Re: [Libguestfs] Provide NBD via Browser over Websockets

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.

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