Re: [Qemu-devel] [RFC PATCH 00/11] qcow2: External data files

[Max Reitz]

On 31.01.19 18:55, Kevin Wolf wrote:
> There are use cases where raw images are given (e.g. existing physical
> disks), but advanced features like dirty bitmaps or backing files are
> wanted that require use of a proper image format like qcow2.
> 
> This series adds an incompatible feature bit to qcow2 which allows to
> use an external data file: Metadata is kept in the qcow2 file like
> usual, but guest data is written to an external file. Clusters in the
> data file are not reference counted, instead we use a flat layout where
> host cluster offset == guest cluster offset. The external data file is
> therefore readable as a raw image (though writing to it invalidates the
> associated qcow2 metadata). Features that require refcounting such as
> internal snapshots or compression are not supposed in such setups.

Overall the design to me looks as simple as it could be, which means
there is equally little I could object to.  I raised some technical
things, but this is an RFC anyway, so, yeah.

Looks good!

About testing...  I really don't know either.  I'll think about it,
maybe I come up with something.

Max

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