block/copy-before-write.c

   1 /*
   2  * copy-before-write filter driver
   3  *
   4  * The driver performs Copy-Before-Write (CBW) operation: it is injected above
   5  * some node, and before each write it copies _old_ data to the target node.
   6  *
   7  * Copyright (c) 2018-2021 Virtuozzo International GmbH.
   8  *
   9  * Author:
  10  *  Sementsov-Ogievskiy Vladimir <vsementsov@virtuozzo.com>
  11  *
  12  * This program is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU General Public License as published by
  14  * the Free Software Foundation; either version 2 of the License, or
  15  * (at your option) any later version.
  16  *
  17  * This program is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  24  */
  25
  26 #include "qemu/osdep.h"
  27 #include "qapi/qmp/qjson.h"
  28
  29 #include "sysemu/block-backend.h"
  30 #include "qemu/cutils.h"
  31 #include "qapi/error.h"
  32 #include "block/block_int.h"
  33 #include "block/qdict.h"
  34 #include "block/block-copy.h"
  35 #include "block/dirty-bitmap.h"
  36
  37 #include "block/copy-before-write.h"
  38 #include "block/reqlist.h"
  39
  40 #include "qapi/qapi-visit-block-core.h"
  41
  42 typedef struct BDRVCopyBeforeWriteState {
  43     BlockCopyState *bcs;
  44     BdrvChild *target;
  45     OnCbwError on_cbw_error;
  46     uint32_t cbw_timeout_ns;
  47
  48     /*
  49      * @lock: protects access to @access_bitmap, @done_bitmap and
  50      * @frozen_read_reqs
  51      */
  52     CoMutex lock;
  53
  54     /*
  55      * @access_bitmap: represents areas allowed for reading by fleecing user.
  56      * Reading from non-dirty areas leads to -EACCES.
  57      */
  58     BdrvDirtyBitmap *access_bitmap;
  59
  60     /*
  61      * @done_bitmap: represents areas that was successfully copied to @target by
  62      * copy-before-write operations.
  63      */
  64     BdrvDirtyBitmap *done_bitmap;
  65
  66     /*
  67      * @frozen_read_reqs: current read requests for fleecing user in bs->file
  68      * node. These areas must not be rewritten by guest.
  69      */
  70     BlockReqList frozen_read_reqs;
  71
  72     /*
  73      * @snapshot_error is normally zero. But on first copy-before-write failure
  74      * when @on_cbw_error == ON_CBW_ERROR_BREAK_SNAPSHOT, @snapshot_error takes
  75      * value of this error (<0). After that all in-flight and further
  76      * snapshot-API requests will fail with that error.
  77      */
  78     int snapshot_error;
  79 } BDRVCopyBeforeWriteState;
  80
  81 static coroutine_fn int cbw_co_preadv(
  82         BlockDriverState *bs, int64_t offset, int64_t bytes,
  83         QEMUIOVector *qiov, BdrvRequestFlags flags)
  84 {
  85     return bdrv_co_preadv(bs->file, offset, bytes, qiov, flags);
  86 }
  87
  88 static void block_copy_cb(void *opaque)
  89 {
  90     BlockDriverState *bs = opaque;
  91
  92     bdrv_dec_in_flight(bs);
  93 }
  94
  95 /*
  96  * Do copy-before-write operation.
  97  *
  98  * On failure guest request must be failed too.
  99  *
 100  * On success, we also wait for all in-flight fleecing read requests in source
 101  * node, and it's guaranteed that after cbw_do_copy_before_write() successful
 102  * return there are no such requests and they will never appear.
 103  */
 104 static coroutine_fn int cbw_do_copy_before_write(BlockDriverState *bs,
 105         uint64_t offset, uint64_t bytes, BdrvRequestFlags flags)
 106 {
 107     BDRVCopyBeforeWriteState *s = bs->opaque;
 108     int ret;
 109     uint64_t off, end;
 110     int64_t cluster_size = block_copy_cluster_size(s->bcs);
 111
 112     if (flags & BDRV_REQ_WRITE_UNCHANGED) {
 113         return 0;
 114     }
 115
 116     if (s->snapshot_error) {
 117         return 0;
 118     }
 119
 120     off = QEMU_ALIGN_DOWN(offset, cluster_size);
 121     end = QEMU_ALIGN_UP(offset + bytes, cluster_size);
 122
 123     /*
 124      * Increase in_flight, so that in case of timed-out block-copy, the
 125      * remaining background block_copy() request (which can't be immediately
 126      * cancelled by timeout) is presented in bs->in_flight. This way we are
 127      * sure that on bs close() we'll previously wait for all timed-out but yet
 128      * running block_copy calls.
 129      */
 130     bdrv_inc_in_flight(bs);
 131     ret = block_copy(s->bcs, off, end - off, true, s->cbw_timeout_ns,
 132                      block_copy_cb, bs);
 133     if (ret < 0 && s->on_cbw_error == ON_CBW_ERROR_BREAK_GUEST_WRITE) {
 134         return ret;
 135     }
 136
 137     WITH_QEMU_LOCK_GUARD(&s->lock) {
 138         if (ret < 0) {
 139             assert(s->on_cbw_error == ON_CBW_ERROR_BREAK_SNAPSHOT);
 140             if (!s->snapshot_error) {
 141                 s->snapshot_error = ret;
 142             }
 143         } else {
 144             bdrv_set_dirty_bitmap(s->done_bitmap, off, end - off);
 145         }
 146         reqlist_wait_all(&s->frozen_read_reqs, off, end - off, &s->lock);
 147     }
 148
 149     return 0;
 150 }
 151
 152 static int coroutine_fn cbw_co_pdiscard(BlockDriverState *bs,
 153                                         int64_t offset, int64_t bytes)
 154 {
 155     int ret = cbw_do_copy_before_write(bs, offset, bytes, 0);
 156     if (ret < 0) {
 157         return ret;
 158     }
 159
 160     return bdrv_co_pdiscard(bs->file, offset, bytes);
 161 }
 162
 163 static int coroutine_fn cbw_co_pwrite_zeroes(BlockDriverState *bs,
 164         int64_t offset, int64_t bytes, BdrvRequestFlags flags)
 165 {
 166     int ret = cbw_do_copy_before_write(bs, offset, bytes, flags);
 167     if (ret < 0) {
 168         return ret;
 169     }
 170
 171     return bdrv_co_pwrite_zeroes(bs->file, offset, bytes, flags);
 172 }
 173
 174 static coroutine_fn int cbw_co_pwritev(BlockDriverState *bs,
 175                                        int64_t offset,
 176                                        int64_t bytes,
 177                                        QEMUIOVector *qiov,
 178                                        BdrvRequestFlags flags)
 179 {
 180     int ret = cbw_do_copy_before_write(bs, offset, bytes, flags);
 181     if (ret < 0) {
 182         return ret;
 183     }
 184
 185     return bdrv_co_pwritev(bs->file, offset, bytes, qiov, flags);
 186 }
 187
 188 static int coroutine_fn cbw_co_flush(BlockDriverState *bs)
 189 {
 190     if (!bs->file) {
 191         return 0;
 192     }
 193
 194     return bdrv_co_flush(bs->file->bs);
 195 }
 196
 197 /*
 198  * If @offset not accessible - return NULL.
 199  *
 200  * Otherwise, set @pnum to some bytes that accessible from @file (@file is set
 201  * to bs->file or to s->target). Return newly allocated BlockReq object that
 202  * should be than passed to cbw_snapshot_read_unlock().
 203  *
 204  * It's guaranteed that guest writes will not interact in the region until
 205  * cbw_snapshot_read_unlock() called.
 206  */
 207 static coroutine_fn BlockReq *
 208 cbw_snapshot_read_lock(BlockDriverState *bs, int64_t offset, int64_t bytes,
 209                        int64_t *pnum, BdrvChild **file)
 210 {
 211     BDRVCopyBeforeWriteState *s = bs->opaque;
 212     BlockReq *req = g_new(BlockReq, 1);
 213     bool done;
 214
 215     QEMU_LOCK_GUARD(&s->lock);
 216
 217     if (s->snapshot_error) {
 218         g_free(req);
 219         return NULL;
 220     }
 221
 222     if (bdrv_dirty_bitmap_next_zero(s->access_bitmap, offset, bytes) != -1) {
 223         g_free(req);
 224         return NULL;
 225     }
 226
 227     done = bdrv_dirty_bitmap_status(s->done_bitmap, offset, bytes, pnum);
 228     if (done) {
 229         /*
 230          * Special invalid BlockReq, that is handled in
 231          * cbw_snapshot_read_unlock(). We don't need to lock something to read
 232          * from s->target.
 233          */
 234         *req = (BlockReq) {.offset = -1, .bytes = -1};
 235         *file = s->target;
 236     } else {
 237         reqlist_init_req(&s->frozen_read_reqs, req, offset, bytes);
 238         *file = bs->file;
 239     }
 240
 241     return req;
 242 }
 243
 244 static coroutine_fn void
 245 cbw_snapshot_read_unlock(BlockDriverState *bs, BlockReq *req)
 246 {
 247     BDRVCopyBeforeWriteState *s = bs->opaque;
 248
 249     if (req->offset == -1 && req->bytes == -1) {
 250         g_free(req);
 251         return;
 252     }
 253
 254     QEMU_LOCK_GUARD(&s->lock);
 255
 256     reqlist_remove_req(req);
 257     g_free(req);
 258 }
 259
 260 static coroutine_fn int
 261 cbw_co_preadv_snapshot(BlockDriverState *bs, int64_t offset, int64_t bytes,
 262                        QEMUIOVector *qiov, size_t qiov_offset)
 263 {
 264     BlockReq *req;
 265     BdrvChild *file;
 266     int ret;
 267
 268     /* TODO: upgrade to async loop using AioTask */
 269     while (bytes) {
 270         int64_t cur_bytes;
 271
 272         req = cbw_snapshot_read_lock(bs, offset, bytes, &cur_bytes, &file);
 273         if (!req) {
 274             return -EACCES;
 275         }
 276
 277         ret = bdrv_co_preadv_part(file, offset, cur_bytes,
 278                                   qiov, qiov_offset, 0);
 279         cbw_snapshot_read_unlock(bs, req);
 280         if (ret < 0) {
 281             return ret;
 282         }
 283
 284         bytes -= cur_bytes;
 285         offset += cur_bytes;
 286         qiov_offset += cur_bytes;
 287     }
 288
 289     return 0;
 290 }
 291
 292 static int coroutine_fn
 293 cbw_co_snapshot_block_status(BlockDriverState *bs,
 294                              bool want_zero, int64_t offset, int64_t bytes,
 295                              int64_t *pnum, int64_t *map,
 296                              BlockDriverState **file)
 297 {
 298     BDRVCopyBeforeWriteState *s = bs->opaque;
 299     BlockReq *req;
 300     int ret;
 301     int64_t cur_bytes;
 302     BdrvChild *child;
 303
 304     req = cbw_snapshot_read_lock(bs, offset, bytes, &cur_bytes, &child);
 305     if (!req) {
 306         return -EACCES;
 307     }
 308
 309     ret = bdrv_block_status(child->bs, offset, cur_bytes, pnum, map, file);
 310     if (child == s->target) {
 311         /*
 312          * We refer to s->target only for areas that we've written to it.
 313          * And we can not report unallocated blocks in s->target: this will
 314          * break generic block-status-above logic, that will go to
 315          * copy-before-write filtered child in this case.
 316          */
 317         assert(ret & BDRV_BLOCK_ALLOCATED);
 318     }
 319
 320     cbw_snapshot_read_unlock(bs, req);
 321
 322     return ret;
 323 }
 324
 325 static int coroutine_fn cbw_co_pdiscard_snapshot(BlockDriverState *bs,
 326                                                  int64_t offset, int64_t bytes)
 327 {
 328     BDRVCopyBeforeWriteState *s = bs->opaque;
 329
 330     WITH_QEMU_LOCK_GUARD(&s->lock) {
 331         bdrv_reset_dirty_bitmap(s->access_bitmap, offset, bytes);
 332     }
 333
 334     block_copy_reset(s->bcs, offset, bytes);
 335
 336     return bdrv_co_pdiscard(s->target, offset, bytes);
 337 }
 338
 339 static void cbw_refresh_filename(BlockDriverState *bs)
 340 {
 341     pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
 342             bs->file->bs->filename);
 343 }
 344
 345 static void cbw_child_perm(BlockDriverState *bs, BdrvChild *c,
 346                            BdrvChildRole role,
 347                            BlockReopenQueue *reopen_queue,
 348                            uint64_t perm, uint64_t shared,
 349                            uint64_t *nperm, uint64_t *nshared)
 350 {
 351     if (!(role & BDRV_CHILD_FILTERED)) {
 352         /*
 353          * Target child
 354          *
 355          * Share write to target (child_file), to not interfere
 356          * with guest writes to its disk which may be in target backing chain.
 357          * Can't resize during a backup block job because we check the size
 358          * only upfront.
 359          */
 360         *nshared = BLK_PERM_ALL & ~BLK_PERM_RESIZE;
 361         *nperm = BLK_PERM_WRITE;
 362     } else {
 363         /* Source child */
 364         bdrv_default_perms(bs, c, role, reopen_queue,
 365                            perm, shared, nperm, nshared);
 366
 367         if (!QLIST_EMPTY(&bs->parents)) {
 368             if (perm & BLK_PERM_WRITE) {
 369                 *nperm = *nperm | BLK_PERM_CONSISTENT_READ;
 370             }
 371             *nshared &= ~(BLK_PERM_WRITE | BLK_PERM_RESIZE);
 372         }
 373     }
 374 }
 375
 376 static BlockdevOptions *cbw_parse_options(QDict *options, Error **errp)
 377 {
 378     BlockdevOptions *opts = NULL;
 379     Visitor *v = NULL;
 380
 381     qdict_put_str(options, "driver", "copy-before-write");
 382
 383     v = qobject_input_visitor_new_flat_confused(options, errp);
 384     if (!v) {
 385         goto out;
 386     }
 387
 388     visit_type_BlockdevOptions(v, NULL, &opts, errp);
 389     if (!opts) {
 390         goto out;
 391     }
 392
 393     /*
 394      * Delete options which we are going to parse through BlockdevOptions
 395      * object for original options.
 396      */
 397     qdict_extract_subqdict(options, NULL, "bitmap");
 398     qdict_del(options, "on-cbw-error");
 399     qdict_del(options, "cbw-timeout");
 400
 401 out:
 402     visit_free(v);
 403     qdict_del(options, "driver");
 404
 405     return opts;
 406 }
 407
 408 static int cbw_open(BlockDriverState *bs, QDict *options, int flags,
 409                     Error **errp)
 410 {
 411     BDRVCopyBeforeWriteState *s = bs->opaque;
 412     BdrvDirtyBitmap *bitmap = NULL;
 413     int64_t cluster_size;
 414     g_autoptr(BlockdevOptions) full_opts = NULL;
 415     BlockdevOptionsCbw *opts;
 416     int ret;
 417
 418     full_opts = cbw_parse_options(options, errp);
 419     if (!full_opts) {
 420         return -EINVAL;
 421     }
 422     assert(full_opts->driver == BLOCKDEV_DRIVER_COPY_BEFORE_WRITE);
 423     opts = &full_opts->u.copy_before_write;
 424
 425     ret = bdrv_open_file_child(NULL, options, "file", bs, errp);
 426     if (ret < 0) {
 427         return ret;
 428     }
 429
 430     s->target = bdrv_open_child(NULL, options, "target", bs, &child_of_bds,
 431                                 BDRV_CHILD_DATA, false, errp);
 432     if (!s->target) {
 433         return -EINVAL;
 434     }
 435
 436     if (opts->bitmap) {
 437         bitmap = block_dirty_bitmap_lookup(opts->bitmap->node,
 438                                            opts->bitmap->name, NULL, errp);
 439         if (!bitmap) {
 440             return -EINVAL;
 441         }
 442     }
 443     s->on_cbw_error = opts->has_on_cbw_error ? opts->on_cbw_error :
 444             ON_CBW_ERROR_BREAK_GUEST_WRITE;
 445     s->cbw_timeout_ns = opts->has_cbw_timeout ?
 446         opts->cbw_timeout * NANOSECONDS_PER_SECOND : 0;
 447
 448     bs->total_sectors = bs->file->bs->total_sectors;
 449     bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
 450             (BDRV_REQ_FUA & bs->file->bs->supported_write_flags);
 451     bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
 452             ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
 453              bs->file->bs->supported_zero_flags);
 454
 455     s->bcs = block_copy_state_new(bs->file, s->target, bitmap, errp);
 456     if (!s->bcs) {
 457         error_prepend(errp, "Cannot create block-copy-state: ");
 458         return -EINVAL;
 459     }
 460
 461     cluster_size = block_copy_cluster_size(s->bcs);
 462
 463     s->done_bitmap = bdrv_create_dirty_bitmap(bs, cluster_size, NULL, errp);
 464     if (!s->done_bitmap) {
 465         return -EINVAL;
 466     }
 467     bdrv_disable_dirty_bitmap(s->done_bitmap);
 468
 469     /* s->access_bitmap starts equal to bcs bitmap */
 470     s->access_bitmap = bdrv_create_dirty_bitmap(bs, cluster_size, NULL, errp);
 471     if (!s->access_bitmap) {
 472         return -EINVAL;
 473     }
 474     bdrv_disable_dirty_bitmap(s->access_bitmap);
 475     bdrv_dirty_bitmap_merge_internal(s->access_bitmap,
 476                                      block_copy_dirty_bitmap(s->bcs), NULL,
 477                                      true);
 478
 479     qemu_co_mutex_init(&s->lock);
 480     QLIST_INIT(&s->frozen_read_reqs);
 481
 482     return 0;
 483 }
 484
 485 static void cbw_close(BlockDriverState *bs)
 486 {
 487     BDRVCopyBeforeWriteState *s = bs->opaque;
 488
 489     bdrv_release_dirty_bitmap(s->access_bitmap);
 490     bdrv_release_dirty_bitmap(s->done_bitmap);
 491
 492     block_copy_state_free(s->bcs);
 493     s->bcs = NULL;
 494 }
 495
 496 BlockDriver bdrv_cbw_filter = {
 497     .format_name = "copy-before-write",
 498     .instance_size = sizeof(BDRVCopyBeforeWriteState),
 499
 500     .bdrv_open                  = cbw_open,
 501     .bdrv_close                 = cbw_close,
 502
 503     .bdrv_co_preadv             = cbw_co_preadv,
 504     .bdrv_co_pwritev            = cbw_co_pwritev,
 505     .bdrv_co_pwrite_zeroes      = cbw_co_pwrite_zeroes,
 506     .bdrv_co_pdiscard           = cbw_co_pdiscard,
 507     .bdrv_co_flush              = cbw_co_flush,
 508
 509     .bdrv_co_preadv_snapshot       = cbw_co_preadv_snapshot,
 510     .bdrv_co_pdiscard_snapshot     = cbw_co_pdiscard_snapshot,
 511     .bdrv_co_snapshot_block_status = cbw_co_snapshot_block_status,
 512
 513     .bdrv_refresh_filename      = cbw_refresh_filename,
 514
 515     .bdrv_child_perm            = cbw_child_perm,
 516
 517     .is_filter = true,
 518 };
 519
 520 BlockDriverState *bdrv_cbw_append(BlockDriverState *source,
 521                                   BlockDriverState *target,
 522                                   const char *filter_node_name,
 523                                   BlockCopyState **bcs,
 524                                   Error **errp)
 525 {
 526     BDRVCopyBeforeWriteState *state;
 527     BlockDriverState *top;
 528     QDict *opts;
 529
 530     assert(source->total_sectors == target->total_sectors);
 531     GLOBAL_STATE_CODE();
 532
 533     opts = qdict_new();
 534     qdict_put_str(opts, "driver", "copy-before-write");
 535     if (filter_node_name) {
 536         qdict_put_str(opts, "node-name", filter_node_name);
 537     }
 538     qdict_put_str(opts, "file", bdrv_get_node_name(source));
 539     qdict_put_str(opts, "target", bdrv_get_node_name(target));
 540
 541     top = bdrv_insert_node(source, opts, BDRV_O_RDWR, errp);
 542     if (!top) {
 543         return NULL;
 544     }
 545
 546     state = top->opaque;
 547     *bcs = state->bcs;
 548
 549     return top;
 550 }
 551
 552 void bdrv_cbw_drop(BlockDriverState *bs)
 553 {
 554     GLOBAL_STATE_CODE();
 555     bdrv_drop_filter(bs, &error_abort);
 556     bdrv_unref(bs);
 557 }
 558
 559 static void cbw_init(void)
 560 {
 561     bdrv_register(&bdrv_cbw_filter);
 562 }
 563
 564 block_init(cbw_init);