Re: [Libguestfs] [PATCH v2v] v2v: Allow output to block devices (RHBZ#1868690).
On Thu, Sep 3, 2020 at 3:36 PM Richard W.M. Jones <rjones(a)redhat.com> wrote:
On Tue, Sep 01, 2020 at 08:38:32PM +0100, Richard W.M. Jones wrote:
> On Tue, Sep 01, 2020 at 10:08:24PM +0300, Nir Soffer wrote:
> > > > I'm completely sure what the question means, but virt-v2v
currently
> > > > does this:
> > > >
> > > > qemu-img create -f FORMAT filename
> > > > qemu-img convert -n overlay filename
> >
> > This works, we also do this with file and block devices in most cases.
> >
> > I was confused by:
> >
> > > > > > + (* It turns out that libguestfs's disk
creation code is
> > > > > > + * considerably more flexible and easier to
use than
> > > > > > + * qemu-img, so create the disk explicitly
using libguestfs
> >
> > I guess you don't create qcow2 image without qemu-img?
> >
> > > > The new code doesn't change that for files, but the proposal
does
> > > > change it for devices to only this command:
> > > >
> > > > qemu-img convert -n overlay device
> >
> > This does not work for qcow2, since -n disable creation of the image.
>
> I'm going to have to play with this. It may be that we need
> to drop -n when using devices.
I had a look at this and you're right:
qemu-img: Could not open '/var/tmp/fedora-32-sda': Image is not in qcow2 format
but maybe if people use block devices they should have to format them
if they want to use qcow2?
It can work. In oVirt, when you get a block device with qcow2 format we already
created the image and you can use -n.
Other users can do the same, I don't know if there are any :-)
So supporting block devices and documenting that the user must prepare
the device
sounds like a good solution for now.
One reason is that they would get control over the qcow2 parameters
like cluster size, which would be hard to do if we had to pass them
all through virt-v2v. (Currently virt-v2v can only set qcow2
compression.)
The compression is not part to the image, I think it affects only
qemu-img convert,
so must be something that virt-v2v will handle.
Rich.
--
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