dm-cache support for active layer in devmapper snapshotter

[leomao10]

We are using devmapper plugin as containerd snapshotter. And we are current exploring options to using dm-cache to improve IO performance. And one of the direction I want to explore is to see if I can add dm-cache to the final active snapshot that use as container rootfs.

After checking the code, I noticed current snapshot interface doesn't provide enough context to identify if the snapshot is for the final active layer unless I update CRI logic to pass in extra label.

Wondering if there is better way to do it.

Also, I am thinking to use one volume per pod for dm-cache, but again, it doesn't seem to be feasible unless I change the CRI.

Any suggestions on how to improve that? Is it more feasible to create a wrapper to runtime instead or maybe using OCI hook for it?