Re: Storing command line options in qcow2 images

[Anthony Liguori <anthony-rdkfGonbjUSkNkDKm+mE6A@public.gmane.org>]

I don't think adding annotations as snapshots is the right approach.  I 
think proper support should be added in the header.  I wouldn't be too 
concerned with breaking compatibility in qcow2.  That's why it's qcow2 
and not just an updated version of qcow, qcow2 is still, AFAIK, open for 
breakage.

Regards,

Anthony Liguori

Jorge Lucángeli Obes wrote:
> Hi Avi, hi all,
>
> I've started some (very minor) groundwork for this task. My idea was
> to add an extra "annotation" field in qcow2 snapshots. In this way, a
> snapshot can hold abitrary information; for example, command line
> arguments.
>
> Before going any further, I wanted to validate the general idea with
> the list. I am planning on using a snapshot with a distinct name to
> store command line options. This approach seems simple yet it is
> powerful enough for what we need to do.
>
> There's a slight overhead as now all qcow2 snapshots have to store a
> extra (probably) empty pointer. An alternative approach would be to
> somehow indicate that some snapshots are "descriptive" snapshots and
> others are "useful" snapshots; however, I felt that this would be more
> complicated.
>
> I have a working patch to qemu-img that allows storing arbitrary
> annotations into qcow2 images. I developed it as a testing utility.
> Right now annotations are implemented as another string alongside the
> snapshot's 'name' and 'id'. I thought about storing annotations as
> key/value pairs but again, it seemed overkill.
>
> >From here, the plan would be to add a command to qemu-img that allows
> embedding of command line options into qcow2 images. These options
> would be stored in a snapshot with a special name, and qemu would
> check for the presence of this snapshot in order to read command line
> options from the qcow2 image.
>
> Ideas? Suggestions? I can send the patches for the functionality
> that's implemented right now.
>
> Cheers,
> Jorge
>
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