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Re: [Qemu-devel] [PATCH v3 03/25] block: Add BDS.backing_overridden

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH v3 03/25] block: Add BDS.backing_overridden
Date: Wed, 11 Jan 2017 13:00:27 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0

On 11/29/2016 07:18 PM, Max Reitz wrote:
> If the backing file is overridden, this most probably does change the
> guest-visible data of a BDS. Therefore, we will need to consider this in
> bdrv_refresh_filename().
> Adding a new field to the BDS is not nice, but it is very simple and
> exactly keeps track of whether the backing file has been overridden.
> This commit adds a FIXME which will be remedied by a follow-up commit.
> Until then, the respective piece of code will not result in any behavior
> that is worse than what we currently have.
> Signed-off-by: Max Reitz <address@hidden>
> ---

> +++ b/include/block/block_int.h
> @@ -461,6 +461,7 @@ struct BlockDriverState {
>      char backing_file[PATH_MAX]; /* if non zero, the image is a diff of
>                                      this file image */
>      char backing_format[16]; /* if non-zero and backing_file exists */
> +    bool backing_overridden; /* backing file has been specified by the user 
> */

Should we group all of the bool in this struct so as to reduce its size
and improve cache locality?  But it's already clunky, so that may be
appropriate as a separate patch.

Reviewed-by: Eric Blake <address@hidden>

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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