linux-kernel - Re: [PATCH bpf-next v2 3/3] bpf: Use BPF_KFUNC macro at all kfunc definitions

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Message-ID: <Y87We/92xiv5/+g+@maniforge.lan>
Date:   Mon, 23 Jan 2023 12:48:27 -0600
From:   David Vernet <void@...ifault.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
        yhs@...a.com, john.fastabend@...il.com, kpsingh@...nel.org,
        sdf@...gle.com, haoluo@...gle.com, jolsa@...nel.org,
        linux-kernel@...r.kernel.org, kernel-team@...a.com,
        memxor@...il.com
Subject: Re: [PATCH bpf-next v2 3/3] bpf: Use BPF_KFUNC macro at all kfunc
 definitions

On Mon, Jan 23, 2023 at 10:33:05AM -0800, Alexei Starovoitov wrote:
> On Mon, Jan 23, 2023 at 11:15:06AM -0600, David Vernet wrote:
> > -void *bpf_obj_new_impl(u64 local_type_id__k, void *meta__ign)
> > +BPF_KFUNC(void *bpf_obj_new_impl(u64 local_type_id__k, void *meta__ign))
> >  {
> >  	struct btf_struct_meta *meta = meta__ign;
> >  	u64 size = local_type_id__k;
> > @@ -1790,7 +1786,7 @@ void *bpf_obj_new_impl(u64 local_type_id__k, void *meta__ign)
> >  	return p;
> >  }
> >  
> > -void bpf_obj_drop_impl(void *p__alloc, void *meta__ign)
> > +BPF_KFUNC(void bpf_obj_drop_impl(void *p__alloc, void *meta__ign))
> >  {
> 
> The following also works:
> -BPF_KFUNC(void *bpf_obj_new_impl(u64 local_type_id__k, void *meta__ign))
> +BPF_KFUNC(
> +void *bpf_obj_new_impl(u64 local_type_id__k, void *meta__ign)
> +)
> 
> and it looks little bit cleaner to me.
> 
> git grep -A1 BPF_KFUNC
> can still find all instances of kfuncs.
> 
> wdyt?

I'm fine with putting it on its own line if that's your preference.
Agreed that it might be a bit cleaner, especially for functions with the
return type on its own line, so we'd have e.g.:

BPF_KFUNC(
struct nf_conn *
bpf_skb_ct_lookup(struct __sk_buff *skb_ctx, struct bpf_sock_tuple *bpf_tuple,
		  u32 tuple__sz, struct bpf_ct_opts *opts, u32 opts__sz)
) {

// ...

}

Note the presence of the { on the closing paren. Are you ok with that?
Otherwise I think it will look a bit odd:

BPF_KFUNC(
struct nf_conn *
bpf_skb_ct_lookup(struct __sk_buff *skb_ctx, struct bpf_sock_tuple *bpf_tuple,
		  u32 tuple__sz, struct bpf_ct_opts *opts, u32 opts__sz)
)
{

}

Thanks,
David