Ceph » Linux kernel client

Off the top of my head:

- get rid of struct rbd_mapping (put actual mapping values into struct rbd_image_header instead of keeping around both base image and actual mapping values with the possibility of confusing them)
- decouple header read-in from running checks (supported features, etc)
- split struct rbd_device into struct rbd_device (dev_id, major, minor, watch, sysfs, etc) and struct rbd_image (the point being not have semi-initialized block layer and sysfs stuff in base image descriptor)
- pack multiple cls method calls into one osd request to reduce the number of osd requests we issue on map (similar to cls_client::get_[im]mutable_metadata(), longer term we should probably work on making that a single request, but that may involve creating new cls methods)
- eliminate asymmetries and inconsistencies (things like rbd_dev_mapping_clear() being called twice on unmap, etc)