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

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Date:   Fri, 27 Sep 2019 15:12:02 +0200
From:   KP Singh <kpsingh@...omium.org>
To:     Song Liu <songliubraving@...com>
Cc:     Anton Protopopov <a.s.protopopov@...il.com>,
        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 30-Aug 19:24, Song Liu wrote:
> 
> 
> > 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. 


I incorporated the suggested fixes and sent a new patch for this as we
ran into pretty much the same issue. (i.e. not being able to set
needs_kver / flags).

https://lore.kernel.org/bpf/20190927130834.18829-1-kpsingh@chromium.org/T/#u

- KP

>  
> > 
> > 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