driver model: change bus refcounting scheme to match devices'.

Based on recent changes to device refcounting/unregistration.

struct bus_type gets a ->present field, which is set when the bus is 
registered. bus_unregister() is added, which only clears ->present and 
calls put_bus(). get_bus() checks the ->present and returns NULL if clear.

This allows all current references to buses to keep valid structures, while
preventing any new references to the bus structure.

0 files changed, 0 insertions, 0 deletions