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

From: David Vernet <void@manifault.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
	andrii@kernel.org, martin.lau@linux.dev, song@kernel.org,
	yhs@meta.com, john.fastabend@gmail.com, kpsingh@kernel.org,
	sdf@google.com, haoluo@google.com, jolsa@kernel.org,
	linux-kernel@vger.kernel.org, kernel-team@meta.com,
	memxor@gmail.com
Subject: Re: [PATCH bpf-next v2 3/3] bpf: Use BPF_KFUNC macro at all kfunc definitions
Date: Mon, 23 Jan 2023 12:48:27 -0600	[thread overview]
Message-ID: <Y87We/92xiv5/+g+@maniforge.lan> (raw)
In-Reply-To: <20230123183305.2mgoxgw4ca3sfk24@macbook-pro-6.dhcp.thefacebook.com>

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