Re: vnc clipboard support

[Christophe de Dinechin <cdupontd@redhat.com>]

> On 29 Jan 2021, at 16:04, Gerd Hoffmann <kraxel@redhat.com> wrote:
> 
>  Hi,
> 
>> Unless we para-virtualize the keyboard?
> 
> The main advantage of paste via key events is that it doesn't require
> guest support.

The main disadvantage, though, is that it does not work at all ;-)

Imagine pasting Ademar's favorite signature, :wq!
Or pasting "ahs" to a guest that thinks the control key is down
(a not uncommon occurence with VNC, in my personal experience).
So now you pasted "Select All, Delete, Save" in many GUI apps.

(insert infinite variations on the "doom" theme here)

>  Requiring any kind of software in the guest (paravirt
> keyboard driver, agent figuring the keymap, whatever else) kills that
> advantage.

Indeed. I was pointing out that any option that brought any modicum
of reasonable paste behavior (ignoring copy for the moment) required
some in-guest piece of software. So we might as well go for one that
is known to work, and also deals with the copy-from-guest issue.


>  And if we need guest cooperation anyway it is much better
> to just read/write the guest clipboard directly.

… which is exactly what VNC in the guest knows how to do in a
reasonable way, on a large number of platforms. So I don't see
any benefit to reinvent that wheel. I'd rather leverage the VNC
code to build a solid, multi-platform agent. You can extract the
clipboard code into some smaller agent that talks to a specific qemu
character device if you think it's a worthy optimization.


> 
> Standard keyboard seems to not be an option either.  The HID specs
> (https://usb.org/document-library/hid-usage-tables-121) lists a
> Unicode Page (Section 18), which looks like it could be used to
> send unicode chars to the guest.  Problem is (a) this is 16bit
> only (so no emoji) and (b) widely unimplemented in guest OSes.

Some operating systems have a way to enter unicode code points.
On Linux, you can sometimes type shift-control u (hex code), but it's a bit
dependent on the some alignment of mysterious planets.
On Windows, you can type <hex> alt-x. Sometimes. Or alt + <hex>.
On macOS, you need to enable Unicode Hex Input, so unreliable.

Not that I would recommend trying any of that ;-)