Re: [PATCH bpf-next v3 03/21] bpf: support bpf tracing/iter programs for BPF_LINK_CREATE

Andrii Nakryiko
2020-05-12T03:15:28Z

On Fri, May 8, 2020 at 6:36 PM Yonghong Song <yhs@fb.com> wrote:
>
>
>
> On 5/8/20 11:24 AM, Andrii Nakryiko wrote:
> > On Wed, May 6, 2020 at 10:41 PM Yonghong Song <yhs@fb.com> wrote:
> >>
> >> Given a bpf program, the step to create an anonymous bpf iterator is:
> >> - create a bpf_iter_link, which combines bpf program and the target.
> >> In the future, there could be more information recorded in the link.
> >> A link_fd will be returned to the user space.
> >> - create an anonymous bpf iterator with the given link_fd.
> >>
> >> The bpf_iter_link can be pinned to bpffs mount file system to
> >> create a file based bpf iterator as well.
> >>
> >> The benefit to use of bpf_iter_link:
> >> - using bpf link simplifies design and implementation as bpf link
> >> is used for other tracing bpf programs.
> >> - for file based bpf iterator, bpf_iter_link provides a standard
> >> way to replace underlying bpf programs.
> >> - for both anonymous and free based iterators, bpf link query
> >> capability can be leveraged.
> >>
> >> The patch added support of tracing/iter programs for BPF_LINK_CREATE.
> >> A new link type BPF_LINK_TYPE_ITER is added to facilitate link
> >> querying. Currently, only prog_id is needed, so there is no
> >> additional in-kernel show_fdinfo() and fill_link_info() hook
> >> is needed for BPF_LINK_TYPE_ITER link.
> >>
> >> Acked-by: Andrii Nakryiko <andriin@fb.com>
> >> Signed-off-by: Yonghong Song <yhs@fb.com>
> >> ---
> >
> > still looks good, but I realized show_fdinfo and fill_link_info is
> > missing, see request for a follow-up below :)
> >
> >
> >> include/linux/bpf.h | 1 +
> >> include/linux/bpf_types.h | 1 +
> >> include/uapi/linux/bpf.h | 1 +
> >> kernel/bpf/bpf_iter.c | 62 ++++++++++++++++++++++++++++++++++
> >> kernel/bpf/syscall.c | 14 ++++++++
> >> tools/include/uapi/linux/bpf.h | 1 +
> >> 6 files changed, 80 insertions(+)
> >>
> >
> > [...]
> >
> >> +static const struct bpf_link_ops bpf_iter_link_lops = {
> >> + .release = bpf_iter_link_release,
> >> + .dealloc = bpf_iter_link_dealloc,
> >> +};
> >
> > Link infra supports .show_fdinfo and .fill_link_info methods, there is
> > no need to block on this, but it would be great to implement them from
> > BPF_LINK_TYPE_ITER as well in the same release as a follow-up. Thanks!
>
> The reason I did not implement is due to we do not have additional
> information beyond prog_id to present. The prog_id itself gives all
> information about this link. I looked at tracing program

Not all, e.g., bpf_iter target is invisible right now. It's good to
have this added in a follow up, but certainly not a blocker.

> show_fdinfo/fill_link_info, the additional attach_type is printed.
> But attach_type is obvious for BPF_LINK_TYPE_ITER which does not
> need print.
>
> In the future when we add more stuff to parameterize the bpf_iter,
> will need to implement these two callbacks as well as bpftool.

yep

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> >
> > [...]
> >