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 int nbd_have_request(void *opaque)
 283 {
 284     BDRVNBDState *s = opaque;
 285
 286     return s->in_flight > 0;
 287 }
 288
 289 static void nbd_reply_ready(void *opaque)
 290 {
 291     BDRVNBDState *s = opaque;
 292     uint64_t i;
 293     int ret;
 294
 295     if (s->reply.handle == 0) {
 296         /* No reply already in flight.  Fetch a header.  It is possible
 297          * that another thread has done the same thing in parallel, so
 298          * the socket is not readable anymore.
 299          */
 300         ret = nbd_receive_reply(s->sock, &s->reply);
 301         if (ret == -EAGAIN) {
 302             return;
 303         }
 304         if (ret < 0) {
 305             s->reply.handle = 0;
 306             goto fail;
 307         }
 308     }
 309
 310     /* There's no need for a mutex on the receive side, because the
 311      * handler acts as a synchronization point and ensures that only
 312      * one coroutine is called until the reply finishes.  */
 313     i = HANDLE_TO_INDEX(s, s->reply.handle);
 314     if (i >= MAX_NBD_REQUESTS) {
 315         goto fail;
 316     }
 317
 318     if (s->recv_coroutine[i]) {
 319         qemu_coroutine_enter(s->recv_coroutine[i], NULL);
 320         return;
 321     }
 322
 323 fail:
 324     for (i = 0; i < MAX_NBD_REQUESTS; i++) {
 325         if (s->recv_coroutine[i]) {
 326             qemu_coroutine_enter(s->recv_coroutine[i], NULL);
 327         }
 328     }
 329 }
 330
 331 static void nbd_restart_write(void *opaque)
 332 {
 333     BDRVNBDState *s = opaque;
 334     qemu_coroutine_enter(s->send_coroutine, NULL);
 335 }
 336
 337 static int nbd_co_send_request(BDRVNBDState *s, struct nbd_request *request,
 338                                QEMUIOVector *qiov, int offset)
 339 {
 340     int rc, ret;
 341
 342     qemu_co_mutex_lock(&s->send_mutex);
 343     s->send_coroutine = qemu_coroutine_self();
 344     qemu_aio_set_fd_handler(s->sock, nbd_reply_ready, nbd_restart_write,
 345                             nbd_have_request, s);
 346     if (qiov) {
 347         if (!s->is_unix) {
 348             socket_set_cork(s->sock, 1);
 349         }
 350         rc = nbd_send_request(s->sock, request);
 351         if (rc >= 0) {
 352             ret = qemu_co_sendv(s->sock, qiov->iov, qiov->niov,
 353                                 offset, request->len);
 354             if (ret != request->len) {
 355                 rc = -EIO;
 356             }
 357         }
 358         if (!s->is_unix) {
 359             socket_set_cork(s->sock, 0);
 360         }
 361     } else {
 362         rc = nbd_send_request(s->sock, request);
 363     }
 364     qemu_aio_set_fd_handler(s->sock, nbd_reply_ready, NULL,
 365                             nbd_have_request, s);
 366     s->send_coroutine = NULL;
 367     qemu_co_mutex_unlock(&s->send_mutex);
 368     return rc;
 369 }
 370
 371 static void nbd_co_receive_reply(BDRVNBDState *s, struct nbd_request *request,
 372                                  struct nbd_reply *reply,
 373                                  QEMUIOVector *qiov, int offset)
 374 {
 375     int ret;
 376
 377     /* Wait until we're woken up by the read handler.  TODO: perhaps
 378      * peek at the next reply and avoid yielding if it's ours?  */
 379     qemu_coroutine_yield();
 380     *reply = s->reply;
 381     if (reply->handle != request->handle) {
 382         reply->error = EIO;
 383     } else {
 384         if (qiov && reply->error == 0) {
 385             ret = qemu_co_recvv(s->sock, qiov->iov, qiov->niov,
 386                                 offset, request->len);
 387             if (ret != request->len) {
 388                 reply->error = EIO;
 389             }
 390         }
 391
 392         /* Tell the read handler to read another header.  */
 393         s->reply.handle = 0;
 394     }
 395 }
 396
 397 static void nbd_coroutine_end(BDRVNBDState *s, struct nbd_request *request)
 398 {
 399     int i = HANDLE_TO_INDEX(s, request->handle);
 400     s->recv_coroutine[i] = NULL;
 401     if (s->in_flight-- == MAX_NBD_REQUESTS) {
 402         qemu_co_mutex_unlock(&s->free_sema);
 403     }
 404 }
 405
 406 static int nbd_establish_connection(BlockDriverState *bs)
 407 {
 408     BDRVNBDState *s = bs->opaque;
 409     int sock;
 410     int ret;
 411     off_t size;
 412     size_t blocksize;
 413
 414     if (s->is_unix) {
 415         sock = unix_socket_outgoing(qemu_opt_get(s->socket_opts, "path"));
 416     } else {
 417         sock = tcp_socket_outgoing_opts(s->socket_opts);
 418         if (sock >= 0) {
 419             socket_set_nodelay(sock);
 420         }
 421     }
 422
 423     /* Failed to establish connection */
 424     if (sock < 0) {
 425         logout("Failed to establish connection to NBD server\n");
 426         return -errno;
 427     }
 428
 429     /* NBD handshake */
 430     ret = nbd_receive_negotiate(sock, s->export_name, &s->nbdflags, &size,
 431                                 &blocksize);
 432     if (ret < 0) {
 433         logout("Failed to negotiate with the NBD server\n");
 434         closesocket(sock);
 435         return ret;
 436     }
 437
 438     /* Now that we're connected, set the socket to be non-blocking and
 439      * kick the reply mechanism.  */
 440     qemu_set_nonblock(sock);
 441     qemu_aio_set_fd_handler(sock, nbd_reply_ready, NULL,
 442                             nbd_have_request, s);
 443
 444     s->sock = sock;
 445     s->size = size;
 446     s->blocksize = blocksize;
 447
 448     logout("Established connection with NBD server\n");
 449     return 0;
 450 }
 451
 452 static void nbd_teardown_connection(BlockDriverState *bs)
 453 {
 454     BDRVNBDState *s = bs->opaque;
 455     struct nbd_request request;
 456
 457     request.type = NBD_CMD_DISC;
 458     request.from = 0;
 459     request.len = 0;
 460     nbd_send_request(s->sock, &request);
 461
 462     qemu_aio_set_fd_handler(s->sock, NULL, NULL, NULL, NULL);
 463     closesocket(s->sock);
 464 }
 465
 466 static int nbd_open(BlockDriverState *bs, QDict *options, int flags)
 467 {
 468     BDRVNBDState *s = bs->opaque;
 469     int result;
 470
 471     qemu_co_mutex_init(&s->send_mutex);
 472     qemu_co_mutex_init(&s->free_sema);
 473
 474     /* Pop the config into our state object. Exit if invalid. */
 475     result = nbd_config(s, options);
 476     if (result != 0) {
 477         return result;
 478     }
 479
 480     /* establish TCP connection, return error if it fails
 481      * TODO: Configurable retry-until-timeout behaviour.
 482      */
 483     result = nbd_establish_connection(bs);
 484
 485     return result;
 486 }
 487
 488 static int nbd_co_readv_1(BlockDriverState *bs, int64_t sector_num,
 489                           int nb_sectors, QEMUIOVector *qiov,
 490                           int offset)
 491 {
 492     BDRVNBDState *s = bs->opaque;
 493     struct nbd_request request;
 494     struct nbd_reply reply;
 495     ssize_t ret;
 496
 497     request.type = NBD_CMD_READ;
 498     request.from = sector_num * 512;
 499     request.len = nb_sectors * 512;
 500
 501     nbd_coroutine_start(s, &request);
 502     ret = nbd_co_send_request(s, &request, NULL, 0);
 503     if (ret < 0) {
 504         reply.error = -ret;
 505     } else {
 506         nbd_co_receive_reply(s, &request, &reply, qiov, offset);
 507     }
 508     nbd_coroutine_end(s, &request);
 509     return -reply.error;
 510
 511 }
 512
 513 static int nbd_co_writev_1(BlockDriverState *bs, int64_t sector_num,
 514                            int nb_sectors, QEMUIOVector *qiov,
 515                            int offset)
 516 {
 517     BDRVNBDState *s = bs->opaque;
 518     struct nbd_request request;
 519     struct nbd_reply reply;
 520     ssize_t ret;
 521
 522     request.type = NBD_CMD_WRITE;
 523     if (!bdrv_enable_write_cache(bs) && (s->nbdflags & NBD_FLAG_SEND_FUA)) {
 524         request.type |= NBD_CMD_FLAG_FUA;
 525     }
 526
 527     request.from = sector_num * 512;
 528     request.len = nb_sectors * 512;
 529
 530     nbd_coroutine_start(s, &request);
 531     ret = nbd_co_send_request(s, &request, qiov, offset);
 532     if (ret < 0) {
 533         reply.error = -ret;
 534     } else {
 535         nbd_co_receive_reply(s, &request, &reply, NULL, 0);
 536     }
 537     nbd_coroutine_end(s, &request);
 538     return -reply.error;
 539 }
 540
 541 /* qemu-nbd has a limit of slightly less than 1M per request.  Try to
 542  * remain aligned to 4K. */
 543 #define NBD_MAX_SECTORS 2040
 544
 545 static int nbd_co_readv(BlockDriverState *bs, int64_t sector_num,
 546                         int nb_sectors, QEMUIOVector *qiov)
 547 {
 548     int offset = 0;
 549     int ret;
 550     while (nb_sectors > NBD_MAX_SECTORS) {
 551         ret = nbd_co_readv_1(bs, sector_num, NBD_MAX_SECTORS, qiov, offset);
 552         if (ret < 0) {
 553             return ret;
 554         }
 555         offset += NBD_MAX_SECTORS * 512;
 556         sector_num += NBD_MAX_SECTORS;
 557         nb_sectors -= NBD_MAX_SECTORS;
 558     }
 559     return nbd_co_readv_1(bs, sector_num, nb_sectors, qiov, offset);
 560 }
 561
 562 static int nbd_co_writev(BlockDriverState *bs, int64_t sector_num,
 563                          int nb_sectors, QEMUIOVector *qiov)
 564 {
 565     int offset = 0;
 566     int ret;
 567     while (nb_sectors > NBD_MAX_SECTORS) {
 568         ret = nbd_co_writev_1(bs, sector_num, NBD_MAX_SECTORS, qiov, offset);
 569         if (ret < 0) {
 570             return ret;
 571         }
 572         offset += NBD_MAX_SECTORS * 512;
 573         sector_num += NBD_MAX_SECTORS;
 574         nb_sectors -= NBD_MAX_SECTORS;
 575     }
 576     return nbd_co_writev_1(bs, sector_num, nb_sectors, qiov, offset);
 577 }
 578
 579 static int nbd_co_flush(BlockDriverState *bs)
 580 {
 581     BDRVNBDState *s = bs->opaque;
 582     struct nbd_request request;
 583     struct nbd_reply reply;
 584     ssize_t ret;
 585
 586     if (!(s->nbdflags & NBD_FLAG_SEND_FLUSH)) {
 587         return 0;
 588     }
 589
 590     request.type = NBD_CMD_FLUSH;
 591     if (s->nbdflags & NBD_FLAG_SEND_FUA) {
 592         request.type |= NBD_CMD_FLAG_FUA;
 593     }
 594
 595     request.from = 0;
 596     request.len = 0;
 597
 598     nbd_coroutine_start(s, &request);
 599     ret = nbd_co_send_request(s, &request, NULL, 0);
 600     if (ret < 0) {
 601         reply.error = -ret;
 602     } else {
 603         nbd_co_receive_reply(s, &request, &reply, NULL, 0);
 604     }
 605     nbd_coroutine_end(s, &request);
 606     return -reply.error;
 607 }
 608
 609 static int nbd_co_discard(BlockDriverState *bs, int64_t sector_num,
 610                           int nb_sectors)
 611 {
 612     BDRVNBDState *s = bs->opaque;
 613     struct nbd_request request;
 614     struct nbd_reply reply;
 615     ssize_t ret;
 616
 617     if (!(s->nbdflags & NBD_FLAG_SEND_TRIM)) {
 618         return 0;
 619     }
 620     request.type = NBD_CMD_TRIM;
 621     request.from = sector_num * 512;
 622     request.len = nb_sectors * 512;
 623
 624     nbd_coroutine_start(s, &request);
 625     ret = nbd_co_send_request(s, &request, NULL, 0);
 626     if (ret < 0) {
 627         reply.error = -ret;
 628     } else {
 629         nbd_co_receive_reply(s, &request, &reply, NULL, 0);
 630     }
 631     nbd_coroutine_end(s, &request);
 632     return -reply.error;
 633 }
 634
 635 static void nbd_close(BlockDriverState *bs)
 636 {
 637     BDRVNBDState *s = bs->opaque;
 638     g_free(s->export_name);
 639     qemu_opts_del(s->socket_opts);
 640
 641     nbd_teardown_connection(bs);
 642 }
 643
 644 static int64_t nbd_getlength(BlockDriverState *bs)
 645 {
 646     BDRVNBDState *s = bs->opaque;
 647
 648     return s->size;
 649 }
 650
 651 static BlockDriver bdrv_nbd = {
 652     .format_name         = "nbd",
 653     .protocol_name       = "nbd",
 654     .instance_size       = sizeof(BDRVNBDState),
 655     .bdrv_parse_filename = nbd_parse_filename,
 656     .bdrv_file_open      = nbd_open,
 657     .bdrv_co_readv       = nbd_co_readv,
 658     .bdrv_co_writev      = nbd_co_writev,
 659     .bdrv_close          = nbd_close,
 660     .bdrv_co_flush_to_os = nbd_co_flush,
 661     .bdrv_co_discard     = nbd_co_discard,
 662     .bdrv_getlength      = nbd_getlength,
 663 };
 664
 665 static BlockDriver bdrv_nbd_tcp = {
 666     .format_name         = "nbd",
 667     .protocol_name       = "nbd+tcp",
 668     .instance_size       = sizeof(BDRVNBDState),
 669     .bdrv_parse_filename = nbd_parse_filename,
 670     .bdrv_file_open      = nbd_open,
 671     .bdrv_co_readv       = nbd_co_readv,
 672     .bdrv_co_writev      = nbd_co_writev,
 673     .bdrv_close          = nbd_close,
 674     .bdrv_co_flush_to_os = nbd_co_flush,
 675     .bdrv_co_discard     = nbd_co_discard,
 676     .bdrv_getlength      = nbd_getlength,
 677 };
 678
 679 static BlockDriver bdrv_nbd_unix = {
 680     .format_name         = "nbd",
 681     .protocol_name       = "nbd+unix",
 682     .instance_size       = sizeof(BDRVNBDState),
 683     .bdrv_parse_filename = nbd_parse_filename,
 684     .bdrv_file_open      = nbd_open,
 685     .bdrv_co_readv       = nbd_co_readv,
 686     .bdrv_co_writev      = nbd_co_writev,
 687     .bdrv_close          = nbd_close,
 688     .bdrv_co_flush_to_os = nbd_co_flush,
 689     .bdrv_co_discard     = nbd_co_discard,
 690     .bdrv_getlength      = nbd_getlength,
 691 };
 692
 693 static void bdrv_nbd_init(void)
 694 {
 695     bdrv_register(&bdrv_nbd);
 696     bdrv_register(&bdrv_nbd_tcp);
 697     bdrv_register(&bdrv_nbd_unix);
 698 }
 699
 700 block_init(bdrv_nbd_init);