Re: [Qemu-devel] [PATCH for-2.12 3/3] block: Deprecate "backing": ""

[Markus Armbruster <armbru@redhat.com>]

Max Reitz <mreitz@redhat.com> writes:

> We have a clear replacement, so let's deprecate it.
>
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  qapi/block-core.json | 4 ++--
>  block.c              | 4 ++++
>  qemu-doc.texi        | 7 +++++++
>  qemu-options.hx      | 4 ++--
>  4 files changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 76bf50f813..dfe4d3650c 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -1090,7 +1090,7 @@
>  # @overlay: reference to the existing block device that will become
>  #           the overlay of @node, as part of creating the snapshot.
>  #           It must not have a current backing file (this can be
> -#           achieved by passing "backing": "" to blockdev-add).
> +#           achieved by passing "backing": null to blockdev-add).
>  #
>  # Since: 2.5
>  ##
> @@ -1238,7 +1238,7 @@
>  #                     "node-name": "node1534",
>  #                     "file": { "driver": "file",
>  #                               "filename": "hd1.qcow2" },
> -#                     "backing": "" } }
> +#                     "backing": null } }
>  #
>  # <- { "return": {} }
>  #
> diff --git a/block.c b/block.c
> index bc92ddd5a0..463c4de25b 100644
> --- a/block.c
> +++ b/block.c
> @@ -2559,6 +2559,10 @@ static BlockDriverState *bdrv_open_inherit(const char *filename,
>      /* See cautionary note on accessing @options above */
>      backing = qdict_get_try_str(options, "backing");
>      if (qdict_is_qnull(options, "backing") || (backing && *backing == '\0')) {
> +        if (backing) {
> +            warn_report("Use of \"backing\": \"\" is deprecated; "
> +                        "use \"backing\": null instead");
> +        }
>          flags |= BDRV_O_NO_BACKING;
>          qdict_del(options, "backing");
>      }
> diff --git a/qemu-doc.texi b/qemu-doc.texi
> index 8c10956a66..8f57d9ad21 100644
> --- a/qemu-doc.texi
> +++ b/qemu-doc.texi
> @@ -2537,6 +2537,13 @@ or ``ivshmem-doorbell`` device types.
>  The ``spapr-pci-vfio-host-bridge'' device type is replaced by
>  the ``spapr-pci-host-bridge'' device type.
>  
> +@section Block device options
> +
> +@subsection "backing": "" (since 2.12.0)
> +
> +In order to prevent QEMU from automatically opening an image's backing
> +chain, use ``"backing": null'' instead.
> +
>  @node License
>  @appendix License
>  
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 3728e9b4dd..0ee1a04d00 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -731,8 +731,8 @@ Reference to or definition of the data source block driver node
>  
>  @item backing
>  Reference to or definition of the backing file block device (default is taken
> -from the image file). It is allowed to pass an empty string here in order to
> -disable the default backing file.
> +from the image file). It is allowed to pass @code{null} here in order to disable
> +the default backing file.
>  
>  @item lazy-refcounts
>  Whether to enable the lazy refcounts feature (on/off; default is taken from the

Missed in commit c42e8742f, I guess.

Reviewed-by: Markus Armbruster <armbru@redhat.com>