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

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Yonghong Song <yhs@fb.com>
Cc: Andrii Nakryiko <andriin@fb.com>, bpf <bpf@vger.kernel.org>,
	Martin KaFai Lau <kafai@fb.com>,
	Networking <netdev@vger.kernel.org>,
	Alexei Starovoitov <ast@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH bpf-next v3 03/21] bpf: support bpf tracing/iter programs for BPF_LINK_CREATE
Date: Fri, 8 May 2020 11:24:52 -0700	[thread overview]
Message-ID: <CAEf4BzaV6u1eTta4h4+mftQCQVOGPf0Q++B8tZxho+Uq3M1=mA@mail.gmail.com> (raw)
In-Reply-To: <20200507053918.1542509-1-yhs@fb.com>

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!

[...]