linux-kernel - Re: [PATCH bpf-next] bpf: Move nf_conn extern declarations to filter.h

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Date:   Fri, 16 Sep 2022 14:43:18 -0700
From:   Martin KaFai Lau <martin.lau@...ux.dev>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc:     Daniel Xu <dxu@...uu.xyz>, pablo@...filter.org, fw@...len.de,
        toke@...nel.org, netfilter-devel@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org
Subject: Re: [PATCH bpf-next] bpf: Move nf_conn extern declarations to
 filter.h

On 9/16/22 2:31 PM, Martin KaFai Lau wrote:
> On 9/16/22 1:35 PM, Kumar Kartikeya Dwivedi wrote:
>> On Fri, 16 Sept 2022 at 22:20, Martin KaFai Lau <martin.lau@...ux.dev> 
>> wrote:
>>>
>>> On 9/11/22 11:19 AM, Daniel Xu wrote:
>>>> We're seeing the following new warnings on netdev/build_32bit and
>>>> netdev/build_allmodconfig_warn CI jobs:
>>>>
>>>>       ../net/core/filter.c:8608:1: warning: symbol
>>>>       'nf_conn_btf_access_lock' was not declared. Should it be static?
>>>>       ../net/core/filter.c:8611:5: warning: symbol 'nfct_bsa' was not
>>>>       declared. Should it be static?
>>>>
>>>> Fix by ensuring extern declaration is present while compiling filter.o.
>>>>
>>>> Signed-off-by: Daniel Xu <dxu@...uu.xyz>
>>>> ---
>>>>    include/linux/filter.h                   | 6 ++++++
>>>>    include/net/netfilter/nf_conntrack_bpf.h | 7 +------
>>>>    2 files changed, 7 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/include/linux/filter.h b/include/linux/filter.h
>>>> index 527ae1d64e27..96de256b2c8d 100644
>>>> --- a/include/linux/filter.h
>>>> +++ b/include/linux/filter.h
>>>> @@ -567,6 +567,12 @@ struct sk_filter {
>>>>
>>>>    DECLARE_STATIC_KEY_FALSE(bpf_stats_enabled_key);
>>>>
>>>> +extern struct mutex nf_conn_btf_access_lock;
>>>> +extern int (*nfct_bsa)(struct bpf_verifier_log *log, const struct 
>>>> btf *btf,
>>>> +                    const struct btf_type *t, int off, int size,
>>>> +                    enum bpf_access_type atype, u32 *next_btf_id,
>>>> +                    enum bpf_type_flag *flag);
>>>
>>> Can it avoid leaking the nfct specific details like
>>> 'nf_conn_btf_access_lock' and the null checking on 'nfct_bsa' to
>>> filter.c?  In particular, this code snippet in filter.c:
>>>
>>>           mutex_lock(&nf_conn_btf_access_lock);
>>>           if (nfct_bsa)
>>>                   ret = nfct_bsa(log, btf, ....);
>>>          mutex_unlock(&nf_conn_btf_access_lock);
>>>
>>>
>>> Can the lock and null check be done as one function (eg.
>>> nfct_btf_struct_access()) in nf_conntrack_bpf.c and use it in filter.c
>>> instead?
>>
>> Don't think so, no. Because we want nf_conntrack to work as a module 
>> as well.
> Ah, got it.
> 
> I don't see nf_conntrack_btf_struct_access() in nf_conntrack_bpf.h is 
> used anywhere.  Can be removed?
> 
>> I was the one who suggested nf_conn specific names for now. There is
>> no other user of such module supplied
>> btf_struct_access callbacks yet, when one appears, we should instead
>> make registration of such callbacks properly generic (i.e. also
>> enforce it is only for module BTF ID etc.).
>> But that would be a lot of code without any users right now.
> 
> The lock is the only one needed to be in btf.c and 
> nfct_btf_struct_access() can be an inline in nf_conntrack_bpf.h instead?


nm. brain leaks.  nfct_bsa pointer is still needed :(  I was just 
thinking if it can avoid this nfct specific bits here.