[Libguestfs] nbdkit does not support NBD_OPT_GO?

[Nir Soffer]

On Thu, Aug 2, 2018 at 8:18 PM Eric Blake <eblake at redhat.com> wrote:

> On 08/02/2018 11:51 AM, Nir Soffer wrote:
> > When trying to connect to nbdkit with imageio nbd client, I get this
> error:
> >
> > $ rm -f /tmp/nbd.sock && nbdkit file file=/var/tmp/fedora-27.img -e
> export
> > -U /tmp/nbd.sock
> >
>
> > ovirt_imageio_common.nbd.Error: The option sent by the client is unknown
> by
> > this server implementation [message=])
>
> Correct, nbdkit has not yet implemented this extension.  (It's on my
> list of things to add, someday...)
>
> >
> > According to the NBD protocol:
> >
> >      For backwards compatibility, clients SHOULD be prepared to also
> handle
> >      NBD_REP_ERR_UNSUP by falling back to using NBD_OPT_EXPORT_NAME.
> >
> > Should I fall back to sending NBD_OPT_EXPORT_NAME, or nbkit needs
> > to implement NBD_OPT_GO?
>
> Both. You need to implement the fallback to NBD_OPT_EXPORT_NAME
> regardless of whether nbdkit is fixed, because there are other servers
> that are also not fixed, and you want to interoperate with all such
> servers. But nbdkit should (eventually) learn how to support NBD_OPT_GO.
>

Thanks, I'll add this to the todo list.

My goal is to support qemu-nbd and qemu for incremental backup and virt-v2v.
Supporting other servers is nice to have at this point.

Nir
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