vfs: add snapshot create/delete hooks
This change adds three new VFS hooks covering snapshot manipulation:
- snap_check_path
Check whether a path supports snapshots.
- snap_create
Request the creation of a snapshot of the provided path.
- snap_delete
Request the deletion of a snapshot.
These VFS call-outs will be used in future by Samba's File Server Remote
VSS Protocol (FSRVP) server.
MS-FSVRP states:
At any given time, Windows servers allow only one shadow copy set to
be going through the creation process.
Therefore, only provide synchronous hooks for now, which can be
converted to asynchronous _send/_recv functions when the corresponding
DCE/RPC server infrastructure is in place.
Signed-off-by: David Disseldorp <ddiss@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>