net/sunrpc/xprtrdma/svc_rdma_backchannel.c - third_party/linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (c) 2015-2018 Oracle.  All rights reserved.
  *
  * Support for backward direction RPCs on RPC/RDMA (server-side).
  */

 #include <linux/module.h>

 #include <linux/sunrpc/svc_rdma.h>

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

 #define RPCDBG_FACILITY	RPCDBG_SVCXPRT

 #undef SVCRDMA_BACKCHANNEL_DEBUG

 /**
  * svc_rdma_handle_bc_reply - Process incoming backchannel reply
  * @xprt: controlling backchannel transport
  * @rdma_resp: pointer to incoming transport header
  * @rcvbuf: XDR buffer into which to decode the reply
  *
  * Returns:
  *	%0 if @rcvbuf is filled in, xprt_complete_rqst called,
  *	%-EAGAIN if server should call ->recvfrom again.
  */
 int svc_rdma_handle_bc_reply(struct rpc_xprt *xprt, __be32 *rdma_resp,
 			     struct xdr_buf *rcvbuf)
 {
 	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
 	struct kvec *dst, *src = &rcvbuf->head[0];
 	struct rpc_rqst *req;
 	unsigned long cwnd;
 	u32 credits;
 	size_t len;
 	__be32 xid;
 	__be32 *p;
 	int ret;

 	p = (__be32 *)src->iov_base;
 	len = src->iov_len;
 	xid = *rdma_resp;

 #ifdef SVCRDMA_BACKCHANNEL_DEBUG
 	pr_info("%s: xid=%08x, length=%zu\n",
 		__func__, be32_to_cpu(xid), len);
 	pr_info("%s: RPC/RDMA: %*ph\n",
 		__func__, (int)RPCRDMA_HDRLEN_MIN, rdma_resp);
 	pr_info("%s:      RPC: %*ph\n",
 		__func__, (int)len, p);
 #endif

 	ret = -EAGAIN;
 	if (src->iov_len < 24)
 		goto out_shortreply;

 	spin_lock(&xprt->recv_lock);
 	req = xprt_lookup_rqst(xprt, xid);
 	if (!req)
 		goto out_notfound;

 	dst = &req->rq_private_buf.head[0];
 	memcpy(&req->rq_private_buf, &req->rq_rcv_buf, sizeof(struct xdr_buf));
 	if (dst->iov_len < len)
 		goto out_unlock;
 	memcpy(dst->iov_base, p, len);

 	credits = be32_to_cpup(rdma_resp + 2);
 	if (credits == 0)
 		credits = 1;	/* don't deadlock */
 	else if (credits > r_xprt->rx_buf.rb_bc_max_requests)
 		credits = r_xprt->rx_buf.rb_bc_max_requests;

 	spin_lock_bh(&xprt->transport_lock);
 	cwnd = xprt->cwnd;
 	xprt->cwnd = credits << RPC_CWNDSHIFT;
 	if (xprt->cwnd > cwnd)
 		xprt_release_rqst_cong(req->rq_task);
 	spin_unlock_bh(&xprt->transport_lock);


 	ret = 0;
 	xprt_complete_rqst(req->rq_task, rcvbuf->len);
 	rcvbuf->len = 0;

 out_unlock:
 	spin_unlock(&xprt->recv_lock);
 out:
 	return ret;

 out_shortreply:
 	dprintk("svcrdma: short bc reply: xprt=%p, len=%zu\n",
 		xprt, src->iov_len);
 	goto out;

 out_notfound:
 	dprintk("svcrdma: unrecognized bc reply: xprt=%p, xid=%08x\n",
 		xprt, be32_to_cpu(xid));
 	goto out_unlock;
 }

 /* Send a backwards direction RPC call.
  *
  * Caller holds the connection's mutex and has already marshaled
  * the RPC/RDMA request.
  *
  * This is similar to svc_rdma_send_reply_msg, but takes a struct
  * rpc_rqst instead, does not support chunks, and avoids blocking
  * memory allocation.
  *
  * XXX: There is still an opportunity to block in svc_rdma_send()
  * if there are no SQ entries to post the Send. This may occur if
  * the adapter has a small maximum SQ depth.
  */
 static int svc_rdma_bc_sendto(struct svcxprt_rdma *rdma,
 			      struct rpc_rqst *rqst,
 			      struct svc_rdma_send_ctxt *ctxt)
 {
 	int ret;

 	ret = svc_rdma_map_reply_msg(rdma, ctxt, &rqst->rq_snd_buf, NULL);
 	if (ret < 0)
 		return -EIO;

 	/* Bump page refcnt so Send completion doesn't release
 	 * the rq_buffer before all retransmits are complete.
 	 */
 	get_page(virt_to_page(rqst->rq_buffer));
 	ctxt->sc_send_wr.opcode = IB_WR_SEND;
 	return svc_rdma_send(rdma, &ctxt->sc_send_wr);
 }

 /* Server-side transport endpoint wants a whole page for its send
  * buffer. The client RPC code constructs the RPC header in this
  * buffer before it invokes ->send_request.
  */
 static int
 xprt_rdma_bc_allocate(struct rpc_task *task)
 {
 	struct rpc_rqst *rqst = task->tk_rqstp;
 	size_t size = rqst->rq_callsize;
 	struct page *page;

 	if (size > PAGE_SIZE) {
 		WARN_ONCE(1, "svcrdma: large bc buffer request (size %zu)\n",
 			  size);
 		return -EINVAL;
 	}

 	page = alloc_page(RPCRDMA_DEF_GFP);
 	if (!page)
 		return -ENOMEM;
 	rqst->rq_buffer = page_address(page);

 	rqst->rq_rbuffer = kmalloc(rqst->rq_rcvsize, RPCRDMA_DEF_GFP);
 	if (!rqst->rq_rbuffer) {
 		put_page(page);
 		return -ENOMEM;
 	}
 	return 0;
 }

 static void
 xprt_rdma_bc_free(struct rpc_task *task)
 {
 	struct rpc_rqst *rqst = task->tk_rqstp;

 	put_page(virt_to_page(rqst->rq_buffer));
 	kfree(rqst->rq_rbuffer);
 }

 static int
 rpcrdma_bc_send_request(struct svcxprt_rdma *rdma, struct rpc_rqst *rqst)
 {
 	struct rpc_xprt *xprt = rqst->rq_xprt;
 	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
 	struct svc_rdma_send_ctxt *ctxt;
 	__be32 *p;
 	int rc;

 	ctxt = svc_rdma_send_ctxt_get(rdma);
 	if (!ctxt)
 		goto drop_connection;

 	p = ctxt->sc_xprt_buf;
 	*p++ = rqst->rq_xid;
 	*p++ = rpcrdma_version;
 	*p++ = cpu_to_be32(r_xprt->rx_buf.rb_bc_max_requests);
 	*p++ = rdma_msg;
 	*p++ = xdr_zero;
 	*p++ = xdr_zero;
 	*p   = xdr_zero;
 	svc_rdma_sync_reply_hdr(rdma, ctxt, RPCRDMA_HDRLEN_MIN);

 #ifdef SVCRDMA_BACKCHANNEL_DEBUG
 	pr_info("%s: %*ph\n", __func__, 64, rqst->rq_buffer);
 #endif

 	rc = svc_rdma_bc_sendto(rdma, rqst, ctxt);
 	if (rc) {
 		svc_rdma_send_ctxt_put(rdma, ctxt);
 		goto drop_connection;
 	}
 	return rc;

 drop_connection:
 	dprintk("svcrdma: failed to send bc call\n");
 	xprt_disconnect_done(xprt);
 	return -ENOTCONN;
 }

 /* Send an RPC call on the passive end of a transport
  * connection.
  */
 static int
 xprt_rdma_bc_send_request(struct rpc_task *task)
 {
 	struct rpc_rqst *rqst = task->tk_rqstp;
 	struct svc_xprt *sxprt = rqst->rq_xprt->bc_xprt;
 	struct svcxprt_rdma *rdma;
 	int ret;

 	dprintk("svcrdma: sending bc call with xid: %08x\n",
 		be32_to_cpu(rqst->rq_xid));

 	if (!mutex_trylock(&sxprt->xpt_mutex)) {
 		rpc_sleep_on(&sxprt->xpt_bc_pending, task, NULL);
 		if (!mutex_trylock(&sxprt->xpt_mutex))
 			return -EAGAIN;
 		rpc_wake_up_queued_task(&sxprt->xpt_bc_pending, task);
 	}

 	ret = -ENOTCONN;
 	rdma = container_of(sxprt, struct svcxprt_rdma, sc_xprt);
 	if (!test_bit(XPT_DEAD, &sxprt->xpt_flags))
 		ret = rpcrdma_bc_send_request(rdma, rqst);

 	mutex_unlock(&sxprt->xpt_mutex);

 	if (ret < 0)
 		return ret;
 	return 0;
 }

 static void
 xprt_rdma_bc_close(struct rpc_xprt *xprt)
 {
 	dprintk("svcrdma: %s: xprt %p\n", __func__, xprt);
 }

 static void
 xprt_rdma_bc_put(struct rpc_xprt *xprt)
 {
 	dprintk("svcrdma: %s: xprt %p\n", __func__, xprt);

 	xprt_free(xprt);
 	module_put(THIS_MODULE);
 }

 static const struct rpc_xprt_ops xprt_rdma_bc_procs = {
 	.reserve_xprt		= xprt_reserve_xprt_cong,
 	.release_xprt		= xprt_release_xprt_cong,
 	.alloc_slot		= xprt_alloc_slot,
 	.free_slot		= xprt_free_slot,
 	.release_request	= xprt_release_rqst_cong,
 	.buf_alloc		= xprt_rdma_bc_allocate,
 	.buf_free		= xprt_rdma_bc_free,
 	.send_request		= xprt_rdma_bc_send_request,
 	.set_retrans_timeout	= xprt_set_retrans_timeout_def,
 	.close			= xprt_rdma_bc_close,
 	.destroy		= xprt_rdma_bc_put,
 	.print_stats		= xprt_rdma_print_stats
 };

 static const struct rpc_timeout xprt_rdma_bc_timeout = {
 	.to_initval = 60 * HZ,
 	.to_maxval = 60 * HZ,
 };

 /* It shouldn't matter if the number of backchannel session slots
  * doesn't match the number of RPC/RDMA credits. That just means
  * one or the other will have extra slots that aren't used.
  */
 static struct rpc_xprt *
 xprt_setup_rdma_bc(struct xprt_create *args)
 {
 	struct rpc_xprt *xprt;
 	struct rpcrdma_xprt *new_xprt;

 	if (args->addrlen > sizeof(xprt->addr)) {
 		dprintk("RPC:       %s: address too large\n", __func__);
 		return ERR_PTR(-EBADF);
 	}

 	xprt = xprt_alloc(args->net, sizeof(*new_xprt),
 			  RPCRDMA_MAX_BC_REQUESTS,
 			  RPCRDMA_MAX_BC_REQUESTS);
 	if (!xprt) {
 		dprintk("RPC:       %s: couldn't allocate rpc_xprt\n",
 			__func__);
 		return ERR_PTR(-ENOMEM);
 	}

 	xprt->timeout = &xprt_rdma_bc_timeout;
 	xprt_set_bound(xprt);
 	xprt_set_connected(xprt);
 	xprt->bind_timeout = RPCRDMA_BIND_TO;
 	xprt->reestablish_timeout = RPCRDMA_INIT_REEST_TO;
 	xprt->idle_timeout = RPCRDMA_IDLE_DISC_TO;

 	xprt->prot = XPRT_TRANSPORT_BC_RDMA;
 	xprt->tsh_size = 0;
 	xprt->ops = &xprt_rdma_bc_procs;

 	memcpy(&xprt->addr, args->dstaddr, args->addrlen);
 	xprt->addrlen = args->addrlen;
 	xprt_rdma_format_addresses(xprt, (struct sockaddr *)&xprt->addr);
 	xprt->resvport = 0;

 	xprt->max_payload = xprt_rdma_max_inline_read;

 	new_xprt = rpcx_to_rdmax(xprt);
 	new_xprt->rx_buf.rb_bc_max_requests = xprt->max_reqs;

 	xprt_get(xprt);
 	args->bc_xprt->xpt_bc_xprt = xprt;
 	xprt->bc_xprt = args->bc_xprt;

 	if (!try_module_get(THIS_MODULE))
 		goto out_fail;

 	/* Final put for backchannel xprt is in __svc_rdma_free */
 	xprt_get(xprt);
 	return xprt;

 out_fail:
 	xprt_rdma_free_addresses(xprt);
 	args->bc_xprt->xpt_bc_xprt = NULL;
 	args->bc_xprt->xpt_bc_xps = NULL;
 	xprt_put(xprt);
 	xprt_free(xprt);
 	return ERR_PTR(-EINVAL);
 }

 struct xprt_class xprt_rdma_bc = {
 	.list			= LIST_HEAD_INIT(xprt_rdma_bc.list),
 	.name			= "rdma backchannel",
 	.owner			= THIS_MODULE,
 	.ident			= XPRT_TRANSPORT_BC_RDMA,
 	.setup			= xprt_setup_rdma_bc,
 };
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Copyright (c) 2015-2018 Oracle. All rights reserved.
	*
	* Support for backward direction RPCs on RPC/RDMA (server-side).
	*/

	#include <linux/module.h>

	#include <linux/sunrpc/svc_rdma.h>

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

	#define RPCDBG_FACILITY RPCDBG_SVCXPRT

	#undef SVCRDMA_BACKCHANNEL_DEBUG

	/**
	* svc_rdma_handle_bc_reply - Process incoming backchannel reply
	* @xprt: controlling backchannel transport
	* @rdma_resp: pointer to incoming transport header
	* @rcvbuf: XDR buffer into which to decode the reply
	*
	* Returns:
	* %0 if @rcvbuf is filled in, xprt_complete_rqst called,
	* %-EAGAIN if server should call ->recvfrom again.
	*/
	int svc_rdma_handle_bc_reply(struct rpc_xprt xprt, __be32 rdma_resp,
	struct xdr_buf *rcvbuf)
	{
	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
	struct kvec dst, src = &rcvbuf->head[0];
	struct rpc_rqst *req;
	unsigned long cwnd;
	u32 credits;
	size_t len;
	__be32 xid;
	__be32 *p;
	int ret;

	p = (__be32 *)src->iov_base;
	len = src->iov_len;
	xid = *rdma_resp;

	#ifdef SVCRDMA_BACKCHANNEL_DEBUG
	pr_info("%s: xid=%08x, length=%zu\n",
	__func__, be32_to_cpu(xid), len);
	pr_info("%s: RPC/RDMA: %*ph\n",
	__func__, (int)RPCRDMA_HDRLEN_MIN, rdma_resp);
	pr_info("%s: RPC: %*ph\n",
	__func__, (int)len, p);
	#endif

	ret = -EAGAIN;
	if (src->iov_len < 24)
	goto out_shortreply;

	spin_lock(&xprt->recv_lock);
	req = xprt_lookup_rqst(xprt, xid);
	if (!req)
	goto out_notfound;

	dst = &req->rq_private_buf.head[0];
	memcpy(&req->rq_private_buf, &req->rq_rcv_buf, sizeof(struct xdr_buf));
	if (dst->iov_len < len)
	goto out_unlock;
	memcpy(dst->iov_base, p, len);

	credits = be32_to_cpup(rdma_resp + 2);
	if (credits == 0)
	credits = 1; /* don't deadlock */
	else if (credits > r_xprt->rx_buf.rb_bc_max_requests)
	credits = r_xprt->rx_buf.rb_bc_max_requests;

	spin_lock_bh(&xprt->transport_lock);
	cwnd = xprt->cwnd;
	xprt->cwnd = credits << RPC_CWNDSHIFT;
	if (xprt->cwnd > cwnd)
	xprt_release_rqst_cong(req->rq_task);
	spin_unlock_bh(&xprt->transport_lock);


	ret = 0;
	xprt_complete_rqst(req->rq_task, rcvbuf->len);
	rcvbuf->len = 0;

	out_unlock:
	spin_unlock(&xprt->recv_lock);
	out:
	return ret;

	out_shortreply:
	dprintk("svcrdma: short bc reply: xprt=%p, len=%zu\n",
	xprt, src->iov_len);
	goto out;

	out_notfound:
	dprintk("svcrdma: unrecognized bc reply: xprt=%p, xid=%08x\n",
	xprt, be32_to_cpu(xid));
	goto out_unlock;
	}

	/* Send a backwards direction RPC call.
	*
	* Caller holds the connection's mutex and has already marshaled
	* the RPC/RDMA request.
	*
	* This is similar to svc_rdma_send_reply_msg, but takes a struct
	* rpc_rqst instead, does not support chunks, and avoids blocking
	* memory allocation.
	*
	* XXX: There is still an opportunity to block in svc_rdma_send()
	* if there are no SQ entries to post the Send. This may occur if
	* the adapter has a small maximum SQ depth.
	*/
	static int svc_rdma_bc_sendto(struct svcxprt_rdma *rdma,
	struct rpc_rqst *rqst,
	struct svc_rdma_send_ctxt *ctxt)
	{
	int ret;

	ret = svc_rdma_map_reply_msg(rdma, ctxt, &rqst->rq_snd_buf, NULL);
	if (ret < 0)
	return -EIO;

	/* Bump page refcnt so Send completion doesn't release
	* the rq_buffer before all retransmits are complete.
	*/
	get_page(virt_to_page(rqst->rq_buffer));
	ctxt->sc_send_wr.opcode = IB_WR_SEND;
	return svc_rdma_send(rdma, &ctxt->sc_send_wr);
	}

	/* Server-side transport endpoint wants a whole page for its send
	* buffer. The client RPC code constructs the RPC header in this
	* buffer before it invokes ->send_request.
	*/
	static int
	xprt_rdma_bc_allocate(struct rpc_task *task)
	{
	struct rpc_rqst *rqst = task->tk_rqstp;
	size_t size = rqst->rq_callsize;
	struct page *page;

	if (size > PAGE_SIZE) {
	WARN_ONCE(1, "svcrdma: large bc buffer request (size %zu)\n",
	size);
	return -EINVAL;
	}

	page = alloc_page(RPCRDMA_DEF_GFP);
	if (!page)
	return -ENOMEM;
	rqst->rq_buffer = page_address(page);

	rqst->rq_rbuffer = kmalloc(rqst->rq_rcvsize, RPCRDMA_DEF_GFP);
	if (!rqst->rq_rbuffer) {
	put_page(page);
	return -ENOMEM;
	}
	return 0;
	}

	static void
	xprt_rdma_bc_free(struct rpc_task *task)
	{
	struct rpc_rqst *rqst = task->tk_rqstp;

	put_page(virt_to_page(rqst->rq_buffer));
	kfree(rqst->rq_rbuffer);
	}

	static int
	rpcrdma_bc_send_request(struct svcxprt_rdma rdma, struct rpc_rqst rqst)
	{
	struct rpc_xprt *xprt = rqst->rq_xprt;
	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
	struct svc_rdma_send_ctxt *ctxt;
	__be32 *p;
	int rc;

	ctxt = svc_rdma_send_ctxt_get(rdma);
	if (!ctxt)
	goto drop_connection;

	p = ctxt->sc_xprt_buf;
	*p++ = rqst->rq_xid;
	*p++ = rpcrdma_version;
	*p++ = cpu_to_be32(r_xprt->rx_buf.rb_bc_max_requests);
	*p++ = rdma_msg;
	*p++ = xdr_zero;
	*p++ = xdr_zero;
	*p = xdr_zero;
	svc_rdma_sync_reply_hdr(rdma, ctxt, RPCRDMA_HDRLEN_MIN);

	#ifdef SVCRDMA_BACKCHANNEL_DEBUG
	pr_info("%s: %*ph\n", __func__, 64, rqst->rq_buffer);
	#endif

	rc = svc_rdma_bc_sendto(rdma, rqst, ctxt);
	if (rc) {
	svc_rdma_send_ctxt_put(rdma, ctxt);
	goto drop_connection;
	}
	return rc;

	drop_connection:
	dprintk("svcrdma: failed to send bc call\n");
	xprt_disconnect_done(xprt);
	return -ENOTCONN;
	}

	/* Send an RPC call on the passive end of a transport
	* connection.
	*/
	static int
	xprt_rdma_bc_send_request(struct rpc_task *task)
	{
	struct rpc_rqst *rqst = task->tk_rqstp;
	struct svc_xprt *sxprt = rqst->rq_xprt->bc_xprt;
	struct svcxprt_rdma *rdma;
	int ret;

	dprintk("svcrdma: sending bc call with xid: %08x\n",
	be32_to_cpu(rqst->rq_xid));

	if (!mutex_trylock(&sxprt->xpt_mutex)) {
	rpc_sleep_on(&sxprt->xpt_bc_pending, task, NULL);
	if (!mutex_trylock(&sxprt->xpt_mutex))
	return -EAGAIN;
	rpc_wake_up_queued_task(&sxprt->xpt_bc_pending, task);
	}

	ret = -ENOTCONN;
	rdma = container_of(sxprt, struct svcxprt_rdma, sc_xprt);
	if (!test_bit(XPT_DEAD, &sxprt->xpt_flags))
	ret = rpcrdma_bc_send_request(rdma, rqst);

	mutex_unlock(&sxprt->xpt_mutex);

	if (ret < 0)
	return ret;
	return 0;
	}

	static void
	xprt_rdma_bc_close(struct rpc_xprt *xprt)
	{
	dprintk("svcrdma: %s: xprt %p\n", __func__, xprt);
	}

	static void
	xprt_rdma_bc_put(struct rpc_xprt *xprt)
	{
	dprintk("svcrdma: %s: xprt %p\n", __func__, xprt);

	xprt_free(xprt);
	module_put(THIS_MODULE);
	}

	static const struct rpc_xprt_ops xprt_rdma_bc_procs = {
	.reserve_xprt = xprt_reserve_xprt_cong,
	.release_xprt = xprt_release_xprt_cong,
	.alloc_slot = xprt_alloc_slot,
	.free_slot = xprt_free_slot,
	.release_request = xprt_release_rqst_cong,
	.buf_alloc = xprt_rdma_bc_allocate,
	.buf_free = xprt_rdma_bc_free,
	.send_request = xprt_rdma_bc_send_request,
	.set_retrans_timeout = xprt_set_retrans_timeout_def,
	.close = xprt_rdma_bc_close,
	.destroy = xprt_rdma_bc_put,
	.print_stats = xprt_rdma_print_stats
	};

	static const struct rpc_timeout xprt_rdma_bc_timeout = {
	.to_initval = 60 * HZ,
	.to_maxval = 60 * HZ,
	};

	/* It shouldn't matter if the number of backchannel session slots
	* doesn't match the number of RPC/RDMA credits. That just means
	* one or the other will have extra slots that aren't used.
	*/
	static struct rpc_xprt *
	xprt_setup_rdma_bc(struct xprt_create *args)
	{
	struct rpc_xprt *xprt;
	struct rpcrdma_xprt *new_xprt;

	if (args->addrlen > sizeof(xprt->addr)) {
	dprintk("RPC: %s: address too large\n", __func__);
	return ERR_PTR(-EBADF);
	}

	xprt = xprt_alloc(args->net, sizeof(*new_xprt),
	RPCRDMA_MAX_BC_REQUESTS,
	RPCRDMA_MAX_BC_REQUESTS);
	if (!xprt) {
	dprintk("RPC: %s: couldn't allocate rpc_xprt\n",
	__func__);
	return ERR_PTR(-ENOMEM);
	}

	xprt->timeout = &xprt_rdma_bc_timeout;
	xprt_set_bound(xprt);
	xprt_set_connected(xprt);
	xprt->bind_timeout = RPCRDMA_BIND_TO;
	xprt->reestablish_timeout = RPCRDMA_INIT_REEST_TO;
	xprt->idle_timeout = RPCRDMA_IDLE_DISC_TO;

	xprt->prot = XPRT_TRANSPORT_BC_RDMA;
	xprt->tsh_size = 0;
	xprt->ops = &xprt_rdma_bc_procs;

	memcpy(&xprt->addr, args->dstaddr, args->addrlen);
	xprt->addrlen = args->addrlen;
	xprt_rdma_format_addresses(xprt, (struct sockaddr *)&xprt->addr);
	xprt->resvport = 0;

	xprt->max_payload = xprt_rdma_max_inline_read;

	new_xprt = rpcx_to_rdmax(xprt);
	new_xprt->rx_buf.rb_bc_max_requests = xprt->max_reqs;

	xprt_get(xprt);
	args->bc_xprt->xpt_bc_xprt = xprt;
	xprt->bc_xprt = args->bc_xprt;

	if (!try_module_get(THIS_MODULE))
	goto out_fail;

	/* Final put for backchannel xprt is in __svc_rdma_free */
	xprt_get(xprt);
	return xprt;

	out_fail:
	xprt_rdma_free_addresses(xprt);
	args->bc_xprt->xpt_bc_xprt = NULL;
	args->bc_xprt->xpt_bc_xps = NULL;
	xprt_put(xprt);
	xprt_free(xprt);
	return ERR_PTR(-EINVAL);
	}

	struct xprt_class xprt_rdma_bc = {
	.list = LIST_HEAD_INIT(xprt_rdma_bc.list),
	.name = "rdma backchannel",
	.owner = THIS_MODULE,
	.ident = XPRT_TRANSPORT_BC_RDMA,
	.setup = xprt_setup_rdma_bc,
	};