linux-kernel - Re: [PATCH bpf-next] tools: libbpf: update extended attributes version of bpf_object_

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Message-ID: <9EC54605-1911-48B0-B33A-02EC46DEF3DD@fb.com>
Date:   Fri, 30 Aug 2019 19:24:50 +0000
From:   Song Liu <songliubraving@...com>
To:     Anton Protopopov <a.s.protopopov@...il.com>
CC:     Andrii Nakryiko <andriin@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin Lau <kafai@...com>, "Yonghong Song" <yhs@...com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next] tools: libbpf: update extended attributes
 version of bpf_object__open()



> On Aug 30, 2019, at 11:53 AM, Anton Protopopov <a.s.protopopov@...il.com> wrote:
> 
> чт, 29 авг. 2019 г. в 16:02, Song Liu <songliubraving@...com>:
>> 
>> 
>> 
>>> On Aug 14, 2019, at 5:03 PM, Anton Protopopov <a.s.protopopov@...il.com> wrote:
>>> 
>> 
>> [...]
>> 
>>> 
>>> 
>>> int bpf_object__unload(struct bpf_object *obj)
>>> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
>>> index e8f70977d137..634f278578dd 100644
>>> --- a/tools/lib/bpf/libbpf.h
>>> +++ b/tools/lib/bpf/libbpf.h
>>> @@ -63,8 +63,13 @@ LIBBPF_API libbpf_print_fn_t libbpf_set_print(libbpf_print_fn_t fn);
>>> struct bpf_object;
>>> 
>>> struct bpf_object_open_attr {
>>> -     const char *file;
>>> +     union {
>>> +             const char *file;
>>> +             const char *obj_name;
>>> +     };
>>>      enum bpf_prog_type prog_type;
>>> +     void *obj_buf;
>>> +     size_t obj_buf_sz;
>>> };
>> 
>> I think this would break dynamically linked libbpf. No?
> 
> Ah, yes, sure. What is the right way to make changes which break ABI in libbpf?

I don't have a good idea here on the top of my head.

Maybe we need a new struct and/or function for this. 
 
> 
> BTW, does the commit ddc7c3042614 ("libbpf: implement BPF CO-RE offset
> relocation algorithm") which adds a new field to the struct
> bpf_object_load_attr also break ABI?

I think this change was in the same release, so it is OK. 

Thanks,
Song