hw/block/dataplane/xen-block.c

   1 /*
   2  * Copyright (c) 2018  Citrix Systems Inc.
   3  * (c) Gerd Hoffmann <kraxel@redhat.com>
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; under version 2 of the License.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License along
  15  * with this program; if not, see <http://www.gnu.org/licenses/>.
  16  *
  17  * Contributions after 2012-01-13 are licensed under the terms of the
  18  * GNU GPL, version 2 or (at your option) any later version.
  19  */
  20
  21 #include "qemu/osdep.h"
  22 #include "qemu/error-report.h"
  23 #include "qemu/main-loop.h"
  24 #include "qapi/error.h"
  25 #include "hw/xen/xen_common.h"
  26 #include "hw/block/xen_blkif.h"
  27 #include "sysemu/block-backend.h"
  28 #include "sysemu/iothread.h"
  29 #include "xen-block.h"
  30
  31 typedef struct XenBlockRequest {
  32     blkif_request_t req;
  33     int16_t status;
  34     off_t start;
  35     QEMUIOVector v;
  36     void *buf;
  37     size_t size;
  38     int presync;
  39     int aio_inflight;
  40     int aio_errors;
  41     XenBlockDataPlane *dataplane;
  42     QLIST_ENTRY(XenBlockRequest) list;
  43     BlockAcctCookie acct;
  44 } XenBlockRequest;
  45
  46 struct XenBlockDataPlane {
  47     XenDevice *xendev;
  48     XenEventChannel *event_channel;
  49     unsigned int *ring_ref;
  50     unsigned int nr_ring_ref;
  51     void *sring;
  52     int protocol;
  53     blkif_back_rings_t rings;
  54     int more_work;
  55     QLIST_HEAD(inflight_head, XenBlockRequest) inflight;
  56     QLIST_HEAD(freelist_head, XenBlockRequest) freelist;
  57     int requests_total;
  58     int requests_inflight;
  59     unsigned int max_requests;
  60     BlockBackend *blk;
  61     unsigned int sector_size;
  62     QEMUBH *bh;
  63     IOThread *iothread;
  64     AioContext *ctx;
  65 };
  66
  67 static int xen_block_send_response(XenBlockRequest *request);
  68
  69 static void reset_request(XenBlockRequest *request)
  70 {
  71     memset(&request->req, 0, sizeof(request->req));
  72     request->status = 0;
  73     request->start = 0;
  74     request->size = 0;
  75     request->presync = 0;
  76
  77     request->aio_inflight = 0;
  78     request->aio_errors = 0;
  79
  80     request->dataplane = NULL;
  81     memset(&request->list, 0, sizeof(request->list));
  82     memset(&request->acct, 0, sizeof(request->acct));
  83
  84     qemu_iovec_reset(&request->v);
  85 }
  86
  87 static XenBlockRequest *xen_block_start_request(XenBlockDataPlane *dataplane)
  88 {
  89     XenBlockRequest *request = NULL;
  90
  91     if (QLIST_EMPTY(&dataplane->freelist)) {
  92         if (dataplane->requests_total >= dataplane->max_requests) {
  93             goto out;
  94         }
  95         /* allocate new struct */
  96         request = g_malloc0(sizeof(*request));
  97         request->dataplane = dataplane;
  98         /*
  99          * We cannot need more pages per requests than this, and since we
 100          * re-use requests, allocate the memory once here. It will be freed
 101          * xen_block_dataplane_destroy() when the request list is freed.
 102          */
 103         request->buf = qemu_memalign(XC_PAGE_SIZE,
 104                                      BLKIF_MAX_SEGMENTS_PER_REQUEST *
 105                                      XC_PAGE_SIZE);
 106         dataplane->requests_total++;
 107         qemu_iovec_init(&request->v, 1);
 108     } else {
 109         /* get one from freelist */
 110         request = QLIST_FIRST(&dataplane->freelist);
 111         QLIST_REMOVE(request, list);
 112     }
 113     QLIST_INSERT_HEAD(&dataplane->inflight, request, list);
 114     dataplane->requests_inflight++;
 115
 116 out:
 117     return request;
 118 }
 119
 120 static void xen_block_complete_request(XenBlockRequest *request)
 121 {
 122     XenBlockDataPlane *dataplane = request->dataplane;
 123
 124     if (xen_block_send_response(request)) {
 125         Error *local_err = NULL;
 126
 127         xen_device_notify_event_channel(dataplane->xendev,
 128                                         dataplane->event_channel,
 129                                         &local_err);
 130         if (local_err) {
 131             error_report_err(local_err);
 132         }
 133     }
 134
 135     QLIST_REMOVE(request, list);
 136     dataplane->requests_inflight--;
 137     reset_request(request);
 138     request->dataplane = dataplane;
 139     QLIST_INSERT_HEAD(&dataplane->freelist, request, list);
 140 }
 141
 142 /*
 143  * translate request into iovec + start offset
 144  * do sanity checks along the way
 145  */
 146 static int xen_block_parse_request(XenBlockRequest *request)
 147 {
 148     XenBlockDataPlane *dataplane = request->dataplane;
 149     size_t len;
 150     int i;
 151
 152     switch (request->req.operation) {
 153     case BLKIF_OP_READ:
 154         break;
 155     case BLKIF_OP_FLUSH_DISKCACHE:
 156         request->presync = 1;
 157         if (!request->req.nr_segments) {
 158             return 0;
 159         }
 160         /* fall through */
 161     case BLKIF_OP_WRITE:
 162         break;
 163     case BLKIF_OP_DISCARD:
 164         return 0;
 165     default:
 166         error_report("error: unknown operation (%d)", request->req.operation);
 167         goto err;
 168     };
 169
 170     if (request->req.operation != BLKIF_OP_READ &&
 171         blk_is_read_only(dataplane->blk)) {
 172         error_report("error: write req for ro device");
 173         goto err;
 174     }
 175
 176     request->start = request->req.sector_number * dataplane->sector_size;
 177     for (i = 0; i < request->req.nr_segments; i++) {
 178         if (i == BLKIF_MAX_SEGMENTS_PER_REQUEST) {
 179             error_report("error: nr_segments too big");
 180             goto err;
 181         }
 182         if (request->req.seg[i].first_sect > request->req.seg[i].last_sect) {
 183             error_report("error: first > last sector");
 184             goto err;
 185         }
 186         if (request->req.seg[i].last_sect * dataplane->sector_size >=
 187             XC_PAGE_SIZE) {
 188             error_report("error: page crossing");
 189             goto err;
 190         }
 191
 192         len = (request->req.seg[i].last_sect -
 193                request->req.seg[i].first_sect + 1) * dataplane->sector_size;
 194         request->size += len;
 195     }
 196     if (request->start + request->size > blk_getlength(dataplane->blk)) {
 197         error_report("error: access beyond end of file");
 198         goto err;
 199     }
 200     return 0;
 201
 202 err:
 203     request->status = BLKIF_RSP_ERROR;
 204     return -1;
 205 }
 206
 207 static int xen_block_copy_request(XenBlockRequest *request)
 208 {
 209     XenBlockDataPlane *dataplane = request->dataplane;
 210     XenDevice *xendev = dataplane->xendev;
 211     XenDeviceGrantCopySegment segs[BLKIF_MAX_SEGMENTS_PER_REQUEST];
 212     int i, count;
 213     bool to_domain = (request->req.operation == BLKIF_OP_READ);
 214     void *virt = request->buf;
 215     Error *local_err = NULL;
 216
 217     if (request->req.nr_segments == 0) {
 218         return 0;
 219     }
 220
 221     count = request->req.nr_segments;
 222
 223     for (i = 0; i < count; i++) {
 224         if (to_domain) {
 225             segs[i].dest.foreign.ref = request->req.seg[i].gref;
 226             segs[i].dest.foreign.offset = request->req.seg[i].first_sect *
 227                 dataplane->sector_size;
 228             segs[i].source.virt = virt;
 229         } else {
 230             segs[i].source.foreign.ref = request->req.seg[i].gref;
 231             segs[i].source.foreign.offset = request->req.seg[i].first_sect *
 232                 dataplane->sector_size;
 233             segs[i].dest.virt = virt;
 234         }
 235         segs[i].len = (request->req.seg[i].last_sect -
 236                        request->req.seg[i].first_sect + 1) *
 237                       dataplane->sector_size;
 238         virt += segs[i].len;
 239     }
 240
 241     xen_device_copy_grant_refs(xendev, to_domain, segs, count, &local_err);
 242
 243     if (local_err) {
 244         error_reportf_err(local_err, "failed to copy data: ");
 245
 246         request->aio_errors++;
 247         return -1;
 248     }
 249
 250     return 0;
 251 }
 252
 253 static int xen_block_do_aio(XenBlockRequest *request);
 254
 255 static void xen_block_complete_aio(void *opaque, int ret)
 256 {
 257     XenBlockRequest *request = opaque;
 258     XenBlockDataPlane *dataplane = request->dataplane;
 259
 260     aio_context_acquire(dataplane->ctx);
 261
 262     if (ret != 0) {
 263         error_report("%s I/O error",
 264                      request->req.operation == BLKIF_OP_READ ?
 265                      "read" : "write");
 266         request->aio_errors++;
 267     }
 268
 269     request->aio_inflight--;
 270     if (request->presync) {
 271         request->presync = 0;
 272         xen_block_do_aio(request);
 273         goto done;
 274     }
 275     if (request->aio_inflight > 0) {
 276         goto done;
 277     }
 278
 279     switch (request->req.operation) {
 280     case BLKIF_OP_READ:
 281         /* in case of failure request->aio_errors is increased */
 282         if (ret == 0) {
 283             xen_block_copy_request(request);
 284         }
 285         break;
 286     case BLKIF_OP_WRITE:
 287     case BLKIF_OP_FLUSH_DISKCACHE:
 288     default:
 289         break;
 290     }
 291
 292     request->status = request->aio_errors ? BLKIF_RSP_ERROR : BLKIF_RSP_OKAY;
 293
 294     switch (request->req.operation) {
 295     case BLKIF_OP_WRITE:
 296     case BLKIF_OP_FLUSH_DISKCACHE:
 297         if (!request->req.nr_segments) {
 298             break;
 299         }
 300         /* fall through */
 301     case BLKIF_OP_READ:
 302         if (request->status == BLKIF_RSP_OKAY) {
 303             block_acct_done(blk_get_stats(dataplane->blk), &request->acct);
 304         } else {
 305             block_acct_failed(blk_get_stats(dataplane->blk), &request->acct);
 306         }
 307         break;
 308     case BLKIF_OP_DISCARD:
 309     default:
 310         break;
 311     }
 312
 313     xen_block_complete_request(request);
 314
 315     if (dataplane->more_work) {
 316         qemu_bh_schedule(dataplane->bh);
 317     }
 318
 319 done:
 320     aio_context_release(dataplane->ctx);
 321 }
 322
 323 static bool xen_block_split_discard(XenBlockRequest *request,
 324                                     blkif_sector_t sector_number,
 325                                     uint64_t nr_sectors)
 326 {
 327     XenBlockDataPlane *dataplane = request->dataplane;
 328     int64_t byte_offset;
 329     int byte_chunk;
 330     uint64_t byte_remaining;
 331     uint64_t sec_start = sector_number;
 332     uint64_t sec_count = nr_sectors;
 333
 334     /* Wrap around, or overflowing byte limit? */
 335     if (sec_start + sec_count < sec_count ||
 336         sec_start + sec_count > INT64_MAX / dataplane->sector_size) {
 337         return false;
 338     }
 339
 340     byte_offset = sec_start * dataplane->sector_size;
 341     byte_remaining = sec_count * dataplane->sector_size;
 342
 343     do {
 344         byte_chunk = byte_remaining > BDRV_REQUEST_MAX_BYTES ?
 345             BDRV_REQUEST_MAX_BYTES : byte_remaining;
 346         request->aio_inflight++;
 347         blk_aio_pdiscard(dataplane->blk, byte_offset, byte_chunk,
 348                          xen_block_complete_aio, request);
 349         byte_remaining -= byte_chunk;
 350         byte_offset += byte_chunk;
 351     } while (byte_remaining > 0);
 352
 353     return true;
 354 }
 355
 356 static int xen_block_do_aio(XenBlockRequest *request)
 357 {
 358     XenBlockDataPlane *dataplane = request->dataplane;
 359
 360     if (request->req.nr_segments &&
 361         (request->req.operation == BLKIF_OP_WRITE ||
 362          request->req.operation == BLKIF_OP_FLUSH_DISKCACHE) &&
 363         xen_block_copy_request(request)) {
 364         goto err;
 365     }
 366
 367     request->aio_inflight++;
 368     if (request->presync) {
 369         blk_aio_flush(request->dataplane->blk, xen_block_complete_aio,
 370                       request);
 371         return 0;
 372     }
 373
 374     switch (request->req.operation) {
 375     case BLKIF_OP_READ:
 376         qemu_iovec_add(&request->v, request->buf, request->size);
 377         block_acct_start(blk_get_stats(dataplane->blk), &request->acct,
 378                          request->v.size, BLOCK_ACCT_READ);
 379         request->aio_inflight++;
 380         blk_aio_preadv(dataplane->blk, request->start, &request->v, 0,
 381                        xen_block_complete_aio, request);
 382         break;
 383     case BLKIF_OP_WRITE:
 384     case BLKIF_OP_FLUSH_DISKCACHE:
 385         if (!request->req.nr_segments) {
 386             break;
 387         }
 388
 389         qemu_iovec_add(&request->v, request->buf, request->size);
 390         block_acct_start(blk_get_stats(dataplane->blk), &request->acct,
 391                          request->v.size,
 392                          request->req.operation == BLKIF_OP_WRITE ?
 393                          BLOCK_ACCT_WRITE : BLOCK_ACCT_FLUSH);
 394         request->aio_inflight++;
 395         blk_aio_pwritev(dataplane->blk, request->start, &request->v, 0,
 396                         xen_block_complete_aio, request);
 397         break;
 398     case BLKIF_OP_DISCARD:
 399     {
 400         struct blkif_request_discard *req = (void *)&request->req;
 401         if (!xen_block_split_discard(request, req->sector_number,
 402                                      req->nr_sectors)) {
 403             goto err;
 404         }
 405         break;
 406     }
 407     default:
 408         /* unknown operation (shouldn't happen -- parse catches this) */
 409         goto err;
 410     }
 411
 412     xen_block_complete_aio(request, 0);
 413
 414     return 0;
 415
 416 err:
 417     request->status = BLKIF_RSP_ERROR;
 418     xen_block_complete_request(request);
 419     return -1;
 420 }
 421
 422 static int xen_block_send_response(XenBlockRequest *request)
 423 {
 424     XenBlockDataPlane *dataplane = request->dataplane;
 425     int send_notify = 0;
 426     int have_requests = 0;
 427     blkif_response_t *resp;
 428
 429     /* Place on the response ring for the relevant domain. */
 430     switch (dataplane->protocol) {
 431     case BLKIF_PROTOCOL_NATIVE:
 432         resp = (blkif_response_t *)RING_GET_RESPONSE(
 433             &dataplane->rings.native,
 434             dataplane->rings.native.rsp_prod_pvt);
 435         break;
 436     case BLKIF_PROTOCOL_X86_32:
 437         resp = (blkif_response_t *)RING_GET_RESPONSE(
 438             &dataplane->rings.x86_32_part,
 439             dataplane->rings.x86_32_part.rsp_prod_pvt);
 440         break;
 441     case BLKIF_PROTOCOL_X86_64:
 442         resp = (blkif_response_t *)RING_GET_RESPONSE(
 443             &dataplane->rings.x86_64_part,
 444             dataplane->rings.x86_64_part.rsp_prod_pvt);
 445         break;
 446     default:
 447         return 0;
 448     }
 449
 450     resp->id = request->req.id;
 451     resp->operation = request->req.operation;
 452     resp->status = request->status;
 453
 454     dataplane->rings.common.rsp_prod_pvt++;
 455
 456     RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&dataplane->rings.common,
 457                                          send_notify);
 458     if (dataplane->rings.common.rsp_prod_pvt ==
 459         dataplane->rings.common.req_cons) {
 460         /*
 461          * Tail check for pending requests. Allows frontend to avoid
 462          * notifications if requests are already in flight (lower
 463          * overheads and promotes batching).
 464          */
 465         RING_FINAL_CHECK_FOR_REQUESTS(&dataplane->rings.common,
 466                                       have_requests);
 467     } else if (RING_HAS_UNCONSUMED_REQUESTS(&dataplane->rings.common)) {
 468         have_requests = 1;
 469     }
 470
 471     if (have_requests) {
 472         dataplane->more_work++;
 473     }
 474     return send_notify;
 475 }
 476
 477 static int xen_block_get_request(XenBlockDataPlane *dataplane,
 478                                  XenBlockRequest *request, RING_IDX rc)
 479 {
 480     switch (dataplane->protocol) {
 481     case BLKIF_PROTOCOL_NATIVE: {
 482         blkif_request_t *req =
 483             RING_GET_REQUEST(&dataplane->rings.native, rc);
 484
 485         memcpy(&request->req, req, sizeof(request->req));
 486         break;
 487     }
 488     case BLKIF_PROTOCOL_X86_32: {
 489         blkif_x86_32_request_t *req =
 490             RING_GET_REQUEST(&dataplane->rings.x86_32_part, rc);
 491
 492         blkif_get_x86_32_req(&request->req, req);
 493         break;
 494     }
 495     case BLKIF_PROTOCOL_X86_64: {
 496         blkif_x86_64_request_t *req =
 497             RING_GET_REQUEST(&dataplane->rings.x86_64_part, rc);
 498
 499         blkif_get_x86_64_req(&request->req, req);
 500         break;
 501     }
 502     }
 503     /* Prevent the compiler from accessing the on-ring fields instead. */
 504     barrier();
 505     return 0;
 506 }
 507
 508 /*
 509  * Threshold of in-flight requests above which we will start using
 510  * blk_io_plug()/blk_io_unplug() to batch requests.
 511  */
 512 #define IO_PLUG_THRESHOLD 1
 513
 514 static bool xen_block_handle_requests(XenBlockDataPlane *dataplane)
 515 {
 516     RING_IDX rc, rp;
 517     XenBlockRequest *request;
 518     int inflight_atstart = dataplane->requests_inflight;
 519     int batched = 0;
 520     bool done_something = false;
 521
 522     dataplane->more_work = 0;
 523
 524     rc = dataplane->rings.common.req_cons;
 525     rp = dataplane->rings.common.sring->req_prod;
 526     xen_rmb(); /* Ensure we see queued requests up to 'rp'. */
 527
 528     /*
 529      * If there was more than IO_PLUG_THRESHOLD requests in flight
 530      * when we got here, this is an indication that there the bottleneck
 531      * is below us, so it's worth beginning to batch up I/O requests
 532      * rather than submitting them immediately. The maximum number
 533      * of requests we're willing to batch is the number already in
 534      * flight, so it can grow up to max_requests when the bottleneck
 535      * is below us.
 536      */
 537     if (inflight_atstart > IO_PLUG_THRESHOLD) {
 538         blk_io_plug(dataplane->blk);
 539     }
 540     while (rc != rp) {
 541         /* pull request from ring */
 542         if (RING_REQUEST_CONS_OVERFLOW(&dataplane->rings.common, rc)) {
 543             break;
 544         }
 545         request = xen_block_start_request(dataplane);
 546         if (request == NULL) {
 547             dataplane->more_work++;
 548             break;
 549         }
 550         xen_block_get_request(dataplane, request, rc);
 551         dataplane->rings.common.req_cons = ++rc;
 552         done_something = true;
 553
 554         /* parse them */
 555         if (xen_block_parse_request(request) != 0) {
 556             switch (request->req.operation) {
 557             case BLKIF_OP_READ:
 558                 block_acct_invalid(blk_get_stats(dataplane->blk),
 559                                    BLOCK_ACCT_READ);
 560                 break;
 561             case BLKIF_OP_WRITE:
 562                 block_acct_invalid(blk_get_stats(dataplane->blk),
 563                                    BLOCK_ACCT_WRITE);
 564                 break;
 565             case BLKIF_OP_FLUSH_DISKCACHE:
 566                 block_acct_invalid(blk_get_stats(dataplane->blk),
 567                                    BLOCK_ACCT_FLUSH);
 568             default:
 569                 break;
 570             };
 571
 572             xen_block_complete_request(request);
 573             continue;
 574         }
 575
 576         if (inflight_atstart > IO_PLUG_THRESHOLD &&
 577             batched >= inflight_atstart) {
 578             blk_io_unplug(dataplane->blk);
 579         }
 580         xen_block_do_aio(request);
 581         if (inflight_atstart > IO_PLUG_THRESHOLD) {
 582             if (batched >= inflight_atstart) {
 583                 blk_io_plug(dataplane->blk);
 584                 batched = 0;
 585             } else {
 586                 batched++;
 587             }
 588         }
 589     }
 590     if (inflight_atstart > IO_PLUG_THRESHOLD) {
 591         blk_io_unplug(dataplane->blk);
 592     }
 593
 594     return done_something;
 595 }
 596
 597 static void xen_block_dataplane_bh(void *opaque)
 598 {
 599     XenBlockDataPlane *dataplane = opaque;
 600
 601     aio_context_acquire(dataplane->ctx);
 602     xen_block_handle_requests(dataplane);
 603     aio_context_release(dataplane->ctx);
 604 }
 605
 606 static bool xen_block_dataplane_event(void *opaque)
 607 {
 608     XenBlockDataPlane *dataplane = opaque;
 609
 610     return xen_block_handle_requests(dataplane);
 611 }
 612
 613 XenBlockDataPlane *xen_block_dataplane_create(XenDevice *xendev,
 614                                               BlockBackend *blk,
 615                                               unsigned int sector_size,
 616                                               IOThread *iothread)
 617 {
 618     XenBlockDataPlane *dataplane = g_new0(XenBlockDataPlane, 1);
 619
 620     dataplane->xendev = xendev;
 621     dataplane->blk = blk;
 622     dataplane->sector_size = sector_size;
 623
 624     QLIST_INIT(&dataplane->inflight);
 625     QLIST_INIT(&dataplane->freelist);
 626
 627     if (iothread) {
 628         dataplane->iothread = iothread;
 629         object_ref(OBJECT(dataplane->iothread));
 630         dataplane->ctx = iothread_get_aio_context(dataplane->iothread);
 631     } else {
 632         dataplane->ctx = qemu_get_aio_context();
 633     }
 634     dataplane->bh = aio_bh_new(dataplane->ctx, xen_block_dataplane_bh,
 635                                dataplane);
 636
 637     return dataplane;
 638 }
 639
 640 void xen_block_dataplane_destroy(XenBlockDataPlane *dataplane)
 641 {
 642     XenBlockRequest *request;
 643
 644     if (!dataplane) {
 645         return;
 646     }
 647
 648     while (!QLIST_EMPTY(&dataplane->freelist)) {
 649         request = QLIST_FIRST(&dataplane->freelist);
 650         QLIST_REMOVE(request, list);
 651         qemu_iovec_destroy(&request->v);
 652         qemu_vfree(request->buf);
 653         g_free(request);
 654     }
 655
 656     qemu_bh_delete(dataplane->bh);
 657     if (dataplane->iothread) {
 658         object_unref(OBJECT(dataplane->iothread));
 659     }
 660
 661     g_free(dataplane);
 662 }
 663
 664 void xen_block_dataplane_stop(XenBlockDataPlane *dataplane)
 665 {
 666     XenDevice *xendev;
 667
 668     if (!dataplane) {
 669         return;
 670     }
 671
 672     xendev = dataplane->xendev;
 673
 674     aio_context_acquire(dataplane->ctx);
 675     if (dataplane->event_channel) {
 676         /* Only reason for failure is a NULL channel */
 677         xen_device_set_event_channel_context(xendev, dataplane->event_channel,
 678                                              qemu_get_aio_context(),
 679                                              &error_abort);
 680     }
 681     /* Xen doesn't have multiple users for nodes, so this can't fail */
 682     blk_set_aio_context(dataplane->blk, qemu_get_aio_context(), &error_abort);
 683     aio_context_release(dataplane->ctx);
 684
 685     /*
 686      * Now that the context has been moved onto the main thread, cancel
 687      * further processing.
 688      */
 689     qemu_bh_cancel(dataplane->bh);
 690
 691     if (dataplane->event_channel) {
 692         Error *local_err = NULL;
 693
 694         xen_device_unbind_event_channel(xendev, dataplane->event_channel,
 695                                         &local_err);
 696         dataplane->event_channel = NULL;
 697
 698         if (local_err) {
 699             error_report_err(local_err);
 700         }
 701     }
 702
 703     if (dataplane->sring) {
 704         Error *local_err = NULL;
 705
 706         xen_device_unmap_grant_refs(xendev, dataplane->sring,
 707                                     dataplane->nr_ring_ref, &local_err);
 708         dataplane->sring = NULL;
 709
 710         if (local_err) {
 711             error_report_err(local_err);
 712         }
 713     }
 714
 715     g_free(dataplane->ring_ref);
 716     dataplane->ring_ref = NULL;
 717 }
 718
 719 void xen_block_dataplane_start(XenBlockDataPlane *dataplane,
 720                                const unsigned int ring_ref[],
 721                                unsigned int nr_ring_ref,
 722                                unsigned int event_channel,
 723                                unsigned int protocol,
 724                                Error **errp)
 725 {
 726     ERRP_GUARD();
 727     XenDevice *xendev = dataplane->xendev;
 728     unsigned int ring_size;
 729     unsigned int i;
 730
 731     dataplane->nr_ring_ref = nr_ring_ref;
 732     dataplane->ring_ref = g_new(unsigned int, nr_ring_ref);
 733
 734     for (i = 0; i < nr_ring_ref; i++) {
 735         dataplane->ring_ref[i] = ring_ref[i];
 736     }
 737
 738     dataplane->protocol = protocol;
 739
 740     ring_size = XC_PAGE_SIZE * dataplane->nr_ring_ref;
 741     switch (dataplane->protocol) {
 742     case BLKIF_PROTOCOL_NATIVE:
 743     {
 744         dataplane->max_requests = __CONST_RING_SIZE(blkif, ring_size);
 745         break;
 746     }
 747     case BLKIF_PROTOCOL_X86_32:
 748     {
 749         dataplane->max_requests = __CONST_RING_SIZE(blkif_x86_32, ring_size);
 750         break;
 751     }
 752     case BLKIF_PROTOCOL_X86_64:
 753     {
 754         dataplane->max_requests = __CONST_RING_SIZE(blkif_x86_64, ring_size);
 755         break;
 756     }
 757     default:
 758         error_setg(errp, "unknown protocol %u", dataplane->protocol);
 759         return;
 760     }
 761
 762     xen_device_set_max_grant_refs(xendev, dataplane->nr_ring_ref,
 763                                   errp);
 764     if (*errp) {
 765         goto stop;
 766     }
 767
 768     dataplane->sring = xen_device_map_grant_refs(xendev,
 769                                               dataplane->ring_ref,
 770                                               dataplane->nr_ring_ref,
 771                                               PROT_READ | PROT_WRITE,
 772                                               errp);
 773     if (*errp) {
 774         goto stop;
 775     }
 776
 777     switch (dataplane->protocol) {
 778     case BLKIF_PROTOCOL_NATIVE:
 779     {
 780         blkif_sring_t *sring_native = dataplane->sring;
 781
 782         BACK_RING_INIT(&dataplane->rings.native, sring_native, ring_size);
 783         break;
 784     }
 785     case BLKIF_PROTOCOL_X86_32:
 786     {
 787         blkif_x86_32_sring_t *sring_x86_32 = dataplane->sring;
 788
 789         BACK_RING_INIT(&dataplane->rings.x86_32_part, sring_x86_32,
 790                        ring_size);
 791         break;
 792     }
 793     case BLKIF_PROTOCOL_X86_64:
 794     {
 795         blkif_x86_64_sring_t *sring_x86_64 = dataplane->sring;
 796
 797         BACK_RING_INIT(&dataplane->rings.x86_64_part, sring_x86_64,
 798                        ring_size);
 799         break;
 800     }
 801     }
 802
 803     dataplane->event_channel =
 804         xen_device_bind_event_channel(xendev, event_channel,
 805                                       xen_block_dataplane_event, dataplane,
 806                                       errp);
 807     if (*errp) {
 808         goto stop;
 809     }
 810
 811     aio_context_acquire(dataplane->ctx);
 812     /* If other users keep the BlockBackend in the iothread, that's ok */
 813     blk_set_aio_context(dataplane->blk, dataplane->ctx, NULL);
 814     /* Only reason for failure is a NULL channel */
 815     xen_device_set_event_channel_context(xendev, dataplane->event_channel,
 816                                          dataplane->ctx, &error_abort);
 817     aio_context_release(dataplane->ctx);
 818
 819     return;
 820
 821 stop:
 822     xen_block_dataplane_stop(dataplane);
 823 }