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Re: [PATCH 2/2] nbd: Add new qemu:joint-allocation metadata context


From: Nir Soffer
Subject: Re: [PATCH 2/2] nbd: Add new qemu:joint-allocation metadata context
Date: Mon, 14 Jun 2021 17:06:46 +0300

On Mon, Jun 14, 2021 at 4:56 PM Eric Blake <eblake@redhat.com> wrote:
>
> On Sat, Jun 12, 2021 at 02:39:44AM +0300, Nir Soffer wrote:
> > Since this change is not simple, and the chance that we also get the dirty
> > bitmap included in the result seems to be very low, I decided to check the
> > direction of merging multiple extents.
> >
> > I started with merging "base:allocation" and "qemu:dirty-bitmap:xxx" since
> > we already have both. It was not hard to do, although it is not completely
> > tested yet.
> >
> > Here is the merging code:
> > https://gerrit.ovirt.org/c/ovirt-imageio/+/115216/1/daemon/ovirt_imageio/_internal/nbdutil.py
> >
> > To make merging easy and safe, we map the NBD_STATE_DIRTY bit to a private 
> > bit
> > so it cannot clash with the NBD_STATE_HOLE bit:
> > https://gerrit.ovirt.org/c/ovirt-imageio/+/115215/1/daemon/ovirt_imageio/_internal/nbd.py
> >
> > Here is a functional test using qemu-nbd showing that it works:
> > https://gerrit.ovirt.org/c/ovirt-imageio/+/115216/1/daemon/test/client_test.py
> >
> > I'll try to use "qemu:allocation-depth" in a similar way next week, probably
> > mapping depth > 0 to EXTENT_EXISTS, to use when reporting holes in
> > single qcow2 images.
> >
> > If this is successful, we can start using this in the next ovirt release, 
> > and we
> > don't need "qemu:joint-allocation".
>
> That's nice to know.  So at this point, we'll drop the patch on
> qemu:joint-allocation, and instead focus on teh patch that improves
> qemu-img map output to make it easier to use in the same way that
> qemu:allocation-depth is.

I can update that everything looks good on our side so far, thanks!




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