RE: [PATCH v2 bpf-next] libbpf: Add bpf_obj_get_opts()

[Roberto Sassu <roberto.sassu@huawei.com>]

> From: Andrii Nakryiko [mailto:andrii.nakryiko@gmail.com]
> Sent: Thursday, July 28, 2022 1:03 AM
> On Tue, Jul 19, 2022 at 12:40 PM Joe Burton <jevburton.kernel@gmail.com>
> wrote:
> >
> > From: Joe Burton <jevburton@google.com>
> >
> > Add an extensible variant of bpf_obj_get() capable of setting the
> > `file_flags` parameter.
> >
> > This parameter is needed to enable unprivileged access to BPF maps.
> > Without a method like this, users must manually make the syscall.
> >
> > Signed-off-by: Joe Burton <jevburton@google.com>
> > ---
> >  tools/lib/bpf/bpf.c      | 10 ++++++++++
> >  tools/lib/bpf/bpf.h      |  9 +++++++++
> >  tools/lib/bpf/libbpf.map |  1 +
> >  3 files changed, 20 insertions(+)
> >
> 
> I agree that bpf_obj_get_opts should be separate from bpf_get_fd_opts.
> Just because both currently have file_flags in them doesn't mean that
> they should/will always stay in sync. So two separate opts for two
> separate APIs makes sense to me.
> 
> So I'd accept this patch, but please see a few small things below and
> send v3. Thanks!

Should map_parse_fds() accept two opts, or just the flags
to be set on locally-defined variables?

Thanks

Roberto

> > diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> > index 5eb0df90eb2b..5acb0e8bd13c 100644
> > --- a/tools/lib/bpf/bpf.c
> > +++ b/tools/lib/bpf/bpf.c
> > @@ -578,12 +578,22 @@ int bpf_obj_pin(int fd, const char *pathname)
> >  }
> >
> >  int bpf_obj_get(const char *pathname)
> > +{
> > +       LIBBPF_OPTS(bpf_obj_get_opts, opts);
> 
> if you were doing it this way, here should be an empty line. But
> really you can/should just pass NULL instead of opts in this case.
> 
> > +       return bpf_obj_get_opts(pathname, &opts);
> > +}
> > +
> > +int bpf_obj_get_opts(const char *pathname, const struct bpf_obj_get_opts
> *opts)
> >  {
> >         union bpf_attr attr;
> >         int fd;
> >
> > +       if (!OPTS_VALID(opts, bpf_obj_get_opts))
> > +               return libbpf_err(-EINVAL);
> > +
> >         memset(&attr, 0, sizeof(attr));
> >         attr.pathname = ptr_to_u64((void *)pathname);
> > +       attr.file_flags = OPTS_GET(opts, file_flags, 0);
> >
> >         fd = sys_bpf_fd(BPF_OBJ_GET, &attr, sizeof(attr));
> >         return libbpf_err_errno(fd);
> > diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> > index 88a7cc4bd76f..f31b493b5f9a 100644
> > --- a/tools/lib/bpf/bpf.h
> > +++ b/tools/lib/bpf/bpf.h
> > @@ -270,8 +270,17 @@ LIBBPF_API int bpf_map_update_batch(int fd, const
> void *keys, const void *values
> >                                     __u32 *count,
> >                                     const struct bpf_map_batch_opts *opts);
> >
> > +struct bpf_obj_get_opts {
> > +       size_t sz; /* size of this struct for forward/backward compatibility */
> > +
> > +       __u32 file_flags;
> 
> please add size_t :0; to avoid non-zero-initialized padding  (we do it
> in a lot of other opts structs)
> 
> 
> > +};
> > +#define bpf_obj_get_opts__last_field file_flags
> > +
> >  LIBBPF_API int bpf_obj_pin(int fd, const char *pathname);
> >  LIBBPF_API int bpf_obj_get(const char *pathname);
> > +LIBBPF_API int bpf_obj_get_opts(const char *pathname,
> > +                               const struct bpf_obj_get_opts *opts);
> >
> >  struct bpf_prog_attach_opts {
> >         size_t sz; /* size of this struct for forward/backward compatibility */
> > diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> > index 0625adb9e888..119e6e1ea7f1 100644
> > --- a/tools/lib/bpf/libbpf.map
> > +++ b/tools/lib/bpf/libbpf.map
> > @@ -355,6 +355,7 @@ LIBBPF_0.8.0 {
> >
> >  LIBBPF_1.0.0 {
> >         global:
> > +               bpf_obj_get_opts;
> >                 bpf_prog_query_opts;
> >                 bpf_program__attach_ksyscall;
> >                 btf__add_enum64;
> > --
> > 2.37.0.170.g444d1eabd0-goog
> >