#util-#linux just merged support for the new #mount-#api.

This includes my original patches for the new mount api and direct support for creating #idmapped #mounts natively:

mount --bind X-mount.idmap=u:1000:0:1 g:1001:1:2 5000:1000:2 /source /target

specifying an idmapping directly or via

mount --bind X-mount.idmap=/proc/<pid>/user /source /target

to delegate it to a userns.

I'm very happy this has landed!