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Date: Tue, 9 Sep 2025 10:26:09 -0700
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Subject: Re: [PATCH RFC net-next 3/5] selftests: drv-net: Test XDP head
 adjustment with bpf_dynptr
To: Nimrod Oren <noren@nvidia.com>
Cc: "David S. Miller" <davem@davemloft.net>,
 Eric Dumazet <edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>,
 Paolo Abeni <pabeni@redhat.com>, Simon Horman <horms@kernel.org>,
 Shuah Khan <shuah@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
 Daniel Borkmann <daniel@iogearbox.net>,
 Jesper Dangaard Brouer <hawk@kernel.org>,
 John Fastabend <john.fastabend@gmail.com>,
 Stanislav Fomichev <sdf@fomichev.me>, Mohsin Bashir
 <mohsin.bashr@gmail.com>, Dragos Tatulea <dtatulea@nvidia.com>,
 Tariq Toukan <tariqt@nvidia.com>, Carolina Jubran <cjubran@nvidia.com>,
 netdev@vger.kernel.org, linux-kselftest@vger.kernel.org,
 linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
 Amery Hung <ameryhung@gmail.com>
References: <20250909085236.2234306-1-noren@nvidia.com>
 <20250909085236.2234306-4-noren@nvidia.com>
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From: Martin KaFai Lau <martin.lau@linux.dev>
In-Reply-To: <20250909085236.2234306-4-noren@nvidia.com>
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On 9/9/25 1:52 AM, Nimrod Oren wrote:
> +	if (bpf_dynptr_read(tmp_buff, hdr_len, &ptr, 0, 0) < 0)
>   		return -1;
>   
> -	if (bpf_xdp_store_bytes(ctx, 0, tmp_buff, hdr_len) < 0)
> +	if (bpf_dynptr_write(&ptr, offset, tmp_buff, hdr_len, 0) < 0)

Instead of bpf_dynptr_read() and then bpf_dynptr_write(), try to use 
bpf_dynptr_copy(). I think you have also noticed that Amery is also modifying 
xdp_native.bpf.c to test the linear access (i.e. data/data_end) with the 
bpf_xdp_pull_data addition. Not sure if xdp_native.bpf.c wants to keep testing 
both (data/data_end and dynptr). In the bpf selftests, it does want to have test 
coverage for both and have some existing selftests for that.

> +		return -1;
> +
> +	if (bpf_xdp_adjust_head(ctx, offset) < 0)
>   		return -1;
>   
>   	return 0;