A standard snapshot notification framework in Linux ?

[Block Device <blockdevice@gmail.com>]

Hi,

   does the linux kernel provide a mechanism whereby applications can
register themselves
to be notified when a snapshot is being taken of the volume they might
be writing to.

   If there is no such framework then how do backup applications
guarantee ( application level ) consistency. I have seen freeze_bdev
and friends which work for file systems and how the device mapper uses
them. But when it comes to application level consistency, a mechanism
is required to give the application a chance to flush &  quiesce its
writes so that the backup taken will be consistent for the application
also. Windows has the VSS ( Volume Shadow Service ) which provides an
elaborate framework for this. Is anyone working on something similar
for Linux and if not why is it not such a worthwhile idea ?

Regards
BD