Re: [Qemu-devel] [PATCH v3 31/39] qcow2: Update qcow2_truncate() to support L2 slices

[Max Reitz <mreitz@redhat.com>]

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On 2018-01-26 15:59, Alberto Garcia wrote:
> The qcow2_truncate() code is mostly independent from whether
> we're using L2 slices or full L2 tables, but in full and
> falloc preallocation modes new L2 tables are allocated using
> qcow2_alloc_cluster_link_l2().  Therefore the code needs to be
> modified to ensure that all nb_clusters that are processed in each
> call can be allocated with just one L2 slice.
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> ---
>  block/qcow2.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 78f067cae7..529becfa30 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -3261,8 +3261,9 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset,
>          guest_offset = old_length;
>          while (nb_new_data_clusters) {
>              int64_t guest_cluster = guest_offset >> s->cluster_bits;
> -            int64_t nb_clusters = MIN(nb_new_data_clusters,
> -                                      s->l2_size - guest_cluster % s->l2_size);
> +            int64_t nb_clusters = MIN(
> +                nb_new_data_clusters,
> +                s->l2_slice_size - guest_cluster % s->l2_slice_size);

An alternative would be the
"s->l2_slice_size - offset_to_l2_slice_index(s, guest_offset)" we
basically have elsewhere, but that's longer and doesn't really matter:

Reviewed-by: Max Reitz <mreitz@redhat.com>

>              QCowL2Meta allocation = {
>                  .offset       = guest_offset,
>                  .alloc_offset = host_offset,
> 



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