[adding qemu list]
On 5/29/20 4:37 AM, Richard W.M. Jones wrote:
Going back to the original email from 2018:
It might be neat to attach ISOs to KVM guests via websockets. Basically
the browser would be the NBD "server" and an NBD client would run on the
hypervisor, then use `virsh change-media vm1 hdc --insert /dev/nbd0` could
use an ISO from my desk to boot from.
Here's an HTML5 open file example:
https://stackoverflow.com/questions/3582671/how-to-open-a-local-disk-file-with-javascript
and the NBD protocol looks simple enough to implement in javascript:
https://stackoverflow.com/questions/17295140/where-is-the-network-block-device-format-describled
So I think what you mean here is that in a browser you'd open a local
(eg) ISO, and then that ISO could be shared with a remote VM. The
browser runs a Javascript NBD server. The remote VM is qemu. Between
the two is a WebSocket.
I've seen this being done with an HP blade server of some kind and
IIRC the client side used a Java applet. No idea what the protocol
was but likely something proprietary. It was nevertheless a useful
feature, eg to boot the server from an install CD that you have
locally.
I guess the problem is two-fold:
(1) You need to write an NBD server in Javascript. Not especially
difficult, particularly if you avoid any complicated features, and I
guess you only need read support.
Or use an existing NBD server over a Unix socket paired to a WebSocket
proxy that forwards all traffic from the Unix socket over a WebSocket.
That may be easier than writing the NBD server itself in Javascript.
(2) You need to persuade qemu's NBD client to read from a WebSocket.
I didn't really know anything about WebSockets until today but it
seems as if they are a full-duplex protocol layered on top of HTTP [a].
Is there a WebSocket proxy that turns WS into plain TCP (a bit like
stunnel)? Google suggests [b].
[a] https://en.wikipedia.org/wiki/WebSocket#Protocol_handshake
[b] https://github.com/novnc/websockify
qemu already knows how to connect as a client to websockets; Dan
Berrange knows more about that setup. I suspect it would not be too
difficult to teach the qemu NBD client code to use a WebSocket instead
of a Unix or TCP socket as its data source.
...
When qemu is running headless using a VNC or Spice display we can access
the display of https+websockets using things like noVNC---which is out of
scope to this converstation---but I'm just saying that such an existing
web front-end for the display could be extended to have an "Insert CDROM"
button and use the javascript file IO for the user to reference a local
file and pass it to qemu over nbd, perhaps via nbdkit.
I'm not sure how nbdkit would be involved, unless it was compiled
to WASM or something like that.
But the plan above sounds feasible, albeit a chunk of work.
Rich.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
