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Re: [Qemu-block] [Qemu-devel] [PATCH v2 10/11] block/backup: support bit

From: Markus Armbruster
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v2 10/11] block/backup: support bitmap sync modes for non-bitmap backups
Date: Tue, 16 Jul 2019 07:18:35 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux)

John Snow <address@hidden> writes:

> Accept bitmaps and sync policies for the other backup modes.
> This allows us to do things like create a bitmap synced to a full backup
> without a transaction, or start a resumable backup process.
> Some combinations don't make sense, though:
> - NEVER policy combined with any non-BITMAP mode doesn't do anything,
>   because the bitmap isn't used for input or output.
>   It's harmless, but is almost certainly never what the user wanted.
> - sync=NONE is more questionable. It can't use on-success because this
>   job never completes with success anyway, and the resulting artifact
>   of 'always' is suspect: because we start with a full bitmap and only
>   copy out segments that get written to, the final output bitmap will
>   always be ... a fully set bitmap.
>   Maybe there's contexts in which bitmaps make sense for sync=none,
>   but not without more severe changes to the current job, and omitting
>   it here doesn't prevent us from adding it later.
> Signed-off-by: John Snow <address@hidden>
> ---
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 5a578806c5..099e4f37b2 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -1352,13 +1352,15 @@
>  # @speed: the maximum speed, in bytes per second. The default is 0,
>  #         for unlimited.
>  #
> -# @bitmap: the name of a dirty bitmap if sync is "bitmap" or "incremental".
> +# @bitmap: The name of a dirty bitmap to use.
>  #          Must be present if sync is "bitmap" or "incremental".
> +#          Can be present if sync is "full" or "top".
>  #          Must not be present otherwise.
>  #          (Since 2.4 (drive-backup), 3.1 (blockdev-backup))
>  #
>  # @bitmap-mode: Specifies the type of data the bitmap should contain after
> -#               the operation concludes. Must be present if sync is "bitmap".
> +#               the operation concludes.
> +#               Must be present if a bitmap was provided,
>  #               Must NOT be present otherwise. (Since 4.2)
>  #
>  # @compress: true to compress data, if the target format supports it.

Do you expect management applications will want to know about the
presence of this patch?

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