Subject: Re: [PATCH v3 bpf-next 2/9] libbpf: introduce concept of bpf_link

From: Stanislav Fomichev <[email-masked]>
Date: Fri, 28 Jun 2019 10:45:33 -0700

On 06/28, Andrii Nakryiko wrote:
> On Fri, Jun 28, 2019 at 9:02 AM Stanislav Fomichev <[email-masked]> wrote:
> >
> > On 06/27, Andrii Nakryiko wrote:
> > > bpf_link is and abstraction of an association of a BPF program and one
> > > of many possible BPF attachment points (hooks). This allows to have
> > > uniform interface for detaching BPF programs regardless of the nature of
> > > link and how it was created. Details of creation and setting up of
> > > a specific bpf_link is handled by corresponding attachment methods
> > > (bpf_program__attach_xxx) added in subsequent commits. Once successfully
> > > created, bpf_link has to be eventually destroyed with
> > > bpf_link__destroy(), at which point BPF program is disassociated from
> > > a hook and all the relevant resources are freed.
> > >
> > > Signed-off-by: Andrii Nakryiko <[email-masked]>
> > > ---
> > >  tools/lib/bpf/libbpf.c   | 17 +++++++++++++++++
> > >  tools/lib/bpf/libbpf.h   |  4 ++++
> > >  tools/lib/bpf/libbpf.map |  3 ++-
> > >  3 files changed, 23 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > > index 6e6ebef11ba3..455795e6f8af 100644
> > > --- a/tools/lib/bpf/libbpf.c
> > > +++ b/tools/lib/bpf/libbpf.c
> > > @@ -3941,6 +3941,23 @@ int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr,
> > >       return 0;
> > >  }
> > >
> > > +struct bpf_link {
> > Maybe call it bpf_attachment? You call the bpf_program__attach_to_blah
> > and you get an attachment?
> 
> I wanted to keep it as short as possible, bpf_attachment is way too
> long (it's also why as an alternative I've proposed bpf_assoc, not
> bpf_association, but bpf_attach isn't great shortening).
Why do you want to keep it short? We have far longer names than
bpf_attachment in libbpf. That shouldn't be a big concern.

> > > +     int (*destroy)(struct bpf_link *link);
> > > +};
> > > +
> > > +int bpf_link__destroy(struct bpf_link *link)
> > > +{
> > > +     int err;
> > > +
> > > +     if (!link)
> > > +             return 0;
> > > +
> > > +     err = link->destroy(link);
> > > +     free(link);
> > > +
> > > +     return err;
> > > +}
> > > +
> > >  enum bpf_perf_event_ret
> > >  bpf_perf_event_read_simple(void *mmap_mem, size_t mmap_size, size_t page_size,
> > >                          void **copy_mem, size_t *copy_size,
> > > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> > > index d639f47e3110..5082a5ebb0c2 100644
> > > --- a/tools/lib/bpf/libbpf.h
> > > +++ b/tools/lib/bpf/libbpf.h
> > > @@ -165,6 +165,10 @@ LIBBPF_API int bpf_program__pin(struct bpf_program *prog, const char *path);
> > >  LIBBPF_API int bpf_program__unpin(struct bpf_program *prog, const char *path);
> > >  LIBBPF_API void bpf_program__unload(struct bpf_program *prog);
> > >
> > > +struct bpf_link;
> > > +
> > > +LIBBPF_API int bpf_link__destroy(struct bpf_link *link);
> > > +
> > >  struct bpf_insn;
> > >
> > >  /*
> > > diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> > > index 2c6d835620d2..3cde850fc8da 100644
> > > --- a/tools/lib/bpf/libbpf.map
> > > +++ b/tools/lib/bpf/libbpf.map
> > > @@ -167,10 +167,11 @@ LIBBPF_0.0.3 {
> > >
> > >  LIBBPF_0.0.4 {
> > >       global:
> > > +             bpf_link__destroy;
> > > +             bpf_object__load_xattr;
> > >               btf_dump__dump_type;
> > >               btf_dump__free;
> > >               btf_dump__new;
> > >               btf__parse_elf;
> > > -             bpf_object__load_xattr;
> > >               libbpf_num_possible_cpus;
> > >  } LIBBPF_0.0.3;
> > > --
> > > 2.17.1
> > >