Re: [PATCH v4 3/5] parallels: Add checking and repairing duplicate offsets in BAT

[Mike Maslenkin]

Sorry for the noise again , but I have another note

On Mon, Apr 24, 2023 at 12:44 PM Alexander Ivanov
<alexander.ivanov@virtuozzo.com> wrote:
>
> Cluster offsets must be unique among all the BAT entries. Find duplicate
> offsets in the BAT and fix it by copying the content of the relevant
> cluster to a newly allocated cluster and set the new cluster offset to the
> duplicated entry.
>
> Add host_cluster_index() helper to deduplicate the code.
>
> Move parallels_fix_leak() call to parallels_co_check() to fix both types
> of leak: real corruption and a leak produced by allocate_clusters()
> during deduplication.
>
> Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
> ---
>  block/parallels.c | 134 ++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 129 insertions(+), 5 deletions(-)
>
> diff --git a/block/parallels.c b/block/parallels.c
> index ec89ed894b..3b992e8173 100644
> --- a/block/parallels.c
> +++ b/block/parallels.c
> @@ -136,6 +136,12 @@ static int cluster_remainder(BDRVParallelsState *s, 
> int64_t sector_num,
>      return MIN(nb_sectors, ret);
>  }
>
> +static uint32_t host_cluster_index(BDRVParallelsState *s, int64_t off)
> +{
> +    off -= s->header->data_off << BDRV_SECTOR_BITS;
> +    return off / s->cluster_size;
> +}
> +
>  static int64_t block_status(BDRVParallelsState *s, int64_t sector_num,
>                              int nb_sectors, int *pnum)
>  {
> @@ -533,7 +539,6 @@ parallels_check_leak(BlockDriverState *bs, 
> BdrvCheckResult *res,
>  {
>      BDRVParallelsState *s = bs->opaque;
>      int64_t count, leak_size;
> -    int ret;
>
>      leak_size = parallels_get_leak_size(bs, res);
>      if (leak_size < 0) {
> @@ -550,16 +555,123 @@ parallels_check_leak(BlockDriverState *bs, 
> BdrvCheckResult *res,
>              fix & BDRV_FIX_LEAKS ? "Repairing" : "ERROR", leak_size);
>
>      if (fix & BDRV_FIX_LEAKS) {
> -        ret = parallels_fix_leak(bs, res);
> -        if (ret < 0) {
> -            return ret;
> -        }
>          res->leaks_fixed += count;
>      }
>
>      return 0;
>  }
>
> +static int parallels_check_duplicate(BlockDriverState *bs,
> +                                     BdrvCheckResult *res,
> +                                     BdrvCheckMode *fix)
> +{
> +    BDRVParallelsState *s = bs->opaque;
> +    QEMUIOVector qiov;
> +    int64_t off, sector;
> +    unsigned long *bitmap;
> +    uint32_t i, bitmap_size, cluster_index;
> +    int n, ret = 0;
> +    uint64_t *buf = NULL;
> +
> +    /*
> +     * Create a bitmap of used clusters.
> +     * If a bit is set, there is a BAT entry pointing to this cluster.
> +     * Loop through the BAT entries, check bits relevant to an entry offset.
> +     * If bit is set, this entry is duplicated. Otherwise set the bit.
> +     *
> +     * We shouldn't worry about newly allocated clusters outside the image
> +     * because they are created higher then any existing cluster pointed by
> +     * a BAT entry.
> +     */
> +    bitmap_size = host_cluster_index(s, res->image_end_offset);
> +    bitmap = bitmap_new(bitmap_size);
> +
> +    buf = qemu_memalign(4096, s->cluster_size);
> +    qemu_iovec_init(&qiov, 0);
> +    qemu_iovec_add(&qiov, buf, s->cluster_size);
> +
> +    for (i = 0; i < s->bat_size; i++) {
> +        off = bat2sect(s, i) << BDRV_SECTOR_BITS;
> +        if (off == 0) {
> +            continue;
> +        }
> +
> +        cluster_index = host_cluster_index(s, off);
> +        if (test_bit(cluster_index, bitmap)) {
> +            /* this cluster duplicates another one */
> +            fprintf(stderr,
> +                    "%s duplicate offset in BAT entry %u\n",
> +                    *fix & BDRV_FIX_ERRORS ? "Repairing" : "ERROR", i);
> +
> +            res->corruptions++;
> +
> +            if (*fix & BDRV_FIX_ERRORS) {
> +                /*
> +                 * Reset the entry and allocate a new cluster
> +                 * for the relevant guest offset. In this way we let
> +                 * the lower layer to place the new cluster properly.
> +                 * Copy the original cluster to the allocated one.
> +                 */
> +                parallels_set_bat_entry(s, i, 0);
> +
> +                ret = bdrv_co_pread(bs->file, off, s->cluster_size, buf, 0);
> +                if (ret < 0) {
> +                    res->check_errors++;
> +                    goto out;
> +                }
> +
> +                sector = (i * s->cluster_size) >> BDRV_SECTOR_BITS;
> +                sector = allocate_clusters(bs, sector, s->tracks, &n);
> +                if (sector < 0) {
> +                    res->check_errors++;
> +                    ret = sector;
> +                    goto out;
> +                }

I can not understand how index in a BAT table related to s->cluster_size.
Probably there should be "cluster_index" used?
Anyway, looks like both cause uint32 truncation as result of
({i,cluster_index} * s->cluster_size)

Regards,
Mike.