alloc_mnt_ns
static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *, bool);
ns = alloc_mnt_ns(user_ns, true);
new_ns = alloc_mnt_ns(user_ns, false);
new_ns = alloc_mnt_ns(user_ns, false);
ns = alloc_mnt_ns(&init_user_ns, true);
ns = alloc_mnt_ns(current->nsproxy->mnt_ns->user_ns, true);