netdev - Re: [PATCH bpf-next v3 2/3] libbpf: add low level TC-BPF API

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Date:   Thu, 22 Apr 2021 00:59:28 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>, bpf@...r.kernel.org
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next v3 2/3] libbpf: add low level TC-BPF API

On 4/20/21 9:37 PM, Kumar Kartikeya Dwivedi wrote:
[...]
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index bec4e6a6e31d..b4ed6a41ea70 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -16,6 +16,8 @@
>   #include <stdbool.h>
>   #include <sys/types.h>  // for size_t
>   #include <linux/bpf.h>
> +#include <linux/pkt_sched.h>
> +#include <linux/tc_act/tc_bpf.h>
>   
>   #include "libbpf_common.h"
>   
> @@ -775,6 +777,48 @@ LIBBPF_API int bpf_linker__add_file(struct bpf_linker *linker, const char *filen
>   LIBBPF_API int bpf_linker__finalize(struct bpf_linker *linker);
>   LIBBPF_API void bpf_linker__free(struct bpf_linker *linker);
>   
> +/* Convenience macros for the clsact attach hooks */
> +#define BPF_TC_CLSACT_INGRESS TC_H_MAKE(TC_H_CLSACT, TC_H_MIN_INGRESS)
> +#define BPF_TC_CLSACT_EGRESS TC_H_MAKE(TC_H_CLSACT, TC_H_MIN_EGRESS)

I would abstract those away into an enum, plus avoid having to pull in
linux/pkt_sched.h and linux/tc_act/tc_bpf.h from main libbpf.h header.

Just add a enum { BPF_TC_DIR_INGRESS, BPF_TC_DIR_EGRESS, } and then the
concrete tc bits (TC_H_MAKE()) can be translated internally.

> +struct bpf_tc_opts {
> +	size_t sz;

Is this set anywhere?

> +	__u32 handle;
> +	__u32 class_id;

I'd remove class_id from here as well given in direct-action a BPF prog can
set it if needed.

> +	__u16 priority;
> +	bool replace;
> +	size_t :0;

What's the rationale for this padding?

> +};
> +
> +#define bpf_tc_opts__last_field replace
> +
> +/* Acts as a handle for an attached filter */
> +struct bpf_tc_attach_id {

nit: maybe bpf_tc_ctx

> +	__u32 handle;
> +	__u16 priority;
> +};
> +
> +struct bpf_tc_info {
> +	struct bpf_tc_attach_id id;
> +	__u16 protocol;
> +	__u32 chain_index;
> +	__u32 prog_id;
> +	__u8 tag[BPF_TAG_SIZE];
> +	__u32 class_id;
> +	__u32 bpf_flags;
> +	__u32 bpf_flags_gen;

Given we do not yet have any setters e.g. for offload, etc, the one thing
I'd see useful and crucial initially is prog_id.

The protocol, chain_index, and I would also include tag should be dropped.
Similarly class_id given my earlier statement, and flags I would extend once
this lib API would support offloading progs.

> +};
> +
> +/* id is out parameter that will be written to, it must not be NULL */
> +LIBBPF_API int bpf_tc_attach(int fd, __u32 ifindex, __u32 parent_id,
> +			     const struct bpf_tc_opts *opts,
> +			     struct bpf_tc_attach_id *id);
> +LIBBPF_API int bpf_tc_detach(__u32 ifindex, __u32 parent_id,
> +			     const struct bpf_tc_attach_id *id);
> +LIBBPF_API int bpf_tc_get_info(__u32 ifindex, __u32 parent_id,
> +			       const struct bpf_tc_attach_id *id,
> +			       struct bpf_tc_info *info);

As per above, for parent_id I'd replace with dir enum.

> +
>   #ifdef __cplusplus
>   } /* extern "C" */
>   #endif