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>
---
 block/qcow2.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index 78f067cae7..28050a4b3e 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -3260,9 +3260,9 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset,
         host_offset = allocation_start;
         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 - offset_to_l2_slice_index(s, guest_offset));
             QCowL2Meta allocation = {
                 .offset       = guest_offset,
                 .alloc_offset = host_offset,
-- 
2.11.0

On 2018-02-05 15:33, 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>
> ---
>  block/qcow2.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)

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

On 02/05/2018 08:33 AM, 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>
> ---
>   block/qcow2.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
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