block/commit.c

   1 /*
   2  * Live block commit
   3  *
   4  * Copyright Red Hat, Inc. 2012
   5  *
   6  * Authors:
   7  *  Jeff Cody   <jcody@redhat.com>
   8  *  Based on stream.c by Stefan Hajnoczi
   9  *
  10  * This work is licensed under the terms of the GNU LGPL, version 2 or later.
  11  * See the COPYING.LIB file in the top-level directory.
  12  *
  13  */
  14
  15 #include "qemu/osdep.h"
  16 #include "qemu/cutils.h"
  17 #include "trace.h"
  18 #include "block/block_int.h"
  19 #include "block/blockjob_int.h"
  20 #include "qapi/error.h"
  21 #include "qapi/qmp/qerror.h"
  22 #include "qemu/ratelimit.h"
  23 #include "sysemu/block-backend.h"
  24
  25 enum {
  26     /*
  27      * Size of data buffer for populating the image file.  This should be large
  28      * enough to process multiple clusters in a single call, so that populating
  29      * contiguous regions of the image is efficient.
  30      */
  31     COMMIT_BUFFER_SIZE = 512 * 1024, /* in bytes */
  32 };
  33
  34 typedef struct CommitBlockJob {
  35     BlockJob common;
  36     BlockDriverState *commit_top_bs;
  37     BlockBackend *top;
  38     BlockBackend *base;
  39     BlockDriverState *base_bs;
  40     BlockDriverState *base_overlay;
  41     BlockdevOnError on_error;
  42     bool base_read_only;
  43     bool chain_frozen;
  44     char *backing_file_str;
  45 } CommitBlockJob;
  46
  47 static int commit_prepare(Job *job)
  48 {
  49     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
  50
  51     bdrv_unfreeze_backing_chain(s->commit_top_bs, s->base_bs);
  52     s->chain_frozen = false;
  53
  54     /* Remove base node parent that still uses BLK_PERM_WRITE/RESIZE before
  55      * the normal backing chain can be restored. */
  56     blk_unref(s->base);
  57     s->base = NULL;
  58
  59     /* FIXME: bdrv_drop_intermediate treats total failures and partial failures
  60      * identically. Further work is needed to disambiguate these cases. */
  61     return bdrv_drop_intermediate(s->commit_top_bs, s->base_bs,
  62                                   s->backing_file_str);
  63 }
  64
  65 static void commit_abort(Job *job)
  66 {
  67     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
  68     BlockDriverState *top_bs = blk_bs(s->top);
  69
  70     if (s->chain_frozen) {
  71         bdrv_unfreeze_backing_chain(s->commit_top_bs, s->base_bs);
  72     }
  73
  74     /* Make sure commit_top_bs and top stay around until bdrv_replace_node() */
  75     bdrv_ref(top_bs);
  76     bdrv_ref(s->commit_top_bs);
  77
  78     if (s->base) {
  79         blk_unref(s->base);
  80     }
  81
  82     /* free the blockers on the intermediate nodes so that bdrv_replace_nodes
  83      * can succeed */
  84     block_job_remove_all_bdrv(&s->common);
  85
  86     /* If bdrv_drop_intermediate() failed (or was not invoked), remove the
  87      * commit filter driver from the backing chain now. Do this as the final
  88      * step so that the 'consistent read' permission can be granted.
  89      *
  90      * XXX Can (or should) we somehow keep 'consistent read' blocked even
  91      * after the failed/cancelled commit job is gone? If we already wrote
  92      * something to base, the intermediate images aren't valid any more. */
  93     bdrv_replace_node(s->commit_top_bs, s->commit_top_bs->backing->bs,
  94                       &error_abort);
  95
  96     bdrv_unref(s->commit_top_bs);
  97     bdrv_unref(top_bs);
  98 }
  99
 100 static void commit_clean(Job *job)
 101 {
 102     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
 103
 104     /* restore base open flags here if appropriate (e.g., change the base back
 105      * to r/o). These reopens do not need to be atomic, since we won't abort
 106      * even on failure here */
 107     if (s->base_read_only) {
 108         bdrv_reopen_set_read_only(s->base_bs, true, NULL);
 109     }
 110
 111     g_free(s->backing_file_str);
 112     blk_unref(s->top);
 113 }
 114
 115 static int coroutine_fn commit_run(Job *job, Error **errp)
 116 {
 117     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
 118     int64_t offset;
 119     uint64_t delay_ns = 0;
 120     int ret = 0;
 121     int64_t n = 0; /* bytes */
 122     QEMU_AUTO_VFREE void *buf = NULL;
 123     int64_t len, base_len;
 124
 125     len = blk_getlength(s->top);
 126     if (len < 0) {
 127         return len;
 128     }
 129     job_progress_set_remaining(&s->common.job, len);
 130
 131     base_len = blk_getlength(s->base);
 132     if (base_len < 0) {
 133         return base_len;
 134     }
 135
 136     if (base_len < len) {
 137         ret = blk_truncate(s->base, len, false, PREALLOC_MODE_OFF, 0, NULL);
 138         if (ret) {
 139             return ret;
 140         }
 141     }
 142
 143     buf = blk_blockalign(s->top, COMMIT_BUFFER_SIZE);
 144
 145     for (offset = 0; offset < len; offset += n) {
 146         bool copy;
 147         bool error_in_source = true;
 148
 149         /* Note that even when no rate limit is applied we need to yield
 150          * with no pending I/O here so that bdrv_drain_all() returns.
 151          */
 152         job_sleep_ns(&s->common.job, delay_ns);
 153         if (job_is_cancelled(&s->common.job)) {
 154             break;
 155         }
 156         /* Copy if allocated above the base */
 157         ret = bdrv_is_allocated_above(blk_bs(s->top), s->base_overlay, true,
 158                                       offset, COMMIT_BUFFER_SIZE, &n);
 159         copy = (ret > 0);
 160         trace_commit_one_iteration(s, offset, n, ret);
 161         if (copy) {
 162             assert(n < SIZE_MAX);
 163
 164             ret = blk_co_pread(s->top, offset, n, buf, 0);
 165             if (ret >= 0) {
 166                 ret = blk_co_pwrite(s->base, offset, n, buf, 0);
 167                 if (ret < 0) {
 168                     error_in_source = false;
 169                 }
 170             }
 171         }
 172         if (ret < 0) {
 173             BlockErrorAction action =
 174                 block_job_error_action(&s->common, s->on_error,
 175                                        error_in_source, -ret);
 176             if (action == BLOCK_ERROR_ACTION_REPORT) {
 177                 return ret;
 178             } else {
 179                 n = 0;
 180                 continue;
 181             }
 182         }
 183         /* Publish progress */
 184         job_progress_update(&s->common.job, n);
 185
 186         if (copy) {
 187             delay_ns = block_job_ratelimit_get_delay(&s->common, n);
 188         } else {
 189             delay_ns = 0;
 190         }
 191     }
 192
 193     return 0;
 194 }
 195
 196 static const BlockJobDriver commit_job_driver = {
 197     .job_driver = {
 198         .instance_size = sizeof(CommitBlockJob),
 199         .job_type      = JOB_TYPE_COMMIT,
 200         .free          = block_job_free,
 201         .user_resume   = block_job_user_resume,
 202         .run           = commit_run,
 203         .prepare       = commit_prepare,
 204         .abort         = commit_abort,
 205         .clean         = commit_clean
 206     },
 207 };
 208
 209 static int coroutine_fn bdrv_commit_top_preadv(BlockDriverState *bs,
 210     int64_t offset, int64_t bytes, QEMUIOVector *qiov, BdrvRequestFlags flags)
 211 {
 212     return bdrv_co_preadv(bs->backing, offset, bytes, qiov, flags);
 213 }
 214
 215 static void bdrv_commit_top_refresh_filename(BlockDriverState *bs)
 216 {
 217     pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
 218             bs->backing->bs->filename);
 219 }
 220
 221 static void bdrv_commit_top_child_perm(BlockDriverState *bs, BdrvChild *c,
 222                                        BdrvChildRole role,
 223                                        BlockReopenQueue *reopen_queue,
 224                                        uint64_t perm, uint64_t shared,
 225                                        uint64_t *nperm, uint64_t *nshared)
 226 {
 227     *nperm = 0;
 228     *nshared = BLK_PERM_ALL;
 229 }
 230
 231 /* Dummy node that provides consistent read to its users without requiring it
 232  * from its backing file and that allows writes on the backing file chain. */
 233 static BlockDriver bdrv_commit_top = {
 234     .format_name                = "commit_top",
 235     .bdrv_co_preadv             = bdrv_commit_top_preadv,
 236     .bdrv_refresh_filename      = bdrv_commit_top_refresh_filename,
 237     .bdrv_child_perm            = bdrv_commit_top_child_perm,
 238
 239     .is_filter                  = true,
 240 };
 241
 242 void commit_start(const char *job_id, BlockDriverState *bs,
 243                   BlockDriverState *base, BlockDriverState *top,
 244                   int creation_flags, int64_t speed,
 245                   BlockdevOnError on_error, const char *backing_file_str,
 246                   const char *filter_node_name, Error **errp)
 247 {
 248     CommitBlockJob *s;
 249     BlockDriverState *iter;
 250     BlockDriverState *commit_top_bs = NULL;
 251     BlockDriverState *filtered_base;
 252     int64_t base_size, top_size;
 253     uint64_t base_perms, iter_shared_perms;
 254     int ret;
 255
 256     assert(top != bs);
 257     if (bdrv_skip_filters(top) == bdrv_skip_filters(base)) {
 258         error_setg(errp, "Invalid files for merge: top and base are the same");
 259         return;
 260     }
 261
 262     base_size = bdrv_getlength(base);
 263     if (base_size < 0) {
 264         error_setg_errno(errp, -base_size, "Could not inquire base image size");
 265         return;
 266     }
 267
 268     top_size = bdrv_getlength(top);
 269     if (top_size < 0) {
 270         error_setg_errno(errp, -top_size, "Could not inquire top image size");
 271         return;
 272     }
 273
 274     base_perms = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE;
 275     if (base_size < top_size) {
 276         base_perms |= BLK_PERM_RESIZE;
 277     }
 278
 279     s = block_job_create(job_id, &commit_job_driver, NULL, bs, 0, BLK_PERM_ALL,
 280                          speed, creation_flags, NULL, NULL, errp);
 281     if (!s) {
 282         return;
 283     }
 284
 285     /* convert base to r/w, if necessary */
 286     s->base_read_only = bdrv_is_read_only(base);
 287     if (s->base_read_only) {
 288         if (bdrv_reopen_set_read_only(base, false, errp) != 0) {
 289             goto fail;
 290         }
 291     }
 292
 293     /* Insert commit_top block node above top, so we can block consistent read
 294      * on the backing chain below it */
 295     commit_top_bs = bdrv_new_open_driver(&bdrv_commit_top, filter_node_name, 0,
 296                                          errp);
 297     if (commit_top_bs == NULL) {
 298         goto fail;
 299     }
 300     if (!filter_node_name) {
 301         commit_top_bs->implicit = true;
 302     }
 303
 304     /* So that we can always drop this node */
 305     commit_top_bs->never_freeze = true;
 306
 307     commit_top_bs->total_sectors = top->total_sectors;
 308
 309     ret = bdrv_append(commit_top_bs, top, errp);
 310     bdrv_unref(commit_top_bs); /* referenced by new parents or failed */
 311     if (ret < 0) {
 312         commit_top_bs = NULL;
 313         goto fail;
 314     }
 315
 316     s->commit_top_bs = commit_top_bs;
 317
 318     /*
 319      * Block all nodes between top and base, because they will
 320      * disappear from the chain after this operation.
 321      * Note that this assumes that the user is fine with removing all
 322      * nodes (including R/W filters) between top and base.  Assuring
 323      * this is the responsibility of the interface (i.e. whoever calls
 324      * commit_start()).
 325      */
 326     s->base_overlay = bdrv_find_overlay(top, base);
 327     assert(s->base_overlay);
 328
 329     /*
 330      * The topmost node with
 331      * bdrv_skip_filters(filtered_base) == bdrv_skip_filters(base)
 332      */
 333     filtered_base = bdrv_cow_bs(s->base_overlay);
 334     assert(bdrv_skip_filters(filtered_base) == bdrv_skip_filters(base));
 335
 336     /*
 337      * XXX BLK_PERM_WRITE needs to be allowed so we don't block ourselves
 338      * at s->base (if writes are blocked for a node, they are also blocked
 339      * for its backing file). The other options would be a second filter
 340      * driver above s->base.
 341      */
 342     iter_shared_perms = BLK_PERM_WRITE_UNCHANGED | BLK_PERM_WRITE;
 343
 344     for (iter = top; iter != base; iter = bdrv_filter_or_cow_bs(iter)) {
 345         if (iter == filtered_base) {
 346             /*
 347              * From here on, all nodes are filters on the base.  This
 348              * allows us to share BLK_PERM_CONSISTENT_READ.
 349              */
 350             iter_shared_perms |= BLK_PERM_CONSISTENT_READ;
 351         }
 352
 353         ret = block_job_add_bdrv(&s->common, "intermediate node", iter, 0,
 354                                  iter_shared_perms, errp);
 355         if (ret < 0) {
 356             goto fail;
 357         }
 358     }
 359
 360     if (bdrv_freeze_backing_chain(commit_top_bs, base, errp) < 0) {
 361         goto fail;
 362     }
 363     s->chain_frozen = true;
 364
 365     ret = block_job_add_bdrv(&s->common, "base", base, 0, BLK_PERM_ALL, errp);
 366     if (ret < 0) {
 367         goto fail;
 368     }
 369
 370     s->base = blk_new(s->common.job.aio_context,
 371                       base_perms,
 372                       BLK_PERM_CONSISTENT_READ
 373                       | BLK_PERM_GRAPH_MOD
 374                       | BLK_PERM_WRITE_UNCHANGED);
 375     ret = blk_insert_bs(s->base, base, errp);
 376     if (ret < 0) {
 377         goto fail;
 378     }
 379     blk_set_disable_request_queuing(s->base, true);
 380     s->base_bs = base;
 381
 382     /* Required permissions are already taken with block_job_add_bdrv() */
 383     s->top = blk_new(s->common.job.aio_context, 0, BLK_PERM_ALL);
 384     ret = blk_insert_bs(s->top, top, errp);
 385     if (ret < 0) {
 386         goto fail;
 387     }
 388     blk_set_disable_request_queuing(s->top, true);
 389
 390     s->backing_file_str = g_strdup(backing_file_str);
 391     s->on_error = on_error;
 392
 393     trace_commit_start(bs, base, top, s);
 394     job_start(&s->common.job);
 395     return;
 396
 397 fail:
 398     if (s->chain_frozen) {
 399         bdrv_unfreeze_backing_chain(commit_top_bs, base);
 400     }
 401     if (s->base) {
 402         blk_unref(s->base);
 403     }
 404     if (s->top) {
 405         blk_unref(s->top);
 406     }
 407     if (s->base_read_only) {
 408         bdrv_reopen_set_read_only(base, true, NULL);
 409     }
 410     job_early_fail(&s->common.job);
 411     /* commit_top_bs has to be replaced after deleting the block job,
 412      * otherwise this would fail because of lack of permissions. */
 413     if (commit_top_bs) {
 414         bdrv_replace_node(commit_top_bs, top, &error_abort);
 415     }
 416 }
 417
 418
 419 #define COMMIT_BUF_SIZE (2048 * BDRV_SECTOR_SIZE)
 420
 421 /* commit COW file into the raw image */
 422 int bdrv_commit(BlockDriverState *bs)
 423 {
 424     BlockBackend *src, *backing;
 425     BlockDriverState *backing_file_bs = NULL;
 426     BlockDriverState *commit_top_bs = NULL;
 427     BlockDriver *drv = bs->drv;
 428     AioContext *ctx;
 429     int64_t offset, length, backing_length;
 430     int ro;
 431     int64_t n;
 432     int ret = 0;
 433     QEMU_AUTO_VFREE uint8_t *buf = NULL;
 434     Error *local_err = NULL;
 435
 436     if (!drv)
 437         return -ENOMEDIUM;
 438
 439     backing_file_bs = bdrv_cow_bs(bs);
 440
 441     if (!backing_file_bs) {
 442         return -ENOTSUP;
 443     }
 444
 445     if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_COMMIT_SOURCE, NULL) ||
 446         bdrv_op_is_blocked(backing_file_bs, BLOCK_OP_TYPE_COMMIT_TARGET, NULL))
 447     {
 448         return -EBUSY;
 449     }
 450
 451     ro = bdrv_is_read_only(backing_file_bs);
 452
 453     if (ro) {
 454         if (bdrv_reopen_set_read_only(backing_file_bs, false, NULL)) {
 455             return -EACCES;
 456         }
 457     }
 458
 459     ctx = bdrv_get_aio_context(bs);
 460     /* WRITE_UNCHANGED is required for bdrv_make_empty() */
 461     src = blk_new(ctx, BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED,
 462                   BLK_PERM_ALL);
 463     backing = blk_new(ctx, BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL);
 464
 465     ret = blk_insert_bs(src, bs, &local_err);
 466     if (ret < 0) {
 467         error_report_err(local_err);
 468         goto ro_cleanup;
 469     }
 470
 471     /* Insert commit_top block node above backing, so we can write to it */
 472     commit_top_bs = bdrv_new_open_driver(&bdrv_commit_top, NULL, BDRV_O_RDWR,
 473                                          &local_err);
 474     if (commit_top_bs == NULL) {
 475         error_report_err(local_err);
 476         goto ro_cleanup;
 477     }
 478
 479     bdrv_set_backing_hd(commit_top_bs, backing_file_bs, &error_abort);
 480     bdrv_set_backing_hd(bs, commit_top_bs, &error_abort);
 481
 482     ret = blk_insert_bs(backing, backing_file_bs, &local_err);
 483     if (ret < 0) {
 484         error_report_err(local_err);
 485         goto ro_cleanup;
 486     }
 487
 488     length = blk_getlength(src);
 489     if (length < 0) {
 490         ret = length;
 491         goto ro_cleanup;
 492     }
 493
 494     backing_length = blk_getlength(backing);
 495     if (backing_length < 0) {
 496         ret = backing_length;
 497         goto ro_cleanup;
 498     }
 499
 500     /* If our top snapshot is larger than the backing file image,
 501      * grow the backing file image if possible.  If not possible,
 502      * we must return an error */
 503     if (length > backing_length) {
 504         ret = blk_truncate(backing, length, false, PREALLOC_MODE_OFF, 0,
 505                            &local_err);
 506         if (ret < 0) {
 507             error_report_err(local_err);
 508             goto ro_cleanup;
 509         }
 510     }
 511
 512     /* blk_try_blockalign() for src will choose an alignment that works for
 513      * backing as well, so no need to compare the alignment manually. */
 514     buf = blk_try_blockalign(src, COMMIT_BUF_SIZE);
 515     if (buf == NULL) {
 516         ret = -ENOMEM;
 517         goto ro_cleanup;
 518     }
 519
 520     for (offset = 0; offset < length; offset += n) {
 521         ret = bdrv_is_allocated(bs, offset, COMMIT_BUF_SIZE, &n);
 522         if (ret < 0) {
 523             goto ro_cleanup;
 524         }
 525         if (ret) {
 526             ret = blk_pread(src, offset, buf, n);
 527             if (ret < 0) {
 528                 goto ro_cleanup;
 529             }
 530
 531             ret = blk_pwrite(backing, offset, buf, n, 0);
 532             if (ret < 0) {
 533                 goto ro_cleanup;
 534             }
 535         }
 536     }
 537
 538     ret = blk_make_empty(src, NULL);
 539     /* Ignore -ENOTSUP */
 540     if (ret < 0 && ret != -ENOTSUP) {
 541         goto ro_cleanup;
 542     }
 543
 544     blk_flush(src);
 545
 546     /*
 547      * Make sure all data we wrote to the backing device is actually
 548      * stable on disk.
 549      */
 550     blk_flush(backing);
 551
 552     ret = 0;
 553 ro_cleanup:
 554     blk_unref(backing);
 555     if (bdrv_cow_bs(bs) != backing_file_bs) {
 556         bdrv_set_backing_hd(bs, backing_file_bs, &error_abort);
 557     }
 558     bdrv_unref(commit_top_bs);
 559     blk_unref(src);
 560
 561     if (ro) {
 562         /* ignoring error return here */
 563         bdrv_reopen_set_read_only(backing_file_bs, true, NULL);
 564     }
 565
 566     return ret;
 567 }