Re: [Qemu-devel] [Qemu-block] [PATCH v4 09/20] block: Add bitmap successors

[Stefan Hajnoczi]

On Fri, Mar 20, 2015 at 03:16:52PM -0400, John Snow wrote:
> A bitmap successor is an anonymous BdrvDirtyBitmap that is intended to
> be created just prior to a sensitive operation (e.g. Incremental Backup)
> that can either succeed or fail, but during the course of which we still
> want a bitmap tracking writes.
> 
> On creating a successor, we "freeze" the parent bitmap which prevents
> its deletion, enabling, anonymization, or creating a bitmap with the
> same name.
> 
> On success, the parent bitmap can "abdicate" responsibility to the
> successor, which will inherit its name. The successor will have been
> tracking writes during the course of the backup operation. The parent
> will be safely deleted.
> 
> On failure, we can "reclaim" the successor from the parent, unifying
> them such that the resulting bitmap describes all writes occurring since
> the last successful backup, for instance. Reclamation will thaw the
> parent, but not explicitly re-enable it.
> 
> BdrvDirtyBitmap operations that target a single bitmap are protected
> by assertions that the bitmap is not frozen and/or disabled.
> 
> BdrvDirtyBitmap operations that target a group of bitmaps, such as
> bdrv_{set,reset}_dirty will ignore frozen/disabled drives with a
> conditional instead.
> 
> QMP transactions that enable/disable bitmaps have extra error checking
> surrounding them that prevent modifying bitmaps that are frozen.
> 
> Signed-off-by: John Snow <address@hidden>
> Reviewed-by: Max Reitz <address@hidden>
> ---
>  block.c               | 104 
> +++++++++++++++++++++++++++++++++++++++++++++++++-
>  blockdev.c            |   7 ++++
>  include/block/block.h |  10 +++++
>  qapi/block-core.json  |   1 +
>  4 files changed, 121 insertions(+), 1 deletion(-)

Reviewed-by: Stefan Hajnoczi <address@hidden>

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