[RFC] Adding /local/lib and /usr/lib to default $XDG_DATA_DIRS search path

[Simon McVittie]

On Mon, 04 Apr 2011 at 18:06:38 +0200, Lennart Poettering wrote:
> Right now the XDG basedir spec says that $XDG_DATA_DIRS should default
> to "/usr/local/share/:/usr/share/" if it is not set. I'd like to make
> one change to this: add "/usr/local/lib" and "/usr/lib" to
> it. Result: "/usr/local/share:/usr/local/lib:/usr/share:/usr/lib".

Adding /usr/[local/]lib seems likely to be a problem in multiarch
environments, since it no longer achieves the division you want:

* in Debian-style multiarch [1][2], arch-specific files go in
  /usr/lib/DEB_HOST_MULTIARCH, where DEB_HOST_MULTIARCH is the GNU tuple
  with the CPU replaced by the most generic in a compatible CPU family
  (e.g. always something like i386-linux-gnu, x86_64-linux-gnu or
  arm-linux-gnueabi, and never a newer or more specific compatible variant like
  i586-linux-gnu or armv7t-linux-gnueabi)

[1]: http://wiki.debian.org/Multiarch
[2]: https://wiki.ubuntu.com/MultiarchSpec

* in Red-Hat-style multilibs, arch-specific files go in /usr/lib or /usr/lib64
  as appropriate

This might not be such a problem in Red-Hat-style multilibs if you're
implicitly assuming that 64-bit CPU families can safely share an
arch-specific data file in /lib with their 32-bit counterpart (for instance
if you care about endianness but not word size), but Debian-style multiarch
aims to support dissimilar CPU types for cross-compiling and development
(via qemu-system-* or similar), so we might have things of different
endianness installed together.

What specific things do you have in mind that would use this feature, and
could they use one of these alternatives?

* search an implementation-defind path before or after XDG_DATA_DIRS
  (e.g. I think it would be OK for D-Bus or systemd to document that it would
  look in its compile-time ${libdir} before or after XDG_DATA_DIRS)

* have some flag or metadata in the file like "OnlyOnArch=i386;x86_64;",
  analogous to the OnlyShowIn=GNOME available in XDG menus

-------------------------

For D-Bus, you asked for /lib/dbus-1/system-services to be in the system
service search path, for things needed during early boot [3]. Do
you want that change to happen to XDG_DATA_DIRS too?

I think adding /lib (in its role as the root-filesystem equivalent of
/usr/share) would be less problematic than the change you proposed here,
if it comes with a note that it always means exactly /lib, and never
(for instance) /lib32, /lib64 or /lib/i386-linux-gnu.

[3]: https://bugs.freedesktop.org/show_bug.cgi?id=35229

Regards,
    S