/*
 * 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

/*
 * Replace the pages in the rq_argpages array with the pages from the SGE in
 * the RDMA_RECV completion. The SGL should contain full pages up until the
 * last one.
 */
static void rdma_build_arg_xdr(struct svc_rqst *rqstp,
                               struct svc_rdma_op_ctxt *ctxt,
                               u32 byte_count)
{
        struct rpcrdma_msg *rmsgp;
        struct page *page;
        u32 bc;
        int sge_no;

        /* Swap the page in the SGE with the page in argpages */
        page = ctxt->pages[0];
        put_page(rqstp->rq_pages[0]);
        rqstp->rq_pages[0] = page;

        /* Set up the XDR head */
        rqstp->rq_arg.head[0].iov_base = page_address(page);
        rqstp->rq_arg.head[0].iov_len =
                min_t(size_t, byte_count, ctxt->sge[0].length);
        rqstp->rq_arg.len = byte_count;
        rqstp->rq_arg.buflen = byte_count;

        /* Compute bytes past head in the SGL */
        bc = byte_count - rqstp->rq_arg.head[0].iov_len;

        /* If data remains, store it in the pagelist */
        rqstp->rq_arg.page_len = bc;
        rqstp->rq_arg.page_base = 0;

        /* RDMA_NOMSG: RDMA READ data should land just after RDMA RECV data */
        rmsgp = (struct rpcrdma_msg *)rqstp->rq_arg.head[0].iov_base;
        if (rmsgp->rm_type == rdma_nomsg)
                rqstp->rq_arg.pages = &rqstp->rq_pages[0];
        else
                rqstp->rq_arg.pages = &rqstp->rq_pages[1];

        sge_no = 1;
        while (bc && sge_no < ctxt->count) {
                page = ctxt->pages[sge_no];
                put_page(rqstp->rq_pages[sge_no]);
                rqstp->rq_pages[sge_no] = page;
                bc -= min_t(u32, bc, ctxt->sge[sge_no].length);
                rqstp->rq_arg.buflen += ctxt->sge[sge_no].length;
                sge_no++;
        }
        rqstp->rq_respages = &rqstp->rq_pages[sge_no];
        rqstp->rq_next_page = rqstp->rq_respages + 1;

        /* If not all pages were used from the SGL, free the remaining ones */
        bc = sge_no;
        while (sge_no < ctxt->count) {
                page = ctxt->pages[sge_no++];
                put_page(page);
        }
        ctxt->count = bc;

        /* Set up tail */
        rqstp->rq_arg.tail[0].iov_base = NULL;
        rqstp->rq_arg.tail[0].iov_len = 0;
}

/* Issue an RDMA_READ using the local lkey to map the data sink */
int rdma_read_chunk_lcl(struct svcxprt_rdma *xprt,
                        struct svc_rqst *rqstp,
                        struct svc_rdma_op_ctxt *head,
                        int *page_no,
                        u32 *page_offset,
                        u32 rs_handle,
                        u32 rs_length,
                        u64 rs_offset,
                        bool last)
{
        struct ib_rdma_wr read_wr;
        int pages_needed = PAGE_ALIGN(*page_offset + rs_length) >> PAGE_SHIFT;
        struct svc_rdma_op_ctxt *ctxt = svc_rdma_get_context(xprt);
        int ret, read, pno;
        u32 pg_off = *page_offset;
        u32 pg_no = *page_no;

        ctxt->direction = DMA_FROM_DEVICE;
        ctxt->read_hdr = head;
        pages_needed = min_t(int, pages_needed, xprt->sc_max_sge_rd);
        read = min_t(int, (pages_needed << PAGE_SHIFT) - *page_offset,
                     rs_length);

        for (pno = 0; pno < pages_needed; pno++) {
                int len = min_t(int, rs_length, PAGE_SIZE - pg_off);

                head->arg.pages[pg_no] = rqstp->rq_arg.pages[pg_no];
                head->arg.page_len += len;

                head->arg.len += len;
                if (!pg_off)
                        head->count++;
                rqstp->rq_respages = &rqstp->rq_arg.pages[pg_no+1];
                rqstp->rq_next_page = rqstp->rq_respages + 1;
                ctxt->sge[pno].addr =
                        ib_dma_map_page(xprt->sc_cm_id->device,
                                        head->arg.pages[pg_no], pg_off,
                                        PAGE_SIZE - pg_off,
                                        DMA_FROM_DEVICE);
                ret = ib_dma_mapping_error(xprt->sc_cm_id->device,
                                           ctxt->sge[pno].addr);
                if (ret)
                        goto err;
                atomic_inc(&xprt->sc_dma_used);

                ctxt->sge[pno].lkey = xprt->sc_pd->local_dma_lkey;
                ctxt->sge[pno].length = len;
                ctxt->count++;

                /* adjust offset and wrap to next page if needed */
                pg_off += len;
                if (pg_off == PAGE_SIZE) {
                        pg_off = 0;
                        pg_no++;
                }
                rs_length -= len;
        }

        if (last && rs_length == 0)
                set_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);
        else
                clear_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);

        memset(&read_wr, 0, sizeof(read_wr));
        ctxt->cqe.done = svc_rdma_wc_read;
        read_wr.wr.wr_cqe = &ctxt->cqe;
        read_wr.wr.opcode = IB_WR_RDMA_READ;
        read_wr.wr.send_flags = IB_SEND_SIGNALED;
        read_wr.rkey = rs_handle;
        read_wr.remote_addr = rs_offset;
        read_wr.wr.sg_list = ctxt->sge;
        read_wr.wr.num_sge = pages_needed;

        ret = svc_rdma_send(xprt, &read_wr.wr);
        if (ret) {
                pr_err("svcrdma: Error %d posting RDMA_READ\n", ret);
                set_bit(XPT_CLOSE, &xprt->sc_xprt.xpt_flags);
                goto err;
        }

        /* return current location in page array */
        *page_no = pg_no;
        *page_offset = pg_off;
        ret = read;
        atomic_inc(&rdma_stat_read);
        return ret;
 err:
        svc_rdma_unmap_dma(ctxt);
        svc_rdma_put_context(ctxt, 0);
        return ret;
}

/* Issue an RDMA_READ using an FRMR to map the data sink */
int rdma_read_chunk_frmr(struct svcxprt_rdma *xprt,
                         struct svc_rqst *rqstp,
                         struct svc_rdma_op_ctxt *head,
                         int *page_no,
                         u32 *page_offset,
                         u32 rs_handle,
                         u32 rs_length,
                         u64 rs_offset,
                         bool last)
{
        struct ib_rdma_wr read_wr;
        struct ib_send_wr inv_wr;
        struct ib_reg_wr reg_wr;
        u8 key;
        int nents = PAGE_ALIGN(*page_offset + rs_length) >> PAGE_SHIFT;
        struct svc_rdma_op_ctxt *ctxt = svc_rdma_get_context(xprt);
        struct svc_rdma_fastreg_mr *frmr = svc_rdma_get_frmr(xprt);
        int ret, read, pno, dma_nents, n;
        u32 pg_off = *page_offset;
        u32 pg_no = *page_no;

        if (IS_ERR(frmr))
                return -ENOMEM;

        ctxt->direction = DMA_FROM_DEVICE;
        ctxt->frmr = frmr;
        nents = min_t(unsigned int, nents, xprt->sc_frmr_pg_list_len);
        read = min_t(int, (nents << PAGE_SHIFT) - *page_offset, rs_length);

        frmr->direction = DMA_FROM_DEVICE;
        frmr->access_flags = (IB_ACCESS_LOCAL_WRITE|IB_ACCESS_REMOTE_WRITE);
        frmr->sg_nents = nents;

        for (pno = 0; pno < nents; pno++) {
                int len = min_t(int, rs_length, PAGE_SIZE - pg_off);

                head->arg.pages[pg_no] = rqstp->rq_arg.pages[pg_no];
                head->arg.page_len += len;
                head->arg.len += len;
                if (!pg_off)
                        head->count++;

                sg_set_page(&frmr->sg[pno], rqstp->rq_arg.pages[pg_no],
                            len, pg_off);

                rqstp->rq_respages = &rqstp->rq_arg.pages[pg_no+1];
                rqstp->rq_next_page = rqstp->rq_respages + 1;

                /* adjust offset and wrap to next page if needed */
                pg_off += len;
                if (pg_off == PAGE_SIZE) {
                        pg_off = 0;
                        pg_no++;
                }
                rs_length -= len;
        }

        if (last && rs_length == 0)
                set_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);
        else
                clear_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);

        dma_nents = ib_dma_map_sg(xprt->sc_cm_id->device,
                                  frmr->sg, frmr->sg_nents,
                                  frmr->direction);
        if (!dma_nents) {
                pr_err("svcrdma: failed to dma map sg %p\n",
                       frmr->sg);
                return -ENOMEM;
        }
        atomic_inc(&xprt->sc_dma_used);

        n = ib_map_mr_sg(frmr->mr, frmr->sg, frmr->sg_nents, PAGE_SIZE);
        if (unlikely(n != frmr->sg_nents)) {
                pr_err("svcrdma: failed to map mr %p (%d/%d elements)\n",
                       frmr->mr, n, frmr->sg_nents);
                return n < 0 ? n : -EINVAL;
        }

        /* Bump the key */
        key = (u8)(frmr->mr->lkey & 0x000000FF);
        ib_update_fast_reg_key(frmr->mr, ++key);

        ctxt->sge[0].addr = frmr->mr->iova;
        ctxt->sge[0].lkey = frmr->mr->lkey;
        ctxt->sge[0].length = frmr->mr->length;
        ctxt->count = 1;
        ctxt->read_hdr = head;

        /* Prepare REG WR */
        ctxt->reg_cqe.done = svc_rdma_wc_reg;
        reg_wr.wr.wr_cqe = &ctxt->reg_cqe;
        reg_wr.wr.opcode = IB_WR_REG_MR;
        reg_wr.wr.send_flags = IB_SEND_SIGNALED;
        reg_wr.wr.num_sge = 0;
        reg_wr.mr = frmr->mr;
        reg_wr.key = frmr->mr->lkey;
        reg_wr.access = frmr->access_flags;
        reg_wr.wr.next = &read_wr.wr;

        /* Prepare RDMA_READ */
        memset(&read_wr, 0, sizeof(read_wr));
        ctxt->cqe.done = svc_rdma_wc_read;
        read_wr.wr.wr_cqe = &ctxt->cqe;
        read_wr.wr.send_flags = IB_SEND_SIGNALED;
        read_wr.rkey = rs_handle;
        read_wr.remote_addr = rs_offset;
        read_wr.wr.sg_list = ctxt->sge;
        read_wr.wr.num_sge = 1;
        if (xprt->sc_dev_caps & SVCRDMA_DEVCAP_READ_W_INV) {
                read_wr.wr.opcode = IB_WR_RDMA_READ_WITH_INV;
                read_wr.wr.ex.invalidate_rkey = ctxt->frmr->mr->lkey;
        } else {
                read_wr.wr.opcode = IB_WR_RDMA_READ;
                read_wr.wr.next = &inv_wr;
                /* Prepare invalidate */
                memset(&inv_wr, 0, sizeof(inv_wr));
                ctxt->inv_cqe.done = svc_rdma_wc_inv;
                inv_wr.wr_cqe = &ctxt->inv_cqe;
                inv_wr.opcode = IB_WR_LOCAL_INV;
                inv_wr.send_flags = IB_SEND_SIGNALED | IB_SEND_FENCE;
                inv_wr.ex.invalidate_rkey = frmr->mr->lkey;
        }

        /* Post the chain */
        ret = svc_rdma_send(xprt, &reg_wr.wr);
        if (ret) {
                pr_err("svcrdma: Error %d posting RDMA_READ\n", ret);
                set_bit(XPT_CLOSE, &xprt->sc_xprt.xpt_flags);
                goto err;
        }

        /* return current location in page array */
        *page_no = pg_no;
        *page_offset = pg_off;
        ret = read;
        atomic_inc(&rdma_stat_read);
        return ret;
 err:
        ib_dma_unmap_sg(xprt->sc_cm_id->device,
                        frmr->sg, frmr->sg_nents, frmr->direction);
        svc_rdma_put_context(ctxt, 0);
        svc_rdma_put_frmr(xprt, frmr);
        return ret;
}

static unsigned int
rdma_rcl_chunk_count(struct rpcrdma_read_chunk *ch)
{
        unsigned int count;

        for (count = 0; ch->rc_discrim != xdr_zero; ch++)
                count++;
        return count;
}

/* If there was additional inline content, append it to the end of arg.pages.
 * Tail copy has to be done after the reader function has determined how many
 * pages are needed for RDMA READ.
 */
static int
rdma_copy_tail(struct svc_rqst *rqstp, struct svc_rdma_op_ctxt *head,
               u32 position, u32 byte_count, u32 page_offset, int page_no)
{
        char *srcp, *destp;
        int ret;

        ret = 0;
        srcp = head->arg.head[0].iov_base + position;
        byte_count = head->arg.head[0].iov_len - position;
        if (byte_count > PAGE_SIZE) {
                dprintk("svcrdma: large tail unsupported\n");
                return 0;
        }

        /* Fit as much of the tail on the current page as possible */
        if (page_offset != PAGE_SIZE) {
                destp = page_address(rqstp->rq_arg.pages[page_no]);
                destp += page_offset;
                while (byte_count--) {
                        *destp++ = *srcp++;
                        page_offset++;
                        if (page_offset == PAGE_SIZE && byte_count)
                                goto more;
                }
                goto done;
        }

more:
        /* Fit the rest on the next page */
        page_no++;
        destp = page_address(rqstp->rq_arg.pages[page_no]);
        while (byte_count--)
                *destp++ = *srcp++;

        rqstp->rq_respages = &rqstp->rq_arg.pages[page_no+1];
        rqstp->rq_next_page = rqstp->rq_respages + 1;

done:
        byte_count = head->arg.head[0].iov_len - position;
        head->arg.page_len += byte_count;
        head->arg.len += byte_count;
        head->arg.buflen += byte_count;
        return 1;
}

static int rdma_read_chunks(struct svcxprt_rdma *xprt,
                            struct rpcrdma_msg *rmsgp,
                            struct svc_rqst *rqstp,
                            struct svc_rdma_op_ctxt *head)
{
        int page_no, ret;
        struct rpcrdma_read_chunk *ch;
        u32 handle, page_offset, byte_count;
        u32 position;
        u64 rs_offset;
        bool last;

        /* If no read list is present, return 0 */
        ch = svc_rdma_get_read_chunk(rmsgp);
        if (!ch)
                return 0;

        if (rdma_rcl_chunk_count(ch) > RPCSVC_MAXPAGES)
                return -EINVAL;

        /* The request is completed when the RDMA_READs complete. The
         * head context keeps all the pages that comprise the
         * request.
         */
        head->arg.head[0] = rqstp->rq_arg.head[0];
        head->arg.tail[0] = rqstp->rq_arg.tail[0];
        head->hdr_count = head->count;
        head->arg.page_base = 0;
        head->arg.page_len = 0;
        head->arg.len = rqstp->rq_arg.len;
        head->arg.buflen = rqstp->rq_arg.buflen;

        ch = (struct rpcrdma_read_chunk *)&rmsgp->rm_body.rm_chunks[0];
        position = be32_to_cpu(ch->rc_position);

        /* RDMA_NOMSG: RDMA READ data should land just after RDMA RECV data */
        if (position == 0) {
                head->arg.pages = &head->pages[0];
                page_offset = head->byte_len;
        } else {
                head->arg.pages = &head->pages[head->count];
                page_offset = 0;
        }

        ret = 0;
        page_no = 0;
        for (; ch->rc_discrim != xdr_zero; ch++) {
                if (be32_to_cpu(ch->rc_position) != position)
                        goto err;

                handle = be32_to_cpu(ch->rc_target.rs_handle),
                byte_count = be32_to_cpu(ch->rc_target.rs_length);
                xdr_decode_hyper((__be32 *)&ch->rc_target.rs_offset,
                                 &rs_offset);

                while (byte_count > 0) {
                        last = (ch + 1)->rc_discrim == xdr_zero;
                        ret = xprt->sc_reader(xprt, rqstp, head,
                                              &page_no, &page_offset,
                                              handle, byte_count,
                                              rs_offset, last);
                        if (ret < 0)
                                goto err;
                        byte_count -= ret;
                        rs_offset += ret;
                        head->arg.buflen += ret;
                }
        }

        /* Read list may need XDR round-up (see RFC 5666, s. 3.7) */
        if (page_offset & 3) {
                u32 pad = 4 - (page_offset & 3);

                head->arg.page_len += pad;
                head->arg.len += pad;
                head->arg.buflen += pad;
                page_offset += pad;
        }

        ret = 1;
        if (position && position < head->arg.head[0].iov_len)
                ret = rdma_copy_tail(rqstp, head, position,
                                     byte_count, page_offset, page_no);
        head->arg.head[0].iov_len = position;
        head->position = position;

 err:
        /* Detach arg pages. svc_recv will replenish them */
        for (page_no = 0;
             &rqstp->rq_pages[page_no] < rqstp->rq_respages; page_no++)
                rqstp->rq_pages[page_no] = NULL;

        return ret;
}

static int rdma_read_complete(struct svc_rqst *rqstp,
                              struct svc_rdma_op_ctxt *head)
{
        int page_no;
        int ret;

        /* Copy RPC pages */
        for (page_no = 0; page_no < head->count; page_no++) {
                put_page(rqstp->rq_pages[page_no]);
                rqstp->rq_pages[page_no] = head->pages[page_no];
        }

        /* Adjustments made for RDMA_NOMSG type requests */
        if (head->position == 0) {
                if (head->arg.len <= head->sge[0].length) {
                        head->arg.head[0].iov_len = head->arg.len -
                                                        head->byte_len;
                        head->arg.page_len = 0;
                } else {
                        head->arg.head[0].iov_len = head->sge[0].length -
                                                                head->byte_len;
                        head->arg.page_len = head->arg.len -
                                                head->sge[0].length;
                }
        }

        /* Point rq_arg.pages past header */
        rqstp->rq_arg.pages = &rqstp->rq_pages[head->hdr_count];
        rqstp->rq_arg.page_len = head->arg.page_len;
        rqstp->rq_arg.page_base = head->arg.page_base;

        /* rq_respages starts after the last arg page */
        rqstp->rq_respages = &rqstp->rq_pages[page_no];
        rqstp->rq_next_page = rqstp->rq_respages + 1;

        /* Rebuild rq_arg head and tail. */
        rqstp->rq_arg.head[0] = head->arg.head[0];
        rqstp->rq_arg.tail[0] = head->arg.tail[0];
        rqstp->rq_arg.len = head->arg.len;
        rqstp->rq_arg.buflen = head->arg.buflen;

        /* Free the context */
        svc_rdma_put_context(head, 0);

        /* XXX: What should this be? */
        rqstp->rq_prot = IPPROTO_MAX;
        svc_xprt_copy_addrs(rqstp, rqstp->rq_xprt);

        ret = rqstp->rq_arg.head[0].iov_len
                + rqstp->rq_arg.page_len
                + rqstp->rq_arg.tail[0].iov_len;
        dprintk("svcrdma: deferred read ret=%d, rq_arg.len=%u, "
                "rq_arg.head[0].iov_base=%p, rq_arg.head[0].iov_len=%zu\n",
                ret, rqstp->rq_arg.len, rqstp->rq_arg.head[0].iov_base,
                rqstp->rq_arg.head[0].iov_len);

        return ret;
}

/* 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
svc_rdma_is_backchannel_reply(struct svc_xprt *xprt, struct rpcrdma_msg *rmsgp)
{
        __be32 *p = (__be32 *)rmsgp;

        if (!xprt->xpt_bc_xprt)
                return false;

        if (rmsgp->rm_type != rdma_msg)
                return false;
        if (rmsgp->rm_body.rm_chunks[0] != xdr_zero)
                return false;
        if (rmsgp->rm_body.rm_chunks[1] != xdr_zero)
                return false;
        if (rmsgp->rm_body.rm_chunks[2] != xdr_zero)
                return false;

        /* sanity */
        if (p[7] != rmsgp->rm_xid)
                return false;
        /* call direction */
        if (p[8] == cpu_to_be32(RPC_CALL))
                return false;

        return true;
}

/*
 * Set up the rqstp thread context to point to the RQ buffer. If
 * necessary, pull additional data from the client with an RDMA_READ
 * request.
 */
int svc_rdma_recvfrom(struct svc_rqst *rqstp)
{
        struct svc_xprt *xprt = rqstp->rq_xprt;
        struct svcxprt_rdma *rdma_xprt =
                container_of(xprt, struct svcxprt_rdma, sc_xprt);
        struct svc_rdma_op_ctxt *ctxt = NULL;
        struct rpcrdma_msg *rmsgp;
        int ret = 0;

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

        spin_lock_bh(&rdma_xprt->sc_rq_dto_lock);
        if (!list_empty(&rdma_xprt->sc_read_complete_q)) {
                ctxt = list_entry(rdma_xprt->sc_read_complete_q.next,
                                  struct svc_rdma_op_ctxt,
                                  dto_q);
                list_del_init(&ctxt->dto_q);
                spin_unlock_bh(&rdma_xprt->sc_rq_dto_lock);
                return rdma_read_complete(rqstp, ctxt);
        } else if (!list_empty(&rdma_xprt->sc_rq_dto_q)) {
                ctxt = list_entry(rdma_xprt->sc_rq_dto_q.next,
                                  struct svc_rdma_op_ctxt,
                                  dto_q);
                list_del_init(&ctxt->dto_q);
        } else {
                atomic_inc(&rdma_stat_rq_starve);
                clear_bit(XPT_DATA, &xprt->xpt_flags);
                ctxt = NULL;
        }
        spin_unlock_bh(&rdma_xprt->sc_rq_dto_lock);
        if (!ctxt) {
                /* This is the EAGAIN path. The svc_recv routine will
                 * return -EAGAIN, the nfsd thread will go to call into
                 * svc_recv again and we shouldn't be on the active
                 * transport list
                 */
                if (test_bit(XPT_CLOSE, &xprt->xpt_flags))
                        goto defer;
                goto out;
        }
        dprintk("svcrdma: processing ctxt=%p on xprt=%p, rqstp=%p, status=%d\n",
                ctxt, rdma_xprt, rqstp, ctxt->wc_status);
        atomic_inc(&rdma_stat_recv);

        /* Build up the XDR from the receive buffers. */
        rdma_build_arg_xdr(rqstp, ctxt, ctxt->byte_len);

        /* Decode the RDMA header. */
        rmsgp = (struct rpcrdma_msg *)rqstp->rq_arg.head[0].iov_base;
        ret = svc_rdma_xdr_decode_req(rmsgp, rqstp);
        if (ret < 0)
                goto out_err;
        if (ret == 0)
                goto out_drop;
        rqstp->rq_xprt_hlen = ret;

        if (svc_rdma_is_backchannel_reply(xprt, rmsgp)) {
                ret = svc_rdma_handle_bc_reply(xprt->xpt_bc_xprt, rmsgp,
                                               &rqstp->rq_arg);
                svc_rdma_put_context(ctxt, 0);
                if (ret)
                        goto repost;
                return ret;
        }

        /* Read read-list data. */
        ret = rdma_read_chunks(rdma_xprt, rmsgp, rqstp, ctxt);
        if (ret > 0) {
                /* read-list posted, defer until data received from client. */
                goto defer;
        } else if (ret < 0) {
                /* Post of read-list failed, free context. */
                svc_rdma_put_context(ctxt, 1);
                return 0;
        }

        ret = rqstp->rq_arg.head[0].iov_len
                + rqstp->rq_arg.page_len
                + rqstp->rq_arg.tail[0].iov_len;
        svc_rdma_put_context(ctxt, 0);
 out:
        dprintk("svcrdma: ret=%d, rq_arg.len=%u, "
                "rq_arg.head[0].iov_base=%p, rq_arg.head[0].iov_len=%zd\n",
                ret, rqstp->rq_arg.len,
                rqstp->rq_arg.head[0].iov_base,
                rqstp->rq_arg.head[0].iov_len);
        rqstp->rq_prot = IPPROTO_MAX;
        svc_xprt_copy_addrs(rqstp, xprt);
        return ret;

out_err:
        svc_rdma_send_error(rdma_xprt, rmsgp, ret);
        svc_rdma_put_context(ctxt, 0);
        return 0;

defer:
        return 0;

out_drop:
        svc_rdma_put_context(ctxt, 1);
repost:
        return svc_rdma_repost_recv(rdma_xprt, GFP_KERNEL);
}