Re: [Qemu-devel] [PATCH 2/4] qcow2: Move sync out of update_refcount

[Anthony Liguori]

On 09/17/2010 11:18 AM, Kevin Wolf wrote:
> Note that the flush is omitted intentionally in qcow2_free_clusters. If
> anything, we can leak clusters here if we lose the writes.
>
> Signed-off-by: Kevin Wolf<address@hidden>
>    

Cluster leaking gets picked up by bdrv_check though, right?

I think I've convinced myself that leaking clusters is not an acceptable 
behavior from a security perspective but as long as it's detectable via 
bdrv_check, qcow2 could implement an online check to address it.

Regards,

Anthony Liguori

> ---
>   block/qcow2-refcount.c |   13 +++++++++++--
>   1 files changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
> index 7dc75d1..4fc3f80 100644
> --- a/block/qcow2-refcount.c
> +++ b/block/qcow2-refcount.c
> @@ -261,6 +261,8 @@ static int64_t alloc_refcount_block(BlockDriverState *bs, 
> int64_t cluster_index)
>               goto fail_block;
>           }
>
> +        bdrv_flush(bs->file);
> +
>           /* Initialize the new refcount block only after updating its refcount,
>            * update_refcount uses the refcount cache itself */
>           memset(s->refcount_block_cache, 0, s->cluster_size);
> @@ -551,8 +553,6 @@ fail:
>           dummy = update_refcount(bs, offset, cluster_offset - offset, -addend);
>       }
>
> -    bdrv_flush(bs->file);
> -
>       return ret;
>   }
>
> @@ -575,6 +575,8 @@ static int update_cluster_refcount(BlockDriverState *bs,
>           return ret;
>       }
>
> +    bdrv_flush(bs->file);
> +
>       return get_refcount(bs, cluster_index);
>   }
>
> @@ -626,6 +628,9 @@ int64_t qcow2_alloc_clusters(BlockDriverState *bs, int64_t 
> size)
>       if (ret<  0) {
>           return ret;
>       }
> +
> +    bdrv_flush(bs->file);
> +
>       return offset;
>   }
>
> @@ -803,6 +808,10 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
>                               if (ret<  0) {
>                                   goto fail;
>                               }
> +
> +                            /* TODO Flushing once for the whole function should
> +                             * be enough */
> +                            bdrv_flush(bs->file);
>                           }
>                           /* compressed clusters are never modified */
>                           refcount = 2;
>