Re: [Qemu-devel] [PATCH v2 1/2] block: Disallow snapshots if the overlay doesn't support backing files

[Eric Blake <eblake@redhat.com>]

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On 11/02/2015 05:15 AM, Alberto Garcia wrote:
> This addresses scenarios like this one:
> 
>   { 'execute': 'blockdev-add', 'arguments':
>     { 'options': { 'driver': 'qcow2',
>                    'node-name': 'new0',
>                    'file': { 'driver': 'file',
>                              'filename': 'new.qcow2',
>                              'node-name': 'file0' } } } }
> 
>   { 'execute': 'blockdev-snapshot', 'arguments':
>     { 'node': 'virtio0',
>       'overlay': 'file0' } }
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> ---
>  blockdev.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/blockdev.c b/blockdev.c
> index a567a05..2774bf5 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -1667,6 +1667,11 @@ static void external_snapshot_prepare(BlkTransactionState *common,
>  
>      if (state->new_bs->backing != NULL) {
>          error_setg(errp, "The snapshot already has a backing image");
> +        return;
> +    }
> +
> +    if (!state->new_bs->drv->supports_backing) {
> +        error_setg(errp, "The snapshot does not support backing images");
>      }
>  }

You could avoid the 'return' by doing:

if (state->new_bs->backing) {
    error_setg(...);
} else if (!state->new_bs->drv->supports_backing) {
    error_setg(...);
}

but I don't care enough to require a respin.

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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