netdev - Re: [PATCH bpf-next v2 2/2] bpf: Introduce bpf user log

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Date: Mon, 10 Jul 2023 16:45:30 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Leon Hwang <hffilwlqm@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	John Fastabend <john.fastabend@...il.com>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Jesper Dangaard Brouer <hawk@...nel.org>, Yizhou Tang <tangyeechou@...il.com>, kernel-patches-bot@...com, 
	bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2 2/2] bpf: Introduce bpf user log

On Fri, Jul 7, 2023 at 9:08 PM Leon Hwang <hffilwlqm@...il.com> wrote:
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 34fa334938ba5..8a458cfcd91bd 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -1549,7 +1549,6 @@ union bpf_attr {
>                 };
>                 __u32           attach_type;    /* attach type */
>                 __u32           flags;          /* extra flags */
> -               struct bpf_generic_user_log log; /* user log */
>                 union {
>                         __u32           target_btf_id;  /* btf_id of target to attach to */
>                         struct {
> @@ -1585,6 +1584,9 @@ union bpf_attr {
>                                 __s32           priority;
>                                 __u32           flags;
>                         } netfilter;
> +                       struct {
> +                               struct bpf_generic_user_log ulog; /* user log */
> +                       } xdp;

1.
You cannot break api in patch 1 and fix it in patch 2.

2.
libbpf side is missing.

3.
selftest is missing.

4.
bpf_vlog_finalize() should be used and error propagated back through
link_create.
Same api must be used: log_level, log_size, log_buf, log_true_size.

But considering all that I agree with Daniel Xu that
tracepoint would be better here.