Re: [PATCH bpf-next 3/3] selftests/bpf: add tests for bpf_dynptr_copy

[Eduard Zingerman <eddyz87@gmail.com>]

On Tue, 2025-02-18 at 19:00 +0000, Mykyta Yatsenko wrote:
> From: Mykyta Yatsenko <yatsenko@meta.com>
> 
> Add XDP setup type for dynptr tests, enabling testing for
> non-contiguous buffer.
> Add 2 tests:
>  - test_dynptr_copy - verify correctness for the fast (contiguous
>  buffer) code path.
>  - test_dynptr_copy_xdp - verifies code paths that handle
>  non-contiguous buffer.
> 
> Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
> ---

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

[...]

> +SEC("xdp")
> +int test_dynptr_copy_xdp(struct xdp_md *xdp)
> +{

Nit: it would be helpful if there were a few comments
     explaining which special cases are tested at each step.

> +	struct bpf_dynptr ptr_buf, ptr_xdp;
> +	char *data = "qwertyuiopasdfghjkl;";
> +	char buf[32] = {'\0'};
> +	__u32 len = strlen(data);
> +	int i, chunks = 200;
> +
> +	bpf_dynptr_from_xdp(xdp, 0, &ptr_xdp);
> +	bpf_ringbuf_reserve_dynptr(&ringbuf, len * chunks, 0, &ptr_buf);
> +
> +	bpf_for(i, 0, chunks) {
> +		err =  err ?: bpf_dynptr_write(&ptr_buf, i * len, data, len, 0);
> +	}
> +
> +	err = err ?: bpf_dynptr_copy(&ptr_xdp, 0, &ptr_buf, 0, len * chunks);
> +
> +	bpf_for(i, 0, chunks) {
> +		memset(buf, 0, sizeof(buf));
> +		err = err ?: bpf_dynptr_read(&buf, len, &ptr_xdp, i * len, 0);
> +		err = err ?: memcmp(data, buf, len);
> +	}
> +
> +	memset(buf, 0, sizeof(buf));
> +	bpf_for(i, 0, chunks) {
> +		err = err ?: bpf_dynptr_write(&ptr_buf, i * len, buf, len, 0);
> +	}
> +
> +	err = err ?: bpf_dynptr_copy(&ptr_buf, 0, &ptr_xdp, 0, len * chunks);
> +
> +	bpf_for(i, 0, chunks) {
> +		memset(buf, 0, sizeof(buf));
> +		err = err ?: bpf_dynptr_read(&buf, len, &ptr_buf, i * len, 0);
> +		err = err ?: memcmp(data, buf, len);
> +	}
> +
> +	bpf_ringbuf_discard_dynptr(&ptr_buf, 0);
> +
> +	err = err ?: bpf_dynptr_copy(&ptr_xdp, 2, &ptr_xdp, len, len * (chunks - 1));
> +
> +	bpf_for(i, 0, chunks - 1) {
> +		memset(buf, 0, sizeof(buf));
> +		err = err ?: bpf_dynptr_read(&buf, len, &ptr_xdp, 2 + i * len, 0);
> +		err = err ?: memcmp(data, buf, len);
> +	}
> +
> +	err = err ?: (bpf_dynptr_copy(&ptr_xdp, 2000, &ptr_xdp, 0, len * chunks) == -E2BIG ? 0 : 1);
> +
> +	return XDP_DROP;
> +}