Re: [Qemu-devel] [PATCH v7 14/25] qcow2: Allow creation with refcount order != 4

[Eric Blake <eblake@redhat.com>]

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On 02/18/2015 03:40 PM, Max Reitz wrote:
> Add a creation option to qcow2 for setting the refcount order of images
> to be created, and respect that option's value.
> 
> This breaks some test outputs, fix them.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/qcow2.c              |  18 ++++++++
>  include/block/block_int.h  |   1 +
>  tests/qemu-iotests/049.out | 108 ++++++++++++++++++++++-----------------------
>  tests/qemu-iotests/082.out |  41 ++++++++++++++---
>  tests/qemu-iotests/085.out |  38 ++++++++--------
>  5 files changed, 126 insertions(+), 80 deletions(-)


> 
> diff --git a/block/qcow2.c b/block/qcow2.c
> index a07f134..4cdbd7e 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -2078,6 +2078,15 @@ static int qcow2_create(const char *filename, QemuOpts *opts, Error **errp)
>          goto finish;
>      }
>  
> +    refcount_bits = qemu_opt_get_number_del(opts, BLOCK_OPT_REFCOUNT_BITS,
> +                                            refcount_bits);
> +    if (refcount_bits > 64 || !is_power_of_2(refcount_bits)) {
> +        error_setg(errp, "Refcount width must be a power of two and may not "
> +                   "exceed 64 bits");
> +        ret = -EINVAL;
> +        goto finish;
> +    }
> +
>      if (version < 3 && refcount_bits != 16) {

The ffs() I complained about in 11/25 occurs shortly after this point,
and is therefore safe even though it is called on a 64-bit number,
because we have capped the number to be in range even after truncation
to int.

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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