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

[Leon Hwang <leon.hwang@linux.dev>]

On 2026/1/16 09:03, Andrii Nakryiko wrote:
> On Mon, Jan 12, 2026 at 6:59 AM Leon Hwang <leon.hwang@linux.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@linux.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.

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
>>