Re: [Qemu-devel] [PATCH v2 10/21] qcow2: refcount_order parameter for qcow2_create2

[Eric Blake <eblake@redhat.com>]

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On 11/14/2014 06:06 AM, Max Reitz wrote:
> Add a refcount_order parameter to qcow2_create2(), use that value for
> the image header and for calculating the size required for
> preallocation.
> 
> For now, always pass 4.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/qcow2.c | 41 ++++++++++++++++++++++++++++++-----------
>  1 file changed, 30 insertions(+), 11 deletions(-)
> 

> @@ -1811,6 +1811,13 @@ static int qcow2_create2(const char *filename, int64_t total_size,
>          int64_t meta_size = 0;
>          uint64_t nreftablee, nrefblocke, nl1e, nl2e;
>          int64_t aligned_total_size = align_offset(total_size, cluster_size);
> +        int refblock_bits, refblock_size;
> +        /* refcount entry size in bytes */
> +        double rces = (1 << refcount_order) / 8.;
> +

Maybe worth a comment that absolute precision is not necessary, and that
we are okay that the result gets us to within a fraction of a percent of
the right value.

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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