// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
/*
 * Copyright (c) 2016-2018 Oracle. All rights reserved.
 * Copyright (c) 2014 Open Grid Computing, Inc. All rights reserved.
 * Copyright (c) 2005-2006 Network Appliance, Inc. 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 BSD-type
 * 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.
 *
 *      Neither the name of the Network Appliance, Inc. nor the names of
 *      its contributors may be used to endorse or promote products
 *      derived from this software without specific prior written
 *      permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Author: Tom Tucker <tom@opengridcomputing.com>
 */

/* Operation
 *
 * The main entry point is svc_rdma_sendto. This is called by the
 * RPC server when an RPC Reply is ready to be transmitted to a client.
 *
 * The passed-in svc_rqst contains a struct xdr_buf which holds an
 * XDR-encoded RPC Reply message. sendto must construct the RPC-over-RDMA
 * transport header, post all Write WRs needed for this Reply, then post
 * a Send WR conveying the transport header and the RPC message itself to
 * the client.
 *
 * svc_rdma_sendto must fully transmit the Reply before returning, as
 * the svc_rqst will be recycled as soon as sendto returns. Remaining
 * resources referred to by the svc_rqst are also recycled at that time.
 * Therefore any resources that must remain longer must be detached
 * from the svc_rqst and released later.
 *
 * Page Management
 *
 * The I/O that performs Reply transmission is asynchronous, and may
 * complete well after sendto returns. Thus pages under I/O must be
 * removed from the svc_rqst before sendto returns.
 *
 * The logic here depends on Send Queue and completion ordering. Since
 * the Send WR is always posted last, it will always complete last. Thus
 * when it completes, it is guaranteed that all previous Write WRs have
 * also completed.
 *
 * Write WRs are constructed and posted. Each Write segment gets its own
 * svc_rdma_rw_ctxt, allowing the Write completion handler to find and
 * DMA-unmap the pages under I/O for that Write segment. The Write
 * completion handler does not release any pages.
 *
 * When the Send WR is constructed, it also gets its own svc_rdma_send_ctxt.
 * The ownership of all of the Reply's pages are transferred into that
 * ctxt, the Send WR is posted, and sendto returns.
 *
 * The svc_rdma_send_ctxt is presented when the Send WR completes.
 * The Send completion handler queues the send_ctxt onto the
 * per-transport sc_send_release_list (a lock-free llist). The
 * nfsd thread drains sc_send_release_list in xpo_release_ctxt
 * between RPCs, DMA-unmapping SGEs, releasing chunk I/O
 * resources and pages, and returning send_ctxts to the free
 * list in a batch.
 *
 * Error Handling
 *
 * - If the Send WR is posted successfully, it will either complete
 *   successfully, or get flushed. Either way, the Send completion
 *   handler queues the send_ctxt for deferred release.
 * - If the Send WR cannot be posted, the forward path releases the
 *   Reply's pages.
 *
 * This handles the case, without the use of page reference counting,
 * where two different Write segments send portions of the same page.
 */

#include <linux/spinlock.h>
#include <linux/unaligned.h>

#include <rdma/ib_verbs.h>
#include <rdma/rdma_cm.h>

#include <linux/sunrpc/debug.h>
#include <linux/sunrpc/svc_rdma.h>

#include "xprt_rdma.h"
#include <trace/events/rpcrdma.h>

static void svc_rdma_wc_send(struct ib_cq *cq, struct ib_wc *wc);

static struct svc_rdma_send_ctxt *
svc_rdma_send_ctxt_alloc(struct svcxprt_rdma *rdma)
{
        struct ib_device *device = rdma->sc_cm_id->device;
        int node = ibdev_to_node(device);
        struct svc_rdma_send_ctxt *ctxt;
        unsigned long pages;
        dma_addr_t addr;
        void *buffer;
        int i;

        ctxt = kzalloc_node(struct_size(ctxt, sc_sges, rdma->sc_max_send_sges),
                            GFP_KERNEL, node);
        if (!ctxt)
                goto fail0;
        pages = svc_serv_maxpages(rdma->sc_xprt.xpt_server);
        ctxt->sc_pages = kcalloc_node(pages, sizeof(struct page *),
                                      GFP_KERNEL, node);
        if (!ctxt->sc_pages)
                goto fail1;
        ctxt->sc_maxpages = pages;
        buffer = kmalloc_node(rdma->sc_max_req_size, GFP_KERNEL, node);
        if (!buffer)
                goto fail2;
        addr = ib_dma_map_single(device, buffer, rdma->sc_max_req_size,
                                 DMA_TO_DEVICE);
        if (ib_dma_mapping_error(device, addr))
                goto fail3;

        svc_rdma_send_cid_init(rdma, &ctxt->sc_cid);

        ctxt->sc_rdma = rdma;
        ctxt->sc_send_wr.next = NULL;
        ctxt->sc_send_wr.wr_cqe = &ctxt->sc_cqe;
        ctxt->sc_send_wr.sg_list = ctxt->sc_sges;
        ctxt->sc_send_wr.send_flags = IB_SEND_SIGNALED;
        ctxt->sc_cqe.done = svc_rdma_wc_send;
        INIT_LIST_HEAD(&ctxt->sc_write_info_list);
        ctxt->sc_xprt_buf = buffer;
        xdr_buf_init(&ctxt->sc_hdrbuf, ctxt->sc_xprt_buf,
                     rdma->sc_max_req_size);
        ctxt->sc_sges[0].addr = addr;

        for (i = 0; i < rdma->sc_max_send_sges; i++)
                ctxt->sc_sges[i].lkey = rdma->sc_pd->local_dma_lkey;
        return ctxt;

fail3:
        kfree(buffer);
fail2:
        kfree(ctxt->sc_pages);
fail1:
        kfree(ctxt);
fail0:
        return NULL;
}

/**
 * svc_rdma_send_ctxts_destroy - Release all send_ctxt's for an xprt
 * @rdma: svcxprt_rdma being torn down
 *
 */
void svc_rdma_send_ctxts_destroy(struct svcxprt_rdma *rdma)
{
        struct ib_device *device = rdma->sc_cm_id->device;
        struct svc_rdma_send_ctxt *ctxt;
        struct llist_node *node;

        while ((node = llist_del_first(&rdma->sc_send_ctxts)) != NULL) {
                ctxt = llist_entry(node, struct svc_rdma_send_ctxt, sc_node);
                ib_dma_unmap_single(device, ctxt->sc_sges[0].addr,
                                    rdma->sc_max_req_size, DMA_TO_DEVICE);
                kfree(ctxt->sc_xprt_buf);
                kfree(ctxt->sc_pages);
                kfree(ctxt);
        }
}

/**
 * svc_rdma_send_ctxt_get - Get a free send_ctxt
 * @rdma: controlling svcxprt_rdma
 *
 * Returns a ready-to-use send_ctxt, or NULL if none are
 * available and a fresh one cannot be allocated.
 */
struct svc_rdma_send_ctxt *svc_rdma_send_ctxt_get(struct svcxprt_rdma *rdma)
{
        struct svc_rdma_send_ctxt *ctxt;
        struct llist_node *node;

        spin_lock(&rdma->sc_send_lock);
        node = llist_del_first(&rdma->sc_send_ctxts);
        spin_unlock(&rdma->sc_send_lock);
        if (!node)
                goto out_empty;

        ctxt = llist_entry(node, struct svc_rdma_send_ctxt, sc_node);

out:
        rpcrdma_set_xdrlen(&ctxt->sc_hdrbuf, 0);
        xdr_init_encode(&ctxt->sc_stream, &ctxt->sc_hdrbuf,
                        ctxt->sc_xprt_buf, NULL);

        svc_rdma_cc_init(rdma, &ctxt->sc_reply_info.wi_cc);
        ctxt->sc_send_wr.num_sge = 0;
        ctxt->sc_cur_sge_no = 0;
        ctxt->sc_page_count = 0;
        ctxt->sc_wr_chain = &ctxt->sc_send_wr;
        ctxt->sc_sqecount = 1;

        return ctxt;

out_empty:
        svc_rdma_send_ctxts_drain(rdma);

        spin_lock(&rdma->sc_send_lock);
        node = llist_del_first(&rdma->sc_send_ctxts);
        spin_unlock(&rdma->sc_send_lock);
        if (node) {
                ctxt = llist_entry(node, struct svc_rdma_send_ctxt, sc_node);
                goto out;
        }

        ctxt = svc_rdma_send_ctxt_alloc(rdma);
        if (!ctxt)
                return NULL;
        goto out;
}

/* Release chunk I/O resources and DMA-unmap SGEs. */
static void svc_rdma_send_ctxt_unmap(struct svcxprt_rdma *rdma,
                                     struct svc_rdma_send_ctxt *ctxt)
{
        struct ib_device *device = rdma->sc_cm_id->device;
        unsigned int i;

        svc_rdma_write_chunk_release(rdma, ctxt);
        svc_rdma_reply_chunk_release(rdma, ctxt);

        /* The first SGE contains the transport header, which
         * remains mapped until @ctxt is destroyed.
         */
        for (i = 1; i < ctxt->sc_send_wr.num_sge; i++) {
                trace_svcrdma_dma_unmap_page(&ctxt->sc_cid,
                                             ctxt->sc_sges[i].addr,
                                             ctxt->sc_sges[i].length);
                ib_dma_unmap_page(device,
                                  ctxt->sc_sges[i].addr,
                                  ctxt->sc_sges[i].length,
                                  DMA_TO_DEVICE);
        }
}

/* Unmap, release pages, and return send_ctxt to the free list. */
static void svc_rdma_send_ctxt_release(struct svcxprt_rdma *rdma,
                                       struct svc_rdma_send_ctxt *ctxt)
{
        svc_rdma_send_ctxt_unmap(rdma, ctxt);

        if (ctxt->sc_page_count)
                release_pages(ctxt->sc_pages, ctxt->sc_page_count);

        llist_add(&ctxt->sc_node, &rdma->sc_send_ctxts);
}

/**
 * svc_rdma_send_ctxts_drain - Release completed send_ctxts
 * @rdma: controlling svcxprt_rdma
 */
void svc_rdma_send_ctxts_drain(struct svcxprt_rdma *rdma)
{
        struct svc_rdma_send_ctxt *ctxt, *next;
        struct llist_node *node;

        node = llist_del_all(&rdma->sc_send_release_list);
        llist_for_each_entry_safe(ctxt, next, node, sc_node)
                svc_rdma_send_ctxt_release(rdma, ctxt);
}

/**
 * svc_rdma_send_ctxt_put - Queue send_ctxt for deferred release
 * @rdma: controlling svcxprt_rdma
 * @ctxt: send_ctxt to queue for deferred release
 *
 * Queues @ctxt onto sc_send_release_list. DMA unmap and
 * page release run later in svc_rdma_send_ctxts_drain(),
 * typically from xpo_release_ctxt.
 *
 * On the empty-to-non-empty transition, set XPT_DATA and
 * enqueue the transport. Without this self-trigger, a Send
 * completion arriving after the last xpo_release_ctxt on an
 * idle connection would leave the send_ctxt's DMA mappings
 * and reply pages pinned until another drain occurred.
 */
void svc_rdma_send_ctxt_put(struct svcxprt_rdma *rdma,
                            struct svc_rdma_send_ctxt *ctxt)
{
        if (llist_add(&ctxt->sc_node, &rdma->sc_send_release_list)) {
                set_bit(XPT_DATA, &rdma->sc_xprt.xpt_flags);
                svc_xprt_enqueue(&rdma->sc_xprt);
        }
}

/**
 * svc_rdma_wake_send_waiters - manage Send Queue accounting
 * @rdma: controlling transport
 * @avail: Number of additional SQEs that are now available
 *
 */
void svc_rdma_wake_send_waiters(struct svcxprt_rdma *rdma, int avail)
{
        atomic_add(avail, &rdma->sc_sq_avail);
        smp_mb__after_atomic();
        if (unlikely(waitqueue_active(&rdma->sc_send_wait)))
                wake_up(&rdma->sc_send_wait);
}

/**
 * svc_rdma_sq_wait - Wait for SQ slots using fair queuing
 * @rdma: controlling transport
 * @cid: completion ID for tracing
 * @sqecount: number of SQ entries needed
 *
 * A ticket-based system ensures fair ordering when multiple threads
 * wait for Send Queue capacity. Each waiter takes a ticket and is
 * served in order, preventing starvation.
 *
 * Protocol invariant: every ticket holder must increment
 * sc_sq_ticket_tail exactly once, whether the reservation
 * succeeds or the connection closes. Failing to advance the
 * tail stalls all subsequent waiters.
 *
 * The ticket counters are signed 32-bit atomics. After
 * wrapping through INT_MAX, the equality check
 * (tail == ticket) remains correct because both counters
 * advance monotonically and the comparison uses exact
 * equality rather than relational operators.
 *
 * Return values:
 *   %0: SQ slots were reserved successfully
 *   %-ENOTCONN: The connection was lost
 */
int svc_rdma_sq_wait(struct svcxprt_rdma *rdma,
                     const struct rpc_rdma_cid *cid, int sqecount)
{
        int ticket;

        /* Fast path: try to reserve SQ slots without waiting.
         *
         * A failed reservation temporarily understates sc_sq_avail
         * until the compensating atomic_add restores it. A Send
         * completion arriving in that window sees a lower count
         * than reality, but the value self-corrects once the add
         * completes. No ordering guarantee is needed here because
         * the slow path serializes all contended waiters.
         */
        if (likely(atomic_sub_return(sqecount, &rdma->sc_sq_avail) >= 0))
                return 0;
        atomic_add(sqecount, &rdma->sc_sq_avail);

        /* Slow path: take a ticket and wait in line */
        ticket = atomic_fetch_inc(&rdma->sc_sq_ticket_head);

        percpu_counter_inc(&svcrdma_stat_sq_starve);
        trace_svcrdma_sq_full(rdma, cid);

        /* Wait until all earlier tickets have been served */
        wait_event(rdma->sc_sq_ticket_wait,
                   test_bit(XPT_CLOSE, &rdma->sc_xprt.xpt_flags) ||
                   atomic_read(&rdma->sc_sq_ticket_tail) == ticket);
        if (test_bit(XPT_CLOSE, &rdma->sc_xprt.xpt_flags))
                goto out_close;

        /* It's our turn. Wait for enough SQ slots to be available. */
        while (atomic_sub_return(sqecount, &rdma->sc_sq_avail) < 0) {
                atomic_add(sqecount, &rdma->sc_sq_avail);

                wait_event(rdma->sc_send_wait,
                           test_bit(XPT_CLOSE, &rdma->sc_xprt.xpt_flags) ||
                           atomic_read(&rdma->sc_sq_avail) >= sqecount);
                if (test_bit(XPT_CLOSE, &rdma->sc_xprt.xpt_flags))
                        goto out_close;
        }

        /* Slots reserved successfully. Let the next waiter proceed. */
        atomic_inc(&rdma->sc_sq_ticket_tail);
        wake_up(&rdma->sc_sq_ticket_wait);
        trace_svcrdma_sq_retry(rdma, cid);

        /*
         * While this thread sat on sc_send_wait or sc_sq_ticket_wait,
         * Send completions that tried to enqueue this transport for a
         * release-list drain were rejected: svc_rdma_has_wspace returns
         * 0 while either waitqueue is active, and svc_xprt_ready
         * rejects the enqueue. Drain the release list now.
         */
        svc_rdma_send_ctxts_drain(rdma);
        return 0;

out_close:
        atomic_inc(&rdma->sc_sq_ticket_tail);
        wake_up(&rdma->sc_sq_ticket_wait);
        return -ENOTCONN;
}

/**
 * svc_rdma_post_send_err - Handle ib_post_send failure
 * @rdma: controlling transport
 * @cid: completion ID for tracing
 * @bad_wr: first WR that was not posted
 * @first_wr: first WR in the chain
 * @sqecount: number of SQ entries that were reserved
 * @ret: error code from ib_post_send
 *
 * Return values:
 *   %0: At least one WR was posted; a completion handles cleanup
 *   %-ENOTCONN: No WRs were posted; SQ slots are released
 */
int svc_rdma_post_send_err(struct svcxprt_rdma *rdma,
                           const struct rpc_rdma_cid *cid,
                           const struct ib_send_wr *bad_wr,
                           const struct ib_send_wr *first_wr,
                           int sqecount, int ret)
{
        trace_svcrdma_sq_post_err(rdma, cid, ret);
        svc_rdma_xprt_deferred_close(rdma);

        /* If even one WR was posted, a Send completion will
         * return the reserved SQ slots.
         */
        if (bad_wr != first_wr)
                return 0;

        svc_rdma_wake_send_waiters(rdma, sqecount);
        return -ENOTCONN;
}

/**
 * svc_rdma_wc_send - Invoked by RDMA provider for each polled Send WC
 * @cq: Completion Queue context
 * @wc: Work Completion object
 *
 * NB: The svc_xprt/svcxprt_rdma is pinned whenever it's possible that
 * the Send completion handler could be running.
 */
static void svc_rdma_wc_send(struct ib_cq *cq, struct ib_wc *wc)
{
        struct svcxprt_rdma *rdma = cq->cq_context;
        struct ib_cqe *cqe = wc->wr_cqe;
        struct svc_rdma_send_ctxt *ctxt =
                container_of(cqe, struct svc_rdma_send_ctxt, sc_cqe);

        svc_rdma_wake_send_waiters(rdma, ctxt->sc_sqecount);

        if (unlikely(wc->status != IB_WC_SUCCESS))
                goto flushed;

        trace_svcrdma_wc_send(&ctxt->sc_cid);
        svc_rdma_send_ctxt_put(rdma, ctxt);
        return;

flushed:
        if (wc->status != IB_WC_WR_FLUSH_ERR)
                trace_svcrdma_wc_send_err(wc, &ctxt->sc_cid);
        else
                trace_svcrdma_wc_send_flush(wc, &ctxt->sc_cid);
        svc_rdma_send_ctxt_put(rdma, ctxt);
        svc_rdma_xprt_deferred_close(rdma);
}

/**
 * svc_rdma_post_send - Post a WR chain to the Send Queue
 * @rdma: transport context
 * @ctxt: WR chain to post
 *
 * Copy fields in @ctxt to stack variables in order to guarantee
 * that these values remain available after the ib_post_send() call.
 * In some error flow cases, svc_rdma_wc_send() releases @ctxt.
 *
 * Return values:
 *   %0: @ctxt's WR chain was posted successfully
 *   %-ENOTCONN: The connection was lost
 */
int svc_rdma_post_send(struct svcxprt_rdma *rdma,
                       struct svc_rdma_send_ctxt *ctxt)
{
        struct ib_send_wr *first_wr = ctxt->sc_wr_chain;
        struct ib_send_wr *send_wr = &ctxt->sc_send_wr;
        const struct ib_send_wr *bad_wr = first_wr;
        struct rpc_rdma_cid cid = ctxt->sc_cid;
        int ret, sqecount = ctxt->sc_sqecount;

        might_sleep();

        /* Sync the transport header buffer */
        ib_dma_sync_single_for_device(rdma->sc_cm_id->device,
                                      send_wr->sg_list[0].addr,
                                      send_wr->sg_list[0].length,
                                      DMA_TO_DEVICE);

        ret = svc_rdma_sq_wait(rdma, &cid, sqecount);
        if (ret < 0)
                return ret;

        trace_svcrdma_post_send(ctxt);
        ret = ib_post_send(rdma->sc_qp, first_wr, &bad_wr);
        if (ret)
                return svc_rdma_post_send_err(rdma, &cid, bad_wr,
                                              first_wr, sqecount, ret);
        return 0;
}

/**
 * svc_rdma_encode_read_list - Encode RPC Reply's Read chunk list
 * @sctxt: Send context for the RPC Reply
 *
 * Return values:
 *   On success, returns length in bytes of the Reply XDR buffer
 *   that was consumed by the Reply Read list
 *   %-EMSGSIZE on XDR buffer overflow
 */
static ssize_t svc_rdma_encode_read_list(struct svc_rdma_send_ctxt *sctxt)
{
        /* RPC-over-RDMA version 1 replies never have a Read list. */
        return xdr_stream_encode_item_absent(&sctxt->sc_stream);
}

/**
 * svc_rdma_encode_write_segment - Encode one Write segment
 * @sctxt: Send context for the RPC Reply
 * @chunk: Write chunk to push
 * @remaining: remaining bytes of the payload left in the Write chunk
 * @segno: which segment in the chunk
 *
 * Return values:
 *   On success, returns length in bytes of the Reply XDR buffer
 *   that was consumed by the Write segment, and updates @remaining
 *   %-EMSGSIZE on XDR buffer overflow
 */
static ssize_t svc_rdma_encode_write_segment(struct svc_rdma_send_ctxt *sctxt,
                                             const struct svc_rdma_chunk *chunk,
                                             u32 *remaining, unsigned int segno)
{
        const struct svc_rdma_segment *segment = &chunk->ch_segments[segno];
        const size_t len = rpcrdma_segment_maxsz * sizeof(__be32);
        u32 length;
        __be32 *p;

        p = xdr_reserve_space(&sctxt->sc_stream, len);
        if (!p)
                return -EMSGSIZE;

        length = min_t(u32, *remaining, segment->rs_length);
        *remaining -= length;
        xdr_encode_rdma_segment(p, segment->rs_handle, length,
                                segment->rs_offset);
        trace_svcrdma_encode_wseg(sctxt, segno, segment->rs_handle, length,
                                  segment->rs_offset);
        return len;
}

/**
 * svc_rdma_encode_write_chunk - Encode one Write chunk
 * @sctxt: Send context for the RPC Reply
 * @chunk: Write chunk to push
 *
 * Copy a Write chunk from the Call transport header to the
 * Reply transport header. Update each segment's length field
 * to reflect the number of bytes written in that segment.
 *
 * Return values:
 *   On success, returns length in bytes of the Reply XDR buffer
 *   that was consumed by the Write chunk
 *   %-EMSGSIZE on XDR buffer overflow
 */
static ssize_t svc_rdma_encode_write_chunk(struct svc_rdma_send_ctxt *sctxt,
                                           const struct svc_rdma_chunk *chunk)
{
        u32 remaining = chunk->ch_payload_length;
        unsigned int segno;
        ssize_t len, ret;

        len = 0;
        ret = xdr_stream_encode_item_present(&sctxt->sc_stream);
        if (ret < 0)
                return ret;
        len += ret;

        ret = xdr_stream_encode_u32(&sctxt->sc_stream, chunk->ch_segcount);
        if (ret < 0)
                return ret;
        len += ret;

        for (segno = 0; segno < chunk->ch_segcount; segno++) {
                ret = svc_rdma_encode_write_segment(sctxt, chunk, &remaining, segno);
                if (ret < 0)
                        return ret;
                len += ret;
        }

        return len;
}

/**
 * svc_rdma_encode_write_list - Encode RPC Reply's Write chunk list
 * @rctxt: Reply context with information about the RPC Call
 * @sctxt: Send context for the RPC Reply
 *
 * Return values:
 *   On success, returns length in bytes of the Reply XDR buffer
 *   that was consumed by the Reply's Write list
 *   %-EMSGSIZE on XDR buffer overflow
 */
static ssize_t svc_rdma_encode_write_list(struct svc_rdma_recv_ctxt *rctxt,
                                          struct svc_rdma_send_ctxt *sctxt)
{
        struct svc_rdma_chunk *chunk;
        ssize_t len, ret;

        len = 0;
        pcl_for_each_chunk(chunk, &rctxt->rc_write_pcl) {
                ret = svc_rdma_encode_write_chunk(sctxt, chunk);
                if (ret < 0)
                        return ret;
                len += ret;
        }

        /* Terminate the Write list */
        ret = xdr_stream_encode_item_absent(&sctxt->sc_stream);
        if (ret < 0)
                return ret;

        return len + ret;
}

/**
 * svc_rdma_encode_reply_chunk - Encode RPC Reply's Reply chunk
 * @rctxt: Reply context with information about the RPC Call
 * @sctxt: Send context for the RPC Reply
 * @length: size in bytes of the payload in the Reply chunk
 *
 * Return values:
 *   On success, returns length in bytes of the Reply XDR buffer
 *   that was consumed by the Reply's Reply chunk
 *   %-EMSGSIZE on XDR buffer overflow
 *   %-E2BIG if the RPC message is larger than the Reply chunk
 */
static ssize_t
svc_rdma_encode_reply_chunk(struct svc_rdma_recv_ctxt *rctxt,
                            struct svc_rdma_send_ctxt *sctxt,
                            unsigned int length)
{
        struct svc_rdma_chunk *chunk;

        if (pcl_is_empty(&rctxt->rc_reply_pcl))
                return xdr_stream_encode_item_absent(&sctxt->sc_stream);

        chunk = pcl_first_chunk(&rctxt->rc_reply_pcl);
        if (length > chunk->ch_length)
                return -E2BIG;

        chunk->ch_payload_length = length;
        return svc_rdma_encode_write_chunk(sctxt, chunk);
}

struct svc_rdma_map_data {
        struct svcxprt_rdma             *md_rdma;
        struct svc_rdma_send_ctxt       *md_ctxt;
};

/**
 * svc_rdma_page_dma_map - DMA map one page
 * @data: pointer to arguments
 * @page: struct page to DMA map
 * @offset: offset into the page
 * @len: number of bytes to map
 *
 * Returns:
 *   %0 if DMA mapping was successful
 *   %-EIO if the page cannot be DMA mapped
 */
static int svc_rdma_page_dma_map(void *data, struct page *page,
                                 unsigned long offset, unsigned int len)
{
        struct svc_rdma_map_data *args = data;
        struct svcxprt_rdma *rdma = args->md_rdma;
        struct svc_rdma_send_ctxt *ctxt = args->md_ctxt;
        struct ib_device *dev = rdma->sc_cm_id->device;
        dma_addr_t dma_addr;

        ++ctxt->sc_cur_sge_no;

        dma_addr = ib_dma_map_page(dev, page, offset, len, DMA_TO_DEVICE);
        if (ib_dma_mapping_error(dev, dma_addr))
                goto out_maperr;

        trace_svcrdma_dma_map_page(&ctxt->sc_cid, dma_addr, len);
        ctxt->sc_sges[ctxt->sc_cur_sge_no].addr = dma_addr;
        ctxt->sc_sges[ctxt->sc_cur_sge_no].length = len;
        ctxt->sc_send_wr.num_sge++;
        return 0;

out_maperr:
        trace_svcrdma_dma_map_err(&ctxt->sc_cid, dma_addr, len);
        return -EIO;
}

/**
 * svc_rdma_iov_dma_map - DMA map an iovec
 * @data: pointer to arguments
 * @iov: kvec to DMA map
 *
 * ib_dma_map_page() is used here because svc_rdma_dma_unmap()
 * handles DMA-unmap and it uses ib_dma_unmap_page() exclusively.
 *
 * Returns:
 *   %0 if DMA mapping was successful
 *   %-EIO if the iovec cannot be DMA mapped
 */
static int svc_rdma_iov_dma_map(void *data, const struct kvec *iov)
{
        if (!iov->iov_len)
                return 0;
        return svc_rdma_page_dma_map(data, virt_to_page(iov->iov_base),
                                     offset_in_page(iov->iov_base),
                                     iov->iov_len);
}

/**
 * svc_rdma_xb_dma_map - DMA map all segments of an xdr_buf
 * @xdr: xdr_buf containing portion of an RPC message to transmit
 * @data: pointer to arguments
 *
 * Returns:
 *   %0 if DMA mapping was successful
 *   %-EIO if DMA mapping failed
 *
 * On failure, any DMA mappings that have been already done must be
 * unmapped by the caller.
 */
static int svc_rdma_xb_dma_map(const struct xdr_buf *xdr, void *data)
{
        unsigned int len, remaining;
        unsigned long pageoff;
        struct page **ppages;
        int ret;

        ret = svc_rdma_iov_dma_map(data, &xdr->head[0]);
        if (ret < 0)
                return ret;

        ppages = xdr->pages + (xdr->page_base >> PAGE_SHIFT);
        pageoff = offset_in_page(xdr->page_base);
        remaining = xdr->page_len;
        while (remaining) {
                len = min_t(u32, PAGE_SIZE - pageoff, remaining);

                ret = svc_rdma_page_dma_map(data, *ppages++, pageoff, len);
                if (ret < 0)
                        return ret;

                remaining -= len;
                pageoff = 0;
        }

        ret = svc_rdma_iov_dma_map(data, &xdr->tail[0]);
        if (ret < 0)
                return ret;

        return xdr->len;
}

struct svc_rdma_pullup_data {
        u8              *pd_dest;
        unsigned int    pd_length;
        unsigned int    pd_num_sges;
};

/**
 * svc_rdma_xb_count_sges - Count how many SGEs will be needed
 * @xdr: xdr_buf containing portion of an RPC message to transmit
 * @data: pointer to arguments
 *
 * Returns:
 *   Number of SGEs needed to Send the contents of @xdr inline
 */
static int svc_rdma_xb_count_sges(const struct xdr_buf *xdr,
                                  void *data)
{
        struct svc_rdma_pullup_data *args = data;
        unsigned int remaining;
        unsigned long offset;

        if (xdr->head[0].iov_len)
                ++args->pd_num_sges;

        offset = offset_in_page(xdr->page_base);
        remaining = xdr->page_len;
        while (remaining) {
                ++args->pd_num_sges;
                remaining -= min_t(u32, PAGE_SIZE - offset, remaining);
                offset = 0;
        }

        if (xdr->tail[0].iov_len)
                ++args->pd_num_sges;

        args->pd_length += xdr->len;
        return 0;
}

/**
 * svc_rdma_pull_up_needed - Determine whether to use pull-up
 * @rdma: controlling transport
 * @sctxt: send_ctxt for the Send WR
 * @write_pcl: Write chunk list provided by client
 * @xdr: xdr_buf containing RPC message to transmit
 *
 * Returns:
 *   %true if pull-up must be used
 *   %false otherwise
 */
static bool svc_rdma_pull_up_needed(const struct svcxprt_rdma *rdma,
                                    const struct svc_rdma_send_ctxt *sctxt,
                                    const struct svc_rdma_pcl *write_pcl,
                                    const struct xdr_buf *xdr)
{
        /* Resources needed for the transport header */
        struct svc_rdma_pullup_data args = {
                .pd_length      = sctxt->sc_hdrbuf.len,
                .pd_num_sges    = 1,
        };
        int ret;

        ret = pcl_process_nonpayloads(write_pcl, xdr,
                                      svc_rdma_xb_count_sges, &args);
        if (ret < 0)
                return false;

        if (args.pd_length < RPCRDMA_PULLUP_THRESH)
                return true;
        return args.pd_num_sges >= rdma->sc_max_send_sges;
}

/**
 * svc_rdma_xb_linearize - Copy region of xdr_buf to flat buffer
 * @xdr: xdr_buf containing portion of an RPC message to copy
 * @data: pointer to arguments
 *
 * Returns:
 *   Always zero.
 */
static int svc_rdma_xb_linearize(const struct xdr_buf *xdr,
                                 void *data)
{
        struct svc_rdma_pullup_data *args = data;
        unsigned int len, remaining;
        unsigned long pageoff;
        struct page **ppages;

        if (xdr->head[0].iov_len) {
                memcpy(args->pd_dest, xdr->head[0].iov_base, xdr->head[0].iov_len);
                args->pd_dest += xdr->head[0].iov_len;
        }

        ppages = xdr->pages + (xdr->page_base >> PAGE_SHIFT);
        pageoff = offset_in_page(xdr->page_base);
        remaining = xdr->page_len;
        while (remaining) {
                len = min_t(u32, PAGE_SIZE - pageoff, remaining);
                memcpy(args->pd_dest, page_address(*ppages) + pageoff, len);
                remaining -= len;
                args->pd_dest += len;
                pageoff = 0;
                ppages++;
        }

        if (xdr->tail[0].iov_len) {
                memcpy(args->pd_dest, xdr->tail[0].iov_base, xdr->tail[0].iov_len);
                args->pd_dest += xdr->tail[0].iov_len;
        }

        args->pd_length += xdr->len;
        return 0;
}

/**
 * svc_rdma_pull_up_reply_msg - Copy Reply into a single buffer
 * @rdma: controlling transport
 * @sctxt: send_ctxt for the Send WR; xprt hdr is already prepared
 * @write_pcl: Write chunk list provided by client
 * @xdr: prepared xdr_buf containing RPC message
 *
 * The device is not capable of sending the reply directly.
 * Assemble the elements of @xdr into the transport header buffer.
 *
 * Assumptions:
 *  pull_up_needed has determined that @xdr will fit in the buffer.
 *
 * Returns:
 *   %0 if pull-up was successful
 *   %-EMSGSIZE if a buffer manipulation problem occurred
 */
static int svc_rdma_pull_up_reply_msg(const struct svcxprt_rdma *rdma,
                                      struct svc_rdma_send_ctxt *sctxt,
                                      const struct svc_rdma_pcl *write_pcl,
                                      const struct xdr_buf *xdr)
{
        struct svc_rdma_pullup_data args = {
                .pd_dest        = sctxt->sc_xprt_buf + sctxt->sc_hdrbuf.len,
        };
        int ret;

        ret = pcl_process_nonpayloads(write_pcl, xdr,
                                      svc_rdma_xb_linearize, &args);
        if (ret < 0)
                return ret;

        sctxt->sc_sges[0].length = sctxt->sc_hdrbuf.len + args.pd_length;
        trace_svcrdma_send_pullup(sctxt, args.pd_length);
        return 0;
}

/* svc_rdma_map_reply_msg - DMA map the buffer holding RPC message
 * @rdma: controlling transport
 * @sctxt: send_ctxt for the Send WR
 * @write_pcl: Write chunk list provided by client
 * @reply_pcl: Reply chunk provided by client
 * @xdr: prepared xdr_buf containing RPC message
 *
 * Returns:
 *   %0 if DMA mapping was successful.
 *   %-EMSGSIZE if a buffer manipulation problem occurred
 *   %-EIO if DMA mapping failed
 *
 * The Send WR's num_sge field is set in all cases.
 */
int svc_rdma_map_reply_msg(struct svcxprt_rdma *rdma,
                           struct svc_rdma_send_ctxt *sctxt,
                           const struct svc_rdma_pcl *write_pcl,
                           const struct svc_rdma_pcl *reply_pcl,
                           const struct xdr_buf *xdr)
{
        struct svc_rdma_map_data args = {
                .md_rdma        = rdma,
                .md_ctxt        = sctxt,
        };

        /* Set up the (persistently-mapped) transport header SGE. */
        sctxt->sc_send_wr.num_sge = 1;
        sctxt->sc_sges[0].length = sctxt->sc_hdrbuf.len;

        /* If there is a Reply chunk, nothing follows the transport
         * header, so there is nothing to map.
         */
        if (!pcl_is_empty(reply_pcl))
                return 0;

        /* For pull-up, svc_rdma_send() will sync the transport header.
         * No additional DMA mapping is necessary.
         */
        if (svc_rdma_pull_up_needed(rdma, sctxt, write_pcl, xdr))
                return svc_rdma_pull_up_reply_msg(rdma, sctxt, write_pcl, xdr);

        return pcl_process_nonpayloads(write_pcl, xdr,
                                       svc_rdma_xb_dma_map, &args);
}

/* The svc_rqst and all resources it owns are released as soon as
 * svc_rdma_sendto returns. Transfer pages under I/O to the ctxt
 * so they are released only after Send completion, and not by
 * svc_rqst_release_pages().
 */
static void svc_rdma_save_io_pages(struct svc_rqst *rqstp,
                                   struct svc_rdma_send_ctxt *ctxt)
{
        int i, pages = rqstp->rq_next_page - rqstp->rq_respages;

        ctxt->sc_page_count += pages;
        for (i = 0; i < pages; i++) {
                ctxt->sc_pages[i] = rqstp->rq_respages[i];
                rqstp->rq_respages[i] = NULL;
        }
}

/* Prepare the portion of the RPC Reply that will be transmitted
 * via RDMA Send. The RPC-over-RDMA transport header is prepared
 * in sc_sges[0], and the RPC xdr_buf is prepared in following sges.
 *
 * Depending on whether a Write list or Reply chunk is present,
 * the server may Send all, a portion of, or none of the xdr_buf.
 * In the latter case, only the transport header (sc_sges[0]) is
 * transmitted.
 *
 * Assumptions:
 * - The Reply's transport header will never be larger than a page.
 */
static int svc_rdma_send_reply_msg(struct svcxprt_rdma *rdma,
                                   struct svc_rdma_send_ctxt *sctxt,
                                   const struct svc_rdma_recv_ctxt *rctxt,
                                   struct svc_rqst *rqstp)
{
        struct ib_send_wr *send_wr = &sctxt->sc_send_wr;
        int ret;

        ret = svc_rdma_map_reply_msg(rdma, sctxt, &rctxt->rc_write_pcl,
                                     &rctxt->rc_reply_pcl, &rqstp->rq_res);
        if (ret < 0)
                return ret;

        /* Transfer pages involved in RDMA Writes to the sctxt's
         * page array. Completion handling releases these pages.
         */
        svc_rdma_save_io_pages(rqstp, sctxt);

        if (rctxt->rc_inv_rkey) {
                send_wr->opcode = IB_WR_SEND_WITH_INV;
                send_wr->ex.invalidate_rkey = rctxt->rc_inv_rkey;
        } else {
                send_wr->opcode = IB_WR_SEND;
        }

        return svc_rdma_post_send(rdma, sctxt);
}

/**
 * svc_rdma_send_error_msg - Send an RPC/RDMA v1 error response
 * @rdma: controlling transport context
 * @sctxt: Send context for the response
 * @rctxt: Receive context for incoming bad message
 * @status: negative errno indicating error that occurred
 *
 * Given the client-provided Read, Write, and Reply chunks, the
 * server was not able to parse the Call or form a complete Reply.
 * Return an RDMA_ERROR message so the client can retire the RPC
 * transaction.
 *
 * The caller does not have to release @sctxt. It is released by
 * Send completion, or by this function on error.
 */
void svc_rdma_send_error_msg(struct svcxprt_rdma *rdma,
                             struct svc_rdma_send_ctxt *sctxt,
                             struct svc_rdma_recv_ctxt *rctxt,
                             int status)
{
        __be32 *rdma_argp = rctxt->rc_recv_buf;
        __be32 *p;

        rpcrdma_set_xdrlen(&sctxt->sc_hdrbuf, 0);
        xdr_init_encode(&sctxt->sc_stream, &sctxt->sc_hdrbuf,
                        sctxt->sc_xprt_buf, NULL);

        p = xdr_reserve_space(&sctxt->sc_stream,
                              rpcrdma_fixed_maxsz * sizeof(*p));
        if (!p)
                goto put_ctxt;

        *p++ = *rdma_argp;
        *p++ = *(rdma_argp + 1);
        *p++ = rdma->sc_fc_credits;
        *p = rdma_error;

        switch (status) {
        case -EPROTONOSUPPORT:
                p = xdr_reserve_space(&sctxt->sc_stream, 3 * sizeof(*p));
                if (!p)
                        goto put_ctxt;

                *p++ = err_vers;
                *p++ = rpcrdma_version;
                *p = rpcrdma_version;
                trace_svcrdma_err_vers(*rdma_argp);
                break;
        default:
                p = xdr_reserve_space(&sctxt->sc_stream, sizeof(*p));
                if (!p)
                        goto put_ctxt;

                *p = err_chunk;
                trace_svcrdma_err_chunk(*rdma_argp);
        }

        /* Remote Invalidation is skipped for simplicity. */
        sctxt->sc_send_wr.num_sge = 1;
        sctxt->sc_send_wr.opcode = IB_WR_SEND;
        sctxt->sc_sges[0].length = sctxt->sc_hdrbuf.len;

        /* Ensure only the error message is posted, not any previously
         * prepared Write chunk WRs.
         */
        sctxt->sc_wr_chain = &sctxt->sc_send_wr;
        sctxt->sc_sqecount = 1;
        if (svc_rdma_post_send(rdma, sctxt))
                goto put_ctxt;
        return;

put_ctxt:
        svc_rdma_send_ctxt_put(rdma, sctxt);
}

/**
 * svc_rdma_sendto - Transmit an RPC reply
 * @rqstp: processed RPC request, reply XDR already in ::rq_res
 *
 * Any resources still associated with @rqstp are released upon return.
 * If no reply message was possible, the connection is closed.
 *
 * Returns:
 *      %0 if an RPC reply has been successfully posted,
 *      %-ENOMEM if a resource shortage occurred (connection is lost),
 *      %-ENOTCONN if posting failed (connection is lost).
 */
int svc_rdma_sendto(struct svc_rqst *rqstp)
{
        struct svc_xprt *xprt = rqstp->rq_xprt;
        struct svcxprt_rdma *rdma =
                container_of(xprt, struct svcxprt_rdma, sc_xprt);
        struct svc_rdma_recv_ctxt *rctxt = rqstp->rq_xprt_ctxt;
        __be32 *rdma_argp = rctxt->rc_recv_buf;
        struct svc_rdma_send_ctxt *sctxt;
        unsigned int rc_size;
        __be32 *p;
        int ret;

        ret = -ENOTCONN;
        if (svc_xprt_is_dead(xprt))
                goto drop_connection;

        ret = -ENOMEM;
        sctxt = svc_rdma_send_ctxt_get(rdma);
        if (!sctxt)
                goto drop_connection;

        ret = -EMSGSIZE;
        p = xdr_reserve_space(&sctxt->sc_stream,
                              rpcrdma_fixed_maxsz * sizeof(*p));
        if (!p)
                goto put_ctxt;

        ret = svc_rdma_prepare_write_list(rdma, rctxt, sctxt, &rqstp->rq_res);
        if (ret < 0)
                goto put_ctxt;

        rc_size = 0;
        if (!pcl_is_empty(&rctxt->rc_reply_pcl)) {
                ret = svc_rdma_prepare_reply_chunk(rdma, &rctxt->rc_write_pcl,
                                                   &rctxt->rc_reply_pcl, sctxt,
                                                   &rqstp->rq_res);
                if (ret < 0)
                        goto reply_chunk;
                rc_size = ret;
        }

        *p++ = *rdma_argp;
        *p++ = *(rdma_argp + 1);
        *p++ = rdma->sc_fc_credits;
        *p = pcl_is_empty(&rctxt->rc_reply_pcl) ? rdma_msg : rdma_nomsg;

        ret = svc_rdma_encode_read_list(sctxt);
        if (ret < 0)
                goto put_ctxt;
        ret = svc_rdma_encode_write_list(rctxt, sctxt);
        if (ret < 0)
                goto put_ctxt;
        ret = svc_rdma_encode_reply_chunk(rctxt, sctxt, rc_size);
        if (ret < 0)
                goto put_ctxt;

        ret = svc_rdma_send_reply_msg(rdma, sctxt, rctxt, rqstp);
        if (ret < 0)
                goto put_ctxt;
        return 0;

reply_chunk:
        if (ret != -E2BIG && ret != -EINVAL)
                goto put_ctxt;

        /* Send completion releases payload pages that were part
         * of previously posted RDMA Writes.
         */
        svc_rdma_save_io_pages(rqstp, sctxt);
        svc_rdma_send_error_msg(rdma, sctxt, rctxt, ret);
        return 0;

put_ctxt:
        svc_rdma_send_ctxt_put(rdma, sctxt);
drop_connection:
        trace_svcrdma_send_err(rqstp, ret);
        svc_rdma_xprt_deferred_close(rdma);
        return -ENOTCONN;
}

/**
 * svc_rdma_result_payload - special processing for a result payload
 * @rqstp: RPC transaction context
 * @offset: payload's byte offset in @rqstp->rq_res
 * @length: size of payload, in bytes
 *
 * Assign the passed-in result payload to the current Write chunk,
 * and advance to cur_result_payload to the next Write chunk, if
 * there is one.
 *
 * Return values:
 *   %0 if successful or nothing needed to be done
 *   %-E2BIG if the payload was larger than the Write chunk
 */
int svc_rdma_result_payload(struct svc_rqst *rqstp, unsigned int offset,
                            unsigned int length)
{
        struct svc_rdma_recv_ctxt *rctxt = rqstp->rq_xprt_ctxt;
        struct svc_rdma_chunk *chunk;

        chunk = rctxt->rc_cur_result_payload;
        if (!length || !chunk)
                return 0;
        rctxt->rc_cur_result_payload =
                pcl_next_chunk(&rctxt->rc_write_pcl, chunk);

        if (length > chunk->ch_length)
                return -E2BIG;
        chunk->ch_position = offset;
        chunk->ch_payload_length = length;
        return 0;
}