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Date:   Wed, 13 May 2020 09:57:16 -0700
From:   Yonghong Song <yhs@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
CC:     Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next v3 03/21] bpf: support bpf tracing/iter programs
 for BPF_LINK_CREATE



On 5/11/20 8:15 PM, Andrii Nakryiko wrote:
> On Fri, May 8, 2020 at 6:36 PM Yonghong Song <yhs@...com> wrote:
>>
>>
>>
>> On 5/8/20 11:24 AM, Andrii Nakryiko wrote:
>>> On Wed, May 6, 2020 at 10:41 PM Yonghong Song <yhs@...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@...com>
>>>> Signed-off-by: Yonghong Song <yhs@...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.

Indeed, bpf_iter target is not visible now. We can add it to program
or to link. Adding to link is a reasonable idea as link itself is
the concept to merge program and target.

Will have a follow up patch for this later.

> 
> 
>> 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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