On Fri, Jan 14, 2011 at 07:18:58AM +1100, NeilBrown wrote:

open(O_EXCL) will fail on a block device if it is being used by anything else
- a filesystem or a dm target or an md array or ....

So if the *only* thing you want is "is this currently an active part of
something else", then O_EXCL works since 2.6.0 (I think).

Unfortunately, that won't distinguish between a currently active file
system, and a device which is being used by a dm target, which is what
we want to do.

						- Ted