netdev - Re: [PATCH bpf-next] libbpf: Skip the pinning of global data map for old kernels.

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Date:   Fri, 10 Dec 2021 11:02:36 +0800
From:   Shuyi Cheng <chengshuyi@...ux.alibaba.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        "open list:BPF (Safe dynamic programs and tools)" 
        <netdev@...r.kernel.org>,
        "open list:BPF (Safe dynamic programs and tools)" 
        <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next] libbpf: Skip the pinning of global data map for
 old kernels.



On 12/10/21 1:26 AM, Andrii Nakryiko wrote:
> On Thu, Dec 9, 2021 at 12:44 AM Shuyi Cheng
> <chengshuyi@...ux.alibaba.com> wrote:
>>
>>
>> Fix error: "failed to pin map: Bad file descriptor, path:
>> /sys/fs/bpf/_rodata_str1_1."
>>
>> In the old kernel, the global data map will not be created, see [0]. So
>> we should skip the pinning of the global data map to avoid
>> bpf_object__pin_maps returning error.
>>
>> [0]: https://lore.kernel.org/bpf/20211123200105.387855-1-andrii@kernel.org
>>
>> Signed-off-by: Shuyi Cheng <chengshuyi@...ux.alibaba.com>
>> ---
>>    tools/lib/bpf/libbpf.c | 4 ++++
>>    1 file changed, 4 insertions(+)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index 6db0b5e8540e..d96cf49cebab 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -7884,6 +7884,10 @@ int bpf_object__pin_maps(struct bpf_object *obj,
>> const char *path)
>>                  char *pin_path = NULL;
>>                  char buf[PATH_MAX];
>>
>> +               if (bpf_map__is_internal(map) &&
>> +                   !kernel_supports(obj, FEAT_GLOBAL_DATA))
> 
> 
> doing the same check in 3 different places sucks. Let's add "bool
> skipped" to struct bpf_map, which will be set in one place (at the map
> creation time) and then check during relocation and during pinning?
>

Agree, thanks.

regards,
Shuyi



>> +                       continue;
>> +
>>                  if (path) {
>>                          int len;
>>
>> --
>> 2.19.1.6.gb485710b