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TOMOYO Linux Cross Reference
Linux/net/sunrpc/xprtrdma/svc_rdma_sendto.c

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  1 /*
  2  * Copyright (c) 2016 Oracle. All rights reserved.
  3  * Copyright (c) 2014 Open Grid Computing, Inc. All rights reserved.
  4  * Copyright (c) 2005-2006 Network Appliance, Inc. All rights reserved.
  5  *
  6  * This software is available to you under a choice of one of two
  7  * licenses.  You may choose to be licensed under the terms of the GNU
  8  * General Public License (GPL) Version 2, available from the file
  9  * COPYING in the main directory of this source tree, or the BSD-type
 10  * license below:
 11  *
 12  * Redistribution and use in source and binary forms, with or without
 13  * modification, are permitted provided that the following conditions
 14  * are met:
 15  *
 16  *      Redistributions of source code must retain the above copyright
 17  *      notice, this list of conditions and the following disclaimer.
 18  *
 19  *      Redistributions in binary form must reproduce the above
 20  *      copyright notice, this list of conditions and the following
 21  *      disclaimer in the documentation and/or other materials provided
 22  *      with the distribution.
 23  *
 24  *      Neither the name of the Network Appliance, Inc. nor the names of
 25  *      its contributors may be used to endorse or promote products
 26  *      derived from this software without specific prior written
 27  *      permission.
 28  *
 29  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 30  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 31  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 32  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 33  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 34  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 35  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 36  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 37  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 38  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 39  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 40  *
 41  * Author: Tom Tucker <tom@opengridcomputing.com>
 42  */
 43 
 44 /* Operation
 45  *
 46  * The main entry point is svc_rdma_sendto. This is called by the
 47  * RPC server when an RPC Reply is ready to be transmitted to a client.
 48  *
 49  * The passed-in svc_rqst contains a struct xdr_buf which holds an
 50  * XDR-encoded RPC Reply message. sendto must construct the RPC-over-RDMA
 51  * transport header, post all Write WRs needed for this Reply, then post
 52  * a Send WR conveying the transport header and the RPC message itself to
 53  * the client.
 54  *
 55  * svc_rdma_sendto must fully transmit the Reply before returning, as
 56  * the svc_rqst will be recycled as soon as sendto returns. Remaining
 57  * resources referred to by the svc_rqst are also recycled at that time.
 58  * Therefore any resources that must remain longer must be detached
 59  * from the svc_rqst and released later.
 60  *
 61  * Page Management
 62  *
 63  * The I/O that performs Reply transmission is asynchronous, and may
 64  * complete well after sendto returns. Thus pages under I/O must be
 65  * removed from the svc_rqst before sendto returns.
 66  *
 67  * The logic here depends on Send Queue and completion ordering. Since
 68  * the Send WR is always posted last, it will always complete last. Thus
 69  * when it completes, it is guaranteed that all previous Write WRs have
 70  * also completed.
 71  *
 72  * Write WRs are constructed and posted. Each Write segment gets its own
 73  * svc_rdma_rw_ctxt, allowing the Write completion handler to find and
 74  * DMA-unmap the pages under I/O for that Write segment. The Write
 75  * completion handler does not release any pages.
 76  *
 77  * When the Send WR is constructed, it also gets its own svc_rdma_op_ctxt.
 78  * The ownership of all of the Reply's pages are transferred into that
 79  * ctxt, the Send WR is posted, and sendto returns.
 80  *
 81  * The svc_rdma_op_ctxt is presented when the Send WR completes. The
 82  * Send completion handler finally releases the Reply's pages.
 83  *
 84  * This mechanism also assumes that completions on the transport's Send
 85  * Completion Queue do not run in parallel. Otherwise a Write completion
 86  * and Send completion running at the same time could release pages that
 87  * are still DMA-mapped.
 88  *
 89  * Error Handling
 90  *
 91  * - If the Send WR is posted successfully, it will either complete
 92  *   successfully, or get flushed. Either way, the Send completion
 93  *   handler releases the Reply's pages.
 94  * - If the Send WR cannot be not posted, the forward path releases
 95  *   the Reply's pages.
 96  *
 97  * This handles the case, without the use of page reference counting,
 98  * where two different Write segments send portions of the same page.
 99  */
100 
101 #include <linux/sunrpc/debug.h>
102 #include <linux/sunrpc/rpc_rdma.h>
103 #include <linux/spinlock.h>
104 #include <asm/unaligned.h>
105 #include <rdma/ib_verbs.h>
106 #include <rdma/rdma_cm.h>
107 #include <linux/sunrpc/svc_rdma.h>
108 
109 #define RPCDBG_FACILITY RPCDBG_SVCXPRT
110 
111 static u32 xdr_padsize(u32 len)
112 {
113         return (len & 3) ? (4 - (len & 3)) : 0;
114 }
115 
116 /* Returns length of transport header, in bytes.
117  */
118 static unsigned int svc_rdma_reply_hdr_len(__be32 *rdma_resp)
119 {
120         unsigned int nsegs;
121         __be32 *p;
122 
123         p = rdma_resp;
124 
125         /* RPC-over-RDMA V1 replies never have a Read list. */
126         p += rpcrdma_fixed_maxsz + 1;
127 
128         /* Skip Write list. */
129         while (*p++ != xdr_zero) {
130                 nsegs = be32_to_cpup(p++);
131                 p += nsegs * rpcrdma_segment_maxsz;
132         }
133 
134         /* Skip Reply chunk. */
135         if (*p++ != xdr_zero) {
136                 nsegs = be32_to_cpup(p++);
137                 p += nsegs * rpcrdma_segment_maxsz;
138         }
139 
140         return (unsigned long)p - (unsigned long)rdma_resp;
141 }
142 
143 /* One Write chunk is copied from Call transport header to Reply
144  * transport header. Each segment's length field is updated to
145  * reflect number of bytes consumed in the segment.
146  *
147  * Returns number of segments in this chunk.
148  */
149 static unsigned int xdr_encode_write_chunk(__be32 *dst, __be32 *src,
150                                            unsigned int remaining)
151 {
152         unsigned int i, nsegs;
153         u32 seg_len;
154 
155         /* Write list discriminator */
156         *dst++ = *src++;
157 
158         /* number of segments in this chunk */
159         nsegs = be32_to_cpup(src);
160         *dst++ = *src++;
161 
162         for (i = nsegs; i; i--) {
163                 /* segment's RDMA handle */
164                 *dst++ = *src++;
165 
166                 /* bytes returned in this segment */
167                 seg_len = be32_to_cpu(*src);
168                 if (remaining >= seg_len) {
169                         /* entire segment was consumed */
170                         *dst = *src;
171                         remaining -= seg_len;
172                 } else {
173                         /* segment only partly filled */
174                         *dst = cpu_to_be32(remaining);
175                         remaining = 0;
176                 }
177                 dst++; src++;
178 
179                 /* segment's RDMA offset */
180                 *dst++ = *src++;
181                 *dst++ = *src++;
182         }
183 
184         return nsegs;
185 }
186 
187 /* The client provided a Write list in the Call message. Fill in
188  * the segments in the first Write chunk in the Reply's transport
189  * header with the number of bytes consumed in each segment.
190  * Remaining chunks are returned unused.
191  *
192  * Assumptions:
193  *  - Client has provided only one Write chunk
194  */
195 static void svc_rdma_xdr_encode_write_list(__be32 *rdma_resp, __be32 *wr_ch,
196                                            unsigned int consumed)
197 {
198         unsigned int nsegs;
199         __be32 *p, *q;
200 
201         /* RPC-over-RDMA V1 replies never have a Read list. */
202         p = rdma_resp + rpcrdma_fixed_maxsz + 1;
203 
204         q = wr_ch;
205         while (*q != xdr_zero) {
206                 nsegs = xdr_encode_write_chunk(p, q, consumed);
207                 q += 2 + nsegs * rpcrdma_segment_maxsz;
208                 p += 2 + nsegs * rpcrdma_segment_maxsz;
209                 consumed = 0;
210         }
211 
212         /* Terminate Write list */
213         *p++ = xdr_zero;
214 
215         /* Reply chunk discriminator; may be replaced later */
216         *p = xdr_zero;
217 }
218 
219 /* The client provided a Reply chunk in the Call message. Fill in
220  * the segments in the Reply chunk in the Reply message with the
221  * number of bytes consumed in each segment.
222  *
223  * Assumptions:
224  * - Reply can always fit in the provided Reply chunk
225  */
226 static void svc_rdma_xdr_encode_reply_chunk(__be32 *rdma_resp, __be32 *rp_ch,
227                                             unsigned int consumed)
228 {
229         __be32 *p;
230 
231         /* Find the Reply chunk in the Reply's xprt header.
232          * RPC-over-RDMA V1 replies never have a Read list.
233          */
234         p = rdma_resp + rpcrdma_fixed_maxsz + 1;
235 
236         /* Skip past Write list */
237         while (*p++ != xdr_zero)
238                 p += 1 + be32_to_cpup(p) * rpcrdma_segment_maxsz;
239 
240         xdr_encode_write_chunk(p, rp_ch, consumed);
241 }
242 
243 /* Parse the RPC Call's transport header.
244  */
245 static void svc_rdma_get_write_arrays(__be32 *rdma_argp,
246                                       __be32 **write, __be32 **reply)
247 {
248         __be32 *p;
249 
250         p = rdma_argp + rpcrdma_fixed_maxsz;
251 
252         /* Read list */
253         while (*p++ != xdr_zero)
254                 p += 5;
255 
256         /* Write list */
257         if (*p != xdr_zero) {
258                 *write = p;
259                 while (*p++ != xdr_zero)
260                         p += 1 + be32_to_cpu(*p) * 4;
261         } else {
262                 *write = NULL;
263                 p++;
264         }
265 
266         /* Reply chunk */
267         if (*p != xdr_zero)
268                 *reply = p;
269         else
270                 *reply = NULL;
271 }
272 
273 /* RPC-over-RDMA Version One private extension: Remote Invalidation.
274  * Responder's choice: requester signals it can handle Send With
275  * Invalidate, and responder chooses one rkey to invalidate.
276  *
277  * Find a candidate rkey to invalidate when sending a reply.  Picks the
278  * first R_key it finds in the chunk lists.
279  *
280  * Returns zero if RPC's chunk lists are empty.
281  */
282 static u32 svc_rdma_get_inv_rkey(__be32 *rdma_argp,
283                                  __be32 *wr_lst, __be32 *rp_ch)
284 {
285         __be32 *p;
286 
287         p = rdma_argp + rpcrdma_fixed_maxsz;
288         if (*p != xdr_zero)
289                 p += 2;
290         else if (wr_lst && be32_to_cpup(wr_lst + 1))
291                 p = wr_lst + 2;
292         else if (rp_ch && be32_to_cpup(rp_ch + 1))
293                 p = rp_ch + 2;
294         else
295                 return 0;
296         return be32_to_cpup(p);
297 }
298 
299 /* ib_dma_map_page() is used here because svc_rdma_dma_unmap()
300  * is used during completion to DMA-unmap this memory, and
301  * it uses ib_dma_unmap_page() exclusively.
302  */
303 static int svc_rdma_dma_map_buf(struct svcxprt_rdma *rdma,
304                                 struct svc_rdma_op_ctxt *ctxt,
305                                 unsigned int sge_no,
306                                 unsigned char *base,
307                                 unsigned int len)
308 {
309         unsigned long offset = (unsigned long)base & ~PAGE_MASK;
310         struct ib_device *dev = rdma->sc_cm_id->device;
311         dma_addr_t dma_addr;
312 
313         dma_addr = ib_dma_map_page(dev, virt_to_page(base),
314                                    offset, len, DMA_TO_DEVICE);
315         if (ib_dma_mapping_error(dev, dma_addr))
316                 return -EIO;
317 
318         ctxt->sge[sge_no].addr = dma_addr;
319         ctxt->sge[sge_no].length = len;
320         ctxt->sge[sge_no].lkey = rdma->sc_pd->local_dma_lkey;
321         svc_rdma_count_mappings(rdma, ctxt);
322         return 0;
323 }
324 
325 static int svc_rdma_dma_map_page(struct svcxprt_rdma *rdma,
326                                  struct svc_rdma_op_ctxt *ctxt,
327                                  unsigned int sge_no,
328                                  struct page *page,
329                                  unsigned int offset,
330                                  unsigned int len)
331 {
332         struct ib_device *dev = rdma->sc_cm_id->device;
333         dma_addr_t dma_addr;
334 
335         dma_addr = ib_dma_map_page(dev, page, offset, len, DMA_TO_DEVICE);
336         if (ib_dma_mapping_error(dev, dma_addr))
337                 return -EIO;
338 
339         ctxt->sge[sge_no].addr = dma_addr;
340         ctxt->sge[sge_no].length = len;
341         ctxt->sge[sge_no].lkey = rdma->sc_pd->local_dma_lkey;
342         svc_rdma_count_mappings(rdma, ctxt);
343         return 0;
344 }
345 
346 /**
347  * svc_rdma_map_reply_hdr - DMA map the transport header buffer
348  * @rdma: controlling transport
349  * @ctxt: op_ctxt for the Send WR
350  * @rdma_resp: buffer containing transport header
351  * @len: length of transport header
352  *
353  * Returns:
354  *      %0 if the header is DMA mapped,
355  *      %-EIO if DMA mapping failed.
356  */
357 int svc_rdma_map_reply_hdr(struct svcxprt_rdma *rdma,
358                            struct svc_rdma_op_ctxt *ctxt,
359                            __be32 *rdma_resp,
360                            unsigned int len)
361 {
362         ctxt->direction = DMA_TO_DEVICE;
363         ctxt->pages[0] = virt_to_page(rdma_resp);
364         ctxt->count = 1;
365         return svc_rdma_dma_map_page(rdma, ctxt, 0, ctxt->pages[0], 0, len);
366 }
367 
368 /* Load the xdr_buf into the ctxt's sge array, and DMA map each
369  * element as it is added.
370  *
371  * Returns the number of sge elements loaded on success, or
372  * a negative errno on failure.
373  */
374 static int svc_rdma_map_reply_msg(struct svcxprt_rdma *rdma,
375                                   struct svc_rdma_op_ctxt *ctxt,
376                                   struct xdr_buf *xdr, __be32 *wr_lst)
377 {
378         unsigned int len, sge_no, remaining, page_off;
379         struct page **ppages;
380         unsigned char *base;
381         u32 xdr_pad;
382         int ret;
383 
384         sge_no = 1;
385 
386         ret = svc_rdma_dma_map_buf(rdma, ctxt, sge_no++,
387                                    xdr->head[0].iov_base,
388                                    xdr->head[0].iov_len);
389         if (ret < 0)
390                 return ret;
391 
392         /* If a Write chunk is present, the xdr_buf's page list
393          * is not included inline. However the Upper Layer may
394          * have added XDR padding in the tail buffer, and that
395          * should not be included inline.
396          */
397         if (wr_lst) {
398                 base = xdr->tail[0].iov_base;
399                 len = xdr->tail[0].iov_len;
400                 xdr_pad = xdr_padsize(xdr->page_len);
401 
402                 if (len && xdr_pad) {
403                         base += xdr_pad;
404                         len -= xdr_pad;
405                 }
406 
407                 goto tail;
408         }
409 
410         ppages = xdr->pages + (xdr->page_base >> PAGE_SHIFT);
411         page_off = xdr->page_base & ~PAGE_MASK;
412         remaining = xdr->page_len;
413         while (remaining) {
414                 len = min_t(u32, PAGE_SIZE - page_off, remaining);
415 
416                 ret = svc_rdma_dma_map_page(rdma, ctxt, sge_no++,
417                                             *ppages++, page_off, len);
418                 if (ret < 0)
419                         return ret;
420 
421                 remaining -= len;
422                 page_off = 0;
423         }
424 
425         base = xdr->tail[0].iov_base;
426         len = xdr->tail[0].iov_len;
427 tail:
428         if (len) {
429                 ret = svc_rdma_dma_map_buf(rdma, ctxt, sge_no++, base, len);
430                 if (ret < 0)
431                         return ret;
432         }
433 
434         return sge_no - 1;
435 }
436 
437 /* The svc_rqst and all resources it owns are released as soon as
438  * svc_rdma_sendto returns. Transfer pages under I/O to the ctxt
439  * so they are released by the Send completion handler.
440  */
441 static void svc_rdma_save_io_pages(struct svc_rqst *rqstp,
442                                    struct svc_rdma_op_ctxt *ctxt)
443 {
444         int i, pages = rqstp->rq_next_page - rqstp->rq_respages;
445 
446         ctxt->count += pages;
447         for (i = 0; i < pages; i++) {
448                 ctxt->pages[i + 1] = rqstp->rq_respages[i];
449                 rqstp->rq_respages[i] = NULL;
450         }
451         rqstp->rq_next_page = rqstp->rq_respages + 1;
452 }
453 
454 /**
455  * svc_rdma_post_send_wr - Set up and post one Send Work Request
456  * @rdma: controlling transport
457  * @ctxt: op_ctxt for transmitting the Send WR
458  * @num_sge: number of SGEs to send
459  * @inv_rkey: R_key argument to Send With Invalidate, or zero
460  *
461  * Returns:
462  *      %0 if the Send* was posted successfully,
463  *      %-ENOTCONN if the connection was lost or dropped,
464  *      %-EINVAL if there was a problem with the Send we built,
465  *      %-ENOMEM if ib_post_send failed.
466  */
467 int svc_rdma_post_send_wr(struct svcxprt_rdma *rdma,
468                           struct svc_rdma_op_ctxt *ctxt, int num_sge,
469                           u32 inv_rkey)
470 {
471         struct ib_send_wr *send_wr = &ctxt->send_wr;
472 
473         dprintk("svcrdma: posting Send WR with %u sge(s)\n", num_sge);
474 
475         send_wr->next = NULL;
476         ctxt->cqe.done = svc_rdma_wc_send;
477         send_wr->wr_cqe = &ctxt->cqe;
478         send_wr->sg_list = ctxt->sge;
479         send_wr->num_sge = num_sge;
480         send_wr->send_flags = IB_SEND_SIGNALED;
481         if (inv_rkey) {
482                 send_wr->opcode = IB_WR_SEND_WITH_INV;
483                 send_wr->ex.invalidate_rkey = inv_rkey;
484         } else {
485                 send_wr->opcode = IB_WR_SEND;
486         }
487 
488         return svc_rdma_send(rdma, send_wr);
489 }
490 
491 /* Prepare the portion of the RPC Reply that will be transmitted
492  * via RDMA Send. The RPC-over-RDMA transport header is prepared
493  * in sge[0], and the RPC xdr_buf is prepared in following sges.
494  *
495  * Depending on whether a Write list or Reply chunk is present,
496  * the server may send all, a portion of, or none of the xdr_buf.
497  * In the latter case, only the transport header (sge[0]) is
498  * transmitted.
499  *
500  * RDMA Send is the last step of transmitting an RPC reply. Pages
501  * involved in the earlier RDMA Writes are here transferred out
502  * of the rqstp and into the ctxt's page array. These pages are
503  * DMA unmapped by each Write completion, but the subsequent Send
504  * completion finally releases these pages.
505  *
506  * Assumptions:
507  * - The Reply's transport header will never be larger than a page.
508  */
509 static int svc_rdma_send_reply_msg(struct svcxprt_rdma *rdma,
510                                    __be32 *rdma_argp, __be32 *rdma_resp,
511                                    struct svc_rqst *rqstp,
512                                    __be32 *wr_lst, __be32 *rp_ch)
513 {
514         struct svc_rdma_op_ctxt *ctxt;
515         u32 inv_rkey;
516         int ret;
517 
518         dprintk("svcrdma: sending %s reply: head=%zu, pagelen=%u, tail=%zu\n",
519                 (rp_ch ? "RDMA_NOMSG" : "RDMA_MSG"),
520                 rqstp->rq_res.head[0].iov_len,
521                 rqstp->rq_res.page_len,
522                 rqstp->rq_res.tail[0].iov_len);
523 
524         ctxt = svc_rdma_get_context(rdma);
525 
526         ret = svc_rdma_map_reply_hdr(rdma, ctxt, rdma_resp,
527                                      svc_rdma_reply_hdr_len(rdma_resp));
528         if (ret < 0)
529                 goto err;
530 
531         if (!rp_ch) {
532                 ret = svc_rdma_map_reply_msg(rdma, ctxt,
533                                              &rqstp->rq_res, wr_lst);
534                 if (ret < 0)
535                         goto err;
536         }
537 
538         svc_rdma_save_io_pages(rqstp, ctxt);
539 
540         inv_rkey = 0;
541         if (rdma->sc_snd_w_inv)
542                 inv_rkey = svc_rdma_get_inv_rkey(rdma_argp, wr_lst, rp_ch);
543         ret = svc_rdma_post_send_wr(rdma, ctxt, 1 + ret, inv_rkey);
544         if (ret)
545                 goto err;
546 
547         return 0;
548 
549 err:
550         pr_err("svcrdma: failed to post Send WR (%d)\n", ret);
551         svc_rdma_unmap_dma(ctxt);
552         svc_rdma_put_context(ctxt, 1);
553         return ret;
554 }
555 
556 /* Given the client-provided Write and Reply chunks, the server was not
557  * able to form a complete reply. Return an RDMA_ERROR message so the
558  * client can retire this RPC transaction. As above, the Send completion
559  * routine releases payload pages that were part of a previous RDMA Write.
560  *
561  * Remote Invalidation is skipped for simplicity.
562  */
563 static int svc_rdma_send_error_msg(struct svcxprt_rdma *rdma,
564                                    __be32 *rdma_resp, struct svc_rqst *rqstp)
565 {
566         struct svc_rdma_op_ctxt *ctxt;
567         __be32 *p;
568         int ret;
569 
570         ctxt = svc_rdma_get_context(rdma);
571 
572         /* Replace the original transport header with an
573          * RDMA_ERROR response. XID etc are preserved.
574          */
575         p = rdma_resp + 3;
576         *p++ = rdma_error;
577         *p   = err_chunk;
578 
579         ret = svc_rdma_map_reply_hdr(rdma, ctxt, rdma_resp, 20);
580         if (ret < 0)
581                 goto err;
582 
583         svc_rdma_save_io_pages(rqstp, ctxt);
584 
585         ret = svc_rdma_post_send_wr(rdma, ctxt, 1 + ret, 0);
586         if (ret)
587                 goto err;
588 
589         return 0;
590 
591 err:
592         pr_err("svcrdma: failed to post Send WR (%d)\n", ret);
593         svc_rdma_unmap_dma(ctxt);
594         svc_rdma_put_context(ctxt, 1);
595         return ret;
596 }
597 
598 void svc_rdma_prep_reply_hdr(struct svc_rqst *rqstp)
599 {
600 }
601 
602 /**
603  * svc_rdma_sendto - Transmit an RPC reply
604  * @rqstp: processed RPC request, reply XDR already in ::rq_res
605  *
606  * Any resources still associated with @rqstp are released upon return.
607  * If no reply message was possible, the connection is closed.
608  *
609  * Returns:
610  *      %0 if an RPC reply has been successfully posted,
611  *      %-ENOMEM if a resource shortage occurred (connection is lost),
612  *      %-ENOTCONN if posting failed (connection is lost).
613  */
614 int svc_rdma_sendto(struct svc_rqst *rqstp)
615 {
616         struct svc_xprt *xprt = rqstp->rq_xprt;
617         struct svcxprt_rdma *rdma =
618                 container_of(xprt, struct svcxprt_rdma, sc_xprt);
619         __be32 *p, *rdma_argp, *rdma_resp, *wr_lst, *rp_ch;
620         struct xdr_buf *xdr = &rqstp->rq_res;
621         struct page *res_page;
622         int ret;
623 
624         /* Find the call's chunk lists to decide how to send the reply.
625          * Receive places the Call's xprt header at the start of page 0.
626          */
627         rdma_argp = page_address(rqstp->rq_pages[0]);
628         svc_rdma_get_write_arrays(rdma_argp, &wr_lst, &rp_ch);
629 
630         dprintk("svcrdma: preparing response for XID 0x%08x\n",
631                 be32_to_cpup(rdma_argp));
632 
633         /* Create the RDMA response header. xprt->xpt_mutex,
634          * acquired in svc_send(), serializes RPC replies. The
635          * code path below that inserts the credit grant value
636          * into each transport header runs only inside this
637          * critical section.
638          */
639         ret = -ENOMEM;
640         res_page = alloc_page(GFP_KERNEL);
641         if (!res_page)
642                 goto err0;
643         rdma_resp = page_address(res_page);
644 
645         p = rdma_resp;
646         *p++ = *rdma_argp;
647         *p++ = *(rdma_argp + 1);
648         *p++ = rdma->sc_fc_credits;
649         *p++ = rp_ch ? rdma_nomsg : rdma_msg;
650 
651         /* Start with empty chunks */
652         *p++ = xdr_zero;
653         *p++ = xdr_zero;
654         *p   = xdr_zero;
655 
656         if (wr_lst) {
657                 /* XXX: Presume the client sent only one Write chunk */
658                 ret = svc_rdma_send_write_chunk(rdma, wr_lst, xdr);
659                 if (ret < 0)
660                         goto err2;
661                 svc_rdma_xdr_encode_write_list(rdma_resp, wr_lst, ret);
662         }
663         if (rp_ch) {
664                 ret = svc_rdma_send_reply_chunk(rdma, rp_ch, wr_lst, xdr);
665                 if (ret < 0)
666                         goto err2;
667                 svc_rdma_xdr_encode_reply_chunk(rdma_resp, rp_ch, ret);
668         }
669 
670         ret = svc_rdma_post_recv(rdma, GFP_KERNEL);
671         if (ret)
672                 goto err1;
673         ret = svc_rdma_send_reply_msg(rdma, rdma_argp, rdma_resp, rqstp,
674                                       wr_lst, rp_ch);
675         if (ret < 0)
676                 goto err0;
677         return 0;
678 
679  err2:
680         if (ret != -E2BIG)
681                 goto err1;
682 
683         ret = svc_rdma_post_recv(rdma, GFP_KERNEL);
684         if (ret)
685                 goto err1;
686         ret = svc_rdma_send_error_msg(rdma, rdma_resp, rqstp);
687         if (ret < 0)
688                 goto err0;
689         return 0;
690 
691  err1:
692         put_page(res_page);
693  err0:
694         pr_err("svcrdma: Could not send reply, err=%d. Closing transport.\n",
695                ret);
696         set_bit(XPT_CLOSE, &xprt->xpt_flags);
697         return -ENOTCONN;
698 }
699 

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