Add a fd_from_pixmap (singular) hook to go with fds_from_pixmap, which
will ensure that the pixmap is allocated without modifiers and is thus
exportable to non-modifier-aware clients.
This makes it possible to run a compositing manager on an old GLX/EGL
stack on top of an X server which allocates internal buffer storage
using exotic modifiers from modifier-aware GBM/EGL/KMS.
Signed-off-by: Daniel Stone <daniels@collabora.com>
Reported-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>