[SPARC64]: Abstract out mdesc accesses for better MD update handling.
Since we have to be able to handle MD updates, having an in-tree set of data structures representing the MD objects actually makes things more painful. The MD itself is easy to parse, and we can implement the existing interfaces using direct parsing of the MD binary image. The MD is now reference counted, so accesses have to now take the form: handle = mdesc_grab(); ... operations on MD ... mdesc_release(handle); The only remaining issue are cases where code holds on to references to MD property values. mdesc_get_property() returns a direct pointer to the property value, most cases just pull in the information they need and discard the pointer, but there are few that use the pointer directly over a long lifetime. Those will be fixed up in a subsequent changeset. A preliminary handler for MD update events from domain services is there, it is rudimentry but it works and handles all of the reference counting. It does not check the generation number of the MDs, and it does not generate a "add/delete" list for notification to interesting parties about MD changes but that will be forthcoming. Signed-off-by: David S. Miller <firstname.lastname@example.org>