qemu/block/qcow2-cluster.c
<<
>>
Prefs
   1/*
   2 * Block driver for the QCOW version 2 format
   3 *
   4 * Copyright (c) 2004-2006 Fabrice Bellard
   5 *
   6 * Permission is hereby granted, free of charge, to any person obtaining a copy
   7 * of this software and associated documentation files (the "Software"), to deal
   8 * in the Software without restriction, including without limitation the rights
   9 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  10 * copies of the Software, and to permit persons to whom the Software is
  11 * furnished to do so, subject to the following conditions:
  12 *
  13 * The above copyright notice and this permission notice shall be included in
  14 * all copies or substantial portions of the Software.
  15 *
  16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  19 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  22 * THE SOFTWARE.
  23 */
  24
  25#include "qemu/osdep.h"
  26#include <zlib.h>
  27
  28#include "qapi/error.h"
  29#include "qcow2.h"
  30#include "qemu/bswap.h"
  31#include "trace.h"
  32
  33int qcow2_shrink_l1_table(BlockDriverState *bs, uint64_t exact_size)
  34{
  35    BDRVQcow2State *s = bs->opaque;
  36    int new_l1_size, i, ret;
  37
  38    if (exact_size >= s->l1_size) {
  39        return 0;
  40    }
  41
  42    new_l1_size = exact_size;
  43
  44#ifdef DEBUG_ALLOC2
  45    fprintf(stderr, "shrink l1_table from %d to %d\n", s->l1_size, new_l1_size);
  46#endif
  47
  48    BLKDBG_EVENT(bs->file, BLKDBG_L1_SHRINK_WRITE_TABLE);
  49    ret = bdrv_pwrite_zeroes(bs->file, s->l1_table_offset +
  50                                       new_l1_size * sizeof(uint64_t),
  51                             (s->l1_size - new_l1_size) * sizeof(uint64_t), 0);
  52    if (ret < 0) {
  53        goto fail;
  54    }
  55
  56    ret = bdrv_flush(bs->file->bs);
  57    if (ret < 0) {
  58        goto fail;
  59    }
  60
  61    BLKDBG_EVENT(bs->file, BLKDBG_L1_SHRINK_FREE_L2_CLUSTERS);
  62    for (i = s->l1_size - 1; i > new_l1_size - 1; i--) {
  63        if ((s->l1_table[i] & L1E_OFFSET_MASK) == 0) {
  64            continue;
  65        }
  66        qcow2_free_clusters(bs, s->l1_table[i] & L1E_OFFSET_MASK,
  67                            s->cluster_size, QCOW2_DISCARD_ALWAYS);
  68        s->l1_table[i] = 0;
  69    }
  70    return 0;
  71
  72fail:
  73    /*
  74     * If the write in the l1_table failed the image may contain a partially
  75     * overwritten l1_table. In this case it would be better to clear the
  76     * l1_table in memory to avoid possible image corruption.
  77     */
  78    memset(s->l1_table + new_l1_size, 0,
  79           (s->l1_size - new_l1_size) * sizeof(uint64_t));
  80    return ret;
  81}
  82
  83int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
  84                        bool exact_size)
  85{
  86    BDRVQcow2State *s = bs->opaque;
  87    int new_l1_size2, ret, i;
  88    uint64_t *new_l1_table;
  89    int64_t old_l1_table_offset, old_l1_size;
  90    int64_t new_l1_table_offset, new_l1_size;
  91    uint8_t data[12];
  92
  93    if (min_size <= s->l1_size)
  94        return 0;
  95
  96    /* Do a sanity check on min_size before trying to calculate new_l1_size
  97     * (this prevents overflows during the while loop for the calculation of
  98     * new_l1_size) */
  99    if (min_size > INT_MAX / sizeof(uint64_t)) {
 100        return -EFBIG;
 101    }
 102
 103    if (exact_size) {
 104        new_l1_size = min_size;
 105    } else {
 106        /* Bump size up to reduce the number of times we have to grow */
 107        new_l1_size = s->l1_size;
 108        if (new_l1_size == 0) {
 109            new_l1_size = 1;
 110        }
 111        while (min_size > new_l1_size) {
 112            new_l1_size = DIV_ROUND_UP(new_l1_size * 3, 2);
 113        }
 114    }
 115
 116    QEMU_BUILD_BUG_ON(QCOW_MAX_L1_SIZE > INT_MAX);
 117    if (new_l1_size > QCOW_MAX_L1_SIZE / sizeof(uint64_t)) {
 118        return -EFBIG;
 119    }
 120
 121#ifdef DEBUG_ALLOC2
 122    fprintf(stderr, "grow l1_table from %d to %" PRId64 "\n",
 123            s->l1_size, new_l1_size);
 124#endif
 125
 126    new_l1_size2 = sizeof(uint64_t) * new_l1_size;
 127    new_l1_table = qemu_try_blockalign(bs->file->bs, new_l1_size2);
 128    if (new_l1_table == NULL) {
 129        return -ENOMEM;
 130    }
 131    memset(new_l1_table, 0, new_l1_size2);
 132
 133    if (s->l1_size) {
 134        memcpy(new_l1_table, s->l1_table, s->l1_size * sizeof(uint64_t));
 135    }
 136
 137    /* write new table (align to cluster) */
 138    BLKDBG_EVENT(bs->file, BLKDBG_L1_GROW_ALLOC_TABLE);
 139    new_l1_table_offset = qcow2_alloc_clusters(bs, new_l1_size2);
 140    if (new_l1_table_offset < 0) {
 141        qemu_vfree(new_l1_table);
 142        return new_l1_table_offset;
 143    }
 144
 145    ret = qcow2_cache_flush(bs, s->refcount_block_cache);
 146    if (ret < 0) {
 147        goto fail;
 148    }
 149
 150    /* the L1 position has not yet been updated, so these clusters must
 151     * indeed be completely free */
 152    ret = qcow2_pre_write_overlap_check(bs, 0, new_l1_table_offset,
 153                                        new_l1_size2, false);
 154    if (ret < 0) {
 155        goto fail;
 156    }
 157
 158    BLKDBG_EVENT(bs->file, BLKDBG_L1_GROW_WRITE_TABLE);
 159    for(i = 0; i < s->l1_size; i++)
 160        new_l1_table[i] = cpu_to_be64(new_l1_table[i]);
 161    ret = bdrv_pwrite_sync(bs->file, new_l1_table_offset,
 162                           new_l1_table, new_l1_size2);
 163    if (ret < 0)
 164        goto fail;
 165    for(i = 0; i < s->l1_size; i++)
 166        new_l1_table[i] = be64_to_cpu(new_l1_table[i]);
 167
 168    /* set new table */
 169    BLKDBG_EVENT(bs->file, BLKDBG_L1_GROW_ACTIVATE_TABLE);
 170    stl_be_p(data, new_l1_size);
 171    stq_be_p(data + 4, new_l1_table_offset);
 172    ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, l1_size),
 173                           data, sizeof(data));
 174    if (ret < 0) {
 175        goto fail;
 176    }
 177    qemu_vfree(s->l1_table);
 178    old_l1_table_offset = s->l1_table_offset;
 179    s->l1_table_offset = new_l1_table_offset;
 180    s->l1_table = new_l1_table;
 181    old_l1_size = s->l1_size;
 182    s->l1_size = new_l1_size;
 183    qcow2_free_clusters(bs, old_l1_table_offset, old_l1_size * sizeof(uint64_t),
 184                        QCOW2_DISCARD_OTHER);
 185    return 0;
 186 fail:
 187    qemu_vfree(new_l1_table);
 188    qcow2_free_clusters(bs, new_l1_table_offset, new_l1_size2,
 189                        QCOW2_DISCARD_OTHER);
 190    return ret;
 191}
 192
 193/*
 194 * l2_load
 195 *
 196 * @bs: The BlockDriverState
 197 * @offset: A guest offset, used to calculate what slice of the L2
 198 *          table to load.
 199 * @l2_offset: Offset to the L2 table in the image file.
 200 * @l2_slice: Location to store the pointer to the L2 slice.
 201 *
 202 * Loads a L2 slice into memory (L2 slices are the parts of L2 tables
 203 * that are loaded by the qcow2 cache). If the slice is in the cache,
 204 * the cache is used; otherwise the L2 slice is loaded from the image
 205 * file.
 206 */
 207static int l2_load(BlockDriverState *bs, uint64_t offset,
 208                   uint64_t l2_offset, uint64_t **l2_slice)
 209{
 210    BDRVQcow2State *s = bs->opaque;
 211    int start_of_slice = sizeof(uint64_t) *
 212        (offset_to_l2_index(s, offset) - offset_to_l2_slice_index(s, offset));
 213
 214    return qcow2_cache_get(bs, s->l2_table_cache, l2_offset + start_of_slice,
 215                           (void **)l2_slice);
 216}
 217
 218/*
 219 * Writes an L1 entry to disk (note that depending on the alignment
 220 * requirements this function may write more that just one entry in
 221 * order to prevent bdrv_pwrite from performing a read-modify-write)
 222 */
 223int qcow2_write_l1_entry(BlockDriverState *bs, int l1_index)
 224{
 225    BDRVQcow2State *s = bs->opaque;
 226    int l1_start_index;
 227    int i, ret;
 228    int bufsize = MAX(sizeof(uint64_t),
 229                      MIN(bs->file->bs->bl.request_alignment, s->cluster_size));
 230    int nentries = bufsize / sizeof(uint64_t);
 231    g_autofree uint64_t *buf = g_try_new0(uint64_t, nentries);
 232
 233    if (buf == NULL) {
 234        return -ENOMEM;
 235    }
 236
 237    l1_start_index = QEMU_ALIGN_DOWN(l1_index, nentries);
 238    for (i = 0; i < MIN(nentries, s->l1_size - l1_start_index); i++) {
 239        buf[i] = cpu_to_be64(s->l1_table[l1_start_index + i]);
 240    }
 241
 242    ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_ACTIVE_L1,
 243            s->l1_table_offset + 8 * l1_start_index, bufsize, false);
 244    if (ret < 0) {
 245        return ret;
 246    }
 247
 248    BLKDBG_EVENT(bs->file, BLKDBG_L1_UPDATE);
 249    ret = bdrv_pwrite_sync(bs->file,
 250                           s->l1_table_offset + 8 * l1_start_index,
 251                           buf, bufsize);
 252    if (ret < 0) {
 253        return ret;
 254    }
 255
 256    return 0;
 257}
 258
 259/*
 260 * l2_allocate
 261 *
 262 * Allocate a new l2 entry in the file. If l1_index points to an already
 263 * used entry in the L2 table (i.e. we are doing a copy on write for the L2
 264 * table) copy the contents of the old L2 table into the newly allocated one.
 265 * Otherwise the new table is initialized with zeros.
 266 *
 267 */
 268
 269static int l2_allocate(BlockDriverState *bs, int l1_index)
 270{
 271    BDRVQcow2State *s = bs->opaque;
 272    uint64_t old_l2_offset;
 273    uint64_t *l2_slice = NULL;
 274    unsigned slice, slice_size2, n_slices;
 275    int64_t l2_offset;
 276    int ret;
 277
 278    old_l2_offset = s->l1_table[l1_index];
 279
 280    trace_qcow2_l2_allocate(bs, l1_index);
 281
 282    /* allocate a new l2 entry */
 283
 284    l2_offset = qcow2_alloc_clusters(bs, s->l2_size * sizeof(uint64_t));
 285    if (l2_offset < 0) {
 286        ret = l2_offset;
 287        goto fail;
 288    }
 289
 290    /* The offset must fit in the offset field of the L1 table entry */
 291    assert((l2_offset & L1E_OFFSET_MASK) == l2_offset);
 292
 293    /* If we're allocating the table at offset 0 then something is wrong */
 294    if (l2_offset == 0) {
 295        qcow2_signal_corruption(bs, true, -1, -1, "Preventing invalid "
 296                                "allocation of L2 table at offset 0");
 297        ret = -EIO;
 298        goto fail;
 299    }
 300
 301    ret = qcow2_cache_flush(bs, s->refcount_block_cache);
 302    if (ret < 0) {
 303        goto fail;
 304    }
 305
 306    /* allocate a new entry in the l2 cache */
 307
 308    slice_size2 = s->l2_slice_size * sizeof(uint64_t);
 309    n_slices = s->cluster_size / slice_size2;
 310
 311    trace_qcow2_l2_allocate_get_empty(bs, l1_index);
 312    for (slice = 0; slice < n_slices; slice++) {
 313        ret = qcow2_cache_get_empty(bs, s->l2_table_cache,
 314                                    l2_offset + slice * slice_size2,
 315                                    (void **) &l2_slice);
 316        if (ret < 0) {
 317            goto fail;
 318        }
 319
 320        if ((old_l2_offset & L1E_OFFSET_MASK) == 0) {
 321            /* if there was no old l2 table, clear the new slice */
 322            memset(l2_slice, 0, slice_size2);
 323        } else {
 324            uint64_t *old_slice;
 325            uint64_t old_l2_slice_offset =
 326                (old_l2_offset & L1E_OFFSET_MASK) + slice * slice_size2;
 327
 328            /* if there was an old l2 table, read a slice from the disk */
 329            BLKDBG_EVENT(bs->file, BLKDBG_L2_ALLOC_COW_READ);
 330            ret = qcow2_cache_get(bs, s->l2_table_cache, old_l2_slice_offset,
 331                                  (void **) &old_slice);
 332            if (ret < 0) {
 333                goto fail;
 334            }
 335
 336            memcpy(l2_slice, old_slice, slice_size2);
 337
 338            qcow2_cache_put(s->l2_table_cache, (void **) &old_slice);
 339        }
 340
 341        /* write the l2 slice to the file */
 342        BLKDBG_EVENT(bs->file, BLKDBG_L2_ALLOC_WRITE);
 343
 344        trace_qcow2_l2_allocate_write_l2(bs, l1_index);
 345        qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
 346        qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
 347    }
 348
 349    ret = qcow2_cache_flush(bs, s->l2_table_cache);
 350    if (ret < 0) {
 351        goto fail;
 352    }
 353
 354    /* update the L1 entry */
 355    trace_qcow2_l2_allocate_write_l1(bs, l1_index);
 356    s->l1_table[l1_index] = l2_offset | QCOW_OFLAG_COPIED;
 357    ret = qcow2_write_l1_entry(bs, l1_index);
 358    if (ret < 0) {
 359        goto fail;
 360    }
 361
 362    trace_qcow2_l2_allocate_done(bs, l1_index, 0);
 363    return 0;
 364
 365fail:
 366    trace_qcow2_l2_allocate_done(bs, l1_index, ret);
 367    if (l2_slice != NULL) {
 368        qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
 369    }
 370    s->l1_table[l1_index] = old_l2_offset;
 371    if (l2_offset > 0) {
 372        qcow2_free_clusters(bs, l2_offset, s->l2_size * sizeof(uint64_t),
 373                            QCOW2_DISCARD_ALWAYS);
 374    }
 375    return ret;
 376}
 377
 378/*
 379 * Checks how many clusters in a given L2 slice are contiguous in the image
 380 * file. As soon as one of the flags in the bitmask stop_flags changes compared
 381 * to the first cluster, the search is stopped and the cluster is not counted
 382 * as contiguous. (This allows it, for example, to stop at the first compressed
 383 * cluster which may require a different handling)
 384 */
 385static int count_contiguous_clusters(BlockDriverState *bs, int nb_clusters,
 386        int cluster_size, uint64_t *l2_slice, uint64_t stop_flags)
 387{
 388    int i;
 389    QCow2ClusterType first_cluster_type;
 390    uint64_t mask = stop_flags | L2E_OFFSET_MASK | QCOW_OFLAG_COMPRESSED;
 391    uint64_t first_entry = be64_to_cpu(l2_slice[0]);
 392    uint64_t offset = first_entry & mask;
 393
 394    first_cluster_type = qcow2_get_cluster_type(bs, first_entry);
 395    if (first_cluster_type == QCOW2_CLUSTER_UNALLOCATED) {
 396        return 0;
 397    }
 398
 399    /* must be allocated */
 400    assert(first_cluster_type == QCOW2_CLUSTER_NORMAL ||
 401           first_cluster_type == QCOW2_CLUSTER_ZERO_ALLOC);
 402
 403    for (i = 0; i < nb_clusters; i++) {
 404        uint64_t l2_entry = be64_to_cpu(l2_slice[i]) & mask;
 405        if (offset + (uint64_t) i * cluster_size != l2_entry) {
 406            break;
 407        }
 408    }
 409
 410        return i;
 411}
 412
 413/*
 414 * Checks how many consecutive unallocated clusters in a given L2
 415 * slice have the same cluster type.
 416 */
 417static int count_contiguous_clusters_unallocated(BlockDriverState *bs,
 418                                                 int nb_clusters,
 419                                                 uint64_t *l2_slice,
 420                                                 QCow2ClusterType wanted_type)
 421{
 422    int i;
 423
 424    assert(wanted_type == QCOW2_CLUSTER_ZERO_PLAIN ||
 425           wanted_type == QCOW2_CLUSTER_UNALLOCATED);
 426    for (i = 0; i < nb_clusters; i++) {
 427        uint64_t entry = be64_to_cpu(l2_slice[i]);
 428        QCow2ClusterType type = qcow2_get_cluster_type(bs, entry);
 429
 430        if (type != wanted_type) {
 431            break;
 432        }
 433    }
 434
 435    return i;
 436}
 437
 438static int coroutine_fn do_perform_cow_read(BlockDriverState *bs,
 439                                            uint64_t src_cluster_offset,
 440                                            unsigned offset_in_cluster,
 441                                            QEMUIOVector *qiov)
 442{
 443    int ret;
 444
 445    if (qiov->size == 0) {
 446        return 0;
 447    }
 448
 449    BLKDBG_EVENT(bs->file, BLKDBG_COW_READ);
 450
 451    if (!bs->drv) {
 452        return -ENOMEDIUM;
 453    }
 454
 455    /* Call .bdrv_co_readv() directly instead of using the public block-layer
 456     * interface.  This avoids double I/O throttling and request tracking,
 457     * which can lead to deadlock when block layer copy-on-read is enabled.
 458     */
 459    ret = bs->drv->bdrv_co_preadv_part(bs,
 460                                       src_cluster_offset + offset_in_cluster,
 461                                       qiov->size, qiov, 0, 0);
 462    if (ret < 0) {
 463        return ret;
 464    }
 465
 466    return 0;
 467}
 468
 469static int coroutine_fn do_perform_cow_write(BlockDriverState *bs,
 470                                             uint64_t cluster_offset,
 471                                             unsigned offset_in_cluster,
 472                                             QEMUIOVector *qiov)
 473{
 474    BDRVQcow2State *s = bs->opaque;
 475    int ret;
 476
 477    if (qiov->size == 0) {
 478        return 0;
 479    }
 480
 481    ret = qcow2_pre_write_overlap_check(bs, 0,
 482            cluster_offset + offset_in_cluster, qiov->size, true);
 483    if (ret < 0) {
 484        return ret;
 485    }
 486
 487    BLKDBG_EVENT(bs->file, BLKDBG_COW_WRITE);
 488    ret = bdrv_co_pwritev(s->data_file, cluster_offset + offset_in_cluster,
 489                          qiov->size, qiov, 0);
 490    if (ret < 0) {
 491        return ret;
 492    }
 493
 494    return 0;
 495}
 496
 497
 498/*
 499 * get_cluster_offset
 500 *
 501 * For a given offset of the virtual disk, find the cluster type and offset in
 502 * the qcow2 file. The offset is stored in *cluster_offset.
 503 *
 504 * On entry, *bytes is the maximum number of contiguous bytes starting at
 505 * offset that we are interested in.
 506 *
 507 * On exit, *bytes is the number of bytes starting at offset that have the same
 508 * cluster type and (if applicable) are stored contiguously in the image file.
 509 * Compressed clusters are always returned one by one.
 510 *
 511 * Returns the cluster type (QCOW2_CLUSTER_*) on success, -errno in error
 512 * cases.
 513 */
 514int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
 515                             unsigned int *bytes, uint64_t *cluster_offset)
 516{
 517    BDRVQcow2State *s = bs->opaque;
 518    unsigned int l2_index;
 519    uint64_t l1_index, l2_offset, *l2_slice;
 520    int c;
 521    unsigned int offset_in_cluster;
 522    uint64_t bytes_available, bytes_needed, nb_clusters;
 523    QCow2ClusterType type;
 524    int ret;
 525
 526    offset_in_cluster = offset_into_cluster(s, offset);
 527    bytes_needed = (uint64_t) *bytes + offset_in_cluster;
 528
 529    /* compute how many bytes there are between the start of the cluster
 530     * containing offset and the end of the l2 slice that contains
 531     * the entry pointing to it */
 532    bytes_available =
 533        ((uint64_t) (s->l2_slice_size - offset_to_l2_slice_index(s, offset)))
 534        << s->cluster_bits;
 535
 536    if (bytes_needed > bytes_available) {
 537        bytes_needed = bytes_available;
 538    }
 539
 540    *cluster_offset = 0;
 541
 542    /* seek to the l2 offset in the l1 table */
 543
 544    l1_index = offset_to_l1_index(s, offset);
 545    if (l1_index >= s->l1_size) {
 546        type = QCOW2_CLUSTER_UNALLOCATED;
 547        goto out;
 548    }
 549
 550    l2_offset = s->l1_table[l1_index] & L1E_OFFSET_MASK;
 551    if (!l2_offset) {
 552        type = QCOW2_CLUSTER_UNALLOCATED;
 553        goto out;
 554    }
 555
 556    if (offset_into_cluster(s, l2_offset)) {
 557        qcow2_signal_corruption(bs, true, -1, -1, "L2 table offset %#" PRIx64
 558                                " unaligned (L1 index: %#" PRIx64 ")",
 559                                l2_offset, l1_index);
 560        return -EIO;
 561    }
 562
 563    /* load the l2 slice in memory */
 564
 565    ret = l2_load(bs, offset, l2_offset, &l2_slice);
 566    if (ret < 0) {
 567        return ret;
 568    }
 569
 570    /* find the cluster offset for the given disk offset */
 571
 572    l2_index = offset_to_l2_slice_index(s, offset);
 573    *cluster_offset = be64_to_cpu(l2_slice[l2_index]);
 574
 575    nb_clusters = size_to_clusters(s, bytes_needed);
 576    /* bytes_needed <= *bytes + offset_in_cluster, both of which are unsigned
 577     * integers; the minimum cluster size is 512, so this assertion is always
 578     * true */
 579    assert(nb_clusters <= INT_MAX);
 580
 581    type = qcow2_get_cluster_type(bs, *cluster_offset);
 582    if (s->qcow_version < 3 && (type == QCOW2_CLUSTER_ZERO_PLAIN ||
 583                                type == QCOW2_CLUSTER_ZERO_ALLOC)) {
 584        qcow2_signal_corruption(bs, true, -1, -1, "Zero cluster entry found"
 585                                " in pre-v3 image (L2 offset: %#" PRIx64
 586                                ", L2 index: %#x)", l2_offset, l2_index);
 587        ret = -EIO;
 588        goto fail;
 589    }
 590    switch (type) {
 591    case QCOW2_CLUSTER_COMPRESSED:
 592        if (has_data_file(bs)) {
 593            qcow2_signal_corruption(bs, true, -1, -1, "Compressed cluster "
 594                                    "entry found in image with external data "
 595                                    "file (L2 offset: %#" PRIx64 ", L2 index: "
 596                                    "%#x)", l2_offset, l2_index);
 597            ret = -EIO;
 598            goto fail;
 599        }
 600        /* Compressed clusters can only be processed one by one */
 601        c = 1;
 602        *cluster_offset &= L2E_COMPRESSED_OFFSET_SIZE_MASK;
 603        break;
 604    case QCOW2_CLUSTER_ZERO_PLAIN:
 605    case QCOW2_CLUSTER_UNALLOCATED:
 606        /* how many empty clusters ? */
 607        c = count_contiguous_clusters_unallocated(bs, nb_clusters,
 608                                                  &l2_slice[l2_index], type);
 609        *cluster_offset = 0;
 610        break;
 611    case QCOW2_CLUSTER_ZERO_ALLOC:
 612    case QCOW2_CLUSTER_NORMAL:
 613        /* how many allocated clusters ? */
 614        c = count_contiguous_clusters(bs, nb_clusters, s->cluster_size,
 615                                      &l2_slice[l2_index], QCOW_OFLAG_ZERO);
 616        *cluster_offset &= L2E_OFFSET_MASK;
 617        if (offset_into_cluster(s, *cluster_offset)) {
 618            qcow2_signal_corruption(bs, true, -1, -1,
 619                                    "Cluster allocation offset %#"
 620                                    PRIx64 " unaligned (L2 offset: %#" PRIx64
 621                                    ", L2 index: %#x)", *cluster_offset,
 622                                    l2_offset, l2_index);
 623            ret = -EIO;
 624            goto fail;
 625        }
 626        if (has_data_file(bs) && *cluster_offset != offset - offset_in_cluster)
 627        {
 628            qcow2_signal_corruption(bs, true, -1, -1,
 629                                    "External data file host cluster offset %#"
 630                                    PRIx64 " does not match guest cluster "
 631                                    "offset: %#" PRIx64
 632                                    ", L2 index: %#x)", *cluster_offset,
 633                                    offset - offset_in_cluster, l2_index);
 634            ret = -EIO;
 635            goto fail;
 636        }
 637        break;
 638    default:
 639        abort();
 640    }
 641
 642    qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
 643
 644    bytes_available = (int64_t)c * s->cluster_size;
 645
 646out:
 647    if (bytes_available > bytes_needed) {
 648        bytes_available = bytes_needed;
 649    }
 650
 651    /* bytes_available <= bytes_needed <= *bytes + offset_in_cluster;
 652     * subtracting offset_in_cluster will therefore definitely yield something
 653     * not exceeding UINT_MAX */
 654    assert(bytes_available - offset_in_cluster <= UINT_MAX);
 655    *bytes = bytes_available - offset_in_cluster;
 656
 657    return type;
 658
 659fail:
 660    qcow2_cache_put(s->l2_table_cache, (void **)&l2_slice);
 661    return ret;
 662}
 663
 664/*
 665 * get_cluster_table
 666 *
 667 * for a given disk offset, load (and allocate if needed)
 668 * the appropriate slice of its l2 table.
 669 *
 670 * the cluster index in the l2 slice is given to the caller.
 671 *
 672 * Returns 0 on success, -errno in failure case
 673 */
 674static int get_cluster_table(BlockDriverState *bs, uint64_t offset,
 675                             uint64_t **new_l2_slice,
 676                             int *new_l2_index)
 677{
 678    BDRVQcow2State *s = bs->opaque;
 679    unsigned int l2_index;
 680    uint64_t l1_index, l2_offset;
 681    uint64_t *l2_slice = NULL;
 682    int ret;
 683
 684    /* seek to the l2 offset in the l1 table */
 685
 686    l1_index = offset_to_l1_index(s, offset);
 687    if (l1_index >= s->l1_size) {
 688        ret = qcow2_grow_l1_table(bs, l1_index + 1, false);
 689        if (ret < 0) {
 690            return ret;
 691        }
 692    }
 693
 694    assert(l1_index < s->l1_size);
 695    l2_offset = s->l1_table[l1_index] & L1E_OFFSET_MASK;
 696    if (offset_into_cluster(s, l2_offset)) {
 697        qcow2_signal_corruption(bs, true, -1, -1, "L2 table offset %#" PRIx64
 698                                " unaligned (L1 index: %#" PRIx64 ")",
 699                                l2_offset, l1_index);
 700        return -EIO;
 701    }
 702
 703    if (!(s->l1_table[l1_index] & QCOW_OFLAG_COPIED)) {
 704        /* First allocate a new L2 table (and do COW if needed) */
 705        ret = l2_allocate(bs, l1_index);
 706        if (ret < 0) {
 707            return ret;
 708        }
 709
 710        /* Then decrease the refcount of the old table */
 711        if (l2_offset) {
 712            qcow2_free_clusters(bs, l2_offset, s->l2_size * sizeof(uint64_t),
 713                                QCOW2_DISCARD_OTHER);
 714        }
 715
 716        /* Get the offset of the newly-allocated l2 table */
 717        l2_offset = s->l1_table[l1_index] & L1E_OFFSET_MASK;
 718        assert(offset_into_cluster(s, l2_offset) == 0);
 719    }
 720
 721    /* load the l2 slice in memory */
 722    ret = l2_load(bs, offset, l2_offset, &l2_slice);
 723    if (ret < 0) {
 724        return ret;
 725    }
 726
 727    /* find the cluster offset for the given disk offset */
 728
 729    l2_index = offset_to_l2_slice_index(s, offset);
 730
 731    *new_l2_slice = l2_slice;
 732    *new_l2_index = l2_index;
 733
 734    return 0;
 735}
 736
 737/*
 738 * alloc_compressed_cluster_offset
 739 *
 740 * For a given offset on the virtual disk, allocate a new compressed cluster
 741 * and put the host offset of the cluster into *host_offset. If a cluster is
 742 * already allocated at the offset, return an error.
 743 *
 744 * Return 0 on success and -errno in error cases
 745 */
 746int qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
 747                                          uint64_t offset,
 748                                          int compressed_size,
 749                                          uint64_t *host_offset)
 750{
 751    BDRVQcow2State *s = bs->opaque;
 752    int l2_index, ret;
 753    uint64_t *l2_slice;
 754    int64_t cluster_offset;
 755    int nb_csectors;
 756
 757    if (has_data_file(bs)) {
 758        return 0;
 759    }
 760
 761    ret = get_cluster_table(bs, offset, &l2_slice, &l2_index);
 762    if (ret < 0) {
 763        return ret;
 764    }
 765
 766    /* Compression can't overwrite anything. Fail if the cluster was already
 767     * allocated. */
 768    cluster_offset = be64_to_cpu(l2_slice[l2_index]);
 769    if (cluster_offset & L2E_OFFSET_MASK) {
 770        qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
 771        return -EIO;
 772    }
 773
 774    cluster_offset = qcow2_alloc_bytes(bs, compressed_size);
 775    if (cluster_offset < 0) {
 776        qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
 777        return cluster_offset;
 778    }
 779
 780    nb_csectors =
 781        (cluster_offset + compressed_size - 1) / QCOW2_COMPRESSED_SECTOR_SIZE -
 782        (cluster_offset / QCOW2_COMPRESSED_SECTOR_SIZE);
 783
 784    /* The offset and size must fit in their fields of the L2 table entry */
 785    assert((cluster_offset & s->cluster_offset_mask) == cluster_offset);
 786    assert((nb_csectors & s->csize_mask) == nb_csectors);
 787
 788    cluster_offset |= QCOW_OFLAG_COMPRESSED |
 789                      ((uint64_t)nb_csectors << s->csize_shift);
 790
 791    /* update L2 table */
 792
 793    /* compressed clusters never have the copied flag */
 794
 795    BLKDBG_EVENT(bs->file, BLKDBG_L2_UPDATE_COMPRESSED);
 796    qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
 797    l2_slice[l2_index] = cpu_to_be64(cluster_offset);
 798    qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
 799
 800    *host_offset = cluster_offset & s->cluster_offset_mask;
 801    return 0;
 802}
 803
 804static int perform_cow(BlockDriverState *bs, QCowL2Meta *m)
 805{
 806    BDRVQcow2State *s = bs->opaque;
 807    Qcow2COWRegion *start = &m->cow_start;
 808    Qcow2COWRegion *end = &m->cow_end;
 809    unsigned buffer_size;
 810    unsigned data_bytes = end->offset - (start->offset + start->nb_bytes);
 811    bool merge_reads;
 812    uint8_t *start_buffer, *end_buffer;
 813    QEMUIOVector qiov;
 814    int ret;
 815
 816    assert(start->nb_bytes <= UINT_MAX - end->nb_bytes);
 817    assert(start->nb_bytes + end->nb_bytes <= UINT_MAX - data_bytes);
 818    assert(start->offset + start->nb_bytes <= end->offset);
 819
 820    if ((start->nb_bytes == 0 && end->nb_bytes == 0) || m->skip_cow) {
 821        return 0;
 822    }
 823
 824    /* If we have to read both the start and end COW regions and the
 825     * middle region is not too large then perform just one read
 826     * operation */
 827    merge_reads = start->nb_bytes && end->nb_bytes && data_bytes <= 16384;
 828    if (merge_reads) {
 829        buffer_size = start->nb_bytes + data_bytes + end->nb_bytes;
 830    } else {
 831        /* If we have to do two reads, add some padding in the middle
 832         * if necessary to make sure that the end region is optimally
 833         * aligned. */
 834        size_t align = bdrv_opt_mem_align(bs);
 835        assert(align > 0 && align <= UINT_MAX);
 836        assert(QEMU_ALIGN_UP(start->nb_bytes, align) <=
 837               UINT_MAX - end->nb_bytes);
 838        buffer_size = QEMU_ALIGN_UP(start->nb_bytes, align) + end->nb_bytes;
 839    }
 840
 841    /* Reserve a buffer large enough to store all the data that we're
 842     * going to read */
 843    start_buffer = qemu_try_blockalign(bs, buffer_size);
 844    if (start_buffer == NULL) {
 845        return -ENOMEM;
 846    }
 847    /* The part of the buffer where the end region is located */
 848    end_buffer = start_buffer + buffer_size - end->nb_bytes;
 849
 850    qemu_iovec_init(&qiov, 2 + (m->data_qiov ?
 851                                qemu_iovec_subvec_niov(m->data_qiov,
 852                                                       m->data_qiov_offset,
 853                                                       data_bytes)
 854                                : 0));
 855
 856    qemu_co_mutex_unlock(&s->lock);
 857    /* First we read the existing data from both COW regions. We
 858     * either read the whole region in one go, or the start and end
 859     * regions separately. */
 860    if (merge_reads) {
 861        qemu_iovec_add(&qiov, start_buffer, buffer_size);
 862        ret = do_perform_cow_read(bs, m->offset, start->offset, &qiov);
 863    } else {
 864        qemu_iovec_add(&qiov, start_buffer, start->nb_bytes);
 865        ret = do_perform_cow_read(bs, m->offset, start->offset, &qiov);
 866        if (ret < 0) {
 867            goto fail;
 868        }
 869
 870        qemu_iovec_reset(&qiov);
 871        qemu_iovec_add(&qiov, end_buffer, end->nb_bytes);
 872        ret = do_perform_cow_read(bs, m->offset, end->offset, &qiov);
 873    }
 874    if (ret < 0) {
 875        goto fail;
 876    }
 877
 878    /* Encrypt the data if necessary before writing it */
 879    if (bs->encrypted) {
 880        ret = qcow2_co_encrypt(bs,
 881                               m->alloc_offset + start->offset,
 882                               m->offset + start->offset,
 883                               start_buffer, start->nb_bytes);
 884        if (ret < 0) {
 885            goto fail;
 886        }
 887
 888        ret = qcow2_co_encrypt(bs,
 889                               m->alloc_offset + end->offset,
 890                               m->offset + end->offset,
 891                               end_buffer, end->nb_bytes);
 892        if (ret < 0) {
 893            goto fail;
 894        }
 895    }
 896
 897    /* And now we can write everything. If we have the guest data we
 898     * can write everything in one single operation */
 899    if (m->data_qiov) {
 900        qemu_iovec_reset(&qiov);
 901        if (start->nb_bytes) {
 902            qemu_iovec_add(&qiov, start_buffer, start->nb_bytes);
 903        }
 904        qemu_iovec_concat(&qiov, m->data_qiov, m->data_qiov_offset, data_bytes);
 905        if (end->nb_bytes) {
 906            qemu_iovec_add(&qiov, end_buffer, end->nb_bytes);
 907        }
 908        /* NOTE: we have a write_aio blkdebug event here followed by
 909         * a cow_write one in do_perform_cow_write(), but there's only
 910         * one single I/O operation */
 911        BLKDBG_EVENT(bs->file, BLKDBG_WRITE_AIO);
 912        ret = do_perform_cow_write(bs, m->alloc_offset, start->offset, &qiov);
 913    } else {
 914        /* If there's no guest data then write both COW regions separately */
 915        qemu_iovec_reset(&qiov);
 916        qemu_iovec_add(&qiov, start_buffer, start->nb_bytes);
 917        ret = do_perform_cow_write(bs, m->alloc_offset, start->offset, &qiov);
 918        if (ret < 0) {
 919            goto fail;
 920        }
 921
 922        qemu_iovec_reset(&qiov);
 923        qemu_iovec_add(&qiov, end_buffer, end->nb_bytes);
 924        ret = do_perform_cow_write(bs, m->alloc_offset, end->offset, &qiov);
 925    }
 926
 927fail:
 928    qemu_co_mutex_lock(&s->lock);
 929
 930    /*
 931     * Before we update the L2 table to actually point to the new cluster, we
 932     * need to be sure that the refcounts have been increased and COW was
 933     * handled.
 934     */
 935    if (ret == 0) {
 936        qcow2_cache_depends_on_flush(s->l2_table_cache);
 937    }
 938
 939    qemu_vfree(start_buffer);
 940    qemu_iovec_destroy(&qiov);
 941    return ret;
 942}
 943
 944int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m)
 945{
 946    BDRVQcow2State *s = bs->opaque;
 947    int i, j = 0, l2_index, ret;
 948    uint64_t *old_cluster, *l2_slice;
 949    uint64_t cluster_offset = m->alloc_offset;
 950
 951    trace_qcow2_cluster_link_l2(qemu_coroutine_self(), m->nb_clusters);
 952    assert(m->nb_clusters > 0);
 953
 954    old_cluster = g_try_new(uint64_t, m->nb_clusters);
 955    if (old_cluster == NULL) {
 956        ret = -ENOMEM;
 957        goto err;
 958    }
 959
 960    /* copy content of unmodified sectors */
 961    ret = perform_cow(bs, m);
 962    if (ret < 0) {
 963        goto err;
 964    }
 965
 966    /* Update L2 table. */
 967    if (s->use_lazy_refcounts) {
 968        qcow2_mark_dirty(bs);
 969    }
 970    if (qcow2_need_accurate_refcounts(s)) {
 971        qcow2_cache_set_dependency(bs, s->l2_table_cache,
 972                                   s->refcount_block_cache);
 973    }
 974
 975    ret = get_cluster_table(bs, m->offset, &l2_slice, &l2_index);
 976    if (ret < 0) {
 977        goto err;
 978    }
 979    qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
 980
 981    assert(l2_index + m->nb_clusters <= s->l2_slice_size);
 982    for (i = 0; i < m->nb_clusters; i++) {
 983        uint64_t offset = cluster_offset + ((uint64_t)i << s->cluster_bits);
 984        /* if two concurrent writes happen to the same unallocated cluster
 985         * each write allocates separate cluster and writes data concurrently.
 986         * The first one to complete updates l2 table with pointer to its
 987         * cluster the second one has to do RMW (which is done above by
 988         * perform_cow()), update l2 table with its cluster pointer and free
 989         * old cluster. This is what this loop does */
 990        if (l2_slice[l2_index + i] != 0) {
 991            old_cluster[j++] = l2_slice[l2_index + i];
 992        }
 993
 994        /* The offset must fit in the offset field of the L2 table entry */
 995        assert((offset & L2E_OFFSET_MASK) == offset);
 996
 997        l2_slice[l2_index + i] = cpu_to_be64(offset | QCOW_OFLAG_COPIED);
 998     }
 999
1000
1001    qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
1002
1003    /*
1004     * If this was a COW, we need to decrease the refcount of the old cluster.
1005     *
1006     * Don't discard clusters that reach a refcount of 0 (e.g. compressed
1007     * clusters), the next write will reuse them anyway.
1008     */
1009    if (!m->keep_old_clusters && j != 0) {
1010        for (i = 0; i < j; i++) {
1011            qcow2_free_any_clusters(bs, be64_to_cpu(old_cluster[i]), 1,
1012                                    QCOW2_DISCARD_NEVER);
1013        }
1014    }
1015
1016    ret = 0;
1017err:
1018    g_free(old_cluster);
1019    return ret;
1020 }
1021
1022/**
1023 * Frees the allocated clusters because the request failed and they won't
1024 * actually be linked.
1025 */
1026void qcow2_alloc_cluster_abort(BlockDriverState *bs, QCowL2Meta *m)
1027{
1028    BDRVQcow2State *s = bs->opaque;
1029    if (!has_data_file(bs) && !m->keep_old_clusters) {
1030        qcow2_free_clusters(bs, m->alloc_offset,
1031                            m->nb_clusters << s->cluster_bits,
1032                            QCOW2_DISCARD_NEVER);
1033    }
1034}
1035
1036/*
1037 * Returns the number of contiguous clusters that can be used for an allocating
1038 * write, but require COW to be performed (this includes yet unallocated space,
1039 * which must copy from the backing file)
1040 */
1041static int count_cow_clusters(BlockDriverState *bs, int nb_clusters,
1042    uint64_t *l2_slice, int l2_index)
1043{
1044    int i;
1045
1046    for (i = 0; i < nb_clusters; i++) {
1047        uint64_t l2_entry = be64_to_cpu(l2_slice[l2_index + i]);
1048        QCow2ClusterType cluster_type = qcow2_get_cluster_type(bs, l2_entry);
1049
1050        switch(cluster_type) {
1051        case QCOW2_CLUSTER_NORMAL:
1052            if (l2_entry & QCOW_OFLAG_COPIED) {
1053                goto out;
1054            }
1055            break;
1056        case QCOW2_CLUSTER_UNALLOCATED:
1057        case QCOW2_CLUSTER_COMPRESSED:
1058        case QCOW2_CLUSTER_ZERO_PLAIN:
1059        case QCOW2_CLUSTER_ZERO_ALLOC:
1060            break;
1061        default:
1062            abort();
1063        }
1064    }
1065
1066out:
1067    assert(i <= nb_clusters);
1068    return i;
1069}
1070
1071/*
1072 * Check if there already is an AIO write request in flight which allocates
1073 * the same cluster. In this case we need to wait until the previous
1074 * request has completed and updated the L2 table accordingly.
1075 *
1076 * Returns:
1077 *   0       if there was no dependency. *cur_bytes indicates the number of
1078 *           bytes from guest_offset that can be read before the next
1079 *           dependency must be processed (or the request is complete)
1080 *
1081 *   -EAGAIN if we had to wait for another request, previously gathered
1082 *           information on cluster allocation may be invalid now. The caller
1083 *           must start over anyway, so consider *cur_bytes undefined.
1084 */
1085static int handle_dependencies(BlockDriverState *bs, uint64_t guest_offset,
1086    uint64_t *cur_bytes, QCowL2Meta **m)
1087{
1088    BDRVQcow2State *s = bs->opaque;
1089    QCowL2Meta *old_alloc;
1090    uint64_t bytes = *cur_bytes;
1091
1092    QLIST_FOREACH(old_alloc, &s->cluster_allocs, next_in_flight) {
1093
1094        uint64_t start = guest_offset;
1095        uint64_t end = start + bytes;
1096        uint64_t old_start = l2meta_cow_start(old_alloc);
1097        uint64_t old_end = l2meta_cow_end(old_alloc);
1098
1099        if (end <= old_start || start >= old_end) {
1100            /* No intersection */
1101        } else {
1102            if (start < old_start) {
1103                /* Stop at the start of a running allocation */
1104                bytes = old_start - start;
1105            } else {
1106                bytes = 0;
1107            }
1108
1109            /* Stop if already an l2meta exists. After yielding, it wouldn't
1110             * be valid any more, so we'd have to clean up the old L2Metas
1111             * and deal with requests depending on them before starting to
1112             * gather new ones. Not worth the trouble. */
1113            if (bytes == 0 && *m) {
1114                *cur_bytes = 0;
1115                return 0;
1116            }
1117
1118            if (bytes == 0) {
1119                /* Wait for the dependency to complete. We need to recheck
1120                 * the free/allocated clusters when we continue. */
1121                qemu_co_queue_wait(&old_alloc->dependent_requests, &s->lock);
1122                return -EAGAIN;
1123            }
1124        }
1125    }
1126
1127    /* Make sure that existing clusters and new allocations are only used up to
1128     * the next dependency if we shortened the request above */
1129    *cur_bytes = bytes;
1130
1131    return 0;
1132}
1133
1134/*
1135 * Checks how many already allocated clusters that don't require a copy on
1136 * write there are at the given guest_offset (up to *bytes). If *host_offset is
1137 * not INV_OFFSET, only physically contiguous clusters beginning at this host
1138 * offset are counted.
1139 *
1140 * Note that guest_offset may not be cluster aligned. In this case, the
1141 * returned *host_offset points to exact byte referenced by guest_offset and
1142 * therefore isn't cluster aligned as well.
1143 *
1144 * Returns:
1145 *   0:     if no allocated clusters are available at the given offset.
1146 *          *bytes is normally unchanged. It is set to 0 if the cluster
1147 *          is allocated and doesn't need COW, but doesn't have the right
1148 *          physical offset.
1149 *
1150 *   1:     if allocated clusters that don't require a COW are available at
1151 *          the requested offset. *bytes may have decreased and describes
1152 *          the length of the area that can be written to.
1153 *
1154 *  -errno: in error cases
1155 */
1156static int handle_copied(BlockDriverState *bs, uint64_t guest_offset,
1157    uint64_t *host_offset, uint64_t *bytes, QCowL2Meta **m)
1158{
1159    BDRVQcow2State *s = bs->opaque;
1160    int l2_index;
1161    uint64_t cluster_offset;
1162    uint64_t *l2_slice;
1163    uint64_t nb_clusters;
1164    unsigned int keep_clusters;
1165    int ret;
1166
1167    trace_qcow2_handle_copied(qemu_coroutine_self(), guest_offset, *host_offset,
1168                              *bytes);
1169
1170    assert(*host_offset == INV_OFFSET || offset_into_cluster(s, guest_offset)
1171                                      == offset_into_cluster(s, *host_offset));
1172
1173    /*
1174     * Calculate the number of clusters to look for. We stop at L2 slice
1175     * boundaries to keep things simple.
1176     */
1177    nb_clusters =
1178        size_to_clusters(s, offset_into_cluster(s, guest_offset) + *bytes);
1179
1180    l2_index = offset_to_l2_slice_index(s, guest_offset);
1181    nb_clusters = MIN(nb_clusters, s->l2_slice_size - l2_index);
1182    assert(nb_clusters <= INT_MAX);
1183
1184    /* Find L2 entry for the first involved cluster */
1185    ret = get_cluster_table(bs, guest_offset, &l2_slice, &l2_index);
1186    if (ret < 0) {
1187        return ret;
1188    }
1189
1190    cluster_offset = be64_to_cpu(l2_slice[l2_index]);
1191
1192    /* Check how many clusters are already allocated and don't need COW */
1193    if (qcow2_get_cluster_type(bs, cluster_offset) == QCOW2_CLUSTER_NORMAL
1194        && (cluster_offset & QCOW_OFLAG_COPIED))
1195    {
1196        /* If a specific host_offset is required, check it */
1197        bool offset_matches =
1198            (cluster_offset & L2E_OFFSET_MASK) == *host_offset;
1199
1200        if (offset_into_cluster(s, cluster_offset & L2E_OFFSET_MASK)) {
1201            qcow2_signal_corruption(bs, true, -1, -1, "Data cluster offset "
1202                                    "%#llx unaligned (guest offset: %#" PRIx64
1203                                    ")", cluster_offset & L2E_OFFSET_MASK,
1204                                    guest_offset);
1205            ret = -EIO;
1206            goto out;
1207        }
1208
1209        if (*host_offset != INV_OFFSET && !offset_matches) {
1210            *bytes = 0;
1211            ret = 0;
1212            goto out;
1213        }
1214
1215        /* We keep all QCOW_OFLAG_COPIED clusters */
1216        keep_clusters =
1217            count_contiguous_clusters(bs, nb_clusters, s->cluster_size,
1218                                      &l2_slice[l2_index],
1219                                      QCOW_OFLAG_COPIED | QCOW_OFLAG_ZERO);
1220        assert(keep_clusters <= nb_clusters);
1221
1222        *bytes = MIN(*bytes,
1223                 keep_clusters * s->cluster_size
1224                 - offset_into_cluster(s, guest_offset));
1225
1226        ret = 1;
1227    } else {
1228        ret = 0;
1229    }
1230
1231    /* Cleanup */
1232out:
1233    qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
1234
1235    /* Only return a host offset if we actually made progress. Otherwise we
1236     * would make requirements for handle_alloc() that it can't fulfill */
1237    if (ret > 0) {
1238        *host_offset = (cluster_offset & L2E_OFFSET_MASK)
1239                     + offset_into_cluster(s, guest_offset);
1240    }
1241
1242    return ret;
1243}
1244
1245/*
1246 * Allocates new clusters for the given guest_offset.
1247 *
1248 * At most *nb_clusters are allocated, and on return *nb_clusters is updated to
1249 * contain the number of clusters that have been allocated and are contiguous
1250 * in the image file.
1251 *
1252 * If *host_offset is not INV_OFFSET, it specifies the offset in the image file
1253 * at which the new clusters must start. *nb_clusters can be 0 on return in
1254 * this case if the cluster at host_offset is already in use. If *host_offset
1255 * is INV_OFFSET, the clusters can be allocated anywhere in the image file.
1256 *
1257 * *host_offset is updated to contain the offset into the image file at which
1258 * the first allocated cluster starts.
1259 *
1260 * Return 0 on success and -errno in error cases. -EAGAIN means that the
1261 * function has been waiting for another request and the allocation must be
1262 * restarted, but the whole request should not be failed.
1263 */
1264static int do_alloc_cluster_offset(BlockDriverState *bs, uint64_t guest_offset,
1265                                   uint64_t *host_offset, uint64_t *nb_clusters)
1266{
1267    BDRVQcow2State *s = bs->opaque;
1268
1269    trace_qcow2_do_alloc_clusters_offset(qemu_coroutine_self(), guest_offset,
1270                                         *host_offset, *nb_clusters);
1271
1272    if (has_data_file(bs)) {
1273        assert(*host_offset == INV_OFFSET ||
1274               *host_offset == start_of_cluster(s, guest_offset));
1275        *host_offset = start_of_cluster(s, guest_offset);
1276        return 0;
1277    }
1278
1279    /* Allocate new clusters */
1280    trace_qcow2_cluster_alloc_phys(qemu_coroutine_self());
1281    if (*host_offset == INV_OFFSET) {
1282        int64_t cluster_offset =
1283            qcow2_alloc_clusters(bs, *nb_clusters * s->cluster_size);
1284        if (cluster_offset < 0) {
1285            return cluster_offset;
1286        }
1287        *host_offset = cluster_offset;
1288        return 0;
1289    } else {
1290        int64_t ret = qcow2_alloc_clusters_at(bs, *host_offset, *nb_clusters);
1291        if (ret < 0) {
1292            return ret;
1293        }
1294        *nb_clusters = ret;
1295        return 0;
1296    }
1297}
1298
1299/*
1300 * Allocates new clusters for an area that either is yet unallocated or needs a
1301 * copy on write. If *host_offset is not INV_OFFSET, clusters are only
1302 * allocated if the new allocation can match the specified host offset.
1303 *
1304 * Note that guest_offset may not be cluster aligned. In this case, the
1305 * returned *host_offset points to exact byte referenced by guest_offset and
1306 * therefore isn't cluster aligned as well.
1307 *
1308 * Returns:
1309 *   0:     if no clusters could be allocated. *bytes is set to 0,
1310 *          *host_offset is left unchanged.
1311 *
1312 *   1:     if new clusters were allocated. *bytes may be decreased if the
1313 *          new allocation doesn't cover all of the requested area.
1314 *          *host_offset is updated to contain the host offset of the first
1315 *          newly allocated cluster.
1316 *
1317 *  -errno: in error cases
1318 */
1319static int handle_alloc(BlockDriverState *bs, uint64_t guest_offset,
1320    uint64_t *host_offset, uint64_t *bytes, QCowL2Meta **m)
1321{
1322    BDRVQcow2State *s = bs->opaque;
1323    int l2_index;
1324    uint64_t *l2_slice;
1325    uint64_t entry;
1326    uint64_t nb_clusters;
1327    int ret;
1328    bool keep_old_clusters = false;
1329
1330    uint64_t alloc_cluster_offset = INV_OFFSET;
1331
1332    trace_qcow2_handle_alloc(qemu_coroutine_self(), guest_offset, *host_offset,
1333                             *bytes);
1334    assert(*bytes > 0);
1335
1336    /*
1337     * Calculate the number of clusters to look for. We stop at L2 slice
1338     * boundaries to keep things simple.
1339     */
1340    nb_clusters =
1341        size_to_clusters(s, offset_into_cluster(s, guest_offset) + *bytes);
1342
1343    l2_index = offset_to_l2_slice_index(s, guest_offset);
1344    nb_clusters = MIN(nb_clusters, s->l2_slice_size - l2_index);
1345    assert(nb_clusters <= INT_MAX);
1346
1347    /* Limit total allocation byte count to INT_MAX */
1348    nb_clusters = MIN(nb_clusters, INT_MAX >> s->cluster_bits);
1349
1350    /* Find L2 entry for the first involved cluster */
1351    ret = get_cluster_table(bs, guest_offset, &l2_slice, &l2_index);
1352    if (ret < 0) {
1353        return ret;
1354    }
1355
1356    entry = be64_to_cpu(l2_slice[l2_index]);
1357    nb_clusters = count_cow_clusters(bs, nb_clusters, l2_slice, l2_index);
1358
1359    /* This function is only called when there were no non-COW clusters, so if
1360     * we can't find any unallocated or COW clusters either, something is
1361     * wrong with our code. */
1362    assert(nb_clusters > 0);
1363
1364    if (qcow2_get_cluster_type(bs, entry) == QCOW2_CLUSTER_ZERO_ALLOC &&
1365        (entry & QCOW_OFLAG_COPIED) &&
1366        (*host_offset == INV_OFFSET ||
1367         start_of_cluster(s, *host_offset) == (entry & L2E_OFFSET_MASK)))
1368    {
1369        int preallocated_nb_clusters;
1370
1371        if (offset_into_cluster(s, entry & L2E_OFFSET_MASK)) {
1372            qcow2_signal_corruption(bs, true, -1, -1, "Preallocated zero "
1373                                    "cluster offset %#llx unaligned (guest "
1374                                    "offset: %#" PRIx64 ")",
1375                                    entry & L2E_OFFSET_MASK, guest_offset);
1376            ret = -EIO;
1377            goto fail;
1378        }
1379
1380        /* Try to reuse preallocated zero clusters; contiguous normal clusters
1381         * would be fine, too, but count_cow_clusters() above has limited
1382         * nb_clusters already to a range of COW clusters */
1383        preallocated_nb_clusters =
1384            count_contiguous_clusters(bs, nb_clusters, s->cluster_size,
1385                                      &l2_slice[l2_index], QCOW_OFLAG_COPIED);
1386        assert(preallocated_nb_clusters > 0);
1387
1388        nb_clusters = preallocated_nb_clusters;
1389        alloc_cluster_offset = entry & L2E_OFFSET_MASK;
1390
1391        /* We want to reuse these clusters, so qcow2_alloc_cluster_link_l2()
1392         * should not free them. */
1393        keep_old_clusters = true;
1394    }
1395
1396    qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
1397
1398    if (alloc_cluster_offset == INV_OFFSET) {
1399        /* Allocate, if necessary at a given offset in the image file */
1400        alloc_cluster_offset = *host_offset == INV_OFFSET ? INV_OFFSET :
1401                               start_of_cluster(s, *host_offset);
1402        ret = do_alloc_cluster_offset(bs, guest_offset, &alloc_cluster_offset,
1403                                      &nb_clusters);
1404        if (ret < 0) {
1405            goto fail;
1406        }
1407
1408        /* Can't extend contiguous allocation */
1409        if (nb_clusters == 0) {
1410            *bytes = 0;
1411            return 0;
1412        }
1413
1414        assert(alloc_cluster_offset != INV_OFFSET);
1415    }
1416
1417    /*
1418     * Save info needed for meta data update.
1419     *
1420     * requested_bytes: Number of bytes from the start of the first
1421     * newly allocated cluster to the end of the (possibly shortened
1422     * before) write request.
1423     *
1424     * avail_bytes: Number of bytes from the start of the first
1425     * newly allocated to the end of the last newly allocated cluster.
1426     *
1427     * nb_bytes: The number of bytes from the start of the first
1428     * newly allocated cluster to the end of the area that the write
1429     * request actually writes to (excluding COW at the end)
1430     */
1431    uint64_t requested_bytes = *bytes + offset_into_cluster(s, guest_offset);
1432    int avail_bytes = nb_clusters << s->cluster_bits;
1433    int nb_bytes = MIN(requested_bytes, avail_bytes);
1434    QCowL2Meta *old_m = *m;
1435
1436    *m = g_malloc0(sizeof(**m));
1437
1438    **m = (QCowL2Meta) {
1439        .next           = old_m,
1440
1441        .alloc_offset   = alloc_cluster_offset,
1442        .offset         = start_of_cluster(s, guest_offset),
1443        .nb_clusters    = nb_clusters,
1444
1445        .keep_old_clusters  = keep_old_clusters,
1446
1447        .cow_start = {
1448            .offset     = 0,
1449            .nb_bytes   = offset_into_cluster(s, guest_offset),
1450        },
1451        .cow_end = {
1452            .offset     = nb_bytes,
1453            .nb_bytes   = avail_bytes - nb_bytes,
1454        },
1455    };
1456    qemu_co_queue_init(&(*m)->dependent_requests);
1457    QLIST_INSERT_HEAD(&s->cluster_allocs, *m, next_in_flight);
1458
1459    *host_offset = alloc_cluster_offset + offset_into_cluster(s, guest_offset);
1460    *bytes = MIN(*bytes, nb_bytes - offset_into_cluster(s, guest_offset));
1461    assert(*bytes != 0);
1462
1463    return 1;
1464
1465fail:
1466    if (*m && (*m)->nb_clusters > 0) {
1467        QLIST_REMOVE(*m, next_in_flight);
1468    }
1469    return ret;
1470}
1471
1472/*
1473 * alloc_cluster_offset
1474 *
1475 * For a given offset on the virtual disk, find the cluster offset in qcow2
1476 * file. If the offset is not found, allocate a new cluster.
1477 *
1478 * If the cluster was already allocated, m->nb_clusters is set to 0 and
1479 * other fields in m are meaningless.
1480 *
1481 * If the cluster is newly allocated, m->nb_clusters is set to the number of
1482 * contiguous clusters that have been allocated. In this case, the other
1483 * fields of m are valid and contain information about the first allocated
1484 * cluster.
1485 *
1486 * If the request conflicts with another write request in flight, the coroutine
1487 * is queued and will be reentered when the dependency has completed.
1488 *
1489 * Return 0 on success and -errno in error cases
1490 */
1491int qcow2_alloc_cluster_offset(BlockDriverState *bs, uint64_t offset,
1492                               unsigned int *bytes, uint64_t *host_offset,
1493                               QCowL2Meta **m)
1494{
1495    BDRVQcow2State *s = bs->opaque;
1496    uint64_t start, remaining;
1497    uint64_t cluster_offset;
1498    uint64_t cur_bytes;
1499    int ret;
1500
1501    trace_qcow2_alloc_clusters_offset(qemu_coroutine_self(), offset, *bytes);
1502
1503again:
1504    start = offset;
1505    remaining = *bytes;
1506    cluster_offset = INV_OFFSET;
1507    *host_offset = INV_OFFSET;
1508    cur_bytes = 0;
1509    *m = NULL;
1510
1511    while (true) {
1512
1513        if (*host_offset == INV_OFFSET && cluster_offset != INV_OFFSET) {
1514            *host_offset = start_of_cluster(s, cluster_offset);
1515        }
1516
1517        assert(remaining >= cur_bytes);
1518
1519        start           += cur_bytes;
1520        remaining       -= cur_bytes;
1521
1522        if (cluster_offset != INV_OFFSET) {
1523            cluster_offset += cur_bytes;
1524        }
1525
1526        if (remaining == 0) {
1527            break;
1528        }
1529
1530        cur_bytes = remaining;
1531
1532        /*
1533         * Now start gathering as many contiguous clusters as possible:
1534         *
1535         * 1. Check for overlaps with in-flight allocations
1536         *
1537         *      a) Overlap not in the first cluster -> shorten this request and
1538         *         let the caller handle the rest in its next loop iteration.
1539         *
1540         *      b) Real overlaps of two requests. Yield and restart the search
1541         *         for contiguous clusters (the situation could have changed
1542         *         while we were sleeping)
1543         *
1544         *      c) TODO: Request starts in the same cluster as the in-flight
1545         *         allocation ends. Shorten the COW of the in-fight allocation,
1546         *         set cluster_offset to write to the same cluster and set up
1547         *         the right synchronisation between the in-flight request and
1548         *         the new one.
1549         */
1550        ret = handle_dependencies(bs, start, &cur_bytes, m);
1551        if (ret == -EAGAIN) {
1552            /* Currently handle_dependencies() doesn't yield if we already had
1553             * an allocation. If it did, we would have to clean up the L2Meta
1554             * structs before starting over. */
1555            assert(*m == NULL);
1556            goto again;
1557        } else if (ret < 0) {
1558            return ret;
1559        } else if (cur_bytes == 0) {
1560            break;
1561        } else {
1562            /* handle_dependencies() may have decreased cur_bytes (shortened
1563             * the allocations below) so that the next dependency is processed
1564             * correctly during the next loop iteration. */
1565        }
1566
1567        /*
1568         * 2. Count contiguous COPIED clusters.
1569         */
1570        ret = handle_copied(bs, start, &cluster_offset, &cur_bytes, m);
1571        if (ret < 0) {
1572            return ret;
1573        } else if (ret) {
1574            continue;
1575        } else if (cur_bytes == 0) {
1576            break;
1577        }
1578
1579        /*
1580         * 3. If the request still hasn't completed, allocate new clusters,
1581         *    considering any cluster_offset of steps 1c or 2.
1582         */
1583        ret = handle_alloc(bs, start, &cluster_offset, &cur_bytes, m);
1584        if (ret < 0) {
1585            return ret;
1586        } else if (ret) {
1587            continue;
1588        } else {
1589            assert(cur_bytes == 0);
1590            break;
1591        }
1592    }
1593
1594    *bytes -= remaining;
1595    assert(*bytes > 0);
1596    assert(*host_offset != INV_OFFSET);
1597
1598    return 0;
1599}
1600
1601/*
1602 * This discards as many clusters of nb_clusters as possible at once (i.e.
1603 * all clusters in the same L2 slice) and returns the number of discarded
1604 * clusters.
1605 */
1606static int discard_in_l2_slice(BlockDriverState *bs, uint64_t offset,
1607                               uint64_t nb_clusters,
1608                               enum qcow2_discard_type type, bool full_discard)
1609{
1610    BDRVQcow2State *s = bs->opaque;
1611    uint64_t *l2_slice;
1612    int l2_index;
1613    int ret;
1614    int i;
1615
1616    ret = get_cluster_table(bs, offset, &l2_slice, &l2_index);
1617    if (ret < 0) {
1618        return ret;
1619    }
1620
1621    /* Limit nb_clusters to one L2 slice */
1622    nb_clusters = MIN(nb_clusters, s->l2_slice_size - l2_index);
1623    assert(nb_clusters <= INT_MAX);
1624
1625    for (i = 0; i < nb_clusters; i++) {
1626        uint64_t old_l2_entry;
1627
1628        old_l2_entry = be64_to_cpu(l2_slice[l2_index + i]);
1629
1630        /*
1631         * If full_discard is false, make sure that a discarded area reads back
1632         * as zeroes for v3 images (we cannot do it for v2 without actually
1633         * writing a zero-filled buffer). We can skip the operation if the
1634         * cluster is already marked as zero, or if it's unallocated and we
1635         * don't have a backing file.
1636         *
1637         * TODO We might want to use bdrv_block_status(bs) here, but we're
1638         * holding s->lock, so that doesn't work today.
1639         *
1640         * If full_discard is true, the sector should not read back as zeroes,
1641         * but rather fall through to the backing file.
1642         */
1643        switch (qcow2_get_cluster_type(bs, old_l2_entry)) {
1644        case QCOW2_CLUSTER_UNALLOCATED:
1645            if (full_discard || !bs->backing) {
1646                continue;
1647            }
1648            break;
1649
1650        case QCOW2_CLUSTER_ZERO_PLAIN:
1651            if (!full_discard) {
1652                continue;
1653            }
1654            break;
1655
1656        case QCOW2_CLUSTER_ZERO_ALLOC:
1657        case QCOW2_CLUSTER_NORMAL:
1658        case QCOW2_CLUSTER_COMPRESSED:
1659            break;
1660
1661        default:
1662            abort();
1663        }
1664
1665        /* First remove L2 entries */
1666        qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
1667        if (!full_discard && s->qcow_version >= 3) {
1668            l2_slice[l2_index + i] = cpu_to_be64(QCOW_OFLAG_ZERO);
1669        } else {
1670            l2_slice[l2_index + i] = cpu_to_be64(0);
1671        }
1672
1673        /* Then decrease the refcount */
1674        qcow2_free_any_clusters(bs, old_l2_entry, 1, type);
1675    }
1676
1677    qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
1678
1679    return nb_clusters;
1680}
1681
1682int qcow2_cluster_discard(BlockDriverState *bs, uint64_t offset,
1683                          uint64_t bytes, enum qcow2_discard_type type,
1684                          bool full_discard)
1685{
1686    BDRVQcow2State *s = bs->opaque;
1687    uint64_t end_offset = offset + bytes;
1688    uint64_t nb_clusters;
1689    int64_t cleared;
1690    int ret;
1691
1692    /* Caller must pass aligned values, except at image end */
1693    assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
1694    assert(QEMU_IS_ALIGNED(end_offset, s->cluster_size) ||
1695           end_offset == bs->total_sectors << BDRV_SECTOR_BITS);
1696
1697    nb_clusters = size_to_clusters(s, bytes);
1698
1699    s->cache_discards = true;
1700
1701    /* Each L2 slice is handled by its own loop iteration */
1702    while (nb_clusters > 0) {
1703        cleared = discard_in_l2_slice(bs, offset, nb_clusters, type,
1704                                      full_discard);
1705        if (cleared < 0) {
1706            ret = cleared;
1707            goto fail;
1708        }
1709
1710        nb_clusters -= cleared;
1711        offset += (cleared * s->cluster_size);
1712    }
1713
1714    ret = 0;
1715fail:
1716    s->cache_discards = false;
1717    qcow2_process_discards(bs, ret);
1718
1719    return ret;
1720}
1721
1722/*
1723 * This zeroes as many clusters of nb_clusters as possible at once (i.e.
1724 * all clusters in the same L2 slice) and returns the number of zeroed
1725 * clusters.
1726 */
1727static int zero_in_l2_slice(BlockDriverState *bs, uint64_t offset,
1728                            uint64_t nb_clusters, int flags)
1729{
1730    BDRVQcow2State *s = bs->opaque;
1731    uint64_t *l2_slice;
1732    int l2_index;
1733    int ret;
1734    int i;
1735    bool unmap = !!(flags & BDRV_REQ_MAY_UNMAP);
1736
1737    ret = get_cluster_table(bs, offset, &l2_slice, &l2_index);
1738    if (ret < 0) {
1739        return ret;
1740    }
1741
1742    /* Limit nb_clusters to one L2 slice */
1743    nb_clusters = MIN(nb_clusters, s->l2_slice_size - l2_index);
1744    assert(nb_clusters <= INT_MAX);
1745
1746    for (i = 0; i < nb_clusters; i++) {
1747        uint64_t old_offset;
1748        QCow2ClusterType cluster_type;
1749
1750        old_offset = be64_to_cpu(l2_slice[l2_index + i]);
1751
1752        /*
1753         * Minimize L2 changes if the cluster already reads back as
1754         * zeroes with correct allocation.
1755         */
1756        cluster_type = qcow2_get_cluster_type(bs, old_offset);
1757        if (cluster_type == QCOW2_CLUSTER_ZERO_PLAIN ||
1758            (cluster_type == QCOW2_CLUSTER_ZERO_ALLOC && !unmap)) {
1759            continue;
1760        }
1761
1762        qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
1763        if (cluster_type == QCOW2_CLUSTER_COMPRESSED || unmap) {
1764            l2_slice[l2_index + i] = cpu_to_be64(QCOW_OFLAG_ZERO);
1765            qcow2_free_any_clusters(bs, old_offset, 1, QCOW2_DISCARD_REQUEST);
1766        } else {
1767            l2_slice[l2_index + i] |= cpu_to_be64(QCOW_OFLAG_ZERO);
1768        }
1769    }
1770
1771    qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
1772
1773    return nb_clusters;
1774}
1775
1776int qcow2_cluster_zeroize(BlockDriverState *bs, uint64_t offset,
1777                          uint64_t bytes, int flags)
1778{
1779    BDRVQcow2State *s = bs->opaque;
1780    uint64_t end_offset = offset + bytes;
1781    uint64_t nb_clusters;
1782    int64_t cleared;
1783    int ret;
1784
1785    /* If we have to stay in sync with an external data file, zero out
1786     * s->data_file first. */
1787    if (data_file_is_raw(bs)) {
1788        assert(has_data_file(bs));
1789        ret = bdrv_co_pwrite_zeroes(s->data_file, offset, bytes, flags);
1790        if (ret < 0) {
1791            return ret;
1792        }
1793    }
1794
1795    /* Caller must pass aligned values, except at image end */
1796    assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
1797    assert(QEMU_IS_ALIGNED(end_offset, s->cluster_size) ||
1798           end_offset >= bs->total_sectors << BDRV_SECTOR_BITS);
1799
1800    /*
1801     * The zero flag is only supported by version 3 and newer. However, if we
1802     * have no backing file, we can resort to discard in version 2.
1803     */
1804    if (s->qcow_version < 3) {
1805        if (!bs->backing) {
1806            return qcow2_cluster_discard(bs, offset, bytes,
1807                                         QCOW2_DISCARD_REQUEST, false);
1808        }
1809        return -ENOTSUP;
1810    }
1811
1812    /* Each L2 slice is handled by its own loop iteration */
1813    nb_clusters = size_to_clusters(s, bytes);
1814
1815    s->cache_discards = true;
1816
1817    while (nb_clusters > 0) {
1818        cleared = zero_in_l2_slice(bs, offset, nb_clusters, flags);
1819        if (cleared < 0) {
1820            ret = cleared;
1821            goto fail;
1822        }
1823
1824        nb_clusters -= cleared;
1825        offset += (cleared * s->cluster_size);
1826    }
1827
1828    ret = 0;
1829fail:
1830    s->cache_discards = false;
1831    qcow2_process_discards(bs, ret);
1832
1833    return ret;
1834}
1835
1836/*
1837 * Expands all zero clusters in a specific L1 table (or deallocates them, for
1838 * non-backed non-pre-allocated zero clusters).
1839 *
1840 * l1_entries and *visited_l1_entries are used to keep track of progress for
1841 * status_cb(). l1_entries contains the total number of L1 entries and
1842 * *visited_l1_entries counts all visited L1 entries.
1843 */
1844static int expand_zero_clusters_in_l1(BlockDriverState *bs, uint64_t *l1_table,
1845                                      int l1_size, int64_t *visited_l1_entries,
1846                                      int64_t l1_entries,
1847                                      BlockDriverAmendStatusCB *status_cb,
1848                                      void *cb_opaque)
1849{
1850    BDRVQcow2State *s = bs->opaque;
1851    bool is_active_l1 = (l1_table == s->l1_table);
1852    uint64_t *l2_slice = NULL;
1853    unsigned slice, slice_size2, n_slices;
1854    int ret;
1855    int i, j;
1856
1857    slice_size2 = s->l2_slice_size * sizeof(uint64_t);
1858    n_slices = s->cluster_size / slice_size2;
1859
1860    if (!is_active_l1) {
1861        /* inactive L2 tables require a buffer to be stored in when loading
1862         * them from disk */
1863        l2_slice = qemu_try_blockalign(bs->file->bs, slice_size2);
1864        if (l2_slice == NULL) {
1865            return -ENOMEM;
1866        }
1867    }
1868
1869    for (i = 0; i < l1_size; i++) {
1870        uint64_t l2_offset = l1_table[i] & L1E_OFFSET_MASK;
1871        uint64_t l2_refcount;
1872
1873        if (!l2_offset) {
1874            /* unallocated */
1875            (*visited_l1_entries)++;
1876            if (status_cb) {
1877                status_cb(bs, *visited_l1_entries, l1_entries, cb_opaque);
1878            }
1879            continue;
1880        }
1881
1882        if (offset_into_cluster(s, l2_offset)) {
1883            qcow2_signal_corruption(bs, true, -1, -1, "L2 table offset %#"
1884                                    PRIx64 " unaligned (L1 index: %#x)",
1885                                    l2_offset, i);
1886            ret = -EIO;
1887            goto fail;
1888        }
1889
1890        ret = qcow2_get_refcount(bs, l2_offset >> s->cluster_bits,
1891                                 &l2_refcount);
1892        if (ret < 0) {
1893            goto fail;
1894        }
1895
1896        for (slice = 0; slice < n_slices; slice++) {
1897            uint64_t slice_offset = l2_offset + slice * slice_size2;
1898            bool l2_dirty = false;
1899            if (is_active_l1) {
1900                /* get active L2 tables from cache */
1901                ret = qcow2_cache_get(bs, s->l2_table_cache, slice_offset,
1902                                      (void **)&l2_slice);
1903            } else {
1904                /* load inactive L2 tables from disk */
1905                ret = bdrv_pread(bs->file, slice_offset, l2_slice, slice_size2);
1906            }
1907            if (ret < 0) {
1908                goto fail;
1909            }
1910
1911            for (j = 0; j < s->l2_slice_size; j++) {
1912                uint64_t l2_entry = be64_to_cpu(l2_slice[j]);
1913                int64_t offset = l2_entry & L2E_OFFSET_MASK;
1914                QCow2ClusterType cluster_type =
1915                    qcow2_get_cluster_type(bs, l2_entry);
1916
1917                if (cluster_type != QCOW2_CLUSTER_ZERO_PLAIN &&
1918                    cluster_type != QCOW2_CLUSTER_ZERO_ALLOC) {
1919                    continue;
1920                }
1921
1922                if (cluster_type == QCOW2_CLUSTER_ZERO_PLAIN) {
1923                    if (!bs->backing) {
1924                        /* not backed; therefore we can simply deallocate the
1925                         * cluster */
1926                        l2_slice[j] = 0;
1927                        l2_dirty = true;
1928                        continue;
1929                    }
1930
1931                    offset = qcow2_alloc_clusters(bs, s->cluster_size);
1932                    if (offset < 0) {
1933                        ret = offset;
1934                        goto fail;
1935                    }
1936
1937                    /* The offset must fit in the offset field */
1938                    assert((offset & L2E_OFFSET_MASK) == offset);
1939
1940                    if (l2_refcount > 1) {
1941                        /* For shared L2 tables, set the refcount accordingly
1942                         * (it is already 1 and needs to be l2_refcount) */
1943                        ret = qcow2_update_cluster_refcount(
1944                            bs, offset >> s->cluster_bits,
1945                            refcount_diff(1, l2_refcount), false,
1946                            QCOW2_DISCARD_OTHER);
1947                        if (ret < 0) {
1948                            qcow2_free_clusters(bs, offset, s->cluster_size,
1949                                                QCOW2_DISCARD_OTHER);
1950                            goto fail;
1951                        }
1952                    }
1953                }
1954
1955                if (offset_into_cluster(s, offset)) {
1956                    int l2_index = slice * s->l2_slice_size + j;
1957                    qcow2_signal_corruption(
1958                        bs, true, -1, -1,
1959                        "Cluster allocation offset "
1960                        "%#" PRIx64 " unaligned (L2 offset: %#"
1961                        PRIx64 ", L2 index: %#x)", offset,
1962                        l2_offset, l2_index);
1963                    if (cluster_type == QCOW2_CLUSTER_ZERO_PLAIN) {
1964                        qcow2_free_clusters(bs, offset, s->cluster_size,
1965                                            QCOW2_DISCARD_ALWAYS);
1966                    }
1967                    ret = -EIO;
1968                    goto fail;
1969                }
1970
1971                ret = qcow2_pre_write_overlap_check(bs, 0, offset,
1972                                                    s->cluster_size, true);
1973                if (ret < 0) {
1974                    if (cluster_type == QCOW2_CLUSTER_ZERO_PLAIN) {
1975                        qcow2_free_clusters(bs, offset, s->cluster_size,
1976                                            QCOW2_DISCARD_ALWAYS);
1977                    }
1978                    goto fail;
1979                }
1980
1981                ret = bdrv_pwrite_zeroes(s->data_file, offset,
1982                                         s->cluster_size, 0);
1983                if (ret < 0) {
1984                    if (cluster_type == QCOW2_CLUSTER_ZERO_PLAIN) {
1985                        qcow2_free_clusters(bs, offset, s->cluster_size,
1986                                            QCOW2_DISCARD_ALWAYS);
1987                    }
1988                    goto fail;
1989                }
1990
1991                if (l2_refcount == 1) {
1992                    l2_slice[j] = cpu_to_be64(offset | QCOW_OFLAG_COPIED);
1993                } else {
1994                    l2_slice[j] = cpu_to_be64(offset);
1995                }
1996                l2_dirty = true;
1997            }
1998
1999            if (is_active_l1) {
2000                if (l2_dirty) {
2001                    qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
2002                    qcow2_cache_depends_on_flush(s->l2_table_cache);
2003                }
2004                qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
2005            } else {
2006                if (l2_dirty) {
2007                    ret = qcow2_pre_write_overlap_check(
2008                        bs, QCOW2_OL_INACTIVE_L2 | QCOW2_OL_ACTIVE_L2,
2009                        slice_offset, slice_size2, false);
2010                    if (ret < 0) {
2011                        goto fail;
2012                    }
2013
2014                    ret = bdrv_pwrite(bs->file, slice_offset,
2015                                      l2_slice, slice_size2);
2016                    if (ret < 0) {
2017                        goto fail;
2018                    }
2019                }
2020            }
2021        }
2022
2023        (*visited_l1_entries)++;
2024        if (status_cb) {
2025            status_cb(bs, *visited_l1_entries, l1_entries, cb_opaque);
2026        }
2027    }
2028
2029    ret = 0;
2030
2031fail:
2032    if (l2_slice) {
2033        if (!is_active_l1) {
2034            qemu_vfree(l2_slice);
2035        } else {
2036            qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
2037        }
2038    }
2039    return ret;
2040}
2041
2042/*
2043 * For backed images, expands all zero clusters on the image. For non-backed
2044 * images, deallocates all non-pre-allocated zero clusters (and claims the
2045 * allocation for pre-allocated ones). This is important for downgrading to a
2046 * qcow2 version which doesn't yet support metadata zero clusters.
2047 */
2048int qcow2_expand_zero_clusters(BlockDriverState *bs,
2049                               BlockDriverAmendStatusCB *status_cb,
2050                               void *cb_opaque)
2051{
2052    BDRVQcow2State *s = bs->opaque;
2053    uint64_t *l1_table = NULL;
2054    int64_t l1_entries = 0, visited_l1_entries = 0;
2055    int ret;
2056    int i, j;
2057
2058    if (status_cb) {
2059        l1_entries = s->l1_size;
2060        for (i = 0; i < s->nb_snapshots; i++) {
2061            l1_entries += s->snapshots[i].l1_size;
2062        }
2063    }
2064
2065    ret = expand_zero_clusters_in_l1(bs, s->l1_table, s->l1_size,
2066                                     &visited_l1_entries, l1_entries,
2067                                     status_cb, cb_opaque);
2068    if (ret < 0) {
2069        goto fail;
2070    }
2071
2072    /* Inactive L1 tables may point to active L2 tables - therefore it is
2073     * necessary to flush the L2 table cache before trying to access the L2
2074     * tables pointed to by inactive L1 entries (else we might try to expand
2075     * zero clusters that have already been expanded); furthermore, it is also
2076     * necessary to empty the L2 table cache, since it may contain tables which
2077     * are now going to be modified directly on disk, bypassing the cache.
2078     * qcow2_cache_empty() does both for us. */
2079    ret = qcow2_cache_empty(bs, s->l2_table_cache);
2080    if (ret < 0) {
2081        goto fail;
2082    }
2083
2084    for (i = 0; i < s->nb_snapshots; i++) {
2085        int l1_size2;
2086        uint64_t *new_l1_table;
2087        Error *local_err = NULL;
2088
2089        ret = qcow2_validate_table(bs, s->snapshots[i].l1_table_offset,
2090                                   s->snapshots[i].l1_size, sizeof(uint64_t),
2091                                   QCOW_MAX_L1_SIZE, "Snapshot L1 table",
2092                                   &local_err);
2093        if (ret < 0) {
2094            error_report_err(local_err);
2095            goto fail;
2096        }
2097
2098        l1_size2 = s->snapshots[i].l1_size * sizeof(uint64_t);
2099        new_l1_table = g_try_realloc(l1_table, l1_size2);
2100
2101        if (!new_l1_table) {
2102            ret = -ENOMEM;
2103            goto fail;
2104        }
2105
2106        l1_table = new_l1_table;
2107
2108        ret = bdrv_pread(bs->file, s->snapshots[i].l1_table_offset,
2109                         l1_table, l1_size2);
2110        if (ret < 0) {
2111            goto fail;
2112        }
2113
2114        for (j = 0; j < s->snapshots[i].l1_size; j++) {
2115            be64_to_cpus(&l1_table[j]);
2116        }
2117
2118        ret = expand_zero_clusters_in_l1(bs, l1_table, s->snapshots[i].l1_size,
2119                                         &visited_l1_entries, l1_entries,
2120                                         status_cb, cb_opaque);
2121        if (ret < 0) {
2122            goto fail;
2123        }
2124    }
2125
2126    ret = 0;
2127
2128fail:
2129    g_free(l1_table);
2130    return ret;
2131}
2132