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client: require WAYLAND_DISPLAY to be set

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Although defaulting to wayland-0 seems convenient, it has an undesirable
side effect: clients may unintentionally connect to the wrong compositor.
Generally, it's safer to fail instead. Here's a real example:

In Fedora 22, Gtk+ prefers Wayland over X11, though the default session is still
a normal X11 Gnome session. When you launch a Gtk+ app, it will try Wayland,
fail, then try X11, and succesfully start up. That works fine.

Now suppose you launch Weston while running the Gnome session. Suddenly, all
of the Gtk+ apps launched from Gnome will show up inside Weston instead.
That's unexpected. There's also no good way to prevent that from happening
(other than perhaps setting WAYLAND_DISPLAY to an invalid value when launching
an app).

Not using wayland-0 as the default will solve that problem: an app launched
from the X11 Gnome session will use the X11 backend regardless of whether
there's a wayland compositor running at the same time.

Everything else should work as before. The compositor already sets
the WAYLAND_DISPLAY when starting the session, so the lack of the default value
should not make a difference to the user.

Signed-off-by: Dima Ryazanov <dima@gmail.com>
Acked-by: Pekka Paalanen <ppaalanen@gmail.com>
Acked-by: Giulio Camuffo <giuliocamuffo@gmail.com>
Acked-by: Daniel Stone <daniel@fooishbar.org>
Acked-by: Jasper St. Pierre <jstpierre@mecheye.net>
Reviewed-by: Ryo Munakata <ryomnktml@gmail.com>

[Pekka: dropped the wayland-server.c hunk, adjusted summary]

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
This commit is contained in:
Dima Ryazanov 2015-08-12 19:34:31 -07:00 • committed by Pekka Paalanen
parent 441f9bb144
commit fb7e130217
3 changed files with 12 additions and 11 deletions
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5
doc/man/wl_display_connect.xml
View file

@ -57,9 +57,8 @@
that was previously opened by a Wayland server. The server socket must
be placed in <envar>XDG_RUNTIME_DIR</envar> for this function to
find it. The <varname>name</varname> argument specifies the name of
the socket or <constant>NULL</constant> to use the default (which is
<constant>"wayland-0"</constant>). The environment variable
<envar>WAYLAND_DISPLAY</envar> replaces the default value. If
the socket or <constant>NULL</constant> to use the default
(which is the value of <envar>WAYLAND_DISPLAY</envar>). If
<envar>WAYLAND_SOCKET</envar> is set, this function behaves like
<function>wl_display_connect_to_fd</function> with the file-descriptor
number taken from the environment variable.</para>

8
doc/publican/sources/Protocol.xml
View file

@ -60,10 +60,10 @@
<title>Wire Format</title>
<para>
The protocol is sent over a UNIX domain stream socket, where the endpoint
usually is named <systemitem class="service">wayland-0</systemitem>
(although it can be changed via <emphasis>WAYLAND_DISPLAY</emphasis>
in the environment). The protocol is message-based. A
message sent by a client to the server is called request. A message
name is determined by the <emphasis>WAYLAND_DISPLAY</emphasis>
environment variable. Its value will usually be
<systemitem class="service">wayland-0</systemitem>. The protocol is message-based.
A message sent by a client to the server is called request. A message
from the server to a client is called event. Every message is
structured as 32-bit words, values are represented in the host's
byte-order.