[libvirt PATCH v2 2/2] storage_file: add support to probe cluster_size from QCOW2 images

[Peter Krempa]

On Thu, May 20, 2021 at 17:14:32 +0200, Pavel Hrdina wrote:
> >From QEMU docs/interop/qcow2.txt :
> 
>    Byte  20 - 23:   cluster_bits
>                     Number of bits that are used for addressing an offset
>                     within a cluster (1 << cluster_bits is the cluster size).
> 
> With this patch libvirt will be able to report the current cluster_size
> for all existing storage volumes managed by storage driver.
> 
> Signed-off-by: Pavel Hrdina <phrdina at redhat.com>
> ---
> 
> Changes in v2:
>     - Reworkded to use callback.
> 
>  src/storage/storage_util.c            |  3 ++
>  src/storage_file/storage_file_probe.c | 70 ++++++++++++++++++++-------
>  2 files changed, 56 insertions(+), 17 deletions(-)

[...]

> @@ -468,6 +477,28 @@ qcow2GetExtensions(const char *buf,
>  }
>  
>  
> +static unsigned long long
> +qcow2GetClusterSize(const char *buf,
> +                    size_t buf_size,
> +                    int endian)

The 'endian' argument makes sense only for generic getters. You know
that qcow2 has always LV_BIG_ENDIAN set.

> +{
> +    int clusterBits = 0;
> +
> +    if ((QCOWX_HDR_CLUSTER_BITS_OFFSET + 4) > buf_size)
> +        return 0;
> +
> +    if (endian == LV_LITTLE_ENDIAN)
> +        clusterBits = virReadBufInt32LE(buf + QCOWX_HDR_CLUSTER_BITS_OFFSET);
> +    else
> +        clusterBits = virReadBufInt32BE(buf + QCOWX_HDR_CLUSTER_BITS_OFFSET);
> +
> +    if (clusterBits > 0)
> +        return 1 << clusterBits;
> +
> +    return 0;
> +}

Drop the 'endian' argument with appropriate cleanup and:

Reviewed-by: Peter Krempa <pkrempa at redhat.com>