Re: [Libguestfs] Provide NBD via Browser over Websockets

[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... > > > > and the NBD protocol looks simple enough to implement in javascript: > > https://stackoverflow.com/questions/17295140/where-is-the-network-block-d... > > 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.