devfs_rule_byid
static struct devfs_krule *devfs_rule_byid(devfs_rid rid);
dk = devfs_rule_byid(dr->dr_id);
dk = devfs_rule_byid(rid);
dk = devfs_rule_byid(rid);
KASSERT(devfs_rule_byid(mkrid(ds->ds_number, *rnump)) == NULL,