Libguestfs - May 2020 - Re: 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-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

On Fri, May 29, 2020 at 07:50:14AM -0500, Eric Blake
wrote:
> [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.
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.

Regards,
Daniel
-- 
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|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
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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

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).

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org