netdev - Re: [PATCH bpf-next] perf/bpf_counter: use bpf_map_create instead of bpf_create

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Date:   Tue, 7 Dec 2021 06:30:22 +0000
From:   Song Liu <songliubraving@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
CC:     Song Liu <song@...nel.org>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        "Kernel Team" <Kernel-team@...com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH bpf-next] perf/bpf_counter: use bpf_map_create instead of
 bpf_create_map



> On Dec 6, 2021, at 9:13 PM, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
> 
> On Mon, Dec 6, 2021 at 8:32 PM Song Liu <songliubraving@...com> wrote:
>> 
>> 
>> 
>>> On Dec 6, 2021, at 6:37 PM, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
>>> 
>>> On Mon, Dec 6, 2021 at 3:08 PM Song Liu <song@...nel.org> wrote:
>>>> 
>>>> bpf_create_map is deprecated. Replace it with bpf_map_create.
>>>> 
>>>> Fixes: 992c4225419a ("libbpf: Unify low-level map creation APIs w/ new bpf_map_create()")
>>> 
>>> This is not a bug fix, it's an improvement. So I don't think "Fixes: "
>>> is warranted here, tbh.
>> 
>> I got compilation errors before this change, like
>> 
>> util/bpf_counter.c: In function ‘bperf_lock_attr_map’:
>> util/bpf_counter.c:323:3: error: ‘bpf_create_map’ is deprecated: libbpf v0.7+: use bpf_map_create() instead [-Werror=deprecated-declarations]
>>   map_fd = bpf_create_map(BPF_MAP_TYPE_HASH,
>>   ^~~~~~
>> In file included from util/bpf_counter.h:7,
>>                 from util/bpf_counter.c:15:
>> /data/users/songliubraving/kernel/linux-git/tools/lib/bpf/bpf.h:91:16: note: declared here
>> LIBBPF_API int bpf_create_map(enum bpf_map_type map_type, int key_size,
>>                ^~~~~~~~~~~~~~
>> cc1: all warnings being treated as errors
>> make[4]: *** [/data/users/songliubraving/kernel/linux-git/tools/build/Makefile.build:96: util/bpf_counter.o] Error 1
>> make[4]: *** Waiting for unfinished jobs....
>> make[3]: *** [/data/users/songliubraving/kernel/linux-git/tools/build/Makefile.build:139: util] Error 2
>> make[2]: *** [Makefile.perf:665: perf-in.o] Error 2
>> make[1]: *** [Makefile.perf:240: sub-make] Error 2
>> make: *** [Makefile:70: all] Error 2
>> 
> 
> Hmm.. is util/bpf_counter.h guarded behind some Makefile arguments?
> I've sent #pragma temporary workarounds just a few days ago ([0]), but
> this one didn't come up during the build.
> 
>  [0] https://patchwork.kernel.org/project/netdevbpf/patch/20211203004640.2455717-1-andrii@kernel.org/

I guess the default build test doesn't enable BUILD_BPF_SKEL? 

> 
>> Do we plan to remove bpf_create_map in the future? If not, we can probably just
>> add '#pragma GCC diagnostic ignored "-Wdeprecated-declarations"' can call it done?
> 
> Yes, it will be removed in a few libbpf releases when we switch to the
> 1.0 version. So suppressing a warning is a temporary work-around.
> 
>> 
>>> 
>>>> Signed-off-by: Song Liu <song@...nel.org>
>>>> ---
>>>> tools/perf/util/bpf_counter.c | 4 ++--
>>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>>> 
>>>> diff --git a/tools/perf/util/bpf_counter.c b/tools/perf/util/bpf_counter.c
>>>> index c17d4a43ce065..ed150a9b3a0c0 100644
>>>> --- a/tools/perf/util/bpf_counter.c
>>>> +++ b/tools/perf/util/bpf_counter.c
>>>> @@ -320,10 +320,10 @@ static int bperf_lock_attr_map(struct target *target)
>>>>       }
>>>> 
>>>>       if (access(path, F_OK)) {
>>>> -               map_fd = bpf_create_map(BPF_MAP_TYPE_HASH,
>>>> +               map_fd = bpf_map_create(BPF_MAP_TYPE_HASH, NULL,
>>> 
>>> I think perf is trying to be linkable with libbpf as a shared library,
>>> so on some older versions of libbpf bpf_map_create() won't be (yet)
>>> available. So to make this work, I think you'll need to define your
>>> own weak bpf_map_create function that will use bpf_create_map().
>> 
>> Hmm... I didn't know the plan to link libbpf as shared library. In this case,
>> maybe the #pragma solution is preferred?
> 
> See "perf tools: Add more weak libbpf functions" sent by Jiri not so
> long ago about what they did with some other used APIs that are now
> marked deprecated.

Do you mean something like this?

int __weak
bpf_map_create(enum bpf_map_type map_type,
               const char *map_name __maybe_unused,
               __u32 key_size,
               __u32 value_size,
               __u32 max_entries,
               const struct bpf_map_create_opts *opts __maybe_unused)
{
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
        return bpf_create_map(map_type, key_size, value_size, max_entries, 0);
#pragma GCC diagnostic pop
}

I guess this won't work when bpf_create_map() is eventually removed, as 
__weak function are still compiled, no?

Thanks,
Song