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 "qemu/memalign.h"
  24 #include "sysemu/block-backend.h"
  25
  26 enum {
  27     /*
  28      * Size of data buffer for populating the image file.  This should be large
  29      * enough to process multiple clusters in a single call, so that populating
  30      * contiguous regions of the image is efficient.
  31      */
  32     COMMIT_BUFFER_SIZE = 512 * 1024, /* in bytes */
  33 };
  34
  35 typedef struct CommitBlockJob {
  36     BlockJob common;
  37     BlockDriverState *commit_top_bs;
  38     BlockBackend *top;
  39     BlockBackend *base;
  40     BlockDriverState *base_bs;
  41     BlockDriverState *base_overlay;
  42     BlockdevOnError on_error;
  43     bool base_read_only;
  44     bool chain_frozen;
  45     char *backing_file_str;
  46 } CommitBlockJob;
  47
  48 static int commit_prepare(Job *job)
  49 {
  50     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
  51
  52     bdrv_unfreeze_backing_chain(s->commit_top_bs, s->base_bs);
  53     s->chain_frozen = false;
  54
  55     /* Remove base node parent that still uses BLK_PERM_WRITE/RESIZE before
  56      * the normal backing chain can be restored. */
  57     blk_unref(s->base);
  58     s->base = NULL;
  59
  60     /* FIXME: bdrv_drop_intermediate treats total failures and partial failures
  61      * identically. Further work is needed to disambiguate these cases. */
  62     return bdrv_drop_intermediate(s->commit_top_bs, s->base_bs,
  63                                   s->backing_file_str);
  64 }
  65
  66 static void commit_abort(Job *job)
  67 {
  68     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
  69     BlockDriverState *top_bs = blk_bs(s->top);
  70
  71     if (s->chain_frozen) {
  72         bdrv_unfreeze_backing_chain(s->commit_top_bs, s->base_bs);
  73     }
  74
  75     /* Make sure commit_top_bs and top stay around until bdrv_replace_node() */
  76     bdrv_ref(top_bs);
  77     bdrv_ref(s->commit_top_bs);
  78
  79     if (s->base) {
  80         blk_unref(s->base);
  81     }
  82
  83     /* free the blockers on the intermediate nodes so that bdrv_replace_nodes
  84      * can succeed */
  85     block_job_remove_all_bdrv(&s->common);
  86
  87     /* If bdrv_drop_intermediate() failed (or was not invoked), remove the
  88      * commit filter driver from the backing chain now. Do this as the final
  89      * step so that the 'consistent read' permission can be granted.
  90      *
  91      * XXX Can (or should) we somehow keep 'consistent read' blocked even
  92      * after the failed/cancelled commit job is gone? If we already wrote
  93      * something to base, the intermediate images aren't valid any more. */
  94     bdrv_replace_node(s->commit_top_bs, s->commit_top_bs->backing->bs,
  95                       &error_abort);
  96
  97     bdrv_unref(s->commit_top_bs);
  98     bdrv_unref(top_bs);
  99 }
 100
 101 static void commit_clean(Job *job)
 102 {
 103     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
 104
 105     /* restore base open flags here if appropriate (e.g., change the base back
 106      * to r/o). These reopens do not need to be atomic, since we won't abort
 107      * even on failure here */
 108     if (s->base_read_only) {
 109         bdrv_reopen_set_read_only(s->base_bs, true, NULL);
 110     }
 111
 112     g_free(s->backing_file_str);
 113     blk_unref(s->top);
 114 }
 115
 116 static int coroutine_fn commit_run(Job *job, Error **errp)
 117 {
 118     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
 119     int64_t offset;
 120     uint64_t delay_ns = 0;
 121     int ret = 0;
 122     int64_t n = 0; /* bytes */
 123     QEMU_AUTO_VFREE void *buf = NULL;
 124     int64_t len, base_len;
 125
 126     len = blk_getlength(s->top);
 127     if (len < 0) {
 128         return len;
 129     }
 130     job_progress_set_remaining(&s->common.job, len);
 131
 132     base_len = blk_getlength(s->base);
 133     if (base_len < 0) {
 134         return base_len;
 135     }
 136
 137     if (base_len < len) {
 138         ret = blk_truncate(s->base, len, false, PREALLOC_MODE_OFF, 0, NULL);
 139         if (ret) {
 140             return ret;
 141         }
 142     }
 143
 144     buf = blk_blockalign(s->top, COMMIT_BUFFER_SIZE);
 145
 146     for (offset = 0; offset < len; offset += n) {
 147         bool copy;
 148         bool error_in_source = true;
 149
 150         /* Note that even when no rate limit is applied we need to yield
 151          * with no pending I/O here so that bdrv_drain_all() returns.
 152          */
 153         job_sleep_ns(&s->common.job, delay_ns);
 154         if (job_is_cancelled(&s->common.job)) {
 155             break;
 156         }
 157         /* Copy if allocated above the base */
 158         ret = bdrv_is_allocated_above(blk_bs(s->top), s->base_overlay, true,
 159                                       offset, COMMIT_BUFFER_SIZE, &n);
 160         copy = (ret > 0);
 161         trace_commit_one_iteration(s, offset, n, ret);
 162         if (copy) {
 163             assert(n < SIZE_MAX);
 164
 165             ret = blk_co_pread(s->top, offset, n, buf, 0);
 166             if (ret >= 0) {
 167                 ret = blk_co_pwrite(s->base, offset, n, buf, 0);
 168                 if (ret < 0) {
 169                     error_in_source = false;
 170                 }
 171             }
 172         }
 173         if (ret < 0) {
 174             BlockErrorAction action =
 175                 block_job_error_action(&s->common, s->on_error,
 176                                        error_in_source, -ret);
 177             if (action == BLOCK_ERROR_ACTION_REPORT) {
 178                 return ret;
 179             } else {
 180                 n = 0;
 181                 continue;
 182             }
 183         }
 184         /* Publish progress */
 185         job_progress_update(&s->common.job, n);
 186
 187         if (copy) {
 188             delay_ns = block_job_ratelimit_get_delay(&s->common, n);
 189         } else {
 190             delay_ns = 0;
 191         }
 192     }
 193
 194     return 0;
 195 }
 196
 197 static const BlockJobDriver commit_job_driver = {
 198     .job_driver = {
 199         .instance_size = sizeof(CommitBlockJob),
 200         .job_type      = JOB_TYPE_COMMIT,
 201         .free          = block_job_free,
 202         .user_resume   = block_job_user_resume,
 203         .run           = commit_run,
 204         .prepare       = commit_prepare,
 205         .abort         = commit_abort,
 206         .clean         = commit_clean
 207     },
 208 };
 209
 210 static int coroutine_fn bdrv_commit_top_preadv(BlockDriverState *bs,
 211     int64_t offset, int64_t bytes, QEMUIOVector *qiov, BdrvRequestFlags flags)
 212 {
 213     return bdrv_co_preadv(bs->backing, offset, bytes, qiov, flags);
 214 }
 215
 216 static void bdrv_commit_top_refresh_filename(BlockDriverState *bs)
 217 {
 218     pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
 219             bs->backing->bs->filename);
 220 }
 221
 222 static void bdrv_commit_top_child_perm(BlockDriverState *bs, BdrvChild *c,
 223                                        BdrvChildRole role,
 224                                        BlockReopenQueue *reopen_queue,
 225                                        uint64_t perm, uint64_t shared,
 226                                        uint64_t *nperm, uint64_t *nshared)
 227 {
 228     *nperm = 0;
 229     *nshared = BLK_PERM_ALL;
 230 }
 231
 232 /* Dummy node that provides consistent read to its users without requiring it
 233  * from its backing file and that allows writes on the backing file chain. */
 234 static BlockDriver bdrv_commit_top = {
 235     .format_name                = "commit_top",
 236     .bdrv_co_preadv             = bdrv_commit_top_preadv,
 237     .bdrv_refresh_filename      = bdrv_commit_top_refresh_filename,
 238     .bdrv_child_perm            = bdrv_commit_top_child_perm,
 239
 240     .is_filter                  = true,
 241 };
 242
 243 void commit_start(const char *job_id, BlockDriverState *bs,
 244                   BlockDriverState *base, BlockDriverState *top,
 245                   int creation_flags, int64_t speed,
 246                   BlockdevOnError on_error, const char *backing_file_str,
 247                   const char *filter_node_name, Error **errp)
 248 {
 249     CommitBlockJob *s;
 250     BlockDriverState *iter;
 251     BlockDriverState *commit_top_bs = NULL;
 252     BlockDriverState *filtered_base;
 253     int64_t base_size, top_size;
 254     uint64_t base_perms, iter_shared_perms;
 255     int ret;
 256
 257     GLOBAL_STATE_CODE();
 258
 259     assert(top != bs);
 260     if (bdrv_skip_filters(top) == bdrv_skip_filters(base)) {
 261         error_setg(errp, "Invalid files for merge: top and base are the same");
 262         return;
 263     }
 264
 265     base_size = bdrv_getlength(base);
 266     if (base_size < 0) {
 267         error_setg_errno(errp, -base_size, "Could not inquire base image size");
 268         return;
 269     }
 270
 271     top_size = bdrv_getlength(top);
 272     if (top_size < 0) {
 273         error_setg_errno(errp, -top_size, "Could not inquire top image size");
 274         return;
 275     }
 276
 277     base_perms = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE;
 278     if (base_size < top_size) {
 279         base_perms |= BLK_PERM_RESIZE;
 280     }
 281
 282     s = block_job_create(job_id, &commit_job_driver, NULL, bs, 0, BLK_PERM_ALL,
 283                          speed, creation_flags, NULL, NULL, errp);
 284     if (!s) {
 285         return;
 286     }
 287
 288     /* convert base to r/w, if necessary */
 289     s->base_read_only = bdrv_is_read_only(base);
 290     if (s->base_read_only) {
 291         if (bdrv_reopen_set_read_only(base, false, errp) != 0) {
 292             goto fail;
 293         }
 294     }
 295
 296     /* Insert commit_top block node above top, so we can block consistent read
 297      * on the backing chain below it */
 298     commit_top_bs = bdrv_new_open_driver(&bdrv_commit_top, filter_node_name, 0,
 299                                          errp);
 300     if (commit_top_bs == NULL) {
 301         goto fail;
 302     }
 303     if (!filter_node_name) {
 304         commit_top_bs->implicit = true;
 305     }
 306
 307     /* So that we can always drop this node */
 308     commit_top_bs->never_freeze = true;
 309
 310     commit_top_bs->total_sectors = top->total_sectors;
 311
 312     ret = bdrv_append(commit_top_bs, top, errp);
 313     bdrv_unref(commit_top_bs); /* referenced by new parents or failed */
 314     if (ret < 0) {
 315         commit_top_bs = NULL;
 316         goto fail;
 317     }
 318
 319     s->commit_top_bs = commit_top_bs;
 320
 321     /*
 322      * Block all nodes between top and base, because they will
 323      * disappear from the chain after this operation.
 324      * Note that this assumes that the user is fine with removing all
 325      * nodes (including R/W filters) between top and base.  Assuring
 326      * this is the responsibility of the interface (i.e. whoever calls
 327      * commit_start()).
 328      */
 329     s->base_overlay = bdrv_find_overlay(top, base);
 330     assert(s->base_overlay);
 331
 332     /*
 333      * The topmost node with
 334      * bdrv_skip_filters(filtered_base) == bdrv_skip_filters(base)
 335      */
 336     filtered_base = bdrv_cow_bs(s->base_overlay);
 337     assert(bdrv_skip_filters(filtered_base) == bdrv_skip_filters(base));
 338
 339     /*
 340      * XXX BLK_PERM_WRITE needs to be allowed so we don't block ourselves
 341      * at s->base (if writes are blocked for a node, they are also blocked
 342      * for its backing file). The other options would be a second filter
 343      * driver above s->base.
 344      */
 345     iter_shared_perms = BLK_PERM_WRITE_UNCHANGED | BLK_PERM_WRITE;
 346
 347     for (iter = top; iter != base; iter = bdrv_filter_or_cow_bs(iter)) {
 348         if (iter == filtered_base) {
 349             /*
 350              * From here on, all nodes are filters on the base.  This
 351              * allows us to share BLK_PERM_CONSISTENT_READ.
 352              */
 353             iter_shared_perms |= BLK_PERM_CONSISTENT_READ;
 354         }
 355
 356         ret = block_job_add_bdrv(&s->common, "intermediate node", iter, 0,
 357                                  iter_shared_perms, errp);
 358         if (ret < 0) {
 359             goto fail;
 360         }
 361     }
 362
 363     if (bdrv_freeze_backing_chain(commit_top_bs, base, errp) < 0) {
 364         goto fail;
 365     }
 366     s->chain_frozen = true;
 367
 368     ret = block_job_add_bdrv(&s->common, "base", base, 0, BLK_PERM_ALL, errp);
 369     if (ret < 0) {
 370         goto fail;
 371     }
 372
 373     s->base = blk_new(s->common.job.aio_context,
 374                       base_perms,
 375                       BLK_PERM_CONSISTENT_READ
 376                       | BLK_PERM_WRITE_UNCHANGED);
 377     ret = blk_insert_bs(s->base, base, errp);
 378     if (ret < 0) {
 379         goto fail;
 380     }
 381     blk_set_disable_request_queuing(s->base, true);
 382     s->base_bs = base;
 383
 384     /* Required permissions are already taken with block_job_add_bdrv() */
 385     s->top = blk_new(s->common.job.aio_context, 0, BLK_PERM_ALL);
 386     ret = blk_insert_bs(s->top, top, errp);
 387     if (ret < 0) {
 388         goto fail;
 389     }
 390     blk_set_disable_request_queuing(s->top, true);
 391
 392     s->backing_file_str = g_strdup(backing_file_str);
 393     s->on_error = on_error;
 394
 395     trace_commit_start(bs, base, top, s);
 396     job_start(&s->common.job);
 397     return;
 398
 399 fail:
 400     if (s->chain_frozen) {
 401         bdrv_unfreeze_backing_chain(commit_top_bs, base);
 402     }
 403     if (s->base) {
 404         blk_unref(s->base);
 405     }
 406     if (s->top) {
 407         blk_unref(s->top);
 408     }
 409     if (s->base_read_only) {
 410         bdrv_reopen_set_read_only(base, true, NULL);
 411     }
 412     job_early_fail(&s->common.job);
 413     /* commit_top_bs has to be replaced after deleting the block job,
 414      * otherwise this would fail because of lack of permissions. */
 415     if (commit_top_bs) {
 416         bdrv_replace_node(commit_top_bs, top, &error_abort);
 417     }
 418 }
 419
 420
 421 #define COMMIT_BUF_SIZE (2048 * BDRV_SECTOR_SIZE)
 422
 423 /* commit COW file into the raw image */
 424 int bdrv_commit(BlockDriverState *bs)
 425 {
 426     BlockBackend *src, *backing;
 427     BlockDriverState *backing_file_bs = NULL;
 428     BlockDriverState *commit_top_bs = NULL;
 429     BlockDriver *drv = bs->drv;
 430     AioContext *ctx;
 431     int64_t offset, length, backing_length;
 432     int ro;
 433     int64_t n;
 434     int ret = 0;
 435     QEMU_AUTO_VFREE uint8_t *buf = NULL;
 436     Error *local_err = NULL;
 437
 438     GLOBAL_STATE_CODE();
 439
 440     if (!drv)
 441         return -ENOMEDIUM;
 442
 443     backing_file_bs = bdrv_cow_bs(bs);
 444
 445     if (!backing_file_bs) {
 446         return -ENOTSUP;
 447     }
 448
 449     if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_COMMIT_SOURCE, NULL) ||
 450         bdrv_op_is_blocked(backing_file_bs, BLOCK_OP_TYPE_COMMIT_TARGET, NULL))
 451     {
 452         return -EBUSY;
 453     }
 454
 455     ro = bdrv_is_read_only(backing_file_bs);
 456
 457     if (ro) {
 458         if (bdrv_reopen_set_read_only(backing_file_bs, false, NULL)) {
 459             return -EACCES;
 460         }
 461     }
 462
 463     ctx = bdrv_get_aio_context(bs);
 464     /* WRITE_UNCHANGED is required for bdrv_make_empty() */
 465     src = blk_new(ctx, BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED,
 466                   BLK_PERM_ALL);
 467     backing = blk_new(ctx, BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL);
 468
 469     ret = blk_insert_bs(src, bs, &local_err);
 470     if (ret < 0) {
 471         error_report_err(local_err);
 472         goto ro_cleanup;
 473     }
 474
 475     /* Insert commit_top block node above backing, so we can write to it */
 476     commit_top_bs = bdrv_new_open_driver(&bdrv_commit_top, NULL, BDRV_O_RDWR,
 477                                          &local_err);
 478     if (commit_top_bs == NULL) {
 479         error_report_err(local_err);
 480         goto ro_cleanup;
 481     }
 482
 483     bdrv_set_backing_hd(commit_top_bs, backing_file_bs, &error_abort);
 484     bdrv_set_backing_hd(bs, commit_top_bs, &error_abort);
 485
 486     ret = blk_insert_bs(backing, backing_file_bs, &local_err);
 487     if (ret < 0) {
 488         error_report_err(local_err);
 489         goto ro_cleanup;
 490     }
 491
 492     length = blk_getlength(src);
 493     if (length < 0) {
 494         ret = length;
 495         goto ro_cleanup;
 496     }
 497
 498     backing_length = blk_getlength(backing);
 499     if (backing_length < 0) {
 500         ret = backing_length;
 501         goto ro_cleanup;
 502     }
 503
 504     /* If our top snapshot is larger than the backing file image,
 505      * grow the backing file image if possible.  If not possible,
 506      * we must return an error */
 507     if (length > backing_length) {
 508         ret = blk_truncate(backing, length, false, PREALLOC_MODE_OFF, 0,
 509                            &local_err);
 510         if (ret < 0) {
 511             error_report_err(local_err);
 512             goto ro_cleanup;
 513         }
 514     }
 515
 516     /* blk_try_blockalign() for src will choose an alignment that works for
 517      * backing as well, so no need to compare the alignment manually. */
 518     buf = blk_try_blockalign(src, COMMIT_BUF_SIZE);
 519     if (buf == NULL) {
 520         ret = -ENOMEM;
 521         goto ro_cleanup;
 522     }
 523
 524     for (offset = 0; offset < length; offset += n) {
 525         ret = bdrv_is_allocated(bs, offset, COMMIT_BUF_SIZE, &n);
 526         if (ret < 0) {
 527             goto ro_cleanup;
 528         }
 529         if (ret) {
 530             ret = blk_pread(src, offset, n, buf, 0);
 531             if (ret < 0) {
 532                 goto ro_cleanup;
 533             }
 534
 535             ret = blk_pwrite(backing, offset, n, buf, 0);
 536             if (ret < 0) {
 537                 goto ro_cleanup;
 538             }
 539         }
 540     }
 541
 542     ret = blk_make_empty(src, NULL);
 543     /* Ignore -ENOTSUP */
 544     if (ret < 0 && ret != -ENOTSUP) {
 545         goto ro_cleanup;
 546     }
 547
 548     blk_flush(src);
 549
 550     /*
 551      * Make sure all data we wrote to the backing device is actually
 552      * stable on disk.
 553      */
 554     blk_flush(backing);
 555
 556     ret = 0;
 557 ro_cleanup:
 558     blk_unref(backing);
 559     if (bdrv_cow_bs(bs) != backing_file_bs) {
 560         bdrv_set_backing_hd(bs, backing_file_bs, &error_abort);
 561     }
 562     bdrv_unref(commit_top_bs);
 563     blk_unref(src);
 564
 565     if (ro) {
 566         /* ignoring error return here */
 567         bdrv_reopen_set_read_only(backing_file_bs, true, NULL);
 568     }
 569
 570     return ret;
 571 }