block/blklogwrites.c

   1 /*
   2  * Write logging blk driver based on blkverify and blkdebug.
   3  *
   4  * Copyright (c) 2017 Tuomas Tynkkynen <tuomas@tuxera.com>
   5  * Copyright (c) 2018 Aapo Vienamo <aapo@tuxera.com>
   6  * Copyright (c) 2018-2024 Ari Sundholm <ari@tuxera.com>
   7  *
   8  * This work is licensed under the terms of the GNU GPL, version 2 or later.
   9  * See the COPYING file in the top-level directory.
  10  */
  11
  12 #include "qemu/osdep.h"
  13 #include "qapi/error.h"
  14 #include "qemu/sockets.h" /* for EINPROGRESS on Windows */
  15 #include "block/block-io.h"
  16 #include "block/block_int.h"
  17 #include "qapi/qmp/qdict.h"
  18 #include "qapi/qmp/qstring.h"
  19 #include "qemu/cutils.h"
  20 #include "qemu/module.h"
  21 #include "qemu/option.h"
  22
  23 /* Disk format stuff - taken from Linux drivers/md/dm-log-writes.c */
  24
  25 #define LOG_FLUSH_FLAG   (1 << 0)
  26 #define LOG_FUA_FLAG     (1 << 1)
  27 #define LOG_DISCARD_FLAG (1 << 2)
  28 #define LOG_MARK_FLAG    (1 << 3)
  29 #define LOG_FLAG_MASK    (LOG_FLUSH_FLAG \
  30                          | LOG_FUA_FLAG \
  31                          | LOG_DISCARD_FLAG \
  32                          | LOG_MARK_FLAG)
  33
  34 #define WRITE_LOG_VERSION 1ULL
  35 #define WRITE_LOG_MAGIC 0x6a736677736872ULL
  36
  37 /* All fields are little-endian. */
  38 struct log_write_super {
  39     uint64_t magic;
  40     uint64_t version;
  41     uint64_t nr_entries;
  42     uint32_t sectorsize;
  43 } QEMU_PACKED;
  44
  45 struct log_write_entry {
  46     uint64_t sector;
  47     uint64_t nr_sectors;
  48     uint64_t flags;
  49     uint64_t data_len;
  50 } QEMU_PACKED;
  51
  52 /* End of disk format structures. */
  53
  54 typedef struct {
  55     BdrvChild *log_file;
  56     uint32_t sectorsize;
  57     uint32_t sectorbits;
  58     uint64_t update_interval;
  59
  60     /*
  61      * The mutable state of the driver, consisting of the current log sector
  62      * and the number of log entries.
  63      *
  64      * May be read and/or written from multiple threads, and the mutex must be
  65      * held when accessing these fields.
  66      */
  67     uint64_t cur_log_sector;
  68     uint64_t nr_entries;
  69     QemuMutex mutex;
  70
  71     /*
  72      * The super block sequence number. Non-zero if a super block update is in
  73      * progress.
  74      *
  75      * The mutex must be held when accessing this field.
  76      */
  77     uint64_t super_update_seq;
  78
  79     /*
  80      * A coroutine-aware queue to serialize super block updates.
  81      *
  82      * Used with the mutex to ensure that only one thread be updating the super
  83      * block at a time.
  84      */
  85     CoQueue super_update_queue;
  86 } BDRVBlkLogWritesState;
  87
  88 static QemuOptsList runtime_opts = {
  89     .name = "blklogwrites",
  90     .head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),
  91     .desc = {
  92         {
  93             .name = "log-append",
  94             .type = QEMU_OPT_BOOL,
  95             .help = "Append to an existing log",
  96         },
  97         {
  98             .name = "log-sector-size",
  99             .type = QEMU_OPT_SIZE,
 100             .help = "Log sector size",
 101         },
 102         {
 103             .name = "log-super-update-interval",
 104             .type = QEMU_OPT_NUMBER,
 105             .help = "Log superblock update interval (# of write requests)",
 106         },
 107         { /* end of list */ }
 108     },
 109 };
 110
 111 static inline uint32_t blk_log_writes_log2(uint32_t value)
 112 {
 113     assert(value > 0);
 114     return 31 - clz32(value);
 115 }
 116
 117 static inline bool blk_log_writes_sector_size_valid(uint32_t sector_size)
 118 {
 119     return is_power_of_2(sector_size) &&
 120         sector_size >= sizeof(struct log_write_super) &&
 121         sector_size >= sizeof(struct log_write_entry) &&
 122         sector_size < (1ull << 24);
 123 }
 124
 125 static uint64_t blk_log_writes_find_cur_log_sector(BdrvChild *log,
 126                                                    uint32_t sector_size,
 127                                                    uint64_t nr_entries,
 128                                                    Error **errp)
 129 {
 130     uint64_t cur_sector = 1;
 131     uint64_t cur_idx = 0;
 132     uint32_t sector_bits = blk_log_writes_log2(sector_size);
 133     struct log_write_entry cur_entry;
 134
 135     while (cur_idx < nr_entries) {
 136         int read_ret = bdrv_pread(log, cur_sector << sector_bits,
 137                                   sizeof(cur_entry), &cur_entry, 0);
 138         if (read_ret < 0) {
 139             error_setg_errno(errp, -read_ret,
 140                              "Failed to read log entry %"PRIu64, cur_idx);
 141             return (uint64_t)-1ull;
 142         }
 143
 144         if (cur_entry.flags & ~cpu_to_le64(LOG_FLAG_MASK)) {
 145             error_setg(errp, "Invalid flags 0x%"PRIx64" in log entry %"PRIu64,
 146                        le64_to_cpu(cur_entry.flags), cur_idx);
 147             return (uint64_t)-1ull;
 148         }
 149
 150         /* Account for the sector of the entry itself */
 151         ++cur_sector;
 152
 153         /*
 154          * Account for the data of the write.
 155          * For discards, this data is not present.
 156          */
 157         if (!(cur_entry.flags & cpu_to_le64(LOG_DISCARD_FLAG))) {
 158             cur_sector += le64_to_cpu(cur_entry.nr_sectors);
 159         }
 160
 161         ++cur_idx;
 162     }
 163
 164     return cur_sector;
 165 }
 166
 167 static int blk_log_writes_open(BlockDriverState *bs, QDict *options, int flags,
 168                                Error **errp)
 169 {
 170     BDRVBlkLogWritesState *s = bs->opaque;
 171     QemuOpts *opts;
 172     Error *local_err = NULL;
 173     int ret;
 174     uint64_t log_sector_size;
 175     bool log_append;
 176
 177     opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
 178     if (!qemu_opts_absorb_qdict(opts, options, errp)) {
 179         ret = -EINVAL;
 180         goto fail;
 181     }
 182
 183     /* Open the file */
 184     ret = bdrv_open_file_child(NULL, options, "file", bs, errp);
 185     if (ret < 0) {
 186         goto fail;
 187     }
 188
 189     /* Open the log file */
 190     s->log_file = bdrv_open_child(NULL, options, "log", bs, &child_of_bds,
 191                                   BDRV_CHILD_METADATA, false, errp);
 192     if (!s->log_file) {
 193         ret = -EINVAL;
 194         goto fail;
 195     }
 196
 197     qemu_mutex_init(&s->mutex);
 198     qemu_co_queue_init(&s->super_update_queue);
 199
 200     log_append = qemu_opt_get_bool(opts, "log-append", false);
 201
 202     if (log_append) {
 203         struct log_write_super log_sb = { 0, 0, 0, 0 };
 204
 205         if (qemu_opt_find(opts, "log-sector-size")) {
 206             ret = -EINVAL;
 207             error_setg(errp, "log-append and log-sector-size are mutually "
 208                        "exclusive");
 209             goto fail_log;
 210         }
 211
 212         /* Read log superblock or fake one for an empty log */
 213         if (!bdrv_getlength(s->log_file->bs)) {
 214             log_sb.magic      = cpu_to_le64(WRITE_LOG_MAGIC);
 215             log_sb.version    = cpu_to_le64(WRITE_LOG_VERSION);
 216             log_sb.nr_entries = cpu_to_le64(0);
 217             log_sb.sectorsize = cpu_to_le32(BDRV_SECTOR_SIZE);
 218         } else {
 219             ret = bdrv_pread(s->log_file, 0, sizeof(log_sb), &log_sb, 0);
 220             if (ret < 0) {
 221                 error_setg_errno(errp, -ret, "Could not read log superblock");
 222                 goto fail_log;
 223             }
 224         }
 225
 226         if (log_sb.magic != cpu_to_le64(WRITE_LOG_MAGIC)) {
 227             ret = -EINVAL;
 228             error_setg(errp, "Invalid log superblock magic");
 229             goto fail_log;
 230         }
 231
 232         if (log_sb.version != cpu_to_le64(WRITE_LOG_VERSION)) {
 233             ret = -EINVAL;
 234             error_setg(errp, "Unsupported log version %"PRIu64,
 235                        le64_to_cpu(log_sb.version));
 236             goto fail_log;
 237         }
 238
 239         log_sector_size = le32_to_cpu(log_sb.sectorsize);
 240         s->cur_log_sector = 1;
 241         s->nr_entries = 0;
 242
 243         if (blk_log_writes_sector_size_valid(log_sector_size)) {
 244             s->cur_log_sector =
 245                 blk_log_writes_find_cur_log_sector(s->log_file, log_sector_size,
 246                                     le64_to_cpu(log_sb.nr_entries), &local_err);
 247             if (local_err) {
 248                 ret = -EINVAL;
 249                 error_propagate(errp, local_err);
 250                 goto fail_log;
 251             }
 252
 253             s->nr_entries = le64_to_cpu(log_sb.nr_entries);
 254         }
 255     } else {
 256         log_sector_size = qemu_opt_get_size(opts, "log-sector-size",
 257                                             BDRV_SECTOR_SIZE);
 258         s->cur_log_sector = 1;
 259         s->nr_entries = 0;
 260     }
 261
 262     s->super_update_seq = 0;
 263
 264     if (!blk_log_writes_sector_size_valid(log_sector_size)) {
 265         ret = -EINVAL;
 266         error_setg(errp, "Invalid log sector size %"PRIu64, log_sector_size);
 267         goto fail_log;
 268     }
 269
 270     s->sectorsize = log_sector_size;
 271     s->sectorbits = blk_log_writes_log2(log_sector_size);
 272     s->update_interval = qemu_opt_get_number(opts, "log-super-update-interval",
 273                                              4096);
 274     if (!s->update_interval) {
 275         ret = -EINVAL;
 276         error_setg(errp, "Invalid log superblock update interval %"PRIu64,
 277                    s->update_interval);
 278         goto fail_log;
 279     }
 280
 281     ret = 0;
 282 fail_log:
 283     if (ret < 0) {
 284         bdrv_graph_wrlock();
 285         bdrv_unref_child(bs, s->log_file);
 286         bdrv_graph_wrunlock();
 287         s->log_file = NULL;
 288         qemu_mutex_destroy(&s->mutex);
 289     }
 290 fail:
 291     qemu_opts_del(opts);
 292     return ret;
 293 }
 294
 295 static void blk_log_writes_close(BlockDriverState *bs)
 296 {
 297     BDRVBlkLogWritesState *s = bs->opaque;
 298
 299     bdrv_graph_wrlock();
 300     bdrv_unref_child(bs, s->log_file);
 301     s->log_file = NULL;
 302     bdrv_graph_wrunlock();
 303     qemu_mutex_destroy(&s->mutex);
 304 }
 305
 306 static int64_t coroutine_fn GRAPH_RDLOCK
 307 blk_log_writes_co_getlength(BlockDriverState *bs)
 308 {
 309     return bdrv_co_getlength(bs->file->bs);
 310 }
 311
 312 static void blk_log_writes_child_perm(BlockDriverState *bs, BdrvChild *c,
 313                                       BdrvChildRole role,
 314                                       BlockReopenQueue *ro_q,
 315                                       uint64_t perm, uint64_t shrd,
 316                                       uint64_t *nperm, uint64_t *nshrd)
 317 {
 318     if (!c) {
 319         *nperm = perm & DEFAULT_PERM_PASSTHROUGH;
 320         *nshrd = (shrd & DEFAULT_PERM_PASSTHROUGH) | DEFAULT_PERM_UNCHANGED;
 321         return;
 322     }
 323
 324     bdrv_default_perms(bs, c, role, ro_q, perm, shrd,
 325                        nperm, nshrd);
 326 }
 327
 328 static void blk_log_writes_refresh_limits(BlockDriverState *bs, Error **errp)
 329 {
 330     const BDRVBlkLogWritesState *s = bs->opaque;
 331     bs->bl.request_alignment = s->sectorsize;
 332 }
 333
 334 static int coroutine_fn GRAPH_RDLOCK
 335 blk_log_writes_co_preadv(BlockDriverState *bs, int64_t offset, int64_t bytes,
 336                          QEMUIOVector *qiov, BdrvRequestFlags flags)
 337 {
 338     return bdrv_co_preadv(bs->file, offset, bytes, qiov, flags);
 339 }
 340
 341 typedef struct BlkLogWritesFileReq {
 342     BlockDriverState *bs;
 343     uint64_t offset;
 344     uint64_t bytes;
 345     int file_flags;
 346     QEMUIOVector *qiov;
 347     int GRAPH_RDLOCK_PTR (*func)(struct BlkLogWritesFileReq *r);
 348     int file_ret;
 349 } BlkLogWritesFileReq;
 350
 351 typedef struct {
 352     BlockDriverState *bs;
 353     QEMUIOVector *qiov;
 354     struct log_write_entry entry;
 355     uint64_t zero_size;
 356     int log_ret;
 357 } BlkLogWritesLogReq;
 358
 359 static void coroutine_fn GRAPH_RDLOCK
 360 blk_log_writes_co_do_log(BlkLogWritesLogReq *lr)
 361 {
 362     BDRVBlkLogWritesState *s = lr->bs->opaque;
 363
 364     /*
 365      * Determine the offsets and sizes of different parts of the entry, and
 366      * update the state of the driver.
 367      *
 368      * This needs to be done in one go, before any actual I/O is done, as the
 369      * log entry may have to be written in two parts, and the state of the
 370      * driver may be modified by other driver operations while waiting for the
 371      * I/O to complete.
 372      */
 373     qemu_mutex_lock(&s->mutex);
 374     const uint64_t entry_start_sector = s->cur_log_sector;
 375     const uint64_t entry_offset = entry_start_sector << s->sectorbits;
 376     const uint64_t qiov_aligned_size = ROUND_UP(lr->qiov->size, s->sectorsize);
 377     const uint64_t entry_aligned_size = qiov_aligned_size +
 378         ROUND_UP(lr->zero_size, s->sectorsize);
 379     const uint64_t entry_nr_sectors = entry_aligned_size >> s->sectorbits;
 380     const uint64_t entry_seq = s->nr_entries + 1;
 381
 382     s->nr_entries = entry_seq;
 383     s->cur_log_sector += entry_nr_sectors;
 384     qemu_mutex_unlock(&s->mutex);
 385
 386     /*
 387      * Write the log entry. Note that if this is a "write zeroes" operation,
 388      * only the entry header is written here, with the zeroing being done
 389      * separately below.
 390      */
 391     lr->log_ret = bdrv_co_pwritev(s->log_file, entry_offset, lr->qiov->size,
 392                                   lr->qiov, 0);
 393
 394     /* Logging for the "write zeroes" operation */
 395     if (lr->log_ret == 0 && lr->zero_size) {
 396         const uint64_t zeroes_offset = entry_offset + qiov_aligned_size;
 397
 398         lr->log_ret = bdrv_co_pwrite_zeroes(s->log_file, zeroes_offset,
 399                                             lr->zero_size, 0);
 400     }
 401
 402     /* Update super block on flush or every update interval */
 403     if (lr->log_ret == 0 && ((lr->entry.flags & LOG_FLUSH_FLAG)
 404         || (entry_seq % s->update_interval == 0)))
 405     {
 406         struct log_write_super super = {
 407             .magic      = cpu_to_le64(WRITE_LOG_MAGIC),
 408             .version    = cpu_to_le64(WRITE_LOG_VERSION),
 409             .nr_entries = 0, /* updated below */
 410             .sectorsize = cpu_to_le32(s->sectorsize),
 411         };
 412         void *zeroes;
 413         QEMUIOVector qiov;
 414
 415         /*
 416          * Wait if a super block update is already in progress.
 417          * Bail out if a newer update got its turn before us.
 418          */
 419         WITH_QEMU_LOCK_GUARD(&s->mutex) {
 420             CoQueueWaitFlags wait_flags = 0;
 421             while (s->super_update_seq) {
 422                 if (entry_seq < s->super_update_seq) {
 423                     return;
 424                 }
 425                 qemu_co_queue_wait_flags(&s->super_update_queue,
 426                     &s->mutex, wait_flags);
 427
 428                 /*
 429                  * In case the wait condition remains true after wakeup,
 430                  * to avoid starvation, make sure that this request is
 431                  * scheduled to rerun next by pushing it to the front of the
 432                  * queue.
 433                  */
 434                 wait_flags = CO_QUEUE_WAIT_FRONT;
 435             }
 436             s->super_update_seq = entry_seq;
 437             super.nr_entries = cpu_to_le64(s->nr_entries);
 438         }
 439
 440         zeroes = g_malloc0(s->sectorsize - sizeof(super));
 441
 442         qemu_iovec_init(&qiov, 2);
 443         qemu_iovec_add(&qiov, &super, sizeof(super));
 444         qemu_iovec_add(&qiov, zeroes, s->sectorsize - sizeof(super));
 445
 446         lr->log_ret =
 447             bdrv_co_pwritev(s->log_file, 0, s->sectorsize, &qiov, 0);
 448         if (lr->log_ret == 0) {
 449             lr->log_ret = bdrv_co_flush(s->log_file->bs);
 450         }
 451
 452         /* The super block has been updated. Let another request have a go. */
 453         qemu_mutex_lock(&s->mutex);
 454         s->super_update_seq = 0;
 455         (void) qemu_co_queue_next(&s->super_update_queue);
 456         qemu_mutex_unlock(&s->mutex);
 457
 458         qemu_iovec_destroy(&qiov);
 459         g_free(zeroes);
 460     }
 461 }
 462
 463 static void coroutine_fn GRAPH_RDLOCK
 464 blk_log_writes_co_do_file(BlkLogWritesFileReq *fr)
 465 {
 466     fr->file_ret = fr->func(fr);
 467 }
 468
 469 static int coroutine_fn GRAPH_RDLOCK
 470 blk_log_writes_co_log(BlockDriverState *bs, uint64_t offset, uint64_t bytes,
 471                       QEMUIOVector *qiov, int flags,
 472                       int /*GRAPH_RDLOCK*/ (*file_func)(BlkLogWritesFileReq *r),
 473                       uint64_t entry_flags, bool is_zero_write)
 474 {
 475     QEMUIOVector log_qiov;
 476     size_t niov = qiov ? qiov->niov : 0;
 477     const BDRVBlkLogWritesState *s = bs->opaque;
 478     BlkLogWritesFileReq fr = {
 479         .bs         = bs,
 480         .offset     = offset,
 481         .bytes      = bytes,
 482         .file_flags = flags,
 483         .qiov       = qiov,
 484         .func       = file_func,
 485     };
 486     BlkLogWritesLogReq lr = {
 487         .bs             = bs,
 488         .qiov           = &log_qiov,
 489         .entry = {
 490             .sector     = cpu_to_le64(offset >> s->sectorbits),
 491             .nr_sectors = cpu_to_le64(bytes >> s->sectorbits),
 492             .flags      = cpu_to_le64(entry_flags),
 493             .data_len   = 0,
 494         },
 495         .zero_size = is_zero_write ? bytes : 0,
 496     };
 497     void *zeroes = g_malloc0(s->sectorsize - sizeof(lr.entry));
 498
 499     assert((1 << s->sectorbits) == s->sectorsize);
 500     assert(bs->bl.request_alignment == s->sectorsize);
 501     assert(QEMU_IS_ALIGNED(offset, bs->bl.request_alignment));
 502     assert(QEMU_IS_ALIGNED(bytes, bs->bl.request_alignment));
 503
 504     qemu_iovec_init(&log_qiov, niov + 2);
 505     qemu_iovec_add(&log_qiov, &lr.entry, sizeof(lr.entry));
 506     qemu_iovec_add(&log_qiov, zeroes, s->sectorsize - sizeof(lr.entry));
 507     if (qiov) {
 508         qemu_iovec_concat(&log_qiov, qiov, 0, qiov->size);
 509     }
 510
 511     blk_log_writes_co_do_file(&fr);
 512     blk_log_writes_co_do_log(&lr);
 513
 514     qemu_iovec_destroy(&log_qiov);
 515     g_free(zeroes);
 516
 517     if (lr.log_ret < 0) {
 518         return lr.log_ret;
 519     }
 520
 521     return fr.file_ret;
 522 }
 523
 524 static int coroutine_fn GRAPH_RDLOCK
 525 blk_log_writes_co_do_file_pwritev(BlkLogWritesFileReq *fr)
 526 {
 527     return bdrv_co_pwritev(fr->bs->file, fr->offset, fr->bytes,
 528                            fr->qiov, fr->file_flags);
 529 }
 530
 531 static int coroutine_fn GRAPH_RDLOCK
 532 blk_log_writes_co_do_file_pwrite_zeroes(BlkLogWritesFileReq *fr)
 533 {
 534     return bdrv_co_pwrite_zeroes(fr->bs->file, fr->offset, fr->bytes,
 535                                  fr->file_flags);
 536 }
 537
 538 static int coroutine_fn GRAPH_RDLOCK
 539 blk_log_writes_co_do_file_flush(BlkLogWritesFileReq *fr)
 540 {
 541     return bdrv_co_flush(fr->bs->file->bs);
 542 }
 543
 544 static int coroutine_fn GRAPH_RDLOCK
 545 blk_log_writes_co_do_file_pdiscard(BlkLogWritesFileReq *fr)
 546 {
 547     return bdrv_co_pdiscard(fr->bs->file, fr->offset, fr->bytes);
 548 }
 549
 550 static int coroutine_fn GRAPH_RDLOCK
 551 blk_log_writes_co_pwritev(BlockDriverState *bs, int64_t offset, int64_t bytes,
 552                           QEMUIOVector *qiov, BdrvRequestFlags flags)
 553 {
 554     return blk_log_writes_co_log(bs, offset, bytes, qiov, flags,
 555                                  blk_log_writes_co_do_file_pwritev, 0, false);
 556 }
 557
 558 static int coroutine_fn GRAPH_RDLOCK
 559 blk_log_writes_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset,
 560                                 int64_t bytes, BdrvRequestFlags flags)
 561 {
 562     return blk_log_writes_co_log(bs, offset, bytes, NULL, flags,
 563                                  blk_log_writes_co_do_file_pwrite_zeroes, 0,
 564                                  true);
 565 }
 566
 567 static int coroutine_fn GRAPH_RDLOCK
 568 blk_log_writes_co_flush_to_disk(BlockDriverState *bs)
 569 {
 570     return blk_log_writes_co_log(bs, 0, 0, NULL, 0,
 571                                  blk_log_writes_co_do_file_flush,
 572                                  LOG_FLUSH_FLAG, false);
 573 }
 574
 575 static int coroutine_fn GRAPH_RDLOCK
 576 blk_log_writes_co_pdiscard(BlockDriverState *bs, int64_t offset, int64_t bytes)
 577 {
 578     return blk_log_writes_co_log(bs, offset, bytes, NULL, 0,
 579                                  blk_log_writes_co_do_file_pdiscard,
 580                                  LOG_DISCARD_FLAG, false);
 581 }
 582
 583 static const char *const blk_log_writes_strong_runtime_opts[] = {
 584     "log-append",
 585     "log-sector-size",
 586
 587     NULL
 588 };
 589
 590 static BlockDriver bdrv_blk_log_writes = {
 591     .format_name            = "blklogwrites",
 592     .instance_size          = sizeof(BDRVBlkLogWritesState),
 593
 594     .bdrv_open              = blk_log_writes_open,
 595     .bdrv_close             = blk_log_writes_close,
 596     .bdrv_co_getlength      = blk_log_writes_co_getlength,
 597     .bdrv_child_perm        = blk_log_writes_child_perm,
 598     .bdrv_refresh_limits    = blk_log_writes_refresh_limits,
 599
 600     .bdrv_co_preadv         = blk_log_writes_co_preadv,
 601     .bdrv_co_pwritev        = blk_log_writes_co_pwritev,
 602     .bdrv_co_pwrite_zeroes  = blk_log_writes_co_pwrite_zeroes,
 603     .bdrv_co_flush_to_disk  = blk_log_writes_co_flush_to_disk,
 604     .bdrv_co_pdiscard       = blk_log_writes_co_pdiscard,
 605
 606     .is_filter              = true,
 607     .strong_runtime_opts    = blk_log_writes_strong_runtime_opts,
 608 };
 609
 610 static void bdrv_blk_log_writes_init(void)
 611 {
 612     bdrv_register(&bdrv_blk_log_writes);
 613 }
 614
 615 block_init(bdrv_blk_log_writes_init);