netdev - Re: [PATCH bpf-next v2 01/13] bpf: Add dynptr type for skb metadata

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Message-ID: <1ae43248-189e-4765-b43c-b80e58160587@linux.dev>
Date: Fri, 18 Jul 2025 12:19:44 -0700
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Jakub Sitnicki <jakub@...udflare.com>
Cc: Alexei Starovoitov <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>,
 Arthur Fabre <arthur@...hurfabre.com>, Daniel Borkmann
 <daniel@...earbox.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Jesper Dangaard Brouer <hawk@...nel.org>,
 Jesse Brandeburg <jbrandeburg@...udflare.com>,
 Joanne Koong <joannelkoong@...il.com>, Lorenzo Bianconi
 <lorenzo@...nel.org>, Toke Høiland-Jørgensen
 <thoiland@...hat.com>, Yan Zhai <yan@...udflare.com>,
 kernel-team@...udflare.com, netdev@...r.kernel.org,
 Stanislav Fomichev <sdf@...ichev.me>, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 01/13] bpf: Add dynptr type for skb metadata

On 7/18/25 3:01 AM, Jakub Sitnicki wrote:
> On Thu, Jul 17, 2025 at 05:06 PM -07, Martin KaFai Lau wrote:
>> On 7/16/25 9:16 AM, Jakub Sitnicki wrote:
>>> +__bpf_kfunc int bpf_dynptr_from_skb_meta(struct __sk_buff *skb, u64 flags,
>>> +					 struct bpf_dynptr *ptr__uninit)
>>> +{
>>> +	return dynptr_from_skb_meta(skb, flags, ptr__uninit, false);
>>> +}
>>> +
>>>    __bpf_kfunc int bpf_dynptr_from_xdp(struct xdp_md *x, u64 flags,
>>>    				    struct bpf_dynptr *ptr__uninit)
>>>    {
>>> @@ -12165,8 +12190,15 @@ int bpf_dynptr_from_skb_rdonly(struct __sk_buff *skb, u64 flags,
>>>    	return 0;
>>>    }
>>>    +int bpf_dynptr_from_skb_meta_rdonly(struct __sk_buff *skb, u64 flags,
>>> +				    struct bpf_dynptr *ptr__uninit)
>>> +{
>>> +	return dynptr_from_skb_meta(skb, flags, ptr__uninit, true);
>>> +}
>>> +
>>>    BTF_KFUNCS_START(bpf_kfunc_check_set_skb)
>>>    BTF_ID_FLAGS(func, bpf_dynptr_from_skb, KF_TRUSTED_ARGS)
>>> +BTF_ID_FLAGS(func, bpf_dynptr_from_skb_meta, KF_TRUSTED_ARGS)
>>
>> I looked at the high level of the set. I have a quick question.
>>
>> Have you considered to create another bpf_kfunc_check_set_xxx that is only for
>> the tc and tracing prog type? No need to expose this kfunc to other prog types

After some more thoughts, lets target it for tc only. I think skb_meta is not 
available in most of the tracepoints now. Lets wait until the skb_meta will be 
supported in other hooks/layers first.

>> if the skb_meta is not available now at those hooks.
>>
>> It seems patch 5 is to ensure other prog types has meta_len 0 and some of the
>> tests are to ensure that the other prog types cannot do useful things with the
>> new skb_meta kfunc. The tests will also be different eventually when the
>> skb_meta can be preserved beyond tc.
> 
> That is a neat idea!
> 
> It will let me drop three patches from this series.  Let me do that.