Subject: Re: [PATCH bpf-next v2 3/3] bpf: Move nf_conn extern declarations to filter.h

From: Martin KaFai Lau <[email-masked]>
Date: Mon, 19 Sep 2022 22:20:47 -0700

On 9/19/22 12:44 PM, 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.
> 
> Fixes: 864b656f82cc ("bpf: Add support for writing to nf_conn:mark")
> Signed-off-by: Daniel Xu <[email-masked]>
> ---
>   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 75335432fcbc..98e28126c24b 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_btf_struct_access)(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);
> +
>   typedef unsigned int (*bpf_dispatcher_fn)(const void *ctx,
>   					  const struct bpf_insn *insnsi,
>   					  unsigned int (*bpf_func)(const void *,
> diff --git a/include/net/netfilter/nf_conntrack_bpf.h b/include/net/netfilter/nf_conntrack_bpf.h
> index d1087e4da440..24d1ccc1f8df 100644
> --- a/include/net/netfilter/nf_conntrack_bpf.h
> +++ b/include/net/netfilter/nf_conntrack_bpf.h
> @@ -5,6 +5,7 @@
>   
>   #include <linux/bpf.h>
>   #include <linux/btf.h>
> +#include <linux/filter.h>

The filter.h is only needed by nf_conntrack_bpf.c?  How about moving 
this include to nf_conntrack_bpf.c.  nf_conntrack_bpf.h is included by 
other conntrack core codes.  I would prefer not to spill over 
unnecessary bpf headers to them.  The same goes for the above bpf.h and 
btf.h which are only needed in nf_conntrack_bpf.c also?

>   #include <linux/kconfig.h>
>   #include <linux/mutex.h>

Also, is mutex.h still needed?

>   
> @@ -14,12 +15,6 @@
>   extern int register_nf_conntrack_bpf(void);
>   extern void cleanup_nf_conntrack_bpf(void);
>   
> -extern struct mutex nf_conn_btf_access_lock;
> -extern int (*nfct_btf_struct_access)(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);
> -
>   #else
>   
>   static inline int register_nf_conntrack_bpf(void)