netdev - Re: [RFC PATCH v8 14/20] bpf: net

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Date: Wed, 22 May 2024 16:55:52 -0700
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Amery Hung <ameryhung@...il.com>
Cc: bpf@...r.kernel.org, netdev@...r.kernel.org, yangpeihao@...u.edu.cn,
 daniel@...earbox.net, andrii@...nel.org, martin.lau@...nel.org,
 sinquersw@...il.com, toke@...hat.com, jhs@...atatu.com, jiri@...nulli.us,
 sdf@...gle.com, xiyou.wangcong@...il.com, yepeilin.cs@...il.com
Subject: Re: [RFC PATCH v8 14/20] bpf: net_sched: Add bpf qdisc kfuncs

On 5/10/24 12:24 PM, Amery Hung wrote:
> +BTF_KFUNCS_START(bpf_qdisc_kfunc_ids)
> +BTF_ID_FLAGS(func, bpf_skb_set_dev)
> +BTF_ID_FLAGS(func, bpf_skb_get_hash)
> +BTF_ID_FLAGS(func, bpf_skb_release, KF_RELEASE)
> +BTF_ID_FLAGS(func, bpf_qdisc_skb_drop, KF_RELEASE)
> +BTF_ID_FLAGS(func, bpf_qdisc_watchdog_schedule)

Thanks for working on the bpf qdisc!

I want to see if we can shrink the set and focus on the core pieces first.

The above kfuncs look ok. bpf_skb_set_dev() will need some thoughts but my 
understanding is that it is also not needed if the patch set did not reuse the 
rb_node in the sk_buff?

> +BTF_ID_FLAGS(func, bpf_skb_tc_classify)
> +BTF_ID_FLAGS(func, bpf_qdisc_create_child)
> +BTF_ID_FLAGS(func, bpf_qdisc_find_class)
> +BTF_ID_FLAGS(func, bpf_qdisc_enqueue, KF_RELEASE)
> +BTF_ID_FLAGS(func, bpf_qdisc_dequeue, KF_ACQUIRE | KF_RET_NULL)

How about starting with classless qdisc first?

I also wonder if the class/hierarchy can be implemented in the 
bpf_map/bpf_rb_root/bpf_list_head alone. That aside, the patch set shows that 
classful qdisc is something tangible with kfuncs. The classless qdisc bpf 
support does not seem to depend on it. Unless there is something on the classful 
side that really needs to be finalized at this point, I would leave it out from 
the core pieces for now and focus on classless. Does it make sense?

> +BTF_KFUNCS_END(bpf_qdisc_kfunc_ids)
> +
> +static const struct btf_kfunc_id_set bpf_qdisc_kfunc_set = {
> +	.owner = THIS_MODULE,
> +	.set   = &bpf_qdisc_kfunc_ids,
> +};
> +
> +BTF_ID_LIST(skb_kfunc_dtor_ids)
> +BTF_ID(struct, sk_buff)
> +BTF_ID_FLAGS(func, bpf_skb_release, KF_RELEASE)
> +
>   static const struct bpf_verifier_ops bpf_qdisc_verifier_ops = {
>   	.get_func_proto		= bpf_qdisc_get_func_proto,
>   	.is_valid_access	= bpf_qdisc_is_valid_access,
> @@ -558,6 +781,20 @@ static struct bpf_struct_ops bpf_Qdisc_ops = {
>   
>   static int __init bpf_qdisc_kfunc_init(void)
>   {
> -	return register_bpf_struct_ops(&bpf_Qdisc_ops, Qdisc_ops);
> +	int ret;
> +	const struct btf_id_dtor_kfunc skb_kfunc_dtors[] = {
> +		{
> +			.btf_id       = skb_kfunc_dtor_ids[0],
> +			.kfunc_btf_id = skb_kfunc_dtor_ids[1]
> +		},
> +	};
> +
> +	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &bpf_qdisc_kfunc_set);
> +	ret = ret ?: register_btf_id_dtor_kfuncs(skb_kfunc_dtors,
> +						 ARRAY_SIZE(skb_kfunc_dtors),
> +						 THIS_MODULE);
> +	ret = ret ?: register_bpf_struct_ops(&bpf_Qdisc_ops, Qdisc_ops);
> +
> +	return ret;
>   }
>   late_initcall(bpf_qdisc_kfunc_init);