/usr/include/directfb-internal/ is in libdirectfb-dev 1.2.10.0-5.1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/directfb-internal/core/
/usr/include/directfb-internal/core/clipboard.h
/usr/include/directfb-internal/core/colorhash.h
/usr/include/directfb-internal/core/core.h
/usr/include/directfb-internal/core/core_parts.h
/usr/include/directfb-internal/core/core_system.h
/usr/include/directfb-internal/core/coredefs.h
/usr/include/directfb-internal/core/coretypes.h
/usr/include/directfb-internal/core/fonts.h
/usr/include/directfb-internal/core/gfxcard.h
/usr/include/directfb-internal/core/graphics_driver.h
/usr/include/directfb-internal/core/input.h
/usr/include/directfb-internal/core/input_driver.h
/usr/include/directfb-internal/core/layer_context.h
/usr/include/directfb-internal/core/layer_control.h
/usr/include/directfb-internal/core/layer_region.h
/usr/include/directfb-internal/core/layers.h
/usr/include/directfb-internal/core/layers_internal.h
/usr/include/directfb-internal/core/palette.h
/usr/include/directfb-internal/core/screen.h
/usr/include/directfb-internal/core/screens.h
/usr/include/directfb-internal/core/screens_internal.h
/usr/include/directfb-internal/core/state.h
/usr/include/directfb-internal/core/surface.h
/usr/include/directfb-internal/core/surface_buffer.h
/usr/include/directfb-internal/core/surface_pool.h
/usr/include/directfb-internal/core/system.h
/usr/include/directfb-internal/core/windows.h
/usr/include/directfb-internal/core/windows_internal.h
/usr/include/directfb-internal/core/windowstack.h
/usr/include/directfb-internal/core/wm.h
/usr/include/directfb-internal/core/wm_module.h
/usr/include/directfb-internal/devmem/
/usr/include/directfb-internal/devmem/devmem.h
/usr/include/directfb-internal/devmem/surfacemanager.h
/usr/include/directfb-internal/display/
/usr/include/directfb-internal/display/idirectfbdisplaylayer.h
/usr/include/directfb-internal/display/idirectfbpalette.h
/usr/include/directfb-internal/display/idirectfbscreen.h
/usr/include/directfb-internal/display/idirectfbsurface.h
/usr/include/directfb-internal/display/idirectfbsurface_layer.h
/usr/include/directfb-internal/display/idirectfbsurface_window.h
/usr/include/directfb-internal/fbdev/
/usr/include/directfb-internal/fbdev/agp.h
/usr/include/directfb-internal/fbdev/fb.h
/usr/include/directfb-internal/fbdev/fbdev.h
/usr/include/directfb-internal/fbdev/surfacemanager.h
/usr/include/directfb-internal/fbdev/vt.h
/usr/include/directfb-internal/gfx/
/usr/include/directfb-internal/gfx/clip.h
/usr/include/directfb-internal/gfx/convert.h
/usr/include/directfb-internal/gfx/generic/
/usr/include/directfb-internal/gfx/generic/generic.h
/usr/include/directfb-internal/gfx/util.h
/usr/include/directfb-internal/idirectfb.h
/usr/include/directfb-internal/input/
/usr/include/directfb-internal/input/idirectfbinputbuffer.h
/usr/include/directfb-internal/input/idirectfbinputdevice.h
/usr/include/directfb-internal/media/
/usr/include/directfb-internal/media/idirectfbdatabuffer.h
/usr/include/directfb-internal/media/idirectfbfont.h
/usr/include/directfb-internal/media/idirectfbimageprovider.h
/usr/include/directfb-internal/media/idirectfbvideoprovider.h
/usr/include/directfb-internal/misc/
/usr/include/directfb-internal/misc/conf.h
/usr/include/directfb-internal/misc/gfx_util.h
/usr/include/directfb-internal/misc/util.h
/usr/include/directfb-internal/windows/
/usr/include/directfb-internal/windows/idirectfbwindow.h