Re: [PATCH bpf-next v9 8/9] libbpf: Add syscall common attributes support for map_create

[Andrii Nakryiko]

On Mon, Feb 2, 2026 at 6:43 AM Leon Hwang <leon.hwang@xxxxxxxxx> 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_log_opts with the following fields:
> log_buf, log_size, log_level, and log_true_size.
>
> Extend bpf_map_create_opts with a new field log_opts, allowing users to
> capture and inspect log messages on map creation failures.
>
> Signed-off-by: Leon Hwang <leon.hwang@xxxxxxxxx>
> ---
>  tools/lib/bpf/bpf.c | 16 +++++++++++++++-
>  tools/lib/bpf/bpf.h | 17 ++++++++++++++++-
>  2 files changed, 31 insertions(+), 2 deletions(-)
>

LGTM

Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>

> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 9d8740761b7a..0c3e40844d80 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -209,6 +209,9 @@ 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 attr_common_sz = sizeof(struct bpf_common_attr);
> +       struct bpf_common_attr attr_common;
> +       struct bpf_log_opts *log_opts;
>         union bpf_attr attr;
>         int fd;
>
> @@ -242,7 +245,18 @@ 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);
> +       log_opts = OPTS_GET(opts, log_opts, NULL);
> +       if (log_opts && feat_supported(NULL, FEAT_BPF_SYSCALL_COMMON_ATTRS)) {
> +               memset(&attr_common, 0, attr_common_sz);
> +               attr_common.log_buf = ptr_to_u64(OPTS_GET(log_opts, log_buf, NULL));
> +               attr_common.log_size = OPTS_GET(log_opts, log_size, 0);
> +               attr_common.log_level = OPTS_GET(log_opts, log_level, 0);
> +               fd = sys_bpf_ext_fd(BPF_MAP_CREATE, &attr, attr_sz, &attr_common, attr_common_sz);
> +               OPTS_SET(log_opts, log_true_size, attr_common.log_true_size);
> +       } else {
> +               fd = sys_bpf_fd(BPF_MAP_CREATE, &attr, attr_sz);
> +               OPTS_SET(log_opts, log_true_size, 0);
> +       }
>         return libbpf_err_errno(fd);
>  }
>
> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> index 2c8e88ddb674..59673f094f86 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_log_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;

please mention in the comment here that this is an out parameter set
by the kernel

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