Comment 1 for bug 1355845

And before someone bothers to point out that partman/filter_mounted is preseedable, that doesn't help. All that does is tell partman not to filter out mounted partitions. So if I set that to false, partman doesn't display the warning, but will attempt to create a partition on a mounted filesystem, which doesn't work. There is absolutely no way to tell partman "No, really, there should not be any local block devices mounted." short of forcing things in an early_command, which is a fairly large hammer.