block/nbd.c

   1 /*
   2  * QEMU Block driver for  NBD
   3  *
   4  * Copyright (C) 2008 Bull S.A.S.
   5  *     Author: Laurent Vivier <Laurent.Vivier@bull.net>
   6  *
   7  * Some parts:
   8  *    Copyright (C) 2007 Anthony Liguori <anthony@codemonkey.ws>
   9  *
  10  * Permission is hereby granted, free of charge, to any person obtaining a copy
  11  * of this software and associated documentation files (the "Software"), to deal
  12  * in the Software without restriction, including without limitation the rights
  13  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  14  * copies of the Software, and to permit persons to whom the Software is
  15  * furnished to do so, subject to the following conditions:
  16  *
  17  * The above copyright notice and this permission notice shall be included in
  18  * all copies or substantial portions of the Software.
  19  *
  20  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  21  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  22  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  23  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  24  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  25  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  26  * THE SOFTWARE.
  27  */
  28
  29 #include "qemu-common.h"
  30 #include "block/nbd.h"
  31 #include "qemu/uri.h"
  32 #include "block/block_int.h"
  33 #include "qemu/module.h"
  34 #include "qemu/sockets.h"
  35 #include "qapi/qmp/qjson.h"
  36 #include "qapi/qmp/qint.h"
  37
  38 #include <sys/types.h>
  39 #include <unistd.h>
  40
  41 #define EN_OPTSTR ":exportname="
  42
  43 /* #define DEBUG_NBD */
  44
  45 #if defined(DEBUG_NBD)
  46 #define logout(fmt, ...) \
  47                 fprintf(stderr, "nbd\t%-24s" fmt, __func__, ##__VA_ARGS__)
  48 #else
  49 #define logout(fmt, ...) ((void)0)
  50 #endif
  51
  52 #define MAX_NBD_REQUESTS        16
  53 #define HANDLE_TO_INDEX(bs, handle) ((handle) ^ ((uint64_t)(intptr_t)bs))
  54 #define INDEX_TO_HANDLE(bs, index)  ((index)  ^ ((uint64_t)(intptr_t)bs))
  55
  56 typedef struct BDRVNBDState {
  57     int sock;
  58     uint32_t nbdflags;
  59     off_t size;
  60     size_t blocksize;
  61
  62     CoMutex send_mutex;
  63     CoMutex free_sema;
  64     Coroutine *send_coroutine;
  65     int in_flight;
  66
  67     Coroutine *recv_coroutine[MAX_NBD_REQUESTS];
  68     struct nbd_reply reply;
  69
  70     bool is_unix;
  71     QemuOpts *socket_opts;
  72
  73     char *export_name; /* An NBD server may export several devices */
  74 } BDRVNBDState;
  75
  76 static int nbd_parse_uri(const char *filename, QDict *options)
  77 {
  78     URI *uri;
  79     const char *p;
  80     QueryParams *qp = NULL;
  81     int ret = 0;
  82     bool is_unix;
  83
  84     uri = uri_parse(filename);
  85     if (!uri) {
  86         return -EINVAL;
  87     }
  88
  89     /* transport */
  90     if (!strcmp(uri->scheme, "nbd")) {
  91         is_unix = false;
  92     } else if (!strcmp(uri->scheme, "nbd+tcp")) {
  93         is_unix = false;
  94     } else if (!strcmp(uri->scheme, "nbd+unix")) {
  95         is_unix = true;
  96     } else {
  97         ret = -EINVAL;
  98         goto out;
  99     }
 100
 101     p = uri->path ? uri->path : "/";
 102     p += strspn(p, "/");
 103     if (p[0]) {
 104         qdict_put(options, "export", qstring_from_str(p));
 105     }
 106
 107     qp = query_params_parse(uri->query);
 108     if (qp->n > 1 || (is_unix && !qp->n) || (!is_unix && qp->n)) {
 109         ret = -EINVAL;
 110         goto out;
 111     }
 112
 113     if (is_unix) {
 114         /* nbd+unix:///export?socket=path */
 115         if (uri->server || uri->port || strcmp(qp->p[0].name, "socket")) {
 116             ret = -EINVAL;
 117             goto out;
 118         }
 119         qdict_put(options, "path", qstring_from_str(qp->p[0].value));
 120     } else {
 121         QString *host;
 122         /* nbd[+tcp]://host[:port]/export */
 123         if (!uri->server) {
 124             ret = -EINVAL;
 125             goto out;
 126         }
 127
 128         /* strip braces from literal IPv6 address */
 129         if (uri->server[0] == '[') {
 130             host = qstring_from_substr(uri->server, 1,
 131                                        strlen(uri->server) - 2);
 132         } else {
 133             host = qstring_from_str(uri->server);
 134         }
 135
 136         qdict_put(options, "host", host);
 137         if (uri->port) {
 138             char* port_str = g_strdup_printf("%d", uri->port);
 139             qdict_put(options, "port", qstring_from_str(port_str));
 140             g_free(port_str);
 141         }
 142     }
 143
 144 out:
 145     if (qp) {
 146         query_params_free(qp);
 147     }
 148     uri_free(uri);
 149     return ret;
 150 }
 151
 152 static void nbd_parse_filename(const char *filename, QDict *options,
 153                                Error **errp)
 154 {
 155     char *file;
 156     char *export_name;
 157     const char *host_spec;
 158     const char *unixpath;
 159
 160     if (qdict_haskey(options, "host")
 161         || qdict_haskey(options, "port")
 162         || qdict_haskey(options, "path"))
 163     {
 164         error_setg(errp, "host/port/path and a file name may not be specified "
 165                          "at the same time");
 166         return;
 167     }
 168
 169     if (strstr(filename, "://")) {
 170         int ret = nbd_parse_uri(filename, options);
 171         if (ret < 0) {
 172             error_setg(errp, "No valid URL specified");
 173         }
 174         return;
 175     }
 176
 177     file = g_strdup(filename);
 178
 179     export_name = strstr(file, EN_OPTSTR);
 180     if (export_name) {
 181         if (export_name[strlen(EN_OPTSTR)] == 0) {
 182             goto out;
 183         }
 184         export_name[0] = 0; /* truncate 'file' */
 185         export_name += strlen(EN_OPTSTR);
 186
 187         qdict_put(options, "export", qstring_from_str(export_name));
 188     }
 189
 190     /* extract the host_spec - fail if it's not nbd:... */
 191     if (!strstart(file, "nbd:", &host_spec)) {
 192         error_setg(errp, "File name string for NBD must start with 'nbd:'");
 193         goto out;
 194     }
 195
 196     if (!*host_spec) {
 197         goto out;
 198     }
 199
 200     /* are we a UNIX or TCP socket? */
 201     if (strstart(host_spec, "unix:", &unixpath)) {
 202         qdict_put(options, "path", qstring_from_str(unixpath));
 203     } else {
 204         InetSocketAddress *addr = NULL;
 205
 206         addr = inet_parse(host_spec, errp);
 207         if (error_is_set(errp)) {
 208             goto out;
 209         }
 210
 211         qdict_put(options, "host", qstring_from_str(addr->host));
 212         qdict_put(options, "port", qstring_from_str(addr->port));
 213         qapi_free_InetSocketAddress(addr);
 214     }
 215
 216 out:
 217     g_free(file);
 218 }
 219
 220 static int nbd_config(BDRVNBDState *s, QDict *options)
 221 {
 222     Error *local_err = NULL;
 223
 224     if (qdict_haskey(options, "path")) {
 225         if (qdict_haskey(options, "host")) {
 226             qerror_report(ERROR_CLASS_GENERIC_ERROR, "path and host may not "
 227                           "be used at the same time.");
 228             return -EINVAL;
 229         }
 230         s->is_unix = true;
 231     } else if (qdict_haskey(options, "host")) {
 232         s->is_unix = false;
 233     } else {
 234         return -EINVAL;
 235     }
 236
 237     s->socket_opts = qemu_opts_create_nofail(&socket_optslist);
 238
 239     qemu_opts_absorb_qdict(s->socket_opts, options, &local_err);
 240     if (error_is_set(&local_err)) {
 241         qerror_report_err(local_err);
 242         error_free(local_err);
 243         return -EINVAL;
 244     }
 245
 246     if (!qemu_opt_get(s->socket_opts, "port")) {
 247         qemu_opt_set_number(s->socket_opts, "port", NBD_DEFAULT_PORT);
 248     }
 249
 250     s->export_name = g_strdup(qdict_get_try_str(options, "export"));
 251     if (s->export_name) {
 252         qdict_del(options, "export");
 253     }
 254
 255     return 0;
 256 }
 257
 258
 259 static void nbd_coroutine_start(BDRVNBDState *s, struct nbd_request *request)
 260 {
 261     int i;
 262
 263     /* Poor man semaphore.  The free_sema is locked when no other request
 264      * can be accepted, and unlocked after receiving one reply.  */
 265     if (s->in_flight >= MAX_NBD_REQUESTS - 1) {
 266         qemu_co_mutex_lock(&s->free_sema);
 267         assert(s->in_flight < MAX_NBD_REQUESTS);
 268     }
 269     s->in_flight++;
 270
 271     for (i = 0; i < MAX_NBD_REQUESTS; i++) {
 272         if (s->recv_coroutine[i] == NULL) {
 273             s->recv_coroutine[i] = qemu_coroutine_self();
 274             break;
 275         }
 276     }
 277
 278     assert(i < MAX_NBD_REQUESTS);
 279     request->handle = INDEX_TO_HANDLE(s, i);
 280 }
 281
 282 static void nbd_reply_ready(void *opaque)
 283 {
 284     BDRVNBDState *s = opaque;
 285     uint64_t i;
 286     int ret;
 287
 288     if (s->reply.handle == 0) {
 289         /* No reply already in flight.  Fetch a header.  It is possible
 290          * that another thread has done the same thing in parallel, so
 291          * the socket is not readable anymore.
 292          */
 293         ret = nbd_receive_reply(s->sock, &s->reply);
 294         if (ret == -EAGAIN) {
 295             return;
 296         }
 297         if (ret < 0) {
 298             s->reply.handle = 0;
 299             goto fail;
 300         }
 301     }
 302
 303     /* There's no need for a mutex on the receive side, because the
 304      * handler acts as a synchronization point and ensures that only
 305      * one coroutine is called until the reply finishes.  */
 306     i = HANDLE_TO_INDEX(s, s->reply.handle);
 307     if (i >= MAX_NBD_REQUESTS) {
 308         goto fail;
 309     }
 310
 311     if (s->recv_coroutine[i]) {
 312         qemu_coroutine_enter(s->recv_coroutine[i], NULL);
 313         return;
 314     }
 315
 316 fail:
 317     for (i = 0; i < MAX_NBD_REQUESTS; i++) {
 318         if (s->recv_coroutine[i]) {
 319             qemu_coroutine_enter(s->recv_coroutine[i], NULL);
 320         }
 321     }
 322 }
 323
 324 static void nbd_restart_write(void *opaque)
 325 {
 326     BDRVNBDState *s = opaque;
 327     qemu_coroutine_enter(s->send_coroutine, NULL);
 328 }
 329
 330 static int nbd_co_send_request(BDRVNBDState *s, struct nbd_request *request,
 331                                QEMUIOVector *qiov, int offset)
 332 {
 333     int rc, ret;
 334
 335     qemu_co_mutex_lock(&s->send_mutex);
 336     s->send_coroutine = qemu_coroutine_self();
 337     qemu_aio_set_fd_handler(s->sock, nbd_reply_ready, nbd_restart_write, s);
 338     if (qiov) {
 339         if (!s->is_unix) {
 340             socket_set_cork(s->sock, 1);
 341         }
 342         rc = nbd_send_request(s->sock, request);
 343         if (rc >= 0) {
 344             ret = qemu_co_sendv(s->sock, qiov->iov, qiov->niov,
 345                                 offset, request->len);
 346             if (ret != request->len) {
 347                 rc = -EIO;
 348             }
 349         }
 350         if (!s->is_unix) {
 351             socket_set_cork(s->sock, 0);
 352         }
 353     } else {
 354         rc = nbd_send_request(s->sock, request);
 355     }
 356     qemu_aio_set_fd_handler(s->sock, nbd_reply_ready, NULL, s);
 357     s->send_coroutine = NULL;
 358     qemu_co_mutex_unlock(&s->send_mutex);
 359     return rc;
 360 }
 361
 362 static void nbd_co_receive_reply(BDRVNBDState *s, struct nbd_request *request,
 363                                  struct nbd_reply *reply,
 364                                  QEMUIOVector *qiov, int offset)
 365 {
 366     int ret;
 367
 368     /* Wait until we're woken up by the read handler.  TODO: perhaps
 369      * peek at the next reply and avoid yielding if it's ours?  */
 370     qemu_coroutine_yield();
 371     *reply = s->reply;
 372     if (reply->handle != request->handle) {
 373         reply->error = EIO;
 374     } else {
 375         if (qiov && reply->error == 0) {
 376             ret = qemu_co_recvv(s->sock, qiov->iov, qiov->niov,
 377                                 offset, request->len);
 378             if (ret != request->len) {
 379                 reply->error = EIO;
 380             }
 381         }
 382
 383         /* Tell the read handler to read another header.  */
 384         s->reply.handle = 0;
 385     }
 386 }
 387
 388 static void nbd_coroutine_end(BDRVNBDState *s, struct nbd_request *request)
 389 {
 390     int i = HANDLE_TO_INDEX(s, request->handle);
 391     s->recv_coroutine[i] = NULL;
 392     if (s->in_flight-- == MAX_NBD_REQUESTS) {
 393         qemu_co_mutex_unlock(&s->free_sema);
 394     }
 395 }
 396
 397 static int nbd_establish_connection(BlockDriverState *bs)
 398 {
 399     BDRVNBDState *s = bs->opaque;
 400     int sock;
 401     int ret;
 402     off_t size;
 403     size_t blocksize;
 404
 405     if (s->is_unix) {
 406         sock = unix_socket_outgoing(qemu_opt_get(s->socket_opts, "path"));
 407     } else {
 408         sock = tcp_socket_outgoing_opts(s->socket_opts);
 409         if (sock >= 0) {
 410             socket_set_nodelay(sock);
 411         }
 412     }
 413
 414     /* Failed to establish connection */
 415     if (sock < 0) {
 416         logout("Failed to establish connection to NBD server\n");
 417         return -errno;
 418     }
 419
 420     /* NBD handshake */
 421     ret = nbd_receive_negotiate(sock, s->export_name, &s->nbdflags, &size,
 422                                 &blocksize);
 423     if (ret < 0) {
 424         logout("Failed to negotiate with the NBD server\n");
 425         closesocket(sock);
 426         return ret;
 427     }
 428
 429     /* Now that we're connected, set the socket to be non-blocking and
 430      * kick the reply mechanism.  */
 431     qemu_set_nonblock(sock);
 432     qemu_aio_set_fd_handler(sock, nbd_reply_ready, NULL, s);
 433
 434     s->sock = sock;
 435     s->size = size;
 436     s->blocksize = blocksize;
 437
 438     logout("Established connection with NBD server\n");
 439     return 0;
 440 }
 441
 442 static void nbd_teardown_connection(BlockDriverState *bs)
 443 {
 444     BDRVNBDState *s = bs->opaque;
 445     struct nbd_request request;
 446
 447     request.type = NBD_CMD_DISC;
 448     request.from = 0;
 449     request.len = 0;
 450     nbd_send_request(s->sock, &request);
 451
 452     qemu_aio_set_fd_handler(s->sock, NULL, NULL, NULL);
 453     closesocket(s->sock);
 454 }
 455
 456 static int nbd_open(BlockDriverState *bs, QDict *options, int flags)
 457 {
 458     BDRVNBDState *s = bs->opaque;
 459     int result;
 460
 461     qemu_co_mutex_init(&s->send_mutex);
 462     qemu_co_mutex_init(&s->free_sema);
 463
 464     /* Pop the config into our state object. Exit if invalid. */
 465     result = nbd_config(s, options);
 466     if (result != 0) {
 467         return result;
 468     }
 469
 470     /* establish TCP connection, return error if it fails
 471      * TODO: Configurable retry-until-timeout behaviour.
 472      */
 473     result = nbd_establish_connection(bs);
 474
 475     return result;
 476 }
 477
 478 static int nbd_co_readv_1(BlockDriverState *bs, int64_t sector_num,
 479                           int nb_sectors, QEMUIOVector *qiov,
 480                           int offset)
 481 {
 482     BDRVNBDState *s = bs->opaque;
 483     struct nbd_request request;
 484     struct nbd_reply reply;
 485     ssize_t ret;
 486
 487     request.type = NBD_CMD_READ;
 488     request.from = sector_num * 512;
 489     request.len = nb_sectors * 512;
 490
 491     nbd_coroutine_start(s, &request);
 492     ret = nbd_co_send_request(s, &request, NULL, 0);
 493     if (ret < 0) {
 494         reply.error = -ret;
 495     } else {
 496         nbd_co_receive_reply(s, &request, &reply, qiov, offset);
 497     }
 498     nbd_coroutine_end(s, &request);
 499     return -reply.error;
 500
 501 }
 502
 503 static int nbd_co_writev_1(BlockDriverState *bs, int64_t sector_num,
 504                            int nb_sectors, QEMUIOVector *qiov,
 505                            int offset)
 506 {
 507     BDRVNBDState *s = bs->opaque;
 508     struct nbd_request request;
 509     struct nbd_reply reply;
 510     ssize_t ret;
 511
 512     request.type = NBD_CMD_WRITE;
 513     if (!bdrv_enable_write_cache(bs) && (s->nbdflags & NBD_FLAG_SEND_FUA)) {
 514         request.type |= NBD_CMD_FLAG_FUA;
 515     }
 516
 517     request.from = sector_num * 512;
 518     request.len = nb_sectors * 512;
 519
 520     nbd_coroutine_start(s, &request);
 521     ret = nbd_co_send_request(s, &request, qiov, offset);
 522     if (ret < 0) {
 523         reply.error = -ret;
 524     } else {
 525         nbd_co_receive_reply(s, &request, &reply, NULL, 0);
 526     }
 527     nbd_coroutine_end(s, &request);
 528     return -reply.error;
 529 }
 530
 531 /* qemu-nbd has a limit of slightly less than 1M per request.  Try to
 532  * remain aligned to 4K. */
 533 #define NBD_MAX_SECTORS 2040
 534
 535 static int nbd_co_readv(BlockDriverState *bs, int64_t sector_num,
 536                         int nb_sectors, QEMUIOVector *qiov)
 537 {
 538     int offset = 0;
 539     int ret;
 540     while (nb_sectors > NBD_MAX_SECTORS) {
 541         ret = nbd_co_readv_1(bs, sector_num, NBD_MAX_SECTORS, qiov, offset);
 542         if (ret < 0) {
 543             return ret;
 544         }
 545         offset += NBD_MAX_SECTORS * 512;
 546         sector_num += NBD_MAX_SECTORS;
 547         nb_sectors -= NBD_MAX_SECTORS;
 548     }
 549     return nbd_co_readv_1(bs, sector_num, nb_sectors, qiov, offset);
 550 }
 551
 552 static int nbd_co_writev(BlockDriverState *bs, int64_t sector_num,
 553                          int nb_sectors, QEMUIOVector *qiov)
 554 {
 555     int offset = 0;
 556     int ret;
 557     while (nb_sectors > NBD_MAX_SECTORS) {
 558         ret = nbd_co_writev_1(bs, sector_num, NBD_MAX_SECTORS, qiov, offset);
 559         if (ret < 0) {
 560             return ret;
 561         }
 562         offset += NBD_MAX_SECTORS * 512;
 563         sector_num += NBD_MAX_SECTORS;
 564         nb_sectors -= NBD_MAX_SECTORS;
 565     }
 566     return nbd_co_writev_1(bs, sector_num, nb_sectors, qiov, offset);
 567 }
 568
 569 static int nbd_co_flush(BlockDriverState *bs)
 570 {
 571     BDRVNBDState *s = bs->opaque;
 572     struct nbd_request request;
 573     struct nbd_reply reply;
 574     ssize_t ret;
 575
 576     if (!(s->nbdflags & NBD_FLAG_SEND_FLUSH)) {
 577         return 0;
 578     }
 579
 580     request.type = NBD_CMD_FLUSH;
 581     if (s->nbdflags & NBD_FLAG_SEND_FUA) {
 582         request.type |= NBD_CMD_FLAG_FUA;
 583     }
 584
 585     request.from = 0;
 586     request.len = 0;
 587
 588     nbd_coroutine_start(s, &request);
 589     ret = nbd_co_send_request(s, &request, NULL, 0);
 590     if (ret < 0) {
 591         reply.error = -ret;
 592     } else {
 593         nbd_co_receive_reply(s, &request, &reply, NULL, 0);
 594     }
 595     nbd_coroutine_end(s, &request);
 596     return -reply.error;
 597 }
 598
 599 static int nbd_co_discard(BlockDriverState *bs, int64_t sector_num,
 600                           int nb_sectors)
 601 {
 602     BDRVNBDState *s = bs->opaque;
 603     struct nbd_request request;
 604     struct nbd_reply reply;
 605     ssize_t ret;
 606
 607     if (!(s->nbdflags & NBD_FLAG_SEND_TRIM)) {
 608         return 0;
 609     }
 610     request.type = NBD_CMD_TRIM;
 611     request.from = sector_num * 512;
 612     request.len = nb_sectors * 512;
 613
 614     nbd_coroutine_start(s, &request);
 615     ret = nbd_co_send_request(s, &request, NULL, 0);
 616     if (ret < 0) {
 617         reply.error = -ret;
 618     } else {
 619         nbd_co_receive_reply(s, &request, &reply, NULL, 0);
 620     }
 621     nbd_coroutine_end(s, &request);
 622     return -reply.error;
 623 }
 624
 625 static void nbd_close(BlockDriverState *bs)
 626 {
 627     BDRVNBDState *s = bs->opaque;
 628     g_free(s->export_name);
 629     qemu_opts_del(s->socket_opts);
 630
 631     nbd_teardown_connection(bs);
 632 }
 633
 634 static int64_t nbd_getlength(BlockDriverState *bs)
 635 {
 636     BDRVNBDState *s = bs->opaque;
 637
 638     return s->size;
 639 }
 640
 641 static BlockDriver bdrv_nbd = {
 642     .format_name         = "nbd",
 643     .protocol_name       = "nbd",
 644     .instance_size       = sizeof(BDRVNBDState),
 645     .bdrv_parse_filename = nbd_parse_filename,
 646     .bdrv_file_open      = nbd_open,
 647     .bdrv_co_readv       = nbd_co_readv,
 648     .bdrv_co_writev      = nbd_co_writev,
 649     .bdrv_close          = nbd_close,
 650     .bdrv_co_flush_to_os = nbd_co_flush,
 651     .bdrv_co_discard     = nbd_co_discard,
 652     .bdrv_getlength      = nbd_getlength,
 653 };
 654
 655 static BlockDriver bdrv_nbd_tcp = {
 656     .format_name         = "nbd",
 657     .protocol_name       = "nbd+tcp",
 658     .instance_size       = sizeof(BDRVNBDState),
 659     .bdrv_parse_filename = nbd_parse_filename,
 660     .bdrv_file_open      = nbd_open,
 661     .bdrv_co_readv       = nbd_co_readv,
 662     .bdrv_co_writev      = nbd_co_writev,
 663     .bdrv_close          = nbd_close,
 664     .bdrv_co_flush_to_os = nbd_co_flush,
 665     .bdrv_co_discard     = nbd_co_discard,
 666     .bdrv_getlength      = nbd_getlength,
 667 };
 668
 669 static BlockDriver bdrv_nbd_unix = {
 670     .format_name         = "nbd",
 671     .protocol_name       = "nbd+unix",
 672     .instance_size       = sizeof(BDRVNBDState),
 673     .bdrv_parse_filename = nbd_parse_filename,
 674     .bdrv_file_open      = nbd_open,
 675     .bdrv_co_readv       = nbd_co_readv,
 676     .bdrv_co_writev      = nbd_co_writev,
 677     .bdrv_close          = nbd_close,
 678     .bdrv_co_flush_to_os = nbd_co_flush,
 679     .bdrv_co_discard     = nbd_co_discard,
 680     .bdrv_getlength      = nbd_getlength,
 681 };
 682
 683 static void bdrv_nbd_init(void)
 684 {
 685     bdrv_register(&bdrv_nbd);
 686     bdrv_register(&bdrv_nbd_tcp);
 687     bdrv_register(&bdrv_nbd_unix);
 688 }
 689
 690 block_init(bdrv_nbd_init);