Merge tag 'media/v4.8-6' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab...

[GitHub/moto-9609/android_kernel_motorola_exynos9610.git] / net / sunrpc / xprtrdma / svc_rdma_sendto.c

/*
 * 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>
 */

#include <linux/sunrpc/debug.h>
#include <linux/sunrpc/rpc_rdma.h>
#include <linux/spinlock.h>
#include <asm/unaligned.h>
#include <rdma/ib_verbs.h>
#include <rdma/rdma_cm.h>
#include <linux/sunrpc/svc_rdma.h>

#define RPCDBG_FACILITY RPCDBG_SVCXPRT

static u32 xdr_padsize(u32 len)
{
        return (len & 3) ? (4 - (len & 3)) : 0;
}

int svc_rdma_map_xdr(struct svcxprt_rdma *xprt,
                     struct xdr_buf *xdr,
                     struct svc_rdma_req_map *vec,
                     bool write_chunk_present)
{
        int sge_no;
        u32 sge_bytes;
        u32 page_bytes;
        u32 page_off;
        int page_no;

        if (xdr->len !=
            (xdr->head[0].iov_len + xdr->page_len + xdr->tail[0].iov_len)) {
                pr_err("svcrdma: %s: XDR buffer length error\n", __func__);
                return -EIO;
        }

        /* Skip the first sge, this is for the RPCRDMA header */
        sge_no = 1;

        /* Head SGE */
        vec->sge[sge_no].iov_base = xdr->head[0].iov_base;
        vec->sge[sge_no].iov_len = xdr->head[0].iov_len;
        sge_no++;

        /* pages SGE */
        page_no = 0;
        page_bytes = xdr->page_len;
        page_off = xdr->page_base;
        while (page_bytes) {
                vec->sge[sge_no].iov_base =
                        page_address(xdr->pages[page_no]) + page_off;
                sge_bytes = min_t(u32, page_bytes, (PAGE_SIZE - page_off));
                page_bytes -= sge_bytes;
                vec->sge[sge_no].iov_len = sge_bytes;

                sge_no++;
                page_no++;
                page_off = 0; /* reset for next time through loop */
        }

        /* Tail SGE */
        if (xdr->tail[0].iov_len) {
                unsigned char *base = xdr->tail[0].iov_base;
                size_t len = xdr->tail[0].iov_len;
                u32 xdr_pad = xdr_padsize(xdr->page_len);

                if (write_chunk_present && xdr_pad) {
                        base += xdr_pad;
                        len -= xdr_pad;
                }

                if (len) {
                        vec->sge[sge_no].iov_base = base;
                        vec->sge[sge_no].iov_len = len;
                        sge_no++;
                }
        }

        dprintk("svcrdma: %s: sge_no %d page_no %d "
                "page_base %u page_len %u head_len %zu tail_len %zu\n",
                __func__, sge_no, page_no, xdr->page_base, xdr->page_len,
                xdr->head[0].iov_len, xdr->tail[0].iov_len);

        vec->count = sge_no;
        return 0;
}

static dma_addr_t dma_map_xdr(struct svcxprt_rdma *xprt,
                              struct xdr_buf *xdr,
                              u32 xdr_off, size_t len, int dir)
{
        struct page *page;
        dma_addr_t dma_addr;
        if (xdr_off < xdr->head[0].iov_len) {
                /* This offset is in the head */
                xdr_off += (unsigned long)xdr->head[0].iov_base & ~PAGE_MASK;
                page = virt_to_page(xdr->head[0].iov_base);
        } else {
                xdr_off -= xdr->head[0].iov_len;
                if (xdr_off < xdr->page_len) {
                        /* This offset is in the page list */
                        xdr_off += xdr->page_base;
                        page = xdr->pages[xdr_off >> PAGE_SHIFT];
                        xdr_off &= ~PAGE_MASK;
                } else {
                        /* This offset is in the tail */
                        xdr_off -= xdr->page_len;
                        xdr_off += (unsigned long)
                                xdr->tail[0].iov_base & ~PAGE_MASK;
                        page = virt_to_page(xdr->tail[0].iov_base);
                }
        }
        dma_addr = ib_dma_map_page(xprt->sc_cm_id->device, page, xdr_off,
                                   min_t(size_t, PAGE_SIZE, len), dir);
        return dma_addr;
}

/* Returns the address of the first read chunk or <nul> if no read chunk
 * is present
 */
struct rpcrdma_read_chunk *
svc_rdma_get_read_chunk(struct rpcrdma_msg *rmsgp)
{
        struct rpcrdma_read_chunk *ch =
                (struct rpcrdma_read_chunk *)&rmsgp->rm_body.rm_chunks[0];

        if (ch->rc_discrim == xdr_zero)
                return NULL;
        return ch;
}

/* Returns the address of the first read write array element or <nul>
 * if no write array list is present
 */
static struct rpcrdma_write_array *
svc_rdma_get_write_array(struct rpcrdma_msg *rmsgp)
{
        if (rmsgp->rm_body.rm_chunks[0] != xdr_zero ||
            rmsgp->rm_body.rm_chunks[1] == xdr_zero)
                return NULL;
        return (struct rpcrdma_write_array *)&rmsgp->rm_body.rm_chunks[1];
}

/* Returns the address of the first reply array element or <nul> if no
 * reply array is present
 */
static struct rpcrdma_write_array *
svc_rdma_get_reply_array(struct rpcrdma_msg *rmsgp,
                         struct rpcrdma_write_array *wr_ary)
{
        struct rpcrdma_read_chunk *rch;
        struct rpcrdma_write_array *rp_ary;

        /* XXX: Need to fix when reply chunk may occur with read list
         *      and/or write list.
         */
        if (rmsgp->rm_body.rm_chunks[0] != xdr_zero ||
            rmsgp->rm_body.rm_chunks[1] != xdr_zero)
                return NULL;

        rch = svc_rdma_get_read_chunk(rmsgp);
        if (rch) {
                while (rch->rc_discrim != xdr_zero)
                        rch++;

                /* The reply chunk follows an empty write array located
                 * at 'rc_position' here. The reply array is at rc_target.
                 */
                rp_ary = (struct rpcrdma_write_array *)&rch->rc_target;
                goto found_it;
        }

        if (wr_ary) {
                int chunk = be32_to_cpu(wr_ary->wc_nchunks);

                rp_ary = (struct rpcrdma_write_array *)
                         &wr_ary->wc_array[chunk].wc_target.rs_length;
                goto found_it;
        }

        /* No read list, no write list */
        rp_ary = (struct rpcrdma_write_array *)&rmsgp->rm_body.rm_chunks[2];

 found_it:
        if (rp_ary->wc_discrim == xdr_zero)
                return NULL;
        return rp_ary;
}

/* Assumptions:
 * - The specified write_len can be represented in sc_max_sge * PAGE_SIZE
 */
static int send_write(struct svcxprt_rdma *xprt, struct svc_rqst *rqstp,
                      u32 rmr, u64 to,
                      u32 xdr_off, int write_len,
                      struct svc_rdma_req_map *vec)
{
        struct ib_rdma_wr write_wr;
        struct ib_sge *sge;
        int xdr_sge_no;
        int sge_no;
        int sge_bytes;
        int sge_off;
        int bc;
        struct svc_rdma_op_ctxt *ctxt;

        if (vec->count > RPCSVC_MAXPAGES) {
                pr_err("svcrdma: Too many pages (%lu)\n", vec->count);
                return -EIO;
        }

        dprintk("svcrdma: RDMA_WRITE rmr=%x, to=%llx, xdr_off=%d, "
                "write_len=%d, vec->sge=%p, vec->count=%lu\n",
                rmr, (unsigned long long)to, xdr_off,
                write_len, vec->sge, vec->count);

        ctxt = svc_rdma_get_context(xprt);
        ctxt->direction = DMA_TO_DEVICE;
        sge = ctxt->sge;

        /* Find the SGE associated with xdr_off */
        for (bc = xdr_off, xdr_sge_no = 1; bc && xdr_sge_no < vec->count;
             xdr_sge_no++) {
                if (vec->sge[xdr_sge_no].iov_len > bc)
                        break;
                bc -= vec->sge[xdr_sge_no].iov_len;
        }

        sge_off = bc;
        bc = write_len;
        sge_no = 0;

        /* Copy the remaining SGE */
        while (bc != 0) {
                sge_bytes = min_t(size_t,
                          bc, vec->sge[xdr_sge_no].iov_len-sge_off);
                sge[sge_no].length = sge_bytes;
                sge[sge_no].addr =
                        dma_map_xdr(xprt, &rqstp->rq_res, xdr_off,
                                    sge_bytes, DMA_TO_DEVICE);
                xdr_off += sge_bytes;
                if (ib_dma_mapping_error(xprt->sc_cm_id->device,
                                         sge[sge_no].addr))
                        goto err;
                atomic_inc(&xprt->sc_dma_used);
                sge[sge_no].lkey = xprt->sc_pd->local_dma_lkey;
                ctxt->count++;
                sge_off = 0;
                sge_no++;
                xdr_sge_no++;
                if (xdr_sge_no > vec->count) {
                        pr_err("svcrdma: Too many sges (%d)\n", xdr_sge_no);
                        goto err;
                }
                bc -= sge_bytes;
                if (sge_no == xprt->sc_max_sge)
                        break;
        }

        /* Prepare WRITE WR */
        memset(&write_wr, 0, sizeof write_wr);
        ctxt->cqe.done = svc_rdma_wc_write;
        write_wr.wr.wr_cqe = &ctxt->cqe;
        write_wr.wr.sg_list = &sge[0];
        write_wr.wr.num_sge = sge_no;
        write_wr.wr.opcode = IB_WR_RDMA_WRITE;
        write_wr.wr.send_flags = IB_SEND_SIGNALED;
        write_wr.rkey = rmr;
        write_wr.remote_addr = to;

        /* Post It */
        atomic_inc(&rdma_stat_write);
        if (svc_rdma_send(xprt, &write_wr.wr))
                goto err;
        return write_len - bc;
 err:
        svc_rdma_unmap_dma(ctxt);
        svc_rdma_put_context(ctxt, 0);
        return -EIO;
}

noinline
static int send_write_chunks(struct svcxprt_rdma *xprt,
                             struct rpcrdma_write_array *wr_ary,
                             struct rpcrdma_msg *rdma_resp,
                             struct svc_rqst *rqstp,
                             struct svc_rdma_req_map *vec)
{
        u32 xfer_len = rqstp->rq_res.page_len;
        int write_len;
        u32 xdr_off;
        int chunk_off;
        int chunk_no;
        int nchunks;
        struct rpcrdma_write_array *res_ary;
        int ret;

        res_ary = (struct rpcrdma_write_array *)
                &rdma_resp->rm_body.rm_chunks[1];

        /* Write chunks start at the pagelist */
        nchunks = be32_to_cpu(wr_ary->wc_nchunks);
        for (xdr_off = rqstp->rq_res.head[0].iov_len, chunk_no = 0;
             xfer_len && chunk_no < nchunks;
             chunk_no++) {
                struct rpcrdma_segment *arg_ch;
                u64 rs_offset;

                arg_ch = &wr_ary->wc_array[chunk_no].wc_target;
                write_len = min(xfer_len, be32_to_cpu(arg_ch->rs_length));

                /* Prepare the response chunk given the length actually
                 * written */
                xdr_decode_hyper((__be32 *)&arg_ch->rs_offset, &rs_offset);
                svc_rdma_xdr_encode_array_chunk(res_ary, chunk_no,
                                                arg_ch->rs_handle,
                                                arg_ch->rs_offset,
                                                write_len);
                chunk_off = 0;
                while (write_len) {
                        ret = send_write(xprt, rqstp,
                                         be32_to_cpu(arg_ch->rs_handle),
                                         rs_offset + chunk_off,
                                         xdr_off,
                                         write_len,
                                         vec);
                        if (ret <= 0)
                                goto out_err;
                        chunk_off += ret;
                        xdr_off += ret;
                        xfer_len -= ret;
                        write_len -= ret;
                }
        }
        /* Update the req with the number of chunks actually used */
        svc_rdma_xdr_encode_write_list(rdma_resp, chunk_no);

        return rqstp->rq_res.page_len;

out_err:
        pr_err("svcrdma: failed to send write chunks, rc=%d\n", ret);
        return -EIO;
}

noinline
static int send_reply_chunks(struct svcxprt_rdma *xprt,
                             struct rpcrdma_write_array *rp_ary,
                             struct rpcrdma_msg *rdma_resp,
                             struct svc_rqst *rqstp,
                             struct svc_rdma_req_map *vec)
{
        u32 xfer_len = rqstp->rq_res.len;
        int write_len;
        u32 xdr_off;
        int chunk_no;
        int chunk_off;
        int nchunks;
        struct rpcrdma_segment *ch;
        struct rpcrdma_write_array *res_ary;
        int ret;

        /* XXX: need to fix when reply lists occur with read-list and or
         * write-list */
        res_ary = (struct rpcrdma_write_array *)
                &rdma_resp->rm_body.rm_chunks[2];

        /* xdr offset starts at RPC message */
        nchunks = be32_to_cpu(rp_ary->wc_nchunks);
        for (xdr_off = 0, chunk_no = 0;
             xfer_len && chunk_no < nchunks;
             chunk_no++) {
                u64 rs_offset;
                ch = &rp_ary->wc_array[chunk_no].wc_target;
                write_len = min(xfer_len, be32_to_cpu(ch->rs_length));

                /* Prepare the reply chunk given the length actually
                 * written */
                xdr_decode_hyper((__be32 *)&ch->rs_offset, &rs_offset);
                svc_rdma_xdr_encode_array_chunk(res_ary, chunk_no,
                                                ch->rs_handle, ch->rs_offset,
                                                write_len);
                chunk_off = 0;
                while (write_len) {
                        ret = send_write(xprt, rqstp,
                                         be32_to_cpu(ch->rs_handle),
                                         rs_offset + chunk_off,
                                         xdr_off,
                                         write_len,
                                         vec);
                        if (ret <= 0)
                                goto out_err;
                        chunk_off += ret;
                        xdr_off += ret;
                        xfer_len -= ret;
                        write_len -= ret;
                }
        }
        /* Update the req with the number of chunks actually used */
        svc_rdma_xdr_encode_reply_array(res_ary, chunk_no);

        return rqstp->rq_res.len;

out_err:
        pr_err("svcrdma: failed to send reply chunks, rc=%d\n", ret);
        return -EIO;
}

/* This function prepares the portion of the RPCRDMA message to be
 * sent in the RDMA_SEND. This function is called after data sent via
 * RDMA has already been transmitted. There are three cases:
 * - The RPCRDMA header, RPC header, and payload are all sent in a
 *   single RDMA_SEND. This is the "inline" case.
 * - The RPCRDMA header and some portion of the RPC header and data
 *   are sent via this RDMA_SEND and another portion of the data is
 *   sent via RDMA.
 * - The RPCRDMA header [NOMSG] is sent in this RDMA_SEND and the RPC
 *   header and data are all transmitted via RDMA.
 * In all three cases, this function prepares the RPCRDMA header in
 * sge[0], the 'type' parameter indicates the type to place in the
 * RPCRDMA header, and the 'byte_count' field indicates how much of
 * the XDR to include in this RDMA_SEND. NB: The offset of the payload
 * to send is zero in the XDR.
 */
static int send_reply(struct svcxprt_rdma *rdma,
                      struct svc_rqst *rqstp,
                      struct page *page,
                      struct rpcrdma_msg *rdma_resp,
                      struct svc_rdma_req_map *vec,
                      int byte_count)
{
        struct svc_rdma_op_ctxt *ctxt;
        struct ib_send_wr send_wr;
        u32 xdr_off;
        int sge_no;
        int sge_bytes;
        int page_no;
        int pages;
        int ret = -EIO;

        /* Prepare the context */
        ctxt = svc_rdma_get_context(rdma);
        ctxt->direction = DMA_TO_DEVICE;
        ctxt->pages[0] = page;
        ctxt->count = 1;

        /* Prepare the SGE for the RPCRDMA Header */
        ctxt->sge[0].lkey = rdma->sc_pd->local_dma_lkey;
        ctxt->sge[0].length = svc_rdma_xdr_get_reply_hdr_len(rdma_resp);
        ctxt->sge[0].addr =
            ib_dma_map_page(rdma->sc_cm_id->device, page, 0,
                            ctxt->sge[0].length, DMA_TO_DEVICE);
        if (ib_dma_mapping_error(rdma->sc_cm_id->device, ctxt->sge[0].addr))
                goto err;
        atomic_inc(&rdma->sc_dma_used);

        ctxt->direction = DMA_TO_DEVICE;

        /* Map the payload indicated by 'byte_count' */
        xdr_off = 0;
        for (sge_no = 1; byte_count && sge_no < vec->count; sge_no++) {
                sge_bytes = min_t(size_t, vec->sge[sge_no].iov_len, byte_count);
                byte_count -= sge_bytes;
                ctxt->sge[sge_no].addr =
                        dma_map_xdr(rdma, &rqstp->rq_res, xdr_off,
                                    sge_bytes, DMA_TO_DEVICE);
                xdr_off += sge_bytes;
                if (ib_dma_mapping_error(rdma->sc_cm_id->device,
                                         ctxt->sge[sge_no].addr))
                        goto err;
                atomic_inc(&rdma->sc_dma_used);
                ctxt->sge[sge_no].lkey = rdma->sc_pd->local_dma_lkey;
                ctxt->sge[sge_no].length = sge_bytes;
        }
        if (byte_count != 0) {
                pr_err("svcrdma: Could not map %d bytes\n", byte_count);
                goto err;
        }

        /* Save all respages in the ctxt and remove them from the
         * respages array. They are our pages until the I/O
         * completes.
         */
        pages = rqstp->rq_next_page - rqstp->rq_respages;
        for (page_no = 0; page_no < pages; page_no++) {
                ctxt->pages[page_no+1] = rqstp->rq_respages[page_no];
                ctxt->count++;
                rqstp->rq_respages[page_no] = NULL;
                /*
                 * If there are more pages than SGE, terminate SGE
                 * list so that svc_rdma_unmap_dma doesn't attempt to
                 * unmap garbage.
                 */
                if (page_no+1 >= sge_no)
                        ctxt->sge[page_no+1].length = 0;
        }
        rqstp->rq_next_page = rqstp->rq_respages + 1;

        /* The loop above bumps sc_dma_used for each sge. The
         * xdr_buf.tail gets a separate sge, but resides in the
         * same page as xdr_buf.head. Don't count it twice.
         */
        if (sge_no > ctxt->count)
                atomic_dec(&rdma->sc_dma_used);

        if (sge_no > rdma->sc_max_sge) {
                pr_err("svcrdma: Too many sges (%d)\n", sge_no);
                goto err;
        }
        memset(&send_wr, 0, sizeof send_wr);
        ctxt->cqe.done = svc_rdma_wc_send;
        send_wr.wr_cqe = &ctxt->cqe;
        send_wr.sg_list = ctxt->sge;
        send_wr.num_sge = sge_no;
        send_wr.opcode = IB_WR_SEND;
        send_wr.send_flags =  IB_SEND_SIGNALED;

        ret = svc_rdma_send(rdma, &send_wr);
        if (ret)
                goto err;

        return 0;

 err:
        svc_rdma_unmap_dma(ctxt);
        svc_rdma_put_context(ctxt, 1);
        return ret;
}

void svc_rdma_prep_reply_hdr(struct svc_rqst *rqstp)
{
}

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 rpcrdma_msg *rdma_argp;
        struct rpcrdma_msg *rdma_resp;
        struct rpcrdma_write_array *wr_ary, *rp_ary;
        enum rpcrdma_proc reply_type;
        int ret;
        int inline_bytes;
        struct page *res_page;
        struct svc_rdma_req_map *vec;

        dprintk("svcrdma: sending response for rqstp=%p\n", rqstp);

        /* Get the RDMA request header. The receive logic always
         * places this at the start of page 0.
         */
        rdma_argp = page_address(rqstp->rq_pages[0]);
        wr_ary = svc_rdma_get_write_array(rdma_argp);
        rp_ary = svc_rdma_get_reply_array(rdma_argp, wr_ary);

        /* Build an req vec for the XDR */
        vec = svc_rdma_get_req_map(rdma);
        ret = svc_rdma_map_xdr(rdma, &rqstp->rq_res, vec, wr_ary != NULL);
        if (ret)
                goto err0;
        inline_bytes = rqstp->rq_res.len;

        /* Create the RDMA response header */
        ret = -ENOMEM;
        res_page = alloc_page(GFP_KERNEL);
        if (!res_page)
                goto err0;
        rdma_resp = page_address(res_page);
        if (rp_ary)
                reply_type = RDMA_NOMSG;
        else
                reply_type = RDMA_MSG;
        svc_rdma_xdr_encode_reply_header(rdma, rdma_argp,
                                         rdma_resp, reply_type);

        /* Send any write-chunk data and build resp write-list */
        if (wr_ary) {
                ret = send_write_chunks(rdma, wr_ary, rdma_resp, rqstp, vec);
                if (ret < 0)
                        goto err1;
                inline_bytes -= ret + xdr_padsize(ret);
        }

        /* Send any reply-list data and update resp reply-list */
        if (rp_ary) {
                ret = send_reply_chunks(rdma, rp_ary, rdma_resp, rqstp, vec);
                if (ret < 0)
                        goto err1;
                inline_bytes -= ret;
        }

        /* Post a fresh Receive buffer _before_ sending the reply */
        ret = svc_rdma_post_recv(rdma, GFP_KERNEL);
        if (ret)
                goto err1;

        ret = send_reply(rdma, rqstp, res_page, rdma_resp, vec,
                         inline_bytes);
        if (ret < 0)
                goto err1;

        svc_rdma_put_req_map(rdma, vec);
        dprintk("svcrdma: send_reply returns %d\n", ret);
        return ret;

 err1:
        put_page(res_page);
 err0:
        svc_rdma_put_req_map(rdma, vec);
        pr_err("svcrdma: Could not send reply, err=%d. Closing transport.\n",
               ret);
        set_bit(XPT_CLOSE, &rdma->sc_xprt.xpt_flags);
        return -ENOTCONN;
}

void svc_rdma_send_error(struct svcxprt_rdma *xprt, struct rpcrdma_msg *rmsgp,
                         int status)
{
        struct ib_send_wr err_wr;
        struct page *p;
        struct svc_rdma_op_ctxt *ctxt;
        enum rpcrdma_errcode err;
        __be32 *va;
        int length;
        int ret;

        ret = svc_rdma_repost_recv(xprt, GFP_KERNEL);
        if (ret)
                return;

        p = alloc_page(GFP_KERNEL);
        if (!p)
                return;
        va = page_address(p);

        /* XDR encode an error reply */
        err = ERR_CHUNK;
        if (status == -EPROTONOSUPPORT)
                err = ERR_VERS;
        length = svc_rdma_xdr_encode_error(xprt, rmsgp, err, va);

        ctxt = svc_rdma_get_context(xprt);
        ctxt->direction = DMA_TO_DEVICE;
        ctxt->count = 1;
        ctxt->pages[0] = p;

        /* Prepare SGE for local address */
        ctxt->sge[0].lkey = xprt->sc_pd->local_dma_lkey;
        ctxt->sge[0].length = length;
        ctxt->sge[0].addr = ib_dma_map_page(xprt->sc_cm_id->device,
                                            p, 0, length, DMA_TO_DEVICE);
        if (ib_dma_mapping_error(xprt->sc_cm_id->device, ctxt->sge[0].addr)) {
                dprintk("svcrdma: Error mapping buffer for protocol error\n");
                svc_rdma_put_context(ctxt, 1);
                return;
        }
        atomic_inc(&xprt->sc_dma_used);

        /* Prepare SEND WR */
        memset(&err_wr, 0, sizeof(err_wr));
        ctxt->cqe.done = svc_rdma_wc_send;
        err_wr.wr_cqe = &ctxt->cqe;
        err_wr.sg_list = ctxt->sge;
        err_wr.num_sge = 1;
        err_wr.opcode = IB_WR_SEND;
        err_wr.send_flags = IB_SEND_SIGNALED;

        /* Post It */
        ret = svc_rdma_send(xprt, &err_wr);
        if (ret) {
                dprintk("svcrdma: Error %d posting send for protocol error\n",
                        ret);
                svc_rdma_unmap_dma(ctxt);
                svc_rdma_put_context(ctxt, 1);
        }
}