Supply dm_add_exception as a callback to the read_metadata function.
Add a status function ready for a later patch and name the functions
consistently.
Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Move the existing snapshot exception store implementations out into
separate files. Later patches will place these behind a new
interface in preparation for alternative implementations.
Signed-off-by: Alasdair G Kergon <agk@redhat.com>