On Thu, Apr 12, 2018 at 2:07 AM Nir Soffer <nir...@gmail.com> wrote:

> On Tue, Apr 10, 2018 at 6:53 PM Richard W.M. Jones <rjo...@redhat.com>
> wrote:
>
...

> Dan Berrange pointed out earlier on that it might be easier if imageio
>>
> just exposed NBD, or if we found a way to tunnel NBD requests over web
>> sockets (in the format case nbdkit would not be needed, in the latter
>> case nbdkit could act as a bridge).
>
>
I think we can expose NBD using ndb-server and dynamic exports.
It can work like this:

0. Install nbd and enable nbd-server on a host, running
   as vdsm:kvm, not exporting anything.

1. User starts transfer session via oVirt API with protocol="nbd"
    (if not specified, use "https" for backward compatibility)

2. oVirt selects a host for the transfer and configures an export
   in that host - for example:

[bbff5ab7-2e8e-45b8-a497-423c2d2b3ff1]
exportname = /path/to/image
trim = yes
timeout = 300

nbd-server supports reloading configuration via SIGHUP.
Looks like it should work for adding export dynamically:
https://github.com/NetworkBlockDevice/nbd/blob/cb6e816c4d2c536cfff5ba9859f210aabe39539b/nbd-server.c#L3007

I could find code handling removing exports.

3. User gets back
- transfer_url: "nbd:hostname:port"
- export_name: bbff5ab7-2e8e-45b8-a497-423c2d2b3ff1

Assuming that if NBD_OPT_EXPORT_NAME is bbff5ab7-2e8e-45b8-a497-423c2d2b3ff1
ndb-server will export the /path/to/image mentioned in the config
exportname.

This seems to be the case based on:
- https://github.com/NetworkBlockDevice/nbd/blob/master/nbd-server.c#L998
-
https://github.com/NetworkBlockDevice/nbd/blob/cb6e816c4d2c536cfff5ba9859f210aabe39539b/nbd-server.c#L2074

4. User transmit data using nbd-client or qemu-img or maybe
   a wrapper script to make it easier

5. During the transfer, oVirt monitors progress and activity.

I don't see how we can do this with current nbd-server.

6. User ends the transfer session via oVirt API

7. oVirt removes the export and finalize the transfer.

I guess this can work in a similar way for KubeVirt. The way
the image is provisioned and attached to a host will be
different, but the way a user will transfer image data can be
the same.

Seems that nbd-server is missing:
- way to remove exports dynamically
- way to monitor export activity and progress

Nir

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