Adding upstream version 5.10.209.upstream/5.10.209

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1006 insertions, 0 deletions

diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
new file mode 100644
index 000000000..c3d588b14
--- /dev/null
+++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
@@ -0,0 +1,1006 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
+/*
+ * Copyright (c) 2016-2018 Oracle. All rights reserved.
+ * Copyright (c) 2014 Open Grid Computing, Inc. All rights reserved.
+ * Copyright (c) 2005-2006 Network Appliance, Inc. All rights reserved.
+ *
+ * This software is available to you under a choice of one of two
+ * licenses.  You may choose to be licensed under the terms of the GNU
+ * General Public License (GPL) Version 2, available from the file
+ * COPYING in the main directory of this source tree, or the BSD-type
+ * license below:
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *      Redistributions of source code must retain the above copyright
+ *      notice, this list of conditions and the following disclaimer.
+ *
+ *      Redistributions in binary form must reproduce the above
+ *      copyright notice, this list of conditions and the following
+ *      disclaimer in the documentation and/or other materials provided
+ *      with the distribution.
+ *
+ *      Neither the name of the Network Appliance, Inc. nor the names of
+ *      its contributors may be used to endorse or promote products
+ *      derived from this software without specific prior written
+ *      permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Author: Tom Tucker <tom@opengridcomputing.com>
+ */
+
+/* Operation
+ *
+ * The main entry point is svc_rdma_sendto. This is called by the
+ * RPC server when an RPC Reply is ready to be transmitted to a client.
+ *
+ * The passed-in svc_rqst contains a struct xdr_buf which holds an
+ * XDR-encoded RPC Reply message. sendto must construct the RPC-over-RDMA
+ * transport header, post all Write WRs needed for this Reply, then post
+ * a Send WR conveying the transport header and the RPC message itself to
+ * the client.
+ *
+ * svc_rdma_sendto must fully transmit the Reply before returning, as
+ * the svc_rqst will be recycled as soon as sendto returns. Remaining
+ * resources referred to by the svc_rqst are also recycled at that time.
+ * Therefore any resources that must remain longer must be detached
+ * from the svc_rqst and released later.
+ *
+ * Page Management
+ *
+ * The I/O that performs Reply transmission is asynchronous, and may
+ * complete well after sendto returns. Thus pages under I/O must be
+ * removed from the svc_rqst before sendto returns.
+ *
+ * The logic here depends on Send Queue and completion ordering. Since
+ * the Send WR is always posted last, it will always complete last. Thus
+ * when it completes, it is guaranteed that all previous Write WRs have
+ * also completed.
+ *
+ * Write WRs are constructed and posted. Each Write segment gets its own
+ * svc_rdma_rw_ctxt, allowing the Write completion handler to find and
+ * DMA-unmap the pages under I/O for that Write segment. The Write
+ * completion handler does not release any pages.
+ *
+ * When the Send WR is constructed, it also gets its own svc_rdma_send_ctxt.
+ * The ownership of all of the Reply's pages are transferred into that
+ * ctxt, the Send WR is posted, and sendto returns.
+ *
+ * The svc_rdma_send_ctxt is presented when the Send WR completes. The
+ * Send completion handler finally releases the Reply's pages.
+ *
+ * This mechanism also assumes that completions on the transport's Send
+ * Completion Queue do not run in parallel. Otherwise a Write completion
+ * and Send completion running at the same time could release pages that
+ * are still DMA-mapped.
+ *
+ * Error Handling
+ *
+ * - If the Send WR is posted successfully, it will either complete
+ *   successfully, or get flushed. Either way, the Send completion
+ *   handler releases the Reply's pages.
+ * - If the Send WR cannot be not posted, the forward path releases
+ *   the Reply's pages.
+ *
+ * This handles the case, without the use of page reference counting,
+ * where two different Write segments send portions of the same page.
+ */
+
+#include <linux/spinlock.h>
+#include <asm/unaligned.h>
+
+#include <rdma/ib_verbs.h>
+#include <rdma/rdma_cm.h>
+
+#include <linux/sunrpc/debug.h>
+#include <linux/sunrpc/svc_rdma.h>
+
+#include "xprt_rdma.h"
+#include <trace/events/rpcrdma.h>
+
+#define RPCDBG_FACILITY	RPCDBG_SVCXPRT
+
+static void svc_rdma_wc_send(struct ib_cq *cq, struct ib_wc *wc);
+
+static inline struct svc_rdma_send_ctxt *
+svc_rdma_next_send_ctxt(struct list_head *list)
+{
+	return list_first_entry_or_null(list, struct svc_rdma_send_ctxt,
+					sc_list);
+}
+
+static void svc_rdma_send_cid_init(struct svcxprt_rdma *rdma,
+				   struct rpc_rdma_cid *cid)
+{
+	cid->ci_queue_id = rdma->sc_sq_cq->res.id;
+	cid->ci_completion_id = atomic_inc_return(&rdma->sc_completion_ids);
+}
+
+static struct svc_rdma_send_ctxt *
+svc_rdma_send_ctxt_alloc(struct svcxprt_rdma *rdma)
+{
+	struct svc_rdma_send_ctxt *ctxt;
+	dma_addr_t addr;
+	void *buffer;
+	size_t size;
+	int i;
+
+	size = sizeof(*ctxt);
+	size += rdma->sc_max_send_sges * sizeof(struct ib_sge);
+	ctxt = kmalloc(size, GFP_KERNEL);
+	if (!ctxt)
+		goto fail0;
+	buffer = kmalloc(rdma->sc_max_req_size, GFP_KERNEL);
+	if (!buffer)
+		goto fail1;
+	addr = ib_dma_map_single(rdma->sc_pd->device, buffer,
+				 rdma->sc_max_req_size, DMA_TO_DEVICE);
+	if (ib_dma_mapping_error(rdma->sc_pd->device, addr))
+		goto fail2;
+
+	svc_rdma_send_cid_init(rdma, &ctxt->sc_cid);
+
+	ctxt->sc_send_wr.next = NULL;
+	ctxt->sc_send_wr.wr_cqe = &ctxt->sc_cqe;
+	ctxt->sc_send_wr.sg_list = ctxt->sc_sges;
+	ctxt->sc_send_wr.send_flags = IB_SEND_SIGNALED;
+	ctxt->sc_cqe.done = svc_rdma_wc_send;
+	ctxt->sc_xprt_buf = buffer;
+	xdr_buf_init(&ctxt->sc_hdrbuf, ctxt->sc_xprt_buf,
+		     rdma->sc_max_req_size);
+	ctxt->sc_sges[0].addr = addr;
+
+	for (i = 0; i < rdma->sc_max_send_sges; i++)
+		ctxt->sc_sges[i].lkey = rdma->sc_pd->local_dma_lkey;
+	return ctxt;
+
+fail2:
+	kfree(buffer);
+fail1:
+	kfree(ctxt);
+fail0:
+	return NULL;
+}
+
+/**
+ * svc_rdma_send_ctxts_destroy - Release all send_ctxt's for an xprt
+ * @rdma: svcxprt_rdma being torn down
+ *
+ */
+void svc_rdma_send_ctxts_destroy(struct svcxprt_rdma *rdma)
+{
+	struct svc_rdma_send_ctxt *ctxt;
+
+	while ((ctxt = svc_rdma_next_send_ctxt(&rdma->sc_send_ctxts))) {
+		list_del(&ctxt->sc_list);
+		ib_dma_unmap_single(rdma->sc_pd->device,
+				    ctxt->sc_sges[0].addr,
+				    rdma->sc_max_req_size,
+				    DMA_TO_DEVICE);
+		kfree(ctxt->sc_xprt_buf);
+		kfree(ctxt);
+	}
+}
+
+/**
+ * svc_rdma_send_ctxt_get - Get a free send_ctxt
+ * @rdma: controlling svcxprt_rdma
+ *
+ * Returns a ready-to-use send_ctxt, or NULL if none are
+ * available and a fresh one cannot be allocated.
+ */
+struct svc_rdma_send_ctxt *svc_rdma_send_ctxt_get(struct svcxprt_rdma *rdma)
+{
+	struct svc_rdma_send_ctxt *ctxt;
+
+	spin_lock(&rdma->sc_send_lock);
+	ctxt = svc_rdma_next_send_ctxt(&rdma->sc_send_ctxts);
+	if (!ctxt)
+		goto out_empty;
+	list_del(&ctxt->sc_list);
+	spin_unlock(&rdma->sc_send_lock);
+
+out:
+	rpcrdma_set_xdrlen(&ctxt->sc_hdrbuf, 0);
+	xdr_init_encode(&ctxt->sc_stream, &ctxt->sc_hdrbuf,
+			ctxt->sc_xprt_buf, NULL);
+
+	ctxt->sc_send_wr.num_sge = 0;
+	ctxt->sc_cur_sge_no = 0;
+	ctxt->sc_page_count = 0;
+	return ctxt;
+
+out_empty:
+	spin_unlock(&rdma->sc_send_lock);
+	ctxt = svc_rdma_send_ctxt_alloc(rdma);
+	if (!ctxt)
+		return NULL;
+	goto out;
+}
+
+/**
+ * svc_rdma_send_ctxt_put - Return send_ctxt to free list
+ * @rdma: controlling svcxprt_rdma
+ * @ctxt: object to return to the free list
+ *
+ * Pages left in sc_pages are DMA unmapped and released.
+ */
+void svc_rdma_send_ctxt_put(struct svcxprt_rdma *rdma,
+			    struct svc_rdma_send_ctxt *ctxt)
+{
+	struct ib_device *device = rdma->sc_cm_id->device;
+	unsigned int i;
+
+	/* The first SGE contains the transport header, which
+	 * remains mapped until @ctxt is destroyed.
+	 */
+	for (i = 1; i < ctxt->sc_send_wr.num_sge; i++) {
+		ib_dma_unmap_page(device,
+				  ctxt->sc_sges[i].addr,
+				  ctxt->sc_sges[i].length,
+				  DMA_TO_DEVICE);
+		trace_svcrdma_dma_unmap_page(rdma,
+					     ctxt->sc_sges[i].addr,
+					     ctxt->sc_sges[i].length);
+	}
+
+	for (i = 0; i < ctxt->sc_page_count; ++i)
+		put_page(ctxt->sc_pages[i]);
+
+	spin_lock(&rdma->sc_send_lock);
+	list_add(&ctxt->sc_list, &rdma->sc_send_ctxts);
+	spin_unlock(&rdma->sc_send_lock);
+}
+
+/**
+ * svc_rdma_wc_send - Invoked by RDMA provider for each polled Send WC
+ * @cq: Completion Queue context
+ * @wc: Work Completion object
+ *
+ * NB: The svc_xprt/svcxprt_rdma is pinned whenever it's possible that
+ * the Send completion handler could be running.
+ */
+static void svc_rdma_wc_send(struct ib_cq *cq, struct ib_wc *wc)
+{
+	struct svcxprt_rdma *rdma = cq->cq_context;
+	struct ib_cqe *cqe = wc->wr_cqe;
+	struct svc_rdma_send_ctxt *ctxt =
+		container_of(cqe, struct svc_rdma_send_ctxt, sc_cqe);
+
+	trace_svcrdma_wc_send(wc, &ctxt->sc_cid);
+
+	atomic_inc(&rdma->sc_sq_avail);
+	wake_up(&rdma->sc_send_wait);
+
+	svc_rdma_send_ctxt_put(rdma, ctxt);
+
+	if (unlikely(wc->status != IB_WC_SUCCESS)) {
+		set_bit(XPT_CLOSE, &rdma->sc_xprt.xpt_flags);
+		svc_xprt_enqueue(&rdma->sc_xprt);
+	}
+}
+
+/**
+ * svc_rdma_send - Post a single Send WR
+ * @rdma: transport on which to post the WR
+ * @ctxt: send ctxt with a Send WR ready to post
+ *
+ * Returns zero the Send WR was posted successfully. Otherwise, a
+ * negative errno is returned.
+ */
+int svc_rdma_send(struct svcxprt_rdma *rdma, struct svc_rdma_send_ctxt *ctxt)
+{
+	struct ib_send_wr *wr = &ctxt->sc_send_wr;
+	int ret;
+
+	might_sleep();
+
+	/* Sync the transport header buffer */
+	ib_dma_sync_single_for_device(rdma->sc_pd->device,
+				      wr->sg_list[0].addr,
+				      wr->sg_list[0].length,
+				      DMA_TO_DEVICE);
+
+	/* If the SQ is full, wait until an SQ entry is available */
+	while (1) {
+		if ((atomic_dec_return(&rdma->sc_sq_avail) < 0)) {
+			atomic_inc(&rdma_stat_sq_starve);
+			trace_svcrdma_sq_full(rdma);
+			atomic_inc(&rdma->sc_sq_avail);
+			wait_event(rdma->sc_send_wait,
+				   atomic_read(&rdma->sc_sq_avail) > 1);
+			if (test_bit(XPT_CLOSE, &rdma->sc_xprt.xpt_flags))
+				return -ENOTCONN;
+			trace_svcrdma_sq_retry(rdma);
+			continue;
+		}
+
+		trace_svcrdma_post_send(ctxt);
+		ret = ib_post_send(rdma->sc_qp, wr, NULL);
+		if (ret)
+			break;
+		return 0;
+	}
+
+	trace_svcrdma_sq_post_err(rdma, ret);
+	set_bit(XPT_CLOSE, &rdma->sc_xprt.xpt_flags);
+	wake_up(&rdma->sc_send_wait);
+	return ret;
+}
+
+/**
+ * svc_rdma_encode_read_list - Encode RPC Reply's Read chunk list
+ * @sctxt: Send context for the RPC Reply
+ *
+ * Return values:
+ *   On success, returns length in bytes of the Reply XDR buffer
+ *   that was consumed by the Reply Read list
+ *   %-EMSGSIZE on XDR buffer overflow
+ */
+static ssize_t svc_rdma_encode_read_list(struct svc_rdma_send_ctxt *sctxt)
+{
+	/* RPC-over-RDMA version 1 replies never have a Read list. */
+	return xdr_stream_encode_item_absent(&sctxt->sc_stream);
+}
+
+/**
+ * svc_rdma_encode_write_segment - Encode one Write segment
+ * @src: matching Write chunk in the RPC Call header
+ * @sctxt: Send context for the RPC Reply
+ * @remaining: remaining bytes of the payload left in the Write chunk
+ *
+ * Return values:
+ *   On success, returns length in bytes of the Reply XDR buffer
+ *   that was consumed by the Write segment
+ *   %-EMSGSIZE on XDR buffer overflow
+ */
+static ssize_t svc_rdma_encode_write_segment(__be32 *src,
+					     struct svc_rdma_send_ctxt *sctxt,
+					     unsigned int *remaining)
+{
+	__be32 *p;
+	const size_t len = rpcrdma_segment_maxsz * sizeof(*p);
+	u32 handle, length;
+	u64 offset;
+
+	p = xdr_reserve_space(&sctxt->sc_stream, len);
+	if (!p)
+		return -EMSGSIZE;
+
+	xdr_decode_rdma_segment(src, &handle, &length, &offset);
+
+	if (*remaining < length) {
+		/* segment only partly filled */
+		length = *remaining;
+		*remaining = 0;
+	} else {
+		/* entire segment was consumed */
+		*remaining -= length;
+	}
+	xdr_encode_rdma_segment(p, handle, length, offset);
+
+	trace_svcrdma_encode_wseg(handle, length, offset);
+	return len;
+}
+
+/**
+ * svc_rdma_encode_write_chunk - Encode one Write chunk
+ * @src: matching Write chunk in the RPC Call header
+ * @sctxt: Send context for the RPC Reply
+ * @remaining: size in bytes of the payload in the Write chunk
+ *
+ * Copy a Write chunk from the Call transport header to the
+ * Reply transport header. Update each segment's length field
+ * to reflect the number of bytes written in that segment.
+ *
+ * Return values:
+ *   On success, returns length in bytes of the Reply XDR buffer
+ *   that was consumed by the Write chunk
+ *   %-EMSGSIZE on XDR buffer overflow
+ */
+static ssize_t svc_rdma_encode_write_chunk(__be32 *src,
+					   struct svc_rdma_send_ctxt *sctxt,
+					   unsigned int remaining)
+{
+	unsigned int i, nsegs;
+	ssize_t len, ret;
+
+	len = 0;
+	trace_svcrdma_encode_write_chunk(remaining);
+
+	src++;
+	ret = xdr_stream_encode_item_present(&sctxt->sc_stream);
+	if (ret < 0)
+		return -EMSGSIZE;
+	len += ret;
+
+	nsegs = be32_to_cpup(src++);
+	ret = xdr_stream_encode_u32(&sctxt->sc_stream, nsegs);
+	if (ret < 0)
+		return -EMSGSIZE;
+	len += ret;
+
+	for (i = nsegs; i; i--) {
+		ret = svc_rdma_encode_write_segment(src, sctxt, &remaining);
+		if (ret < 0)
+			return -EMSGSIZE;
+		src += rpcrdma_segment_maxsz;
+		len += ret;
+	}
+
+	return len;
+}
+
+/**
+ * svc_rdma_encode_write_list - Encode RPC Reply's Write chunk list
+ * @rctxt: Reply context with information about the RPC Call
+ * @sctxt: Send context for the RPC Reply
+ * @length: size in bytes of the payload in the first Write chunk
+ *
+ * The client provides a Write chunk list in the Call message. Fill
+ * in the segments in the first Write chunk in the Reply's transport
+ * header with the number of bytes consumed in each segment.
+ * Remaining chunks are returned unused.
+ *
+ * Assumptions:
+ *  - Client has provided only one Write chunk
+ *
+ * Return values:
+ *   On success, returns length in bytes of the Reply XDR buffer
+ *   that was consumed by the Reply's Write list
+ *   %-EMSGSIZE on XDR buffer overflow
+ */
+static ssize_t
+svc_rdma_encode_write_list(const struct svc_rdma_recv_ctxt *rctxt,
+			   struct svc_rdma_send_ctxt *sctxt,
+			   unsigned int length)
+{
+	ssize_t len, ret;
+
+	ret = svc_rdma_encode_write_chunk(rctxt->rc_write_list, sctxt, length);
+	if (ret < 0)
+		return ret;
+	len = ret;
+
+	/* Terminate the Write list */
+	ret = xdr_stream_encode_item_absent(&sctxt->sc_stream);
+	if (ret < 0)
+		return ret;
+
+	return len + ret;
+}
+
+/**
+ * svc_rdma_encode_reply_chunk - Encode RPC Reply's Reply chunk
+ * @rctxt: Reply context with information about the RPC Call
+ * @sctxt: Send context for the RPC Reply
+ * @length: size in bytes of the payload in the Reply chunk
+ *
+ * Assumptions:
+ * - Reply can always fit in the client-provided Reply chunk
+ *
+ * Return values:
+ *   On success, returns length in bytes of the Reply XDR buffer
+ *   that was consumed by the Reply's Reply chunk
+ *   %-EMSGSIZE on XDR buffer overflow
+ */
+static ssize_t
+svc_rdma_encode_reply_chunk(const struct svc_rdma_recv_ctxt *rctxt,
+			    struct svc_rdma_send_ctxt *sctxt,
+			    unsigned int length)
+{
+	return svc_rdma_encode_write_chunk(rctxt->rc_reply_chunk, sctxt,
+					   length);
+}
+
+static int svc_rdma_dma_map_page(struct svcxprt_rdma *rdma,
+				 struct svc_rdma_send_ctxt *ctxt,
+				 struct page *page,
+				 unsigned long offset,
+				 unsigned int len)
+{
+	struct ib_device *dev = rdma->sc_cm_id->device;
+	dma_addr_t dma_addr;
+
+	dma_addr = ib_dma_map_page(dev, page, offset, len, DMA_TO_DEVICE);
+	trace_svcrdma_dma_map_page(rdma, dma_addr, len);
+	if (ib_dma_mapping_error(dev, dma_addr))
+		goto out_maperr;
+
+	ctxt->sc_sges[ctxt->sc_cur_sge_no].addr = dma_addr;
+	ctxt->sc_sges[ctxt->sc_cur_sge_no].length = len;
+	ctxt->sc_send_wr.num_sge++;
+	return 0;
+
+out_maperr:
+	return -EIO;
+}
+
+/* ib_dma_map_page() is used here because svc_rdma_dma_unmap()
+ * handles DMA-unmap and it uses ib_dma_unmap_page() exclusively.
+ */
+static int svc_rdma_dma_map_buf(struct svcxprt_rdma *rdma,
+				struct svc_rdma_send_ctxt *ctxt,
+				unsigned char *base,
+				unsigned int len)
+{
+	return svc_rdma_dma_map_page(rdma, ctxt, virt_to_page(base),
+				     offset_in_page(base), len);
+}
+
+/**
+ * svc_rdma_pull_up_needed - Determine whether to use pull-up
+ * @rdma: controlling transport
+ * @sctxt: send_ctxt for the Send WR
+ * @rctxt: Write and Reply chunks provided by client
+ * @xdr: xdr_buf containing RPC message to transmit
+ *
+ * Returns:
+ *	%true if pull-up must be used
+ *	%false otherwise
+ */
+static bool svc_rdma_pull_up_needed(struct svcxprt_rdma *rdma,
+				    struct svc_rdma_send_ctxt *sctxt,
+				    const struct svc_rdma_recv_ctxt *rctxt,
+				    struct xdr_buf *xdr)
+{
+	int elements;
+
+	/* For small messages, copying bytes is cheaper than DMA mapping.
+	 */
+	if (sctxt->sc_hdrbuf.len + xdr->len < RPCRDMA_PULLUP_THRESH)
+		return true;
+
+	/* Check whether the xdr_buf has more elements than can
+	 * fit in a single RDMA Send.
+	 */
+	/* xdr->head */
+	elements = 1;
+
+	/* xdr->pages */
+	if (!rctxt || !rctxt->rc_write_list) {
+		unsigned int remaining;
+		unsigned long pageoff;
+
+		pageoff = xdr->page_base & ~PAGE_MASK;
+		remaining = xdr->page_len;
+		while (remaining) {
+			++elements;
+			remaining -= min_t(u32, PAGE_SIZE - pageoff,
+					   remaining);
+			pageoff = 0;
+		}
+	}
+
+	/* xdr->tail */
+	if (xdr->tail[0].iov_len)
+		++elements;
+
+	/* assume 1 SGE is needed for the transport header */
+	return elements >= rdma->sc_max_send_sges;
+}
+
+/**
+ * svc_rdma_pull_up_reply_msg - Copy Reply into a single buffer
+ * @rdma: controlling transport
+ * @sctxt: send_ctxt for the Send WR; xprt hdr is already prepared
+ * @rctxt: Write and Reply chunks provided by client
+ * @xdr: prepared xdr_buf containing RPC message
+ *
+ * The device is not capable of sending the reply directly.
+ * Assemble the elements of @xdr into the transport header buffer.
+ *
+ * Returns zero on success, or a negative errno on failure.
+ */
+static int svc_rdma_pull_up_reply_msg(struct svcxprt_rdma *rdma,
+				      struct svc_rdma_send_ctxt *sctxt,
+				      const struct svc_rdma_recv_ctxt *rctxt,
+				      const struct xdr_buf *xdr)
+{
+	unsigned char *dst, *tailbase;
+	unsigned int taillen;
+
+	dst = sctxt->sc_xprt_buf + sctxt->sc_hdrbuf.len;
+	memcpy(dst, xdr->head[0].iov_base, xdr->head[0].iov_len);
+	dst += xdr->head[0].iov_len;
+
+	tailbase = xdr->tail[0].iov_base;
+	taillen = xdr->tail[0].iov_len;
+	if (rctxt && rctxt->rc_write_list) {
+		u32 xdrpad;
+
+		xdrpad = xdr_pad_size(xdr->page_len);
+		if (taillen && xdrpad) {
+			tailbase += xdrpad;
+			taillen -= xdrpad;
+		}
+	} else {
+		unsigned int len, remaining;
+		unsigned long pageoff;
+		struct page **ppages;
+
+		ppages = xdr->pages + (xdr->page_base >> PAGE_SHIFT);
+		pageoff = xdr->page_base & ~PAGE_MASK;
+		remaining = xdr->page_len;
+		while (remaining) {
+			len = min_t(u32, PAGE_SIZE - pageoff, remaining);
+
+			memcpy(dst, page_address(*ppages) + pageoff, len);
+			remaining -= len;
+			dst += len;
+			pageoff = 0;
+			ppages++;
+		}
+	}
+
+	if (taillen)
+		memcpy(dst, tailbase, taillen);
+
+	sctxt->sc_sges[0].length += xdr->len;
+	trace_svcrdma_send_pullup(sctxt->sc_sges[0].length);
+	return 0;
+}
+
+/* svc_rdma_map_reply_msg - DMA map the buffer holding RPC message
+ * @rdma: controlling transport
+ * @sctxt: send_ctxt for the Send WR
+ * @rctxt: Write and Reply chunks provided by client
+ * @xdr: prepared xdr_buf containing RPC message
+ *
+ * Load the xdr_buf into the ctxt's sge array, and DMA map each
+ * element as it is added. The Send WR's num_sge field is set.
+ *
+ * Returns zero on success, or a negative errno on failure.
+ */
+int svc_rdma_map_reply_msg(struct svcxprt_rdma *rdma,
+			   struct svc_rdma_send_ctxt *sctxt,
+			   const struct svc_rdma_recv_ctxt *rctxt,
+			   struct xdr_buf *xdr)
+{
+	unsigned int len, remaining;
+	unsigned long page_off;
+	struct page **ppages;
+	unsigned char *base;
+	u32 xdr_pad;
+	int ret;
+
+	/* Set up the (persistently-mapped) transport header SGE. */
+	sctxt->sc_send_wr.num_sge = 1;
+	sctxt->sc_sges[0].length = sctxt->sc_hdrbuf.len;
+
+	/* If there is a Reply chunk, nothing follows the transport
+	 * header, and we're done here.
+	 */
+	if (rctxt && rctxt->rc_reply_chunk)
+		return 0;
+
+	/* For pull-up, svc_rdma_send() will sync the transport header.
+	 * No additional DMA mapping is necessary.
+	 */
+	if (svc_rdma_pull_up_needed(rdma, sctxt, rctxt, xdr))
+		return svc_rdma_pull_up_reply_msg(rdma, sctxt, rctxt, xdr);
+
+	++sctxt->sc_cur_sge_no;
+	ret = svc_rdma_dma_map_buf(rdma, sctxt,
+				   xdr->head[0].iov_base,
+				   xdr->head[0].iov_len);
+	if (ret < 0)
+		return ret;
+
+	/* If a Write chunk is present, the xdr_buf's page list
+	 * is not included inline. However the Upper Layer may
+	 * have added XDR padding in the tail buffer, and that
+	 * should not be included inline.
+	 */
+	if (rctxt && rctxt->rc_write_list) {
+		base = xdr->tail[0].iov_base;
+		len = xdr->tail[0].iov_len;
+		xdr_pad = xdr_pad_size(xdr->page_len);
+
+		if (len && xdr_pad) {
+			base += xdr_pad;
+			len -= xdr_pad;
+		}
+
+		goto tail;
+	}
+
+	ppages = xdr->pages + (xdr->page_base >> PAGE_SHIFT);
+	page_off = xdr->page_base & ~PAGE_MASK;
+	remaining = xdr->page_len;
+	while (remaining) {
+		len = min_t(u32, PAGE_SIZE - page_off, remaining);
+
+		++sctxt->sc_cur_sge_no;
+		ret = svc_rdma_dma_map_page(rdma, sctxt, *ppages++,
+					    page_off, len);
+		if (ret < 0)
+			return ret;
+
+		remaining -= len;
+		page_off = 0;
+	}
+
+	base = xdr->tail[0].iov_base;
+	len = xdr->tail[0].iov_len;
+tail:
+	if (len) {
+		++sctxt->sc_cur_sge_no;
+		ret = svc_rdma_dma_map_buf(rdma, sctxt, base, len);
+		if (ret < 0)
+			return ret;
+	}
+
+	return 0;
+}
+
+/* The svc_rqst and all resources it owns are released as soon as
+ * svc_rdma_sendto returns. Transfer pages under I/O to the ctxt
+ * so they are released by the Send completion handler.
+ */
+static void svc_rdma_save_io_pages(struct svc_rqst *rqstp,
+				   struct svc_rdma_send_ctxt *ctxt)
+{
+	int i, pages = rqstp->rq_next_page - rqstp->rq_respages;
+
+	ctxt->sc_page_count += pages;
+	for (i = 0; i < pages; i++) {
+		ctxt->sc_pages[i] = rqstp->rq_respages[i];
+		rqstp->rq_respages[i] = NULL;
+	}
+
+	/* Prevent svc_xprt_release from releasing pages in rq_pages */
+	rqstp->rq_next_page = rqstp->rq_respages;
+}
+
+/* Prepare the portion of the RPC Reply that will be transmitted
+ * via RDMA Send. The RPC-over-RDMA transport header is prepared
+ * in sc_sges[0], and the RPC xdr_buf is prepared in following sges.
+ *
+ * Depending on whether a Write list or Reply chunk is present,
+ * the server may send all, a portion of, or none of the xdr_buf.
+ * In the latter case, only the transport header (sc_sges[0]) is
+ * transmitted.
+ *
+ * RDMA Send is the last step of transmitting an RPC reply. Pages
+ * involved in the earlier RDMA Writes are here transferred out
+ * of the rqstp and into the sctxt's page array. These pages are
+ * DMA unmapped by each Write completion, but the subsequent Send
+ * completion finally releases these pages.
+ *
+ * Assumptions:
+ * - The Reply's transport header will never be larger than a page.
+ */
+static int svc_rdma_send_reply_msg(struct svcxprt_rdma *rdma,
+				   struct svc_rdma_send_ctxt *sctxt,
+				   const struct svc_rdma_recv_ctxt *rctxt,
+				   struct svc_rqst *rqstp)
+{
+	int ret;
+
+	ret = svc_rdma_map_reply_msg(rdma, sctxt, rctxt, &rqstp->rq_res);
+	if (ret < 0)
+		return ret;
+
+	svc_rdma_save_io_pages(rqstp, sctxt);
+
+	if (rctxt->rc_inv_rkey) {
+		sctxt->sc_send_wr.opcode = IB_WR_SEND_WITH_INV;
+		sctxt->sc_send_wr.ex.invalidate_rkey = rctxt->rc_inv_rkey;
+	} else {
+		sctxt->sc_send_wr.opcode = IB_WR_SEND;
+	}
+	return svc_rdma_send(rdma, sctxt);
+}
+
+/**
+ * svc_rdma_send_error_msg - Send an RPC/RDMA v1 error response
+ * @rdma: controlling transport context
+ * @sctxt: Send context for the response
+ * @rctxt: Receive context for incoming bad message
+ * @status: negative errno indicating error that occurred
+ *
+ * Given the client-provided Read, Write, and Reply chunks, the
+ * server was not able to parse the Call or form a complete Reply.
+ * Return an RDMA_ERROR message so the client can retire the RPC
+ * transaction.
+ *
+ * The caller does not have to release @sctxt. It is released by
+ * Send completion, or by this function on error.
+ */
+void svc_rdma_send_error_msg(struct svcxprt_rdma *rdma,
+			     struct svc_rdma_send_ctxt *sctxt,
+			     struct svc_rdma_recv_ctxt *rctxt,
+			     int status)
+{
+	__be32 *rdma_argp = rctxt->rc_recv_buf;
+	__be32 *p;
+
+	rpcrdma_set_xdrlen(&sctxt->sc_hdrbuf, 0);
+	xdr_init_encode(&sctxt->sc_stream, &sctxt->sc_hdrbuf,
+			sctxt->sc_xprt_buf, NULL);
+
+	p = xdr_reserve_space(&sctxt->sc_stream,
+			      rpcrdma_fixed_maxsz * sizeof(*p));
+	if (!p)
+		goto put_ctxt;
+
+	*p++ = *rdma_argp;
+	*p++ = *(rdma_argp + 1);
+	*p++ = rdma->sc_fc_credits;
+	*p = rdma_error;
+
+	switch (status) {
+	case -EPROTONOSUPPORT:
+		p = xdr_reserve_space(&sctxt->sc_stream, 3 * sizeof(*p));
+		if (!p)
+			goto put_ctxt;
+
+		*p++ = err_vers;
+		*p++ = rpcrdma_version;
+		*p = rpcrdma_version;
+		trace_svcrdma_err_vers(*rdma_argp);
+		break;
+	default:
+		p = xdr_reserve_space(&sctxt->sc_stream, sizeof(*p));
+		if (!p)
+			goto put_ctxt;
+
+		*p = err_chunk;
+		trace_svcrdma_err_chunk(*rdma_argp);
+	}
+
+	/* Remote Invalidation is skipped for simplicity. */
+	sctxt->sc_send_wr.num_sge = 1;
+	sctxt->sc_send_wr.opcode = IB_WR_SEND;
+	sctxt->sc_sges[0].length = sctxt->sc_hdrbuf.len;
+	if (svc_rdma_send(rdma, sctxt))
+		goto put_ctxt;
+	return;
+
+put_ctxt:
+	svc_rdma_send_ctxt_put(rdma, sctxt);
+}
+
+/**
+ * svc_rdma_sendto - Transmit an RPC reply
+ * @rqstp: processed RPC request, reply XDR already in ::rq_res
+ *
+ * Any resources still associated with @rqstp are released upon return.
+ * If no reply message was possible, the connection is closed.
+ *
+ * Returns:
+ *	%0 if an RPC reply has been successfully posted,
+ *	%-ENOMEM if a resource shortage occurred (connection is lost),
+ *	%-ENOTCONN if posting failed (connection is lost).
+ */
+int svc_rdma_sendto(struct svc_rqst *rqstp)
+{
+	struct svc_xprt *xprt = rqstp->rq_xprt;
+	struct svcxprt_rdma *rdma =
+		container_of(xprt, struct svcxprt_rdma, sc_xprt);
+	struct svc_rdma_recv_ctxt *rctxt = rqstp->rq_xprt_ctxt;
+	__be32 *rdma_argp = rctxt->rc_recv_buf;
+	__be32 *wr_lst = rctxt->rc_write_list;
+	__be32 *rp_ch = rctxt->rc_reply_chunk;
+	struct xdr_buf *xdr = &rqstp->rq_res;
+	struct svc_rdma_send_ctxt *sctxt;
+	__be32 *p;
+	int ret;
+
+	ret = -ENOTCONN;
+	if (svc_xprt_is_dead(xprt))
+		goto err0;
+
+	ret = -ENOMEM;
+	sctxt = svc_rdma_send_ctxt_get(rdma);
+	if (!sctxt)
+		goto err0;
+
+	p = xdr_reserve_space(&sctxt->sc_stream,
+			      rpcrdma_fixed_maxsz * sizeof(*p));
+	if (!p)
+		goto err0;
+	*p++ = *rdma_argp;
+	*p++ = *(rdma_argp + 1);
+	*p++ = rdma->sc_fc_credits;
+	*p   = rp_ch ? rdma_nomsg : rdma_msg;
+
+	if (svc_rdma_encode_read_list(sctxt) < 0)
+		goto err0;
+	if (wr_lst) {
+		/* XXX: Presume the client sent only one Write chunk */
+		unsigned long offset;
+		unsigned int length;
+
+		if (rctxt->rc_read_payload_length) {
+			offset = rctxt->rc_read_payload_offset;
+			length = rctxt->rc_read_payload_length;
+		} else {
+			offset = xdr->head[0].iov_len;
+			length = xdr->page_len;
+		}
+		ret = svc_rdma_send_write_chunk(rdma, wr_lst, xdr, offset,
+						length);
+		if (ret < 0)
+			goto err2;
+		if (svc_rdma_encode_write_list(rctxt, sctxt, length) < 0)
+			goto err0;
+	} else {
+		if (xdr_stream_encode_item_absent(&sctxt->sc_stream) < 0)
+			goto err0;
+	}
+	if (rp_ch) {
+		ret = svc_rdma_send_reply_chunk(rdma, rctxt, &rqstp->rq_res);
+		if (ret < 0)
+			goto err2;
+		if (svc_rdma_encode_reply_chunk(rctxt, sctxt, ret) < 0)
+			goto err0;
+	} else {
+		if (xdr_stream_encode_item_absent(&sctxt->sc_stream) < 0)
+			goto err0;
+	}
+
+	ret = svc_rdma_send_reply_msg(rdma, sctxt, rctxt, rqstp);
+	if (ret < 0)
+		goto err1;
+	return 0;
+
+ err2:
+	if (ret != -E2BIG && ret != -EINVAL)
+		goto err1;
+
+	/* Send completion releases payload pages that were part
+	 * of previously posted RDMA Writes.
+	 */
+	svc_rdma_save_io_pages(rqstp, sctxt);
+	svc_rdma_send_error_msg(rdma, sctxt, rctxt, ret);
+	return 0;
+
+ err1:
+	svc_rdma_send_ctxt_put(rdma, sctxt);
+ err0:
+	trace_svcrdma_send_err(rqstp, ret);
+	set_bit(XPT_CLOSE, &xprt->xpt_flags);
+	return -ENOTCONN;
+}
+
+/**
+ * svc_rdma_read_payload - special processing for a READ payload
+ * @rqstp: svc_rqst to operate on
+ * @offset: payload's byte offset in @xdr
+ * @length: size of payload, in bytes
+ *
+ * Returns zero on success.
+ *
+ * For the moment, just record the xdr_buf location of the READ
+ * payload. svc_rdma_sendto will use that location later when
+ * we actually send the payload.
+ */
+int svc_rdma_read_payload(struct svc_rqst *rqstp, unsigned int offset,
+			  unsigned int length)
+{
+	struct svc_rdma_recv_ctxt *rctxt = rqstp->rq_xprt_ctxt;
+
+	/* XXX: Just one READ payload slot for now, since our
+	 * transport implementation currently supports only one
+	 * Write chunk.
+	 */
+	rctxt->rc_read_payload_offset = offset;
+	rctxt->rc_read_payload_length = length;
+
+	return 0;
+}