Re: [PATCH bpf-next 2/3] bpf: allow passing struct bpf_iter_<type> as kfunc arguments

[Eduard Zingerman <eddyz87@gmail.com>]

On Thu, 2024-08-08 at 16:22 -0700, Andrii Nakryiko wrote:
> There are potentially useful cases where a specific iterator type might
> need to be passed into some kfunc. So, in addition to existing
> bpf_iter_<type>_{new,next,destroy}() kfuncs, allow to pass iterator
> pointer to any kfunc.
> 
> We employ "__iter" naming suffix for arguments that are meant to accept
> iterators. We also enforce that they accept PTR -> STRUCT btf_iter_<type>
> type chain and point to a valid initialized on-the-stack iterator state.
> 
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---

In current form this allows the following usage:

    SEC("?socket")
    __success
    int testmod_seq_getter_good(const void *ctx)
    {
    	struct bpf_iter_testmod_seq it;
    	s64 sum = 0;
    
    	bpf_iter_testmod_seq_new(&it, 100, 100);
    	sum *= bpf_iter_testmod_seq_value(0, &it);
    	bpf_iter_testmod_seq_destroy(&it);
    
    	return sum;
    }

Do we want to ensure that iterator is not drained before the call to
bpf_iter_testmod_seq_value()?

Otherwise this patch lgtm.

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