[dm-devel] Why is device mapper unable to remove a mapped device which is open?

[Edward Goggin <egoggin emc com>]

It seems very un-posix like to not be able to remove a 
dm mapped device file even when the mapped device is open.

Why shouldn't the kernel's reference counting for the
mapped device's md structure account for properly 
handling the de-allocation of the md structure upon
the last close in this case?