[libvirt PATCH 0/3] Enable copy/paste for vnc displays

[Daniel P. Berrangé]

On Wed, Mar 23, 2022 at 09:44:53AM -0500, Jonathon Jongsma wrote:
> On 3/23/22 4:17 AM, Daniel P. Berrangé wrote:
> > On Wed, Mar 23, 2022 at 12:01:19PM +0400, Marc-André Lureau wrote:
> > > Hi
> > > 
> > > On Wed, Mar 23, 2022 at 12:47 AM Jonathon Jongsma <jjongsma at redhat.com> wrote:
> > > > 
> > > > This patch series enables support for the qemu-vdagent character device which
> > > > enables copy/paste support between guest and client when using vnc graphics.
> > > > 
> > > > The guest must be configured with something like the following:
> > > > 
> > > >      <channel type='qemu-vdagent'>
> > > >        <source clipboard='on' mouse='on'/>
> > > >        <target type='virtio' name='com.redhat.spice.0'/>
> > > >      </channel>
> > > > 
> > > > Copy/paste sync requires a vnc client that has support for copy/paste commands.
> > > > Currently virt-viewer does not work, but the version of tigervnc provided by
> > > > fedora (executable name 'vncviewer') does work.
> > > > 
> > > > More details about this device on Gerd's blog:
> > > > https://www.kraxel.org/blog/2021/05/qemu-cut-paste/
> > > > 
> > > > OPEN QUESTIONS:
> > > > 
> > > > - I'm not fully convinced that the `<source>` element is the right place for
> > > >    the new `clipboard` / `mouse` configuration options, but I'm not sure that
> > > >    adding a new xml element to the `<channel>` is the right approach either.
> > > >    Suggestions welcome.
> > > 
> > > I am not convinced <channel> is appropriate either for -chardev
> > > qemu-vdagent. That's why in my dbus display series it's an
> > > implementation detail
> > > (https://patchew.org/Libvirt/20211222194345.766352-1-marcandre.lureau@redhat.com/20211222194345.766352-13-marcandre.lureau@redhat.com/),
> > > and it's not exposed to the domain XML directly. However I realize
> > > that my approach is probably broken, as it looks like I totally missed
> > > the associated virtserialport! :)
> > > 
> > > As you say "source" is strange to put those extra channel options too.
> > > 
> > > And the only really valid associated device is a virtserialport of
> > > name "com.redhat.spice.0", so what's the point in exposing that detail
> > > to the user?
> 
> You could say the same thing about the normal spice vdagent, right? And we
> allow the user to specify a different virtio name for the spicevmc channel.
> spice-vdagent does offer a --virtio-serial-port-path option that can be used
> to connect to a different name within the guest, after all.
> 
> > 
> > At the QEMU level we have one serial port with chardv
> > 
> >    -chardev qemu-vdagent,id=ch1,name=vdagent,clipboard=on
> >    -device virtio-serial-pci \
> >    -device virtserialport,chardev=ch1,id=ch1,name=com.redhat.spice.0
> > 
> > 
> > but IIUC, we can have multiple frontends - ie both VNC and DBus
> > display, and in that case the clipboard=on property on the
> > chardev will apply to both VNC & DBus displays. We can't
> > control clipboard independantly for the displays, so it is
> > right to put the control in the XML for the <channel> for
> > both VNC and DBus.
> > 
> 
> In addition to <channel>, there are several other xml elements that
> essentially map to a qemu character device: <serial>, <console>, etc. Would
> it make more sense to introduce a new element like this for the
> qemu-vdagent? This might make it easier to introduce new configuration
> options that wouldn't really fit in the general <channel>. For example,
> something like:
> 
> <qemuvdagent>
>   <clipboard copypaste="yes"/>
>   <target type='virtio' name='com.redhat.spice.0'/>
> </qemuvdagent>

The devices in libvirt represent the guest exposed devics, and that's
still a virtio-serial port,  so <channel> is the right place.

The chardev is merely a backend and doesn't need it own top level
XML element.  This does mean yuo can use qemu-vgagent chardev with
any of serial, parallel, channel, etc but that's harmless from
libvirt's POV.

With regards,
Daniel
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