On 07/03/2017 11:10 AM, Eric Blake wrote:
> When subdividing a bitmap serialization, the code in hbitmap.c
> enforces that start/count parameters are aligned (except that
> count can end early at end-of-bitmap). We exposed this required
> alignment through bdrv_dirty_bitmap_serialization_align(), but
> forgot to actually check that we comply with it.
>
> Fortunately, qcow2 is never dividing bitmap serialization smaller
> than one cluster (which is a minimum of 512 bytes); so we are
> always compliant with the serialization alignment (which insists
> that we partition at least 64 bits per chunk) because we are doing
> at least 4k bits per chunk.
>
> Still, it's safer to add an assertion (for the unlikely case that
> we'd ever support a cluster smaller than 512 bytes, or if the
> hbitmap implementation changes what it considers to be aligned),
> rather than leaving bdrv_dirty_bitmap_serialization_align()
> without a caller.
>
> Signed-off-by: Eric Blake <ebl...@redhat.com>
Reviewed-by: John Snow <js...@redhat.com>
>
> ---
> v4: new patch
> ---
> block/qcow2-bitmap.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c
> index 8448bec..75ee238 100644
> --- a/block/qcow2-bitmap.c
> +++ b/block/qcow2-bitmap.c
> @@ -274,10 +274,13 @@ static int free_bitmap_clusters(BlockDriverState *bs,
> Qcow2BitmapTable *tb)
> static uint64_t sectors_covered_by_bitmap_cluster(const BDRVQcow2State *s,
> const BdrvDirtyBitmap
> *bitmap)
> {
> - uint32_t sector_granularity =
> + uint64_t sector_granularity =
> bdrv_dirty_bitmap_granularity(bitmap) >> BDRV_SECTOR_BITS;
> + uint64_t sbc = sector_granularity * (s->cluster_size << 3);
>
> - return (uint64_t)sector_granularity * (s->cluster_size << 3);
> + assert(QEMU_IS_ALIGNED(sbc,
> + bdrv_dirty_bitmap_serialization_align(bitmap)));
> + return sbc;
> }
>
> /* load_bitmap_data
>
