Function build_ukify 

pub(crate) async fn build_ukify(
    rootfs: &Utf8Path,
    extra_kargs: &[String],
    args: &[OsString],
    kernel_dir: Option<&Utf8Path>,
    allow_missing_fsverity: bool,
    erofs_version: Option<BootArtifactErofsVersionArg>,
    write_dumpfile_to: Option<&Utf8Path>,
) -> Result<()>

Build a UKI from the given rootfs.

Finds the kernel, computes the composefs digest, reads kernel arguments from kargs.d, then invokes ukify with any additional pass-through arguments.