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     BlockdevOnError on_error;
  41     bool base_read_only;
  42     bool chain_frozen;
  43     char *backing_file_str;
  44 } CommitBlockJob;
  45
  46 static int coroutine_fn commit_populate(BlockBackend *bs, BlockBackend *base,
  47                                         int64_t offset, uint64_t bytes,
  48                                         void *buf)
  49 {
  50     int ret = 0;
  51
  52     assert(bytes < SIZE_MAX);
  53
  54     ret = blk_co_pread(bs, offset, bytes, buf, 0);
  55     if (ret < 0) {
  56         return ret;
  57     }
  58
  59     ret = blk_co_pwrite(base, offset, bytes, buf, 0);
  60     if (ret < 0) {
  61         return ret;
  62     }
  63
  64     return 0;
  65 }
  66
  67 static int commit_prepare(Job *job)
  68 {
  69     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
  70
  71     bdrv_unfreeze_backing_chain(s->commit_top_bs, s->base_bs);
  72     s->chain_frozen = false;
  73
  74     /* Remove base node parent that still uses BLK_PERM_WRITE/RESIZE before
  75      * the normal backing chain can be restored. */
  76     blk_unref(s->base);
  77     s->base = NULL;
  78
  79     /* FIXME: bdrv_drop_intermediate treats total failures and partial failures
  80      * identically. Further work is needed to disambiguate these cases. */
  81     return bdrv_drop_intermediate(s->commit_top_bs, s->base_bs,
  82                                   s->backing_file_str);
  83 }
  84
  85 static void commit_abort(Job *job)
  86 {
  87     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
  88     BlockDriverState *top_bs = blk_bs(s->top);
  89
  90     if (s->chain_frozen) {
  91         bdrv_unfreeze_backing_chain(s->commit_top_bs, s->base_bs);
  92     }
  93
  94     /* Make sure commit_top_bs and top stay around until bdrv_replace_node() */
  95     bdrv_ref(top_bs);
  96     bdrv_ref(s->commit_top_bs);
  97
  98     if (s->base) {
  99         blk_unref(s->base);
 100     }
 101
 102     /* free the blockers on the intermediate nodes so that bdrv_replace_nodes
 103      * can succeed */
 104     block_job_remove_all_bdrv(&s->common);
 105
 106     /* If bdrv_drop_intermediate() failed (or was not invoked), remove the
 107      * commit filter driver from the backing chain now. Do this as the final
 108      * step so that the 'consistent read' permission can be granted.
 109      *
 110      * XXX Can (or should) we somehow keep 'consistent read' blocked even
 111      * after the failed/cancelled commit job is gone? If we already wrote
 112      * something to base, the intermediate images aren't valid any more. */
 113     bdrv_child_try_set_perm(s->commit_top_bs->backing, 0, BLK_PERM_ALL,
 114                             &error_abort);
 115     bdrv_replace_node(s->commit_top_bs, backing_bs(s->commit_top_bs),
 116                       &error_abort);
 117
 118     bdrv_unref(s->commit_top_bs);
 119     bdrv_unref(top_bs);
 120 }
 121
 122 static void commit_clean(Job *job)
 123 {
 124     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
 125
 126     /* restore base open flags here if appropriate (e.g., change the base back
 127      * to r/o). These reopens do not need to be atomic, since we won't abort
 128      * even on failure here */
 129     if (s->base_read_only) {
 130         bdrv_reopen_set_read_only(s->base_bs, true, NULL);
 131     }
 132
 133     g_free(s->backing_file_str);
 134     blk_unref(s->top);
 135 }
 136
 137 static int coroutine_fn commit_run(Job *job, Error **errp)
 138 {
 139     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
 140     int64_t offset;
 141     uint64_t delay_ns = 0;
 142     int ret = 0;
 143     int64_t n = 0; /* bytes */
 144     void *buf = NULL;
 145     int bytes_written = 0;
 146     int64_t len, base_len;
 147
 148     ret = len = blk_getlength(s->top);
 149     if (len < 0) {
 150         goto out;
 151     }
 152     job_progress_set_remaining(&s->common.job, len);
 153
 154     ret = base_len = blk_getlength(s->base);
 155     if (base_len < 0) {
 156         goto out;
 157     }
 158
 159     if (base_len < len) {
 160         ret = blk_truncate(s->base, len, PREALLOC_MODE_OFF, NULL);
 161         if (ret) {
 162             goto out;
 163         }
 164     }
 165
 166     buf = blk_blockalign(s->top, COMMIT_BUFFER_SIZE);
 167
 168     for (offset = 0; offset < len; offset += n) {
 169         bool copy;
 170
 171         /* Note that even when no rate limit is applied we need to yield
 172          * with no pending I/O here so that bdrv_drain_all() returns.
 173          */
 174         job_sleep_ns(&s->common.job, delay_ns);
 175         if (job_is_cancelled(&s->common.job)) {
 176             break;
 177         }
 178         /* Copy if allocated above the base */
 179         ret = bdrv_is_allocated_above(blk_bs(s->top), blk_bs(s->base),
 180                                       offset, COMMIT_BUFFER_SIZE, &n);
 181         copy = (ret == 1);
 182         trace_commit_one_iteration(s, offset, n, ret);
 183         if (copy) {
 184             ret = commit_populate(s->top, s->base, offset, n, buf);
 185             bytes_written += n;
 186         }
 187         if (ret < 0) {
 188             BlockErrorAction action =
 189                 block_job_error_action(&s->common, false, s->on_error, -ret);
 190             if (action == BLOCK_ERROR_ACTION_REPORT) {
 191                 goto out;
 192             } else {
 193                 n = 0;
 194                 continue;
 195             }
 196         }
 197         /* Publish progress */
 198         job_progress_update(&s->common.job, n);
 199
 200         if (copy) {
 201             delay_ns = block_job_ratelimit_get_delay(&s->common, n);
 202         } else {
 203             delay_ns = 0;
 204         }
 205     }
 206
 207     ret = 0;
 208
 209 out:
 210     qemu_vfree(buf);
 211
 212     return ret;
 213 }
 214
 215 static const BlockJobDriver commit_job_driver = {
 216     .job_driver = {
 217         .instance_size = sizeof(CommitBlockJob),
 218         .job_type      = JOB_TYPE_COMMIT,
 219         .free          = block_job_free,
 220         .user_resume   = block_job_user_resume,
 221         .drain         = block_job_drain,
 222         .run           = commit_run,
 223         .prepare       = commit_prepare,
 224         .abort         = commit_abort,
 225         .clean         = commit_clean
 226     },
 227 };
 228
 229 static int coroutine_fn bdrv_commit_top_preadv(BlockDriverState *bs,
 230     uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags)
 231 {
 232     return bdrv_co_preadv(bs->backing, offset, bytes, qiov, flags);
 233 }
 234
 235 static void bdrv_commit_top_refresh_filename(BlockDriverState *bs)
 236 {
 237     pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
 238             bs->backing->bs->filename);
 239 }
 240
 241 static void bdrv_commit_top_child_perm(BlockDriverState *bs, BdrvChild *c,
 242                                        const BdrvChildRole *role,
 243                                        BlockReopenQueue *reopen_queue,
 244                                        uint64_t perm, uint64_t shared,
 245                                        uint64_t *nperm, uint64_t *nshared)
 246 {
 247     *nperm = 0;
 248     *nshared = BLK_PERM_ALL;
 249 }
 250
 251 /* Dummy node that provides consistent read to its users without requiring it
 252  * from its backing file and that allows writes on the backing file chain. */
 253 static BlockDriver bdrv_commit_top = {
 254     .format_name                = "commit_top",
 255     .bdrv_co_preadv             = bdrv_commit_top_preadv,
 256     .bdrv_co_block_status       = bdrv_co_block_status_from_backing,
 257     .bdrv_refresh_filename      = bdrv_commit_top_refresh_filename,
 258     .bdrv_child_perm            = bdrv_commit_top_child_perm,
 259 };
 260
 261 void commit_start(const char *job_id, BlockDriverState *bs,
 262                   BlockDriverState *base, BlockDriverState *top,
 263                   int creation_flags, int64_t speed,
 264                   BlockdevOnError on_error, const char *backing_file_str,
 265                   const char *filter_node_name, Error **errp)
 266 {
 267     CommitBlockJob *s;
 268     BlockDriverState *iter;
 269     BlockDriverState *commit_top_bs = NULL;
 270     Error *local_err = NULL;
 271     int ret;
 272
 273     assert(top != bs);
 274     if (top == base) {
 275         error_setg(errp, "Invalid files for merge: top and base are the same");
 276         return;
 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     commit_top_bs->total_sectors = top->total_sectors;
 304     bdrv_set_aio_context(commit_top_bs, bdrv_get_aio_context(top));
 305
 306     bdrv_set_backing_hd(commit_top_bs, top, &local_err);
 307     if (local_err) {
 308         bdrv_unref(commit_top_bs);
 309         commit_top_bs = NULL;
 310         error_propagate(errp, local_err);
 311         goto fail;
 312     }
 313     bdrv_replace_node(top, commit_top_bs, &local_err);
 314     if (local_err) {
 315         bdrv_unref(commit_top_bs);
 316         commit_top_bs = NULL;
 317         error_propagate(errp, local_err);
 318         goto fail;
 319     }
 320
 321     s->commit_top_bs = commit_top_bs;
 322     bdrv_unref(commit_top_bs);
 323
 324     /* Block all nodes between top and base, because they will
 325      * disappear from the chain after this operation. */
 326     assert(bdrv_chain_contains(top, base));
 327     for (iter = top; iter != base; iter = backing_bs(iter)) {
 328         /* XXX BLK_PERM_WRITE needs to be allowed so we don't block ourselves
 329          * at s->base (if writes are blocked for a node, they are also blocked
 330          * for its backing file). The other options would be a second filter
 331          * driver above s->base. */
 332         ret = block_job_add_bdrv(&s->common, "intermediate node", iter, 0,
 333                                  BLK_PERM_WRITE_UNCHANGED | BLK_PERM_WRITE,
 334                                  errp);
 335         if (ret < 0) {
 336             goto fail;
 337         }
 338     }
 339
 340     if (bdrv_freeze_backing_chain(commit_top_bs, base, errp) < 0) {
 341         goto fail;
 342     }
 343     s->chain_frozen = true;
 344
 345     ret = block_job_add_bdrv(&s->common, "base", base, 0, BLK_PERM_ALL, errp);
 346     if (ret < 0) {
 347         goto fail;
 348     }
 349
 350     s->base = blk_new(BLK_PERM_CONSISTENT_READ
 351                       | BLK_PERM_WRITE
 352                       | BLK_PERM_RESIZE,
 353                       BLK_PERM_CONSISTENT_READ
 354                       | BLK_PERM_GRAPH_MOD
 355                       | BLK_PERM_WRITE_UNCHANGED);
 356     ret = blk_insert_bs(s->base, base, errp);
 357     if (ret < 0) {
 358         goto fail;
 359     }
 360     s->base_bs = base;
 361
 362     /* Required permissions are already taken with block_job_add_bdrv() */
 363     s->top = blk_new(0, BLK_PERM_ALL);
 364     ret = blk_insert_bs(s->top, top, errp);
 365     if (ret < 0) {
 366         goto fail;
 367     }
 368
 369     s->backing_file_str = g_strdup(backing_file_str);
 370     s->on_error = on_error;
 371
 372     trace_commit_start(bs, base, top, s);
 373     job_start(&s->common.job);
 374     return;
 375
 376 fail:
 377     if (s->chain_frozen) {
 378         bdrv_unfreeze_backing_chain(commit_top_bs, base);
 379     }
 380     if (s->base) {
 381         blk_unref(s->base);
 382     }
 383     if (s->top) {
 384         blk_unref(s->top);
 385     }
 386     if (s->base_read_only) {
 387         bdrv_reopen_set_read_only(base, true, NULL);
 388     }
 389     job_early_fail(&s->common.job);
 390     /* commit_top_bs has to be replaced after deleting the block job,
 391      * otherwise this would fail because of lack of permissions. */
 392     if (commit_top_bs) {
 393         bdrv_replace_node(commit_top_bs, top, &error_abort);
 394     }
 395 }
 396
 397
 398 #define COMMIT_BUF_SIZE (2048 * BDRV_SECTOR_SIZE)
 399
 400 /* commit COW file into the raw image */
 401 int bdrv_commit(BlockDriverState *bs)
 402 {
 403     BlockBackend *src, *backing;
 404     BlockDriverState *backing_file_bs = NULL;
 405     BlockDriverState *commit_top_bs = NULL;
 406     BlockDriver *drv = bs->drv;
 407     int64_t offset, length, backing_length;
 408     int ro;
 409     int64_t n;
 410     int ret = 0;
 411     uint8_t *buf = NULL;
 412     Error *local_err = NULL;
 413
 414     if (!drv)
 415         return -ENOMEDIUM;
 416
 417     if (!bs->backing) {
 418         return -ENOTSUP;
 419     }
 420
 421     if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_COMMIT_SOURCE, NULL) ||
 422         bdrv_op_is_blocked(bs->backing->bs, BLOCK_OP_TYPE_COMMIT_TARGET, NULL)) {
 423         return -EBUSY;
 424     }
 425
 426     ro = bs->backing->bs->read_only;
 427
 428     if (ro) {
 429         if (bdrv_reopen_set_read_only(bs->backing->bs, false, NULL)) {
 430             return -EACCES;
 431         }
 432     }
 433
 434     src = blk_new(BLK_PERM_CONSISTENT_READ, BLK_PERM_ALL);
 435     backing = blk_new(BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL);
 436
 437     ret = blk_insert_bs(src, bs, &local_err);
 438     if (ret < 0) {
 439         error_report_err(local_err);
 440         goto ro_cleanup;
 441     }
 442
 443     /* Insert commit_top block node above backing, so we can write to it */
 444     backing_file_bs = backing_bs(bs);
 445
 446     commit_top_bs = bdrv_new_open_driver(&bdrv_commit_top, NULL, BDRV_O_RDWR,
 447                                          &local_err);
 448     if (commit_top_bs == NULL) {
 449         error_report_err(local_err);
 450         goto ro_cleanup;
 451     }
 452     bdrv_set_aio_context(commit_top_bs, bdrv_get_aio_context(backing_file_bs));
 453
 454     bdrv_set_backing_hd(commit_top_bs, backing_file_bs, &error_abort);
 455     bdrv_set_backing_hd(bs, commit_top_bs, &error_abort);
 456
 457     ret = blk_insert_bs(backing, backing_file_bs, &local_err);
 458     if (ret < 0) {
 459         error_report_err(local_err);
 460         goto ro_cleanup;
 461     }
 462
 463     length = blk_getlength(src);
 464     if (length < 0) {
 465         ret = length;
 466         goto ro_cleanup;
 467     }
 468
 469     backing_length = blk_getlength(backing);
 470     if (backing_length < 0) {
 471         ret = backing_length;
 472         goto ro_cleanup;
 473     }
 474
 475     /* If our top snapshot is larger than the backing file image,
 476      * grow the backing file image if possible.  If not possible,
 477      * we must return an error */
 478     if (length > backing_length) {
 479         ret = blk_truncate(backing, length, PREALLOC_MODE_OFF, &local_err);
 480         if (ret < 0) {
 481             error_report_err(local_err);
 482             goto ro_cleanup;
 483         }
 484     }
 485
 486     /* blk_try_blockalign() for src will choose an alignment that works for
 487      * backing as well, so no need to compare the alignment manually. */
 488     buf = blk_try_blockalign(src, COMMIT_BUF_SIZE);
 489     if (buf == NULL) {
 490         ret = -ENOMEM;
 491         goto ro_cleanup;
 492     }
 493
 494     for (offset = 0; offset < length; offset += n) {
 495         ret = bdrv_is_allocated(bs, offset, COMMIT_BUF_SIZE, &n);
 496         if (ret < 0) {
 497             goto ro_cleanup;
 498         }
 499         if (ret) {
 500             ret = blk_pread(src, offset, buf, n);
 501             if (ret < 0) {
 502                 goto ro_cleanup;
 503             }
 504
 505             ret = blk_pwrite(backing, offset, buf, n, 0);
 506             if (ret < 0) {
 507                 goto ro_cleanup;
 508             }
 509         }
 510     }
 511
 512     if (drv->bdrv_make_empty) {
 513         ret = drv->bdrv_make_empty(bs);
 514         if (ret < 0) {
 515             goto ro_cleanup;
 516         }
 517         blk_flush(src);
 518     }
 519
 520     /*
 521      * Make sure all data we wrote to the backing device is actually
 522      * stable on disk.
 523      */
 524     blk_flush(backing);
 525
 526     ret = 0;
 527 ro_cleanup:
 528     qemu_vfree(buf);
 529
 530     blk_unref(backing);
 531     if (backing_file_bs) {
 532         bdrv_set_backing_hd(bs, backing_file_bs, &error_abort);
 533     }
 534     bdrv_unref(commit_top_bs);
 535     blk_unref(src);
 536
 537     if (ro) {
 538         /* ignoring error return here */
 539         bdrv_reopen_set_read_only(bs->backing->bs, true, NULL);
 540     }
 541
 542     return ret;
 543 }