The "source" field for overlayfs isn't strictly meaningful, by default; but it's useful to identify at least the software that created the mount.
Motivated by https://gitlab.com/redhat/centos-stream/containers/bootc/-/issues/301 where some QE testing noticed that an updated composefs using the new mount API didn't specify the source at all, so it ends up as none, but if we fall back to the legacy one it uses overlayfs.
The "source" field for overlayfs isn't strictly meaningful, by default; but it's useful to identify at least the software that created the mount.
Motivated by https://gitlab.com/redhat/centos-stream/containers/bootc/-/issues/301 where some QE testing noticed that an updated composefs using the new mount API didn't specify the source at all, so it ends up as
none, but if we fall back to the legacy one it usesoverlayfs.Change both to be
composefs.