Re: [PATCH bpf-next 1/2] libbpf: Support uniform BTF-defined key/value specification across all BPF maps

[Hengqi Chen <hengqi.chen@gmail.com>]

On 9/9/21 12:26 PM, Andrii Nakryiko wrote:
> On Sun, Sep 5, 2021 at 3:09 AM Hengqi Chen <hengqi.chen@gmail.com> wrote:
>>
>> A bunch of BPF maps do not support specifying types for key and value.
> 
> s/types/BTF types/, it's a bit confusing otherwise
> 
>> This is non-uniform and inconvenient[0]. Currently, libbpf uses a retry
>> logic which removes BTF type IDs when BPF map creation failed. Instead
>> of retrying, this commit recognizes those specialized map and removes
> 
> s/map/maps/
> 
>> BTF type IDs when creating BPF map.
>>
>>   [0] Closes: https://github.com/libbpf/libbpf/issues/355
>>
>> Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
>> ---
> 
> For patch sets consisting of two or more patches, we ask for a cover
> letter, so for the next revision please provide a cover letter with an
> overall description of what the series is about.
> 

Hello, Andrii



Sorry for the long delay. Will send a v2 for review.

>>  tools/lib/bpf/libbpf.c | 35 ++++++++++++++++++++---------------
>>  1 file changed, 20 insertions(+), 15 deletions(-)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index 88d8825fc6f6..7068c4d07337 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -4613,6 +4613,26 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b
>>                         create_attr.inner_map_fd = map->inner_map_fd;
>>         }
>>
>> +       if (def->type == BPF_MAP_TYPE_PERF_EVENT_ARRAY ||
>> +           def->type == BPF_MAP_TYPE_STACK_TRACE ||
>> +           def->type == BPF_MAP_TYPE_CGROUP_ARRAY ||
>> +           def->type == BPF_MAP_TYPE_ARRAY_OF_MAPS ||
>> +           def->type == BPF_MAP_TYPE_HASH_OF_MAPS ||
>> +           def->type == BPF_MAP_TYPE_DEVMAP ||
>> +           def->type == BPF_MAP_TYPE_SOCKMAP ||
>> +           def->type == BPF_MAP_TYPE_CPUMAP ||
>> +           def->type == BPF_MAP_TYPE_XSKMAP ||
>> +           def->type == BPF_MAP_TYPE_SOCKHASH ||
>> +           def->type == BPF_MAP_TYPE_QUEUE ||
>> +           def->type == BPF_MAP_TYPE_STACK ||
>> +           def->type == BPF_MAP_TYPE_DEVMAP_HASH) {
>> +               create_attr.btf_fd = 0;
>> +               create_attr.btf_key_type_id = 0;
>> +               create_attr.btf_value_type_id = 0;
>> +               map->btf_key_type_id = 0;
>> +               map->btf_value_type_id = 0;
>> +       }
> 
> Let's do this as a more succinct switch statement. Consider also
> slightly rearranging entries to keep "related" map types together:
>   - SOCKMAP + SOCKHASH
>   - DEVMAP + DEVMAP_HASH + CPUMAP + XSKMAP
> 
> Thanks!
>> 
>> +
>>         if (obj->gen_loader) {
>>                 bpf_gen__map_create(obj->gen_loader, &create_attr, is_inner ? -1 : map - obj->maps);
>>                 /* Pretend to have valid FD to pass various fd >= 0 checks.
>> @@ -4622,21 +4642,6 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b
>>         } else {
>>                 map->fd = bpf_create_map_xattr(&create_attr);
>>         }
>> -       if (map->fd < 0 && (create_attr.btf_key_type_id ||
>> -                           create_attr.btf_value_type_id)) {
>> -               char *cp, errmsg[STRERR_BUFSIZE];
>> -
>> -               err = -errno;
>> -               cp = libbpf_strerror_r(err, errmsg, sizeof(errmsg));
>> -               pr_warn("Error in bpf_create_map_xattr(%s):%s(%d). Retrying without BTF.\n",
>> -                       map->name, cp, err);
>> -               create_attr.btf_fd = 0;
>> -               create_attr.btf_key_type_id = 0;
>> -               create_attr.btf_value_type_id = 0;
>> -               map->btf_key_type_id = 0;
>> -               map->btf_value_type_id = 0;
>> -               map->fd = bpf_create_map_xattr(&create_attr);
>> -       }
>>
> 
> Please don't remove this fallback logic. There are multiple situations
> where libbpf might need to retry map creation without BTF.
> 
>>         err = map->fd < 0 ? -errno : 0;
>>
>> --
>> 2.25.1
>>