Drill the hole through the meta_ckpt.c and txn_ckpt.c code into the block manager so the block manager returns a list of blocks that have been allocated in the checkpoint. The block manager already creates an allocation extent list (8B offset/size pairs), that is written as part of the checkpoint. That list plus a couple of additional blocks is what you want, and I believe you can take most of that code from the branch I pushed. The returned list has to be written into the metadata file as part of the checkpoint.