[Libguestfs] Provide NBD via Browser over Websockets

[Eric Wheeler]

On Fri, 29 May 2020, Richard W.M. Jones wrote:
> On Fri, May 29, 2020 at 08:58:06AM -0500, Eric Blake wrote:
> > On 5/29/20 8:50 AM, Daniel P. Berrangé wrote:
> > 
> > >>>(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.
> > >
> > >Actually the inverse. The QIOChannelWebsocket impl is only the server
> > >side of the problem, as used by QEMU's VNC server. We've never implemented
> > >the client side. There is nothing especially stopping us doing that - just
> > >needs someone motivated with time to work on it.
> > 
> > In the meantime, you may still be able to set up something like:
> > 
> > local machine:
> > iso -> NBD server -> Unix socket -> websockify -> WebSocket
> 
> I guess the idea is to have a zero-install solution for the browser.
> As I said in the email earlier this is very common for IPMI-type
> remote access to blade servers and in my experience is implemented
> using a Java applet and a proprietary protocol terminated at the BMC
> (which then emulates a virtual CDROM to the server).  There are some
> HP blade servers on Red Hat's internal Beaker instance where you can
> play with this.  For qemu we wouldn't need to invent a new protocol
> when NBD is available and already implemented (albeit not yet on top
> of WebSockets).
> 
> The NBD server must run inside the browser and therefore be either
> written from scratch in Javascript, or an existing server
> cross-compiled to WASM (if that is possible - I don't really know).

Interesting idea about WASM.  I'll see if I can build one of the simple 
nbd servers that are around.  Not sure how to link it to the JS file IO, 
however.

--
Eric Wheeler


> > remote machine:
> > WebSocket -> websockify -> Unix socket -> qemu NBD client
> > 
> > Adding websocket client support into qemu would reduce the length of
> > the chain slightly (for less data copying) by getting rid of a
> > websockify proxy middleman, but would not necessarily improve
> > performance (it's hard to say where the latency bottlenecks will be
> > in the chain).
> 
> Rich.
> 
> -- 
> Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> libguestfs lets you edit virtual machines.  Supports shell scripting,
> bindings from many languages.  http://libguestfs.org
> 
>