Re: [Libguestfs] Provide NBD via Browser over Websockets
On Tue, 2 Jun 2020, Alex King wrote:
> I started writing an NBD server in rust as a learning project a while back,
> which I why I subscribed to the list. I understand rust can be compiled into
> webassembly although it's not something I've done. If there were others also
> interested in doing that I'd be interested. I haven't checked lately to see
> if there is a rust server published now, there may be.
https://docs.rs/nbd/0.2.1/nbd/server/index.html
--
Eric Wheeler
>
> Thanks,
> Alex
>
> On 2/06/20 8:04 am, Eric Wheeler wrote:
> > On Sat, 30 May 2020, Richard W.M. Jones wrote:
> > > On Fri, May 29, 2020 at 09:08:29PM +0000, Eric Wheeler wrote:
> > > > 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. Berrang�© 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.
> > > After reading a bit about compiling to WebSockets it sounds like you
> > > can cross-compile a C program, but there's no library support at all.
> > > IOW to port an existing server you'd have to implement enough of POSIX
> > > to make it work. nbdkit has a liberal license deliberately to make it
> > > possible to chop it up and incorporate it into completely forked
> > > codebases (nbdkit is a plot to make NBD more popular).
> > >
> > > But since NBD is pretty simple, a fresh Javascript server might be
> > > easier, especially if you stick to only implementing reads.
> > Good point, I'll wait on trying WASM.
> >
> > If anyone plans to implement NBD in JS let me know, otherwise I'll
> > probably implement a stripped down verion to integrate as an nbdkit plugin
> > to avoid re-writing all the handshake and version bits.
> >
> > --
> > Eric Wheeler
> >
> > > Rich.
> > >
> > > --
> > > Richard Jones, Virtualization Group, Red Hat
> > > http://people.redhat.com/~rjones
> > > Read my programming and virtualization blog: http://rwmj.wordpress.com
> > > virt-top is 'top' for virtual machines. Tiny program with many
> > > powerful monitoring features, net stats, disk stats, logging, etc.
> > > http://people.redhat.com/~rjones/virt-top
> > >
>
>
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