migration.c

   1 /*
   2  * QEMU live migration
   3  *
   4  * Copyright IBM, Corp. 2008
   5  *
   6  * Authors:
   7  *  Anthony Liguori   <aliguori@us.ibm.com>
   8  *
   9  * This work is licensed under the terms of the GNU GPL, version 2.  See
  10  * the COPYING file in the top-level directory.
  11  *
  12  * Contributions after 2012-01-13 are licensed under the terms of the
  13  * GNU GPL, version 2 or (at your option) any later version.
  14  */
  15
  16 #include "qemu-common.h"
  17 #include "migration/migration.h"
  18 #include "monitor/monitor.h"
  19 #include "migration/qemu-file.h"
  20 #include "sysemu/sysemu.h"
  21 #include "block/block.h"
  22 #include "qemu/sockets.h"
  23 #include "migration/block.h"
  24 #include "qemu/thread.h"
  25 #include "qmp-commands.h"
  26
  27 //#define DEBUG_MIGRATION
  28
  29 #ifdef DEBUG_MIGRATION
  30 #define DPRINTF(fmt, ...) \
  31     do { printf("migration: " fmt, ## __VA_ARGS__); } while (0)
  32 #else
  33 #define DPRINTF(fmt, ...) \
  34     do { } while (0)
  35 #endif
  36
  37 enum {
  38     MIG_STATE_ERROR,
  39     MIG_STATE_SETUP,
  40     MIG_STATE_CANCELLED,
  41     MIG_STATE_ACTIVE,
  42     MIG_STATE_COMPLETED,
  43 };
  44
  45 #define MAX_THROTTLE  (32 << 20)      /* Migration speed throttling */
  46
  47 /* Amount of time to allocate to each "chunk" of bandwidth-throttled
  48  * data. */
  49 #define BUFFER_DELAY     100
  50 #define XFER_LIMIT_RATIO (1000 / BUFFER_DELAY)
  51
  52 /* Migration XBZRLE default cache size */
  53 #define DEFAULT_MIGRATE_CACHE_SIZE (64 * 1024 * 1024)
  54
  55 static NotifierList migration_state_notifiers =
  56     NOTIFIER_LIST_INITIALIZER(migration_state_notifiers);
  57
  58 /* When we add fault tolerance, we could have several
  59    migrations at once.  For now we don't need to add
  60    dynamic creation of migration */
  61
  62 MigrationState *migrate_get_current(void)
  63 {
  64     static MigrationState current_migration = {
  65         .state = MIG_STATE_SETUP,
  66         .bandwidth_limit = MAX_THROTTLE,
  67         .xbzrle_cache_size = DEFAULT_MIGRATE_CACHE_SIZE,
  68     };
  69
  70     return &current_migration;
  71 }
  72
  73 void qemu_start_incoming_migration(const char *uri, Error **errp)
  74 {
  75     const char *p;
  76
  77     if (strstart(uri, "tcp:", &p))
  78         tcp_start_incoming_migration(p, errp);
  79 #if !defined(WIN32)
  80     else if (strstart(uri, "exec:", &p))
  81         exec_start_incoming_migration(p, errp);
  82     else if (strstart(uri, "unix:", &p))
  83         unix_start_incoming_migration(p, errp);
  84     else if (strstart(uri, "fd:", &p))
  85         fd_start_incoming_migration(p, errp);
  86 #endif
  87     else {
  88         error_setg(errp, "unknown migration protocol: %s", uri);
  89     }
  90 }
  91
  92 static void process_incoming_migration_co(void *opaque)
  93 {
  94     QEMUFile *f = opaque;
  95     int ret;
  96
  97     ret = qemu_loadvm_state(f);
  98     qemu_fclose(f);
  99     if (ret < 0) {
 100         fprintf(stderr, "load of migration failed\n");
 101         exit(0);
 102     }
 103     qemu_announce_self();
 104     DPRINTF("successfully loaded vm state\n");
 105
 106     bdrv_clear_incoming_migration_all();
 107     /* Make sure all file formats flush their mutable metadata */
 108     bdrv_invalidate_cache_all();
 109
 110     if (autostart) {
 111         vm_start();
 112     } else {
 113         runstate_set(RUN_STATE_PAUSED);
 114     }
 115 }
 116
 117 void process_incoming_migration(QEMUFile *f)
 118 {
 119     Coroutine *co = qemu_coroutine_create(process_incoming_migration_co);
 120     int fd = qemu_get_fd(f);
 121
 122     assert(fd != -1);
 123     socket_set_nonblock(fd);
 124     qemu_coroutine_enter(co, f);
 125 }
 126
 127 /* amount of nanoseconds we are willing to wait for migration to be down.
 128  * the choice of nanoseconds is because it is the maximum resolution that
 129  * get_clock() can achieve. It is an internal measure. All user-visible
 130  * units must be in seconds */
 131 static uint64_t max_downtime = 30000000;
 132
 133 uint64_t migrate_max_downtime(void)
 134 {
 135     return max_downtime;
 136 }
 137
 138 MigrationCapabilityStatusList *qmp_query_migrate_capabilities(Error **errp)
 139 {
 140     MigrationCapabilityStatusList *head = NULL;
 141     MigrationCapabilityStatusList *caps;
 142     MigrationState *s = migrate_get_current();
 143     int i;
 144
 145     for (i = 0; i < MIGRATION_CAPABILITY_MAX; i++) {
 146         if (head == NULL) {
 147             head = g_malloc0(sizeof(*caps));
 148             caps = head;
 149         } else {
 150             caps->next = g_malloc0(sizeof(*caps));
 151             caps = caps->next;
 152         }
 153         caps->value =
 154             g_malloc(sizeof(*caps->value));
 155         caps->value->capability = i;
 156         caps->value->state = s->enabled_capabilities[i];
 157     }
 158
 159     return head;
 160 }
 161
 162 static void get_xbzrle_cache_stats(MigrationInfo *info)
 163 {
 164     if (migrate_use_xbzrle()) {
 165         info->has_xbzrle_cache = true;
 166         info->xbzrle_cache = g_malloc0(sizeof(*info->xbzrle_cache));
 167         info->xbzrle_cache->cache_size = migrate_xbzrle_cache_size();
 168         info->xbzrle_cache->bytes = xbzrle_mig_bytes_transferred();
 169         info->xbzrle_cache->pages = xbzrle_mig_pages_transferred();
 170         info->xbzrle_cache->cache_miss = xbzrle_mig_pages_cache_miss();
 171         info->xbzrle_cache->overflow = xbzrle_mig_pages_overflow();
 172     }
 173 }
 174
 175 MigrationInfo *qmp_query_migrate(Error **errp)
 176 {
 177     MigrationInfo *info = g_malloc0(sizeof(*info));
 178     MigrationState *s = migrate_get_current();
 179
 180     switch (s->state) {
 181     case MIG_STATE_SETUP:
 182         /* no migration has happened ever */
 183         break;
 184     case MIG_STATE_ACTIVE:
 185         info->has_status = true;
 186         info->status = g_strdup("active");
 187         info->has_total_time = true;
 188         info->total_time = qemu_get_clock_ms(rt_clock)
 189             - s->total_time;
 190         info->has_expected_downtime = true;
 191         info->expected_downtime = s->expected_downtime;
 192
 193         info->has_ram = true;
 194         info->ram = g_malloc0(sizeof(*info->ram));
 195         info->ram->transferred = ram_bytes_transferred();
 196         info->ram->remaining = ram_bytes_remaining();
 197         info->ram->total = ram_bytes_total();
 198         info->ram->duplicate = dup_mig_pages_transferred();
 199         info->ram->normal = norm_mig_pages_transferred();
 200         info->ram->normal_bytes = norm_mig_bytes_transferred();
 201         info->ram->dirty_pages_rate = s->dirty_pages_rate;
 202
 203
 204         if (blk_mig_active()) {
 205             info->has_disk = true;
 206             info->disk = g_malloc0(sizeof(*info->disk));
 207             info->disk->transferred = blk_mig_bytes_transferred();
 208             info->disk->remaining = blk_mig_bytes_remaining();
 209             info->disk->total = blk_mig_bytes_total();
 210         }
 211
 212         get_xbzrle_cache_stats(info);
 213         break;
 214     case MIG_STATE_COMPLETED:
 215         get_xbzrle_cache_stats(info);
 216
 217         info->has_status = true;
 218         info->status = g_strdup("completed");
 219         info->total_time = s->total_time;
 220         info->has_downtime = true;
 221         info->downtime = s->downtime;
 222
 223         info->has_ram = true;
 224         info->ram = g_malloc0(sizeof(*info->ram));
 225         info->ram->transferred = ram_bytes_transferred();
 226         info->ram->remaining = 0;
 227         info->ram->total = ram_bytes_total();
 228         info->ram->duplicate = dup_mig_pages_transferred();
 229         info->ram->normal = norm_mig_pages_transferred();
 230         info->ram->normal_bytes = norm_mig_bytes_transferred();
 231         break;
 232     case MIG_STATE_ERROR:
 233         info->has_status = true;
 234         info->status = g_strdup("failed");
 235         break;
 236     case MIG_STATE_CANCELLED:
 237         info->has_status = true;
 238         info->status = g_strdup("cancelled");
 239         break;
 240     }
 241
 242     return info;
 243 }
 244
 245 void qmp_migrate_set_capabilities(MigrationCapabilityStatusList *params,
 246                                   Error **errp)
 247 {
 248     MigrationState *s = migrate_get_current();
 249     MigrationCapabilityStatusList *cap;
 250
 251     if (s->state == MIG_STATE_ACTIVE) {
 252         error_set(errp, QERR_MIGRATION_ACTIVE);
 253         return;
 254     }
 255
 256     for (cap = params; cap; cap = cap->next) {
 257         s->enabled_capabilities[cap->value->capability] = cap->value->state;
 258     }
 259 }
 260
 261 /* shared migration helpers */
 262
 263 static int migrate_fd_cleanup(MigrationState *s)
 264 {
 265     int ret = 0;
 266
 267     if (s->file) {
 268         DPRINTF("closing file\n");
 269         ret = qemu_fclose(s->file);
 270         s->file = NULL;
 271     }
 272
 273     assert(s->fd == -1);
 274     return ret;
 275 }
 276
 277 void migrate_fd_error(MigrationState *s)
 278 {
 279     DPRINTF("setting error state\n");
 280     s->state = MIG_STATE_ERROR;
 281     notifier_list_notify(&migration_state_notifiers, s);
 282     migrate_fd_cleanup(s);
 283 }
 284
 285 static void migrate_fd_completed(MigrationState *s)
 286 {
 287     DPRINTF("setting completed state\n");
 288     if (migrate_fd_cleanup(s) < 0) {
 289         s->state = MIG_STATE_ERROR;
 290     } else {
 291         s->state = MIG_STATE_COMPLETED;
 292         runstate_set(RUN_STATE_POSTMIGRATE);
 293     }
 294     notifier_list_notify(&migration_state_notifiers, s);
 295 }
 296
 297 static ssize_t migrate_fd_put_buffer(MigrationState *s, const void *data,
 298                                      size_t size)
 299 {
 300     ssize_t ret;
 301
 302     if (s->state != MIG_STATE_ACTIVE) {
 303         return -EIO;
 304     }
 305
 306     do {
 307         ret = s->write(s, data, size);
 308     } while (ret == -1 && ((s->get_error(s)) == EINTR));
 309
 310     if (ret == -1)
 311         ret = -(s->get_error(s));
 312
 313     return ret;
 314 }
 315
 316 static void migrate_fd_cancel(MigrationState *s)
 317 {
 318     if (s->state != MIG_STATE_ACTIVE)
 319         return;
 320
 321     DPRINTF("cancelling migration\n");
 322
 323     s->state = MIG_STATE_CANCELLED;
 324     notifier_list_notify(&migration_state_notifiers, s);
 325     qemu_savevm_state_cancel();
 326
 327     migrate_fd_cleanup(s);
 328 }
 329
 330 int migrate_fd_close(MigrationState *s)
 331 {
 332     int rc = 0;
 333     if (s->fd != -1) {
 334         rc = s->close(s);
 335         s->fd = -1;
 336     }
 337     return rc;
 338 }
 339
 340 void add_migration_state_change_notifier(Notifier *notify)
 341 {
 342     notifier_list_add(&migration_state_notifiers, notify);
 343 }
 344
 345 void remove_migration_state_change_notifier(Notifier *notify)
 346 {
 347     notifier_remove(notify);
 348 }
 349
 350 bool migration_is_active(MigrationState *s)
 351 {
 352     return s->state == MIG_STATE_ACTIVE;
 353 }
 354
 355 bool migration_has_finished(MigrationState *s)
 356 {
 357     return s->state == MIG_STATE_COMPLETED;
 358 }
 359
 360 bool migration_has_failed(MigrationState *s)
 361 {
 362     return (s->state == MIG_STATE_CANCELLED ||
 363             s->state == MIG_STATE_ERROR);
 364 }
 365
 366 static MigrationState *migrate_init(const MigrationParams *params)
 367 {
 368     MigrationState *s = migrate_get_current();
 369     int64_t bandwidth_limit = s->bandwidth_limit;
 370     bool enabled_capabilities[MIGRATION_CAPABILITY_MAX];
 371     int64_t xbzrle_cache_size = s->xbzrle_cache_size;
 372
 373     memcpy(enabled_capabilities, s->enabled_capabilities,
 374            sizeof(enabled_capabilities));
 375
 376     memset(s, 0, sizeof(*s));
 377     s->bandwidth_limit = bandwidth_limit;
 378     s->params = *params;
 379     memcpy(s->enabled_capabilities, enabled_capabilities,
 380            sizeof(enabled_capabilities));
 381     s->xbzrle_cache_size = xbzrle_cache_size;
 382
 383     s->bandwidth_limit = bandwidth_limit;
 384     s->state = MIG_STATE_SETUP;
 385     s->total_time = qemu_get_clock_ms(rt_clock);
 386
 387     return s;
 388 }
 389
 390 static GSList *migration_blockers;
 391
 392 void migrate_add_blocker(Error *reason)
 393 {
 394     migration_blockers = g_slist_prepend(migration_blockers, reason);
 395 }
 396
 397 void migrate_del_blocker(Error *reason)
 398 {
 399     migration_blockers = g_slist_remove(migration_blockers, reason);
 400 }
 401
 402 void qmp_migrate(const char *uri, bool has_blk, bool blk,
 403                  bool has_inc, bool inc, bool has_detach, bool detach,
 404                  Error **errp)
 405 {
 406     Error *local_err = NULL;
 407     MigrationState *s = migrate_get_current();
 408     MigrationParams params;
 409     const char *p;
 410
 411     params.blk = blk;
 412     params.shared = inc;
 413
 414     if (s->state == MIG_STATE_ACTIVE) {
 415         error_set(errp, QERR_MIGRATION_ACTIVE);
 416         return;
 417     }
 418
 419     if (qemu_savevm_state_blocked(errp)) {
 420         return;
 421     }
 422
 423     if (migration_blockers) {
 424         *errp = error_copy(migration_blockers->data);
 425         return;
 426     }
 427
 428     s = migrate_init(&params);
 429
 430     if (strstart(uri, "tcp:", &p)) {
 431         tcp_start_outgoing_migration(s, p, &local_err);
 432 #if !defined(WIN32)
 433     } else if (strstart(uri, "exec:", &p)) {
 434         exec_start_outgoing_migration(s, p, &local_err);
 435     } else if (strstart(uri, "unix:", &p)) {
 436         unix_start_outgoing_migration(s, p, &local_err);
 437     } else if (strstart(uri, "fd:", &p)) {
 438         fd_start_outgoing_migration(s, p, &local_err);
 439 #endif
 440     } else {
 441         error_set(errp, QERR_INVALID_PARAMETER_VALUE, "uri", "a valid migration protocol");
 442         return;
 443     }
 444
 445     if (local_err) {
 446         migrate_fd_error(s);
 447         error_propagate(errp, local_err);
 448         return;
 449     }
 450 }
 451
 452 void qmp_migrate_cancel(Error **errp)
 453 {
 454     migrate_fd_cancel(migrate_get_current());
 455 }
 456
 457 void qmp_migrate_set_cache_size(int64_t value, Error **errp)
 458 {
 459     MigrationState *s = migrate_get_current();
 460
 461     /* Check for truncation */
 462     if (value != (size_t)value) {
 463         error_set(errp, QERR_INVALID_PARAMETER_VALUE, "cache size",
 464                   "exceeding address space");
 465         return;
 466     }
 467
 468     s->xbzrle_cache_size = xbzrle_cache_resize(value);
 469 }
 470
 471 int64_t qmp_query_migrate_cache_size(Error **errp)
 472 {
 473     return migrate_xbzrle_cache_size();
 474 }
 475
 476 void qmp_migrate_set_speed(int64_t value, Error **errp)
 477 {
 478     MigrationState *s;
 479
 480     if (value < 0) {
 481         value = 0;
 482     }
 483
 484     s = migrate_get_current();
 485     s->bandwidth_limit = value;
 486     qemu_file_set_rate_limit(s->file, s->bandwidth_limit);
 487 }
 488
 489 void qmp_migrate_set_downtime(double value, Error **errp)
 490 {
 491     value *= 1e9;
 492     value = MAX(0, MIN(UINT64_MAX, value));
 493     max_downtime = (uint64_t)value;
 494 }
 495
 496 int migrate_use_xbzrle(void)
 497 {
 498     MigrationState *s;
 499
 500     s = migrate_get_current();
 501
 502     return s->enabled_capabilities[MIGRATION_CAPABILITY_XBZRLE];
 503 }
 504
 505 int64_t migrate_xbzrle_cache_size(void)
 506 {
 507     MigrationState *s;
 508
 509     s = migrate_get_current();
 510
 511     return s->xbzrle_cache_size;
 512 }
 513
 514 /* migration thread support */
 515
 516
 517 static ssize_t buffered_flush(MigrationState *s)
 518 {
 519     size_t offset = 0;
 520     ssize_t ret = 0;
 521
 522     DPRINTF("flushing %zu byte(s) of data\n", s->buffer_size);
 523
 524     while (s->bytes_xfer < s->xfer_limit && offset < s->buffer_size) {
 525         size_t to_send = MIN(s->buffer_size - offset, s->xfer_limit - s->bytes_xfer);
 526         ret = migrate_fd_put_buffer(s, s->buffer + offset, to_send);
 527         if (ret <= 0) {
 528             DPRINTF("error flushing data, %zd\n", ret);
 529             break;
 530         } else {
 531             DPRINTF("flushed %zd byte(s)\n", ret);
 532             offset += ret;
 533             s->bytes_xfer += ret;
 534         }
 535     }
 536
 537     DPRINTF("flushed %zu of %zu byte(s)\n", offset, s->buffer_size);
 538     memmove(s->buffer, s->buffer + offset, s->buffer_size - offset);
 539     s->buffer_size -= offset;
 540
 541     if (ret < 0) {
 542         return ret;
 543     }
 544     return offset;
 545 }
 546
 547 static int buffered_put_buffer(void *opaque, const uint8_t *buf,
 548                                int64_t pos, int size)
 549 {
 550     MigrationState *s = opaque;
 551     ssize_t error;
 552
 553     DPRINTF("putting %d bytes at %" PRId64 "\n", size, pos);
 554
 555     error = qemu_file_get_error(s->file);
 556     if (error) {
 557         DPRINTF("flush when error, bailing: %s\n", strerror(-error));
 558         return error;
 559     }
 560
 561     if (size <= 0) {
 562         return size;
 563     }
 564
 565     if (size > (s->buffer_capacity - s->buffer_size)) {
 566         DPRINTF("increasing buffer capacity from %zu by %zu\n",
 567                 s->buffer_capacity, size + 1024);
 568
 569         s->buffer_capacity += size + 1024;
 570
 571         s->buffer = g_realloc(s->buffer, s->buffer_capacity);
 572     }
 573
 574     memcpy(s->buffer + s->buffer_size, buf, size);
 575     s->buffer_size += size;
 576
 577     return size;
 578 }
 579
 580 static int buffered_close(void *opaque)
 581 {
 582     MigrationState *s = opaque;
 583     ssize_t ret = 0;
 584     int ret2;
 585
 586     DPRINTF("closing\n");
 587
 588     s->xfer_limit = INT_MAX;
 589     while (!qemu_file_get_error(s->file) && s->buffer_size) {
 590         ret = buffered_flush(s);
 591         if (ret < 0) {
 592             break;
 593         }
 594     }
 595
 596     ret2 = migrate_fd_close(s);
 597     if (ret >= 0) {
 598         ret = ret2;
 599     }
 600     s->complete = true;
 601     return ret;
 602 }
 603
 604 static int buffered_get_fd(void *opaque)
 605 {
 606     MigrationState *s = opaque;
 607
 608     return s->fd;
 609 }
 610
 611 /*
 612  * The meaning of the return values is:
 613  *   0: We can continue sending
 614  *   1: Time to stop
 615  *   negative: There has been an error
 616  */
 617 static int buffered_rate_limit(void *opaque)
 618 {
 619     MigrationState *s = opaque;
 620     int ret;
 621
 622     ret = qemu_file_get_error(s->file);
 623     if (ret) {
 624         return ret;
 625     }
 626
 627     if (s->bytes_xfer >= s->xfer_limit) {
 628         return 1;
 629     }
 630
 631     return 0;
 632 }
 633
 634 static int64_t buffered_set_rate_limit(void *opaque, int64_t new_rate)
 635 {
 636     MigrationState *s = opaque;
 637     if (qemu_file_get_error(s->file)) {
 638         goto out;
 639     }
 640     if (new_rate > SIZE_MAX) {
 641         new_rate = SIZE_MAX;
 642     }
 643
 644     s->xfer_limit = new_rate / XFER_LIMIT_RATIO;
 645
 646 out:
 647     return s->xfer_limit;
 648 }
 649
 650 static int64_t buffered_get_rate_limit(void *opaque)
 651 {
 652     MigrationState *s = opaque;
 653
 654     return s->xfer_limit;
 655 }
 656
 657 static void *buffered_file_thread(void *opaque)
 658 {
 659     MigrationState *s = opaque;
 660     int64_t initial_time = qemu_get_clock_ms(rt_clock);
 661     int64_t sleep_time = 0;
 662     int64_t max_size = 0;
 663     bool last_round = false;
 664     int ret;
 665
 666     qemu_mutex_lock_iothread();
 667     DPRINTF("beginning savevm\n");
 668     ret = qemu_savevm_state_begin(s->file, &s->params);
 669     if (ret < 0) {
 670         DPRINTF("failed, %d\n", ret);
 671         qemu_mutex_unlock_iothread();
 672         goto out;
 673     }
 674     qemu_mutex_unlock_iothread();
 675
 676     while (true) {
 677         int64_t current_time;
 678         uint64_t pending_size;
 679
 680         qemu_mutex_lock_iothread();
 681         if (s->state != MIG_STATE_ACTIVE) {
 682             DPRINTF("put_ready returning because of non-active state\n");
 683             qemu_mutex_unlock_iothread();
 684             break;
 685         }
 686         if (s->complete) {
 687             qemu_mutex_unlock_iothread();
 688             break;
 689         }
 690         if (s->bytes_xfer < s->xfer_limit) {
 691             DPRINTF("iterate\n");
 692             pending_size = qemu_savevm_state_pending(s->file, max_size);
 693             DPRINTF("pending size %lu max %lu\n", pending_size, max_size);
 694             if (pending_size && pending_size >= max_size) {
 695                 ret = qemu_savevm_state_iterate(s->file);
 696                 if (ret < 0) {
 697                     qemu_mutex_unlock_iothread();
 698                     break;
 699                 }
 700             } else {
 701                 int old_vm_running = runstate_is_running();
 702                 int64_t start_time, end_time;
 703
 704                 DPRINTF("done iterating\n");
 705                 start_time = qemu_get_clock_ms(rt_clock);
 706                 qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
 707                 if (old_vm_running) {
 708                     vm_stop(RUN_STATE_FINISH_MIGRATE);
 709                 } else {
 710                     vm_stop_force_state(RUN_STATE_FINISH_MIGRATE);
 711                 }
 712                 ret = qemu_savevm_state_complete(s->file);
 713                 if (ret < 0) {
 714                     qemu_mutex_unlock_iothread();
 715                     break;
 716                 } else {
 717                     migrate_fd_completed(s);
 718                 }
 719                 end_time = qemu_get_clock_ms(rt_clock);
 720                 s->total_time = end_time - s->total_time;
 721                 s->downtime = end_time - start_time;
 722                 if (s->state != MIG_STATE_COMPLETED) {
 723                     if (old_vm_running) {
 724                         vm_start();
 725                     }
 726                 }
 727                 last_round = true;
 728             }
 729         }
 730         qemu_mutex_unlock_iothread();
 731         current_time = qemu_get_clock_ms(rt_clock);
 732         if (current_time >= initial_time + BUFFER_DELAY) {
 733             uint64_t transferred_bytes = s->bytes_xfer;
 734             uint64_t time_spent = current_time - initial_time - sleep_time;
 735             double bandwidth = transferred_bytes / time_spent;
 736             max_size = bandwidth * migrate_max_downtime() / 1000000;
 737
 738             DPRINTF("transferred %" PRIu64 " time_spent %" PRIu64
 739                     " bandwidth %g max_size %" PRId64 "\n",
 740                     transferred_bytes, time_spent, bandwidth, max_size);
 741             /* if we haven't sent anything, we don't want to recalculate
 742                10000 is a small enough number for our purposes */
 743             if (s->dirty_bytes_rate && transferred_bytes > 10000) {
 744                 s->expected_downtime = s->dirty_bytes_rate / bandwidth;
 745             }
 746
 747             s->bytes_xfer = 0;
 748             sleep_time = 0;
 749             initial_time = current_time;
 750         }
 751         if (!last_round && (s->bytes_xfer >= s->xfer_limit)) {
 752             /* usleep expects microseconds */
 753             g_usleep((initial_time + BUFFER_DELAY - current_time)*1000);
 754             sleep_time += qemu_get_clock_ms(rt_clock) - current_time;
 755         }
 756         ret = buffered_flush(s);
 757         if (ret < 0) {
 758             break;
 759         }
 760     }
 761
 762 out:
 763     if (ret < 0) {
 764         migrate_fd_error(s);
 765     }
 766     g_free(s->buffer);
 767     return NULL;
 768 }
 769
 770 static const QEMUFileOps buffered_file_ops = {
 771     .get_fd =         buffered_get_fd,
 772     .put_buffer =     buffered_put_buffer,
 773     .close =          buffered_close,
 774     .rate_limit =     buffered_rate_limit,
 775     .get_rate_limit = buffered_get_rate_limit,
 776     .set_rate_limit = buffered_set_rate_limit,
 777 };
 778
 779 void migrate_fd_connect(MigrationState *s)
 780 {
 781     s->state = MIG_STATE_ACTIVE;
 782     s->bytes_xfer = 0;
 783     s->buffer = NULL;
 784     s->buffer_size = 0;
 785     s->buffer_capacity = 0;
 786     /* This is a best 1st approximation. ns to ms */
 787     s->expected_downtime = max_downtime/1000000;
 788
 789     s->xfer_limit = s->bandwidth_limit / XFER_LIMIT_RATIO;
 790     s->complete = false;
 791
 792     s->file = qemu_fopen_ops(s, &buffered_file_ops);
 793
 794     qemu_thread_create(&s->thread, buffered_file_thread, s,
 795                        QEMU_THREAD_DETACHED);
 796     notifier_list_notify(&migration_state_notifiers, s);
 797 }