On Mon, Jul 09, 2018 at 05:52:42PM +0100, Richard W.M. Jones wrote: > On Mon, Jul 09, 2018 at 07:38:05PM +0300, Nir Soffer wrote: > > We are discussing importing VM images to KubVirt. The goal is to be > > able to import an existing qcow2 disk, probably some appliance stored > > on http server, and and convert it to raw format for writing to storage. > > > > This can be also useful for for oVirt for importing OVA, since we like to > > pack > > disks in qcow2 format inside OVA, but the user may like to use raw disks, or > > for uploading existing disks. > > > > Of course converting the image using qemu-img is easy, but requires > > downloading the image to temporary disk. We would like to avoid temporary > > disks, or telling users to convert the image. > > > > Base on the discussion we had here: > > https://lists.ovirt.org/archives/list/us...@ovirt.org/thread/GNAVJ253FP65QUSOONES5XZGRIDX5ABC/#YMLSEGU7PN3MX5MUORGEGGAQLLSL4KKJ > > > > I think this is impossible since qcow2 is not built for streaming. But both > > Richard and Eric suggested some solutions. > > > > The flow is: > > > > qcow2 image -- http --> importer -> raw file > > > > Is it possible to implement the importer using qemu-img and qemu-nbd, > > or maybe nbdkit? > > Strictly speaking streaming qcow2 to raw is not possible. However > placing an overlay on top of the original remote image will allow > streaming to raw with only a modest amount of local storage consumed. > > You can demonstrate this fairly easily: > > $ qemu-img create -f qcow2 -b 'json: { "file.driver": "https", "file.url": > "https://uk-mirrors.evowise.com/fedora/releases/28/Cloud/x86_64/images/Fedora-Cloud-Base-28-1.1.x86_64.qcow2", > "file.timeout": 10000 }' /var/tmp/overlay.qcow2 > $ qemu-img convert -p -f qcow2 -O raw overlay.qcow2 fedora.img > > There are various tricks you can play with caching and copy-on-read to > make the process more efficient (note that copy-on-read will result in > a full local copy, but there are maybe some optimizations we could do > in qcow2 for that).
Sorry, I meant "in qemu". > For the other cases such as xz-compressed remote images, I'd recommend > using nbdkit (and/or a plugin, but maybe you can do it with the > default plugins and filters). An actual example is not going to fit > into this email and I'm short of time to write it, but for some ideas > how to do this you can look at my blog and the nbdkit docs: > > https://rwmj.wordpress.com/2013/06/24/xz-plugin-for-nbdkit/ > https://github.com/libguestfs/nbdkit Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v