[dm-devel] Getting dm extent mapping

[Christophe Varoqui]

On lun., 2011-10-17 at 13:15 -0400, markw at mohawksoft.com wrote:
> 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.
> 
The ddsnap tool might fit your need. It is hosted on the git space of
http://www.opensvc.com

Regards,
cvaroqui