linux-kernel - Re: [PATCH bpf-next v5 8/9] libbpf: Add common attr support for map

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Message-ID: <CAEf4BzarSrW1aTRcjrheLWqxFCh1FFd7vwJ4OQup1dbT13EapQ@mail.gmail.com>
Date: Thu, 15 Jan 2026 17:03:48 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Leon Hwang <leon.hwang@...ux.dev>
Cc: 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>, linux-kernel@...r.kernel.org, linux-api@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, kernel-patches-bot@...com
Subject: Re: [PATCH bpf-next v5 8/9] libbpf: Add common attr support for map_create

On Mon, Jan 12, 2026 at 6:59 AM Leon Hwang <leon.hwang@...ux.dev> wrote:
>
> With the previous commit adding common attribute support for
> BPF_MAP_CREATE, users can now retrieve detailed error messages when map
> creation fails via the log_buf field.
>
> Introduce struct bpf_syscall_common_attr_opts with the following fields:
> log_buf, log_size, log_level, and log_true_size.
>
> Extend bpf_map_create_opts with a new field common_attr_opts, allowing
> users to capture and inspect log messages on map creation failures.
>
> Signed-off-by: Leon Hwang <leon.hwang@...ux.dev>
> ---
>  tools/lib/bpf/bpf.c | 15 ++++++++++++++-
>  tools/lib/bpf/bpf.h | 17 ++++++++++++++++-
>  2 files changed, 30 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index d44e667aaf02..d65df1b7b2be 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -207,6 +207,9 @@ int bpf_map_create(enum bpf_map_type map_type,
>                    const struct bpf_map_create_opts *opts)
>  {
>         const size_t attr_sz = offsetofend(union bpf_attr, excl_prog_hash_size);
> +       const size_t common_attr_sz = sizeof(struct bpf_common_attr);
> +       struct bpf_syscall_common_attr_opts *common_attr_opts;
> +       struct bpf_common_attr common_attr;
>         union bpf_attr attr;
>         int fd;
>
> @@ -240,7 +243,17 @@ int bpf_map_create(enum bpf_map_type map_type,
>         attr.excl_prog_hash = ptr_to_u64(OPTS_GET(opts, excl_prog_hash, NULL));
>         attr.excl_prog_hash_size = OPTS_GET(opts, excl_prog_hash_size, 0);
>
> -       fd = sys_bpf_fd(BPF_MAP_CREATE, &attr, attr_sz);
> +       common_attr_opts = OPTS_GET(opts, common_attr_opts, NULL);
> +       if (common_attr_opts && feat_supported(NULL, FEAT_EXTENDED_SYSCALL)) {
> +               memset(&common_attr, 0, common_attr_sz);
> +               common_attr.log_buf = ptr_to_u64(OPTS_GET(common_attr_opts, log_buf, NULL));
> +               common_attr.log_size = OPTS_GET(common_attr_opts, log_size, 0);
> +               common_attr.log_level = OPTS_GET(common_attr_opts, log_level, 0);
> +               fd = sys_bpf_ext_fd(BPF_MAP_CREATE, &attr, attr_sz, &common_attr, common_attr_sz);
> +               OPTS_SET(common_attr_opts, log_true_size, common_attr.log_true_size);
> +       } else {
> +               fd = sys_bpf_fd(BPF_MAP_CREATE, &attr, attr_sz);

OPTS_SET(log_true_size) to zero here, maybe?

> +       }
>         return libbpf_err_errno(fd);
>  }
>
> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> index 2c8e88ddb674..c4a26e6b71ea 100644
> --- a/tools/lib/bpf/bpf.h
> +++ b/tools/lib/bpf/bpf.h
> @@ -37,6 +37,18 @@ extern "C" {
>
>  LIBBPF_API int libbpf_set_memlock_rlim(size_t memlock_bytes);
>
> +struct bpf_syscall_common_attr_opts {
> +       size_t sz; /* size of this struct for forward/backward compatibility */
> +
> +       char *log_buf;
> +       __u32 log_size;
> +       __u32 log_level;
> +       __u32 log_true_size;
> +
> +       size_t :0;
> +};
> +#define bpf_syscall_common_attr_opts__last_field log_true_size

see below, let's drop this struct and just add these 4 fields directly
to bpf_map_create_opts

> +
>  struct bpf_map_create_opts {
>         size_t sz; /* size of this struct for forward/backward compatibility */
>
> @@ -57,9 +69,12 @@ struct bpf_map_create_opts {
>
>         const void *excl_prog_hash;
>         __u32 excl_prog_hash_size;
> +
> +       struct bpf_syscall_common_attr_opts *common_attr_opts;

maybe let's just add those log_xxx fields here directly? This whole
extra bpf_syscall_common_attr_opts pointer and struct seems like a
cumbersome API.

> +
>         size_t :0;
>  };
> -#define bpf_map_create_opts__last_field excl_prog_hash_size
> +#define bpf_map_create_opts__last_field common_attr_opts
>
>  LIBBPF_API int bpf_map_create(enum bpf_map_type map_type,
>                               const char *map_name,
> --
> 2.52.0
>