Re: [Qemu-devel] [PATCH] qcow2: Simplify calculation for COW area at the end

[Paolo Bonzini <pbonzini@redhat.com>]

Il 12/06/2012 15:47, Kevin Wolf ha scritto:
> copy_sectors() always uses the sum (cluster_offset + n_start) or
> (start_sect + n_start), so if some value is added to both cluster_offset
> and start_sect, and subtracted from n_start, it's cancelled out anyway.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/qcow2-cluster.c |    5 ++---
>  1 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index 9aee9fc..763b724 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -640,11 +640,10 @@ int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m)
>      }
>  
>      if (m->nb_available & (s->cluster_sectors - 1)) {
> -        uint64_t end = m->nb_available & ~(uint64_t)(s->cluster_sectors - 1);
>          cow = true;
>          qemu_co_mutex_unlock(&s->lock);
> -        ret = copy_sectors(bs, start_sect + end, cluster_offset + (end << 9),
> -                m->nb_available - end, s->cluster_sectors);
> +        ret = copy_sectors(bs, start_sect, cluster_offset,
> +                m->nb_available, s->cluster_sectors);

Do you need to add end to s->cluster_sectors too, so that "start_sect +
n_end" and "n_end - n_start" remain the same?

Paolo