Just feeding google and interested readers. DRI worked with X.org 6.9 but with version 7.0 it’s failing?
% LIBGL_DEBUG=verbose glxgears libGL: XF86DRIGetClientDriverName: 1.5.1 i915 (screen 0) libGL: OpenDriver: trying /usr/lib/dri/i915_dri.so libGL error: dlopen /usr/lib/dri/i915_dri.so failed (/usr/lib/dri/i915_dri.so: cannot open shared object file: No such file or directory) libGL error: unable to find driver: i915_dri.so
Ok, missing libgl1-mesa-dri of course. But when running glxinfo after installing the package you might notice something like:
ERROR! sizeof(I830DRIRec) does not match passed size from device driver
Solution (thanks for hint, formorer!):
apt-get install libgl1-mesa-dri/experimental libgl1-mesa-glx/experimental