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References: <20180509165530.29561-1-mreitz@redhat.com>
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From: Eric Blake <eblake@redhat.com>
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Date: Thu, 10 May 2018 09:24:24 -0500
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Subject: Re: [Qemu-devel] [PATCH 05/13] qapi: Formalize qcow encryption
 probing
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To: Max Reitz <mreitz@redhat.com>, qemu-block@nongnu.org
Cc: qemu-devel@nongnu.org, Markus Armbruster <armbru@redhat.com>, Kevin Wolf <kwolf@redhat.com>, Michael Roth <mdroth@linux.vnet.ibm.com>

On 05/09/2018 11:55 AM, Max Reitz wrote:
> Currently, you can give no encryption format for a qcow file while still
> passing a key-secret.  That does not conform to the schema, so this
> patch changes the schema to allow it.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---

>   ##
>   # @BlockdevQcowEncryptionFormat:
>   #
>   # @aes: AES-CBC with plain64 initialization vectors
>   #
> +# @from-image:      Determine the encryption format from the image
> +#                   header.  This only allows the use of the
> +#                   key-secret option.  (Since: 2.13)
> +#
>   # Since: 2.10
>   ##
>   { 'enum': 'BlockdevQcowEncryptionFormat',
> -  'data': [ 'aes' ] }
> +  'data': [ 'aes', 'from-image' ] }

Overkill.  Why not just:

>   
>   ##
>   # @BlockdevQcowEncryption:
> @@ -2728,9 +2748,11 @@
>   # Since: 2.10
>   ##
>   { 'union': 'BlockdevQcowEncryption',
> -  'base': { 'format': 'BlockdevQcowEncryptionFormat' },
> +  'base': { '*format': 'BlockdevQcowEncryptionFormat' },
>     'discriminator': 'format',
> -  'data': { 'aes': 'QCryptoBlockOptionsQCow' } }
> +  'default-variant': 'from-image',

'default-variant': 'aes'

> +  'data': { 'aes': 'QCryptoBlockOptionsQCow',

and call it good, because there are no other options to pick from, so 
'from-image' would always resolve to 'aes' anyway.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org