Re: [PATCH v2 1/2] block: commit: Allow users to request only format driver names in backing file format

[Eric Blake]

On Thu, Nov 30, 2023 at 05:06:03PM +0100, Peter Krempa wrote:
> Introduce a new flag 'backing_file_format_no_protocol' for the
> block-commit QMP command which instructs the internals to use 'raw'
> instead of the protocol driver in case when a image is used without a
> dummy 'raw' wrapper.
> 
> The flag is designed such that it can be always asserted by management
> tools even when there isn't any update to backing files.
> 
> The flag will be used by libvirt so that the backing images still
> reference the proper format even when libvirt will stop using the dummy
> raw driver (raw driver with no other config). Libvirt needs this so that
> the images stay compatible with older libvirt versions which didn't
> expect that a protocol driver name can appear in the backing file format
> field.
> 
> Signed-off-by: Peter Krempa <pkrempa@redhat.com>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> ---

> +++ b/qapi/block-core.json
> @@ -1810,6 +1810,14 @@
>  #     Care should be taken when specifying the string, to specify a
>  #     valid filename or protocol.  (Since 2.1)
>  #
> +# @backing-file-format-no-protocol: If true always use a 'format' driver name
> +#     for the 'backing file format' field if updating the image header of the
> +#     overlay of 'top'. Otherwise the real name of the driver of the backing
> +#     image may be used which may be a protocol driver.
> +#
> +#     Can be used also when no image header will be updated.
> +#     (default: false; since: 9.0)

This is a long name.  What about:

@backing-mask-protocol: If true, replace any protocol mentioned in the
    'backing file format' with 'raw', rather than storing the protocol
    name as the backing format.  Can be used even when no image header
    will be updated (default false; since 9.0).

or s/mask/hide/ if that sounds better.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization:  qemu.org | libguestfs.org