Interesting, and good to hear. I know the other BSDs have a very different view of things. I had heard that Linux was the only OS with a stable kernel ABI guarantee. If FreeBSD does too, that certainly is better.
Windows for example makes zero guarantees there. There are a lot of syscalls that they won't renumber because some applications have taken a dependency on using them directly, but officially using a syscall without going through NTDLL (or wherever the stub is located for private syscalls) is unsupported. Those syscalls they are not keeping fixed for compatibility can and do change from version to version. Mostly in numbering, but changes to semantics or arguments can happen too. Hence Windows Containers can only run in separate namespaces on a matching kernel version, and the hyper-v isolation (a.k.a. virtualization) option for containers is needed for mismatched versions.
So creating an OCI runtime that wraps jails, adding any needed support for FreeBSD specific OCI container settings to containerd, and adding the needed code for things like networking to moby/moby (a.k.a. docker) sounds very feasible to me if some FreeBSD hacker wanted to get proper docker support. Offering Linux Emulation as an experimental option top be able to run more containers would be an added bonus, and should be feasible, since they once had that working with their old unofficial (presumably pre-containerd) builds of docker.
Windows for example makes zero guarantees there. There are a lot of syscalls that they won't renumber because some applications have taken a dependency on using them directly, but officially using a syscall without going through NTDLL (or wherever the stub is located for private syscalls) is unsupported. Those syscalls they are not keeping fixed for compatibility can and do change from version to version. Mostly in numbering, but changes to semantics or arguments can happen too. Hence Windows Containers can only run in separate namespaces on a matching kernel version, and the hyper-v isolation (a.k.a. virtualization) option for containers is needed for mismatched versions.
So creating an OCI runtime that wraps jails, adding any needed support for FreeBSD specific OCI container settings to containerd, and adding the needed code for things like networking to moby/moby (a.k.a. docker) sounds very feasible to me if some FreeBSD hacker wanted to get proper docker support. Offering Linux Emulation as an experimental option top be able to run more containers would be an added bonus, and should be feasible, since they once had that working with their old unofficial (presumably pre-containerd) builds of docker.