[dm-devel] Getting dm extent mapping

[markw at mohawksoft.com]

Is it possible to get a list of extents mapped to an object from an ioctl
call?

The reason why I am asking is that I need to be able to calculate the
deltas between a snapshot and a real device. For instance:

Suppose I have a virtual machine on device /dev/lvmvol/vmserver. I create
a snapshot of that device named /dev/lvmvol/vmsnap.

If I could get a list of the extents used to constitute "vmserver" and the
extents that constitute "vmsnap" I could calculate how much has changed
and what ranges I need to actually backup. Obviously, there has to be some
way to map "extents" to locations on the device itself in order for this
to work.

I have looked in the dm code and can not see if this is possible.

Thanks,

Mark