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Message-ID: <5811eb10-bc93-0b81-2ee4-10490388f238@iogearbox.net>
Date: Tue, 27 Apr 2021 17:04:30 +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 v4 2/3] libbpf: add low level TC-BPF API
On 4/23/21 5:05 PM, Kumar Kartikeya Dwivedi wrote:
[...]
> tools/lib/bpf/libbpf.h | 92 ++++++++
> tools/lib/bpf/libbpf.map | 5 +
> tools/lib/bpf/netlink.c | 478 ++++++++++++++++++++++++++++++++++++++-
> 3 files changed, 574 insertions(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index bec4e6a6e31d..1c717c07b66e 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -775,6 +775,98 @@ 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);
>
> +enum bpf_tc_attach_point {
> + BPF_TC_INGRESS,
> + BPF_TC_EGRESS,
> + BPF_TC_CUSTOM_PARENT,
> + _BPF_TC_PARENT_MAX,
I don't think we need to expose _BPF_TC_PARENT_MAX as part of the API, I would drop
the latter.
> +};
> +
> +/* The opts structure is also used to return the created filters attributes
> + * (e.g. in case the user left them unset). Some of the options that were left
> + * out default to a reasonable value, documented below.
> + *
> + * protocol - ETH_P_ALL
> + * chain index - 0
> + * class_id - 0 (can be set by bpf program using skb->tc_classid)
> + * bpf_flags - TCA_BPF_FLAG_ACT_DIRECT (direct action mode)
> + * bpf_flags_gen - 0
> + *
> + * The user must fulfill documented requirements for each function.
Not sure if this is overly relevant as part of the bpf_tc_opts in here. For the
2nd part, I would probably just mention that libbpf internally attaches the bpf
programs with direct action mode. The hw offload may be future todo, and the other
bits are little used anyway; mentioning them here, what value does it have to
libbpf users? I'd rather just drop the 2nd part and/or simplify this paragraph
just stating that the progs are attached in direct action mode.
> + */
> +struct bpf_tc_opts {
> + size_t sz;
> + __u32 handle;
> + __u32 parent;
> + __u16 priority;
> + __u32 prog_id;
> + bool replace;
> + size_t :0;
> +};
> +
> +#define bpf_tc_opts__last_field replace
> +
> +struct bpf_tc_ctx;
> +
> +struct bpf_tc_ctx_opts {
> + size_t sz;
> +};
> +
> +#define bpf_tc_ctx_opts__last_field sz
> +
> +/* Requirements */
> +/*
> + * @ifindex: Must be > 0.
> + * @parent: Must be one of the enum constants < _BPF_TC_PARENT_MAX
> + * @opts: Can be NULL, currently no options are supported.
> + */
Up to Andrii, but we don't have such API doc in general inside libbpf.h, I
would drop it for the time being to be consistent with the rest (same for
others below).
> +LIBBPF_API struct bpf_tc_ctx *bpf_tc_ctx_init(__u32 ifindex,
nit: in user space s/__u32 ifindex/int ifindex/
> + enum bpf_tc_attach_point parent,
> + struct bpf_tc_ctx_opts *opts);
Should we enforce opts being NULL or non-NULL here, or drop the arg from here
for now altogether? (And if later versions of the functions show up this could
be mapped to the right one?)
> +/*
> + * @ctx: Can be NULL, if not, must point to a valid object.
> + * If the qdisc was attached during ctx_init, it will be deleted if no
> + * filters are attached to it.
> + * When ctx == NULL, this is a no-op.
> + */
> +LIBBPF_API int bpf_tc_ctx_destroy(struct bpf_tc_ctx *ctx);
> +/*
> + * @ctx: Cannot be NULL.
> + * @fd: Must be >= 0.
> + * @opts: Cannot be NULL, prog_id must be unset, all other fields can be
> + * optionally set. All fields except replace will be set as per created
> + * filter's attributes. parent must only be set when attach_point of ctx is
> + * BPF_TC_CUSTOM_PARENT, otherwise parent must be unset.
> + *
> + * Fills the following fields in opts:
> + * handle
> + * parent
> + * priority
> + * prog_id
> + */
> +LIBBPF_API int bpf_tc_attach(struct bpf_tc_ctx *ctx, int fd,
> + struct bpf_tc_opts *opts);
> +/*
> + * @ctx: Cannot be NULL.
> + * @opts: Cannot be NULL, replace and prog_id must be unset, all other fields
> + * must be set.
> + */
> +LIBBPF_API int bpf_tc_detach(struct bpf_tc_ctx *ctx,
> + const struct bpf_tc_opts *opts);
One thing that I find a bit odd from this API is that BPF_TC_INGRESS / BPF_TC_EGRESS
needs to be set each time via bpf_tc_ctx_init(). So whenever a specific program would
be attached to both we need to 're-init' in between just to change from hook a to b,
whereas when you have BPF_TC_CUSTOM_PARENT, you could just use a different opts->parent
without going this detour (unless the clsact wasn't loaded there in the first place).
Could we add a BPF_TC_UNSPEC to enum bpf_tc_attach_point, which the user would pass to
bpf_tc_ctx_init(), so that opts.direction = BPF_TC_INGRESS with subsequent bpf_tc_attach()
can be called, and same opts.direction = BPF_TC_EGRESS with bpf_tc_attach() for different
fd. The only thing we cared about in bpf_tc_ctx_init() resp. the ctx was that qdisc was
ready.
> +/*
> + * @ctx: Cannot be NULL.
> + * @opts: Cannot be NULL, replace and prog_id must be unset, all other fields
> + * must be set.
> + *
> + * Fills the following fields in opts:
> + * handle
> + * parent
> + * priority
> + * prog_id
> + */
> +LIBBPF_API int bpf_tc_query(struct bpf_tc_ctx *ctx,
> + struct bpf_tc_opts *opts);
> +
> #ifdef __cplusplus
> } /* extern "C" */
> #endif
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