create_and_enter_userns
err = create_and_enter_userns();
create_and_enter_userns();
create_and_enter_userns();
create_and_enter_userns();
EXPECT_EQ(create_and_enter_userns(), 0);
if (create_and_enter_userns())
EXPECT_EQ(create_and_enter_userns(), 0);
if (create_and_enter_userns())