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

[Daniel Borkmann]

On 1/23/23 7:54 PM, Alexei Starovoitov wrote:
> On Mon, Jan 23, 2023 at 12:48:27PM -0600, David Vernet wrote:
> > 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)
>
> Yeah. Especially for those.
>
> > ) {
> >
> > // ...
> >
> > }
> >
> > Note the presence of the { on the closing paren. Are you ok with that?
> > Otherwise I think it will look a bit odd:
>
> Yep. Good idea. Either ){ or ) { look good to me.
>
> > 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)
> > )
> > {
> >
> > }

Did you look into making this similar to the EXPORT_SYMBOL() infra? If possible
that would look much more natural to developers, e.g. :

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)
{
	[...]
}

EXPORT_BPF_KFUNC(bpf_skb_ct_lookup);