Re: [PATCH bpf-next 6/6] selftests/bpf: test detaching struct_ops links.

[Martin KaFai Lau <martin.lau@linux.dev>]

On 4/29/24 2:36 PM, Kui-Feng Lee wrote:
> @@ -572,6 +576,12 @@ static int bpf_dummy_reg(void *kdata)
>   	if (ops->test_2)
>   		ops->test_2(4, ops->data);
>   
> +	if (ops->do_unreg) {
> +		rcu_read_lock();
> +		bpf_struct_ops_kvalue_unreg(kdata);

Instead of unreg() immediately before the reg() has returned, the test should 
reflect more on how the subsystem can use it in practice. The subsystem does not 
do unreg() during reg().

It also needs to test a case when the link is created and successfully 
registered to the subsystem. The user space does BPF_LINK_DETACH first and then 
the subsystem does link->ops->detach() by itself later.

It can create a kfunc in bpf_testmod.c to trigger the subsystem to do 
link->ops->detach(). The kfunc can be called by a SEC("syscall") bpf prog which 
is run by bpf_prog_test_run_opts(). The test_progs can then decide on the timing 
when to do link->ops->detach() to test different cases.

> +		rcu_read_unlock();
> +	}
> +
>   	return 0;
>   }