Hi I released new patches for shared snapshots. The functionality is the same as in previous releases, but the two snapshot exception stores, one created by Fujita Tomonori and one by me, are consolidated and common code is shared. The patches are at: http://people.redhat.com/mpatocka/patches/kernel/new-snapshots/ The patches don't alter existing snapshot implementation, they contain just new files (they alter only Kconfig and Makefile to make the new files compilable). The new architecture is as follows: The module dm-multisnapshot.ko contains common code for both exception stores. It has basically processing and queuing IOs and attaching snapshots and interfacing with device mapper. This module loads the specific module for a given exception store: dm-store-mikulas.ko for my store or dm-store-fujita-daniel.ko for Zumastor store. In the target constructor, there's an argument "mikulas" or "fujita-daniel" that tells which module to load. The interface is what I designed --- the point is that Fujita's code can be converted to use my interface, but my code cannot be converted to use Fujita's interface --- so if we want to drive both exception stores with the same userspace code (we definitely want!), then there's no other option but to use my interface. The difference from Fujita's old interface is that in my interface the kernel selects snapshot ID when creating a new snapshots and in old Fujita's interface the user selected it. For my snapshot store, it is a design requirement that the snapshot ID is seleted by the kernel driver. There is really almost nothing to be shared with the old snapshot code. The data structures and the interface are have different logic --- for the old snapshots, there was one small structure for the origin and several big structures for the snapshots; for the new snapshots, there is one big structure for the origin and several small structures for the snapshots. So I wouldn't recommend to attempt to glue the new code on the old snapshots. For Fujita: You can take the file that I created and continue development on it. I fixed some other bugs or non-portable constructs in the code, I marked them as comments so that you can review the fixes. I took the code from ftp://ftp.kernel.org/pub/linux/kernel/people/tomo/dm-snap/2008-11-26/ and ported it, so if you meanwhile made some other changes your the code, diff your changes against 2008-11-26 version and apply the diff by hand to the file that I release. Mikulas -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
