/*
   * 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/slab.h>

  #include <linux/pci.h>
  #include <linux/dma-mapping.h>
  #include <rdma/rdma_cm.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 * sizeof(struct rds_header));
  		sge->length = sizeof(struct rds_header);
  		sge->lkey = ic->i_mr->lkey;

  
  		sge = &recv->r_sge[1];
  		sge->addr = 0;
  		sge->length = RDS_FRAG_SIZE;
  		sge->lkey = ic->i_mr->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)
  {
  	struct rds_ib_cache_head *head;
  	int cpu;
  
  	cache->percpu = alloc_percpu(struct rds_ib_cache_head);
  	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)
  {
  	int ret;
  
  	ret = rds_ib_recv_alloc_cache(&ic->i_cache_incs);
  	if (!ret) {
  		ret = rds_ib_recv_alloc_cache(&ic->i_cache_frags);
  		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);
  	}
  
  	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
  ", frag, sg_page(&frag->f_sg));
  
  	rds_ib_recv_cache_put(&frag->f_cache_entry, &ic->i_cache_frags);
  }
  
  /* 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
  ", 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;
  		}
  	}
  	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);
  	} 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;
  		}
  	}
  
  	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, int prefill)

  {
  	struct rds_ib_connection *ic = conn->c_transport_data;

  	struct ib_sge *sge;
  	int ret = -ENOMEM;

  	gfp_t slab_mask = GFP_NOWAIT;
  	gfp_t page_mask = GFP_NOWAIT;
  
  	if (prefill) {
  		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) * sizeof(struct rds_header);
  	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;
  }
  
  /*
   * 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.

   *
   * -1 is returned if posting fails due to temporary resource exhaustion.
   */

  void rds_ib_recv_refill(struct rds_connection *conn, int prefill)

  {
  	struct rds_ib_connection *ic = conn->c_transport_data;
  	struct rds_ib_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_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
  ",
  					pos);

  			break;
  		}
  
  		recv = &ic->i_recvs[pos];

  		ret = rds_ib_recv_refill_one(conn, recv, prefill);

  		if (ret) {

  			break;
  		}
  
  		/* XXX when can this fail? */
  		ret = ib_post_recv(ic->i_cm_id->qp, &recv->r_wr, &failed_wr);
  		rdsdebug("recv %p ibinc %p page %p addr %lu ret %d
  ", recv,

  			 recv->r_ibinc, sg_page(&recv->r_frag->f_sg),
  			 (long) sg_dma_address(&recv->r_frag->f_sg), ret);

  		if (ret) {
  			rds_ib_conn_error(conn, "recv post on "
  			       "%pI4 returned %d, disconnecting and "
  			       "reconnecting
  ", &conn->c_faddr,
  			       ret);

  			break;
  		}
  
  		posted++;
  	}
  
  	/* 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);

  }

  /*
   * 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 rds_ib_cache_head *chp;
  	struct list_head *old;

  	local_irq_save(flags);

  	chp = per_cpu_ptr(cache->percpu, smp_processor_id());
  	if (!chp->first)
  		INIT_LIST_HEAD(new_item);
  	else /* put on front */
  		list_add_tail(new_item, chp->first);
  	chp->first = new_item;
  	chp->count++;
  
  	if (chp->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, chp->first);
  		old = cmpxchg(&cache->xfer, NULL, chp->first);
  	} while (old);
  
  	chp->first = NULL;
  	chp->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 iovec *first_iov,
  			    size_t size)
  {
  	struct rds_ib_incoming *ibinc;
  	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;
  
  	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 (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, %u] + %lu
  ",

  			 to_copy, iov->iov_base, iov->iov_len, iov_off,

  			 sg_page(&frag->f_sg), frag->f_sg.offset, frag_off);

  
  		/* XXX needs + offset for multiple recvs per page */

  		ret = rds_page_copy_to_user(sg_page(&frag->f_sg),
  					    frag->f_sg.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_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_mr->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

  static 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
  static 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_clear_bit();
  		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_clear_bit();

  	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;
  	struct ib_send_wr *failed_wr;
  	u64 seq;
  	int ret;
  
  	seq = rds_ib_get_ack(ic);
  
  	rdsdebug("send_ack: ic %p ack %llu
  ", 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_ib_stats_inc(s_ib_ack_send_failure);

  
  		rds_ib_conn_error(ic->conn, "sending ack failed
  ");

  	} 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;
  	uint64_t 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) {
  		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(sg_page(&frag->f_sg), 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_ib_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_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;
  
  	/* XXX shut down the connection if port 0,0 are seen? */
  
  	rdsdebug("ic %p ibinc %p recv %p byte len %u
  ", ic, ibinc, recv,

  		 data_len);

  	if (data_len < sizeof(struct rds_header)) {

  		rds_ib_conn_error(conn, "incoming message "
  		       "from %pI4 didn't inclue a "
  		       "header, disconnecting and "
  		       "reconnecting
  ",
  		       &conn->c_faddr);
  		return;
  	}

  	data_len -= sizeof(struct rds_header);

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

  
  	/* Validate the checksum. */
  	if (!rds_message_verify_checksum(ihdr)) {
  		rds_ib_conn_error(conn, "incoming message "
  		       "from %pI4 has corrupted header - "
  		       "forcing a reconnect
  ",
  		       &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_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;

  		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 (!ibinc) {

  		ibinc = recv->r_ibinc;
  		recv->r_ibinc = NULL;
  		ic->i_ibinc = ibinc;
  
  		hdr = &ibinc->ii_inc.i_hdr;
  		memcpy(hdr, ihdr, sizeof(*hdr));
  		ic->i_recv_data_rem = be32_to_cpu(hdr->h_len);
  
  		rdsdebug("ic %p ibinc %p rem %u flag 0x%x
  ", 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
  ");
  			return;
  		}
  	}
  
  	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,
  					  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(&ibinc->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_ib_recv_cq_comp_handler(struct ib_cq *cq, void *context)
  {
  	struct rds_connection *conn = context;
  	struct rds_ib_connection *ic = conn->c_transport_data;

  
  	rdsdebug("conn %p cq %p
  ", conn, cq);
  
  	rds_ib_stats_inc(s_ib_rx_cq_call);

  	tasklet_schedule(&ic->i_recv_tasklet);
  }

  static inline void rds_poll_cq(struct rds_ib_connection *ic,
  			       struct rds_ib_ack_state *state)
  {
  	struct rds_connection *conn = ic->conn;
  	struct ib_wc wc;
  	struct rds_ib_recv_work *recv;
  
  	while (ib_poll_cq(ic->i_recv_cq, 1, &wc) > 0) {

  		rdsdebug("wc wr_id 0x%llx status %u (%s) byte_len %u imm_data %u
  ",
  			 (unsigned long long)wc.wr_id, wc.status,
  			 rds_ib_wc_status_str(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 %pI4 had "
  						  "status %u (%s), disconnecting and "

  						  "reconnecting
  ", &conn->c_faddr,

  						  wc.status,
  						  rds_ib_wc_status_str(wc.status));

  		}

  		/*
  		 * It's very important that we only free this ring entry if we've truly
  		 * freed the resources allocated to the entry.  The refilling path can
  		 * leak if we don't.
  		 */

  		rds_ib_ring_free(&ic->i_recv_ring, 1);
  	}

  }
  
  void rds_ib_recv_tasklet_fn(unsigned long data)
  {
  	struct rds_ib_connection *ic = (struct rds_ib_connection *) data;
  	struct rds_connection *conn = ic->conn;
  	struct rds_ib_ack_state state = { 0, };
  
  	rds_poll_cq(ic, &state);
  	ib_req_notify_cq(ic->i_recv_cq, IB_CQ_SOLICITED);
  	rds_poll_cq(ic, &state);

  
  	if (state.ack_next_valid)
  		rds_ib_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_ib_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_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);

  }
  
  int rds_ib_recv(struct rds_connection *conn)
  {
  	struct rds_ib_connection *ic = conn->c_transport_data;
  	int ret = 0;
  
  	rdsdebug("conn %p
  ", conn);

  	if (rds_conn_up(conn))
  		rds_ib_attempt_ack(ic);
  
  	return ret;
  }

  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("rds_ib_incoming",
  					sizeof(struct rds_ib_incoming),

  					0, SLAB_HWCACHE_ALIGN, 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);
  	else
  		ret = 0;
  out:
  	return ret;
  }
  
  void rds_ib_recv_exit(void)
  {
  	kmem_cache_destroy(rds_ib_incoming_slab);
  	kmem_cache_destroy(rds_ib_frag_slab);
  }