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

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Message-ID: <CAEf4Bza7d8sdo2Y-D0U5BQos6Z2C6i-4f4B4oe8sApfua0uNAg@mail.gmail.com>
Date: Fri, 16 Jan 2026 14:33:09 -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 Fri, Jan 16, 2026 at 6:17 AM Leon Hwang <leon.hwang@...ux.dev> wrote:
>
>
>
> On 2026/1/16 09:03, Andrii Nakryiko wrote:
> > 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?
> >
>
> Unnecessary, but ok to do it.
>
> >> +       }
> >>         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.
> >
>
> Oops... This struct was suggested by the v3 discussion [1].
>
> This struct was used to report 'log_true_size' without changing
> 'bpf_map_create()' API.
>

Ah, I already forgot. log_true_size being an output parameter here...
Sigh. I don't like the verboseness of bpf_syscall_common_attr_opts and
"common_attr_opts" and all that stuff...

What if we make it struct bpf_log_opts {} and keep it log-specific?

> Links
> [1]
> https://lore.kernel.org/bpf/CAEf4Bzaw9cboFSf1OXmD84S7pKaeyj=bcQg_diUzGwAkFsjUgg@mail.gmail.com/
>
> Thanks,
> Leon
>
> >> +
> >>         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
> >>
>