED, &ic->i_ack_flags);
        smp_mb__after_atomic();

        return atomic64_read(&ic->i_ack_next);
}
#endif


static void rds_ib_send_ack(struct rds_ib_connection *ic, unsigned int adv_credits)
{
        struct rds_header *hdr = ic->i_ack;
        u64 seq;
        int ret;

        seq = rds_ib_get_ack(ic);

        rdsdebug("send_ack: ic %p ack %llu\n", ic, (unsigned long long) seq);

        ib_dma_sync_single_for_cpu(ic->rds_ibdev->dev, ic->i_ack_dma,
                                   sizeof(*hdr), DMA_TO_DEVICE);
        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);
        ib_dma_sync_single_for_device(ic->rds_ibdev->dev, ic->i_ack_dma,
                                      sizeof(*hdr), DMA_TO_DEVICE);

        ic->i_ack_queued = jiffies;

        ret = ib_post_send(ic->i_cm_id->qp, &ic->i_ack_wr, NULL);
        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_ib_stats_inc(s_ib_ack_send_failure);

                rds_ib_conn_error(ic->conn, "sending ack failed\n");
        } else
                rds_ib_stats_inc(s_ib_ack_sent);
}

/*
 * There are 3 ways of getting acknowledgements to the peer:
 *  1.  We call rds_ib_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.
 * It would be nice to not have to use a spinlock to synchronize things,
 * but the one problem that rules this out is that 64bit updates are
 * not atomic on all platforms. Things would be a lot simpler if
 * we had atomic64 or maybe cmpxchg64 everywhere.
 *
 * 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_ib_attempt_ack(struct rds_ib_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_ib_stats_inc(s_ib_ack_send_delayed);
                return;
        }

        /* Can we get a send credit? */
        if (!rds_ib_send_grab_credits(ic, 1, &adv_credits, 0, RDS_MAX_ADV_CREDIT)) {
                rds_ib_stats_inc(s_ib_tx_throttle);
                clear_bit(IB_ACK_IN_FLIGHT, &ic->i_ack_flags);
                return;
        }

        clear_bit(IB_ACK_REQUESTED, &ic->i_ack_flags);
        rds_ib_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_ib_ack_send_complete(struct rds_ib_connection *ic)
{
        clear_bit(IB_ACK_IN_FLIGHT, &ic->i_ack_flags);
        rds_ib_attempt_ack(ic);
}

/*
 * This is called by the regular xmit code when it wants to piggyback
 * an ACK on an outgoing frame.
 */
u64 rds_ib_piggyb_ack(struct rds_ib_connection *ic)
{
        if (test_and_clear_bit(IB_ACK_REQUESTED, &ic->i_ack_flags))
                rds_ib_stats_inc(s_ib_ack_send_piggybacked);
        return rds_ib_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_ib_cong_recv(struct rds_connection *conn,
                              struct rds_ib_incoming *ibinc)
{
        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;
        __le64 uncongested = 0;
        void *addr;

        /* catch completely corrupt packets */
        if (be32_to_cpu(ibinc->ii_inc.i_hdr.h_len) != RDS_CONG_MAP_BYTES)
                return;

        map = conn->c_fcong;
        map_page = 0;
        map_off = 0;

        frag = list_entry(ibinc->ii_frags.next, struct rds_page_frag, f_item);
        frag_off = 0;

        copied = 0;

        while (copied < RDS_CONG_MAP_BYTES) {
                __le64 *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(sg_page(&frag->f_sg));

                src = addr + frag->f_sg.offset + 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);

                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 */
        rds_cong_map_updated(map, le64_to_cpu(uncongested));
}

static void rds_ib_process_recv(struct rds_connection *conn,
                                struct rds_ib_recv_work *recv, u32 data_len,
                                struct rds_ib_ack_state *state)
{
        struct rds_ib_connection *ic = conn->c_transport_data;
        struct rds_ib_incoming *ibinc = ic->i_ibinc;
        struct rds_header *ihdr, *hdr;
        dma_addr_t dma_addr = ic->i_recv_hdrs_dma[recv - ic->i_recvs];

        /* XXX shut down the connection if port 0,0 are seen? */

        rdsdebug("ic %p ibinc %p recv %p byte len %u\n", ic, ibinc, recv,
                 data_len);

        if (data_len < sizeof(struct rds_header)) {
                rds_ib_conn_error(conn, "incoming message "
                       "from %pI6c didn't include a "
                       "header, disconnecting and "
                       "reconnecting\n",
                       &conn->c_faddr);
                return;
        }
        data_len -= sizeof(struct rds_header);

        ihdr = ic->i_recv_hdrs[recv - ic->i_recvs];

        ib_dma_sync_single_for_cpu(ic->rds_ibdev->dev, dma_addr,
                                   sizeof(*ihdr), DMA_FROM_DEVICE);
        /* Validate the checksum. */
        if (!rds_message_verify_checksum(ihdr)) {
                rds_ib_conn_error(conn, "incoming message "
                       "from %pI6c has corrupted header - "
                       "forcing a reconnect\n",
                       &conn->c_faddr);
                rds_stats_inc(s_recv_drop_bad_checksum);
                goto done;
        }

        /* 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_ib_send_add_credits(conn, ihdr->h_credit);

        if (ihdr->h_sport == 0 && ihdr->h_dport == 0 && data_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_ib_stats_inc(s_ib_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.
                 *
                 * FIXME: Fold this into the code path below.
                 */
                rds_ib_frag_free(ic, recv->r_frag);
                recv->r_frag = NULL;
                goto done;
        }

        /*
         * 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 (!ibinc) {
                ibinc = recv->r_ibinc;
                recv->r_ibinc = NULL;
                ic->i_ibinc = ibinc;

                hdr = &ibinc->ii_inc.i_hdr;
                ibinc->ii_inc.i_rx_lat_trace[RDS_MSG_RX_HDR] =
                                local_clock();
                memcpy(hdr, ihdr, sizeof(*hdr));
                ic->i_recv_data_rem = be32_to_cpu(hdr->h_len);
                ibinc->ii_inc.i_rx_lat_trace[RDS_MSG_RX_START] =
                                local_clock();

                rdsdebug("ic %p ibinc %p rem %u flag 0x%x\n", ic, ibinc,
                         ic->i_recv_data_rem, hdr->h_flags);
        } else {
                hdr = &ibinc->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_ib_conn_error(conn,
                                "fragment header mismatch; forcing reconnect\n");
                        goto done;
                }
        }

        list_add_tail(&recv->r_frag->f_item, &ibinc->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_ibinc = NULL;

                if (ibinc->ii_inc.i_hdr.h_flags == RDS_FLAG_CONG_BITMAP) {
                        rds_ib_cong_recv(conn, ibinc);
                } else {
                        rds_recv_incoming(conn, &conn->c_faddr, &conn->c_laddr,
                                          &ibinc->ii_inc, GFP_ATOMIC);
                        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(&ibinc->ii_inc);
        }
done:
        ib_dma_sync_single_for_device(ic->rds_ibdev->dev, dma_addr,
                                      sizeof(*ihdr), DMA_FROM_DEVICE);
}

void rds_ib_recv_cqe_handler(struct rds_ib_connection *ic,
                             struct ib_wc *wc,
                             struct rds_ib_ack_state *state)
{
        struct rds_connection *conn = ic->conn;
        struct rds_ib_recv_work *recv;

        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_rx_cq_event);
        recv = &ic->i_recvs[rds_ib_ring_oldest(&ic->i_recv_ring)];
        ib_dma_unmap_sg(ic->i_cm_id->device, &recv->r_frag->f_sg, 1,
                        DMA_FROM_DEVICE);

        /* Also process recvs in connecting state because it is possible
         * to get a recv completion _before_ the rdmacm ESTABLISHED

         * event is processed.
         */
        if (wc->status == IB_WC_SUCCESS) {
                rds_ib_process_recv(conn, recv, wc->byte_len, state);
        } else {
                /* We expect errors as the qp is drained during shutdown */
                if (rds_conn_up(conn) || rds_conn_connecting(conn))
                        rds_ib_conn_error(conn, "recv 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);
        }

        /* rds_ib_process_recv() doesn't always consume the frag, and
         * we might not have called it at all if the wc didn't indicate
         * success. We already unmapped the frag's pages, though, and
         * the following rds_ib_ring_free() call tells the refill path
         * that it will not find an allocated frag here. Make sure we
         * keep that promise by freeing a frag that's still on the ring.
         */
        if (recv->r_frag) {
                rds_ib_frag_free(ic, recv->r_frag);
                recv->r_frag = NULL;
        }
        rds_ib_ring_free(&ic->i_recv_ring, 1);

        /* 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_ib_ring_empty(&ic->i_recv_ring))
                rds_ib_stats_inc(s_ib_rx_ring_empty);

        if (rds_ib_ring_low(&ic->i_recv_ring)) {
                rds_ib_recv_refill(conn, 0, GFP_NOWAIT | __GFP_NOWARN);
                rds_ib_stats_inc(s_ib_rx_refill_from_cq);
        }
}

int rds_ib_recv_path(struct rds_conn_path *cp)
{
        struct rds_connection *conn = cp->cp_conn;
        struct rds_ib_connection *ic = conn->c_transport_data;

        rdsdebug("conn %p\n", conn);
        if (rds_conn_up(conn)) {
                rds_ib_attempt_ack(ic);
                rds_ib_recv_refill(conn, 0, GFP_KERNEL);
                rds_ib_stats_inc(s_ib_rx_refill_from_thread);
        }

        return 0;
}

int rds_ib_recv_init(void)
{
        struct sysinfo si;
        int ret = -ENOMEM;

        /* Default to 30% of all available RAM for recv memory */
        si_meminfo(&si);
        rds_ib_sysctl_max_recv_allocation = si.totalram / 3 * PAGE_SIZE / RDS_FRAG_SIZE;

        rds_ib_incoming_slab =
                kmem_cache_create_usercopy("rds_ib_incoming",
                                           sizeof(struct rds_ib_incoming),
                                           0, SLAB_HWCACHE_ALIGN,
                                           offsetof(struct rds_ib_incoming,
                                                    ii_inc.i_usercopy),
                                           sizeof(struct rds_inc_usercopy),
                                           NULL);
        if (!rds_ib_incoming_slab)
                goto out;

        rds_ib_frag_slab = kmem_cache_create("rds_ib_frag",
                                        sizeof(struct rds_page_frag),
                                        0, SLAB_HWCACHE_ALIGN, NULL);
        if (!rds_ib_frag_slab) {
                kmem_cache_destroy(rds_ib_incoming_slab);
                rds_ib_incoming_slab = NULL;
        } else
                ret = 0;
out:
        return ret;
}

void rds_ib_recv_exit(void)
{
        WARN_ON(atomic_read(&rds_ib_allocation));

        kmem_cache_destroy(rds_ib_incoming_slab);
        kmem_cache_destroy(rds_ib_frag_slab);
}