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

["Benoît Canet" <benoit.canet@irqsave.net>]

The Friday 29 Aug 2014 à 23:45:27 (+0200), 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

Now if the refblock entry size is smaller than a byte

> accordingly.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  docs/specs/qcow2.txt | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/docs/specs/qcow2.txt b/docs/specs/qcow2.txt
> index cfbc8b0..531c478 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 / (refcount_bits / 8))

This give a divide by zero error.                   ^

>  
>      refcount_block_index = (offset / cluster_size) % refcount_block_entries
>      refcount_table_index = (offset / cluster_size) / refcount_block_entries
> -- 
> 2.1.0
> 
>