// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
/*
 * Copyright (c) 2014-2017 Oracle.  All rights reserved.
 * Copyright (c) 2003-2007 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.
 */

/*
 * rpc_rdma.c
 *
 * This file contains the guts of the RPC RDMA protocol, and
 * does marshaling/unmarshaling, etc. It is also where interfacing
 * to the Linux RPC framework lives.
 */

#include <linux/highmem.h>

#include <linux/sunrpc/svc_rdma.h>

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

#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
# define RPCDBG_FACILITY        RPCDBG_TRANS
#endif

/* Returns size of largest RPC-over-RDMA header in a Call message
 *
 * The largest Call header contains a full-size Read list and a
 * minimal Reply chunk.
 */
static unsigned int rpcrdma_max_call_header_size(unsigned int maxsegs)
{
        unsigned int size;

        /* Fixed header fields and list discriminators */
        size = RPCRDMA_HDRLEN_MIN;

        /* Maximum Read list size */
        size = maxsegs * rpcrdma_readchunk_maxsz * sizeof(__be32);

        /* Minimal Read chunk size */
        size += sizeof(__be32); /* segment count */
        size += rpcrdma_segment_maxsz * sizeof(__be32);
        size += sizeof(__be32); /* list discriminator */

        return size;
}

/* Returns size of largest RPC-over-RDMA header in a Reply message
 *
 * There is only one Write list or one Reply chunk per Reply
 * message.  The larger list is the Write list.
 */
static unsigned int rpcrdma_max_reply_header_size(unsigned int maxsegs)
{
        unsigned int size;

        /* Fixed header fields and list discriminators */
        size = RPCRDMA_HDRLEN_MIN;

        /* Maximum Write list size */
        size = sizeof(__be32);          /* segment count */
        size += maxsegs * rpcrdma_segment_maxsz * sizeof(__be32);
        size += sizeof(__be32); /* list discriminator */

        return size;
}

/**
 * rpcrdma_set_max_header_sizes - Initialize inline payload sizes
 * @r_xprt: transport instance to initialize
 *
 * The max_inline fields contain the maximum size of an RPC message
 * so the marshaling code doesn't have to repeat this calculation
 * for every RPC.
 */
void rpcrdma_set_max_header_sizes(struct rpcrdma_xprt *r_xprt)
{
        unsigned int maxsegs = r_xprt->rx_ia.ri_max_rdma_segs;
        struct rpcrdma_ep *ep = &r_xprt->rx_ep;

        ep->rep_max_inline_send =
                ep->rep_inline_send - rpcrdma_max_call_header_size(maxsegs);
        ep->rep_max_inline_recv =
                ep->rep_inline_recv - rpcrdma_max_reply_header_size(maxsegs);
}

/* The client can send a request inline as long as the RPCRDMA header
 * plus the RPC call fit under the transport's inline limit. If the
 * combined call message size exceeds that limit, the client must use
 * a Read chunk for this operation.
 *
 * A Read chunk is also required if sending the RPC call inline would
 * exceed this device's max_sge limit.
 */
static bool rpcrdma_args_inline(struct rpcrdma_xprt *r_xprt,
                                struct rpc_rqst *rqst)
{
        struct xdr_buf *xdr = &rqst->rq_snd_buf;
        unsigned int count, remaining, offset;

        if (xdr->len > r_xprt->rx_ep.rep_max_inline_send)
                return false;

        if (xdr->page_len) {
                remaining = xdr->page_len;
                offset = offset_in_page(xdr->page_base);
                count = RPCRDMA_MIN_SEND_SGES;
                while (remaining) {
                        remaining -= min_t(unsigned int,
                                           PAGE_SIZE - offset, remaining);
                        offset = 0;
                        if (++count > r_xprt->rx_ep.rep_attr.cap.max_send_sge)
                                return false;
                }
        }

        return true;
}

/* The client can't know how large the actual reply will be. Thus it
 * plans for the largest possible reply for that particular ULP
 * operation. If the maximum combined reply message size exceeds that
 * limit, the client must provide a write list or a reply chunk for
 * this request.
 */
static bool rpcrdma_results_inline(struct rpcrdma_xprt *r_xprt,
                                   struct rpc_rqst *rqst)
{
        return rqst->rq_rcv_buf.buflen <= r_xprt->rx_ep.rep_max_inline_recv;
}

/* The client is required to provide a Reply chunk if the maximum
 * size of the non-payload part of the RPC Reply is larger than
 * the inline threshold.
 */
static bool
rpcrdma_nonpayload_inline(const struct rpcrdma_xprt *r_xprt,
                          const struct rpc_rqst *rqst)
{
        const struct xdr_buf *buf = &rqst->rq_rcv_buf;

        return (buf->head[0].iov_len + buf->tail[0].iov_len) <
                r_xprt->rx_ep.rep_max_inline_recv;
}

/* Split @vec on page boundaries into SGEs. FMR registers pages, not
 * a byte range. Other modes coalesce these SGEs into a single MR
 * when they can.
 *
 * Returns pointer to next available SGE, and bumps the total number
 * of SGEs consumed.
 */
static struct rpcrdma_mr_seg *
rpcrdma_convert_kvec(struct kvec *vec, struct rpcrdma_mr_seg *seg,
                     unsigned int *n)
{
        u32 remaining, page_offset;
        char *base;

        base = vec->iov_base;
        page_offset = offset_in_page(base);
        remaining = vec->iov_len;
        while (remaining) {
                seg->mr_page = NULL;
                seg->mr_offset = base;
                seg->mr_len = min_t(u32, PAGE_SIZE - page_offset, remaining);
                remaining -= seg->mr_len;
                base += seg->mr_len;
                ++seg;
                ++(*n);
                page_offset = 0;
        }
        return seg;
}

/* Convert @xdrbuf into SGEs no larger than a page each. As they
 * are registered, these SGEs are then coalesced into RDMA segments
 * when the selected memreg mode supports it.
 *
 * Returns positive number of SGEs consumed, or a negative errno.
 */

static int
rpcrdma_convert_iovs(struct rpcrdma_xprt *r_xprt, struct xdr_buf *xdrbuf,
                     unsigned int pos, enum rpcrdma_chunktype type,
                     struct rpcrdma_mr_seg *seg)
{
        unsigned long page_base;
        unsigned int len, n;
        struct page **ppages;

        n = 0;
        if (pos == 0)
                seg = rpcrdma_convert_kvec(&xdrbuf->head[0], seg, &n);

        len = xdrbuf->page_len;
        ppages = xdrbuf->pages + (xdrbuf->page_base >> PAGE_SHIFT);
        page_base = offset_in_page(xdrbuf->page_base);
        while (len) {
                /* ACL likes to be lazy in allocating pages - ACLs
                 * are small by default but can get huge.
                 */
                if (unlikely(xdrbuf->flags & XDRBUF_SPARSE_PAGES)) {
                        if (!*ppages)
                                *ppages = alloc_page(GFP_NOWAIT | __GFP_NOWARN);
                        if (!*ppages)
                                return -ENOBUFS;
                }
                seg->mr_page = *ppages;
                seg->mr_offset = (char *)page_base;
                seg->mr_len = min_t(u32, PAGE_SIZE - page_base, len);
                len -= seg->mr_len;
                ++ppages;
                ++seg;
                ++n;
                page_base = 0;
        }

        /* When encoding a Read chunk, the tail iovec contains an
         * XDR pad and may be omitted.
         */
        if (type == rpcrdma_readch && r_xprt->rx_ia.ri_implicit_roundup)
                goto out;

        /* When encoding a Write chunk, some servers need to see an
         * extra segment for non-XDR-aligned Write chunks. The upper
         * layer provides space in the tail iovec that may be used
         * for this purpose.
         */
        if (type == rpcrdma_writech && r_xprt->rx_ia.ri_implicit_roundup)
                goto out;

        if (xdrbuf->tail[0].iov_len)
                seg = rpcrdma_convert_kvec(&xdrbuf->tail[0], seg, &n);

out:
        if (unlikely(n > RPCRDMA_MAX_SEGS))
                return -EIO;
        return n;
}

static inline int
encode_item_present(struct xdr_stream *xdr)
{
        __be32 *p;

        p = xdr_reserve_space(xdr, sizeof(*p));
        if (unlikely(!p))
                return -EMSGSIZE;

        *p = xdr_one;
        return 0;
}

static inline int
encode_item_not_present(struct xdr_stream *xdr)
{
        __be32 *p;

        p = xdr_reserve_space(xdr, sizeof(*p));
        if (unlikely(!p))
                return -EMSGSIZE;

        *p = xdr_zero;
        return 0;
}

static void
xdr_encode_rdma_segment(__be32 *iptr, struct rpcrdma_mr *mr)
{
        *iptr++ = cpu_to_be32(mr->mr_handle);
        *iptr++ = cpu_to_be32(mr->mr_length);
        xdr_encode_hyper(iptr, mr->mr_offset);
}

static int
encode_rdma_segment(struct xdr_stream *xdr, struct rpcrdma_mr *mr)
{
        __be32 *p;

        p = xdr_reserve_space(xdr, 4 * sizeof(*p));
        if (unlikely(!p))
                return -EMSGSIZE;

        xdr_encode_rdma_segment(p, mr);
        return 0;
}

static int
encode_read_segment(struct xdr_stream *xdr, struct rpcrdma_mr *mr,
                    u32 position)
{
        __be32 *p;

        p = xdr_reserve_space(xdr, 6 * sizeof(*p));
        if (unlikely(!p))
                return -EMSGSIZE;

        *p++ = xdr_one;                 /* Item present */
        *p++ = cpu_to_be32(position);
        xdr_encode_rdma_segment(p, mr);
        return 0;
}

static struct rpcrdma_mr_seg *rpcrdma_mr_prepare(struct rpcrdma_xprt *r_xprt,
                                                 struct rpcrdma_req *req,
                                                 struct rpcrdma_mr_seg *seg,
                                                 int nsegs, bool writing,
                                                 struct rpcrdma_mr **mr)
{
        *mr = rpcrdma_mr_pop(&req->rl_free_mrs);
        if (!*mr) {
                *mr = rpcrdma_mr_get(r_xprt);
                if (!*mr)
                        goto out_getmr_err;
                trace_xprtrdma_mr_get(req);
                (*mr)->mr_req = req;
        }

        rpcrdma_mr_push(*mr, &req->rl_registered);
        return frwr_map(r_xprt, seg, nsegs, writing, req->rl_slot.rq_xid, *mr);

out_getmr_err:
        trace_xprtrdma_nomrs(req);
        xprt_wait_for_buffer_space(&r_xprt->rx_xprt);
        rpcrdma_mrs_refresh(r_xprt);
        return ERR_PTR(-EAGAIN);
}

/* Register and XDR encode the Read list. Supports encoding a list of read
 * segments that belong to a single read chunk.
 *
 * Encoding key for single-list chunks (HLOO = Handle32 Length32 Offset64):
 *
 *  Read chunklist (a linked list):
 *   N elements, position P (same P for all chunks of same arg!):
 *    1 - PHLOO - 1 - PHLOO - ... - 1 - PHLOO - 0
 *
 * Returns zero on success, or a negative errno if a failure occurred.
 * @xdr is advanced to the next position in the stream.
 *
 * Only a single @pos value is currently supported.
 */
static int rpcrdma_encode_read_list(struct rpcrdma_xprt *r_xprt,
                                    struct rpcrdma_req *req,
                                    struct rpc_rqst *rqst,
                                    enum rpcrdma_chunktype rtype)
{
        struct xdr_stream *xdr = &req->rl_stream;
        struct rpcrdma_mr_seg *seg;
        struct rpcrdma_mr *mr;
        unsigned int pos;
        int nsegs;

        if (rtype == rpcrdma_noch_pullup || rtype == rpcrdma_noch_mapped)
                goto done;

        pos = rqst->rq_snd_buf.head[0].iov_len;
        if (rtype == rpcrdma_areadch)
                pos = 0;
        seg = req->rl_segments;
        nsegs = rpcrdma_convert_iovs(r_xprt, &rqst->rq_snd_buf, pos,
                                     rtype, seg);
        if (nsegs < 0)
                return nsegs;

        do {
                seg = rpcrdma_mr_prepare(r_xprt, req, seg, nsegs, false, &mr);
                if (IS_ERR(seg))
                        return PTR_ERR(seg);

                if (encode_read_segment(xdr, mr, pos) < 0)
                        return -EMSGSIZE;

                trace_xprtrdma_chunk_read(rqst->rq_task, pos, mr, nsegs);
                r_xprt->rx_stats.read_chunk_count++;
                nsegs -= mr->mr_nents;
        } while (nsegs);

done:
        return encode_item_not_present(xdr);
}

/* Register and XDR encode the Write list. Supports encoding a list
 * containing one array of plain segments that belong to a single
 * write chunk.
 *
 * Encoding key for single-list chunks (HLOO = Handle32 Length32 Offset64):
 *
 *  Write chunklist (a list of (one) counted array):
 *   N elements:
 *    1 - N - HLOO - HLOO - ... - HLOO - 0
 *
 * Returns zero on success, or a negative errno if a failure occurred.
 * @xdr is advanced to the next position in the stream.
 *
 * Only a single Write chunk is currently supported.
 */
static int rpcrdma_encode_write_list(struct rpcrdma_xprt *r_xprt,
                                     struct rpcrdma_req *req,
                                     struct rpc_rqst *rqst,
                                     enum rpcrdma_chunktype wtype)
{
        struct xdr_stream *xdr = &req->rl_stream;
        struct rpcrdma_mr_seg *seg;
        struct rpcrdma_mr *mr;
        int nsegs, nchunks;
        __be32 *segcount;

        if (wtype != rpcrdma_writech)
                goto done;

        seg = req->rl_segments;
        nsegs = rpcrdma_convert_iovs(r_xprt, &rqst->rq_rcv_buf,
                                     rqst->rq_rcv_buf.head[0].iov_len,
                                     wtype, seg);
        if (nsegs < 0)
                return nsegs;

        if (encode_item_present(xdr) < 0)
                return -EMSGSIZE;
        segcount = xdr_reserve_space(xdr, sizeof(*segcount));
        if (unlikely(!segcount))
                return -EMSGSIZE;
        /* Actual value encoded below */

        nchunks = 0;
        do {
                seg = rpcrdma_mr_prepare(r_xprt, req, seg, nsegs, true, &mr);
                if (IS_ERR(seg))
                        return PTR_ERR(seg);

                if (encode_rdma_segment(xdr, mr) < 0)
                        return -EMSGSIZE;

                trace_xprtrdma_chunk_write(rqst->rq_task, mr, nsegs);
                r_xprt->rx_stats.write_chunk_count++;
                r_xprt->rx_stats.total_rdma_request += mr->mr_length;
                nchunks++;
                nsegs -= mr->mr_nents;
        } while (nsegs);

        /* Update count of segments in this Write chunk */
        *segcount = cpu_to_be32(nchunks);

done:
        return encode_item_not_present(xdr);
}

/* Register and XDR encode the Reply chunk. Supports encoding an array
 * of plain segments that belong to a single write (reply) chunk.
 *
 * Encoding key for single-list chunks (HLOO = Handle32 Length32 Offset64):
 *
 *  Reply chunk (a counted array):
 *   N elements:
 *    1 - N - HLOO - HLOO - ... - HLOO
 *
 * Returns zero on success, or a negative errno if a failure occurred.
 * @xdr is advanced to the next position in the stream.
 */
static int rpcrdma_encode_reply_chunk(struct rpcrdma_xprt *r_xprt,
                                      struct rpcrdma_req *req,
                                      struct rpc_rqst *rqst,
                                      enum rpcrdma_chunktype wtype)
{
        struct xdr_stream *xdr = &req->rl_stream;
        struct rpcrdma_mr_seg *seg;
        struct rpcrdma_mr *mr;
        int nsegs, nchunks;
        __be32 *segcount;

        if (wtype != rpcrdma_replych)
                return encode_item_not_present(xdr);

        seg = req->rl_segments;
        nsegs = rpcrdma_convert_iovs(r_xprt, &rqst->rq_rcv_buf, 0, wtype, seg);
        if (nsegs < 0)
                return nsegs;

        if (encode_item_present(xdr) < 0)
                return -EMSGSIZE;
        segcount = xdr_reserve_space(xdr, sizeof(*segcount));
        if (unlikely(!segcount))
                return -EMSGSIZE;
        /* Actual value encoded below */

        nchunks = 0;
        do {
                seg = rpcrdma_mr_prepare(r_xprt, req, seg, nsegs, true, &mr);
                if (IS_ERR(seg))
                        return PTR_ERR(seg);

                if (encode_rdma_segment(xdr, mr) < 0)
                        return -EMSGSIZE;

                trace_xprtrdma_chunk_reply(rqst->rq_task, mr, nsegs);
                r_xprt->rx_stats.reply_chunk_count++;
                r_xprt->rx_stats.total_rdma_request += mr->mr_length;
                nchunks++;
                nsegs -= mr->mr_nents;
        } while (nsegs);

        /* Update count of segments in the Reply chunk */
        *segcount = cpu_to_be32(nchunks);

        return 0;
}

static void rpcrdma_sendctx_done(struct kref *kref)
{
        struct rpcrdma_req *req =
                container_of(kref, struct rpcrdma_req, rl_kref);
        struct rpcrdma_rep *rep = req->rl_reply;

        rpcrdma_complete_rqst(rep);
        rep->rr_rxprt->rx_stats.reply_waits_for_send++;
}

/**
 * rpcrdma_sendctx_unmap - DMA-unmap Send buffer
 * @sc: sendctx containing SGEs to unmap
 *
 */
void rpcrdma_sendctx_unmap(struct rpcrdma_sendctx *sc)
{
        struct rpcrdma_regbuf *rb = sc->sc_req->rl_sendbuf;
        struct ib_sge *sge;

        if (!sc->sc_unmap_count)
                return;

        /* The first two SGEs contain the transport header and
         * the inline buffer. These are always left mapped so
         * they can be cheaply re-used.
         */
        for (sge = &sc->sc_sges[2]; sc->sc_unmap_count;
             ++sge, --sc->sc_unmap_count)
                ib_dma_unmap_page(rdmab_device(rb), sge->addr, sge->length,
                                  DMA_TO_DEVICE);

        kref_put(&sc->sc_req->rl_kref, rpcrdma_sendctx_done);
}

/* Prepare an SGE for the RPC-over-RDMA transport header.
 */
static void rpcrdma_prepare_hdr_sge(struct rpcrdma_xprt *r_xprt,
                                    struct rpcrdma_req *req, u32 len)
{
        struct rpcrdma_sendctx *sc = req->rl_sendctx;
        struct rpcrdma_regbuf *rb = req->rl_rdmabuf;
        struct ib_sge *sge = &sc->sc_sges[req->rl_wr.num_sge++];

        sge->addr = rdmab_addr(rb);
        sge->length = len;
        sge->lkey = rdmab_lkey(rb);

        ib_dma_sync_single_for_device(rdmab_device(rb), sge->addr, sge->length,
                                      DMA_TO_DEVICE);
}

/* The head iovec is straightforward, as it is usually already
 * DMA-mapped. Sync the content that has changed.
 */
static bool rpcrdma_prepare_head_iov(struct rpcrdma_xprt *r_xprt,
                                     struct rpcrdma_req *req, unsigned int len)
{
        struct rpcrdma_sendctx *sc = req->rl_sendctx;
        struct ib_sge *sge = &sc->sc_sges[req->rl_wr.num_sge++];
        struct rpcrdma_regbuf *rb = req->rl_sendbuf;

        if (!rpcrdma_regbuf_dma_map(r_xprt, rb))
                return false;

        sge->addr = rdmab_addr(rb);
        sge->length = len;
        sge->lkey = rdmab_lkey(rb);

        ib_dma_sync_single_for_device(rdmab_device(rb), sge->addr, sge->length,
                                      DMA_TO_DEVICE);
        return true;
}

/* If there is a page list present, DMA map and prepare an
 * SGE for each page to be sent.
 */
static bool rpcrdma_prepare_pagelist(struct rpcrdma_req *req,
                                     struct xdr_buf *xdr)
{
        struct rpcrdma_sendctx *sc = req->rl_sendctx;
        struct rpcrdma_regbuf *rb = req->rl_sendbuf;
        unsigned int page_base, len, remaining;
        struct page **ppages;
        struct ib_sge *sge;

        ppages = xdr->pages + (xdr->page_base >> PAGE_SHIFT);
        page_base = offset_in_page(xdr->page_base);
        remaining = xdr->page_len;
        while (remaining) {
                sge = &sc->sc_sges[req->rl_wr.num_sge++];
                len = min_t(unsigned int, PAGE_SIZE - page_base, remaining);
                sge->addr = ib_dma_map_page(rdmab_device(rb), *ppages,
                                            page_base, len, DMA_TO_DEVICE);
                if (ib_dma_mapping_error(rdmab_device(rb), sge->addr))
                        goto out_mapping_err;

                sge->length = len;
                sge->lkey = rdmab_lkey(rb);

                sc->sc_unmap_count++;
                ppages++;
                remaining -= len;
                page_base = 0;
        }

        return true;

out_mapping_err:
        trace_xprtrdma_dma_maperr(sge->addr);
        return false;
}

/* The tail iovec may include an XDR pad for the page list,
 * as well as additional content, and may not reside in the
 * same page as the head iovec.
 */
static bool rpcrdma_prepare_tail_iov(struct rpcrdma_req *req,
                                     struct xdr_buf *xdr,
                                     unsigned int page_base, unsigned int len)
{
        struct rpcrdma_sendctx *sc = req->rl_sendctx;
        struct ib_sge *sge = &sc->sc_sges[req->rl_wr.num_sge++];
        struct rpcrdma_regbuf *rb = req->rl_sendbuf;
        struct page *page = virt_to_page(xdr->tail[0].iov_base);

        sge->addr = ib_dma_map_page(rdmab_device(rb), page, page_base, len,
                                    DMA_TO_DEVICE);
        if (ib_dma_mapping_error(rdmab_device(rb), sge->addr))
                goto out_mapping_err;

        sge->length = len;
        sge->lkey = rdmab_lkey(rb);
        ++sc->sc_unmap_count;
        return true;

out_mapping_err:
        trace_xprtrdma_dma_maperr(sge->addr);
        return false;
}

/* Copy the tail to the end of the head buffer.
 */
static void rpcrdma_pullup_tail_iov(struct rpcrdma_xprt *r_xprt,
                                    struct rpcrdma_req *req,
                                    struct xdr_buf *xdr)
{
        unsigned char *dst;

        dst = (unsigned char *)xdr->head[0].iov_base;
        dst += xdr->head[0].iov_len + xdr->page_len;
        memmove(dst, xdr->tail[0].iov_base, xdr->tail[0].iov_len);
        r_xprt->rx_stats.pullup_copy_count += xdr->tail[0].iov_len;
}

/* Copy pagelist content into the head buffer.
 */
static void rpcrdma_pullup_pagelist(struct rpcrdma_xprt *r_xprt,
                                    struct rpcrdma_req *req,
                                    struct xdr_buf *xdr)
{
        unsigned int len, page_base, remaining;
        struct page **ppages;
        unsigned char *src, *dst;

        dst = (unsigned char *)xdr->head[0].iov_base;
        dst += xdr->head[0].iov_len;
        ppages = xdr->pages + (xdr->page_base >> PAGE_SHIFT);
        page_base = offset_in_page(xdr->page_base);
        remaining = xdr->page_len;
        while (remaining) {
                src = page_address(*ppages);
                src += page_base;
                len = min_t(unsigned int, PAGE_SIZE - page_base, remaining);
                memcpy(dst, src, len);
                r_xprt->rx_stats.pullup_copy_count += len;

                ppages++;
                dst += len;
                remaining -= len;
                page_base = 0;
        }
}

/* Copy the contents of @xdr into @rl_sendbuf and DMA sync it.
 * When the head, pagelist, and tail are small, a pull-up copy
 * is considerably less costly than DMA mapping the components
 * of @xdr.
 *
 * Assumptions:
 *  - the caller has already verified that the total length
 *    of the RPC Call body will fit into @rl_sendbuf.
 */
static bool rpcrdma_prepare_noch_pullup(struct rpcrdma_xprt *r_xprt,
                                        struct rpcrdma_req *req,
                                        struct xdr_buf *xdr)
{
        if (unlikely(xdr->tail[0].iov_len))
                rpcrdma_pullup_tail_iov(r_xprt, req, xdr);

        if (unlikely(xdr->page_len))
                rpcrdma_pullup_pagelist(r_xprt, req, xdr);

        /* The whole RPC message resides in the head iovec now */
        return rpcrdma_prepare_head_iov(r_xprt, req, xdr->len);
}

static bool rpcrdma_prepare_noch_mapped(struct rpcrdma_xprt *r_xprt,
                                        struct rpcrdma_req *req,
                                        struct xdr_buf *xdr)
{
        struct kvec *tail = &xdr->tail[0];

        if (!rpcrdma_prepare_head_iov(r_xprt, req, xdr->head[0].iov_len))
                return false;
        if (xdr->page_len)
                if (!rpcrdma_prepare_pagelist(req, xdr))
                        return false;
        if (tail->iov_len)
                if (!rpcrdma_prepare_tail_iov(req, xdr,
                                              offset_in_page(tail->iov_base),
                                              tail->iov_len))
                        return false;

        if (req->rl_sendctx->sc_unmap_count)
                kref_get(&req->rl_kref);
        return true;
}

static bool rpcrdma_prepare_readch(struct rpcrdma_xprt *r_xprt,
                                   struct rpcrdma_req *req,
                                   struct xdr_buf *xdr)
{
        if (!rpcrdma_prepare_head_iov(r_xprt, req, xdr->head[0].iov_len))
                return false;

        /* If there is a Read chunk, the page list is being handled
         * via explicit RDMA, and thus is skipped here.
         */

        /* Do not include the tail if it is only an XDR pad */
        if (xdr->tail[0].iov_len > 3) {
                unsigned int page_base, len;

                /* If the content in the page list is an odd length,
                 * xdr_write_pages() adds a pad at the beginning of
                 * the tail iovec. Force the tail's non-pad content to
                 * land at the next XDR position in the Send message.
                 */
                page_base = offset_in_page(xdr->tail[0].iov_base);
                len = xdr->tail[0].iov_len;
                page_base += len & 3;
                len -= len & 3;
                if (!rpcrdma_prepare_tail_iov(req, xdr, page_base, len))
                        return false;
                kref_get(&req->rl_kref);
        }

        return true;
}

/**
 * rpcrdma_prepare_send_sges - Construct SGEs for a Send WR
 * @r_xprt: controlling transport
 * @req: context of RPC Call being marshalled
 * @hdrlen: size of transport header, in bytes
 * @xdr: xdr_buf containing RPC Call
 * @rtype: chunk type being encoded
 *
 * Returns 0 on success; otherwise a negative errno is returned.
 */
inline int rpcrdma_prepare_send_sges(struct rpcrdma_xprt *r_xprt,
                                     struct rpcrdma_req *req, u32 hdrlen,
                                     struct xdr_buf *xdr,
                                     enum rpcrdma_chunktype rtype)
{
        int ret;

        ret = -EAGAIN;
        req->rl_sendctx = rpcrdma_sendctx_get_locked(r_xprt);
        if (!req->rl_sendctx)
                goto out_nosc;
        req->rl_sendctx->sc_unmap_count = 0;
        req->rl_sendctx->sc_req = req;
        kref_init(&req->rl_kref);
        req->rl_wr.wr_cqe = &req->rl_sendctx->sc_cqe;
        req->rl_wr.sg_list = req->rl_sendctx->sc_sges;
        req->rl_wr.num_sge = 0;
        req->rl_wr.opcode = IB_WR_SEND;

        rpcrdma_prepare_hdr_sge(r_xprt, req, hdrlen);

        ret = -EIO;
        switch (rtype) {
        case rpcrdma_noch_pullup:
                if (!rpcrdma_prepare_noch_pullup(r_xprt, req, xdr))
                        goto out_unmap;
                break;
        case rpcrdma_noch_mapped:
                if (!rpcrdma_prepare_noch_mapped(r_xprt, req, xdr))
                        goto out_unmap;
                break;
        case rpcrdma_readch:
                if (!rpcrdma_prepare_readch(r_xprt, req, xdr))
                        goto out_unmap;
                break;
        case rpcrdma_areadch:
                break;
        default:
                goto out_unmap;
        }

        return 0;

out_unmap:
        rpcrdma_sendctx_unmap(req->rl_sendctx);
out_nosc:
        trace_xprtrdma_prepsend_failed(&req->rl_slot, ret);
        return ret;
}

/**
 * rpcrdma_marshal_req - Marshal and send one RPC request
 * @r_xprt: controlling transport
 * @rqst: RPC request to be marshaled
 *
 * For the RPC in "rqst", this function:
 *  - Chooses the transfer mode (eg., RDMA_MSG or RDMA_NOMSG)
 *  - Registers Read, Write, and Reply chunks
 *  - Constructs the transport header
 *  - Posts a Send WR to send the transport header and request
 *
 * Returns:
 *      %0 if the RPC was sent successfully,
 *      %-ENOTCONN if the connection was lost,
 *      %-EAGAIN if the caller should call again with the same arguments,
 *      %-ENOBUFS if the caller should call again after a delay,
 *      %-EMSGSIZE if the transport header is too small,
 *      %-EIO if a permanent problem occurred while marshaling.
 */
int
rpcrdma_marshal_req(struct rpcrdma_xprt *r_xprt, struct rpc_rqst *rqst)
{
        struct rpcrdma_req *req = rpcr_to_rdmar(rqst);
        struct xdr_stream *xdr = &req->rl_stream;
        enum rpcrdma_chunktype rtype, wtype;
        struct xdr_buf *buf = &rqst->rq_snd_buf;
        bool ddp_allowed;
        __be32 *p;
        int ret;

        rpcrdma_set_xdrlen(&req->rl_hdrbuf, 0);
        xdr_init_encode(xdr, &req->rl_hdrbuf, rdmab_data(req->rl_rdmabuf),
                        rqst);

        /* Fixed header fields */
        ret = -EMSGSIZE;
        p = xdr_reserve_space(xdr, 4 * sizeof(*p));
        if (!p)
                goto out_err;
        *p++ = rqst->rq_xid;
        *p++ = rpcrdma_version;
        *p++ = r_xprt->rx_buf.rb_max_requests;

        /* When the ULP employs a GSS flavor that guarantees integrity
         * or privacy, direct data placement of individual data items
         * is not allowed.
         */
        ddp_allowed = !(rqst->rq_cred->cr_auth->au_flags &
                                                RPCAUTH_AUTH_DATATOUCH);

        /*
         * Chunks needed for results?
         *
         * o If the expected result is under the inline threshold, all ops
         *   return as inline.
         * o Large read ops return data as write chunk(s), header as
         *   inline.
         * o Large non-read ops return as a single reply chunk.
         */
        if (rpcrdma_results_inline(r_xprt, rqst))
                wtype = rpcrdma_noch;
        else if ((ddp_allowed && rqst->rq_rcv_buf.flags & XDRBUF_READ) &&
                 rpcrdma_nonpayload_inline(r_xprt, rqst))
                wtype = rpcrdma_writech;
        else
                wtype = rpcrdma_replych;

        /*
         * Chunks needed for arguments?
         *
         * o If the total request is under the inline threshold, all ops
         *   are sent as inline.
         * o Large write ops transmit data as read chunk(s), header as
         *   inline.
         * o Large non-write ops are sent with the entire message as a
         *   single read chunk (protocol 0-position special case).
         *
         * This assumes that the upper layer does not present a request
         * that both has a data payload, and whose non-data arguments
         * by themselves are larger than the inline threshold.
         */
        if (rpcrdma_args_inline(r_xprt, rqst)) {
                *p++ = rdma_msg;
                rtype = buf->len < rdmab_length(req->rl_sendbuf) ?
                        rpcrdma_noch_pullup : rpcrdma_noch_mapped;
        } else if (ddp_allowed && buf->flags & XDRBUF_WRITE) {
                *p++ = rdma_msg;
                rtype = rpcrdma_readch;
        } else {
                r_xprt->rx_stats.nomsg_call_count++;
                *p++ = rdma_nomsg;
                rtype = rpcrdma_areadch;
        }

        /* This implementation supports the following combinations
         * of chunk lists in one RPC-over-RDMA Call message:
         *
         *   - Read list
         *   - Write list
         *   - Reply chunk
         *   - Read list + Reply chunk
         *
         * It might not yet support the following combinations:
         *
         *   - Read list + Write list
         *
         * It does not support the following combinations:
         *
         *   - Write list + Reply chunk
         *   - Read list + Write list + Reply chunk
         *
         * This implementation supports only a single chunk in each
         * Read or Write list. Thus for example the client cannot
         * send a Call message with a Position Zero Read chunk and a
         * regular Read chunk at the same time.
         */
        ret = rpcrdma_encode_read_list(r_xprt, req, rqst, rtype);
        if (ret)
                goto out_err;
        ret = rpcrdma_encode_write_list(r_xprt, req, rqst, wtype);
        if (ret)
                goto out_err;
        ret = rpcrdma_encode_reply_chunk(r_xprt, req, rqst, wtype);
        if (ret)
                goto out_err;

        ret = rpcrdma_prepare_send_sges(r_xprt, req, req->rl_hdrbuf.len,
                                        buf, rtype);
        if (ret)
                goto out_err;

        trace_xprtrdma_marshal(req, rtype, wtype);
        return 0;

out_err:
        trace_xprtrdma_marshal_failed(rqst, ret);
        r_xprt->rx_stats.failed_marshal_count++;
        frwr_reset(req);
        return ret;
}

static void __rpcrdma_update_cwnd_locked(struct rpc_xprt *xprt,
                                         struct rpcrdma_buffer *buf,
                                         u32 grant)
{
        buf->rb_credits = grant;
        xprt->cwnd = grant << RPC_CWNDSHIFT;
}

static void rpcrdma_update_cwnd(struct rpcrdma_xprt *r_xprt, u32 grant)
{
        struct rpc_xprt *xprt = &r_xprt->rx_xprt;

        spin_lock(&xprt->transport_lock);
        __rpcrdma_update_cwnd_locked(xprt, &r_xprt->rx_buf, grant);
        spin_unlock(&xprt->transport_lock);
}

/**
 * rpcrdma_reset_cwnd - Reset the xprt's congestion window
 * @r_xprt: controlling transport instance
 *
 * Prepare @r_xprt for the next connection by reinitializing
 * its credit grant to one (see RFC 8166, Section 3.3.3).
 */
void rpcrdma_reset_cwnd(struct rpcrdma_xprt *r_xprt)
{
        struct rpc_xprt *xprt = &r_xprt->rx_xprt;

        spin_lock(&xprt->transport_lock);
        xprt->cong = 0;
        __rpcrdma_update_cwnd_locked(xprt, &r_xprt->rx_buf, 1);
        spin_unlock(&xprt->transport_lock);
}

/**
 * rpcrdma_inline_fixup - Scatter inline received data into rqst's iovecs
 * @rqst: controlling RPC request
 * @srcp: points to RPC message payload in receive buffer
 * @copy_len: remaining length of receive buffer content
 * @pad: Write chunk pad bytes needed (zero for pure inline)
 *
 * The upper layer has set the maximum number of bytes it can
 * receive in each component of rq_rcv_buf. These values are set in
 * the head.iov_len, page_len, tail.iov_len, and buflen fields.
 *
 * Unlike the TCP equivalent (xdr_partial_copy_from_skb), in
 * many cases this function simply updates iov_base pointers in
 * rq_rcv_buf to point directly to the received reply data, to
 * avoid copying reply data.
 *
 * Returns the count of bytes which had to be memcopied.
 */
static unsigned long
rpcrdma_inline_fixup(struct rpc_rqst *rqst, char *srcp, int copy_len, int pad)
{
        unsigned long fixup_copy_count;
        int i, npages, curlen;
        char *destp;
        struct page **ppages;
        int page_base;

        /* The head iovec is redirected to the RPC reply message
         * in the receive buffer, to avoid a memcopy.
         */
        rqst->rq_rcv_buf.head[0].iov_base = srcp;
        rqst->rq_private_buf.head[0].iov_base = srcp;

        /* The contents of the receive buffer that follow
         * head.iov_len bytes are copied into the page list.
         */
        curlen = rqst->rq_rcv_buf.head[0].iov_len;
        if (curlen > copy_len)
                curlen = copy_len;
        srcp += curlen;
        copy_len -= curlen;

        ppages = rqst->rq_rcv_buf.pages +
                (rqst->rq_rcv_buf.page_base >> PAGE_SHIFT);
        page_base = offset_in_page(rqst->rq_rcv_buf.page_base);
        fixup_copy_count = 0;
        if (copy_len && rqst->rq_rcv_buf.page_len) {
                int pagelist_len;

                pagelist_len = rqst->rq_rcv_buf.page_len;
                if (pagelist_len > copy_len)
                        pagelist_len = copy_len;
                npages = PAGE_ALIGN(page_base + pagelist_len) >> PAGE_SHIFT;
                for (i = 0; i < npages; i++) {
                        curlen = PAGE_SIZE - page_base;
                        if (curlen > pagelist_len)
                                curlen = pagelist_len;

                        destp = kmap_atomic(ppages[i]);
                        memcpy(destp + page_base, srcp, curlen);
                        flush_dcache_page(ppages[i]);
                        kunmap_atomic(destp);
                        srcp += curlen;
                        copy_len -= curlen;
                        fixup_copy_count += curlen;
                        pagelist_len -= curlen;
                        if (!pagelist_len)
                                break;
                        page_base = 0;
                }

                /* Implicit padding for the last segment in a Write
                 * chunk is inserted inline at the front of the tail
                 * iovec. The upper layer ignores the content of
                 * the pad. Simply ensure inline content in the tail
                 * that follows the Write chunk is properly aligned.
                 */
                if (pad)
                        srcp -= pad;
        }

        /* The tail iovec is redirected to the remaining data
         * in the receive buffer, to avoid a memcopy.
         */
        if (copy_len || pad) {
                rqst->rq_rcv_buf.tail[0].iov_base = srcp;
                rqst->rq_private_buf.tail[0].iov_base = srcp;
        }

        if (fixup_copy_count)
                trace_xprtrdma_fixup(rqst, fixup_copy_count);
        return fixup_copy_count;
}

/* By convention, backchannel calls arrive via rdma_msg type
 * messages, and never populate the chunk lists. This makes
 * the RPC/RDMA header small and fixed in size, so it is
 * straightforward to check the RPC header's direction field.
 */
static bool
rpcrdma_is_bcall(struct rpcrdma_xprt *r_xprt, struct rpcrdma_rep *rep)
#if defined(CONFIG_SUNRPC_BACKCHANNEL)
{
        struct xdr_stream *xdr = &rep->rr_stream;
        __be32 *p;

        if (rep->rr_proc != rdma_msg)
                return false;

        /* Peek at stream contents without advancing. */
        p = xdr_inline_decode(xdr, 0);

        /* Chunk lists */
        if (*p++ != xdr_zero)
                return false;
        if (*p++ != xdr_zero)
                return false;
        if (*p++ != xdr_zero)
                return false;

        /* RPC header */
        if (*p++ != rep->rr_xid)
                return false;
        if (*p != cpu_to_be32(RPC_CALL))
                return false;

        /* Now that we are sure this is a backchannel call,
         * advance to the RPC header.
         */
        p = xdr_inline_decode(xdr, 3 * sizeof(*p));
        if (unlikely(!p))
                goto out_short;

        rpcrdma_bc_receive_call(r_xprt, rep);
        return true;

out_short:
        pr_warn("RPC/RDMA short backward direction call\n");
        return true;
}
#else   /* CONFIG_SUNRPC_BACKCHANNEL */
{
        return false;
}
#endif  /* CONFIG_SUNRPC_BACKCHANNEL */

static int decode_rdma_segment(struct xdr_stream *xdr, u32 *length)
{
        u32 handle;
        u64 offset;
        __be32 *p;

        p = xdr_inline_decode(xdr, 4 * sizeof(*p));
        if (unlikely(!p))
                return -EIO;

        handle = be32_to_cpup(p++);
        *length = be32_to_cpup(p++);
        xdr_decode_hyper(p, &offset);

        trace_xprtrdma_decode_seg(handle, *length, offset);
        return 0;
}

static int decode_write_chunk(struct xdr_stream *xdr, u32 *length)
{
        u32 segcount, seglength;
        __be32 *p;

        p = xdr_inline_decode(xdr, sizeof(*p));
        if (unlikely(!p))
                return -EIO;

        *length = 0;
        segcount = be32_to_cpup(p);
        while (segcount--) {
                if (decode_rdma_segment(xdr, &seglength))
                        return -EIO;
                *length += seglength;
        }

        return 0;
}

/* In RPC-over-RDMA Version One replies, a Read list is never
 * expected. This decoder is a stub that returns an error if
 * a Read list is present.
 */
static int decode_read_list(struct xdr_stream *xdr)
{
        __be32 *p;

        p = xdr_inline_decode(xdr, sizeof(*p));
        if (unlikely(!p))
                return -EIO;
        if (unlikely(*p != xdr_zero))
                return -EIO;
        return 0;
}

/* Supports only one Write chunk in the Write list
 */
static int decode_write_list(struct xdr_stream *xdr, u32 *length)
{
        u32 chunklen;
        bool first;
        __be32 *p;

        *length = 0;
        first = true;
        do {
                p = xdr_inline_decode(xdr, sizeof(*p));
                if (unlikely(!p))
                        return -EIO;
                if (*p == xdr_zero)
                        break;
                if (!first)
                        return -EIO;

                if (decode_write_chunk(xdr, &chunklen))
                        return -EIO;
                *length += chunklen;
                first = false;
        } while (true);
        return 0;
}

static int decode_reply_chunk(struct xdr_stream *xdr, u32 *length)
{
        __be32 *p;

        p = xdr_inline_decode(xdr, sizeof(*p));
        if (unlikely(!p))
                return -EIO;

        *length = 0;
        if (*p != xdr_zero)
                if (decode_write_chunk(xdr, length))
                        return -EIO;
        return 0;
}

static int
rpcrdma_decode_msg(struct rpcrdma_xprt *r_xprt, struct rpcrdma_rep *rep,
                   struct rpc_rqst *rqst)
{
        struct xdr_stream *xdr = &rep->rr_stream;
        u32 writelist, replychunk, rpclen;
        char *base;

        /* Decode the chunk lists */
        if (decode_read_list(xdr))
                return -EIO;
        if (decode_write_list(xdr, &writelist))
                return -EIO;
        if (decode_reply_chunk(xdr, &replychunk))
                return -EIO;

        /* RDMA_MSG sanity checks */
        if (unlikely(replychunk))
                return -EIO;

        /* Build the RPC reply's Payload stream in rqst->rq_rcv_buf */
        base = (char *)xdr_inline_decode(xdr, 0);
        rpclen = xdr_stream_remaining(xdr);
        r_xprt->rx_stats.fixup_copy_count +=
                rpcrdma_inline_fixup(rqst, base, rpclen, writelist & 3);

        r_xprt->rx_stats.total_rdma_reply += writelist;
        return rpclen + xdr_align_size(writelist);
}

static noinline int
rpcrdma_decode_nomsg(struct rpcrdma_xprt *r_xprt, struct rpcrdma_rep *rep)
{
        struct xdr_stream *xdr = &rep->rr_stream;
        u32 writelist, replychunk;

        /* Decode the chunk lists */
        if (decode_read_list(xdr))
                return -EIO;
        if (decode_write_list(xdr, &writelist))
                return -EIO;
        if (decode_reply_chunk(xdr, &replychunk))
                return -EIO;

        /* RDMA_NOMSG sanity checks */
        if (unlikely(writelist))
                return -EIO;
        if (unlikely(!replychunk))
                return -EIO;

        /* Reply chunk buffer already is the reply vector */
        r_xprt->rx_stats.total_rdma_reply += replychunk;
        return replychunk;
}

static noinline int
rpcrdma_decode_error(struct rpcrdma_xprt *r_xprt, struct rpcrdma_rep *rep,
                     struct rpc_rqst *rqst)
{
        struct xdr_stream *xdr = &rep->rr_stream;
        __be32 *p;

        p = xdr_inline_decode(xdr, sizeof(*p));
        if (unlikely(!p))
                return -EIO;

        switch (*p) {
        case err_vers:
                p = xdr_inline_decode(xdr, 2 * sizeof(*p));
                if (!p)
                        break;
                dprintk("RPC:       %s: server reports "
                        "version error (%u-%u), xid %08x\n", __func__,
                        be32_to_cpup(p), be32_to_cpu(*(p + 1)),
                        be32_to_cpu(rep->rr_xid));
                break;
        case err_chunk:
                dprintk("RPC:       %s: server reports "
                        "header decoding error, xid %08x\n", __func__,
                        be32_to_cpu(rep->rr_xid));
                break;
        default:
                dprintk("RPC:       %s: server reports "
                        "unrecognized error %d, xid %08x\n", __func__,
                        be32_to_cpup(p), be32_to_cpu(rep->rr_xid));
        }

        r_xprt->rx_stats.bad_reply_count++;
        return -EREMOTEIO;
}

/* Perform XID lookup, reconstruction of the RPC reply, and
 * RPC completion while holding the transport lock to ensure
 * the rep, rqst, and rq_task pointers remain stable.
 */
void rpcrdma_complete_rqst(struct rpcrdma_rep *rep)
{
        struct rpcrdma_xprt *r_xprt = rep->rr_rxprt;
        struct rpc_xprt *xprt = &r_xprt->rx_xprt;
        struct rpc_rqst *rqst = rep->rr_rqst;
        int status;

        switch (rep->rr_proc) {
        case rdma_msg:
                status = rpcrdma_decode_msg(r_xprt, rep, rqst);
                break;
        case rdma_nomsg:
                status = rpcrdma_decode_nomsg(r_xprt, rep);
                break;
        case rdma_error:
                status = rpcrdma_decode_error(r_xprt, rep, rqst);
                break;
        default:
                status = -EIO;
        }
        if (status < 0)
                goto out_badheader;

out:
        spin_lock(&xprt->queue_lock);
        xprt_complete_rqst(rqst->rq_task, status);
        xprt_unpin_rqst(rqst);
        spin_unlock(&xprt->queue_lock);
        return;

/* If the incoming reply terminated a pending RPC, the next
 * RPC call will post a replacement receive buffer as it is
 * being marshaled.
 */
out_badheader:
        trace_xprtrdma_reply_hdr(rep);
        r_xprt->rx_stats.bad_reply_count++;
        goto out;
}

static void rpcrdma_reply_done(struct kref *kref)
{
        struct rpcrdma_req *req =
                container_of(kref, struct rpcrdma_req, rl_kref);

        rpcrdma_complete_rqst(req->rl_reply);
}

/**
 * rpcrdma_reply_handler - Process received RPC/RDMA messages
 * @rep: Incoming rpcrdma_rep object to process
 *
 * Errors must result in the RPC task either being awakened, or
 * allowed to timeout, to discover the errors at that time.
 */
void rpcrdma_reply_handler(struct rpcrdma_rep *rep)
{
        struct rpcrdma_xprt *r_xprt = rep->rr_rxprt;
        struct rpc_xprt *xprt = &r_xprt->rx_xprt;
        struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
        struct rpcrdma_req *req;
        struct rpc_rqst *rqst;
        u32 credits;
        __be32 *p;

        /* Any data means we had a useful conversation, so
         * then we don't need to delay the next reconnect.
         */
        if (xprt->reestablish_timeout)
                xprt->reestablish_timeout = 0;

        /* Fixed transport header fields */
        xdr_init_decode(&rep->rr_stream, &rep->rr_hdrbuf,
                        rep->rr_hdrbuf.head[0].iov_base, NULL);
        p = xdr_inline_decode(&rep->rr_stream, 4 * sizeof(*p));
        if (unlikely(!p))
                goto out_shortreply;
        rep->rr_xid = *p++;
        rep->rr_vers = *p++;
        credits = be32_to_cpu(*p++);
        rep->rr_proc = *p++;

        if (rep->rr_vers != rpcrdma_version)
                goto out_badversion;

        if (rpcrdma_is_bcall(r_xprt, rep))
                return;

        /* Match incoming rpcrdma_rep to an rpcrdma_req to
         * get context for handling any incoming chunks.
         */
        spin_lock(&xprt->queue_lock);
        rqst = xprt_lookup_rqst(xprt, rep->rr_xid);
        if (!rqst)
                goto out_norqst;
        xprt_pin_rqst(rqst);
        spin_unlock(&xprt->queue_lock);

        if (credits == 0)
                credits = 1;    /* don't deadlock */
        else if (credits > r_xprt->rx_ep.rep_max_requests)
                credits = r_xprt->rx_ep.rep_max_requests;
        if (buf->rb_credits != credits)
                rpcrdma_update_cwnd(r_xprt, credits);
        rpcrdma_post_recvs(r_xprt, false);

        req = rpcr_to_rdmar(rqst);
        if (req->rl_reply) {
                trace_xprtrdma_leaked_rep(rqst, req->rl_reply);
                rpcrdma_recv_buffer_put(req->rl_reply);
        }
        req->rl_reply = rep;
        rep->rr_rqst = rqst;

        trace_xprtrdma_reply(rqst->rq_task, rep, req, credits);

        if (rep->rr_wc_flags & IB_WC_WITH_INVALIDATE)
                frwr_reminv(rep, &req->rl_registered);
        if (!list_empty(&req->rl_registered))
                frwr_unmap_async(r_xprt, req);
                /* LocalInv completion will complete the RPC */
        else
                kref_put(&req->rl_kref, rpcrdma_reply_done);
        return;

out_badversion:
        trace_xprtrdma_reply_vers(rep);
        goto out;

out_norqst:
        spin_unlock(&xprt->queue_lock);
        trace_xprtrdma_reply_rqst(rep);
        goto out;

out_shortreply:
        trace_xprtrdma_reply_short(rep);

out:
        rpcrdma_recv_buffer_put(rep);
}