Re: [Qemu-devel] [PATCH v3 07/22] qcow2: Helper function for refcount modification

[Eric Blake <eblake@redhat.com>]

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On 11/20/2014 10:06 AM, Max Reitz wrote:
> Since refcounts do not always have to be a uint16_t, all refcount blocks
> and arrays in memory should not have a specific type (thus they become
> pointers to void) and for accessing them, two helper functions are used
> (a getter and a setter). Those functions are called indirectly through
> function pointers in the BDRVQcowState so they may later be exchanged
> for different refcount orders.
> 
> With the check and repair functions using this function, the refcount
> array they are creating will be in big endian byte order; additionally,
> using realloc_refcount_array() makes the size of this refcount array
> always cluster-aligned. Both combined allow rebuild_refcount_structure()
> to drop the bounce buffer which was used to convert parts of the
> refcount array to big endian byte order and store them on disk. Instead,
> those parts can now be written directly.

Thanks, that helps.

> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/qcow2-refcount.c | 131 ++++++++++++++++++++++++++++++-------------------
>  block/qcow2.h          |   8 +++
>  2 files changed, 89 insertions(+), 50 deletions(-)
> 

> @@ -2101,7 +2132,7 @@ int qcow2_check_refcounts(BlockDriverState *bs, BdrvCheckResult *res,
>          /* Because the old reftable has been exchanged for a new one the
>           * references have to be recalculated */
>          rebuild = false;
> -        memset(refcount_table, 0, nb_clusters * sizeof(uint16_t));
> +        memset(refcount_table, 0, refcount_array_byte_size(s, nb_clusters));

Yep, that makes more sense than what you had in v2.

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

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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