Re: [Qemu-devel] [PATCH v2 2/3] docs/qcow2: Correct refcount_block_entries

[Eric Blake]

On 09/02/2014 04:25 PM, Max Reitz wrote:
> A refblock entry may have a different size than 16 bits, it may even be
> smaller than a byte. Correct the refcount_block_entries calculation
> accordingly.
> 
> Signed-off-by: Max Reitz <address@hidden>
> ---
>  docs/specs/qcow2.txt | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Eric Blake <address@hidden>

> 
> diff --git a/docs/specs/qcow2.txt b/docs/specs/qcow2.txt
> index cfbc8b0..0a878aa 100644
> --- a/docs/specs/qcow2.txt
> +++ b/docs/specs/qcow2.txt
> @@ -183,7 +183,7 @@ blocks and are exactly one cluster in size.
>  Given a offset into the image file, the refcount of its cluster can be 
> obtained
>  as follows:
>  
> -    refcount_block_entries = (cluster_size / sizeof(uint16_t))
> +    refcount_block_entries = (cluster_size * 8 / refcount_bits)
>  
>      refcount_block_index = (offset / cluster_size) % refcount_block_entries
>      refcount_table_index = (offset / cluster_size) / refcount_block_entries
> 

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

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