Re: [PATCH v2 bpf-next 2/3] libbpf: add bpf_object__open_{file,mem} w/ extensible opts

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Thu, Oct 3, 2019 at 11:38 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> Andrii Nakryiko <andriin@fb.com> writes:
>
> > Add new set of bpf_object__open APIs using new approach to optional
> > parameters extensibility allowing simpler ABI compatibility approach.
> >
> > This patch demonstrates an approach to implementing libbpf APIs that
> > makes it easy to extend existing APIs with extra optional parameters in
> > such a way, that ABI compatibility is preserved without having to do
> > symbol versioning and generating lots of boilerplate code to handle it.
> > To facilitate succinct code for working with options, add OPTS_VALID,
> > OPTS_HAS, and OPTS_GET macros that hide all the NULL, size, and zero
> > checks.
> >
> > Additionally, newly added libbpf APIs are encouraged to follow similar
> > pattern of having all mandatory parameters as formal function parameters
> > and always have optional (NULL-able) xxx_opts struct, which should
> > always have real struct size as a first field and the rest would be
> > optional parameters added over time, which tune the behavior of existing
> > API, if specified by user.
> >
> > Signed-off-by: Andrii Nakryiko <andriin@fb.com>
> > ---
> >  tools/lib/bpf/libbpf.c          | 51 ++++++++++++++++++++++++++++-----
> >  tools/lib/bpf/libbpf.h          | 36 +++++++++++++++++++++--
> >  tools/lib/bpf/libbpf.map        |  3 ++
> >  tools/lib/bpf/libbpf_internal.h | 32 +++++++++++++++++++++
> >  4 files changed, 112 insertions(+), 10 deletions(-)
> >
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index 056769ce4fd0..503fba903e99 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -3620,16 +3620,33 @@ struct bpf_object *bpf_object__open(const char *path)
> >       return bpf_object__open_xattr(&attr);
> >  }
> >
> > -struct bpf_object *bpf_object__open_buffer(void *obj_buf,
> > -                                        size_t obj_buf_sz,
> > -                                        const char *name)
> > +struct bpf_object *
> > +bpf_object__open_file(const char *path, struct bpf_object_open_opts *opts)
> > +{
> > +     if (!OPTS_VALID(opts, bpf_object_open_opts))
> > +             return ERR_PTR(-EINVAL);
> > +     if (!path)
> > +             return ERR_PTR(-EINVAL);
> > +
> > +     pr_debug("loading %s\n", path);
> > +
> > +     return __bpf_object__open(path, NULL, 0, 0);
> > +}
>
> This is not doing anything with opts...

oh, my bad, was concentrating on bpf_object__open_mem too much. Good
thing v3 is necessary anyway..

>
> [...]
>
> > +struct bpf_object_open_opts {
> > +     /* size of this struct, for forward/backward compatiblity */
> > +     size_t sz;
> > +     /* object name override, if provided:
> > +      * - for object open from file, this will override setting object
> > +      *   name from file path's base name;
>
> ... but this says it should be, no?
>
> -Toke
>