linux-kernel - Re: [PATCH bpf-next v8 4/9] bpf: Add syscall common attributes support for prog

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Message-ID: <CAADnVQ+PDCV=YrFhxG3gXPC3jDPdbTmsaAOKBsFceKgEware0Q@mail.gmail.com>
Date: Mon, 26 Jan 2026 18:43:33 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Leon Hwang <leon.hwang@...ux.dev>
Cc: bpf <bpf@...r.kernel.org>, 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>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	Shuah Khan <shuah@...nel.org>, Christian Brauner <brauner@...nel.org>, 
	Seth Forshee <sforshee@...nel.org>, Yuichiro Tsuji <yuichtsu@...zon.com>, 
	Andrey Albershteyn <aalbersh@...hat.com>, Willem de Bruijn <willemb@...gle.com>, 
	Jason Xing <kerneljasonxing@...il.com>, Tao Chen <chen.dylane@...ux.dev>, 
	Mykyta Yatsenko <yatsenko@...a.com>, Kumar Kartikeya Dwivedi <memxor@...il.com>, 
	Anton Protopopov <a.s.protopopov@...il.com>, Amery Hung <ameryhung@...il.com>, 
	Rong Tao <rongtao@...tc.cn>, LKML <linux-kernel@...r.kernel.org>, 
	Linux API <linux-api@...r.kernel.org>, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, kernel-patches-bot@...com
Subject: Re: [PATCH bpf-next v8 4/9] bpf: Add syscall common attributes
 support for prog_load

,


On Mon, Jan 26, 2026 at 7:15 AM Leon Hwang <leon.hwang@...ux.dev> wrote:
>
> The log buffer of common attributes would be confusing with the one in
> 'union bpf_attr' for BPF_PROG_LOAD.
>
> In order to clarify the usage of these two log buffers, they both can be
> used for logging if:
>
> * They are same, including 'log_buf', 'log_level' and 'log_size'.
> * One of them is missing, then another one will be used for logging.
>
> If they both have 'log_buf' but they are not same totally, return -EINVAL.
>
> Signed-off-by: Leon Hwang <leon.hwang@...ux.dev>
> ---
>  include/linux/bpf_verifier.h |  4 +++-
>  kernel/bpf/log.c             | 29 ++++++++++++++++++++++++++---
>  kernel/bpf/syscall.c         |  9 ++++++---
>  3 files changed, 35 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> index 4a0c5ef296b9..7eb024e83d2d 100644
> --- a/include/linux/bpf_verifier.h
> +++ b/include/linux/bpf_verifier.h
> @@ -637,9 +637,11 @@ struct bpf_log_attr {
>         u32 log_level;
>         struct bpf_attrs *attrs;
>         u32 offsetof_log_true_size;
> +       struct bpf_attrs *attrs_common;
>  };
>
> -int bpf_prog_load_log_attr_init(struct bpf_log_attr *log_attr, struct bpf_attrs *attrs);
> +int bpf_prog_load_log_attr_init(struct bpf_log_attr *log_attr, struct bpf_attrs *attrs,
> +                               struct bpf_attrs *attrs_common);
>  int bpf_log_attr_finalize(struct bpf_log_attr *log_attr, struct bpf_verifier_log *log);
>
>  #define BPF_MAX_SUBPROGS 256
> diff --git a/kernel/bpf/log.c b/kernel/bpf/log.c
> index 457b724c4176..c0b816e84384 100644
> --- a/kernel/bpf/log.c
> +++ b/kernel/bpf/log.c
> @@ -865,23 +865,41 @@ void print_insn_state(struct bpf_verifier_env *env, const struct bpf_verifier_st
>  }
>
>  static int bpf_log_attr_init(struct bpf_log_attr *log_attr, struct bpf_attrs *attrs, u64 log_buf,
> -                            u32 log_size, u32 log_level, int offsetof_log_true_size)
> +                            u32 log_size, u32 log_level, int offsetof_log_true_size,
> +                            struct bpf_attrs *attrs_common)
>  {
> +       const struct bpf_common_attr *common = attrs_common ? attrs_common->attr : NULL;
> +

It seems the only point of struct bpf_attrs is to pass the attrs
here and remember them in bpf_log_attr.
It looks unnecessary. Also the cast to void and back to actual
type doesn't look pretty.
It seems all of it is to do two copy_to_bpfptr_offset() of log_true_size
in different places,
but libbpf will use only one, so let's do only one
copy_to_bpfptr_offset() and simply the whole thing.
struct bpf_log_attr only needs
  u32 offsetof_true_size;
  bpfptr_t uattr;

No need to introduce bpf_attrs and bpf_attrs_init() either.
When bpf_log_attr is inited make the choice of uattr and offset.
uattr will point at either new bpf_common_attr or old bpf_attr,
and offsetof_true_size will have 3 possible offsets.

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