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

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Message-ID: <20210421230858.ruwqw5jvsy7cjioy@apollo>
Date:   Thu, 22 Apr 2021 04:38:58 +0530
From:   Kumar Kartikeya Dwivedi <memxor@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     bpf@...r.kernel.org,
        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 Thu, Apr 22, 2021 at 04:29:28AM IST, Daniel Borkmann wrote:
> 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.
>

Ok, will do.

> > +struct bpf_tc_opts {
> > +	size_t sz;
>
> Is this set anywhere?
>

This is needed by the OPTS_* infrastructure.

> > +	__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.
>

Ok, makes sense.

> > +	__u16 priority;
> > +	bool replace;
> > +	size_t :0;
>
> What's the rationale for this padding?
>

dde7b3f5f2f4 ("libbpf: Add explicit padding to bpf_xdp_set_link_opts")

> > +};
> > +
> > +#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
>

Noted.

> > +	__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.

A future user of this API needs to know the tag, so I would like to keep that.
The rest we can drop, and probably document the default values explicitly.

> 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

--
Kartikeya