build: Show a warning if the system bus socket is not interoperable

We would like to start using ${runstatedir}/dbus/system_bus_socket,
so that distributors who make /var/run a symbolic link to /run will
usually get their dbus-daemon listening on /run/dbus/system_bus_socket,
which has some advantages in corner cases, such as when /var is mediated
by an automounter or is unmounted during system shutdown.

Unfortunately, the interoperable path in the D-Bus Specification is
/var/run/dbus/system_bus_socket for historical reasons (D-Bus is older
than /run), and older versions of Slackware are known to have had /run
and /var/run as distinct directories. Do a check during configuration
to catch systems configured like this and show a warning.

When cross-compiling, this assumes that the system where dbus is built
(the build system in Autotools/Meson, or the "host" in CMake terminology)
has its /var/run and /run set up in a way that is compatible with the
system where dbus will run (the host system in Autotools/Meson, or the
"target" in CMake terminology). This is not 100% correct, but seems good
enough for a warning that will hopefully only trigger for misguided OS
distributors.

Signed-off-by: Simon McVittie <smcv@collabora.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/meson.build b/meson.build
index 20e9dbc6..caaaccf2 100644
--- a/meson.build
+++ b/meson.build
@@ -831,6 +831,25 @@ if system_socket == ''
         /'run'/'dbus'/'system_bus_socket'
     )
 endif
+
+# This check assumes that the disposition of /run and /var/run on the
+# system where we're building is the same as on the system we're building
+# for, so we can't usefully do this check if we're building for Windows,
+# or if we're cross-building for Unix on a Windows machine.
+#
+# The check is shared between Autotools, CMake and Meson.
+# Because we only run it on Unix, it's fine to make it a shell script.
+if platform_unix and build_machine.system() != 'windows'
+    msg = run_command(
+        find_program('tools/check-runstatedir.sh'),
+        system_socket,
+        check: false,
+    ).stdout()
+    if msg != ''
+        warning(msg)
+    endif
+endif
+
 data_config.set('DBUS_SYSTEM_SOCKET', system_socket)
 
 ## System bus only listens on local domain sockets, and never