Can we apply patches in place? It might be nice if we could, because we could then do things like rsync the contents of block devices. One complication is that we must make sure blocks are not used as a basis after they've been updated. We can fairly easily impose this constrain while generating the delta, and check it while applying. Also, if the patch fails halfway through then there is no easy way to recover. But if this was done inside rsync then it would be OK to just run the command again.