[Libguestfs] [PATCH virt-v2v] v2v: -o rhv-upload: Enable multi-conn

Richard W.M. Jones rjones at redhat.com
Mon Aug 2 21:46:39 UTC 2021

On Tue, Aug 03, 2021 at 12:16:48AM +0300, Nir Soffer wrote:
> On Mon, Aug 2, 2021 at 6:49 PM Richard W.M. Jones <rjones at redhat.com> wrote:
> >
> > On Mon, Aug 02, 2021 at 01:50:05PM +0100, Richard W.M. Jones wrote:
> > > However it didn't appear to create multiple disks, unless it only
> > > attached one and the others are hidden somehow.  I'll PM you the admin
> > > details for my RHV cluster so you can take a look.
> >
> > It turns out that it does create a new disk on every connection -- I
> > can see it under the Storage tab -- so that's quite bad.  I'll see if
> > I can come up with a patch.
> It shows that the code is robust, but not very useful :-)
> I guess that the vm was created with the last disk id written
> to disk.
> The issue is not only creating the disk, but creating an image transfer
> per plugin open(). The wanted flow is:
> 1. precheck (vm already exists? etc.)
> 2. convert source disk
> We need to know the size and required allocation of the disk
> before creating the disk, for example for qcow2 disks on block
> storage.
> 3. create disk
> Note that the disk id can be an input to ovirt, there is no need
> to depend on ovirt for generating the disk id, and pass it  back
> to the code creating the vm.
> See https://gerrit.ovirt.org/c/ovirt-engine-sdk/+/115630
> This step is slow (for no good reason), so it you have multiple
> disks you may want to create them in parallel.
> See https://gerrit.ovirt.org/c/ovirt-engine-sdk/+/113862
> 4. create image_transfer, keep transfer_url, proxy_url
> 5. run nbdkit with the rhv plugin and the transfer urls from step 4.
> There is no need to create more than one connection to imageio
> per plugin instance.

What does this sentence mean?  Do you mean one HTTP connection?

> 6. finalize image_transfer
> 7. create the vm using disk id generated for step 3
> Nir

I have something:

This creates the disk in .get_ready (refer to the lifecycle diagram
here: https://libguestfs.org/nbdkit-plugin.3.html#Callback-lifecycle )

Doing finalization one time is more complicated.  The obvious place
would be in .cleanup() but for various reasons we cannot use that with
the architecture of new virt-v2v, so instead we use a hack to signal
to the plugin that we want to finalize.

(Aside: I really wish the RHV API was more sane.  What even is
"finalization"?  I still don't understand why this step is necessary.)

The above works, as in it doesn't give any errors, but there are two
very large problems.  For some reason I don't understand it still
slower than the old method using qemu-img convert.

But the bigger problem is that it corrupts the disks.  Is the target
disk always filled with zeroes before we start copying?

I think architecturally your suggested flow above will be better, if
AIUI you mean that we should run the creation and finalization code
outside the nbdkit plugin, and only pass the transfer URLs to nbdkit.
I might have a go at that tomorrow when I'm less tired.


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.

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