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Re: [PATCH v3 0/6] block: add block-dirty-bitmap-populate job


From: Kevin Wolf
Subject: Re: [PATCH v3 0/6] block: add block-dirty-bitmap-populate job
Date: Tue, 23 Jun 2020 13:47:14 +0200

Am 19.06.2020 um 21:56 hat Eric Blake geschrieben:
> [From John's original cover letter:]
> This is a new (very small) block job that writes a pattern into a
> bitmap. The only pattern implemented is the top allocation information.
> 
> This can be used to "recover" an incremental bitmap chain if an external
> snapshot was taken without creating a new bitmap first: any writes made
> to the image will be reflected by the allocation status and can be
> written back into a bitmap.
> 
> This is useful for e.g. libvirt managing backup chains if a user creates
> an external snapshot outside of libvirt.
> 
> v3:
>  - Addressed a bit more feedback
>  - Make it easier to decide if we want an x- prefix if we think there
>  are more tweaks to be made to the interface
>  - Drop dependency on John's JobRunner iotest series
>  - Renumber the new iotest
> 
> I know there was a lot of discussion about whether there are
> optimizations to be made with populating directly into the target
> bitmap rather than into a temporary that then gets merged in at the
> completion of the job, but the QMP aspect seems fairly stable.  Even
> so, we may still want to consider using an x- prefix until we know for
> sure whether libvirt can make decent use of the interface.

Fair enough, as long as everyone agrees that the QMP aspect includes
that merging the bits only at the end of the job is an implementation
detail and not something that client may rely on.

Kevin




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