Identifying the real display server

[Mattias Andrée]

On Mon, 13 Apr 2015 12:14:02 +0100
Simon McVittie <simon.mcvittie at collabora.co.uk> wrote:

> On 11/04/15 02:48, Giovanni Campagna wrote:
> > Well, at this point you're essentially reinventing
> > GDK_BACKEND, but at server side.
> 
> GDK_BACKEND, or a cross-toolkit generalization of it,
> seems like a better model: a list of protocols, not a
> list of environment variables.
> 
> XDG_RUNTIME_DIR gives us the opportunity to reduce the
> number of miscellaneous environment variables that need
> to be copied around, and I would prefer to be aiming for
> a future where nobody needs to set WAYLAND_DISPLAY or
> DBUS_SESSION_BUS_ADDRESS or GPG_AGENT_INFO or
> SSH_AUTH_SOCK or whatever Mir's DISPLAY-equivalent is
> (maybe even not DISPLAY either, on a sufficiently
> legacy-free system) unless they are doing something
> unusual.

Have you considered that you may want to have two
displays (for example two instances of X or two
instances of Mir) with the same $XDG_RUNTIME_DIR?

> 
> dbus 1.9 defaults to using $XDG_RUNTIME_DIR/bus if it

I hope you mean $XDG_RUNTIME_DIR/dbus, otherwise someone
need to make an amendment to dbus.

> exists and DBUS_SESSION_BUS_ADDRESS is unset, and my
> understanding is that Wayland does something similar.
> People have been talking about a similar thing for
> DISPLAY for a long time, although nothing seems to have
> come of it. That's a future that I'd prefer to head
> towards.

Whilst irrelevant, I am going to comment. I think this
is a bad idea. It makes the systems more complex for
no significant benefit.

> 
> (tl;dr: PREFERRED_DISPLAY="wayland mir x11" would be
> better than PREFERRED_DISPLAY="WAYLAND_DISPLAY
> MIR_DISPLAY DISPLAY".)
> 

I don't know how you came to that conclusing, but
after some consideration I agree. It makes it easier
to use an abstraction layer. We will have to restrict
the protocol names to [a-z0-9+-]-characters only.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 819 bytes
Desc: OpenPGP digital signature
URL: <http://lists.freedesktop.org/archives/xdg/attachments/20150413/c1f71978/attachment.sig>